Precoded ternary data transmission

Abstract

A digital data transmission rate of three bits per cycle of bandwidth is achieved in precoded partial-response band-limited communication channels by partitioning binary digits into groups of three two-level digits and translating these binary groups of three into pairs of three-level digits prior to transmission. Correct pairwise association of received signals is accomplished by reserving a three-level digit pair for monitoring purposes. This reserved pair can validly occur only at a transition between allowable pairs. By monitoring the presence of the reserved pair, correct pairwise association of ternary digits is assured and binary digits are properly decoded without having to provide a special framing signal.

What is claimed is: 
     
       1. Apparatus for communicating a binary data signal over a transmission channel of bandwidth W at an effective binary bit rate that is a nonintegral multiple of the channel symbol rate, comprising means for mapping each possible first block of binary digits taken m at a time into second blocks of n preassigned N-level digits such that 2 m  is less than N n  and there exists at least one unassigned N-level block,   means for precoding N-level digits from said mapping means in accordance with the inverse of the impulse response of said channel such that precoded N-level digits can be decoded from single samples of the received signal,   means for exciting said channel with precoded digits from said precoding means at a signaling rate of 2W symbols per second such that channel signals occupy (2N-1) levels,   means for reconstructing said N-level digits from said channel signals,   means for monitoring N-level digits from said reconstructing means for the presence of said unassigned N-level block therein and producing a framing control signal,   means responsive to said framing control signal for partitioning reconstructed N-level digits into n-length blocks such that said unassigned block does not occur within partitioned blocks to be decoded, and   means under the control of said partitioning means for translating partitioned blocks of N-level digits into a serial train of binary digits.   
     
     
       2. The apparatus of claim 1 in which m and N equal 3 and n equals 2 and there is only one unassigned three-level signal block. 
     
     
       3. Apparatus for communicating a binary data signal train to achieve an effective signaling rate of three bits per second per Hertz of bandwidth comprising means for mapping first blocks of serial binary data taken three digits at a time into preassigned second blocks of three-level digits taken two digits at a time, there being one unassigned three-level digit pair which can occur only between properly mapped second blocks,   means for exciting a communication channel of limited bandwidth with said second blocks of digits at a symbol rate equal to twice the bandwidth of said channel,   means at a receiver connected to said channel for recovering said three-level digits,   means for monitoring pairs of three-level digits from said recovering means for the presence of said unassigned digit pair and generating a framing signal therefrom,   means responsive to said framing signal for partitioning recovered three-level digits into pairs such that said unassigned pair occurs only as the last and first digit respectively of consecutive partitioned blocks, and   means for decoding three-level digit pairs from said partitioning means into a serial binary data train.   
     
     
       4. Apparatus as defined in claim 3 in which said three-level digits are precoded before exciting said channel in accordance with the inverse of the impulse response of said channel. 
     
     
       5. Apparatus as defined in claim 3 in which said three-level digits are coded in two-rail binary form. 
     
     
       6. Apparatus as defined in claim 3 in which said partitioning means comprises a timing-wave source having a square-wave output at half the channel symbol rate,   means jointly responsive to said timing-wave source and said framing signal for generating a first control output when said framing signal occurs during the first half-cycle of said timing wave and a second control output when said framing signal occurs during said second half-cycle thereof,   a reversible counter controlled by first and second control outputs of said generating means, an excess of said second over said first control outputs yielding an overflow signal, and   means responsive to said overflow signal for reversing the phase of said timing-wave output.   
     
     
       7. The method of communicating a binary data signal train in a precoded multilevel format to achieve an effective signaling rate of three bits per cycle of bandwidth of a communications channel comprising the steps of performing a serial to parallel conversion of serial binary data bits taken three at a time into first blocks,   mapping said first blocks of binary data into second blocks of paired ternary digits, there being one nonallowed ternary pair which can only occur between valid second blocks,   applying the ternary digits of said second blocks to said communications channel to form precoded multilevel signals at two-thirds the binary signaling rate,   recovering at a receiver said ternary digits by a modulo-three reduction of said multilevel signals,   monitoring pairs of recovered ternary digits for the occurrence of said nonallowed ternary pair,   partitioning responsive to the occurrence of said nonallowed ternary pair said recovered ternary digits into valid second blocks, and   decoding properly partitioned second blocks of ternary digits into first blocks of binary digits. .Iadd. 8. A data transmission system having a carrier signal to be transmitted over a communication link, said system comprising:   means at a transmitter for grouping, into a multi-bit word, input binary data having a data rate defined by a given number of input bit periods per second with one data bit represented in each input bit period;   means responsive to said grouping means for generating a discrete signal level during at least a pair of modulation periods per multi-bit word for representing the identity of the multi-bit word, said signal generating means characterized by emitting a signal having a data bit-to-baud ratio of a mixed number and by emitting said discrete signal levels in a continuous sequence that represents a plurality of adjacent ones of said multi-bit data words;   means for modulating said carrier signal with said signal from said generating means; and   means at a receiver for deriving a clock signal from said signal that modulated the carrier, which clock signal is synchronized in time with the baud rate of said generating means at said transmitter. .Iaddend..Iadd.   
     
     
            A system in accordance with claim 8 wherein each multi-bit word comprises three binary bits and said mixed number bit-to-baud ratio is 1.5. .Iaddend..Iadd. 10. A system in accordance with claim 9 wherein the bits of binary values are identified by occupying one of two possible signal levels during sequentially-appearing input bit periods, and said generating means comprises an encoder employing a trinary format which comprises three signal levels and a modulation period equal to 11/2 bit periods; said system comprising: means modulating said carrier with a discrete signal level during a first modulation period of a pair of adjacent modulation periods for partially identifying the bits for a multi-bit word to be represented in that modulation period; and   means modulating a given signal level during the second modulation period of said pair for completing the identity of the bits of said multi-bit word.