Apparatus and method for digital data transmission using orthogonal codes

A method for transmitting multiple channels of upstream digital data to a central unit modem from a plurality of remote unit modems, said transmission carried out over a transmission media simultaneously with transmissions carrying other services, comprising:

• receiving at each of said remote unit modems multiple input channels of upstream digital data
• at each remote unit modem generating upstream frames of data from said upstream data received by said remote unit modems by interleaving portions of said upstream digital data from each of said multiple channels and organizing said portions as an information vector having n elements, each element of each said information vector corresponding to one upstream logical channel, and only elements corresponding to an upstream logical channel assigned to said remote unit modem containing data from one or more input channels;
• performing code division multiplexing on said information vector using n orthogonal, cyclic spreading codes and a chip clock which is synchronous to a chip clock in said central unit modem to generate a result vector having n elements each containing spread spectrum data resulting from the matrix multiplication partial product sums of said information vector elements that contain data times said n spreading codes;
• using the n elements of said result vector to create the information content in one or more radio frequency signals, each said radio frequency signal being synchronized in frequency with a local oscillator signal in said central unit modem and each radio frequency signal being selected and filtered so as to have a center frequency and bandwidth so as to not interfere with said other services, and transmitting the resulting radio frequency signals on said transmission media using a predetermined transmit frame timing delay which will cause frame synchronization to exist;
• performing a ranging process in each said remote unit modem so as to establish said transmit frame timing delay at a proper interval for each said remote unit modem such that each frame transmitted from each remote unit modem is staggered in time to compensate for the different propagation delays from said remote unit modem to said central unit modem so that said frame arrives at said central unit modem from each different remote unit modem with their frame boundaries aligned in time with the frame boundaries of frames transmitted by other remote unit modems regardless of differences in propagation time from each remote unit modem to said central unit modem.

A method for transmitting multiple channels of digital data from a central unit transceiver to a plurality of remote unit transceivers, and transmitting different multiple channels of digital data from at least some of said remote unit transceivers to said central unit transceiver, said transmission carried out over a transmission media simultaneously with transmissions carrying other services, comprising:

• receiving at said central unit transceiver multiple channels of digital data encoding downstream data of some or all of said supplemental services served by different sources, said multiple channels organized as a time division multiple access (hereafter TDMA) stream with n timeslots comprising each frame, one or more timeslots assigned to carry data from said server for each different source of a supplemental service but not necessarily carrying data of the assigned supplemental service during each frame;
• receiving at each said remote unit transceiver multiple different channels of digital data than are received by said central unit transceiver, said multiple different channels encoding upstream data of some or all of said supplemental services served by different sources, said multiple channels organized as a time division multiple access (hereafter TDMA) stream with n timeslots comprising each frame, one or more timeslots assigned to carry data from said server for each different source of a supplemental service but not necessarily carrying data of the assigned supplemental service during each frame;
• establishing CU frame boundary timing reference signals in said central unit transmitter from the frame boundaries of said TDMA stream received at said central unit transceiver and synchronizing downstream frame transmissions from said central unit transceiver to said remote unit transceiver to said CU frame boundary timing reference signals;
• at each remote unit transceiver, selecting portions of said digital data from each timeslot of the TDMA stream received by each said remote unit transceiver and organizing said portions as an information vector having n elements, each element having interleaved data, and each element corresponding to one upstream logical channel with at least one information vector generated per frame, each frame in said remote unit having the same duration as any central unit frame, and inserting known preamble data in at least some of said information vectors of each transmission from a remote unit transceiver;
• Trellis encoding each said information vector to generate in phase and quadrature information vectors that have been encoded with redundant error correction data;
• performing a ranging process in each remote unit transceiver to establish frame synchronization by finding a suitable transmit frame timing delay such that each frame transmitted from each remote unit transceiver will arrive at said central unit transceiver aligned with the CU frame boundaries of said central unit transceiver regardless of differences in propagation time from each remote unit transceiver to said central unit transceiver;
• after remote unit transceiver achieves frame synchronization, transmitting data from said central unit transceiver to each said remote unit transceiver which will enable each remote unit transceiver to synchronize a local oscillator used to generate one or more radio frequency carriers to the frequency of a local oscillator in said central unit transceiver used to generate one or more downstream carriers, and which will also enable each remote unit transceiver to synchronize a local chip clock to a chip clock in said central unit transceiver;
• transmitting upstream training data from each said remote unit transceiver which has achieved frame synchronization;
• in said central unit transceiver, receiving said training data transmission from each said remote unit transceiver and performing an equalization process on each said training data transmission to derive equalization coefficients for use by said remote unit transceiver which sent said training data in filtering its upstream transmissions so as to predistort the spectrum thereof to compensate for channel impairments, and sending each set of equalization coefficients downstream to the appropriate remote unit transceiver;
• transmitting downstream data from said central unit transceiver to said remote unit transceivers that is payload data and also includes spreading code allocations to remote unit transceivers which have requested bandwidth, and recovering said downstream data and spreading code allocations in some or all of said remote unit transceivers;
• in at least each remote unit transceiver which has received a spreading code allocation, performing code division multiplexing of upstream data by performing a matrix multiplication of each said in phase and quadrature information vector times a code matrix comprised of n orthogonal spreading codes using said chip clock of said remote unit transceiver that has been synchronized to said chip clock of said central unit transceiver, each spreading code permanently or temporarily assigned to one said logical channel and having n elements, said matrix multiplication generating an in phase and quadrature result vector for each in phase and quadrature information vector, each said result vector having n elements, each element of said result vector containing spread spectrum data resulting from said matrix multiplication of the corresponding information vector times the spreading codes in said code matrix;
• filtering each said in phase and quadrature result vector using an equalization filter having said equalization filter coefficients received from said central unit transceiver derived from said equalization training process performed on said training data transmitted by said remote unit transceiver;
• in at least the remote unit transceivers that have generated result vectors, using the n elements of each said in phase and quadrature result vectors to create the information content in two quadrature radio frequency signals that are frequency synchronized with a local oscillator in said central unit transceiver by carrierless modulation, or by using two quadrature radio frequency carriers which have been generated from said remote unit transceiver local oscillator that has been synchronized in frequency with a local oscillator in said central unit transceiver and each said quadrature radio frequency carrier having the same frequency but one being an integer multiple of 90 degrees out of phase with the other and each quadrature radio frequency carrier having a center frequency selected so as to not interfere with other transmissions of other services simultaneously transmitted on said media, and transmitting the resulting radio frequency carriers on said transmission media using said predetermined transmit frame timing delay established for the remote unit transceiver making the transmission during said ranging process while limiting the overall bandwidth of the resulting radio frequency signals so as to not interfere with said other services being simultaneously transmitted on said transmission media;
• in said central unit transceiver, using said known preamble data in each transmission from each said remote unit transceiver to generate phase and amplitude error correction factors for use in receiving transmissions from said remote unit transceiver and using said phase and amplitude error correction factors calculated for each remote unit transceiver to recover the data transmitted by that remote unit transceiver.

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 medium designed to carry radio frequency signals, said multiple channels of digital data being transmitted simultaneously over said cable television medium as a plurality of frames of digital data, said cable television medium also carrying frequency division multiplexed cable television programming, comprising:

• establishing frame synchronization at each remote unit by determining a transmit frame timing delay for each said remote unit such that, when each remote unit transmits a numbered upstream frame of data using that remote unit's transmit frame timing delay, said frame will arrive at said central unit simultaneously with like numbered frames transmitted by other remote units;
• in each remote unit, after achieving initial frame synchronization, setting default values for initial transmit power, upstream equalization coefficients and fine timing alignment values;
• in each remote unit after achieving initial frame synchronization, periodically adjusting said fine timing alignment value by sending training data spread by a predetermined one of a plurality of orthogonal, cyclic spreading codes and determining from feedback messages from said central unit if the value of said transmit frame timing delay is still correct, and, if not, performing a fine tuning process to adjust the value of said fine timing alignment value so as to achieve a transmit frame timing delay which achieves precise frame synchronization;
• in each remote unit after achieving initial frame synchronization, periodically performing a power alignment process by transmitting training data to said central unit using said initial transmit power level and monitoring one or more feedback messages from said central unit until a message is received which instructs said remote unit what transmit power level to use which will cause errors in receiving data transmitted by this remote unit to be minimized and adjusting said transmit power level to the value received from said central unit;
• in each remote unit after achieving initial frame synchronization, periodically transmitting training data spread by a plurality of predetermined orthogonal, cyclic spreading codes and monitoring feedback messages received from said central unit until one or more messages is received which include upstream equalization coefficients for use by this remote unit to derive new upstream equalization coefficients to use in subsequent upstream transmissions, and using said upstream equalization coefficients received from said central unit to derive new upstream equalization coefficients and using said new upstream equalization coefficients for subsequent upstream transmissions;
• 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 interleaving said portions as selected elements of said information vector having n elements where each element of said information vector corresponds to a single upstream logical channel but wherein any element of said information vector corresponding to a logical channel which is not assigned to said remote unit has no upstream payload data therein, and inserting known preamble data in at least some of said information vectors of each transmission from a remote unit;
• Trellis encoding each element of each said information vector to add a selectable number of redundant bits and mapping the resulting bits of each element of each information vector into a constellation point of a quadrature amplitude modulation constellation so as to generate an inphase and quadrature information vector from each information vector;
• at each remote unit, performing code division multiplexing by performing a matrix multiplication of each inphase and quadrature information vector times a code matrix comprised of n orthogonal, cyclic spreading codes, said matrix multiplication being performed using a chip clock which has been synchronized with a chip clock in said central unit generating inphase and quadrature result vectors corresponding to said inphase and quadrature information vectors, each inphase and quadrature result vector having n elements;
• at each remote unit, after frame synchronization has been achieved by that remote unit, modulating the n elements of each said inphase and quadrature result vectors onto two radio frequency carriers of the same frequency but offset in phase by 90 degrees using QAM modulation, said radio frequency carriers being synchronized in frequency to a master carrier in said central unit.

A process carried out in each of a plurality of physically dispersed remote transceivers for simultaneously transmitting multiple channels of digital data which has been encoded with supplemental services data and other services over the same transmission medium to a headend transceiver while substantially reducing interference, comprising:

• receiving said one or more time division multiplexed data streams at one or more remote units and Trellis encoding the data bits from each timeslot into real and imaginary components and using said real and imaginary components to fill elements of inphase and quadrature information vectors that correspond to assigned logical channels characterized by the use of specified spreading codes used during specified upstream frames, each said inphase and quadrature information vector having N elements, the first element of each inphase and quadrature information vector corresponding to a first logical channel and the second element of each inphase and quadrature information vector corresponding to a second logical channel and so on for all elements, each of said upstream logical channels being one of a plurality of logical channels that are shared by a plurality of remote transceivers according to spreading code assignments from a said headend transceiver, the elements of said inphase and quadrature information vectors which are filled with data corresponding to one or more logical channels assigned to said remote transceiver by downstream code assignment messages from said central transceiver with all other elements containing no data, and inserting known preamble data into at least some of said information vectors;
• recovering any modulated waveform encoding the central transceiver master carrier frequency and phase information in any way, and generating a synchronized local upstream carrier from said recovered waveform;
• recovering in any way a master clock signal transmitted by said central transceiver and synchronizing a local chip clock to said recovered master clock signal;
• recovering a downstream kiloframe signal transmitted by said central transceiver and using said kiloframe signal to synchronize an upstream frame counter in each remote transceiver to an upstream frame counter in said central transceiver;
• performing any ranging process at each said remote transceiver to establish a transmit frame timing delay for said remote transceiver which will cause numbered frames of data transmitted from said remote transceiver to arrive aligned in time with the frame boundaries of like-numbered frames transmitted by others of said remote transceivers;
• performing a training process initially after achieving frame synchronization and from time to time thereafter by transmitting training data spread by predetermined spreading codes to said central transceiver and receiving messages from said central transceiver addressed to specific remote transceivers containing instructions on how to fine tune said transmit frame timeing delay to maintain precise frame synchronization and containing instructions on how to adjust the transmit power of subsequent transmissions and containing upstream equalization coefficient data to use in deriving new upstream equalization coefficients for use in filtering subsequent upstream data transmissions;
• individually spreading the energy of said inphase and quadrature information vector having data therein which is to be transmitted on one or more of said logical channels assigne to said remote transceiver using one or more of N orthogonal codes and said local chip clock to spread the spectrum of each inphase and quadrature information vector to generate an inphase and quadrature spread spectrum result vector for each corresponding pair of inphase and quadrature information vectors;
• filtering said inphase and quadrature result vectors in a filter having equalization coefficients derived from said equalization coefficients transmitted from said central transceiver in response to transmission of said training data;
• filtering each said inphase result vector using a real component shaping filter having a squared raised cosine transfer function in a real plane of the frequency domain and centered on a predetermined intermediate frequency synchronized to the frequency of said recovered master carrier and with a bandwidth selected to limit the bandwidth of the Fourier components of output signals from said real component shaping filter in said real plane of said frequency domain to a predetermined bandwidth selected so as to not interfere with other signals being transmitted on said transmission medium;
• filtering each said quadrature result vector using an imaginary component shaping filter having a squared raised cosine transfer function in an imaginary plane of the frequency domain, the Fourier spectrum of the signals output by said imaginary component shaping filter being centered on said predetermined intermediate frequency synchronized to the frequency of said recovered master carrier and with a bandwidth selected to limit the bandwidth of the Fourier components of output signals from said imaginary component shaping filter in said imaginary plane of said frequency domain to a predetermined bandwidth selected so as to not interfere with other signals being transmitted on said transmission medium, and wherein the transfer function of said imaginary component shaping filter is the Hilbert transform of the transfer function of said real component shaping filter;
• summing the output data from said real and imaginery component shaping filters;
• converting said digital data output from said summing step to an analog radio frequency signal at an intermediate frequency;
• and
• altering the frequency of said intermediate frequency analog signal to a frequency that will not interfere with other services carried on said shared transmission medium such that said supplemental services are frequency division multiplexed with said other services and time division multiplexed between supplemental service data from different sources connected to the same remote transceiver and code division multiplexed between upstream transmissions from different remote transceivers.

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

• first 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 and interleaving and Trellis encoding the data of said N channels into a frame comprised of M contiguous inphase and quadrature information vectors a plurality of which comprise each upstream frame for transmission plus a guardband during which no data from said time division multiple access stream is transmitted, said reorganizing carried out by reorganizing and interleaving a portion of the data from each of said N channels into specific assigned elements of each of said M inphase and quadrature information vectors for each upstream frame, each information vector comprised of N elements, said specific assigned elements corresponding to logical upstream channels assigned to said remote unit, said elements comprising a subgroup of bits from one or more channels or timeslots of said time division multiple access stream plus a predetermined number of error detection and correction bits generated by a Trellis encoder, each inphase and quadrature information vector containing data only in elements that correspond to logical channels assigned to said remote unit, said Trellis encoder mapping each element of each said information vector into a real and imaginary components in said inphase and quadrature information vectors such that M inphase and quadrature information vectors are generated in each frame, said first means also for inserting known preamble bits in at least some of said information vectors;
• means for synchronizing a local chip clock with a master chip clock in said central unit and for synchronizing a local carrier with a master carrier oscillator in said central unit;
• second means for using said synchronized local chip clock to direct sequence spread spectrum encode each of said M inphase and quadrature information vectors using N orthogonal, cyclic spreading codes to generate M inphase and quadrature result vectors, said second means also for passing the data of said real and imaginary result vectors for each frame through an equalizating filter having filter coefficients received in a message from said central unit and 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 represented by data exiting said shaping, passband filters to a predetermined bandwidth which will not interfere with other transmissions on said shared transmission medium and for summing the resulting data encoding intermediate frequency signals to generate M upstream frames of spread spectrum data for transmission, and converting the data encoding said M upstream frames into an analog signal of said intermediate frequency, and for converting said intermediate frequency signal encoding said M upstream frames to a radio frequency signal synchronized to said local carrier synchronized to said master carrier oscillator in said central unit, and which will not interfere with other services being carried on said transmission medium, the resulting radio frequency signal being M-ary QAM modulated, and for transmitting said modulated radio frequency carrier signals over said shared transmission medium;
• and
• third 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 frames transmitted by other remote units.

An apparatus in each remote unit of a system comprised of a plurality of physically dispersed remote units transmitting multiple channels of digital data from said plurality of remote units to a central unit over a cable television transmission medium using synchronous code division multiple access, comprising:

• framer means in each remote unit for accepting incoming data of a time division multiple access stream comprised of N timeslots and for interleaving the data of said N channels over a frame comprised of M contiguous information vectors and a guardband, said interleaving being carried out by reorganizing said data from said N channels into one or more of N elements said M information vectors corresponding to N upstream logical channels assigned to said remote unit;
• code division multiplexing means in each remote unit for providing code division multiple access spreading by encoding said M information vectors using a plurality of orthogonal, cyclic codes to generate M result vectors, and for using said M result vectors to modulate one or more radio frequency carrier signals to generate modulated RF signals, and for transmitting said modulated RF signals over said cable television transmission medium;
• and
• ranging means in each said remote unit for adjusting the timing of transmissions to said central unit from said remote unit of each frame such that each transmitted frame from said remote unit arrives at said central unit simultaneously with frames transmitted from other remote units.

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

• a framer circuit including interleaving circuitry to generate information vectors and to insert known preamble data;
• a convolutional encoder to add error correction bits to each information vector to generate an inphase and quadrature information vectors from each information vector;
• a carrier recovery circuit to synchronize a local carrier signal to a master carrier signal;
• a clock recovery circuit for synchronizing a local chip clock to a master chip clock;
• a code division multiplexer circuit coupled to said chip clock recovery circuit for spreading the spectrum of said inphase and quadrature information vectors using said synchronized local chip clock to generate inphase and quadrature result vectors;
• an upstream equalization filter having coefficients received from a central transceiver to which said multiple channels of digital data are being transmitted which will equalize the channel between said transmitter and said central transceiver and coupled to filter said inphase and quadrature result vectors;
• a scaling circuit for selectively altering the amplitude of the transmitted signal by said transmitter apparatus;
• a modulator coupled to said carrier recovery circuit for using said inphase and quadrature result vectors to create the information content in one or more radio frequency signals which are synchronized in frequency to said local carrier signal and said master carrier signal;
• and
• a ranging circuit to carry out one or more processes to determine the proper transmit frame timing delay to achieve frame synchronization such that frames transmitted to said central transceiver arrive there with their frame boundaries aligned in time with frames transmitted to said central transceiver from other transmitter apparatus.