Apparatus and method for synchronizing an SCDMA upstream or any other type upstream to an MCNS downstream or any other type downstream with a different clock rate than the upstream

• US 6,353,604 B2
• Filed: 03/01/2001
• Issued: 03/05/2002
• Est. Priority Date: 05/06/1998
• Status: Expired due to Term

• Current Assignee: Avago Technologies International Sales Pte Limited (Broadcom, Inc.), ARRIS Enterprises LLC (CommScope Holding Company, Inc.)
• Original Assignee: Terayon Communications Systems Incorporated (Motorola Solutions, Inc.)
• Inventors: Richardson, Paul, Lind, Paul Alan, Grimwood, Michael, Artman, Doug, Knittel, Jim, Rakib, Selim Shlomo
• Primary Examiner(s): Pham, Chi
• Assistant Examiner(s): Bayard, Emmanuel
• Application Number:
  US09/798,845
• Publication Number:
  US 20010033611A1
• Time in Patent Office: 369 Days
• Field of Search: 375/141, 375/146, 375/147, 375/133, 375/135, 375/136, 375/137, 375/211, 375/219, 375/220, 375/222, 375/356, 375/358, 455/39, 455/75, 455/78, 455/85, 455/86, 455/88, 455/557, 370/278, 370/282, 370/320, 370/335, 370/321, 370/342, 370/347, 370/350, 370/442, 370/441, 370/337, 370/498, 370/503, 370/509
• US Class Current: 370/335
• CPC Class Codes: H04J 13/16 Code allocation
• CPC Class Codes: H04J 3/0682 by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging
• CPC Class Codes: H04L 7/033 using the transitions of the received signal to control the phase of the synchronising-signal-generating means, e.g. using a phase-locked loop

Abstract

A bidirectional digital data communication system which generate phase coherent upstream clock and carrier signals from recovered downstream clock generated from a master clock in a central unit. The preferred species uses any downstream clock rate and generates a phase coherent upstream clock so long as the two clock rates can be related by the ratio M/N where M and N are integers. One embodiment uses an MCNS downstream and an SCDMA upstream and uses MNCN timestamp messages in the downstream to achieve an estimate of RU frame offset prior to establishing frame alignment using a ranging process. The use of timestamp messages to estimate the offset is aided by a low jitter method for inserting timestamp messages by avoiding straddling of MPEG packet headers with the sync message. Clock slip is detected by counting upstream clock cycles over a predetermined downstream clock interval and the RU transmitter is shut down if slip is detected to prevent ISI interference from misaligned codes. An SCDMA transmitter for the minislot environment of 802.14 and MCNS is disclosed along with a receiver for the minislot environment using TDMA or SCDMA demultiplexing.

Claims

1. A remote modem in a digital data communication system comprised of a headend modem coupled by a shared transmission medium to a plurality of distributed remote modems, comprising:

a receiver and clock recovery circuit for recovering a downstream clock and using said downstream clock to recover downstream data including a ranging offset value and equalization coefficients and assigned minislots;

an upstream clock generator for using said recovered downstream clock to generate an upstream clock said upstream clock having a frequency which is M/N times the frequency of said downstream clock, where M and N are integers;

a computer programmed with media access control and transmission convergence layer programs that control said modem to use said ranging offset to achieve frame synchronization and using said equalization coefficients to achieve upstream equalization;

a symbol counter having an input for receiving said ranging offset value from said computer, for providing a current symbol count which defines where the transmitter is in every upstream minislot at any particular time;

a buffer for storing upstream data bits to be transmitted;

an information vector assembly circuit coupled to receive said minislot assignment data and said current symbol count and coupled to said buffer, for assembling symbols from bits in said buffer and using said current symbol count and said minislot assignment data to place said symbols into symbol positions in one or more information vectors that map to said assigned minislots;

a code division multiplexer for matrix multiplying each information vector times a code matrix of spreading codes to generate one or more result vectors for each information vector;

a pre-emphasis filter for filtering said result vectors; and

a modulator circuit for converting said result vectors into one or more radio frequency carrier signals having said upstream data encoded therein as spread spectrum signals.

2. A remote modem in a digital data communication system comprised of a headend modem coupled by a shared transmission medium to a plurality of distributed remote modems, comprising:

a receiver and clock recovery circuit for recovering a downstream clock which is phase coherent with a master clock in said headend from data transmitted by said headend over said transmission medium and for using said recovered downstream clock to generate a downstream carrier and an upstream carrier both of which are phase coherent with said master clock such that any changes in frequency or phase of said master clock will cause corresponding changes in frequency or phase of said recovered downstream clock and said downstream and upstream carriers generated therefrom, and for using said recovered downstream clock and said downstream carrier to demodulate downstream signals transmitted by said headend modem and to recover downstream data from said demodulated downstream signals;

an upstream clock generator for using said recovered downstream clock to generate an upstream clock which is phase coherent with said recovered downstream clock and said master clock such that any changes in frequency or phase of said master clock will cause corresponding changes in frequency or phase of said upstream clock, said upstream clock having a frequency which is M/N times the frequency of said downstream clock, where M and N are integers;

a computer programmed with media access control and transmission convergence layer programs that control said computer to deliver upstream data to be transmitted and controlling said computer to monitor downstream messages received by said receiver from said headend modem to receive minislot assignments for upstream bursts by this transmitter and for controlling said computer to control said transmitter to carry out any ranging and training process to determine a ranging offset value which will cause frame synchronization to exist for SCDMA frames transmitted by this transmitter and will cause said headend modem to develop equalization coefficients and send them to said transmitter in downstream messages, and for controlling said computer to use said equalization coefficients received from said headend modem and existing upstream coefficients of said transmitter to develop new upstream equalization coefficients to be used by said transmitter for transmitting bursts of symbols upstream;

a symbol counter having an input for receiving said ranging offset value from said computer, for providing a current symbol count which defines where the transmitter is in every upstream minislot at any particular time;

a buffer for storing upstream data bits to be transmitted;

an information vector assembly circuit coupled to receive said minislot assignment data and said current symbol count and coupled to said buffer, for assembling symbols from bits in said buffer and using said current symbol count and said minislot assignment data to place said symbols into symbol positions in one or more information vectors that map to said assigned minislots;

a code division multiplexer for matrix multiplying each information vector times a code matrix of spreading codes to generate one or more result vectors for each information vector;

a pre-emphasis filter for using said new equalization coefficients to control the filter characteristics of an equalization filter and for filtering the spectrum of said result vectors; and

a modulator circuit for converting said result vectors into one or more radio frequency carrier signals having said upstream data encoded therein as spread spectrum signals.

3. A customer premises modem for use in a bidirectional, distributed digital data communication system having a headend modem and a plurality of distributed customer premises modems coupled to said headend modem by a shared transmission medium, comprising:

a receiver and clock recovery circuit for recovering a downstream clock which is phase coherent with a master clock in said headend from data transmitted by said headend over said transmission medium and for using said recovered downstream clock to generate a downstream carrier and an upstream carrier both of which are phase coherent with said master clock such that any changes in frequency or phase of said master clock will cause corresponding changes in frequency or phase of said recovered downstream clock and said downstream and upstream carriers generated therefrom, and for using said recovered downstream clock and said downstream carrier to demodulate downstream signals transmitted by said headend modem and to recover downstream data from said demodulated downstream signals;

an upstream clock generator for using said recovered downstream clock to generate an upstream clock which is phase coherent with said recovered downstream clock and said master clock such that any changes in frequency or phase of said master clock will cause corresponding changes in frequency or phase of said upstream clock, said upstream clock having a frequency which is M/N times the frequency of said downstream clock, where M and N are integers; and

a transmitter for using said upstream clock to transmit upstream data from a plurality of different sources as frames in upstream signals to said headend modem over said transmission medium using any form of multiplexing to separate signals from different sources and frequency division multiplexing to separate said upstream signals on said transmission medium from said downstream signals, said transmitter including ranging circuitry for performing a ranging process to achieve frame synchronization so as to align said upstream clock generated in said customer premises modem with an upstream clock generated in said headend modem and for aligning in time the boundaries of said frames of data in upstream signals with frame boundaries signalled by a frame counter in said headend modem.

4. The apparatus of claim 3 wherein said transmitter includes a circuit to count upstream kiloframes and output a kiloframe marker signal at each upstream kiloframe boundary, and wherein said transmitter further comprises:

a computer programmed with media access control (MAC) and transmission convergence (TC) layer programs which controls said computer to deliver a stream of bytes of data to be transmitted upstream or management and control data for transmission upstream, and controlling said computer to perform the following functions;

monitor downstream messages and receive management and control data generated from downstream messages received by said receiver from said headend modem, said management and control data including;

grants defining upstream minislot assignments for each burst of upstream symbol data to be transmitted, and

a symbol clock rate select signal that indicates the symbol rate at which to transmit each burst of upstream symbols,

a modulation type,

a transmit power level,

a guardtime length,

a preamble length,

wether to Trellis encode or not,

interleaving depth,

other burst parameters,

a rollover count for the number of symbols to put in each upstream superframe,

said TC layer programs controlling said computer to also perform the following functions;

generate a rollover count output from said management and control data which defines how many symbols will be mapped to each minislot and defines a frame and superframe boundary,

calculation of an initial ranging offset by receiving a sync detect signal and reading a sample from a local upstream kiloframe counter and extracting timestamp counter samples of a timestamp counter in said headend modem received in sync and UCD messages sent from said headend modem in said management and control data and using the locally generated and headend modem generated counter samples to calculate therefrom a ranging offset that defines the time offset between a kiloframe boundary or minislot counter rollover event in said headend modem and a corresponding upstream kiloframe boundary in said transmitter,

generate burst parameter control data from said management and control data to control said transmitter to implement;

Reed-Solomon encoding on or off,

coarse and fine transmit power level,

a specified interleaving depth,

a specified codebook size,

mapping of upstream symbol data and known preamble data to the assigned minislots to be spread by codes that map to the assigned minislots,

whether Trellis encoding is on or off;

control of transmission so that bandwidth requests and ranging bursts are transmitted during the minislots of specified contention intervals for these purposes,

the type of modulation to use for each burst,

the size of the guardband and preamble for the first minislot of each burst so that each burst consumes an integer number of minislots,

a minislot counter that rolls over at the same count as a minislot counter in said headend modem,

any ranging and training protocol including the ranging protocol defined in the IEEE 802.14 specification as it existed at the time this patent application was filed so as to adjust the value of said ranging offset to achieve precise frame synchronization and so as to transmit training bursts that allow said headend modem to develop equalization coefficients for this transmitter and to receive said equalization coefficients from said headend modem in said downstream management and control messages and provide said equalization coefficients for use by said transmitter,

any other other burst parameters specified by the headend modem in the downstream messages;

a timebase means for generating a variable frequency symbol clock which is phase coherent with said recovered downstream clock and coupled to receive said symbol clock rate select signal;

a symbol counter having an input for receiving a rollover count from said computer derived from data transmitted downstream from said headend modem and which defines when said symbol counter rolls over thereby defining the number of symbols in a superframe and a minislot and superframe boundary on each rollover event, and having an input for receiving a chip clock and an input for receiving said ranging offset value calculated by said computer, said ranging offset value controlling release of said information vectors for spectrum spreading so as to achieve frame and minislot synchronization and time alignment between the upstream clock signal generated by said customer premises modem and an upstream clock signal of the same frequency generated in said headend modem;

a Reed-Solomon encoder means coupled to receive said upstream data and said management and control data and coupled to receive control data controlling how many error detection and correction bits (ECC bits) will be generated for each coding block and how long each coding block will be, for breaking said data down into RS coding blocks of the specified length and encoding each RS coding block with the specified number of ECC bits;

an interleaver means coupled to receive said encoded RS coding blocks and said depth control signal, for interleaving said RS coding blocks at the depth specified in said depth control signal;

a buffer for storing the interleaved RS coding blocks;

mapping means for for receiving data from said computer defining minislot and symbol assignments and a modulation type and a codebook size, and for receiving the current symbol number from said symbol counter, and for retrieving enough upstream payload bits from said RS coding blocks in said buffer to create the number of symbols needed to fill the minislots in said grant, and grouping said bits into symbols according to said modulation type, and programmably mapping said numbered symbols to minislots, spreading codes and frame numbers according to said codebook size and said minislot and symbol assignment data using the current symbol number supplied by said symbol counter so as to create one information vector per subframe, said information vector having a number of elements which matches said codebook size and with symbols populating only those element positions of information vectors that correspond to subframes and frames and symbol numbers that map to said assigned minislots, and for varying the number of symbols mapped to the guardtime and preamble of the first minislot in a grant of minislots in accordance with control data received from said computer such that each burst of upstream symbols is transmitted during an integer number of minislots;

Trellis coded modulation means for receiving control data from said computer controlling the modulation type and whether Trellis encoding is on or off and, if Trellis encoding is on, for trellis encoding each symbol in each said input information vector to generate one or more Trellis encoded information vectors from each input information vector with real and imaginary output information vectors being generated from each said input information vector when quadrature modulation types are specified by said burst parameter control data, the elements of said one or more Trellis encoded output information vectors defining a constellation point for each symbol in said input information vector, the number of Trellis encoded information vectors generated from each said input information vector depending upon the modulation type specified in said burst parameter control data received from said computer, and, if Trellis encoding is not to be implemented, for mapping each input information vector into one or more output information vectors in accordance with the modulation type defined in said burst parameter control data;

spectrum spreading means for receiving codebook size data from said computer and said output information vectors generated by said Trellis coded modulation means and for spreading the spectrum of each said output information vector to generate a result vector for each output information vector, each said result vector having as its elements a number of chips equal to the number of elements in each spreading code, said spectrum spreading accomplished by matrix multiplication of each output information vector times a spreading code matrix populated by codes from the set of spreading codes selected by said codebook size data received from said computer;

concatenation means coupled to said computer to receive burst parameter control data, for concatenating groups of said result vectors into SCDMA frames having a programmable length gap or no gap at all in each SCDMA frame if said ranging algorithm carried out by said transmitter is as defined in the IEEE 802.14 specification as it existed at the time this application was filed;

pre-emphasis filter means for receiving said equalization filter coefficients from said computer and filtering said SCDMA frames using a filter the characteristics are controlled by equalization filter coefficients developed by convolving said equalization filter coefficients received from said headend modem with the existing equalization filter coefficients in said pre-emphasis filter means;

a polyphase transmit filter means for receiving burst parameter control data from said computer, and for increasing the sampe rate of said result vectors in said SCDMA frames to satisfy the Nyquist criteria, filtering the frequency spectrum of each resulting result vectors using a pair of square root raised cosine filters, one for each result vector in a pair of result vectors if quadrature modulation is in use, each filter in said pair of filters having a transfer function which the Hilbert transform of the transfer function of the other filter, said filtering causing output of a frequency spectrum centered on a predetermined frequency and having a bandwidth equal to a predetermined factor times the symbol rate which satisfies the Nyquist criteria in a predetermined way to optimize signal-to-noise enhancement and minimize intersymbol interference, and for amplifying the spectrum output from said square root raised cosine filter(s) by an amount of gain controlled by said computer via said control data, and for doubling the sample rate of the output from said amplification process so as to leave only images of the spectrum centered at integer multiples of two times the sample rate and for filtering out every over image; and

frequency translation means for receiving burst parameter control data and for converting the data of said result vectors output by said polyphase transmit filter means to analog form and limiting the bandwidth of the upstream signal to be transmitted to a bandwidth appropriate to the symbol clock rate of the burst and establishing a center frequency of said upstream signal to be transmitted at a frequency controlled by said burst parameter data, and for amplifying the upstream transmitted signal using an amplifier whose gain is controlled by coarse power control data from said computer;

and wherein said ranging circuitry includes;

a sync message detector means coupled to receive said downstream data recovered by said receiver and detect sync and UCD messages therein and for outputting a sync detect signal upon detection of said sync and UCD messages and for supplying said sync and UCD messages to said computer;

a kiloframe counter means a kiloframe marker signal from said transmitter and reset itself upon receipt of said kiloframe marker signal, said kiloframe counter means for counting a clock signal that is phase coherent with said upstream clock signal; and

a kiloframe sampler means for sampling the count of said kiloframe counter means each time said sync detect signal occurs.

5. The apparatus of claim 3 wherein said transmitter transmits data upstream using synchronous code division multiplexing.

6. The apparatus of claim 3 wherein said transmitter transmits data upstream using synchronous time division multiple access multiplexing by mapping symbols to assigned minislots.

7. The apparatus of claim 3 wherein said transmitter transmits data upstream using discrete multitone multiple access multiplexing.

8. The apparatus of claim 3 wherein said transmitter includes means for transmitting symbol data upstream using synchronous code division multiplexing by mapping minislots assigned to said modem to one or more symbols and one or more spreading codes.

9. The apparatus of claim 3 wherein said transmitter transmits symbol data upstream using discrete multitone multiplexing by mapping minislots assigned to said modem to one or more symbols and one or more frequencies.

10. The apparatus of claim 8 wherein said transmitter is structured to selectively alter the mapping between minislots and symbols and spreading codes to achieve code diversity.

11. The apparatus of claim 8 wherein said transmitter multiplexes upstream data in said upstream signals on the basis of assigned minislots counted by a minislot counter in said headend modem using minislot assignment data received in said downstream signals, said minislot counter having a rollover value that defines a superframe boundary, said ranging circuitry in said transmitter structured to carry out the communications of a ranging algorithm to use timestamp messages in said downstream signals to determine a ranging offset value for a symbol counter in said transmitter of said customer premises modem to achieve frame synchronization, said symbol counter also having a rollover value which defines a superframe of symbols which exactly corresponds in duration with said superframe of minislots, said ranging offset being of a value which will cause frame synchronization such that if a superframe of symbols were to be transmitted upstream, the superframe of symbols would arrive at said headend with its frame boundaries closely aligned in time with boundaries of a superframe of minislots.

12. The apparatus of claim 11 wherein said downstream signals include sync messages and UCD messages, each said sync message carrying a timestamp sample from a timestamp counter in said headend modem and each said UCD message containing a timestamp at the time of a kiloframe or superframe boundary occurring at said headend modem, and further comprising means in said modem for recovering said sync and UCD messages and calculating an initial ranging offset value from a sync message and a UCD message and for using said initial ranging offset as a starting point for said ranging circuitry.

13. The apparatus of claim 3 wherein said transmitter includes offset calculation means for using sync messages and UCD messages in said downstream signals to calculate an initial ranging offset to load into a symbol counter in said transmitter to speed up said ranging process such that the superframe boundaries of a superframe of said upstream symbols transmitted by said transmitter will be almost exactly or exactly superimposed in time at said headend modem with superframe boundaries of a superframe of minislots at said headend modem.

14. The apparatus of claim 13 wherein said transmitter performs said ranging process starting from said initial ranging offset value and using a trial and error protocol adapted for the IEEE 802.14 and MCNS environment including responding to a ranging invitation message by sending start bit barker code with a timing intended to hit a gap identified in said ranging invitation message followed by sending an even number of on or off bits that define a unique signature sequence in an even number of gaps defining a ranging interval, said gaps of said ranging interval following the gap that was identified in said ranging invitation, the number of on bits being exactly half the number of an even number of gaps in said ranging interval, and iteratively repeating the process for subsequent ranging invitations and ranging intervals using different ranging offset values until a message is received that said customer premises modem has hit a gap with its start bit, and wherein said transmitter is also structured to perform a training process to adjust said ranging offset value to achieve precise frame synchronization and allow said headend modem to calculate upstream equalization coefficients that equalize the channel between said customer premises modem and said headend modem, and wherein said transmitter achieves frame synchronization more quickly by using said initial ranging offset calculated by said offset calculation means as a starting point to carry out said trial and error ranging protocol, said ranging and training processes resulting in the determination of an exact ranging offset for said symbol counter which will cause superframe boundaries of each said superframe of upstream symbols to be superimposed in time at said headend modem with a superframe boundary of minislots at said headend modem.

15. The apparatus of claim 3 further comprising a clock slip detector in every said customer premises modem coupled to said receiver and clock recovery circuit so as to receive said recovered downstream clock signal and coupled to said upstream clock generator so as to receive the upstream clock signal generated thereby, said clock slip detector for counting and storing the count of the clock cycles of said upstream clock signal over each predetermined interval of said recovered downstream clock and generating a clock slip signal if more than a predetermined acceptable amount of clock slip has occurred.

16. The apparatus of claim 15 further comprising a computer programmed with a media access control and a transmission convergence program for receiving said clock slip signal and for controlling said third means to cease transmitting said upstream signals.

17. The apparatus of claim 3 wherein said ranging circuitry is a computer programmed to perform ranging by performing the following steps:

extract from said downstream data recovered by said receiver message data that assigns specific minislots as a ranging contention intervals and defines a reference time in said interval;

control said transmitter to transmit a ranging burst that starts at a time which said transmitter thinks is said reference time according to a minislot count in said transmitter, said ranging burst including identification data that identifies said customer premises modem;

extracting a ranging offset from said downstream data recovered by said receiver message data that includes the offset in time between said reference time in said ranging contention interval specified by said headend modem and the start of the ranging burst transmitted by said transmitter; and

loading said ranging offset into a symbol counter in said transmitter.

18. The apparatus of claim 3 wherein said transmitter includes a circuit to count upstream kiloframes and output a kiloframe marker signal at each upstream kiloframe boundary, and wherein said ranging circuitry in said transmitter comprises:

a computer controlled by media access control (MAC) and transmission convergence (TC) layer programs;

a sync message detector means coupled to receive said downstream data recovered by said receiver and detect sync and UCD messages therein and for outputting a sync detect signal upon detection of said sync and UCD messages and for supplying said sync and UCD messages to said computer;

a kiloframe counter means coupled to receive a kiloframe marker signal from said transmitter and reset itself upon receipt of said kiloframe marker signal, said kiloframe counter means for counting a clock signal that is phase coherent with said upstream clock signal; and

a kiloframe sampler means for sampling the count of said kiloframe counter means each time said sync detect signal occurs;

and wherein said computer controls said transmitter to perform the following steps;

wait until said upstream clock signal generated by said upstream clock generator has achieved phase coherence with said recovered downstream clock;

waiting until at least one sync message and one UCD message has arrived from said headend modem;

if necessary because a headend modem timestamp counter clock is not phase locked to said clock signal counted by said kiloframe counter means, calculate a timebase conversion factor by waiting for a second UCD message by calculating the difference between the timestamps in the two UCD messages received and then performing predetermined calculations thereon;

calculating the upstream kiloframe adjustment portion of a ranging offset value and shifting the upstream kiloframe boundary in said transmitter by the amount of said upstream kiloframe adjustment;

waiting for at least one upstream kiloframe to pass;

performing a trial and error ranging process to adjust a transmit frame timing delay value TD;

using said value of TD and said kiloframe adjustment portion to adjust the timing of upstream bursts transmitted by said transmitter so as to achieve frame synchronization and upstream kiloframe and minislot boundary alignment between kiloframes and minislots of upstream data transmitted by said transmitter and minislot and kiloframe boundaries counted by said headend modem.

19. The apparatus of claim 3 further comprising a headend modem having an upstream receiver and a downstream transmitter, both coupled to each said customer premises modem by a shared transmission medium, and wherein said ranging circuitry in said transmitter of each said customer premises modem is structured to perform the following ranging algorithm:

wherein each said transmitter comprises means for inserting gaps of predetermined size in every upstream frame;

and wherein said receiver is structured to receive from a downstream transmitter in said headend modem a downstream ranging invitation message to all customer premises modems identifying a ranging sequence of gaps or minislots during which no customer premises modem will be authorized to send upstream payload data, said ranging sequence of gaps or minislots (hereafter referred to as minislots) starting with a specified minislot number, hereafter referred to as minislot X, in which any customer premises modem that needs to perform a ranging process should send a unique sequence of barker code ranging bursts, and wherein each minislot is numbered and the beginning of each minislot is mapped to a particular count of said master clock in said headend modem, and for sending said ranging invitation messages from time to time or periodically;

and wherein each said customer premises modem transmitter includes means for sending a unique sequence of barker code transmissions over said ranging sequence of minislots starting at said minislot X, said barker code sequence acting as a temporary ID identifying the particular customer premises modem that sent the sequence and allowing said headend modem to address messages to this particular customer premises modem, said unique barker code sequence having an initial barker code followed by an even number of “

on and off bits”

where an “

on bit”

is defined as a minislot in which a barker code is sent and an “

off bit”

is defined as a minislot in which a barker code is not sent, said sequence containing exactly 50% on bits, said unique barker code sequence being transmitted at an initial power level and transmitted at an initial transmit time picked by said customer premises modem at a transmit frame timing delay that said customer premises modem thinks will cause said initial bit of said unique barker code sequence to arrive during said minislot X, said transmit frame timing delay determined according to a clock in said customer premises modem that is kept phase synchronous with said headend modem master clock by said clock recovery means, said downstream receiver structured to monitor downstream transmissions from said headend modem after transmission of said unique barker code sequence for a message indicating that said headend modem detected the temporary ID barker code sequence in the series of minislots starting with minislot X;

and wherein said upstream transmitter and downstream receiver of each customer premises modem are structured to wait for another ranging invitation if no message is received indicating the temparary ID of the customer premises modem was seen by the headend modem in the ranging sequence minislots, and upon receiving another ranging invitation message, for retransmitting said unique sequence of barker codes at a different power level or a different transmit frame timing delay or both, and repeating this process of searching for the right combination of power level and transmit frame timing delay until a status message is received that said temporary ID was seen by said headend modem during said ranging sequence minislots, and upon receiving a status message indicating success for holding the power level and transmit frame timing delay values at the values which caused said temporary ID to be heard in the ranging sequence minislots so as to achieve a coarse alignment;

and wherein said upstream transmitter and downstream receiver of each customer premises modem are structured to cooperate to listen for a collision message from said headend modem after each transmission of a temporary ID sequence, and, if a collision message is received, for performing a collision resolution protocol to determine whether or not to continue ranging transmissions or to stop for some interval before resuming attempts to perform ranging;

and wherein said receiver in each customer premises modems is structured to receive a downstream message from said headend modem indicating which temporary ID was received during the ranging sequence minislots if a temporary ID was received and to receive a training invitation message addressed to the particular customer premises modem that achieved said coarse alignment state and defining the minislots or minislots during which said customer premises modem is to send known training data bursts, and wherein said receiver in said customer premises modem is structured to receive a collision message from said headend modem if said headend modem determines that a collision has occurred;

and wherein said upstream transmitter and downstream receiver of each customer premises modem are structured to cooperate to listen for said training invitation message, and respond thereto by transmitting one or more bursts of known training data during the minislots identified in said training invitation having the spectrum of said training data spread by one or more predetermined, cyclic, neighboring spreading codes;

and wherein said upstream receiver and downstream transmitter of said headend modem are structured to cooperate to use said training data transmissions to do an equalization process and a process to determine a transmit frame timing delay offset that will minimize intersymbol interference so as to develop equalization coefficients and a transmit frame timing delay fine tuning adjustment, and to use one or more training data bursts to do a power alignment process to develop a gain level for said customer premises modem that transmitted said training data that will cause transmissions from said modem to arrive at said headend modem at close to the same or the same power level as data transmitted from other customer premises modems, and to send a message said equalization coefficients and said transmit frame timing delay offset value and said gain level downstream to the customer premises modem which transmitted said training data, and to send a message indicating that training is complete and requesting the customer premises modem to send its media access control layer address to said customer premises modem for use in further communications;

and wherein said upstream transmitter and downstream receiver are structured to cooperate to said training complete message by sending the media access control layer address of said customer premises modem to said headend modem.

20. A process for transmitting data upstream in a bidirectional digital data communication system having a headend transceiver and a plurality of distributed remote transceivers coupled to said headend transceiver by a shared communication medium, comprising:

in each said remote transceiver, recovering at least said downstream clock signal and using it to generate a downstream carrier signal which is phase coherent with said downstream carrier signal used to transmit said downstream data and using said downstream clock and downstream carrier signals to recover said downstream data, and using said recovered downstream clock signal to generate an upstream clock signal and an upstream carrier signal both of which are phase coherent with said recovered downstream clock signal such that changes in phase and/or frequency of said recovered downstream clock will cause corresponding changes in phase and/or frequency of said upstream clock and upstream carrier signals, said upstream clock and upstream carriers signals each having a frequency which is the same as the frequency of upstream clock and upstream carriers signals, respectively, generated from a master clock in said headend transceiver;

in each remote transceiver performing any ranging process to achieve at least frame synchronization such that frames of upstream data transmitted by said remote transceiver arrive at said headend transceiver with their frame boundaries aligned in time with boundaries of assigned minislots that coincide with boundaries of upstream frames to which said assigned minislots were mapped and such that said upstream clock signal generated in said remote transceiver is aligned in time with said upstream clock signal generated in said headend transceiver; and

in each remote transceiver using said upstream clock and carrier signals generated in said remote transceiver from said recovered downstream clock to transmit upstream symbol data with known preamble data from said remote transceiver upstream to said headend transceiver using either time division multiplexing or synchronous code division multiplexing such that said upstream symbol data arrives at said headend transceiver during said assigned minislots.

21. The process of claim 20 further comprising the steps performed in each remote transceiver of:

receiving a minislot assignment naming one or more numbered minislots on which transmission is authorized;

mapping the specific minislot numbers in said assignment to specific symbols and spreading codes and frame and subframes that map to said assigned minislots;

constructing an information vector for every subframe mapped to the minislot assignment by placing the numbered symbols that map to the numbered minislots in the assignment in the elements of the information vectors that maps to the symbol numbers, codes, frames and subframes that correspond to the assigned minislots;

optionally Trellis encoding each said information vector to generate real and imaginary component information vectors from each information vector;

spreading the spectrum of each information vector or each real and imaginary component information vector by matrix multiplication of the information vector times a code matrix having a plurality of codes therein which corresponds to the number of elements in the information vector to generate a result vector for each information vector that maps to a particular subframe that maps to one of the one or more assigned minislots; and

transmitting RF signals the information content of which is controlled by said result vectors.

22. The process of claim 20 further comprising the following steps performed in said headend transceiver to transmit payload data downstream and to enable said remote transceivers to generate upstream clock and carrier signals that are phase coherent with a master clock signal in said headend transceiver for upstream transmissions and to enable said headend transceiver to receive said upstream transmissions:

generating a master clock signal in said headend transceiver, and generating a downstream clock and a downstream carrier signal from said master clock signal both of which are phase coherent therewith, and generating upstream clock and upstream carrier signals in said headend transceiver from said master clock signal both of which are phase coherent therewith and the same frequencies as said upstream clock and upstream carrier signals, respectively, generated from said recovered downstream clock in each said remote transceiver, said phase coherence being such that any frequency or phase changes in said master clock signal will cause similar changes in frequency or phase of said upstream and downstream clock and said upstream and downstream carrier signals even though each said signal may be at a different frequency from said master clock, said upstream clock signal having a frequency which is M/N times the frequency of said downstream clock, where M and N are integers;

transmitting downstream data to said plurality of remote transceivers using said downstream clock and downstream carrier signals and said shared transmission medium;

using said preamble data prepended to each upstream burst transmitted by a remote transceiver to generate phase and amplitude correction factors and using said correction factors and said upstream clock and carrier signals generated in said headend transceiver to recover said upstream symbol data.

23. The process of claim 22 further comprising the steps of:

using a timestamp counter, counting the ticks of a timestamp counter clock which may or may not be said master clock in said headend transceiver, and periodically sampling said timestamp counter and including the timestamp sample in occasional synchronization messages and transmitting said synchronization messages as part of said downstream data with no more than a predetermined amount of time between adjacent synchronization messages,

and wherein said upstream data is transmitted in kiloframes counted by a kiloframe counter in each remote transceiver,

and sampling said timestamp counter each time an upstream kiloframe boundary is detected in said upstream data and generating and transmitting a UCD messages as part of said downstream data from time to time with each UCD message containing a sample of said timestamp counter at an upstream kiloframe boundary of said headend modem, each synchronization message containing the count of said timestamp counter.

24. The process of claim 20 further comprising a training process resulting in equalization coefficients being developed in said headend transceiver for said remote transceiver that equalize the channel between said remote transceiver and said headend transceiver and transmission of these equalization coefficients from said headend transceiver to said remote transceiver comprising the steps:

transmitting a training burst containing known preamble symbols from said remote transceiver to said headend transceiver, said training burst including a data portion that identifies the remote transceiver which transmitted it;

receiving a message from said headend transceiver that includes upstream equalization coefficients developed from said known preamble symbols and using said equalization coefficients in said messages to generate new upstream equalization coefficients for use by said remote transceiver for subsequent upstream transmissions.

25. The process of claim 20 wherein the step of performing any ranging process includes the steps:

(1) establishing an initial upstream kiloframe boundary in said remote transceiver;

(2) counting ticks of said upstream clock in a local kiloframe counter in said remote transceiver and resetting said counter to zero at the beginning of each new upstream kiloframe;

(3) sampling the count of said local kiloframe counter each time a synchronization message is received from said headend transceiver in downstream data;

(4) detecting when a synchronization message is received in said downstream data and when a UCD message is received in said downstream data and extracting timestamp data from each;

(5) determining the number of local kiloframe counter clock cycles in N frames where N is the number of upstream frames in the interval between the time that an upstream kiloframe boundary is detected at said headend transceiver minus the downstream propagation delay between this remote transceiver and said headend transceiver;

(6) using a timebase conversion factor between a clock frequency that drives a timestamp counter in said headend transceiver and said upstream clock being counted by said local kiloframe counter and the timestamp data extracted in step (4) and the data calculated in step (5) to calculate an offset value;

(7) using said offset value to speed up said ranging process to achieve frame synchronization.

26. The process of claim 24 wherein the step of performing any ranging process includes the steps:

(1) establishing an initial upstream kiloframe boundary in said remote transceiver;

(2) counting ticks of said upstream clock in a local kiloframe counter in said remote transceiver and resetting said counter to zero at the beginning of each new upstream kiloframe;

(3) sampling the count of said local kiloframe counter each time a synchronization message is received from said headend transceiver in downstream data;

(4) detecting when a synchronization message is received in said downstream data and when a UCD message is received in said downstream data and extracting timestamp data from each;

(5) determining the number of local kiloframe counter clock cycles in N frames where N is the number of upstream frames in the interval between the time that an upstream kiloframe boundary is detected at said headend transceiver minus the downstream propagation delay between this remote transceiver and said headend transceiver;

(6) using a timebase conversion factor between a clock frequency that drives a timestamp counter in said headend transceiver and said upstream clock being counted by said local kiloframe counter and the timestamp data extracted in step (4) and the data calculated in step (5) to calculate an offset value;

(7) using said offset value to speed up said ranging process to achieve frame synchronization.

27. The process of claim 20 wherein said step of performing any ranging process comprises the steps of:

extracting from downstream data recovered by said remote transceiver message data that assigns specific minislots as a ranging contention intervals and defines a reference time in said interval;

controlling each said remote transceiver that needs to accomplish ranging to transmit a ranging burst that starts at a time which said remote transceiver thinks is said reference time according to a minislot count in said remote transceiver, said ranging burst including identification data that identifies said remote transceiver;

receiving a downstream message from said headend transceiver which includes a ranging offset measured by said headend transceiver, said ranging offset being the interval between said reference time in said ranging contention interval and the start of said ranging burst;

extracting said ranging offset from said downstream message and loading said ranging offset into a symbol counter in said remote transceiver.

28. The process of claim 20 wherein said step of performing any ranging process comprises the steps of:

waiting for said remote transceiver to recover said downstream clock and using said recovered downstream clock to generate a local upstream clock which is phase coherent with said master clock in said headend transceiver;

establising an initial arbitrary upstream kiloframe boundary;

waiting to receive at least one synchronization message and one UCD message in said remote transceiver from said headend transceiver;

computing an upstream kiloframe boundary adjustment using timestamp data in said synchronization and UCD messages;

waiting for at least one upstream kiloframe to pass and performing a training process using said upstream kiloframe boundary adjustment value to determine an upstream transmission delay value TD to achieve precise kiloframe boundary frame synchronization, said training process comprising the steps of;

sending a training burst with known data and having its spectrum spread by each of a plurality of orthogonal, cyclic, neighboring spreading codes;

receiving a message from said headend transceiver containing a fine tuning ranging offset calculated in said headend transceiver using said training burst;

adjusting said upstream kiloframe boundary adjustment by the value of said fine tuning ranging offset to arrive at a ranging offset to use for subsequent upstream transmissions.

29. The process of claim 20 wherein said step of performing any ranging process comprises the steps of:

extracting from downstream data recovered by said remote transceiver message data that assigns specific minislots as a ranging contention intervals and defines a reference time in said interval;

controlling each said remote transceiver that needs to accomplish ranging to transmit a ranging burst that starts at a time which said remote transceiver thinks is said reference time according to a minislot count in said remote transceiver, said ranging burst including identification data that identifies said remote transceiver;

receiving a downstream message from said headend transceiver which includes a ranging offset measured by said headend transceiver, said ranging offset being the interval between said reference time in said ranging contention interval and the start of said ranging burst;

extracting said ranging offset from said downstream message and storing it;

performing a training process to develop at least a fine tuning ranging offset comprising at least the following steps;

sending a training burst with known data and having its spectrum spread by each of a plurality of orthogonal, cyclic, neighboring spreading codes;

receiving a message from said headend transceiver containing a fine tuning ranging offset calculated in said headend transceiver using said training burst;

adjusting said ranging offset by the value of said fine tuning ranging offset to arrive at a final ranging offset to use for subsequent upstream transmissions.