High speed data communication system using phase shift key coding

• US 5,185,765 A
• Filed: 07/23/1990
• Issued: 02/09/1993
• Est. Priority Date: 05/08/1986
• Status: Expired due to Fees

• Current Assignee: Walker, Harold R.
• Original Assignee: Walker, Harold R.
• Inventors: Walker, Harold R.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US07/557,322
• Time in Patent Office: 932 Days
• Field of Search: 360/40, 360/44, 332/106, 332/109, 332/110, 332/111, 375/22, 375/25, 375/27, 375/37, 375/59, 375/121, 375/122, 375/7, 375/8, 455/45, 341/52, 341/53, 370/69.1, 379/90, 379/97
• US Class Current: 375/238
• CPC Class Codes: H04L 27/2035 using a single or unspecified number of carriers
• CPC Class Codes: H04L 27/2272 using phase locked loops H04L27/2273 takes precedence

Abstract

An improved binary data communication system employs an improved VPSK encoding procedure wherein each input data bit has a bit period of M clock periods, and the data bit polarity changes are phase shift key coded with waveform widths of M/M, M+1/M, and M+2/M bit periods wherein M is an even integer greater than 3. Each of the data bits (except the last one in an encoding cycle) is encoded in an encoding signal which switches back and forth between "1" and "0" polarities and has assigned widths representing whether or not the polarity of the data bit is changed from that of the previous data bit, and whether it is the last (M-1th) polarity change in the encoding cycle. At the receiving end, a complementary procedure is used to decode the encoded signal. For transmission, the encoded signal is filtered for higher order harmonics and integrated in order to provide a sine wave output shifted 90 degrees in phase. Upon reception, the received signal is differentiated and a zero crossover detector is used to regenerate the encoded signal for decoding. The improved encoding technique can achieve Nyquist efficiencies of 10, 12.6, and 15.3 bits/Hz-bandwidth, or higher, for M equal to 6, 8, and 10 modulation levels, respectively. The encoded signal spectrum fits typically within about 1/6 of the bandwidth of the baseband NRZ signal. The encoded signal is particularly useful for transmission at high data rates in telephone, RF modulated carriers, and other transmission systems.

Claims

1. An encoder apparatus for use in a high speed data transmission system for transmitting an input NRZ signal over a communications path as a data signal, said NRZ signal representing a series of binary data bits of "1" and "0" polarities clocked at a given clock rate, comprising:

polarity change detecting means responsive to said NRZ signal for detecting whether a current data bit of said NRZ signal has the same or a changed polarity as a previous data bit, wherein each data bit of said NRZ signal has a bit period of M clock periods;

counting means for 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 means for encoding an encoded 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 by said polarity change detecting means and the count maintained by said counting means, 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 count of said counting means being thereupon 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 of said counting means including the current polarity change is equal to M-1 and a 101 bit pattern is present in the data stream to the encoding means, the count of said counting means being thereupon reset to define the beginning reset point for the next encoding cycle,

wherein, in all of the above said means, M is a positive even integer greater than 3.

2. An encoder apparatus according to claim 1 further comprising filtering means for filtering said encoded signal such that said filtered encoded signal as transmitted has a Nyquist data compression efficiency of approximately 15.3 bits/HZ-bandwidth.

3. An encoder apparatus according to claim 2, wherein M is equal to 8, said counting means is set upon each reset to count 7 polarity changes in the ensuing encoding cycle, and the width of the polarity switch of said encoding signal is set 10/8 bit periods after a previous polarity switch upon the 7th polarity change counted in the encoding cycle.

4. An encoder apparatus according to claim 1, wherein each polarity change of the data bits is detected by a leading edge transition from one polarity to another, and upon said M-1th polarity change between a current data bit and a following data bit, the width of the polarity switch of said encoding signal is set M+2/M bit periods after a previous polarity switch, the following data bit is omitted as the last bit in the current encoding cycle, and the counting means is reset for a next encoding cycle defined by a beginning reset point at a next following data bit.

5. An encoder apparatus according to claim 1, further comprising decoding means for receiving said encoded signal as transmitted and regenerating said NRZ input signal therefrom.

6. An encoder apparatus according to claim 5, wherein said decoding means includes detecting means for detecting said widths of M/M, M+1/M, and M+2/M bit periods between the polarity switches of said encoded signal in a current decoding cycle defined by a current reset point, data signal generating means for clocking data bits out for an output signal at M/M bit periods having polarities depending upon the widths of said encoded signal detected by said detecting means, and reset means responsive to detection of an M+2/M width by said detecting means for defining a next reset point and synchronizing said decoding means for a next decoding cycle.

7. An encoder apparatus according to claim 6, wherein each polarity change of the data bits is detected by a leading edge transition from one polarity to another, and upon said M-1th polarity change between a current data bit and a following data bit, the width of the polarity switch of said encoding signal is set M+2/M bit periods after a previous polarity switch when the data pattern is 101, the following data bit is omitted as the last bit in the current encoding cycle, and the counting means is reset for a next encoding cycle defined by a beginning reset point at a next following data bit, and wherein upon detection of said width of M+2/M bit periods by said decoding means, said data signal generating means inserts two data bits including said omitted data bit with the first inserted bit being a "0" and the second inserted bit being a "1".

8. 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.

9. A method of encoding according to claim 8, comprising the further step of filtering said encoded signal such that said filtered encoded signal as transmitted has a Nyquist data compression efficiency of at least 10 bits/Hz-bandwidth.

10. A method of encoding according to claim 9, wherein M is set equal to 8, and said filtered encoded signal as transmitted has a Nyquist data compression efficiency of approximately 15.3 bit/HZ-bandwidth.

11. 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.

13. A high speed data transmission system according to claim 11, wherein said transmitting means includes a balanced modulator having one input for said encoded signal and another input for receiving a carrier signal, in order to provide at an output thereof a double-sideband suppresses carrier output signal which after filtering by means of a simple sideband filter included in said transmitting means becomes a single-sideband signal.

14. A high speed data transmission system according to claim 13, wherein said communications channel is a radio link.

15. A high speed data transmission system according to claim 11, wherein said transmitting means includes an FM modulator for modulating an FM subcarrier signal with said encoded signal such that the FM subcarrier signal shifts in phase according to the polarity switches of said encoded signal.

16. A high speed data transmission system according to claim 11, wherein said encoding means includes:

polarity change detecting means responsive to said NRZ signal for detecting whether a current data bit of said NRZ signal has the same or a changed polarity as a previous data bit, wherein each data bit of said NRZ signal has a bit period of M clock periods;

counting means for 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; and

further means for encoding an encoded 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 by said polarity change detecting means and the count maintained by said counting means, 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 count of said counting means being thereupon 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 of said counting means including the current polarity change is equal to M-1 and the bit pattern present in said data stream to said further means is 101, the count of said counting means being thereupon reset to define the beginning reset point for the next encoding cycle, and the polarity of the output device set to remove ambiguity;

wherein, in all of the above said means, M is a positive even integer greater than 3.

17. A high speed data transmission system according to claim 16, wherein said filtering means filters said encoded signal such that said signal as transmitted has a Nyquist data compression efficiency approximately equal to 15.3 bits/HZ bandwidth.

18. A high speed data transmission system according to claim 16, wherein M is equal to 8, said counting means is set upon each reset to count 7 polarity changes in the ensuing encoding cycle, and the width of the polarity switch of said encoding signal is set 10/8 bit periods after a previous polarity switch upon the 7th polarity change counted in the encoding cycle and the bit pattern is 101.

19. A high speed data transmission system according to claim 16, wherein said filtering means provides a sine wave output signal, and said transmitting means includes integrating means for shifting the peaks of said sine wave output by 90 degrees of phase.

20. A high speed data transmission system according to claim 19, further comprising receiving means for said encoded signal as transmitted, said receiving means including differentiating means for shifting the received signal by 90 degrees of phase, and a zero crossing detector for detecting zero crossings in the received signal.

21. A high speed data transmission system according to claim 20, further comprising decoding means for regenerating said NRZ input signal from the received signal, said decoding means including detecting means for detecting said widths of M/M, M+1/M, and M+2/M bit periods between the polarity switches of said encoded signal in a current decoding cycle defined by a current reset point, data signal generating means for clocking data bits out for an output signal at M/M bit periods having polarities depending upon the widths of said encoded signal detected by said detecting means, and reset means responsive to detection of an M+2/M width by said detecting means for defining a next reset point and synchronizing said decoding means for a next decoding cycle.

22. A high speed data transmission system according to claim 11, wherein said filtering means has an effective bandwidth and is operative such that the effect of noise is reduced by a factor of the given bit rate divided by the filter bandwidth.

12. A high speed data transmission system according to claim wherein said transmitting means is a modem and the communications channel is a telephone line.