Method and system for controlling medium access in a wireless network

• US 20060164969A1
• Filed: 07/16/2004
• Published: 07/27/2006
• Est. Priority Date: 07/18/2003
• Status: Active Grant

• Current Assignee: Sovereign Peak Ventures, LLC (Dominion Harbor Enterprises, LLC)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Malik, Rahul, Tan, Pek Yew
• Granted Patent: US 7,889,701 B2
• Time in Patent Office: Days
• US Class Current: 370/203
• CPC Class Codes: H04B 7/0408 using two or more beams, i.e. beam diversity
• CPC Class Codes: H04W 16/28 using beam steering
• CPC Class Codes: H04W 72/046 the resource being in the space domain, e.g. beams
• CPC Class Codes: H04W 84/12 WLAN [Wireless Local Area Networks]
• CPC Class Codes: Y02D 30/70 in wireless communication networks

Abstract

A method and system are disclosed that can be applied to achieve high-throughput in a WLAN. Central to the present invention is the use of an SDMA compatible multi-beam antenna system by a WLAN access point. A system based on two types of antennas-dynamic beam forming and fixed beam antennas—is described. A mechanism and protocol are described that implement simultaneous transmissions with respect to an SDMA compatible access point and thereby improve spectral efficiency, and by extension achieve higher throughput. Based on the recognition that current WLAN MAC has major limitations in throughput, certain MAC extensions (that can be applied independently of SDMA) are described. Also disclosed are power-saving and power control techniques that improve battery performance and contribute to a reduction in station size, and a means of reducing channel interference. The present invention also deals with the problem of backward compatibility with conventional devices that implement the protocol that is a subset covered by the present invention.

Claims

1-32. -32. (canceled)

33. A medium access control system in a wireless network, comprising:

(i) an access point equipped with an SDMA compatible multi-beam antenna and a plurality of transceivers that can respectively be simultaneously connected to different antenna beams; and

(ii) one or more stations scattered in reception space of a wireless LAN.

34. The system according to claim 33, further including a timing structure comprising:

(i) a periodically transmitted beacon frame that reports existence of a wireless network and provides a timing reference to each station on said network;

(ii) a supervised access mode that is a period in which an access point effectively improves network throughput by controlling access to a wireless channel and adjusting transmission with users so that antenna characteristics are utilized and a plurality of simultaneous transmissions can be implemented on a same channel;

(iii) an unsupervised access mode that is a period in which an access point antenna is configured in an omni-directional pattern, and each station accesses a channel freely so as to be able to perform transmission using conventional carrier sensing technology; and

(iv) signaling whereby an access point starts or terminates a supervised or unsupervised access period.

35. The system according to claim 33, further including a protocol stack comprising:

(i) a medium access control layer that defines an access rule whereby a plurality of wireless stations access a common medium;

(ii) a physical layer that performs actual data transmission and reception on a wireless channel; and

(iii) a management entity that manages and adjusts operation of said medium access control layer and said physical layer in order to improve overall wireless network throughput.

36. The system according to claim 35, wherein said medium access control layer comprises:

(i) a contention based access mechanism whereby a carrier sensing mechanism is used and stations compete for a transmission medium based on one set of rules;

(ii) a polling based channel access mechanism whereby an access point can satisfy a band request of a specific station while maintaining a service quality level specified beforehand by that station; and

(iii) a beam access coordinator that implements high-throughput by adjusting data transfer between antennas and an access point and utilizing a function of a multi-beam antenna using said contention based and said polling based access mechanisms.

37. The system according to claim 34, wherein said beacon frame described is broadcast by an access point, and has a function that reports existence of a WLAN and provides a timing reference to stations scattered on a network, and comprises:

(i) an identifier unique to said wireless network whereby each station can uniquely and explicitly identify an access point and therefore a specific network;

(ii) wireless network function and protocol related information specially defined by implementation of an access point;

(iii) information describing a used frequency of a beacon broadcast by an access point on a wireless network; and

(iv) a period in which a wireless network operates in supervised access mode, and whereby a conventional station does not execute association or transmission in that superframe period, as a result of which effects on wireless network throughput due to such transmissions/collisions are minimized.

38. The system according to claim 37, wherein said wireless network function and protocol related information comprises:

(i) a protocol reference number that enables a station'"'"'s medium access control protocol type to be confirmed;

(ii) antenna type and pattern;

(iii) antenna switching/operating functions; and

(iv) station direction finding/positioning functions.

39. The system according to claim 33, wherein said station, when wishing to associate with a specific wireless network, transmits an Association Request frame that comprises information elements described in following (i), (iv), and (v), and further arbitrarily comprises information elements described in (ii) and (iii) according to a network configuration and station function, and reduces signaling overhead:

(i) a wireless network identifier received in a beacon frame for notifying an access point that a station wishes to associate with a WLAN;

(ii) a group identifier of a beam group that includes a station in its range and for which that station desires association, determined by that station by detecting presence or absence of a Beam Start Beacon and Beam End Beacon;

(iii) a beam identifier of a specific beam that includes a station in its range and for which that station desires association, determined by that station by detecting presence or absence of a Beam Start Beacon and Beam End Beacon;

(iv) an address of a station itself enabling unique identification by an access point in a next communication; and

(v) information relating to characteristics and functions of a protocol implemented by a station, that determines a possibility or otherwise of association with an access point, and determines a method of providing the best service to that station when association is accepted.

40. The system according to claim 39, wherein said access point, in response to said Association Request frame, transmits an Association Response frame request that accepts or denies a request of each station, and comprises information elements described in following (i), (iv), and (v), and further comprises arbitrarily information elements described in (ii) and (iii) according to a network configuration, said access point and station functions, and a structure of a transmitted Association Request:

(i) a wireless network identifier for acknowledging and responding to an Association Request created by a station;

(ii) a group identifier of a beam group used by an access point for communication with that station;

(iii) a beam identifier of a beam used by an access point for communication with that station;

(iv) an address of a station itself that is an Association Response transmission destination; and

(v) information relating to request status (that is, success or failure) and characteristics and functions supported by an access point.

41. The system according to claim 33, wherein said access point transmits an Acquisition Request that requests transmission of a predetermined training sequence to a station for a certain period, and identifies a spatial location of that station with respect to itself using that transmission, said Acquisition Request comprising:

(i) an address of a station that makes an Acquisition Request;

(ii) an address of a station that is an Acquisition Request transmission destination; and

(iii) transmission period or length of a training sequence requested in order to transmit an address to a specified station.

42. The system according to claim 33, wherein said access point transmits to a station a group ID assignment (Group-ID Assign) frame that performs assignment to a specific beam group for further transmit/receive operations, said Group-ID Assign frame comprising:

(i) an access point address/WLAN ID;

(ii) an address of a station that is a transmission destination of said Group-ID Assign frame;

(iii) a group ID determined by an access point and assigned to a station whose address was specified; and

(iv) a beam identifier of a beam used by an access point in a next communication with a station whose address was specified.

43. The system according to claim 33, wherein said access point broadcasts to each station of a specific beam group a Beam Start Beacon frame that indicates a start of operation to users of that beam group, said Beam Start Beacon frame comprising:

(i) an access point address/WLAN ID enabling identification of a transmission source for each station;

(ii) information relating to wireless network functions and protocol;

(iii) a group ID of said beam;

(iv) a beam ID of said beam;

(v) a period in which said group is active—

that is, a period in which an access point performs transmission/reception with users of said group before switching to a different pattern in order to handle users of another group;

(vi) a frequency for transmitting a Beam Start Beacon that makes it possible for stations of said group and beam to achieve mutual synchronization; and

(vii) a schedule of outbound transmissions created by an access point in a current group period.

44. The system according to claim 33, wherein said access point broadcasts to each station of a specific beam group a Beam End Beacon that indicates termination of operation to users of that beam group, said Beam End Beacon comprising:

(i) an access point address/WLAN ID enabling identification of a transmission source for each station;

(ii) information relating to wireless network functions and protocol;

(iii) a group ID of said beam;

(iv) a beam ID of said beam; and

(v) a period in which said group is inactive, and said users can adopt an operating mode that facilitates a reduction in power consumption.

45. The system according to claim 33, wherein said access point transmits to each station of specific beam a Poll+Supervised Contention Announcement frame that defines a wireless medium polling based medium access and contention based access schedule, said Poll+Supervised Contention Announcement frame comprising:

(i) a polling list assigned to respective stations; and

(ii) an information element that declares a medium for uplink contention based access use of a specified period known as a supervised contention access period.

46. The system according to claim 45, wherein said polling list comprises:

(i) an address of a station for which polling based access is permitted;

(ii) a polling time—

that is, a time when a station can start transmission;

(iii) a polling period—

that is, a period for which a station can execute transmission; and

(iv) a purpose of polling or permission for indicating to a station that polling is for a stream that requested a band beforehand, or to request reception confirmation for a downlink frame or the like transmitted in the past.

47. The system according to claim 33, wherein said access point uses an SDMA compatible antenna capable of forming a sector-shaped beam, characterized by:

(i) comparatively stable gain in a passband that minimizes fluctuation of a reception power level for a user belonging to that beam; and

(ii) sharp roll-off-that is, a narrow transition width—

such that a beam is generated at short intervals by an access point by suppressing occurrence of interference due to transmission from a particular beam to a user of a different beam, spectral efficiency is increased, and consequently high-throughput is obtained.

49. The system according to claim 43, wherein a downlink schedule element of said Beam Start Beacon:

(i) shows an outbound transmission schedule composed of a transmission destination address, transmission length, and time at which said transmission is performed; and

(ii) shows an end of an outbound transmission schedule—

that is, a transmission time corresponding to a Poll+Supervised Contention Announcement frame—

and enables a station that is not scheduled to receive an outbound transmission in a given group period to execute power-saving in a downlink period of that group period.

48. A medium access control method in a wireless network that has stations and an access point, said medium access control method comprising:

(i) a step of an access point transmitting an Acquisition Request frame to a station;

(ii) a step of a station responding to said Acquisition Request with a predetermined training sequence;

(iii) a step of an access point switching various beams that can be generated, and detecting a location of a user as being in a direction of a beam in which a training sequence is received at greatest strength; and

(iv) a step of updating a user location after identifying an initial location of a station.

50. A medium access control method in a wireless network that has stations and an access point, wherein, in order to minimize collisions due to a rogue station that uses carrier sensing not in accordance with a protocol of a WLAN system, said medium access control method comprises:

(i) a step of transmitting dummy or pad data and equalizing transmission times in all beams, preventing a station that uses a rogue carrier sensing method from detecting a vacant medium, and as a result avoiding transmission from a rogue station, thereby eliminating variance of outbound transmission times by different beams of a given group; and

(ii) a step of each station polled with the object of a confirmation response in an uplink phase transmitting a confirmation response frame indicating a negative response—

that is, each station ignoring a confirmation response request—

thereby not permitting a gap exceeding a CIFS period in a transmission structure.

51. A medium access control method in a wireless network that has stations and an access point, wherein, in order to detect and handle existence of a rogue station in a wireless network, said medium access control method comprises:

(i) a step of detecting that there is a rogue station if observing that transmission ended in failure in all beams at a same time; and

(ii) a step of, in case of detection of existence of said rogue station, switching to unsupervised access mode and directing that rogue station to transfer to another channel.