US 2003/0156603 A1 · Apparatus and method for trellis encoding data for transmission in digital data transmission systems

An apparatus comprising:

a central unit transmitter having an input to receive downstream digital data, and having an input for receiving a master clock signal and an input for receiving a master carrier signal, said transmitter transmitting signals from which said master clock and master carrier signals can be recovered and from which said downstream data can be recovered;
a transmission media coupled to said modulator through which signals from said central transmitter propagate;
a remote unit receiver coupled to said transmission media to receive said signals transmitted from said central unit transmitter and having a local clock reference input for receiving a local clock reference signal and a local carrier reference input for receiving a local carrier reference signal, said remote unit received for recovering and outputting said downstream data;
a tracking loop circuit in said remote unit receiver and coupled to said local clock reference input and said local carrier reference input and having a frame detector coupled to a first voltage controlled oscillator for supplying to said remote unit receiver said local clock reference signal and having a slicer coupled to a second voltage controlled oscillator for supplying said local carrier reference signal, said tracking loop circuit for locking the phase and frequency of said local clock reference signal and said local carrier reference signal to the phase and frequency of said master clock and master carrier signals from said signals transmitted by said central unit transmitter;
a remote unit transmitter coupled to said transmission media and having an input for upstream digital data and having an input coupled to receive a carrier reference signal which is phase coherent with said local master carrier reference signal and having an input coupled to receive a carrier reference signal which is phase coherent with said local clock reference signal, said remote unit transmitter, for transmitting signals from which said clock and carrier reference signals can be detected and for transmitting signals from which said upstream digital data can be extracted;
a central unit receiver coupled to said transmission media and having inputs for receiving a phase adjusted clock signal and a phase adjusted carrier signal, said central unit receiver recovering and outputting said upstream digital data;
a phase detect and adjust circuit coupled to receive said master clock and master carrier signals and said signals transmitted from said remote unit transmitter, for supplying a phase adjusted master clock signal and a phase adjusted master carrier signal to said central unit receiver, and occasionally or periodically adjusting the phase of said phase adjusted master carrier signal and said phase adjusted master clock signal to be phase coherent with the local master carrier reference signal and the local master clock reference signal, respectively, used by said remote unit transmitter to transmit said upstream digital data.

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A process of bidirectionally communicating digital data comprising:

using a master clock signal to modulate downstream digital data onto a master carrier signal, and transmitting signals through a transmission media from which said downstream digital data and said master clock signal and said master carrier signal can be recovered;
receiving said signals propagating through said transmission media, and recovering said master carrier and master clock signals and using said master carrier and master clock signals to generate local master clock reference and local master carrier reference signals which are phase coherent with said recovered master clock signal and said recovered master carrier signals, respectively, and using said local master clock reference and local master carrier reference signals to recover said downstream digital data;
using said local master clock reference and local master carrier reference signals to modulate upstream digital data onto said local master carrier reference signal, and transmitting through said transmission media signals from which said local master clock reference signal and said local master carrier reference signal can be recovered and transmitting signals from which said upstream digital data can be recovered;
receiving said signals bearing said local master clock reference and said local master carrier reference signal information and bearing said upstream digital data information, and receiving said master clock signal and said master carrier signal and occasionally or periodically adjusting the phase or frequency or both of said master clock signal and said master carrier signal so as to be phase coherent with said local master clock reference signal and said local master carrier reference signal, respectively, to generate a phase adjusted master clock signal and a phase adjusted master carrier signal, and using said phase adjusted master clock signal and said phase adjusted master carrier signal to recover said upstream digital data.

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A system comprising:

a central unit transceiver which uses a master clock signal and master carrier signal to transmit downstream payload data;
a plurality of remote unit transceivers each coupled to said central unit transceiver through a transmission media, and each having a receiver section including a tracking loop to recover said master clock signal and a tracking loop to recovers said master carrier signal from signals transmitted from said central unit transceiver, and including circuitry to use said recovered master clock signal, as signals generated therefrom, and said recovered master carrier signal, or signals generated therefrom, to recover said downstream payload data and to transmit upstream payload data, each said remote unit transceiver including circuitry to transmit preamble data preceding upstream payload data for use by said central unit transceiver;
and wherein said central unit transceiver includes circuitry for using said preamble data for determining the phase difference for the particular remote unit transceiver which transmitted said preamble data between the master clock signal of the central unit transceiver and that remote unit transceiver's recovered master clock signal, or signals generated therefrom, and between the master carrier signal of the central unit transceiver and the remote unit transceivers recovered master carrier signal, or signals generated therefrom, and for using the phase difference(s) so determined for each remote unit and a rotational amplifier and circuitry associated therewith to get the proper phase adjustment factor for a particular remote unit applied to said rotational amplifier when payload data from that particular remote unit transceiver is being received so as to recover said upstream payload data transmitted by that particular remote unit transceiver thereby eliminating the need for tracking loops in said central unit transceiver to continuously track the clock and carrier signals used by each said remote unit transceiver to transmit upstream payload data.

A central unit modem apparatus comprising:

a framing circuit having a memory and circuitry to receive downstream data and store it in said memory organized as frames of data each frame comprising one or more symbols, and having circuitry to read data out of said memory and present said downstream data at an output;
a transmitter coupled to receive said downstream data from said output and having circuitry to multiplex said downstream data onto a transmission media using any form of multiplexing and any form of modulation;
and
a synchronous code division multiplexed receiver coupled to receive modulated upstream signals from a plurality of remote unit modems and having circuitry to demodulate and demultiplex said upstream signals and detect upstream data from said demodulated, demultiplexed upstream signals.

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A remote unit modem comprising:

a receiver circuit capable of demodulating and demultiplexing downstream signals transmitted from a central unit modem regardless of the type of modulation and multiplexing used by said central unit modem, and detecting and recovering downstream payload data from said demodulated, demultiplexed downstream signals, and wherein said downstream signals include information from which can be recovered a master clock and master carrier signal used by said central unit modem in generating said downstream signals, and wherein said receiver circuit further comprises circuitry to recover from said downstream signals said master clock and master carrier signals and generate remote unit clock and carrier signals therefrom which are locked in phase and frequency with said recovered master clock and master carrier signals, and using said remote unit clock and carrier signals so generated to demodulate and demultiplex said downstream signals and to detect said downstream payload data from the demodulated, demultiplexed downstream signals, said receiver including circuitry to detect a marker signal transmitted from said central unit modem which marks a fixed reference time in each frame of downstream data transmitted by said central unit modem and to generate a signal indicating when said marker signal arrives, said receiver including circuitry to receive management and control data from said central unit even before frame synchronization is achieved;
a synchronous code division multiplexed transmitter coupled to receive said remote unit clock and carrier signals, or clock and carrier signals which are at least phase coherent with said remote unit clock and carrier signals, and coupled to receive upstream payload data, said synchronous code division multiplexed transmitter including ranging circuitry for achieving frame synchronization by transmitting ranging signals with good correlation properties which can be found easily in noise and can be found even if they arrive in the middle of payload data, said ranging circuitry for transmitting said ranging signals at a series of different trial and error delays relative to said fixed reference time in each frame of data transmitted by said central unit modem, the amount of said delays established by a time delay input signal, said synchronous code division multiplexed transmitter including multiplexing and modulation circuitry for code division multiplexing said upstream payload data to generate spread spectrum data and modulating the resulting spread spectrum data onto one or more RF carriers for transmission to said central unit modem;
and
a computer coupled to said receiver to receive said management and control data and coupled to receive said signal indicating when said marker signal arrived from said central unit modem, and including circuitry programmed to generate said time delay input signal to control said trial and error delays used by said transmitter to transmit said ranging signal and programmed to transmit said time delay input signal to said synchronous code division multiplexed transmitter and programmed to vary the amount of delay commanded by said time delay input signal relative to the time of receipt of said marker signal and controlling the amount of power used to transmit said ranging signals until said management and control data received from said central unit modem indicate that a delay value Td and a power level has been found which causes said ranging signals to arrive within gaps in the central unit frames thereby achieving approximate frame boundary alignment, and, thereafter, for holding the amount of delay Td commanded by said time delay input signal constant at the amount of delay which caused said approximate frame boundary alignment.

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A remote unit modem comprising:

a receiver circuit capable of demodulating and demultiplexing downstream signals transmitted from a central unit modem regardless of the type of modulation and multiplexing used by said central unit modem, and detecting and recovering downstream payload data from said demodulated, demultiplexed downstream signals, and wherein said downstream signals include information from which can be recovered a master clock and master carrier signal used by said central unit modem in generating said downstream signals, and wherein said receiver circuit further comprises circuitry to recover from said downstream signals said master clock and master carrier signals and generate remote unit clock and carrier signals therefrom which are locked in phase and frequency with said recovered master clock and master carrier signals, and using said remote unit clock and carrier signals so generated to demodulate and demultiplex said downstream signals and to detect said downstream payload data from the demodulated, demultiplexed downstream signals, said receiver including frame detector circuitry to detect a Barker code transmitted from said central unit modem during each gap between frames of downstream data transmitted by said central unit, said Barker code marking the position of each said gap in said stream of downstream data, said frame detector generating a marker signal indicating when said barker code arrives, said receiver including circuitry to receive management and control data from said central unit;
a synchronous code division multiplexed transmitter coupled to receive said remote unit clock and carrier signals, or clock and carrier signals which are at least phase coherent with said remote unit clock and carrier signals, and coupled to receive upstream payload data, said synchronous code division multiplexed transmitter including ranging circuitry for achieving exact frame synchronization by transmitting Barker codes back to said central unit at a series of different trial and error delays Td relative to receipt of said marker signal, the amount of said delays Td being controlled by a time delay input signal, said synchronous code division multiplexed transmitter including multiplexing and modulation circuitry for using said remote unit clock and carrier signals or said clock and carrier signals which are at least phase coherent with said remote unit clock and carrier signals to code division multiplex said upstream payload data to generate spread spectrum data and to modulate the resulting spread spectrum data onto one or more RF carriers for transmission as modulated RF signals to said central unit modem, said synchronous code division multiplexed transmitter transmitting said modulated RF signals in frames, each frame transmitted at an interval following occurrence of said marker signal, said interval defined by the value of Td which causes each said frame to arrive with its frame boundaries exactly aligned in time with receive frame boundaries of said central unit;
and
a computer coupled to said receiver to receive said management and control data and said marker signal, and including circuitry programmed to generate and increment said time delay input signal to control said trial and error delays Td used by said transmitter to transmit said Barker code, said time delay input signal being coupled to said synchronous code division multiplexed transmitter, said computer also programmed to vary the amount of delay commanded by said time delay input signal relative to the time of receipt of said marker signal until said management and control data received from said central unit modem indicate that a delay value Td has been found which causes said Barker codes transmitted by said transmitter to arrive within gaps in central unit frames, said computer programmed to further fine tune the value of said time delay input signals until said Barker codes transmitted by said remote unit arrive exactly in the middle of gaps in said central unit frames thereby achieving exact frame boundary alignment with central unit frame boundaries.

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A remote unit modem for use in a distributed system comprised of a plurality of remote unit modems coupled by a shared transmission media to a central unit modem, comprising:

a receiver circuit capable of demodulating and demultiplexing downstream signals transmitted from a central unit modem regardless of the type of modulation and multiplexing used by said central unit modem, and detecting and recovering downstream payload data from said demodulated, demultiplexed downstream signals, and wherein said downstream signals include information from which can be recovered a master clock and master carrier signal used by said central unit modem in generating said downstream signals, and wherein said receiver circuit further comprises circuitry to recover from said downstream signals said master clock and master carrier signals and generate remote unit clock and carrier signals therefrom which are locked in phase and frequency with said recovered master clock and master carrier signals, and using said remote unit clock and carrier signals so generated to demodulate and demultiplex said downstream signals and to detect said downstream payload data from the demodulated, demultiplexed downstream signals, said receiver including frame detector circuitry to detect a Barker code transmitted from said central unit modem during each gap between frames of downstream data transmitted by said central unit, said Barker code marking the position of each said gap in said stream of downstream data, said frame detector generating a marker signal indicating when said barker code arrives, said receiver including circuitry to receive management and control data from said central unit;
a synchronous code division multiplexed transmitter coupled to receive said remote unit clock and carrier signals, or clock and carrier signals which are at least phase coherent with said remote unit clock and carrier signals, and coupled to receive upstream payload data, said synchronous code division multiplexed transmitter including boundless ranging circuitry for achieving exact frame synchronization by transmitting Barker codes back to said central unit at a series of different trial and error delays Td relative to receipt of said marker signal, the amount of said delays Td being controlled by a time delay input signal, said synchronous code division multiplexed transmitter including multiplexing and modulation circuitry for using said remote unit clock and carrier signals or said clock and carrier signals which are at least phase coherent with said remote unit clock and carrier signals to code division multiplex said upstream payload data to generate spread spectrum data and to modulate the resulting spread spectrum data onto one or more RF carriers for transmission as modulated RF signals to said central unit modem, said synchronous code division multiplexed transmitter transmitting said modulated RF signals in frames, each frame transmitted at an interval following occurrence of said marker signal, said interval defined by the value of Td which causes each said frame to arrive with its frame boundaries approximately aligned in time with receive frame boundaries of said central unit;
and
a computer coupled to said receiver to receive said management and control data and said marker signal, and including circuitry programmed to generate and increment said time delay input signal to control said trial and error delays Td used by said transmitter to transmit said Barker code, said time delay input signal being coupled to said synchronous code division multiplexed transmitter, said receiver and ranging circuitry being structured in each remote unit and said computer so programmed in each said remote unit so as to cooperate with said receiver and said ranging circuitry in said transmitter of each said remote unit modem to function in a way to carry out the following process to achieve approximate frame synchronization and rough power alignment:
(1) transmitting a Barker code a predetermined delay Td following the occurrence of every marker signal, said computer programmed to start said Barker code transmissions at a first power level and at a first minimum value for delay Td and to increase said delay every frame and re-transmit another Barker code while leaving the power level the same until a maximum value for delay Td is reached, and then to repeat the process of incrementing the value of the delay Td at a new higher power level than the power level used during the previous cycle, and continue increasing the power level and trying all of said predetermined delays at that power level until a first command and control message is received from said central unit indicating that a possible Barker code has been detected in a gap in said central unit frames;
(2) once said first message has been received from said central unit that a possible Barker code has been detected in a gap, said computer assumes the activity detected was one of the prior Barker code transmissions from this remote unit, and determines which delay value Td of the multiple values for Td previously used to send Barker codes caused a Barker code from this remote unit to arrive during a central unit gap by setting the delay Td to the value used X frames before said first message was received where X is equal to the total turnaround time in whole frames to the farthest remote unit in the distributed system, sending a single Barker code transmission using that delay value, and waiting at least X frames for a second reply message from said central unit indicating that a Barker code was received during a central unit receive frame gap;
(3) if no second reply message is received during said X frames, incrementing the value for delay Td in said computer to the value used to transmit the Barker code in the X+1 frame which is defined as the frame which followed the frame corresponding to the value for Td selected in step 2 and sending said incremented delay value to said ranging circuitry to cause it to transmit another Barker code at a time following receipt of the next marker signal by an interval equal to said incremented delay value, and waiting the duration of X frames for said second reply message, and continuing this process of incrementing the value of Td to each of the values used at each of the X preceding frames, transmitting a single Barker code and waiting X frames for receipt of said second reply message until said second reply message is received from the central unit indicating activity has been detected in a gap and naming a first central unit frame number having a gap in which a Barker code was detected and requesting the remote unit to send the ID code for that remote unit, and holding the value of delay Td steady at the value which resulted in transmission of said second reply message;
(4) using said ranging circuitry at the request of said computer to transmit an ID code comprising a start bit which is always a 1 and a predetermined number of ID bits a predetermined number of which are 1s and the rest of which are 0s, with a 1 being defined as the transmission of a Barker code in a gap and a 0 defined as the lack of transmission of a Barker code in a gap;
(5) receiving a third reply message from said central unit when said central unit receives said start bit and said ID code and detects therein a predetermined number of 1s indicative of the fact that no other remote unit's ID code arrived at the same time at the central unit thereby indicating no contention, said third reply message containing at least the ID code detected by the central unit and the central unit frame number during which said start bit of said ID code arrived, said ranging circuitry and said computer structured and programmed to compare the ID code in said third reply message against the ID code transmitted by said remote unit modem, and, if there is a match, to calculate a frame offset number needed to achieve boundless ranging, said frame offset number being comprised of the frame number given in said third reply message minus the frame number given in said second reply message;
and
(6) thereafter receiving command and control messages assigning particular orthogonal spreading codes to be used during particular central unit receive frame numbers and counting marker signals to generate a count indicating the central unit frame number just received and subtracting said offset number therefrom to generate a new frame count and controlling said synchronous code division multiplexed transmitter in said remote unit to transmit each numbered frame to the central unit delayed by the current value for the delay Td when said new frame count reaches a frame number authorized for transmission by said central unit and using the orthogonal spreading codes assigned by said central unit to code division multiplex the data to be transmitted during said assigned frame number.

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A process for fine tuning the amount of power with which data is transmitted to a central unit receiver by each of a plurality of remote unit transmitters which are physically spread throughout a distributed digital data communication system, using code division multiple access multiplexing accomplished with orthogonal, cyclic spreading codes for transmissions, each said remote unit transmitter having a variable gain amplifier, and wherein said central unit has a receiver having an adaptive gain control circuit comprised of a slicer and an amplifier having a variable gain the gain control factor of which is controlled by an amplitude correction factor stored in memory, said memory storing an amplitude correction factor for each said spreading code and a control circuit that receives slicer amplitude error signals from said slicer and controls the gain number applied to said amplifier, comprising the following steps performed one at a time in each remote unit transmitter:

(b 1) transmitting training data from a remote unit transmitter to said central unit receiver using a gain level of one in said remote unit transmitter variable gain amplifier, the spectrum of said training data having been spread using each of a plurality of consecutive, orthogonal, cyclic spreading codes, and modulating the training data using BPSK modulation;
(2) setting the gain of said variable gain amplifier using the amplitude correction factor for a particular one of the codes in the midst of said consecutive, orthogonal, cyclic spreading codes, and allowing said adaptive gain control circuit to converge on an amplitude correction factor for the training data that results in proper decisions on said training data made by said slicer and adjusting the gain of said variable gain amplifier to a new gain value in accordance with said amplitude correction factor so determined;
(3) transmitting said new gain value to said remote unit transmitter and setting the power level of transmissions by said remote unit transmitter in accordance with said new gain value;
and
(4) setting the gain control factor of said variable gain amplifier in said central unit to one.

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A process for fine tuning the amount of power with which data is transmitted to a central unit receiver by each of a plurality of remote unit transmitters which are physically spread throughout a distributed digital data communication system, using code division multiple access multiplexing accomplished with orthogonal, cyclic spreading codes for transmissions, and wherein said central unit has a receiver having an symbol equalizer having at least an FFE digital adaptive filter having a main tap and one or more side taps, comprising the following steps performed one at a time in each remote unit transmitter:

(1) setting an adaptation coefficient in said symbol equalizer to a value selected to insure rapid convergence;
(2) transmitting training data from a remote unit transmitter to said central unit receiver the spectrum of said training data having been spread using each of a plurality of consecutive, orthogonal, cyclic spreading codes, and modulating the training data using BPSK modulation;
(3) disabling said one or more side taps and enabling said symbol equalizer filter to converge for an interval sufficient to train said main tap adequately for purposes of power alignment;
(4) calculating the amplitude of the main tap correction factor after said interval has elapsed and comparing said amplitude the expected amplitude of said main tap when proper power alignment has been achieved and calculating the difference and comparing said difference or said difference divided by a constant to a threshold;
(5) if said threshold is exceeded, transmitting a new gain value to said remote unit transmitter, said new gain value being equal to said difference times a constant and setting the power level of transmissions by said remote unit transmitter in accordance with said new gain value;
and
(4) repeating steps 1 through 5 until said difference is less than said threshold or a predetermined number of iteratins of steps 1 through 5 has been exceeded.

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A digital data communication apparatus including frame synchronization fine tuning circuitry, comprising:

a central unit transceiver having a transmitter which transmits downstream data in CU downstream frames separated by gaps using master clock and master carrier signals which are both synthesized from a single crystal oscillator source and which transmits a marker signal during every CU downstream frame gap, said marker signal bearing at least phase information defining the phase of said master clock, said central unit transceiver also having a receiver which receives upstream data in CU upstream frames separated by gaps;
a remote unit transceiver having a transmitter which transmits said upstream data in RU upstream frames separated by gaps, said RU upstream frames and gaps having the same duration as said CU upstream frames and gaps to said central unit receiver and including ranging circuitry which transmits a ranging signal to achieve frame synchronization so as to exactly align said RU upstream frame boundaries with said CU upstream frame boundaries, said remote unit transceiver having a receiver circuitry to receive said marker signal and command and control messages transmitted in said CU downstream frames, said ranging signal transmitted during the process of achieving frame synchronization during selected RU upstream frames at a delay Td following receipt of said marker signal, said remote unit receiver including synchronization circuitry to recover said master clock and master carrier signals from said marker signal, a correlator to correlate said received downstream signals against a signal having the shape and duration of said marker signal so as to locate said marker signal so as to generate a correlation peak when said marker signal is found and said CU downstream frame gap is located thereby, and having early-late gating circuitry to sample said correlation peak at two different points on either side of the maximum amplitude of said correlation peak to generate a clock steering signal during each CU downstream frame and having clock tracking loop circuitry to generate a local master clock signal from said clock steering signal, and having synthesizer circuitry to generate a local master carrier signal from phase information in said local master clock signal, said remote unit transmitter using said local master clock and local master carrier signals or signals that are phase coherent therewith to transmit said RU upstream frames, and including circuitry to transmit, at predetermined times, preamble data before transmitting said RU upstream frames, said preamble data being such that said central unit receiver can determine phase and amplitude error correction factors therefrom so that said central unit receiver can recover said local master clock and local master carrier signals used by said remote unit transmitter and to properly demodulate and detect data in said RU upstream frames, said correction factors being made necessary by latency and channel impairments, said remote unit transmitter including circuitry to alter said delay Td by trial and error for different transmissions of said ranging signal, and wherein said remote unit receiver includes circuitry to receive command and control messages from said central unit transmitter regarding changing the value of said delay Td, and changing the value of delay Td in accordance therewith;
and wherein said central unit receiver includes ranging circuitry, including correlation circuitry structured so as to find said ranging signals, and including circuitry to compare the position of said ranging signals to the centers of said CU upstream frame gaps and generate messages for transmission to said remote unit to cause said delay Td to be altered until said ranging signals arrive exactly in the center of CU upstream frame gaps so as to exactly align said RU upstream frame boundaries with said CU upstream frame boundaries, and further including circuitry to receive said preamble data from each remote unit and derive therefrom amplitude and phase error correction factors to aid in the process of recovering digital data transmitted in said RU upstream frames.

A distributed communication system having a central unit transceiver coupled by a shared transmission media to a plurality of remote unit transceivers wherein said remote unit transceivers and said central unit transceiver include circuitry to bidirectionally communicate digital data in synchronized frames separated by gaps using any form of multiplexing and any form of modulation wherein each said remote unit transceiver and said central unit transceiver include ranging circuitry to carry out a ranging process before upstream data is transmitted whereby each said remote unit transceiver receives a marker signal from said central unit transceiver and transmits ranging signals at different values of a delay Td following receipt of said marker signal until a delay Td is found which causes the ranging signals to arrive at said central unit transceiver exactly in the middle of a gap between central unit transceiver frames such that frame boundaries of frames transmitted by each said remote unit transceiver arrive exactly aligned in time with frame boundaries of said central unit frames, and wherein said central unit transceiver transmits said said marker signals and data in downstream frames using a single master clock and a single master carrier, both said master clock and said master carrier being synthesized in said central unit transceiver from a single crystal controlled oscillator, said master clock and master carrier signals being transmitted downstream to said remote units in any known fashion and recovered there and used by each remote unit transceiver to transmit data upstream to said central unit in frames, each said remote unit transceiver transmitting its upstream data after transmitting at least some preamble data, said central unit transceiver including circuitry to use said preamble data from each remote unit transceiver to determine amplitude and phase correction factors for use in conjunction with said master clock and master carrier signals generated in said central unit transceiver to receive data from said remote unit transceiver by correcting for phase and amplitude errors caused by channel impairments and the transmission delay between said remote unit transceiver and said central unit transceiver thereby eliminating the need for continuous tracking loops in said central unit transceiver to recover the clock and carrier signals used by said remote unit to transmit upstream data.

A digital data communication system having a plurality of transceivers bidirectionally communicating digital data wherein said transceivers transmitting data in at least one direction use code division multiple access multiplexing to keep different conversations separate, where conversation is defined as transmission of data from one source or computer process to another different source or computer process via at least two transceivers, and wherein said transceivers include means for transmitting data in frames and in a frame synchronous manner such that frames of data from physically distributed transceivers all arrive at a predetermined location with their frame boundaries aligned in time.

A digital data communication system having a plurality of transceivers bidirectionally communicating digital data between a central unit transceiver and a plurality of distributed remote unit transceivers, and wherein at least said remote unit transceivers transmit data to said central unit transceiver using code division multiple access multiplexing to keep conversations between different remote unit transceivers and said central unit transceiver separate, where conversation is defined as transmission of data from one source or computer process to another different source or computer process via at least two transceivers, and wherein said central unit transceiver transmits data downstream to said remote unit transceivers in numbered frames separated by gaps, and wherein each remote unit transceiver uses temporarily assigned cyclic, orthogonal time shared spreading codes during specific frame numbers for transmission to said central unit transceiver after receiving assignments of specific codes to use during specific frames from said central unit transceiver, and wherein each said remote unit transceiver includes boundless ranging means for transmitting data in upstream frames in a frame synchronous manner such that all upstream frames of data transmitted from physically distributed transceivers at different delays after receipt of any particular frame number from the central unit transceiver and having the spectra thereof spread with codes assigned to said remote unit transceivers for use during a specific central unit transceiver frame number arrive at said central unit transceiver with their frame boundaries exactly aligned in time with the boundaries of the central unit frame having said specific frame number.

A digital data communication system having a plurality of transceivers bidirectionally communicating digital data between a central unit transceiver and a plurality of distributed remote unit transceivers, and wherein at least said remote unit transceivers transmit data to said central unit transceiver using code division multiple access multiplexing to keep conversations between different remote unit transceivers and said central unit transceiver separate, where conversation is defined as transmission of data from one source or computer process to another different source or computer process via at least two transceivers, and wherein said central unit transceiver transmits data downstream to said remote unit transceivers in frames separated by gaps, and wherein said remote unit transceivers include ranging means for transmitting data in upstream frames in a frame synchronous manner such that upstream frames of data from physically distributed transceivers all arrive at said central unit transceiver with their frame boundaries exactly aligned in time to a same central unit frame, all remote unit transceivers having their frame boundaries aligned in time with the frame boundaries of the same central unit frame, and wherein each remote unit transceiver uses temporarily assigned orthogonal spreading codes.

A method for transmitting multiple channels of digital data simultaneously over a cable television media carrying cable television programming, comprising:

receiving multiple channels of digital data;
selecting portions of said digital data from each channel and organizing said portions as an information vector having n elements;
performing code division multiplexing by performing a matrix multiplication of said information vector times a code matrix comprised of n orthogonal spreading codes, each code comprising one row or one column of said code matrix and having n elements, said matrix multiplication generating a result vector having n elements, each element comprised of the sum of the partial products of multiplication of each of the n elements of said information vector times the n elements of one of said orthogonal spreading codes;
modulating the n elements of said result vector onto one or more radio frequency carriers and transmitting the resulting radio frequency carriers on a cable television media carrying cable television programming while limiting the overall bandwidth of the resulting radio frequency signals so as to not interfere with said cable television programming.

1 more element

A method for transmitting to a central unit multiple channels of digital data generated by a plurality of sources coupled to a plurality of physically distributed remote units which are coupled to said central unit via a cable television media designed to carry radio frequency signals, said multiple channels of digital data being transmitted simultaneously over said cable television media as a plurality of frames of digital data, said cable television media also carrying frequency division multiplexed cable television programming, comprising:

etablishing frame synchronization at each remote unit by determining a transmit frame timing reference for each said remote unit such that, when each remote unit transmits data using that remote unit's transmit frame timing reference, said data will arrive at said central unit simultaneously;
receiving one or more channels of digital data at each remote unit;
at each remote unit, constructing an information vector by selecting portions of said digital data from each channel of digital data received at said remote unit and organizing said portions as selected elements of said information vector having n elements where each element of said information vector corresponds to one of said channels but wherein any element of said information vector corresponding to a channel from which no data is received by any particular remote unit is set to zero;
at each remote unit, performing code division multiplexing by performing a matrix multiplication of the information vector generated at said remote unit times a code matrix comprised of n orthogonal spreading codes, each code comprising one row or one column of said code matrix and having n elements, said matrix multiplication generating a result vector having n elements, each element of said result vector comprised of the sum of the partial products of multiplication of each of the n elements of said information vector times the n elements of one of said orthogonal spreading codes, and wherein zero elements of said information vector cause zero elements in said result vector;
at each remote unit, after frame synchronization has been achieved by that remote unit, modulating the n elements of said result vector onto one or more radio frequency carriers;
summing the one or more radio frequency carriers generated by each remote unit with one or more radio frequency carriers generated by other remote units and transmitting the resulting radio frequency carriers on a cable television media carrying cable television programming while limiting the overall bandwidth of the resulting radio frequency signals so as to not interfere with said cable television programming.

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A method for transmitting multiple channels of digital data over a transmission media simultaneously with transmissions carrying other services in a distributed communication system comprised of at least one central unit modem coupled by said transmission media to a plurality of remote unit modems, comprising:

receiving multiple channels of digital data;
in each of said central unit modem and said remote unit modems composing frames of data for transmission by selecting portions of said digital data from each channel received by said modem and organizing said portions as an information vector having n elements with at least one information vector per frame;
in at least said remote unit modems, performing code division multiplexing by performing a matrix multiplication of said information vector times a code matrix comprised of n orthogonal spreading codes, each channel having data therein having at least one code assigned thereto, each code comprising one row or one column of said code matrix and having n elements, said matrix multiplication generating a result vector having n elements;
using the n elements of the result vectors that comprise one frame of data in said remote unit modems or, in said central unit modems, using the n elements of the result vectors that define one frame of data if code division multiplexing is performed or, if code division multiplexing is not performed in said central unit modem, using the n elements of the information vectors that define one frame of data in said central unit modem to create the information content in one or more radio frequency carriers and transmitting the resulting radio frequency carriers carrying the data from each remote unit frame on said transmission media toward said central unit modem (hereafter referred to as the upstream channel), and transmitting the resulting radio frequency carriers carrying the data from each central unit frame on said transmission media toward said remote unit modems (hereafter referred to as the downstream channel), while limiting the overall bandwidth of the resulting radio frequency carriers transmitted in each direction so as to not interfere with said other services being simultaneously transmitted on said transmission media;
and wherein said step of composing frames of data in said central and remote unit modems further comprises the steps of composing equal sized frames of data in each of said central unit and remote unit modems, and wherein said step of transmitting the resulting radio frequency carriers carrying the data from each remote unit frame on said transmission media toward said central unit modem further comprises the step of waiting for a selected transmit frame timing delay for each remote unit before transmitting a frame from that remote unit, and further comprising the step of performing a ranging process to determine for each said remote unit modem a suitable transmit frame timing delay value which will cause frames transmitted from that remote unit modem to arrive at said central unit modem with frame boundaries aligned in time with the frame boundaries of said central unit modem frames;
and further comprising the step of, prior to transmission of any frames of data in the upstream direction from a remote unit modem, performing a training process for the remote unit modem by performing the following steps following the conclusion of said ranging process for said remote unit modem:
checking the accuracy of the frame synchronization established by said ranging process in each remote unit modem by using a predetermined one of a plurality of neighboring, orthogonal, cyclic spreading codes to send training data to said central unit modem from each remote unit modem, one remote unit modem at a time, and correlating said received data against each of said predetermined number of orthogonal, cyclic spreading codes in said central unit modem to determine how much crosstalk into neighboring cyclic spreading codes exists, and, if crosstalk exists for any remote unit modem, adjusting said transmit frame timing delay for said remote unit modem and rechecking the accuracy of said frame synchronization using the new transmit frame timing delay value, and, if an acceptably small level of crosstalk exists, proceeding to the next step;
setting the power level of transmissions from said remote unit modem such that said training sequence data transmitted by said remote unit modem is detected by said central unit modem with an acceptably low error rate and at approximately the same power level as transmissions from all the other remote unit modems;
performing upstream equalization by sending training sequence data to said central unit modem from said remote unit modem using each of a plurality of different, neighboring orthogonal, cyclic spreading codes;
adjusting tap weight coefficients of one or more adaptive equalizer circuits in a receiver in said central unit modem to minimize detection errors and reiterating for a plurality of iterations the process of sending said training sequence data to said central unit modem using each of a plurality of different, neighboring orthogonal spreading codes to spread the spectrum of the data and again adjusting the tap weight coefficients of said adaptive equalizer in said central unit modem to minimize errors, and when detection errors have been minimized after a plurality of iterations, sending the final tap weight coefficients for use as the tap weight coefficients for an adaptive precode filter in said remote unit transmitter and setting the tap weight coefficients of said adaptive equalizer in said receiver of said central unit modem to one;
and
performing downstream equalization by sending training sequence data to said remote unit modem from said central unit modem using each of a plurality of different, neighboring orthogonal spreading codes;
adjusting tap weight coefficients of a first adaptive equalizer circuits in a receiver in said remote unit modem to minimize detection errors and reiterating for a said training sequence data from said central unit mo unit modem using each of a plurality of different, neighboring orthogonal spreading codes to spread the spectrum of the data and again adjusting the tap weight coefficients of said first adaptive equalizer in said remote unit modem to minimize errors, and when detection errors have been minimized after a plurality of iterations, sending the final tap weight coefficients for use as the tap weight coefficients for a second adaptive equalizer in said receiver of said remote unit modem and setting the tap weight coefficients of said first adaptive equalizer in said receiver of said remote unit modem to initialization values.

10 more elements

A bidirectional digital data communication system having a central unit transceiver coupled by a transmission media to a plurality of distributed remote unit transceivers wherein said central unit transceiver includes a transmitter having an encoder for receiving data and encoding it into frame for multiplexing, a multiplexer for multiplexing the encoding data to generate multiplexed data and a modulator for using said multiplexed data to modulate one or more RF carriers so as to send downstream data to said remote unit transceivers wherein said multiplexer uses any form of multiplexing to keep data directed to different remote units separate, and wherein each said remote unit transceiver sends upstream data to said central unit transciever using synchronous time division multiple access multiplexing using an encoder to receive upstream data and divide it into groups suitable for transmission in timeslots of an upstream frame, said upstream frame being of the same size as said downstream frames, and a time division multiple access multiplexer for receiving said smaller groups of data from said encoder and placing said groups of data into timeslots in an upstream frame assigned to this remote unit transceiver and a modulator to receive the TDMA multiplexed data and modulate it onto one or more RF carriers, each said remote unit transceiver including a frame detector circuit to recognize a marker signal in each downstream frame to establish a receive frame timing reference, and a ranging circuit for cooperating with said central unit transceiver and said frame detector circuit to establish a delay Td relative to said receive frame timing reference for each frame and for transmitting each said upstream frame at a time Td after receipt of said marker signal marking receipt of a downstream frame, said ranging circuit in each remote unit transceiver cooperating with said central unit transceiver to establish the value for Td in each remote unit transceiver at a value which will cause all upstream frames from all remote unit transceivers to arrive at said central unit transceiver having their frame boundaries exactly aligned in time with the frame boundaries of said central unit frames.

An apparatus for transmitting multiple channels of digital data encoding supplemental services from a remote unit to a central unit over a shared transmission media using synchronous code division multiple access transmission, comprising:

means for accepting incoming data of a time division multiple access stream comprised of N time slots or channels each of which contains one or more bits of digital data encoding said supplemental services and organizing the data of said N channels into a frame comprised of M contiguous information vectors from each of which a symbol for transmission will be generated and a guardband during which no data from said time divsion multiple access stream is transmitted, said reorganizing carried out by reorganizing a portion of the data from each of said N channels into elements of each of said M information vectors each comprised of N elements, each element comprising a subgroup of bits from one channel or timeslot of said time divsion multiple access stream plus error detection and correction bits generated by a Trellis encoder, each information vector containing at least one element from each said channel plus error detection and corrections bits, and for dividing each element of each said information vector into a real and imaginary component;
means for direct sequence spread spectrum encoding of each of said M information vectors using N orthogonal, cyclic codes by matrix multiplying both the real and imaginary components of each information vector times a matrix embodying said N orthogonal, cyclic codes such that the data from each channel is multiplied by an orthogonal, cyclic spreading code assigned to that channel so as to generate M result vectors, each result vector being the basis for one symbol, each result vector having N elements, each element of each result vector having real and imaginary components and passing the data of said real and imaginary result vectors for each frame through shaping passband filters having transfer functions which satisfy the Nyquist criteria and which are orthogonal to each other in the frequency domain by a Hilbert transform relationship and which have bandwidths which limit the resulting intermediate frequency signals exiting said filters to a predetermined bandwidth and for summing the resulting data encoding intermediate frequency signals to generate M symbols for transmission, and converting the data encoding said M symbols into an analog signal of said intermediate frequency and for converting said intermediate frequency signal encoding said M symbols to a radio frequency signal which will not interfere with other services being carried on said transmission media, the resulting radio frequency signal being M-ary QAM modulated, and for transmitting said modulated radio frequency carrier signals over said shared transmission media said composition of said information vectors and said encoding of said information vectors using orthogonal codes being such that the temporal relationships of the data bits in said time divsion multiple access stream is altered in said symbols, and such that when modulated radio frequency carrier is transmitted over said shared transmission media, the energy distribution of the signals resulting from said data from said N channels is spread out over substantially all of said frame and all of the bandwidth of the band of frequencies devoted to said supplemental services;
and
means for adjusting the timing of said transmission of each frame from said remote unit to said central unit such that each transmitted frame arrives at said central unit aligned in time with frame boundaries of frames of said central unit.

1 more element

A head end modem for providing multiple-user, multiple-source simultaneous digital communication over a limited bandwidth with one or more remote unit modems in a distributed systems linked by a transmission medium, comprising:

a framing/addressing/packetizing circuit for receiving payload data bytes and organizing said payload data into frames and organizing said payload data such that information as to which remote unit modem and peripheral each payload data byte is directed can be determined;
a master clock for generating a master clock signal;
a master carrier local oscillator for generating one or more carrier signals which will be modulated with digital data to be transmitted;
a transmitter for receiving said data from said framing/addressing/packetizing circuit and said master clock signal and said one or more carrier signals and using said data to modulate said one or more carrier signals using any modulation process which can also transmit said master clock reference signal and said carrier signals to said remote unit modems for use there for synchronization including synchronization to said frame boundaries, said transmitter coupled to said transmission media so as to output said one or more modulated carrier signals as downstream radio frequency signals;
and
an SCDMA receiver coupled to receive upstream RF signals with digital data by said remote unit modems and coupled to said master clock and said master carrier local oscillator to receive said master clock signal and said master clock local oscillator, said SCDMA receiver functioning to synchronously extract payload data from said upstream RF signals by performing the inverse code transformation of a code transformation which was performed by an SCDMA transmitter in a remote unit modem which modulated said upstream RF signals by spreading the spectrum thereof using orthogonal, pseudorandom spreading codes assigned to that modem, said inverse code transformation performed on signals received from a particular remote unit modem using the same orthogonal spreading codes used by said remote unit modem, said extracted payload data being presented at an output;
a gap monitor circuit coupled to said SCDMA receiver for aiding the process of achieving frame synchronization by said remote unit modesm by monitoring an interval during each frame for the presence of unique codes transmitted by said remote unit modems and for generating status data indicating how many codes have been received during said interval;
a circuit for receiving said status data from said gap monitor circuit and generating suitable management and control data needed by the remote units to achieve frame synchronization such that all frames of like number transmitted by the various remote unit modems arrive at said central unit modem at the same time;
and
a data transfer circuit for receiving said management and control data and causing said transmitter to transmit same during an interval dedicated to transmission of said management and control data.

7 more elements

A remote unit modem for providing multiple-user, multiple-source simultaneous digital communication over a limited bandwidth with a central unit modem in a distributed system linked by a transmission medium, comprising:

a receiver coupled to receive downstream radio frequency signals organized into frames from said central unit, said receiver functioning to synchronously extract payload data for use by peripheral devices or processes coupled to said remote unit modem and synchronously extract any management and control data transmitted by the CU to said said remote unit modem to achieve frame synchronization or in support of other management function, and further functioning to recover master clock and carrier reference signals transmitted by said central unit modem, and wherein said central unit modem organizes data sent to said remote unit modem into frames each of which has a gap therein during which no payload data is sent, said central unit modem transmitting a barker code during at least one said gap, said receiver further functioning to detect when said barker code transmitted by said central unit modem during a gap is received and generating a receive frame timing reference signal establishing a receive frame timing reference as to when the frames of data transmitted by said central unit modem start, said receiver including at least a gap monitor circuit, a demodulator, a detector, and, if necessary a decoder/despreader circuit which are compatible with the central unit transmitter such that said receiver is capable of performing said extraction of payload and management and control data and detecting said barker code;
an SCDMA transmitter coupled to receive said master clock and carrier reference signals recovered by said receiver, and coupled to receive payload data from said peripheral devices or processes coupled to said remote unit modem, and coupled to receive management and control data to be transmitted to said central unit modem, said SCDMA transmitter functioning to organize said payload data and said management and control data into frames of the same size as the frames of data transmitted to said receiver by said central unit modem and to spread the Fourier spectrum of said payload data and said management and control data over a bandwidth which is much greater than the Fourier spectrum said payload data and said management and control data originally had, and further functioning to use said spread spectrum data to modulate one or more carrier signals for transmission on said transmission media, said process of organizing payload and management and control data into frames, spreading the spectrum of said data and using said spread spectrum data to modulate one or more carriers being done synchronously using said master clock and carrier reference signals recovered by said receiver, said transmitter also functioning to transmit each frame of modulated signals to said central unit to said central unit modem over said transmission media a predetermined transmit frame timing delay after a frame of data has been received from said central unit modem, as established by said receive frame timing reference signal;
a ranging generator circuit functioning to generate and send to said SCDMA transmitter data defining a barker code for transmission to said central unit modem during a ranging process;
a control circuit coupled to receive said management and control data extracted by said receiver and said receive frame timing reference signal generated by said receiver and for controlling said SCDMA transmitter to carry out a ranging process by calculating a trial and error value for said transmit frame timing delay Td and sending Td to said SCDMA transmitter to control the time of transmission of a barker code, said control circuit also for monitoring said management and control data to determine if the barker code arrived at said central unit modem during a gap, and for continuing to vary the value of Td until said barker codes transmitted by said SCDMA transmitter arrive in said gap as indicated by said management and control data thereby achieving frame synchronization and thereafter holding the value of Td steady.

1 more element

A transmitter apparatus for simultaneously transmitting to a receiver multiple channels of digital data over a cable television media carrying cable television programming, comprising:

a framer circuit for receiving a time division multiplexed stream of data comprised of N timeslots per frame, each timeslot carrying digital data from one of N channels, said framer for storing in a memory the data from selected ones of said timeslots assigned to said transmitter, and for generating an information vector having N elements corresponding to said N timeslots, predetermined ones of said information vector elements corresponding to said selected timeslots assigned to said transmitter from which data was stored by said framer circuit, each of said predetermined elements of said information vector corresponding to timeslots assigned to said transmitter comprised of a plurality of bits which constitute a fraction of the data of one of said timeslots assigned to said transmitter;
a convolutional encoder for selectively adding one or more redundant bits to each element of said information vector to implement trellis modulation to generate a new information vector;
a code division multiplexer circuit for matrix multiplying said new information vector times a code matrix comprised of N mathematically orthogonal codes, each row comprised of an orthogonal code having N elements to generate a result vector having N elements;
a modulator for using each element of said result vector to quadrature amplitude modulate two radio frequency carriers having the same frequency but separated in phase by 90 degrees to generate inphase and quadrature RF signals, said modulation being achieved by dividing the bits of each element of said result vector into first and second parts and using the number represented by each part to define the amplitude of said inphase and quadrature RF signals, respectively, and summing said inphase and quadrature RF signals prior to transmission on said cable television media;
means for achieving frame synchronization between frames transmitted by said transmitter apparatus and the frame boundaries of frames within said receiver.

2 more elements

A system for bidirectional communication of digital data comprising:

a central unit comprising a code division multiple access transmitter and a code division multiple access transmitter;
a transmission media coupled to said central unit transmitter and receiver;
a plurality of physically distributed remote units coupled to said central unit by said transmission media, each remote unit having a code division multiple access transmitter and a code division multiple access receiver;
and wherein said central unit transmitter includes means for assigning each remote unit one or more codes from a set of orthogonal codes and wherein each said remote unit transmitter and said central unit transmitter include means for using said orthogonal codes assigned to that remote unit to encode all payload data intended for exchange between said remote unit and said central unit;
and wherein each said transmitter includes a modulator to use said digital data, after encoding using said orthogonal codes, to modulate a radio frequency carrier to generate modulated RF signals for transmission on said transmission media;
and wherein said transmitters in said central unit and said remote units are structured to transmit said modulated RF signals in frames, each frame defined as one or more symbols comprising encoded payload data and a guardband during which no payload data is transmitted, each frame separated from adjacent frames by said guardband;
and wherein central unit transmitter includes a circuit to transmit a barker code during each frame;
and wherein each remote unit transmitter includes means for carrying out a trial and error process of adjusting a transmit frame timing delay and transmitting said barker code back toward said central unit, hereafter referred to as the ranging process, and wherein each central unit receiver includes means for monitoring each guardband to determine when a barker code transmitted by a single remote unit transmitter has arrived during said guardband or if multiple barker codes have arrived, and wherein said central unit transmitter is coupled to said central unit receiver and receives status information therefrom regarding whether a single or multiple barker codes have been received within a guardband and transmits said status information to said remote units, and wherein each remote unit receiver includes means for monitoring said status information transmitted from said central unit and for receiving information from said remote unit transmitter regarding whether said remote unit transmitter is currently carrying out said ranging process, and, when said status information received from said central unit indicates only a single barker code was received during said guardband and information from said remote unit transmitter indicates that remote unit is currently carrying out said ranging process, said remote unit receiver controls said remote unit transmitter to transmit an identification code unique to only that remote unit, and wherein said central unit receiver includes means to determine what identification code was received and to control said central unit transmitter to transmit the received identification code back to all remote units, and wherein said remote unit receivers includes means for comparing the identification code transmitted by said central unit to the identification code of said remote unit, and, if there is a match, for controlling said remote unit transmitter to set said transmit frame timing delay at the delay value which resulted in said barker code arriving at said central unit during said guardband.

5 more elements

Apparatus and method for trellis encoding data for transmission in digital data transmission systems

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Apparatus and method for trellis encoding data for transmission in digital data transmission systems

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Abstract

Claims83