Apparatus and method for SCDMA digital data transmission using orthogonal codes and a head end modem with no tracking loops

A process of bidirectional digital data communication carried out by remote unit modem to exchange digital data transmissions with a headend modem comprising the steps of:

• receiving downstream digital data transmitted in frames from said headend modem modulated by a modulation scheme;
• recovering said downstream payload data and a master clock encoded in a downstream frame marker signal;
• presenting said downstream data at an output;
• receiving upstream digital payload data having a first clock rate from one or more sources;
• organizing upstream digital payload data into upstream frames of the same length as said downstream frames;
• transmitting a ranging signal at various trial and error transmit frame timing delay values;
• receiving messages back from said headend modem that are used to adjust said transmit frame timing delay value until a value is found which causes frame synchronization to exist, frame synchronization being defined as the arrival of upstream frames at said headend modem with their frame boundaries aligned in time with the frame boundaries of upstream frames transmitted from other remote unit modems to said head end modem;
• generating a chip clock that is phase coherent with said recovered master clock and at a much higher rate than said first clock rate;
• generating an upstream carrier that is phase coherent with said recovered master clock;
• using said chip clock to multiply one or more orthogonal spreading codes times the upstream data in one or more upstream frames to generate one or more upstream frames of upstream spread spectrum payload data;
• transmitting said frames of upstream spread spectrum payload digital data using a modulation method and said upstream carrier, and using the transmit frame timing delay in transmitting each upstream frame which caused frame synchronization to exist;
• interleaving upstream payload data to form one or more information vectors for each upstream frame;
• Trellis encoding each element of said information vectors with redundant error detection and correction bits;
• mapping the resulting bits into real and imaginary components of constellation points to generate real and imaginary information vectors from each said information vectors, each said real and imaginary information vector comprised of the same number of elements as there were elements in the information vector from which it was generated;
• multiplying said elements of said real and imaginary information vectors by one or more said orthogonal, cyclic spreading codes at the chip clock rate times to generate real and imaginary result vectors each comprised of a plurality of chips;
• using said chips of said real and imaginary result vectors to generate upstream signals to transmit using carrierless Quadrature amplitude modulation;
• and
• transmitting said upstream signals to said headend modem over a cable television hybrid fiber coaxial cable transmission medium which is simultaneously carrying downstream analog cable television signals and downstream digital data without interfering therewith by using frequency division multiplexing between said upstream and said downstream.

A remote unit modem to transmit digital data upstream to a headend modem comprising:

• a digital data receiver for receiving downstream digital data transmitted from said headend modem modulated by a modulation scheme, said downstream digital data either encoding a master clock generated at said headend modem in payload data or other data, said master clock being used to transmit said downstream data, or said downstream data including said master clock as well as payload data, said digital data receiver functioning to recover said downstream payload data and said master clock and generating an upstream clock from said recovered master clock;
• a digital data transmitter for coupling to a source of upstream digital payload data from one or more sources, and coupled to receive said upstream clock generated from said recovered master clock and using said upstream clock to transmit known preamble data and, subsequently, transmitting said upstream payload digital data using a modulation method, and, if necessary to separate upstream payload data from several upstream data sources, using a multiplexing method;
• a framer circuit functioning to receive said upstream digital payload data as input streams from one or more sources and interleave same into a plurality of frames, said framer circuit outputting one or more information vectors per frame, said information vectors containing data from said input streams of upstream digital payload data organized as individual elements, each element comprised of a plurality of bits;
• a trellis encoder coupled to receive said information vectors and trellis encode each element to add redundant bits that can be used at said headend modem to recover said data elements and correct for reception errors caused by channel impairments, said trellis encoder outputting trellis encode information vectors including real and imaginary information vectors;
• a code division multiple access multiplexer circuit functioning to receive said trellis encoded information vectors and spread the Fourier spectrum thereof using orthogonal spreading codes to perform a coding transformation so as to generate one or more symbols from each trellis encoded information vector having a spread power spectrum;
• and
• a carrierless shaping filter modulator comprised of a first filter to passband filter the spread spectrum resulting from code division multiplexing of said real information vectors to pass only a first passband of predetermined limited bandwidth and center frequency and further comprised of a second filter having a filter transfer function which is the Hilbert transform of the transfer function of said first filter and functioning to passband filter the spread spectrum resulting from code division multiplexing of said imaginary information vectors to pass only a first passband of predetermined limited bandwidth and center frequency.

A process of bidirectional digital data communication carried out by remote unit modem to exchange digital data transmissions with a headend modem comprising the steps of:

• receiving downstream digital data transmitted in frames from said headend modem modulated by a modulation scheme;
• recovering said downstream payload data and a master clock encoded in a downstream frame marker signal;
• presenting said downstream data at an output;
• receiving upstream digital payload data having a first clock rate from one or more sources;
• organizing upstream digital payload data into upstream frames of the same length as said downstream frames;
• transmitting a ranging signal at various trial and error transmit frame timing delay values;
• receiving messages back from said headend modem that are used to adjust said transmit frame timing delay value until a value is found which causes frame synchronization to exist, frame synchronization being defined as the arrival of upstream frames at said headend modem with their frame boundaries aligned in time with the frame boundaries of upstream frames transmitted from other remote unit modems to said head end modem;
• generating a chip clock that is phase coherent with said recovered master clock and at a much higher rate than said first clock rate;
• generating an upstream carrier that is phase coherent with said recovered master clock;
• using said chip clock to multiply one or more orthogonal spreading codes times the upstream data in one or more upstream frames to generate one or more upstream frames of upstream spread spectrum payload data;
• transmitting said frames of upstream spread spectrum payload digital data using a modulation method and said upstream carrier, and using the transmit frame timing delay in transmitting each upstream frame which caused frame synchronization to exist;
• checking the continued accuracy of the frame synchronization;
• and
• cooperating with said head end modem to adjust said frame synchronization when necessary;
• cooperating with said head end modem to adjust the power level of transmissions by said remote unit modem such that transmissions therefrom arrive at said head end modem at approximately the same power level as transmissions from other remote unit modems;
• cooperating with said head end modem to adjust filter coefficients to predistort upstream data transmissions to compensate for upstream channel impairments;
• and
• interleaving said upstream payload data over time to form a plurality of information vectors for each upstream frame, and Trellis encoding each element to add redundant error correction bits and map each element into corresponding inphase and quadrature elements of corresponding inphase and quadrature information vectors and code division multiplexing each inphase and quadrature information vector,
• wherein using said chip clock to multiply one or more orthogonal spreading codes times the upstream data in one or more upstream frames comprises code division multiplexing each of said inphase and quadrature information vectors to generate inphase and quadrature result vectors, and wherein said step of transmitting said frames of upstream spread spectrum payload digital data using a modulation method comprises the steps of using said inphase and quadrature result vectors to set the information content of two quadrature amplitude modulated radio frequency signals formed by carrierless modulation using two shaping filters having filter transfer functions which are the Hilbert transform of one another.