Apparatus and method for digital data transmission using orthogonal codes

• US 6,154,456 A
• Filed: 08/04/1998
• Issued: 11/28/2000
• Est. Priority Date: 08/25/1995
• Status: Expired due to Term

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Terayon Communications Systems Incorporated (Motorola Solutions, Inc.)
• Inventors: Azenkot, Yehuda, Rakib, Selim Shlomo
• Primary Examiner(s): RAO, SEEMA SRINIVAS
• Application Number:
  US09/129,111
• Time in Patent Office: 847 Days
• Field of Search: 370/319-231, 370/324, 370/335, 370/342, 370/444, 370/503, 370/504, 370/508-510, 370/512, 370/517, 370/519, 370/345, 370/347, 370/330, 370/337, 370/479, 370/507 , 370/516, 370/252, 370/350, 375/219, 375/316, 375/354, 375/356, 375/360, 375/361, 375/363, 375/131, 375/140, 455/3.1, 455/38.1, 340/825.04, 340/825.44, 348/6, 348/13
• US Class Current: 370/342
• CPC Class Codes: H03M 13/256 with trellis coding, e.g. with convolutional codes and TCM
• CPC Class Codes: H03M 13/41 using the Viterbi algorithm or Viterbi processors
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 2201/709709 Methods of preventing interference
• CPC Class Codes: H04B 7/2668 Arrangements for Wireless Code-Division Multiple Access [CDMA] System Synchronisation, for code acquisition H04B1/7075, for code tracking H04B1/7085
• CPC Class Codes: H04H 60/97 using uplink of the CATV systems
• CPC Class Codes: H04J 13/004 Orthogonal
• CPC Class Codes: H04J 13/16 Code allocation
• CPC Class Codes: H04L 12/2801 Broadband local area networks
• CPC Class Codes: H04L 2025/03414 Multicarrier
• CPC Class Codes: H04L 25/03343 Arrangements at the transmitter end
• CPC Class Codes: H04L 27/362 Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated H04L27/366 takes precedence
• CPC Class Codes: H04L 5/023 Multiplexing of multicarrier modulation signals multicarrier modulation H04L27/2601
• CPC Class Codes: H04L 5/026 using code division
• CPC Class Codes: H04L 5/06 the signals being represented by different frequencies combined with time-division multiplexing H04L5/26
• CPC Class Codes: H04L 7/042 Detectors therefor, e.g. correlators, state machines digital correlators in general G06F17/15
• CPC Class Codes: H04N 21/6168 involving cable transmission, e.g. using a cable modem
• CPC Class Codes: H04N 7/141 between two video terminals, e.g. videophone telephonic communication systems combined with television receiver for reception of entertainment or information matter H04M11/085
• CPC Class Codes: H04N 7/17309 Transmission or handling of upstream communications
• CPC Class Codes: H04W 48/16 Discovering, processing access restriction or access information
• CPC Class Codes: H04W 56/00 : Synchronisation arrangements
• CPC Class Codes: H04W 74/0866 : using a dedicated channel for access

Abstract

A method and apparatus for carrying out synchronous co-division multiple access (SCDMA) communication of multiple channels of digital data over a shared transmission media such as a cable television system coaxial cable, a fiber optic or copper conductor telephone link, terrestial microwave, satellite link, local or wide area network, wireless including cellur network or some combination of these media using suitable interface circuitry. The system includes modems at remote units and a central unit to receive time division multiplexed digital data arranged into timeslots or channels and uses orthogonal codes to encode each channel of multiple data and spread the energy of each channel data over a frame of data transmitted in the code domain. Spreading the data this way makes the system less susceptible to impulse noise. Frames are synchronized as between remote and central units using a ranging scheme which is also useful in any other system transmitting data by frames in a distributed system where synchronizing the frames as between all units regardless of differences in propagation delays is necessary. Each frame in the SCDMA modulation scheme includes a gap or guardband containing no other data. The ranging process involves training each remote unit to impose enough delay prior to re-transmission of a barker code received from the CU such that a barker code sent by the RU arrives at the CU during the gap. The process of setting the delay in each RU is a trial and error process, and each RU starts the ranging process asynchronously. Contention resolution protocols such that only one RU is aligning to the gap at any particular time are taught.

Claims

1. A ranging process for use in a distributed digital data communication system requiring frame synchronization of frames of time division multiplexed data transmitted to a central unit transceiver by a plurality of remote unit transceivers at physically different locations in a shared transmission media, comprising the steps:

in all said remote unit transceivers that need to achieve frame synchronization, starting the frame synchronization process independently of whether any other remote unit transceiver is also starting the frame synchronization process by picking an initial transmit frame timing delay value;

in each remote unit transceiver that has started the frame synchronization process, determining the the proper transmit frame timing delay following a reference time that must elapse before transmitting an upstream frame so as to achieve frame synchronization by selecting said initial transmit frame timing delay value and, when said initial transmit frame timing delay value has elapsed following said reference time, transmitting from said remote unit transceiver to said central unit transceiver a ranging signal with properties such that it can be detected in the presence of noise;

in said central unit transceiver, monitoring for received ranging signals in an upstream frame gap, and broadcasting status data to all said remote unit transceivers that informs said remote unit transceivers whether or not any said ranging signal has arrived at said central unit transceiver during said upstream frame gap; and

receiving said broadcast status data in all said remote unit transceivers, and, in each remote unit transceiver that is carrying out said frame synchronization process, if said broadcast status data does not indicate a ranging signal has been received during said upstream frame gap, continuing to adjust said transmit frame timing delay value in all said remote unit transceivers until a message is received from said central unit tranceiver in said broadcast status data that a single said ranging signal has arrived in said upstream frame gap;

if the broadcast data indicates more than one ranging signal arrived during said upstream gap, making a random determination in each remote unit transceiver whether to continue said frame synchronization process, and, if the decision is to stop, then stopping transmissions of said ranging signals and resuming some time later;

when said broadcast status data indicates only one ranging signal has been received during said gap, sending identifying data from each remote unit transmitter using the same transmit frame timing delay used to send the last ranging signal to identify itself;

receiving said identification data that arrives in said upstream frame gap in said central unit transceiver and broadcasting said identifying data as said broadcast status data; and

receiving said broadcast identifying data in all said remote unit transceivers that are performing the frame synchronization process or which have resumed said frame synchronization process, and if the identifying data does not correspond to the identity of a particular remote unit transceiver that is performing the frame synchronization process, continuing the trial and error adjustment of said transmit frame timing delay value until identifying data is broadcast indicating that the ranging signal from said particular remote unit transceiver has arrived in said upstream frame gap.

2. A ranging process for use in a distributed digital data communication system requiring frame synchronization of frames of code division multiplexed data transmitted to a central unit transceiver by a plurality of remote unit transceivers at physically different locations in a shared transmission media, comprising the steps:

(1) transmitting data downstream from said central unit transceiver to said remote unit transceivers;

(2) in each remote unit transceiver which has already achieved frame synchronization transmitting upstream frames each of which is separated from its neighboring frames by a small gap that represents less than 15% of the total duration of each said upstream frame interval, each upstream frame carrying interleaved, code division multiplexed data that has been encoded with error detection and correction bits, each said upstream frame being transmitted to said central unit transceiver using whatever transmit frame timing delay value each remote unit transceiver that has achieved frame synchronization previously determined was necessary to achieve frame synchronization such that each such upstream frame transmitted to said central unit transceiver arrives with its frame boundaries aligned in time with the frame boundaries of upstream frames transmitted by other remote unit transceivers that have also achieved frame synchronization;

(3) in a remote unit transceiver that has not yet achieved frame synchronization selecting an initial value for a transmit frame timing delay, and then, without invitation from said central unit transceiver and regardless of whether other remote unit transceivers are or are not starting the frame synchronization process, determining the a transmit frame timing delay that will result in frame synchronization for upstream frame transmissions from said remote unit transceiver by transmitting from said remote unit transmitter to said central unit transceiver a ranging signal during each upstream frame with properties such that it can be detected in the presence of noise even if it arrives during reception of upstream frames transmitted by other remote unit transceivers that have already achieved frame synchronization, said transmission of said ranging signal carried out using a said initial transmit frame timing delay value;

(4) in said central unit transceiver monitoring each gap in at least some of said upstream frames for a received upstream ranging signal, and transmitting data downstream to said remote unit transceiver that informs said remote unit transceiver whether or not said ranging signal has arrived at said central unit transceiver in an upstream frame gap;

(5) continuing to adjust said transmit frame timing delay value in said remote unit transceiver until a message is received from said central unit tranceiver that the ranging signal has arrived in said small upstream frame gap; and

(6) thereafter, if necessary, adjusting said transmit frame timing delay value in accordance with an instruction message from said central unit transceiver such that each said ranging signal arrives at a precise location in said small upstream frame gap.

3. The process of claim 2 wherein step (3) comprises the step of transmitting a barker code as said ranging signal where each said remote unit transceiver transmits the same barker code which is known to said central unit transceiver.

4. The process of claim 3 wherein step (4) comprises monitoring each gap to determine if one or more barker codes has arrived, and, if so, broadcasting an authentication request message to all remote unit transmitters indicating activity has been found in said gap and requesting each remote unit transceiver which is transmitting ranging signals to hold the trial and error delay value at the current value and transmit a signature sequence comprised of the transmission or lack of transmission of said barker code during an even number of frames and the gaps between said frames such that, if only one remote unit transceiver'"'"'s barker code is arriving during this even number of gaps, exactly 50% of said gaps will have barker codes arriving therein at said central unit transceiver, and 50% will not, with the sequence of gaps having barker codes and not having barker codes of each remote unit transceiver being unique, and further comprising a determination if only 50% of the gaps have barker codes therein, and, if so, determining the identity of the remote unit transceiver from the signature sequence and transmitting said identity downstream, and, if more than 50% of the signature sequence gaps have barker codes therein, transmitting a collision message downstream requesting all remote unit transceivers that are attempting to achieve frame synchronization to execute predetermined collision resolution protocols such that some random number of said remote unit transceivers stop attempting to achieve frame synchronization and start the process again later, and repeating the steps of transmitting the authentication request message and monitoring for collisions and transmitting a collision message downstream if a collision is detected and execution of said collision resolution protocol by the remaining remote unit transceivers still attempting to achieve frame synchronization until a single unique signature sequence is successfully received in the authentication sequence gaps at said central unit transceiver, and then transmitting the identity of the remote unit transceiver that is assigned to the signature sequence so received downstream along with an instruction as to how to adjust said trial and error delay value so as to cause said ranging signals to arrive at a specific, predetermined location in every gap, and wherein step (5) comprises continuing to adjust said trial and error delay value until said authentication request message is received and then holding said trial and error delay value constant during the transmission of said signature sequence, and wherein step (6) further comprises holding said trial and error delay value constant at the value it had when said authentication request message was received and monitoring said downstream messages from said central unit transceiver until said remote unit transceiver recognizes its own identification in the messages received from said central unit transceiver and then adjusting said trial and error delay value by the amount and in the direction specified for this particular remote unit transceiver in the downstream message or messages from said central unit transceiver.

5. A process for ranging in any digital data communication system requiring frame synchronization of frames transmitted over a shared transmission media by a plurality of physically distributed remote transceivers to a central transceiver such that all such frames arrive at said central transceiver with their frame boundaries aligned in time, comprising:

(1) in each remote transceiver which has not achieved frame synchronization, receiving a downstream reference signal that marks a reference time which lies within a gap during each frame during which no transmission of payload data is allowed, and establishing a first trial and error delay value relative to said reference time for transmission of a ranging signal to said central transceiver and transmitting said ranging signal;

(2) at said central transceiver listening for said ranging signals from said remote transceivers during each upstream frame and transmitting a status message to said remote transceivers that indicate if a ranging signal has been detected during said gap or not, and, if so, requesting transmission of a signature;

(3) in each said remote transceiver which has not achieved frame synchronization, doing substantially all the processing necessary to achieve frame synchronization by receiving said status message and, if said status message indicates no ranging signal was received during said gap, adjusting said trial and error delay value and transmitting another ranging signal in response to the next reference signal received from said central transceiver, and continuing this receipt of a status message and trial and error adjustment until a status message is received indicating a ranging signal has been received during said gap and requesting transmission of a signature, and then holding the delay value steady at its then existing value and using said delay value to transmit a signature that identifies said remote transceiver;

(4) in said central transceiver, listening for said signature and determining from it if more than one remote transceiver'"'"'s ranging transmissions are being received during the same gap, and, if so, transmitting a downstream contention message so indicating and requesting each remote transceiver which has not achieved frame synchronization to execute a contention resolution protocol that will cause some of said remote transceivers to temporarily suspend further attempts to achieve frame synchronization, and if the signature indicates that only one remote transceiver'"'"'s ranging transmissions are being received during said gaps, identifying the particular remote transceiver that sent said signature and sending a downstream fine tuning message indicating the identity of the remote transceiver to whom the fine tuning message is directed and by how much and in which direction to adjust that remote transceiver'"'"'s trial and error delay value such that said ranging transmissions will be received at a predetermined reference time within each gap;

(5) in each remote transceiver that is attempting to achieve frame synchronization, receiving said contention message or said fine tuning message, and, if a fine tuning message is received identifying the particular remote transceiver that sent said signature, adjusting said trial and error delay value in accordance with the fine tuning message and commencing transmissions of frames of upstream payload data using this value for said trial and error delay value as a time reference at which to start transmission of each upstream frame, and if a contention message is received, randomly deciding whether or not to continue ranging and, if a decision to continue ranging has been made, retransmitting said signature using the same value for said trial and error delay as was used for the last signature transmission from this remote transceiver;

(6) in said central transceiver, monitoring said gaps for receipt of a signature, and, if only one remote transceiver'"'"'s signature is received in said gap or gaps, identifying said remote transceiver and transmitting a fine tuning message to said remote transceiver identifying it and instructing it by how much and in which direction to adjust said trial and error delay value, and if more than one signature is received, repeating steps (4), (5) and (6) until only one signature is received and a fine tuning message has been sent to the remote transceiver having that signature, but if no signature has been received, sending a re-execution message requesting all remote transceivers that have not yet achieved frame synchronization to re-execute their contention resolution protocols to again randomly decided whether to continue ranging or to stop ranging which will cause some remote transceivers to resume the ranging process;

(7) in any remote transceiver which has decided to continue ranging or resume ranging, retransmitting its signature using the same delay as was used the last time the signature was transmitted; and

(8) if no more than a predetermined number of attempts have been made to achieve frame synchronization, repeating steps (6), (7) and (8) until frame synchronization has been achieved, but if more than a predetermined number of attempts have been made to achieve frame synchronization without success, repeating steps (1) through (8).

6. The process of claim 5 further comprising the steps:

transmitting said downstream reference signal from said central transceiver to each remote transceiver using a variable delay relative to the start of each frame and which is set at a first value initially such that the furthest remote transceiver can achieve frame synchronization to the same gap as all the other remote transceivers that have already achieved frame synchronization;

monitoring the frame synchronization status of one or more of said remote transceivers and, when one or more remote transceivers have lost frame synchronization because of increased propagation time and cannot achieve frame synchronization anew because the trial and error delay for said one or more transceivers has reached its limit of adjustment, altering the delay imposed in said central transceiver before transmission of said reference signal in such a way that all remote transceivers can again achieve frame synchronization to the same gap.

7. A method of achieving frame synchronization in a distributed digital data communications network implemented on a hybrid fiber coax cable TV network having a central transceiver coupled by an optical fiber link to an optical node which is directly coupled to one or more remote transceivers and is coupled by a plurality of coaxial cable links to a plurality of remote transceivers, comprising:

transmitting a barker code or other reference signal, hereafter referred to as the reference signal, during every downstream frame of data transmitted from said central transceiver to said remote transceivers, said reference signal transmitted at a time relative to the beginning of each downstream frame established by a first delay value T_cu ;

at a remote transceiver directly coupled to said optical node, responding to receipt of said reference signal by transmitting a ranging signal at a first remote delay value in an attempt to cause said ranging signal to arrive at said central transceiver during a gap between frames which is some integer number of frames in the future following the frame during which said reference signal was transmitted where every downstream frame is followed by a gap during which no payload data is transmitted and every upstream frame is numbered and is the same size as the downstream frames and is followed by a gap also where the first and all subsequent downstream frames are offset in time from the first and all subsequent upstream frames, said first remote delay value set at an interval T_ru which is equal to

space="preserve" listing-type="equation">T.sub.near =T.sub.F -T.sub.u

where the mathematical relationship that defines the gap which is an integer n frame times, T_F, into the future to which all the remote transcievers attempt to align is given by

space="preserve" listing-type="equation">TTA=T.sub.cu +T.sub.ru +2×

T=constant=n×

T.sub.F

where

TTA=the total turnaround time from the central transceiver to the farthest remote transceiver coupled by a coaxial cable to said optical node, and

T_ru =the delay imposed by the furthest remote transceiver from said central transceiver along said fiber optic link and coaxial cable link before transmitting said ranging signal;

2×

T_P =two times the propagation delay T_P from said central transceiver to the furthest remote transceiver from said central transceiver along said fiber optic link and coaxial cable link;

n×

T_F =an integer multiple of the frame interval T_F ;

and wherein there are three additional requirements imposed with respect to how much delay said central transceiver and said remote transceivers must be able to impose, the first of which is;

space="preserve" listing-type="equation">T.sub.cu =(T.sub.d +T.sub.u)modulo T.sub.F

where

T_d =the span of the network which is equal to the quantity (TTA₂ -TTA₁) where TTA₂ is equal to the total turnaround propagation time for a signal to propagate from the central transceiver to the farthest remote transceiver and back and TTA₁ equals the total turnaround propagation time for a signal to propagate from the central transceiver to the nearest remote transceiver and back and modulo T_F equals the remainder of ##EQU1## and where T_u equals the uncertain additional propagation delay caused by network expansion, the second requirement being;

space="preserve" listing-type="equation">T.sub.far >

T.sub.u

where

T_far =the small possible T_ru of the farthest remote transceiver which is equal to the smallest possible delay which can be imposed by the farthest remote transceiver, and where the third requirement is;

space="preserve" listing-type="equation">T.sub.near <

T.sub.F -T.sub.u

where T_near is equal to the maximum possible T_ru of the nearest remote transceiver; and

assuming said remote transceiver which had its delay value T_ru set equal to T_near =T_F -T_u does not hit any gap with its ranging signal, adjusting the delay value T_cu of said central transceiver until the remote transceiver which had its delay value T_ru set equal to T_near =T_F -T_u does hit a gap with its ranging signal, thereby causing the condition T_cu =(T_d +T_u) modulo T_F to be true thereby indicating that the central transceiver has adjusted its delay value T_cu adequately to compensate for the uncertain amount of propagation delay T_u caused by network expansion.