Apparatus and method for digital data transmission over video cable using orthogonal cyclic codes

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:

• 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, 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.

A method for transmitting to a central unit a plurality of frames of data generated by a plurality of physically distributed remote units which receive a plurality of channels of digital data generated by a plurality of sources coupled to said plurality of physically distributed remote units, said plurality of remote units being 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 said plurality of frames, said cable television media also carrying frequency division multiplexed cable television programming, comprising:

• establishing frame synchronization at each remote unit by determining a transmit frame timing reference delay for each said remote unit such that, when each remote unit transmits data using that remote unit's transmit frame timing reference delay, said data will arrive at said central unit with its frame boundaries aligned in time with the frame boundaries of frames tranmitted from other remote units;
• receiving one or more channels of digital data at each remote unit where said channels of digital data received by each remote unit are received in the form of a time division multiplexed data stream comprised of a plurality of timeslots wherein each timeslot contains one or more data bits from one channel such that all channels have a timeslot into which data from that channel may be tranmitted in said time division multiplexed data stream to a remote unit, and wherein each timeslot contains a number of bits divisible by an integer of 1 or more, said integer being the number of symbols to be transmitted during each frame;
• at each remote unit, constructing an information vector having n elements by selecting portions of the bits of said digital data from each timeslot of digital data received at said remote unit and organizing said portions of bits as selected elements of said n elements of said information vector, where each element of said information vector corresponds to one of said timeslots but wherein any element of said information vector corresponding to a timeslot from which no data is received by any particular remote unit is set to zero, and wherein each said frame of data transmitted from each remote unit to said central unit comprises transmission of data generated from a sufficient number of code division multiplexed information vectors so as to code division spread all data from all timeslots to be transmitted during a single frame, and wherein the process of constructing said information vector comprises taking from each timeslot as an element of said information vector a predetermined number of bits equal to the total number of bits in each timeslot divided by said integer and encoding each predetermined number of bits taken from each timeslot with one or more redundant bits and storing said predetermined number of bits taken from each timeslot plus the redundant bits as an element of said information vector, said redundant bits being calculated based upon the present state of said predetermined number of bits taken from each timeslot and upon the previous state of these same predetermined bits for this same timeslot during the last frame, said calculation being performed using an algorithm designed to generate redundant bits which will aid a Viterbi Decoder in a receiver in said central unit to better determine from received data corrupted by media impairments what said predetermined bits were prior to encoding with said redundant bits;
• 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, modulating the n elements of said result vector onto one or more radio frequency carriers and transmitting each frame of modulated radio frequency signals to said central unit using the transmit frame timing reference delay determined for this particular remote unit so as to achieve upstream frame synchronization with other remote units;
• 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.

A method for transmitting to a central unit multiple channels of digital data generated by a plurality of sources coupled to a plurality of remote units which are coupled to said central unit via a cable television media designed to carry radio frequency signals but which are physically distributed from said central unit, said multiple channels of digital data being transmitted simultaneously over said cable television media as a plurality of frames of digital data, each said frame being separated from adjacent frames by guardbands, said cable television media 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, said transmit frame timing delay for each said remote unit being established by a trial and error process of setting an initial value for said transmit frame timing delay and transmitting a timing signal during a frame, said timing signal recognizable by said central unit as a timing signal and monitoring a guardband following said frame during which said timing signal was transmitted with said central unit to determine if said timing signal appeared in said guardband, and transmitting a signal from said central unit indicating whether or not said timing signal appeared in said guardband, and, if said remote unit determines from the transmission from said central unit that a timing signal did not appear in said guardband, adjusting said transmit frame timing delay to a new value and retransmitting a new timing signal, and monitoring a guardband following the frame during which said new timing signal was transmitted with said central unit and transmitting from said central unit a signal indicating whether a timing signal appeared in said guardband, and, when said remote unit determines from said transmission from said central unit that a timing signal has appeared in said guardband, transmitting from said remote unit an identification code using the latest value for said transmit frame timing delay, said identification code indicating the identity of said remote unit, and monitoring said guardbands for said identification code with said central unit and transmitting a message from said central unit indicating which identification code was received, and monitoring said transmission with said remote units and comparing in each remote unit the identification code received by said central unit with the remote unit's identification code, and, if there is a match, stopping the process of adjusting said transmit frame timing delay value, and subsequently using the transmit frame timing delay value that resulted in said timing signal arriving during a guardband for all subsequent transmissions from said remote unit whose identification code was received from said central unit, and repeating the above described frame synchronization process for each remote unit that needs to achieve frame synchronization until frame synchronization is achieved, such that, when more than one remote unit transmits data using their respective transmit frame timing delays, said data from all transmitting remote units 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 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.

An apparatus for transmitting multiple channels of digital data from a remote unit to a central unit over a shared transmission media using synchronous code division multiple access modulation, 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 and spreading the data of said N channels over a frame comprised of M contiguous symbols and a guardband during which no data from said time divsion multiple access stream is transmitted, said spreading being carried out by reorganizing said data from said N channels into said M information vectors each comprised of a plurality of subgroups of bits from said time divsion multiple access stream, each information vector containing at least one subgroup of data from each said channel;
• means for encoding said M information vectors using a plurality of orthogonal codes to generate M result vectors and using said result vectors to modulate radio frequency carrier signals using M-ary QAM modulation and for transmitting said modulated radio frequency carrier signals over said shared transmission media said composition of said information vectors and said encoding 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;
• 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 timing established by said central unit.