METHOD FOR GENERATING PREAMBLE SEQUENCE IN WIRELESS LAN SYSTEM

0Associated
Cases 
0Associated
Defendants 
0Accused
Products 
3Forward
Citations 
0
Petitions 
1
Assignment
First Claim
1. A method of generating a sequence to be inserted into a preamble by an access point (AP) in a wireless local area network (LAN) system, the method comprising:
 generating a basic sequence structure comprising C_{48 }comprising 48 tones and having 12 nonzero values, X_{6 }comprising 6 tones and having one nonzero value, and X_{5 }comprising five tones and having one nonzero value;
determining X1 that is a nonzero value included in the X_{6 }and X2 that is a nonzero value included in the X_{5};
selecting any one of a plurality of predetermined phase rotation factors with respect to a bandwidth for communication with a user equipment (UE); and
generating a sequence inserted into a preamble to be transmitted to the UE using the basic sequence structure and the selected phase rotation factor,wherein the selected phase rotation factor is applied in a unit of the basic sequence structure that is repeatedly included in the sequence once or more.
1 Assignment
0 Petitions
Accused Products
Abstract
Disclosed is a sequence generation method comprising: generating a basic sequence structure including C_{48 }having 48 tones, X_{6 }having six tones, and X_{5 }having five tones; selecting any one of a plurality of phase rotation factors predetermined for a bandwidth; and generating a sequence to be inputted into a preamble to be transmitted to a terminal, by using the phase rotation factor, applied in basic sequence structural units, and the basic sequence structure.
7 Citations
View as Search Results
PREAMBLE SEQUENCE GENERATION METHOD IN WIRELESS LAN SYSTEM  
Patent #
US 20170310516A1
Filed 10/05/2015

Current Assignee
LG Electronics Inc.

Sponsoring Entity
LG Electronics Inc.

SEQUENCE GENERATION FOR SYSTEMS SUPPORTING MIXED NUMEROLOGIES  
Patent #
US 20180131493A1
Filed 09/22/2017

Current Assignee
Qualcomm Inc.

Sponsoring Entity
Qualcomm Inc.

Preamble sequence generation method in wireless LAN system  
Patent #
US 10,454,733 B2
Filed 10/05/2015

Current Assignee
LG Electronics Inc.

Sponsoring Entity
LG Electronics Inc.

Preamble design for synchronization and cell search  
Patent #
US 8,027,329 B2
Filed 02/07/2007

Current Assignee
Telefonaktiebolaget LM Ericsson

Sponsoring Entity
Telefonaktiebolaget LM Ericsson

Method and system for a new packet preamble for wideband wireless local area network (LAN) systems  
Patent #
US 7,515,581 B2
Filed 02/03/2005

Current Assignee
Bell Northern Research LLC

Sponsoring Entity
Broadcom Corporation

Method of and generator for generating preamble sequences in communication systems  
Patent #
US 8,619,902 B2
Filed 11/08/2012

Current Assignee
Industrial Technology Research Institute

Sponsoring Entity
Industrial Technology Research Institute

Control mode PHY for WLAN  
Patent #
US 9,178,745 B2
Filed 10/02/2013

Current Assignee
Cavium International

Sponsoring Entity
Marvell World Trade Limited

18 Claims
 1. A method of generating a sequence to be inserted into a preamble by an access point (AP) in a wireless local area network (LAN) system, the method comprising:
generating a basic sequence structure comprising C_{48 }comprising 48 tones and having 12 nonzero values, X_{6 }comprising 6 tones and having one nonzero value, and X_{5 }comprising five tones and having one nonzero value; determining X1 that is a nonzero value included in the X_{6 }and X2 that is a nonzero value included in the X_{5}; selecting any one of a plurality of predetermined phase rotation factors with respect to a bandwidth for communication with a user equipment (UE); and generating a sequence inserted into a preamble to be transmitted to the UE using the basic sequence structure and the selected phase rotation factor, wherein the selected phase rotation factor is applied in a unit of the basic sequence structure that is repeatedly included in the sequence once or more.  View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
 10. An access point (AP) for generating a sequence to be inserted into a preamble in a wireless local area network (LAN) system, the AP comprising:
a transmitter; a receiver; and a processor connected to the transmitter and the receiver and configured to generate a sequence, wherein; the processor generates a basic sequence structure comprising C_{48 }comprising 48 tones and having 12 nonzero values, X_{6 }comprising 6 tones and having one nonzero value, and X_{5 }comprising five tones and having one nonzero value, determines X1 that is a nonzero value included in the X_{6 }and X2 that is a nonzero value included in the X_{5}, selects any one of a plurality of predetermined phase rotation factors with respect to a bandwidth for communication with a user equipment (UE), and generates a sequence inserted into a preamble to be transmitted to the UE using the basic sequence structure and the selected phase rotation factor; and the selected phase rotation factor is applied in a unit of the basic sequence structure that is repeatedly included in the sequence once or more.  View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18)
1 Specification
The present invention relates to a wireless communication system, and more particularly, to a method and apparatus for generating a sequence to be used between a user equipment (UE) and a base station (BS).
Recently, with development of information communication technology, various wireless communication technologies have been developed. Among others, a wireless local area network (WLAN) enables wireless access to the Internet using a portable terminal such as a personal digital assistant (PDA), a laptop, a portable multimedia player (PMP) in a home, an enterprise or a specific service provision area based on radio frequency technology.
In order to overcome limitations in communication rate which have been pointed out as weakness of a WLAN, in recent technical standards, a system for increasing network speed and reliability and extending wireless network distance has been introduced. For example, in IEEE 802.11n, multiple input and multiple output (MIMO) technology using multiple antennas in a transmitter and a receiver has been introduced in order to support high throughput (HT) with a maximum data rate of 540 Mbps or more, to minimize transmission errors, and to optimize data rate.
As nextgeneration communication technology, machinetomachine (M2M) communication technology has been discussed. Even in an IEEE 802.11 WLAN system, technical standards supporting M2M communication have been developed as IEEE 802.11ah. In M2M communication, a scenario in which a small amount of data is communicated at a low rate may be considered in an environment in which many apparatuses are present.
Communication in a WLAN system is performed in a medium shared between all apparatuses. As in M2M communication, if the number of apparatuses is increased, in order to reduce unnecessary power consumption and interference, a channel access mechanism needs to be more efficiently improved.
An object of the present invention devised to enhance performance of a sequence to be transmitted to a user equipment (UE) in a new communication system.
An object of the present invention devised to maximize gain in terms of adaptive gain control (AGC) while minimizing performance degradation in terms of a peak to average power ratio (PAPR).
An object of the present invention devised to variously provide sequences to be used by a communication system by proposing a plurality of phase rotation factors for obtaining the same PAPR according to a communication bandwidth.
The technical problems solved by the present invention are not limited to the above technical problems and other technical problems which are not described herein will become apparent to those skilled in the art from the following description.
The object of the present invention can be achieved by providing a method of generating a sequence, including generating a basic sequence structure including C_{48 }including 48 tones and having 12 nonzero values, X_{6 }including 6 tones and having one nonzero value, and X_{5 }including five tones and having one nonzero value, determining X1 that is a nonzero value included in the X_{6 }and X2 that is a nonzero value included in the X_{5}, selecting any one of a plurality of predetermined phase rotation factors with respect to a bandwidth for communication with a user equipment (UE), and generating a sequence inserted into a preamble to be transmitted to the UE using the basic sequence structure and the phase rotation factor, wherein the phase rotation factor is applied in a unit of the basic sequence structure that is repeatedly included in the sequence once or more.
The basic sequence structure may be configured in the form of X_{6}C_{48(1:24)}0_{5}C_{48(25:48)}X_{5}, the C_{48(1:24) }may indicate first to 24^{th }tones of the C_{48}, the C_{48(25:48) }may indicate 25^{th }to 48^{th }tones of the C_{48}, and 0_{5 }may indicate five consecutive 0.
The X_{6 }may be configured in the form of [0, 0, 0, 0, X1, 0] and the X_{5 }may be configured in the form of [0, X2, 0, 0, 0].
The X1 and the X2 may satisfy Mathematical Expression
The basic sequence structure may be configured in the form of X_{6}C_{48(1:24)}A_{5}C_{48(25:48)}X_{5}, the C_{48(1:24) }indicates first to 24^{th }tones of the C_{48}, the C_{48(25:48) }indicates 25^{th }to 48^{th }tones of the C_{48}, and A_{5 }may include 5 tones and may include one nonzero value in a central part.
The basic sequence structure may be repeated once to generate the sequence with respect to a bandwidth of 20 MHz, the basic sequence structure is repeated twice and the sequence is generated using two corresponding phase rotation values with respect to a bandwidth of 40 MHz, and the basic sequence structure is repeated four times and the sequence is generated using four corresponding phase rotation values with respect to a bandwidth of 80 MHz.
The basic sequence structure may be repeated once to generate the sequence with respect to a bandwidth of 20 MHz, a sequence obtained by removing X_{6 }and X_{5 }from the basic sequence structure may be repeated twice and a sequence may be generated using two corresponding phase rotation values and A_{11}, X_{6}, and X_{5 }with respect to a bandwidth of 40 MHz, and a sequence obtained by removing X_{6 }and X_{5 }from the sequence of a bandwidth of 40 MHz may be repeated twice and a sequence may be generated using two corresponding phase rotation values with respect to a bandwidth of 80 MHz.
The A_{11 }may be configured in the form of [0, A2, 0, 0, 0, A3, 0, 0, 0, A4, 0] and the A2, A3, and A4 may be a complex number that is not 0.
The method may further include inserting the generated sequence into the preamble and transmitting the sequence to the UE.
In another aspect of the present invention, provided herein is an access point (AP) including a transmitter, a receiver, and a processor connected to the transmitter and the receiver and configured to generate a sequence, wherein the processor may generate a basic sequence structure including C_{48 }including 48 tones and having 12 nonzero values, X_{6 }including 6 tones and having one nonzero value, and X_{5 }including five tones and having one nonzero value, determines X1 that is a nonzero value included in the X_{6 }and X2 that is a nonzero value included in the X_{5}, select any one of a plurality of predetermined phase rotation factors with respect to a bandwidth for communication with a user equipment (UE), and generate a sequence inserted into a preamble to be transmitted to the UE using the basic sequence structure and the phase rotation factor, and the phase rotation factor may be applied in a unit of the basic sequence structure that is repeatedly included in the sequence once or more.
According to the embodiments of the present invention have the following effects.
First, a preamble sequence with enhanced performance may be used in a new communication with an increased bandwidth.
Second, performance degradation may be minimized in terms of a peak to average power ratio (PAPR) while obtaining gain of adaptive gain control (AGC) performance.
Third, a communication system may select and use any one of among various sequence candidates by proposing a plurality of sequences with respect to a bandwidth.
The effects of the present invention are not limited to the abovedescribed effects and other effects which are not described herein may be derived by those skilled in the art from the following description of the embodiments of the present invention. That is, effects which are not intended by the present invention may be derived by those skilled in the art from the embodiments of the present invention.
The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. The technical features of the present invention are not limited to specific drawings and the features shown in the drawings are combined to construct a new embodiment. Reference numerals of the drawings mean structural elements.
Although the terms used in the present invention are selected from generally known and used terms, terms used herein may be varied depending on operator'"'"'s intention or customs in the art, appearance of new technology, or the like. In addition, some of the terms mentioned in the description of the present invention have been selected by the applicant at his or her discretion, the detailed meanings of which are described in relevant parts of the description herein. Furthermore, it is required that the present invention is understood, not simply by the actual terms used but by the meanings of each term lying within.
The following embodiments are proposed by combining constituent components and characteristics of the present invention according to a predetermined format. The individual constituent components or characteristics should be considered optional factors on the condition that there is no additional remark. If required, the individual constituent components or characteristics may not be combined with other components or characteristics. In addition, some constituent components and/or characteristics may be combined to implement the embodiments of the present invention. The order of operations to be disclosed in the embodiments of the present invention may be changed. Some components or characteristics of any embodiment may also be included in other embodiments, or may be replaced with those of the other embodiments as necessary.
In describing the present invention, if it is determined that the detailed description of a related known function or construction renders the scope of the present invention unnecessarily ambiguous, the detailed description thereof will be omitted.
In the entire specification, when a certain portion “comprises or includes” a certain component, this indicates that the other components are not excluded and may be further included unless specially described otherwise. The terms “unit”, “or/er” and “module” described in the specification indicate a unit for processing at least one function or operation, which may be implemented by hardware, software or a combination thereof. The words “a or an”, “one”, “the” and words related thereto may be used to include both a singular expression and a plural expression unless the context describing the present invention (particularly, the context of the following claims) clearly indicates otherwise.
In this document, the embodiments of the present invention have been described centering on a data transmission and reception relationship between a mobile station and a base station. The base station may mean a terminal node of a network which directly performs communication with a mobile station. In this document, a specific operation described as performed by the base station may be performed by an upper node of the base station.
Namely, it is apparent that, in a network comprised of a plurality of network nodes including a base station, various operations performed for communication with a mobile station may be performed by the base station, or network nodes other than the base station. The term base station may be replaced with the terms fixed station, Node B, eNode B (eNB), advanced base station (ABS), access point, etc.
The term mobile station (MS) may be replaced with user equipment (UE), subscriber station (SS), mobile subscriber station (MSS), mobile terminal, advanced mobile station (AMS), terminal, etc.
A transmitter refers to a fixed and/or mobile node for transmitting a data or voice service and a receiver refers to a fixed and/or mobile node for receiving a data or voice service. Accordingly, in uplink, a mobile station becomes a transmitter and a base station becomes a receiver. Similarly, in downlink transmission, a mobile station becomes a receiver and a base station becomes a transmitter.
Communication of a device with a “cell” may mean that the device transmit and receive a signal to and from a base station of the cell. That is, although a device substantially transmits and receives a signal to a specific base station, for convenience of description, an expression “transmission and reception of a signal to and from a cell formed by the specific base station” may be used. Similarly, the term “macro cell” and/or “small cell” may mean not only specific coverage but also a “macro base station supporting the macro cell” and/or a “small cell base station supporting the small cell”.
The embodiments of the present invention can be supported by the standard documents disclosed in any one of wireless access systems, such as an IEEE 802.xx system, a 3rd Generation Partnership Project (3GPP) system, a 3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. That is, the steps or portions, which are not described in order to make the technical spirit of the present invention clear, may be supported by the above documents.
In addition, all the terms disclosed in the present document may be described by the above standard documents. In particular, the embodiments of the present invention may be supported by at least one of P802.162004, P802.16e2005, P802.16.1, P802.16p and P802.16.1b documents, which are the standard documents of the IEEE 802.16 system.
Hereinafter, the preferred embodiments of the present invention will be described with reference to the accompanying drawings. It is to be understood that the detailed description which will be disclosed along with the accompanying drawings is intended to describe the exemplary embodiments of the present invention, and is not intended to describe a unique embodiment which the present invention can be carried out.
It should be noted that specific terms disclosed in the present invention are proposed for convenience of description and better understanding of the present invention, and the use of these specific terms may be changed to another format within the technical scope or spirit of the present invention.
1. IEEE 802.11 System Overview
1.1 Structure of WLAN System
An IEEE 802.11 structure may be composed of a plurality of components and a wireless local area network (WLAN) supporting station (STA) mobility transparent to a higher layer may be provided by interaction among the components. A basic service set (BSS) may correspond to a basic component block in an IEEE 802.11 LAN. In
In an IEEE 802.11 LAN, a BSS is basically an independent BSS (IBSS). For example, the IBSS may have only two STAs. In addition, the simplest BSS (BSS1 or BSS2) of
If an STA is turned on or off or if an STA enters or moves out of a BSS, the membership of the STA in the BSS may be dynamically changed. An STA may join a BSS using a synchronization process in order to become a member of the BSS. In order to access all services of a BSS based structure, an STA should be associated with the BSS. Such association may be dynamically set and may include use of a distribution system service (DSS).
In a LAN, a direct stationtostation distance may be restricted by PHY performance. Although such distance restriction may be possible, communication between stations located at a longer distance may be necessary. In order to support extended coverage, a DS may be configured.
The DS means a structure in which BSSs are mutually connected. More specifically, the BSSs are not independently present as shown in
The DS is a logical concept and may be specified by characteristics of the DSM. In IEEE 802.11 standards, a wireless medium (WM) and a DSM are logically distinguished. Logical media are used for different purposes and are used by different components. In IEEE 802.11 standards, such media are not restricted to the same or different media. Since plural media are logically different, an IEEE 802.11 LAN structure (a DS structure or another network structure) may be flexible. That is, the IEEE 802.11 LAN structure may be variously implemented and a LAN structure may be independently specified by physical properties of each implementation.
The DS provides seamless integration of a plurality of BSSs and provides logical services necessary to treat an address to a destination so as to support a mobile apparatus.
The AP means an entity which enables associated STAs to access the DS via the WM and has STA functionality. Data transfer between the BSS and the DS may be performed via the AP. For example, STA2 and STA3 shown in
Data transmitted from one of STAs associated with the AP to the STA address of the AP may always be received by an uncontrolled port and processed by an IEEE 802.1X port access entity. In addition, if a controlled port is authenticated, transmission data (or frames) may be transmitted to the DS.
A wireless network having an arbitrary size and complexity may be composed of a DS and BSSs. In an IEEE 802.11 system, such a network is referred to as an ESS network. The ESS may correspond to a set of BSSs connected to one DS. However, the ESS does not include the DS. The ESS network appears as an IBSS network at a logical link control (LLC) layer. STAs included in the ESS may communicate with each other and mobile STAs may move from one BSS to another BSS (within the same ESS) transparently to the LLC layer.
In IEEE 802.11, relative physical locations of the BSSs in
In the example of
In the following description, the nonAP STA may be referred to as a terminal, a wireless transmit/receive unit (WTRU), a user equipment (UE), a mobile station (MS), a mobile terminal or a mobile subscriber station (MSS). In addition, the AP may correspond to a base station (BS), a NodeB, an evolved NodeB (eNB), a base transceiver system (BTS) or a femto BS.
1.2 Link Setup Process
In order to establish a link with respect to a network and perform data transmission and reception, an STA discovers the network, performs authentication, establishes association and performs an authentication process for security. The link setup process may be referred to as a session initiation process or a session setup process. In addition, discovery, authentication, association and security setup of the link setup process may be collectively referred to as an association process.
An exemplary link setup process will be described with reference to
In step S510, the STA may perform a network discovery operation. The network discovery operation may include a scanning operation of the STA. That is, the STA discovers the network in order to access the network. The STA should identify a compatible network before participating in a wireless network and a process of identifying a network present in a specific area is referred to as scanning. The scanning method includes an active scanning method and a passive scanning method.
In
Although not shown in
Active scanning has delay and power consumption less than those of passive scanning.
After the STA has discovered the network, an authentication process may be performed in step S520. Such an authentication process may be referred to as a first authentication process to be distinguished from a security setup operation of step S540.
The authentication process includes a process of, at the STA, transmitting an authentication request frame to the AP and, at the AP, transmitting an authentication response frame to the STA in response thereto. The authentication frame used for authentication request/response corresponds to a management frame.
The authentication frame may include information about an authentication algorithm number, an authentication transaction sequence number, a status code, a challenge text, a robust security network (RSN), a finite cyclic group, etc. The information may be examples of information included in the authentication request/response frame and may be replaced with other information. The information may further include additional information.
The STA may transmit the authentication request frame to the AP. The AP may determine whether authentication of the STA is allowed, based on the information included in the received authentication request frame. The AP may provide the STA with the authentication result via the authentication response frame.
After the STA is successfully authenticated, an association process may be performed in step S530. The association process includes a process of, at the STA, transmitting an association request frame to the AP and, at the AP, transmitting an association response frame to the STA in response thereto.
For example, the association request frame may include information about various capabilities, beacon listen interval, service set identifier (SSID), supported rates, RSN, mobility domain, supported operating classes, traffic indication map (TIM) broadcast request, interworking service capability, etc.
For example, the association response frame may include information about various capabilities, status code, association ID (AID), supported rates, enhanced distributed channel access (EDCA) parameter set, received channel power indicator (RCPI), received signal to noise indicator (RSNI), mobility domain, timeout interval (association comeback time), overlapping BSS scan parameter, TIM broadcast response, QoS map, etc.
This information is purely exemplary information included in the association request/response frame and may be replaced with other information. This information may further include additional information.
After the STA is successfully authenticated, a security setup process may be performed in step S540. The security setup process of step S540 may be referred to as an authentication process through a robust security network association (RSNA) request/response. The authentication process of step S520 may be referred to as the first authentication process and the security setup process of step S540 may be simply referred to as an authentication process.
The security setup process of step S540 may include a private key setup process through 4way handshaking of an extensible authentication protocol over LAN (EAPOL) frame. In addition, the security setup process may be performed according to a security method which is not defined in the IEEE 802.11 standard.
2.1 Evolution of WLAN
As a technical standard recently established in order to overcome limitations in communication speed in a WLAN, IEEE 802.11n has been devised. IEEE 802.11n aims at increasing network speed and reliability and extending wireless network distance. More specifically, IEEE 802.11n is based on multiple input and multiple output (MIMO) technology using multiple antennas in a transmitter and a receiver in order to support high throughput (HT) with a maximum data rate of 540 Mbps or more, to minimize transmission errors, and to optimize data rate.
As WLANs have come into widespread use and applications using the same have been diversified, recently, there is a need for a new WLAN system supporting throughput higher than a data rate supported by IEEE 802.11n. A nextgeneration WLAN system supporting very high throughput (VHT) is a next version (e.g., IEEE 802.11ac) of the IEEE 802.11n WLAN system and is an IEEE 802.11 WLAN system newly proposed in order to support a data rate of 1 Gbps or more at a MAC service access point (SAP).
The nextgeneration WLAN system supports a multiuser MIMO (MUMIMO) transmission scheme by which a plurality of STAs simultaneously accesses a channel in order to efficiently use a radio channel. According to the MUMIMO transmission scheme, the AP may simultaneously transmit packets to one or more MIMOpaired STAs.
In addition, support of a WLAN system operation in a whitespace is being discussed. For example, introduction of a WLAN system in a TV whitespace (WS) such as a frequency band (e.g., 54 to 698 MHz) in an idle state due to digitalization of analog TVs is being discussed as the IEEE 802.11af standard. However, this is only exemplary and the whitespace may be incumbently used by a licensed user. The licensed user means a user who is allowed to use a licensed band and may be referred to as a licensed device, a primary user or an incumbent user.
For example, the AP and/or the STA which operate in the WS should provide a protection function to the licensed user. For example, if a licensed user such as a microphone already uses a specific WS channel which is a frequency band divided on regulation such that a WS band has a specific bandwidth, the AP and/or the STA cannot use the frequency band corresponding to the WS channel in order to protect the licensed user. In addition, the AP and/or the STA must stop use of the frequency band if the licensed user uses the frequency band used for transmission and/or reception of a current frame.
Accordingly, the AP and/or the STA should perform a procedure of determining whether a specific frequency band in a WS band is available, that is, whether a licensed user uses the frequency band. Determining whether a licensed user uses a specific frequency band is referred to as spectrum sensing. As a spectrum sensing mechanism, an energy detection method, a signature detection method, etc. may be used. It may be determined that the licensed user uses the frequency band if received signal strength is equal to or greater than a predetermined value or if a DTV preamble is detected.
In addition, as nextgeneration communication technology, machinetomachine (M2M) communication technology is being discussed. Even in an IEEE 802.11 WLAN system, a technical standard supporting M2M communication has been developed as IEEE 802.11ah. M2M communication means a communication scheme including one or more machines and may be referred to as machine type communication (MTC). Here, a machine means an entity which does not require direct operation or intervention of a person. For example, a device including a mobile communication module, such as a meter or a vending machine, may include a user equipment such as a smart phone which is capable of automatically accessing a network without operation/intervention of a user to perform communication. M2M communication includes communication between devices (e.g., devicetodevice (D2D) communication) and communication between a device and an application server. Examples of communication between a device and a server include communication between a vending machine and a server, communication between a point of sale (POS) device and a server and communication between an electric meter, a gas meter or a water meter and a server. An M2M communication based application may include security, transportation, health care, etc. If the characteristics of such examples are considered, in general, M2M communication should support transmission and reception of a small amount of data at a low rate in an environment in which very many apparatuses are present.
More specifically, M2M communication should support a larger number of STAs. In a currently defined WLAN system, it is assumed that a maximum of 2007 STAs is associated with one AP. However, in M2M communication, methods supporting the case in which a larger number of STAs (about 6000) are associated with one AP are being discussed. In addition, in M2M communication, it is estimated that there are many applications supporting/requiring a low transfer rate. In order to appropriately support the low transfer rate, for example, in a WLAN system, the STA may recognize presence of data to be transmitted thereto based on a traffic indication map (TIM) element and methods of reducing a bitmap size of the TIM are being discussed. In addition, in M2M communication, it is estimated that there is traffic having a very long transmission/reception interval. For example, in electricity/gas/water consumption, a very small amount of data is required to be exchanged at a long period (e.g., one month). In a WLAN system, although the number of STAs associated with one AP is increased, methods of efficiently supporting the case in which the number of STAs, in which a data frame to be received from the AP is present during one beacon period, is very small are being discussed.
WLAN technology has rapidly evolved. In addition to the abovedescribed examples, technology for direct link setup, improvement of media streaming performance, support of fast and/or largescale initial session setup, support of extended bandwidth and operating frequency, etc. is being developed.
2.2 Medium Access Mechanism
In a WLAN system according to IEEE 802.11, the basic access mechanism of medium access control (MAC) is a carrier sense multiple access with collision avoidance (CSMA/CA) mechanism. The CSMA/CA mechanism is also referred to as a distributed coordination function (DCF) of IEEE 802.11 MAC and employs a “listen before talk” access mechanism. According to such an access mechanism, the AP and/or the STA may perform clear channel assessment (CCA) for sensing a radio channel or medium during a predetermined time interval (for example, a DCF interframe space (DIFS)) before starting transmission. If it is determined that the medium is in an idle state as the sensed result, frame transmission starts via the medium. If it is determined that the medium is in an occupied state, the AP and/or the STA may set and wait for a delay period (e.g., a random backoff period) for medium access without starting transmission and then attempt to perform frame transmission. Since several STAs attempt to perform frame transmission after waiting for different times by applying the random backoff period, it is possible to minimize collision.
In addition, the IEEE 802.11 MAC protocol provides a hybrid coordination function (HCF). The HCF is based on the DCF and a point coordination function (PCF). The PCF refers to a periodic polling method for enabling all reception AP and/or STAs to receive data frames using a polling based synchronous access method. In addition, the HCF has enhanced distributed channel access (EDCA) and HCF controlled channel access (HCCA). The EDCA uses a contention access method for providing data frames to a plurality of users by a provider and the HCCA uses a contentionfree channel access method using a polling mechanism. In addition, the HCF includes a medium access mechanism for improving quality of service (QoS) of a WLAN and may transmit QoS data both in a contention period (CP) and a contention free period (CFP).
Operation based on a random backoff period will be described with reference to
If the random backoff process starts, the STA continuously monitors the medium while the backoff slots are counted down according to the set backoff count value. If the medium is in the occupied state, countdown is stopped and, if the medium is in the idle state, countdown is resumed.
In the example of
In the example of
If STA2 occupies the medium, data to be transmitted may be generated in the STA4. At this time, STA4 may wait for the DIFS if the medium enters the idle state, perform countdown according to a random backoff count value selected thereby, and start frame transmission. In the example of
2.3 Sensing Operation of STA
As described above, the CSMA/CA mechanism includes not only physical carrier sensing for directly sensing a medium by an AP and/or an STA but also virtual carrier sensing. Virtual carrier sensing solves a problem which may occur in medium access, such as a hidden node problem. For virtual carrier sensing, MAC of a WLAN may use a network allocation vector (NAV). The NAV refers to a value of a time until a medium becomes available, which is indicated to another AP and/or STA by an AP and/or an STA, which is currently utilizing the medium or has rights to utilize the medium. Accordingly, the NAV value corresponds to a period of time when the medium will be used by the AP and/or the STA for transmitting the frame, and medium access of the STA which receives the NAV value is prohibited during that period of time. The NAV may be set according to the value of the “duration” field of a MAC header of a frame.
A robust collision detection mechanism for reducing collision has been introduced, which will be described with reference to
In the example of
2.4 Power Management
As described above, in a WLAN system, channel sensing should be performed before an STA performs transmission and reception. When the channel is always sensed, continuous power consumption of the STA is caused. Power consumption in a reception state is not substantially different from power consumption in a transmission state and continuously maintaining the reception state imposes a burden on an STA with limited power (that is, operated by a battery). Accordingly, if a reception standby state is maintained such that the STA continuously senses the channel, power is inefficiently consumed without any special advantage in terms of WLAN throughput. In order to solve such a problem, in a WLAN system, a power management (PM) mode of the STA is supported.
The PM mode of the STA is divided into an active mode and a power save (PS) mode. The STA fundamentally operates in an active mode. The STA which operates in the active mode is maintained in an awake state. The awake state refers to a state in which normal operation such as frame transmission and reception or channel scanning is possible. The STA which operates in the PS mode operates while switching between a sleep state or an awake state. The STA which operates in the sleep state operates with minimum power and does not perform frame transmission and reception or channel scanning.
Since power consumption is reduced as the sleep state of the STA is increased, the operation period of the STA is increased. However, since frame transmission and reception is impossible in the sleep state, the STA may not unconditionally operate in the sleep state. If a frame to be transmitted from the STA, which operates in the sleep state, to the AP is present, the STA may be switched to the awake state to transmit the frame. If a frame to be transmitted from the AP to the STA is present, the STA in the sleep state may not receive the frame and may not confirm that the frame to be received is present. Accordingly, the STA needs to perform an operation for switching to the awake state according to a specific period in order to confirm presence of the frame to be transmitted thereto (to receive the frame if the frame to be transmitted is present).
Referring to
The AP 210 may transmit the DTIM once whenever the beacon frame is transmitted three times. An STA1 220 and an STA2 222 operate in the PS mode. The STA1 220 and the STA2 222 may be switched from the sleep state to the awake state at a predetermined wakeup interval to receive a TIM element transmitted by the AP 210. Each STA may compute a time to switch to the awake state based on a local clock thereof. In the example of
For example, the predetermined awake interval may be set such that the STA1 220 is switched to the awake state every beacon interval to receive a TIM element. Accordingly, the STA1 220 may be switched to the awake state (S211) when the AP 210 first transmits the beacon frame (S211). The STA1 220 may receive the beacon frame and acquire the TIM element. If the acquired TIM element indicates that a frame to be transmitted to the STA1 220 is present, the STA1 220 may transmit, to the AP 210, a power savePoll (PSPoll) frame for requesting frame transmission from the AP 210 (S221a). The AP 210 may transmit the frame to the STA1 220 in correspondence with the PSPoll frame (S231). The STA1 220 which completes frame reception is switched to the sleep state.
When the AP 210 secondly transmits the beacon frame, since another device access the medium and thus the medium is busy, the AP 210 may not transmit the beacon frame at an accurate beacon interval and may transmit the beacon frame at a delayed time (S212). In this case, the operation mode of the STA1 220 is switched to the awake state according to the beacon interval but the delayed beacon frame is not received. Therefore, the operation mode of the STA1 220 is switched to the sleep state again (S222).
When the AP 210 thirdly transmits the beacon frame, the beacon frame may include a TIM element set to a DTIM. Since the medium is busy, the AP 210 transmits the beacon frame at a delayed time (S213). The STA1 220 is switched to the awake state according to the beacon interval and may acquire the DTIM via the beacon frame transmitted by the AP 210. Assume that the DTIM acquired by the STA1 220 indicates that a frame to be transmitted to the STA1 220 is not present and a frame for another STA is present. In this case, the STA1 220 may confirm that a frame transmitted thereby is not present and may be switched to the sleep state again. The AP 210 transmits the beacon frame and then transmits the frame to the STA (S232).
The AP 210 fourthly transmits the beacon frame (S214). Since the STA1 220 cannot acquire information indicating that buffered traffic therefor is present via reception of the TIM element twice, the wakeup interval for receiving the TIM element may be controlled. Alternatively, if signaling information for controlling the wakeup interval of the STA1 220 is included in the beacon frame transmitted by the AP 210, the wakeup interval value of the STA1 220 may be controlled. In the present example, the STA1 220 may change switching of the operation state for receiving the TIM element every beacon interval to switching of the operation state every three beacon intervals. Accordingly, since the STA1 220 is maintained in the sleep state when the AP 210 transmits the fourth beacon frame (S214) and transmits the fifth beacon frame (S215), the TIM element cannot be acquired.
When the AP 210 sixthly transmits the beacon frame (S216), the STA1 220 may be switched to the awake state to acquire the TIM element included in the beacon frame (S224). Since the TIM element is a DTIM indicating that a broadcast frame is present, the STA1 220 may not transmit the PSPoll frame to the AP 210 but may receive a broadcast frame transmitted by the AP 210 (S234). The wakeup interval set in the STA2 230 may be set to be greater than that of the STA1 220. Accordingly, the STA2 230 may be switched to the awake state to receive the TIM element (S241), when the AP 210 fifthly transmits the beacon frame (S215). The STA2 230 may confirm that a frame to be transmitted thereto is present via the TIM element and transmits the PSPoll frame to the AP 210 (S241a) in order to request frame transmission. The AP 210 may transmit the frame to the STA2 230 in correspondence with the PSPoll frame (S233).
For PM management shown in
Referring to
As shown in
In the example of
2.5 TIM Structure
In the PM mode management method based on the TIM (or DTIM) protocol described with reference to
The AID is used as a unique identifier for each STA within one BSS. For example, in a current WLAN system, the AID may be one of values of 1 to 2007. In a currently defined WLAN system, 14 bits are assigned to the AID in a frame transmitted by the AP and/or the STA. Although up to 16383 may be assigned as the AID value, 2008 to 16383 may be reserved.
The TIM element according to an existing definition is not appropriately applied to an M2M application in which a large number (e.g., more than 2007) of STAs is associated with one AP. If the existing TIM structure extends without change, the size of the TIM bitmap is too large to be supported in an existing frame format and to be suitable for M2M communication considering an application with a low transfer rate. In addition, in M2M communication, it is predicted that the number of STAs, in which a reception data frame is present during one beacon period, is very small. Accordingly, in M2M communication, since the size of the TIM bitmap is increased but most bits have a value of 0, there is a need for technology for efficiently compressing the bitmap.
As an existing bitmap compression technology, a method of omitting 0 which continuously appears at a front part of a bitmap and defining an offset (or a start point) is provided. However, if the number of STAs in which a buffered frame is present is small but a difference between the AID values of the STAs is large, compression efficiency is bad. For example, if only frames to be transmitted to only two STAs respectively having AID values of 10 and 2000 are buffered, the length of the compressed bitmap is 1990 but all bits other than both ends have a value of 0. If the number of STAs which may be associated with one AP is small, bitmap compression inefficiency is not problematic but, if the number of STAs is increased, bitmap compression inefficiency deteriorates overall system performance.
As a method of solving this problem, AIDs may be divided into several groups to more efficiently perform data transmission. A specific group ID (GID) is assigned to each group. AIDs assigned based on the group will be described with reference to
If the AIDs assigned based on the group are introduced, channel access is allowed at a time interval which is changed according to the GID to solve lack of TIM elements for a large number of STAs and to efficiently perform data transmission and reception. For example, only channel access of STA(s) corresponding to a specific group may be granted during a specific time interval and channel access of the remaining STA(s) may be restricted. A predetermined time interval at which only access of specific STA(s) is granted may also be referred to as a restricted access window (RAW).
Channel access according to GID will be described with reference to
Although the order of GIDs allowed according to the beacon interval is cyclic or periodic in
The abovedescribed group based AID assignment method may also be referred to as a hierarchical structure of a TIM. That is, an entire AID space may be divided into a plurality of blocks and only channel access of STA(s) corresponding to a specific block having a nonzero value (that is, STAs of a specific group) may be granted. A TIM having a large size is divided into small blocks/groups such that the STA easily maintains TIM information and easily manages blocks/groups according to class, QoS or usage of the STA. Although a 2level layer is shown in the example of
In the following examples of the present invention, various methods of dividing and managing STAs (or AIDs assigned to the STAs) on a predetermined hierarchical group basis are applied and the group based AID assignment method is not limited to the above examples.
2.6 Improved Channel Access Method
If AIDs are assigned/managed based on a group, STAs belonging to a specific group may use a channel only at a “group channel access interval (or RAW)” assigned to the group. If an STA supports an M2M application, traffic for the STA may have a property which may be generated at a long period (e.g., several tens of minutes or several hours). Since such an STA does not need to be in the awake state frequently, the STA may be in the sleep mode for g a long period of time and be occasionally switched to the awake state (that is, the awake interval of the STA may be set to be long). An STA having a long wakeup interval may be referred to as an STA which operates in a “longsleeper” or “longsleep” mode. The case in which the wakeup interval is set to be long is not limited to M2M communication and the wakeup interval may be set to be long according to the state of the STA or surroundings of the STA even in normal WLAN operation.
If the wakeup interval is set, the STA may determine whether a local clock thereof exceeds the wakeup interval. However, since the local clock of the STA generally uses a cheap oscillator, an error probability is high. In addition, if the STA operates in longsleep mode, the error may be increased with time. Accordingly, time synchronization of the STA which occasionally wakes up may not match time synchronization of the AP. For example, although the STA computes when the STA may receive the beacon frame to be switched to the awake state, the STA may not actually receive the beacon frame from the AP at that timing. That is, due to clock drift, the STA may miss the beacon frame and such a problem may frequently occur if the STA operates in the long sleep mode.
In the example of
Since a time when STA3 transmits PSPoll belongs to the channel access interval for group 1, even if data to be transmitted to STA3 is present, the AP does not immediately transmit data after transmitting the ACK frame but transmits data to STA3 at a channel access interval (GID 3 channel access of
Since STA3 receives the ACK frame set to MD=1 from the AP, STA3 continuously waits for transmission of data from the AP. That is, in the example of
In particular, if STA3 operates in the longsleep mode, the beacon frame may frequently not be received, CCA may be performed even at the channel access interval, to which STA2 does not belong, thereby causing unnecessary power consumption.
Next, in the example of
In the example of
3. Proposed Method of Generating Sequence
The conventional WiFi standard defines sequences of a short training field (STF) and long training field (LTF). In particular, for cases in which a frequency is 20, 40, and 80 MHz, an STF sequence and an LTF sequence are separately defined. When a bandwidth is extended (BW extension), a phase rotation factor applied to an STF sequence and an LTF sequence may also be defined for bandwidths of 20, 40, and 80 MHz.
As interest in future WiFi and demand for improvement of throughput and QoE (quality of experience) after 802.11ac increase, it is necessary to define a new frame format for future WLAN systems. The most important part in a new frame format is a preamble part because design of a preamble used for synchronization, channel tracking, channel estimation, adaptive gain control (AGC) and the like may directly affect system performance.
In the future WiFi system in which a large number of APs and STAs simultaneously access and attempt data transmission and reception, system performance may be limited when legacy preamble design is employed. That is, if each preamble block (e.g., a short training field (STF) in charge of AGC, CFO estimation/compensation, timing control and the like or a long training field (LTF) in charge of channel estimation/compensation, residual CFO compensation and the like) executes only the function thereof defined in the legacy preamble structure, frame length increases, causing overhead. Accordingly, if a specific preamble block can support various functions in addition to the function designated therefor, an efficient frame structure can be designed.
Furthermore, since the future WiFi system considers data transmission in outdoor environments as well as indoor environments, the preamble structure may need to be designed differently depending on environments. Although design of a unified preamble format independent of environment variation can aid in system implementation and operation, of course, it is desirable that preamble design be adapted to system environment.
Preamble design for efficiently supporting various functions is described hereinafter. For convenience, a new WLAN system is referred to as an HE (High Efficiency) system and a frame and a PPDU (PLCP (Physical Layer Convergence Procedure) Protocol Data Unit) of the HE system are respectively referred to as an HE frame and an HE PPDU. However, it is obvious to those skilled in the art that the proposed preamble is applicable to other WLAN systems and cellular systems in addition to the HE system.
The following table 1 shows OFDM numerology which is a premise of a pilot sequence transmission method described below. Table 1 shows an example of new OFDM numerology proposed in the HE system and numerals and items shown in Table 1 are merely examples and other values may be applied. Table 1 is based on the assumption that FFT having a size four times the legacy one is applied to a given BW and 3 DCs are used per BW.
Hereinafter, a sequence that is newly defined as an enhanced preamble is defined as described above will be described. In addition, a corresponding sequence generating method will also be described below.
First, preconditions of the proposed sequence generating method will be described. Hereinafter, 0_{5 }refers to 5 consecutive 0, 0_{7 }refers to 7 consecutive 0, and 0_{12 }refers to 12 consecutive 0. C_{52 }refers to a vector with a size of 52 and is defined according to Mathematical Expression 1 below.
C_{52}=√{square root over (½)}{0,0,0,c1,0,0,0,c2, . . . ,c12} [Mathematical Expression 1]
4 null tones including a DC component are present in a center of 52 components included in C_{52}. C_{52 }includes a total of 52 components including 12 (c1, c2, . . . , c12) coefficient values, 12*3 values of 0 positioned between the coefficient values, and 4 null tones. The 12 coefficient values c1 to c12 may reuse an STF sequence corresponding to a bandwidth of 20 MHz in a legacy VHT system.
Hereinafter, a sequence for each of bandwidths of 20, 40, and 80 MHz using the aforementioned vector C_{52 }will be described in detail.
First, in a system to which FFT with a size of 256 is applied, a sequence for a bandwidth of 20 MHz is defined. The sequence for a bandwidth of 20 MHz may be defined according to Mathematical Expression 2 below.
0_{5}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{7} [Mathematical Expression 2]
The sequence for 20 MHz defined according to Mathematical Expression 2 includes a total of 256 tones (5+52+12+52+12+52+12+52+7=256).
Mathematical Expression 3 below defines a sequence for a bandwidth of 40 MHz.
0_{5}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{7} [Mathematical Expression 3]
The sequence for 40 MHz defined according to Mathematical Expression 3 above includes a total of 512 tones and a component C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52 }obtained by removing 0_{5 }and 0_{7 }at opposite ends in a structure of the 20 MHz sequence described in Mathematical Expression 2 above are positioned at right and left sides based on 0_{12 }positioned in a center. That is, a sequence for 40 MHz is defined in the form in which parts of 0_{12}20 MHz0_{7 }sequences of parts of 0_{5}20 MHz sequences are sequentially arranged. In addition, the sequence for 40 MHz may be understood as the form in which sequences for 20 MHz are consecutive twice (0_{5}+0_{7}=0_{12}).
Mathematical Expression 4 below defines a sequence for a bandwidth of 80 MHz.
0_{5}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52 }. . . 0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}0_{7} [Mathematical Expression 4]
As defined according to Mathematical Expression 4 above, a sequence for 80 MHz is defined as a total of 1024 tones and sequences for a bandwidth of 20 MHz are defined to be consecutively arranged a total of four times (0_{5}+0_{7}=0_{12}). A DC component may be inserted into a component 0_{12 }that is positioned in a center in the aforementioned sequences for 20, 40, and 80 MHz.
Hereinafter, an STF sequence that is newly defined by adding a specific tone that is repeated at an interval of 4 tones or 2 tones to a component 0_{12 }will be desired based on the aforementioned sequence structures. Even if a UE is allocated a subband of new sequences, even a subband including only 0 may not be present invention. A sequence applied to legacy STF and LTF may be applied to component C_{52 }of the aforementioned sequence for 20, 40, and 80 MHz in the same way.
According to an exemplary embodiment of the present invention, in a sequence defined according to Mathematical Expression 2 to Mathematical Expression 4 above, one or more components 0_{12 }may be replaced with D_{12 }to generate a sequence. As described above, a component D_{12 }may refer to the form in which nonzero components that are not 0 are repeated at an interval of 4 tones or 2 tones in a component 0_{12}. For example, a component D_{12 }according to an exemplary embodiment of the present invention may be defined according to Mathematical Expression 5 below.
D_{12}={0 0 0 1+j 0 0 0 −1−j 0 0 0 −1−j} [Mathematical Expression 5]
According to an exemplary embodiment according to Mathematical Expression 5 above, D_{12 }may include components that have 1+j as a fourth tone, −1−j as an eighth tone, −1−j as a twelfth tone, and are not 0. In the aforementioned defined sequences for 20, 40, and 80 MHz, one or more components 0_{12 }may be replaced with a component D_{12 }according to Mathematical Expression 5 above.
According to the replacement procedure, a peak to average power ratio (PAPR) is increased compared with a component 0_{12}. Accordingly, according to an exemplary embodiment of the present invention, a UE/AP may rotate a phase in a unit of {C_{12}D_{12}} and/or {C_{12}} in order to reduce a PAPR. In other words, a phase rotation factor _{k }may be applied to the proposed sequence.
For example, when C_{52 }is defined in the same way as in an STF system of a VHT system, C_{52 }may be defined according to Mathematical Expression 6 below.
C_{52}=√{square root over (½)}{0 0 0 1+j 0 0 0 −1−j 0 0 0 1+j 0 0 0 −1−j 0 0 0 −1−j 0 0 0 1+j 0 0 0 0 −0 0 0 −1−j 0 0 0 −1−j 0 0 0 1+j 0 0 0 1+j 0 0 0 1+0 0 0 1+j} [Mathematical Expression 6]
In this case, according to the proposed exemplary embodiment, a 20 MHz sequence with D_{12 }applied thereto may be defined according to Mathematical Expression 7.
S_{20 MHz}=[0_{5}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}0_{7}] [Mathematical Expression 7]
Then, a procedure of applying a phase rotation factor to a sequence of Mathematical Expression 7 will be described with regard to Mathematical Expression 8 below.
In Mathematical Expression 8 above, k of _{k }may refer to an index of a phase rotation factor applied to each sequence and an upper subscript 20 may indicate that the corresponding phase rotation factor is applied to a 20 MHz sequence.
With regard to the proposed exemplary embodiment according to Mathematical Expression 7 above, a procedure of determining a phase rotation factor for optimizing PAPR (=1.7379) will be described. First, Table 2 below shows the number of 8 cases for _{k }for obtaining 1.7379 as an optimal PAPR value. In Table 2 below, a column may refer to an index (k=1, 2, 3, 4) of a phase rotation factor and a row refers to examples of 8 independent types.
In Table 2 above, when 0_{12− }is used instead of D_{12 }(that is, all components 0_{12 }are set to 0), PAPR may be further reduced and may have a value of 1.6747. Table 3 below shows an example of a phase rotation factor for a sequence for 20 MHz when 0_{12 }is used and there are a total of 32 cases.
The sequence for 20 MHz described in Mathematical Expression 7 above may be extended to generate sequences for 40 MHz and 80 MHz. That is, the sequence for 40 MHz may be generated based on a sequence for 20 MHz and the sequence for 80 MHz may be generated based on a sequence for 40 MHz.
Hereinafter, a procedure of generating sequences for 40 and 80 MHz and an example of a phase rotation factor for each of sequences for 40 and 80 MHz will be described. First, a sequence for 40 MHz obtained by extending a sequence S_{20 MHz }for 20 MHz may be defined according to Mathematical Expression 9 below.
In Mathematical Expression 9 above, S′_{20 MHz }may refer to parts of sequences obtained by removing a headmost component 0_{5 }and a backmost component 0_{7 }from a sequence S_{20 MHz }for 20 MHz. That is, a sequence S_{40 MHz }for 40 MHz may be understood in the form of parts of sequences for 20 MHz are repeatedly extended. Similarly, a sequence S_{80 MHz }for 80 MHz may be defined by extending S′_{40 MHz }and may be defined according to Mathematical Expression 10 below. S′_{40 MHz }may refer to parts of sequences obtained by removing a headmost component 0_{5 }and a backmost component 0_{7 }from S_{40 MHz}.
Table 4 below shows optimal PAPR in a sequence defined for each frequency bandwidth according to FFT applied to a proposed communication system.
Table 5 below shows PAPR according to a sequence and FFT defined in a legacy 802.11ac system.
As seen from Tables 4 and 5 above, when a proposed sequence is used, PAPR may be increased. Accordingly, in order to reduce a PAPR, it may be necessary to adjust the phase rotation factor _{k }and, herinafter, a phase rotation factor will be described below.
First, an embodiment of setting a phase rotation factor for a sequence for 40 MHz will be described. In Mathematical Expression 10 above, an embodiment of setting a phase rotation factor for S′_{20 MHz }that is a part of seqeunces for 20 MHz has been described. Hereinafter, differently from Mathematical Expression 9 above, an embodiment of subdividing S_{40 MHz }and setting a phase rotation factor will be described.
First, S_{40 MHz }may be divided and represented into two parts according to Mathematical Expression 11 below.
S_{40 MHz}=[0_{5}S_{40 MHz}^{1}S_{40 MHz}^{2}0_{7}]
S_{40 MHz}^{1}=[C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}]
S_{40 MHz}^{2}=[C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}] [Mathematical Expression 11]
Then, S_{40 MHz}^{1 }and S_{40 MHz}^{2 }are defined according to Mathematical Expression 11 above, a phase rotation factor may be defined and applied in a unit of {C_{12}D_{12}} according to Mathematical Expression 12 below.
In other words, similarly to the case in which a phase rotation factor for a sequence for 20 MHz is set in a unit of {C_{12}D_{12}} and/or {C_{12}} in Mathematical Expression 9 above, the phase rotation factor may also be defined in a unit of {C_{12}D_{12}} and/or {C_{12}} with respect to a sequence for 40 MHz. This embodiment may be represented according to Mathematical Expression 12 below.
As such, when a phase rotation factor for 40 MHz is subdivided and set, PAPR may be obtained as 2.0227 lower than 2.2941 in Table 4 above. The number of cases of embodiments of a phase rotation factors that satisfy PAPR=2.0227 is 8 as follows. In Table 6 below, each column refers to an index (k=1, 2, . . . , 8) of a phase rotation factor and each row refers to the number of 8 independent cases.
When 0_{12 }is used instead of D_{12 }in a 40 MHz sequence, PAPR may be lowered to 1.6747 and 128 different embodiments may be possible according to a phase rotation factor. A total of 128 different sequences with PAPR=1.6747 may be generated and each phase rotation factor may be represented according to Table 7 below.
Hereinafter, an embodiment of subdividing a phase rotation factor for a sequence for 80 MHz will be described. Two different embodiments may be applied to a sequence for 80 MHz.
As a first method, a sequence for 20 MHz defined as 256 components may be first generated and a sequence for 20 MHz may be repeated four times to generate a 80 MHz sequence with 1024 components, which is represented according to Mathematical Expression 13 below.
In Mathematical Expression 13 above, _{k }is determined according to a direction of minimizing PAPR of an 80 MHz sequence. In other words, Mathematical Expression 14, components of _{k }(k=1, 2, 3, 4) of a phase rotation factor for 20 MHz is not determined as an optimal value for a 20 MHz sequence and is determined as an optimal value for a 80 MHz sequence. That is, in Mathematical Expression 13, components of _{k }(k=5, 6, 7, 8) of a phase rotation factor for a 80 MHz sequence is not simple fourtime repetition of a 20 MHz sequence and components of a phase rotation factor of 20 MHz and components of a phase rotation factor of 80 MHz may be determined together.
In the case of an 80 MHz sequence according to the first method, PAPR=2.1348 may be obtained and there are 4 number of cases shown in Table 8 below.
As a second method for 80 MHz, a similar method to an embodiment of subdividing 40 MHz may be applied. That is, for an 80 MHz sequence, a value of a phase rotation factor may be determined in a unit of {C_{12}D_{12}} and/or {C_{12}}. First, a 80 MHz sequence according to the second method may be represented according to Mathematical Expression 14 below.
S_{80 MHz}=[0_{5}S_{80 MHz}^{1}S_{80 MHz}^{2}0_{7}]
S_{80 MHz}^{1}=[C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}]
S_{80 MHz}^{2}=[C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}D_{12}C_{52}] [Mathematical Expression 14]
A 80 MHz sequence may be divided into two parts (S_{80 MHz}^{1}, S_{80 MHz}^{2}) as shown in Mathematical Expression 14 above and the respective parts may include a total of 16 including 8 components {C_{12}D_{12}} (here, only C_{12 }is pre sent in 16 last components. Accordingly, a phase rotation factor may be applied in a unit of {C_{12}D_{12}} and a total of 16 phase rotation factor values may be defined for one sequence. Mathematical Expression 15 below states this embodiment and this method may be a method of obtaining optimal PAPR.
In the case of D_{12}=0_{12 }in Mathematical Expression 15 above, 6144 phase rotation factors that satisfy PAPR=1.6747 may be generated and each phase rotation factor may include 16 components (γ={γ_{1}, γ_{2}, . . . γ_{16}}).
Table 9 below shows only 704 sequences as a base sequence among the 6144 phase rotation factors. Table 9 below shows only 704 sequences as a base sequence among the 6144 phase rotation factors. In Table 9 below, a total of 704 rows are present and a baseline sequence with 16 components are indicated in one row. In addition, in each room in Table 9 below, 704 rows are divided into an arbitrary number of parts in order to easily distinguish sequences.
5440 sequences other than 704 baseline sequences shown in Table 9 among a total of 6144 phase rotation factor sequences may be induced using methods to be described below. Hereinafter, an example of inducing the remaining sequences from a baseline sequence will be described. In Mathematical Expression 16 to Mathematical Expression 18 below, γ_{k,l }referes to a baseline sequence and k and l are a row and an order of a corresponding baseline sequence in Table 9 (1≦k≦352, l={1,2}). For example, k=3 and l=2 refer to a baseline sequence indicated a right column of a third row. χ_{k,l }refers to a sequence inducted according to Mathematical Expression 16 to Mathematical Expression 18 below from a baseline sequence.
According to a first embodiment, the case in which a baseline sequencer is multiplied with a predetermined constant α may be considered according to Mathematical Expression 16 below.
χ_{k,l}=αγ_{k,l} [Mathematical Expression 16]
In Mathematical Expression 16 above, α may be {1, −1, i, −i}.
As a second embodiment, a baseline sequence may be cyclicshifted to generate a sequence according to Mathematical Expression 17 below.
χ_{k,l}=γ_{k,l}^{(m)} [Mathematical Expression 17]
In Mathematical Expression 17 above, m may refer to a cyclic shifting value.
Lastly, baseline sequences may be arranged at an opposite order to generate a sequence according to Mathematical Expression 18 below.
χ_{k,l}=rev(γ_{k,l}) [Mathematical Expression 18]
In Mathematical Expression 18 above, calculation rev(•) may refer to calculation for arranging specific sequences at an opposite order and, for example, rev([1 2 3])=[3 2 1] may be satisfied.
Two or more embodiments among embodiments proposed according to Mathematical Expression 16 to Mathematical Expression 18 above may be simultaneously applied to generate a new sequence.
First, the AP may generate a basic sequence structure (S1810). The basic sequence structure may refer to a series of values that are repeatedly used to generate a sequence for bandwidths of 20, 40, and 80 MHz. For example, the basic sequence structure may refer to 244 tones obtained by removing headmost component 0_{5 }and a backmost component 0_{7 }among the aforementioned sequence of a band of 20 MHz in Mathematical Expression 2 above (C_{52}0_{12}C_{52}0_{12}C_{52}0_{12}C_{52}).
When a basic sequence structure is generated, an AP may replace 0_{12 }with D_{12 }in the basic sequence structure (S1820). D_{12 }may be defined according to Mathematical Expression 5 and, differently from Mathematical Expression 5 above, D_{12 }may be defined in the form of repeatedly arranging values that are not 0 at an interval of 2 tones. For convenience of description, a structure of applying D_{12 }to a basic sequence structure is referred to as a replaced sequence structure or a D_{12 }sequence structure.
Then, the AP may select a phase rotation factor to be used to generate a sequence (S1830). According to each bandwidth, a plurality of optimal or suboptimal phase rotation factors may be predetermined in terms of PAPR and a UE may select any one of a plurality of phase rotation factors. The phase rotation factor may include different numbers of components for respective bandwidths.
The AP may lastly generate a sequence for a corresponding bandwidth using a D_{12 }sequence structure and a phase rotation factor (S1840). This procedure may be performed via a procedure of applying a phase rotation factor in a unit of {C_{12}D_{12}} or {C_{12}} as described above. That is, with respect to a bandwidth of 20 MHz, a sequence may be generated through a procedure of applying a phase rotation factor according to Mathematical Expression 8 above.
Although a bandwidth of 20 MHz has been exemplified, operations S1830 and S1840 may be differently performed on bandwidths of 40 and 80 MHz. As described with reference to Mathematical Expression 9 and Mathematical Expression 10 above, a sequence may be defined in the form of repeatedly arranging parts (headmost components 0_{5 }and backmost components 0_{7 }are removed) of a sequence of 20 MHz with respect to a bandwidth of 40 MHz and a sequence may be defined in the form of repeatedly arranging parts (headmost components 0_{5 }and backmost components 0_{7 }are removed) of a sequence of 40 MHz with respect to a bandwidth of 80 MHz.
In this case, the phase rotation factor may include two components of bandwidths of 40 and 80 MHz and the UE may select any one from a plurality of predetermined sequences.
On the other hand, a phase rotation factor may also be determined in a unit of {C_{12}D_{12}} or {C_{12}} with respect to a bandwidth of 40 and 80 MHz as described with regard to Mathematical Expressions 11, 12, 13, and 14 above. In this case, the phase rotation factor may be defined as 8 or 16 components and an AP may select any one of a plurality of predetermined phase rotation factors to generate a sequence.
According to another exemplary embodiment of the present invention, a sequence derived from a baseline sequence may be used as a phase rotation factor according to the exemplary embodiment described with regard to Mathematical Expression 166 to Mathematical Expression 18 above.
When the sequence is generated according to the proposed exemplary embodiment, the AP may transmit the corresponding sequence to a UE. That is, the generated sequence may be inserted into a preamble part of a frame and transmitted and used for synchronization between the UE and the AP, channel measurement, AGC, and so on. Needless to say, the exemplary embodiments described with reference to
4. Proposed Method 2 of Generating Sequence
Hereinafter, an exemplary embodiment of using a conventional sequence that is defined for each frequency bandwidth instead of defining a new sequence like in the exemplary embodiment described with reference to
First, a parameter to be used in the proposed exemplary embodiment is defined. 0_{X }refers to a vector with x tones that are all 0. C_{48 }refers to a vector including 48 tones and is defined as a total of 48 tones obtained by excluding first two 0, last two 0, and intermediate five tones of seven consecutive tones positioned in a central portion among a sequence HTS_{−28, 28 }(57 tones) defined in an HTS system. C_{48 }may contain a total of nonzero coefficients that are not 0 and may be represented according to Mathematical Expression 20 below.
C_{48}=√{square root over (½)}{0,0,c1,0,0,0,c2,0, . . . ,0,0,c6,0,0,c7,0,0, . . . 0,c12,0,0} [Mathematical Expression 20]
When 0_{X }and C_{48 }are used, conventional STF sequences for 20, 40, and 80 MHz may be represented according to Mathematical Expressions 21, 22, and 23 below, respectively.
0_{6}C_{48(1:24)}0_{5}C_{48(25:48)}0_{5} [Mathematical Expression 21]
In Mathematical Expression 21 above, C_{48(x:y) }refers to some vectors including x^{th }to y^{th }tones among vectors of C_{48}.
0_{6}C_{53}0_{11}C_{53}0_{5}=0_{6}C_{46(1:24)}0_{5}C_{48(25:48)}0_{11}C_{48(1:24)}0_{5}C_{48(25:48)}0_{5} [Mathematical Expression 22]
In Mathematical Expression 22 above, C_{53}=C_{48(1:24)}0_{5}C_{48(25:48) }is defined.
0_{6}C_{117}0_{11}C_{117}0_{5}=0_{6}C_{53}0_{11}C_{53}0_{11}C_{53}0_{11}C_{53}0_{5}= . . . =0_{6}C_{48(1:24)}0_{5}C_{48(1:24)}0_{11}C_{48(1:24)}0_{5}C_{48(1:24)}0_{11}C_{48(1:24)}0_{5}C_{48(1:24)}0_{11}C_{48(1:24)}0_{5}C_{48(25:48)}0_{5} [Mathematical Expression 23]
In Mathematical Expression 23 above, C_{117 }is defined according to Mathematical Expression 24 below.
C_{117}=C_{53}0_{11}C_{53}=C_{48(1:24)}0_{5}C_{48(25:48)}0_{11}C_{48(1:24)}0_{5}C_{48(25:48)} [Mathematical Expression 24]
Hereinafter, an exemplary embodiment of generating a new sequence by defining X_{N }instead of 0_{X }in a conventional STF sequence will be described.
First, an exemplary embodiment using X_{N }instead of 0_{X }in Mathematical Expression 21 above in a bandwidth of 20 MHz used in 64 FFT will be described. When X_{6}=[0, 0, 0, 0, X1, 0] is defined and X_{5}=[0, X2, 0, 0, 0] is defined, a sequence defined according to Mathematical Expression 25 below may be derived a sequence described with regard to Mathematical Expression 21 above.
X_{6}C_{48(1:24)}0_{5}C_{48(25:48)}X_{5} [Mathematical Expression 25]
When X1 and X2 are set according to Mathematical Expression 26 below in Mathematical Expression 25 above, a sequence defined in Mathematical Expression 25 above may correspond to PAPR=1.5469 and the number of Pilots=14. As seen from this result, PAPR may be further enhanced compared with PAPR=1.6179 in the case of X1=X2=0.
Then, with respect to a bandwidth of 40 MHz used by 128 FFT, in Mathematical Expression 22 above, a new sequence derived by defining X_{6 }and X_{5 }instead of 0_{6 }and 0_{5 }may be used. A sequence that is newly defined with respect to 40 MHz may be represented according to Mathematical Expression 27 below.
In Mathematical Expression 27 above, s1 and s2 are a plurality of color scalar values and are components for changing a phase of A_{64}. Z_{n }is a zero vector with n 0. When X1 and X2 are defined according to Mathematical Expression 26 above, different A_{128 }may be generated according to a combination of Bland s2 in Mathematical Expression 27 below. According to the exemplary embodiments, Table 10 below shows a combination of s1 and s2 corresponding to PAPR=1.5469 and the number of Pilots=28. That is, similarly to the aforementioned exemplary embodiment, Table 10 below shows combinations of phase rotation factors s1 and s2.
In Table 10 above, a left column indicates s1, a right column indicates s2, and each row indicates examples of a combination of independent s1 and s2.
With respect to a bandwidth of 40 MHz, a sequence A_{128 }defined according to another method instead of the exemplary embodiment described with regard to Mathematical Expression 27 above and Table 10 above may be used. Mathematical Expression 28 below indicates the second exemplary embodiment.
A_{128}=[A_{64}^{1}A_{64}^{2}]
where A_{64}=[X_{6}C_{48}(1:24)A_{5}C_{48}(25:48)X_{5}]
A_{5}=[00A_{1}00]
A_{64}^{1}=s_{1}×A_{64}, A_{54}^{2}=s_{2}×A_{64},
s_{1},s_{2}ε{1,−1,i,−i} [Mathematical Expression 28]
Comparing Mathematical Expression 28 above and Mathematical Expression 27 above, five tones defined in a central part of A_{64 }are Z_{5 }that are all 0 in Mathematical Expression 27 above but a central value of five toes defined in a center in A_{64 }may have a value that is not 0 in Mathematical Expression 28 above. That is, according to the second exemplary embodiment proposed in Mathematical Expression 28 above, when X1 and X2 are defined according to Mathematical Expression 26 above, a combination of A_{1}, s1, and s2 corresponding to PAPR=1.6667 and the number of Pilots=30 may be considered. The combinations are shown in Table 11 below.
In Table 11 above, a first column indicates a value of A_{1}, a second column indicates s1, a third column indicates s2, and 8 rows indicate examples of independent combinations.
A third exemplary embodiment of 40 MHz proposes a method of using a sequence defined according to Mathematical Expression 29 below.
0_{6}A_{53}A_{11}A_{53}0_{5} [Mathematical Expression 29]
In Mathematical Expression 29 above, A_{53}=C_{48(1:24)}A_{5}C_{48(25:48) }may be defined and A_{5}=[0, 0, A_{1}, 0, 0]. A_{1 }may be determined as a value for minimizing PAPR and determined as an arbitrary value that is not 0. Alternatively, A_{1 }may be 0.
In Mathematical Expression 29 above, A_{11}=[0, A_{2}, 0, 0, 0, A_{3}, 0, 0, 0, A_{4}, 0]. In this case, A_{2}, A_{3}, and A_{4 }may be all determined as a value for minimizing PAPR and 0 may be applied like in the conventional case. Alternatively, when a DC component is considered, A_{11}=[0, A_{2}, 0, 0, 0, 0, 0, 0, 0, A_{4}, 0] may be defined and only A_{2 }and A_{4 }for minimizing PAPR may be determined to define A_{11}. In the case of A_{1}=A_{2}=A_{3}=A_{4}=0 in Mathematical Expression 29 below, the same STF sequence as a conventional HTS system may be used.
A forth exemplary embodiment with respect to 40 MHz proposes a method of using a sequence defined according to Mathematical Expression 30 below.
X_{6}A_{56}A_{11}A_{53}X_{5} [Mathematical Expression 30]
In Mathematical Expression 30 above, X_{6}=[0, 0, 0, 0, X1, 0] and X_{5}=[0, X2, 0, 0, 0]. That is, in the exemplary embodiment of Mathematical Expression 30 above, 0_{6 }and 0_{5 }may be changed to X_{6 }and X_{5 }in Mathematical Expression 29 above. Through the procedure of changing a phase according to the exemplary embodiment of Mathematical Expression 30, a sequence Mathematical Expression 31 may be derived.
X_{6}A_{53}^{1}A_{11}A_{53}^{2}X_{5},
where A_{53}^{1}=s_{1}×A_{53}, A_{53}^{2}=s_{2}×A_{53},
A_{53}=[C_{48(1:24)}A_{5}C_{48(25:48)}]
A_{5}=[0 0 A_{1 }0 0]
s_{1},s_{2}ε{1,−1,i,−i}
A_{11}=[0 A_{2 }0 0 0 A_{3 }0 0 0 A_{4 }0] [Mathematical Expression 31]
That is, in Mathematical Expression 31 above, s1 and s2 are scalar values for changing a phase of a vector A_{53}. In Mathematical Expression 31 above, 16 independent sequences with PAPR=1.7714 and the number of Pilots=31 may be generated and a combination of A_{1}, A_{2}, A_{3}, A_{4}, X1, X2, s1, and s2 for generating these sequences is shown in Table 12 below.
Table 13 below shows a combination of A_{2}, A_{3}, A_{4}, X1, X2, s1, and s2 when A_{1}=0 is fixed unlike in Table 12 above. Sequences shown in Table 13 below may correspond to PAPR=1.6669 and the number of Pilots=29.
Table 14 below shows a combination of A_{2}, A_{4}, X1, X2, s1, and s2 corresponding to PAPR=1.5469 and the number of Pilots=28. In sequences in an exemplary embodiment of Table 14 below, A_{1}=A_{3}=0.
Table 15 below shows a combination of A_{1}, A_{2}, A_{4}, X1, X2, s1, and s2 with PAPR=1.7121 and the number of Pilots=30. In sequences shown in an exemplary embodiment of Table 15, A_{3}=0 and a value A_{3 }are positioned adjacent to a DC value.
Hereinafter, a sequence with respect to a bandwidth of 80 MHz with 256 FFT applied thereto may be newly proposed. Sequences generated using four different methods will be sequentially described.
First, a sequence A_{256 }including 256 tones defined according to Mathematical Expression 32 below is proposed.
In Mathematical Expression 32 above, s1, s2, s3, and s4 are all complex scalars and Z_{n }is a zero vector with n 0. When X1 and X2 in Mathematical Expression 32 above satisfy Mathematical Expression 26 above, a combination of s1, s2, s3, and s4 shown in Table 16 below may be generated. Sequences generated according to a combination of Table 16 below may be sequences with PAPR=1.9527 and the number of Pilots=56.
A second exemplary embodiment with respect to a bandwidth of 80 MHz proposes a sequence A_{256 }defined according to Mathematical Expression 33 below.
A_{256}=[A_{64}^{1}A_{64}^{2}A_{64}^{3}A_{64}^{4}]
where A_{64}=[X_{6}C_{48}(1:24)A_{5}C_{48}(25:48)X_{5}]
A_{5}=[00A_{1}00]
A
_{64}
^{1}
=s
_{1}
×A
_{64}
, A
_{64}
^{2}
=s
_{2}
×A
_{64}
, A
_{64}
^{3}
=s
_{3}
×A
_{64}
, A
_{64}
^{4}
=s
_{4}
×A
_{64 }
s_{1},s_{2},s_{3},s_{4}ε{1,−1,i,−i} [Mathematical Expression 33]
With respect to Mathematical Expression 33 above, Table 17 below shows examples of sequences with PAPR=1.6667 and the number of Pilots=60 when X1 and X2 satisfy Mathematical Expression 26 above. Table 17 below shows combinations of A_{1}, s1, s2, s3, and s4 in Mathematical Expression 33 above.
According to a third exemplary embodiment with respect to a bandwidth of 80 MHz, a sequence generated according to Mathematical Expression 34 below may be considered.
0_{6}A_{117}A_{11}A_{117}0_{5} [Mathematical Expression 34]
In Mathematical Expression 34 above, A_{117}=A_{53}A_{11}A_{53 }and A_{11}=[0, A_{−2}, 0, 0, 0, A_{3}, 0, 0, 0, A_{4}, 0]. In this case, A_{2}, A_{3}, and A_{4 }may be determined as values for minimizing PAPR or may be set to 0. When a DC component is considered, A_{11 }to A_{3}=0 may be set and, in this case, A_{2 }and A_{4 }may be determined as a value for minimizing PAPR.
In Mathematical Expression 34 above, A_{53}=C_{48(1:24)}A_{5}C_{48(25:48) }and A_{5}=[0, 0, A_{1}, 0, 0]. In this case, A_{1 }may be determined as a value for minimizing PAPR and may be an arbitrary value that is not 0. A_{11 }may be defined as A_{11}={0, 1+j, 0, 0, 0, −1−j, 0, 0, 0, −1−j, 0} similarly to the description with regard to Mathematical Expression 5 above.
Since 0_{6}A_{117}A_{11}A_{117}0_{5}=[0_{6}A_{53}A_{11}A_{53}A_{11}A_{53}A_{11}A_{53}0_{5}], the phase rotation factor values described with regard to Mathematical Expression 9 above and Table 2 above may be applied to the same form to the present exemplary embodiment. In other words, phase rotation factor values may be generated and applied so as to correspond a vector C_{52}D_{12 }in Mathematical Expression 9 above to a vector A_{53}A_{11 }according to the present embodiment and to correspond to C_{52 }of Mathematical Expression 9 above to A_{53 }according to the present embodiment.
According to a fourth exemplary embodiment of the present invention, a sequence generated according to Mathematical Expression 35 below with respect to a bandwidth of 80 MHz may be applied.
X_{6}A_{117}A_{11}A_{117}X_{5} [Mathematical Expression 35]
Mathematical Expression 35 above may be an exemplary embodiment in which X_{6 }and X_{5 }are applied instead of 0_{6 }and 0_{5 }in Mathematical Expression 34 above, and X_{6}=[0, 0, 0, 0, X1, 0] and X_{5}=[0, X2, 0, 0, 0]. X1 and X2 may be determined as a value for minimizing PAPR of a sequence. Mathematical Expression 35 above may be represented according to Mathematical Expression 36 below.
X
_{6}
A
_{117}
^{1}
A
_{11}
A
_{117}
^{2}
X
_{5 }
where A_{117}^{1}=[s_{1}×A_{53}A_{11}s_{2}×A_{53}], A_{117}^{2}=[s_{3}×A_{53}A_{11}s_{4}×A_{53}],
s_{1},s_{2},s_{3},s_{4}ε{1,−1,i−i}
A_{11}=[0 A_{2 }0 0 0 A_{3 }0 0 0 A_{4 }0] [Mathematical Expression 36]
In Mathematical Expression 36 above, s1, s2, s3, and s4 are a complex scalar value and may constantly change a phase of A_{53}. Table 18 below shows combinations of A_{2}, A_{3}, A_{4}, s1, s2, s3, and s4 with PAPR=1.7719 and the number of Pilots=57 with respect to a sequence of Mathematical Expression 36 above.
Table 19 below shows combinations of A_{1}, X1, X2, s1, s2, s3, and s4 with PAPR=1.9529 and the number of Pilots=54 with respect to a sequence of Mathematical Expression 36 above.
Table 20 below shows combinations of A_{2}, A_{3}, A_{4}, X1, X2, s1, s2, s3, and s4 with PAPR=1.9529 and the number of Pilots=59 with respect to a sequence of Mathematical Expression 36 above.
Table 21 below shows combinations of A_{1}, A_{2}, A_{3}, A_{4}, X1, X2, s1, s2, s3, and s4 with PAPR=2.0054 and the number of Pilots=63 with respect to a sequence of Mathematical Expression 36 above.
In Mathematical Expression 36 above, A_{11 }positioned in a central portion of a sequence A_{6}A_{117}^{1}A_{11}A_{117}^{2}X_{5 }may be changed according to Mathematical Expression 37 below.
X_{6}A_{117}^{1}A_{11}^{3}A_{117}^{2}X_{5},
where A_{11}^{3}=[0 A_{2 }0 0 0 0 0 0 0 A_{4 }0] [Mathematical Expression 37]
Table 22 below shows combinations of A_{2}, A_{3}, A_{4}, s1, s2, s3, and s4 with PAPR=1.8588 and the number of Pilots=56 with respect to a sequence of Mathematical Expression 37 above.
Table 23 below shows combinations of A_{2}, A_{3}, A_{4}, X1, X2, s1, s2, s3, and s4 with PAPR=1.8688 and the number of Pilots=58 with respect to a sequence of Mathematical Expression 37 above.
Table 24 below shows combinations of A_{1}, A_{2}, A_{3}, A_{4}, X1, X2, s1, s2, s3, and s4 with PAPR=1.9889 and the number of Pilots=62 with respect to a sequence of Mathematical Expression 37 above.
Differently from the aforementioned exemplary embodiments, hereinafter, a sequence with a sequence length defined to be doubled compared with a conventional case with respect to each bandwidth is proposed. That is, a sequence of the case in which an FFT size is applied to be doubled is proposed.
First, when 128 FFT is applied to a bandwidth of 20 MHz, a sequence of Mathematical Expression 38 below may be generated.
B_{6}A_{53}A_{11}A_{53}B_{5} [Mathematical Expression 38]
In Mathematical Expression 38 above, B_{6}=[0, 0, 0, 0, B1, 0] and B_{5}=[0, B2, 0, 0, 0]. B1 and B2 may be determined as a value for minimizing PAPR and may be determined as an arbitrary value that is not 0. A_{53 }and A_{11 }are the same as definition of Mathematical Expression 29 above. In the case of A_{1}=A_{2}=A_{3}=A_{4}=B1=B2=0 in Mathematical Expression 38 above, the same sequence as 40 MHz in a conventional STF system may be used.
Then, when 256 FFT is applied with respect to a bandwidth of 40 MHz, a sequence of Mathematical Expression 39 below may be generaed.
B_{6}A_{117}A_{11}A_{117}B_{5} [Mathematical Expression 39]
Similarly to Mathematical Expression 38 above, B_{6}=[0, 0, 0, 0, B1, 0] and B_{5}=[0, B2, 0, 0, 0] also in Mathematical Expression 39 above. A_{117}=A_{53}A_{11}A_{53 }and A_{11}=[0, A2, 0, 0, 0, A3, 0, 0, 0, A4, 0] may be defined. In this case, A2, A3, and A4 may be determined as values for minimizing PAPR. In addition, in consideration with a DC component, A_{11 }to A3 may be 0.
In Mathematical Expression 39 above, A_{53 }may be C_{48(1:24)}A_{5}C_{48(25:48) }and A_{5}=[0, 0, A1, 0, 0]. A1 may also be determined as a value for minimizing PAPR. In Mathematical Expression 39 above, A_{11 }may be defined as A_{11}={0, 1+j, 0, 0, 0, −1−j, 0, 0, 0, −1−j, 0} similarly to the description of Mathematical Expression 5 above.
When 0_{6 }and 0_{5 }are applied instead of B_{6 }and B_{5}, 0_{6}A_{117}A_{11}A_{117}0_{5}=[0_{6}A_{53}A_{11}A_{53}A_{11}A_{53}A_{11}A_{53}0_{5}] as described with regard to Mathematical Expression 34 above and, thus, phase rotation factors described with regard to Mathematical Expression 9 and Table 2 above may be applied in the same form to the present exemplary embodiment. In other words, phase rotation factor values may be generated and applied to correspond a vector C_{52}D_{12 }in Mathematical Expression 9 above to a vector A_{53}A_{11 }according to the present embodiment and to correspond to C_{52 }in Mathematical Expression 9 to A_{53 }according to the present embodiment. In the case of A_{1}=A_{2}=A_{3}=A_{4}=B1=B2=0 in Mathematical Expression 39 above, the same sequence as 80 MHz in a conventional STF system may be used.
Then, when 512 FFT is applied to a band of 80 MHz, a sequence of Mathematical Expression 40 below may be generated.
B_{6}A_{245}A_{11}A_{245}B_{5} [Mathematical Expression 40]
In Mathematical Expression 40 above, B_{6}=[0, 0, 0, 0, B1, 0] and B_{5}=[0, B2, 0, 0, 0] like in Mathematical Expressions 38 and 39 above. A_{245}=A_{117}A_{11}A_{117 }and A_{11}=[0, A2, 0, 0, 0, A3, 0, 0, 0, A4, 0] may be defined. In this case, A2, A3, and A4 may be determined as values for minimizing PAPR. In addition, in consideration of a DC component, A_{11 }to A3 may also be 0. As described with regard to Mathematical Expression 39 above, A_{53 }in Mathematical Expression 40 may be C_{48(1:24)}A_{5}C_{48(25:48) }and A_{5}=[0, 0, A1, 0, 0]. A1 may also be determined as a value for minimizing PAPR.
With respect to a sequence of Mathematical Expression 40 above, the aforementioned phase rotation factor value described with regard to Mathematical Expression 10 above may be applied in a similar way. In other words, a phase rotation factor may be applied to A_{245}A_{11 }and another phase rotation factor may be applied to subsequent A_{245}.
When Mathematical Expression 40 above is separately considered with respect to [B_{6}A_{117}A_{11}A_{117}A_{11}A_{117}A_{11}A_{117 }B_{5}], four phase rotation factors may be applied. In other words, a phase rotation factor may be applied to three A_{117}A_{11 }and a fourth phase rotation factor may be applied to A_{117 }before last B_{5 }to generate a sequence for 80 MHz.
Differently from the exemplary embodiment with regard to Mathematical Expressions 38 to Mathematical Expression 40 above, a sequence with a sequence length defined with respect to each bandwidth to be lengthened four times compared with the conventional case is also proposed.
When 256 FFT is applied with respect to a bandwidth of 20 MHz, a sequence form proposed with respect to a bandwidth of 40 MHz in Mathematical Expression 39 above may be used. B_{6}=[0, 0, 0, 0, B1, 0] and B_{5}=[0, B2, 0, 0, 0] may be defined. A_{117}=A_{53}A_{11}A_{53 }and A_{11}=[0, A2, 0, 0, 0, A3, 0, 0, 0, A4, 0] may be defined. In this case, A2, A3, and A4 may be determined as values for minimizing PAPR. In addition, in consideration of a DC component, A_{11 }to A3 values may be 0.
In Mathematical Expression 39 above, A_{53 }may be C_{48(1:24)}A_{5}C_{48(25:48) }and A_{5}=[0, 0, A1, 0, 0]. A1 may also be determined as a value for minimizing PAPR. In Mathematical Expression 39 above, A_{11 }may be defined as A_{11}={0, 1+j, 0, 0, 0, −1−j, 0, 0, 0, −1−j, 0} similarly to the description with regard to Mathematical Expression 5 above.
When 0_{6 }and 0_{5 }are applied instead of B_{6 }and B_{5}, 0_{6}A_{117}A_{11}A_{117}0_{5}=[0_{6}A_{53}A_{11}A_{53}A_{11}A_{53}A_{11}A_{53}0_{5}] is defined as described with regard to Mathematical Expression 34 above and, thus, the phase rotation factor values described with regard to Mathematical Expression 9 and Table 2 above may be applied in the same form to the present exemplary embodiment. In other words, phase rotation factor values may be generated and applied to correspond to a vector C_{52}D_{12 }in Mathematical Expression 9 to a vector A_{53}A_{11 }according to the present exemplary embodiment and to correspond to C_{52 }in Mathematical Expression 9 above to A_{53 }according to the present exemplary embodiment. In the case of A_{1}=A_{2}=A_{3}=A_{4}=B1=B2=0, the same sequence as 80 MHz in a conventional STF system may be used.
Similarly to this method, when 512 FFT is applied to a bandwidth of 40 MHz, the sequence form proposed with respect to a bandwidth of 80 MHz in Mathematical Expression 40 above may be used. B_{6}=[0, 0, 0, 0, B1, 0] and B_{5}=[0, B2, 0, 0, 0] may be defined. A_{245}=A_{117}A_{11}A_{117 }and A_{11}=[0, A2, 0, 0, 0, A3, 0, 0, 0, A4, 0] may be defined. In this case, A2, A3, and A4 may be determined as values for minimizing PAPR. In addition, in consideration of a DC component, A_{11 }to A3 values may also be 0. In addition, as described with regard to Mathematical Expression 39 above, A_{53 }in Mathematical Expression 40 above may be C_{48(1:24)}A_{5}C_{48(25:48) }and A_{5}=[0, 0, A1, 0, 0]. A1 may also be determined as a value for minimizing PAPR.
With respect to a sequence of Mathematical Expression 40 above, the phase rotation factor value described with regard to Mathematical Expression 10 above may be applied in a similar way. In other words, a phase rotation factor may be applied to A_{245}A_{11 }and another phase rotation factor may be applied to subsequent A_{245}.
When Mathematical Expression 40 above is separately considered with respect to [B_{6}A_{117}A_{11}A_{117}A_{11}A_{117}A_{11}A_{117}B_{5}], four phase rotation factors may be applied. In other words, a phase rotation factor may be applied to three A_{117}A_{11 }and a fourth phase rotation factor may be applied to A_{117 }before last B_{5 }to generate a sequence for 80 MHz.
Furthermore, Mathematical Expression 40 above may be subdivided and may be separately considered with respect to [B_{6}A_{53}A_{11}A_{53}A_{11}A_{53}A_{11}A_{53}A_{11}A_{53}A_{11}A_{53}A_{11}A_{53}A_{11}A_{53 }B_{5}]. In this case, eight phase rotation factors may be applied to generate a sequence by applying respective phase rotation factors to seven A_{53}A_{11 }and one last A_{53}.
Lastly, when 1024 FFT is applied with respect to a bandwidth of 80 MHz, a sequence form of Mathematical Expression 41 below may be applied.
B_{6}A_{501}A_{11}A_{501}B_{5} [Mathematical Expression 41]
B_{6}=[0, 0, 0, 0, B1, 0] and B_{5}=[0, B2, 0, 0, 0] may be defined and B1 and B2 may be determined as values for minimizing PAPR. A_{501}=A_{245}A_{11}A_{245 }and A_{11}=[0, A2, 0, 0, 0, A3, 0, 0, 0, A4, 0] may be defined. In this case, A2, A3, and A4 may be determined as values for minimizing PAPR. In consideration of a DC component, A_{11 }to A3 values may be 0. As described with regard to Mathematical Expression 39 above, A_{53 }may be C_{48(1:24)}A_{5}C_{48(25:48) }and A_{5}=[0, 0, A1, 0, 0]. A1 may also be determined as a value for minimizing PAPR.
When the form of Mathematical Expression 41 above is considered, the method of applying the phase rotation factor described with regard to Mathematical Expression 11 above may also be used. That is, a phase rotation factor may be applied to A_{501}A_{11 }and another phase rotation factor may be applied to A_{501 }before last B_{5}.
Furthermore, when a sequence of Mathematical Expression 41 above is separately considered with respect to [B_{6}A_{245}A_{11}A_{245}A_{11}A_{245}A_{11}A_{245 }B_{5}], four phase rotation factors may be applied in a unit of A_{245}A_{11 }or A_{245}. In addition, when the sequence is understood to be subdivided as A_{245}=A_{117}A_{11}A_{117}, the sequence may be designed as applying eight phase rotation factors. Lastly, the sequence may also be subdivided as A_{117}=A_{53}A_{11}A_{53 }to design a sequence with 16 phase rotation factors applied thereto.
First, the AP may generate a basic sequence structure (S1910). The basic sequence structure refers to a vector including a series of tones that are repeatedly used in a procedure of generating a sequence with respect to a bandwidth of 20, 40, and 80 MHz. For example, as described with regard to Mathematical Expression 21 above, a basic sequence structure with respect to a bandwidth of 20 MHz may include 0_{6}C_{48(1:24)}0_{5}C_{48(25:48)}0_{5 }with 112 tones. A basic sequence structure with respect to a band of 40 and 80 MHz may be determined by repeating a basic sequence structure of a band of 20 MHz.
When the basic sequence structure is generated, the AP may replace 0_{6 }and 0_{5 }with X_{6 }and X_{5 }in the basic sequence structure, respectively (S1920). X_{6}=[0, 0, 0, 0, X1, 0] and X_{5}=[0, X2, 0, 0, 0] may be defined and X1 and X2 may be a nonzero value that is not 0. That is, a series of tones generated according to operation S1920 may be represented according to Mathematical Expression 25 above.
Then, the AP may determine X1 and X2 as a value for lowering PAPR (S1930). According to an exemplary embodiment,
may be defined (Mathematical Expression 26) but X1 and X2 values may not be limited to the present exemplary embodiment and a plurality of candidate values for obtaining the same PAPR may be present. A basic sequence structure with X_{6 }and X_{5 }inserted thereinto may also be referred to as a replacement sequence structure for convenience of description.
The AP may select a phase rotation factor to be used to generate a sequence (S1940). Differently from the phase rotation factor in
Then, the AP may generate a sequence with respect to a bandwidth (S1950). A sequence generating procedure may be understood as repeating a replacement sequence structure a predetermined number of times according to a bandwidth. In the repetition procedure, one or more values that are not 0 may be inserted into consecutive values of 0 positioned between replacement sequence structures. For example, arbitrary values that are not 0, such as A_{5 }of Mathematical Expression 28 or A_{11 }of Mathematical Expression 29, may be inserted and one may be selected as an arbitrary value that is not 0 among a plurality of equivalent candidate values similarly to the exemplary embodiments described with regard to Table 11 to 14 above.
When a sequence is generated according to the above proposed exemplary embodiments, the AP may insert the corresponding sequence into a preamble and transmit the sequence to the UE. As described above with reference to
5. Apparatus Configuration
The RF units 110 and 210 may include transmitters 112 and 212 and receivers 114 and 214, respectively. The transmitter 112 and the receiver 114 of the user equipment 100 are configured to transmit and receive signals to and from the base station 200 and other reception modules and the processor 120 is functionally connected to the transmitter 112 and the receiver 114 to control a process of, at the transmitter 112 and the receiver 114, transmitting and receiving signals to and from other apparatuses. The processor 120 processes a signal to be transmitted, sends the processed signal to the transmitter 112 and processes a signal received by the receiver 114.
If necessary, the processor 120 may store information included in an exchanged message in the memory 130. By this structure, the user equipment 100 may perform the methods of the various embodiments of the present invention.
The transmitter 212 and the receiver 214 of the base station 200 are configured to transmit and receive signals to and from another transmission module and repcetion modules and the processor 220 are functionally connected to the transmitter 212 and the receiver 214 to control a process of, at the transmitter 212 and the receiver 214, transmitting and receiving signals to and from other apparatuses. The processor 220 processes a signal to be transmitted, sends the processed signal to the transmitter 212 and processes a signal received by the receiver 214. If necessary, the processor 220 may store information included in an exchanged message in the memory 230. By this structure, the base station 200 may perform the methods of the various embodiments of the present invention.
The processors 120 and 220 of the user equipment 100 and the base station 200 instruct (for example, control, adjust, or manage) the operations of the user equipment 100 and the base station 200, respectively. The processors 120 and 220 may be connected to the memories 130 and 230 for storing program code and data, respectively. The memories 130 and 230 are respectively connected to the processors 120 and 220 so as to store operating systems, applications and general files.
The processors 120 and 220 of the present invention may be called controllers, microcontrollers, microprocessors, microcomputers, etc. The processors 120 and 220 may be implemented by hardware, firmware, software, or a combination thereof. If the embodiments of the present invention are implemented by hardware, Application Specific Integrated Circuits (ASICs), Digital Signal Processors (DSPs), Digital Signal Processing Devices (DSPDs), Programmable Logic Devices (PLDs), Field Programmable Gate Arrays (FPGAs), etc. may be included in the processors 120 and 220.
Meanwhile, the aforementioned method may be implemented as programs executable in computers and executed in general computers that operate the programs using computer readable media. In addition, data used in the aforementioned method may be recorded in computer readable recording media through various means. It should be understood that program storage devices that can be used to describe storage devices including computer code executable to perform various methods of the present invention do not include temporary objects such as carrier waves or signals. The computer readable media include storage media such as magnetic recording media (e.g. ROM, floppy disk and hard disk) and optical reading media (e.g. CDROM and DVD).
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the inventions. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
Although the aforementioned sequence generating method has been described in terms of an example applied to an IEEE 802.11 system and an HEW system, the method may be applied to various wireless communication system including IEEE 802.16, 3GPP LTE, and LTEA other than an IEEE 802.11 system and a HEW system.