High speed data communication system using phase shift key coding

A method of encoding a binary NRZ data signal representing a series of binary data bits of "1" and "0" polarities clocked at a given clock rate to a data output signal of a different apparent bit period rate, comprising the steps of:

• clocking each data bit of said NRZ signal with a bit period of M clock periods, wherein M is a positive even integer greater than 3;
• detecting whether a current data bit of said NRZ signal has the same or a changed polarity as a previous data bit;
• maintaining a count of the number of polarity changes of the data bits in each encoding cycle defined from a beginning reset point of said NRZ signal;
• encoding an encoded output signal representing said NRZ signal, said encoded signal having a waveform which switches between two opposing polarities with each polarity change of the data bits in each encoding cycle, wherein the polarity of the encoding signal is switched with widths of M/M, M+1/M, and M+2/M bit periods after a previous polarity switch depending upon whether a polarity change is detected and the count of the polarity changes as follows:
• (1) a width of M/M when a current data bit is the same as a previous data bit (no polarity change);
• (2) a width of M+1/M when a current data bit has a polarity that is changed from that of a previous data bit, the bit pattern present in said output signal is 101, the count of polarity changes thereupon being indexed by one;
• (3) a width of M+2/M when a current data bit has a polarity that is changed from that of a previous data bit and the count being thereupon reset to define the beginning reset point for the next encoding cycle, and the decoder polarity being set to a "1" to remove any decoding ambiguity.

A high speed data transmission system for transmitting a binary NRZ data signal representing data bits of a given bit period over a communications channel, comprising:

• encoding means responsive to said binary NRZ data signal for encoding an output encoded signal incorporating signal polarity switches encoded at a plurality of time periods which are equal to and fractionally larger than the bit period of said NRZ data signal and at a given bit rate;
• filtering means for filtering extraneous frequencies from said encoded signal other than a baseband frequency thereof, such that said filtered encoded signal occupies a bandwidth which is about 1/6 of the bandwidth of said binary NRZ signal;
• and
• transmitting means for transmitting said filtered encoded signal over the communications channel.