CSK communication system

• US 5,132,986 A
• Filed: 12/21/1990
• Issued: 07/21/1992
• Est. Priority Date: 12/22/1989
• Status: Expired due to Term

• Current Assignee: NEC Corporation
• Original Assignee: NEC Home Electronics, Ltd. (NEC Corporation)
• Inventors: Endo, Kaoru, Takahashi, Naomichi, Tsumura, Soichi
• Primary Examiner(s): Gregory, Bernarr E.
• Application Number:
  US07/631,921
• Time in Patent Office: 578 Days
• Field of Search: 375/1, 375/64, 375/66-68, 375/84, 375/87, 375/90, 375/91, 380/34, 380/46, 380/47, 370/18
• US Class Current: 375/142
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/709 Correlator structure
• CPC Class Codes: H04J 13/0074 Code shifting or hopping
• CPC Class Codes: H04L 23/02 adapted for orthogonal signalling

Abstract

The present invention provides new arrangements for various components of a CSK communication system: modulator, correlators, demodulator, carrier detection circuit, and synchronization control circuit. The various improvements provide more accurate demodulation of data from the received signal in the presence of noise and signal deterioration. A modulator configuration permits the CSK system to use two M series codes in which the second code is simply a phase shifted version of the first code. The PN correlators, via shift-registers, efficiently output two correlation signals. The demodulator accepts two correlation signals from the correlators, detects auto-correlation peaks in the correlation signals, and uses the peaks to accurately determine whether the received bit has a value of "1" or "0". The carrier detecting circuit detects the presence of data in the received signal. A carrier detecting circuit conveniently allows demodulation of data without exact synchronization of the center of demodulator'"'"'s monitoring window to auto-correlation peaks. The synchronization control circuit generates accurate timing pulses that mark the start and end of each data bit. If auto-correlation peaks appear consistently in one location for the duration of N consecutive data bits, subsequent timing pulses are delayed in accordance with weighted averages of the stored locations of auto-correlation peaks. In one embodiment, separate correlation signal monitoring windows for demodulation and synchronization tracking may be set independently of each other, enabling the demodulator to clearly distinguish between an actual auto-correlation peaks and an inter-correlation peak, and the synchronization control circuit to attain stability by "averaging" out temporal effects of noise.

Claims

1. A Code Shift Keying (CSK) communication system for transmitting and receiving digital data each of which is a bit having a value of either "1" or "0," the system comprising:

a transmitter including

means for processing each of its input bits,

means for continuously generating two M-series codes, a first M-series code being identical to a second M-series code except in its phase,

means for selecting one of said two M-series codes depending on the value of a particular bit being processed, and

means for outputting as a transmitted signal the selected code in a period of time spanning the duration of the particular bit; and

a receiver including

means for recapturing the transmitted signal as a received signal,

means for obtaining two correlation signals by correlating the received signal with each copy of the two M-series codes,

means for partitioning each correlation signal into a sequence of consecutive periods,

means for comparing during each period the largest peak of one correlation signal with the largest peak of the other correlation signal,

means for deciding during each period whether the received signal spanning the period has value of "1" or "0" depending on the result of comparing the sizes of the peaks, and

means for generating a sequence of bits each of which has value of either "1" or "0."

2. A communication system as in claim 1, wherein said receiver comprises:

window generating means for generating periodic pulses each of whose center is synchronized to each peak of a signal formed by performing an operation on two correlation signals; and

peak detection means for detecting and storing location and size of said each peak within a duration of time spanned by one of the periodic pulses generated by said window generating means.

3. A Code Shift Keying (CSK) communication system transmitter for processing and transmitting digital data each of which is a bit having a value of either "1" or "0," the transmitter comprising:

M-series code generating means for continuously generating a first and a second M-series codes in a period of time spanning the duration of a particular bit, the first M-series code being identical to the second M-series code in its sequence of 1'"'"'s and 0'"'"'s but different in its phase; and

a switching circuit for selecting one of said two M-series codes depending on the value of said particular bit, and for outputting, as transmitted signal, the selected code in a period of time spanning the duration of the particular bit.

4. A transmitter as in claim 3, wherein said M-series code generating means comprises:

two identical M-series code generators, a first M-series code generator for generating said first M-series code and a second M-series code generator for generating said second M-series code; and

a phase setting circuit for causing the second M-series code generator to generate said second M-series code with its phase different from the phase of said first M-series code.

5. A transmitter as in claim 3, wherein said M-series code generating means comprises:

an M-series code generator for generating said first M-series code; and

a delay element for generating said second M-series code by accepting as its input said first M-series code, by delaying its inputted first M-series code, and by outputting the delayed first M-series code as said second M-series code.

6. A Code Shift Keying (CSK) communication system receiver for receiving a signal and processing the received signal which is capable of including series of a first and a second M-series codes which is identical to the first code except in its phase, the receiver comprising:

a first correlator for generating a first correlation signal by correlating a local replica of the first code and the received signal;

a second correlator for generating a second correlation signal by correlating a local replica of the second code and the received signal; and

a demodulator for periodically monitoring the first and the second correlation signals, for comparing during each monitoring period the largest peak of the first correlation signal with the largest peak of the second correlation signal, for deciding during each monitoring period whether the received signal spanning the monitoring period has value of "1" or "0" depending on the result of comparing sizes of said largest peaks, and for generating sequence of bits each of which has value of either "1" or "0."

7. A receiver as in claim 6, wherein said demodulator comprises:

window generating means for generating periodic pulses each of whose center is synchronized to a main peak of a signal formed by performing an operation on two correlation signals during a period of time spanning one of said bits; and

peak detection means for detecting said main peak within a duration of time spanned by one of the periodic pulses.

8. A Code Shift Keying (CSK) communication system receiver which includes two correlators for generating two correlation signals from a received signal, a demodulator for generating sequence of data bits based on two correlation signals and periodic timing pulses, a carrier detecting circuit for providing signals to and accepting signals from a timing pulse generator and accepting signals from two correlators, and the timing pulse generator for generating the timing pulses partly based on signals within or from the carrier detecting circuit, wherein the carrier detecting circuit comprises:

a peak position detecting circuit including

operating means for outputting peaks of a signal formed by processing two correlation signals,

means for detecting each position of said peaks, each peak within a single period of time spanned by one bit, and

means for outputting a peak position detection signal;

a peak position memory buffer for storing detected peak positions over a duration of time spanned by N data bits;

partitioning means for assigning, for each of N periods of time, M number of subintervals, each subinterval within one period having corresponding N-1 subintervals in other N-1 periods, all corresponding subintervals forming a single subinterval group, and all subintervals forming M subinterval groups;

first means for determining, for each duration of time spanning one bit of data, which of M subintervals contain a correlation peak, whose position is stored in said peak position memory buffer;

means for counting the total number of correlation peaks contained within each subinterval group based on outputs from said first determining means, and for outputting each of M counts resulting from the counting;

second means for determining if any of M counts is equal to or greater than a prescribed number m, deciding that a carrier has been detected if one of the counts is not less than m, and for outputting various signals including a carrier detection signal thereafter.

9. A receiver as in claim 8, wherein said carrier detecting circuit further comprises means for outputting non-detection signal if each of said M counts is less than m.

10. A receiver as in claim 8, wherein said carrier detecting circuit further comprises means for allowing those components within and dependent on numbers m and N to switch their dependency from numbers m and N to numbers m'"'"' and N'"'"'.

11. A receiver as in claim 8, wherein said operating means comprises:

means for adding two correlation signals;

means for evaluating and outputting the absolute value of added signals.

12. A receiver as in claim 8, wherein said operating means comprises:

means for evaluating the absolute value of each of two said correlation signals;

means for outputting larger one of the two absolute values.

13. A receiver as in claim 8, wherein said partitioning means includes means for preventing any one subinterval within one period from overlapping any other subintervals within the same period.

14. A receiver as in claim 8, wherein said partitioning means includes means for causing any one subinterval within one period to partially overlap its adjacent subintervals within the same period.

15. A Code Shift Keying (CSK) communication system receiver which includes two correlators for generating two correlation signals from a received signal, a demodulator for generating a sequence of data bits based on two correlation signals and periodic timing pulses, a carrier detecting circuit for providing signals to and accepting signals from a timing pulse generator and accepting signals from two correlators, and the timing pulse generator for generating the timing pulses partly based on signals from the carrier detecting circuit, wherein the carrier detecting circuit comprises:

a peak position detecting circuit including

operating means for outputting peaks of a signal formed by processing two correlation signals,

means for detecting each position of said peaks, each peak within a single period of time spanned by one bit, and

means for outputting a peak position detection signal;

a peak position determining circuit including

partitioning means for assigning, for each of N periods of time, M number of subintervals, each subinterval within one period having corresponding N-1 subintervals in other N-1 periods, all corresponding subintervals forming a single subinterval group, and all subintervals forming M subinterval groups, and

means for determining, for each duration of time spanning one bit of data, which of M subintervals contain a correlation peak based on said peak position detection signal;

counting means for counting the total number of correlation peaks contained within each subinterval group based on outputs from said peak position determining circuit, and for outputting each of M counts resulting from the counting;

an m/N determining circuit for determining if any of said M counts is equal to or greater than a prescribed number m, for deciding that a carrier has been detected if one of the counts is not less than m, and for outputting various signals including a carrier detection signal thereafter.

16. A receiver as in claim 15, said timing pulse generator comprising:

extracting means for accepting as inputs signals from various lines interconnecting internal components of said carrier detecting circuit and for outputting quantities to a pulse generating means; and

pulse generating means for outputting timing pulses synchronized to said peaks, each position of timing pulses depending on the values of outputs from said extracting means and from carrier detecting circuit.

17. A receiver as in claim 15, said timing pulse generator comprising:

extracting means for accepting as inputs, signals from various lines interconnecting internal components of said carrier detecting circuit and for outputting quantities to an arithmetic operating means; and

arithmetic operating means for abstracting from its inputs and operating on,

the number of subinterval groups each of which contains greater than or equal to m peaks,

the number of subinterval groups,

a numeric label of each of subinterval groups,

the starting position of each subinterval group,

the end position of each subinterval group,

a numeric label of each subinterval group which does not contain m peaks,

the number of occurrences of peaks in each subinterval group,

the total number of occurrences of peaks in all subinterval groups, and

the sum of every peak amplitude in each subinterval group, so as to compute and output a weighted mean peak position every N periods; and

means for outputting timing pulses synchronized to said peaks, each position of timing pulses depending on the weighted mean peak position and said outputs from carrier detecting circuit.

18. A receiver as in claim 15, wherein the arithmetic operating means comprises means for computing the weighted mean peak position P₀ according to the following equation, ##EQU5## wherein r denotes the number of subinterval groups each of which contains greater than or equal to m peaks,

j denotes the number of subinterval groups,

u denotes a numeric label of each of subinterval groups,

LSu denotes the starting position of each subinterval group u,

LEu denotes the end position of each subinterval group u, and

v denotes a numeric label of each subinterval group which does not contain m peaks.

19. A receiver as in claim 15, wherein the arithmetic operating means comprises means for computing the weighted mean peak position P₀ according to the following equation ##EQU6## wherein j denotes the number of subinterval groups,

u denotes a numeric label of each of subinterval groups,

LSu denotes the starting position of each subinterval group u,

LEu denotes the end position of each subinterval group u,

Vu denotes the number of occurrences of peaks in each subinterval group u, and

V denotes the total number of occurrences of peaks in all subinterval groups.

20. A receiver as in claim 15, wherein the arithmetic operating means comprises means for computing the weighted mean peak position P₀ according to the following equation, ##EQU7## wherein r denotes the number of subinterval groups each of which contains greater than or equal to m peaks,

j denotes the number of subinterval groups,

u denotes a numeric label of each of subinterval groups,

LSu denotes the starting position of each subinterval group u,

LEu denotes the end position of each subinterval group u,

v denotes a numeric label of each subinterval group which does not contain m peaks,

Vu denotes the number of occurrences of peaks in each subinterval group u,

V denotes the total number of occurrences of peaks in all subinterval groups, and

Xu denotes the sum of every peak amplitude in each subinterval group u.

21. A receiver as in claim 15, wherein the arithmetic operating means comprises means for computing the weighted mean peak position P₀ according to the following equation, ##EQU8## wherein r denotes the number of subinterval groups each of which contains greater than or equal to m peaks,

j denotes the number of subinterval groups,

u denotes a numeric label of each of subinterval groups,

LSu denotes the starting position of each subinterval group u,

LEu denotes the end position of each subinterval group u,

v denotse a numeric label of each subinterval group which does not contain m peaks,

Vu denotes the number of occurrences of peaks in each subinterval group u,

V denotes the total number of occurrences of peaks in all subinterval groups, and

Xu denotes the sum of every peak amplitude in each subinterval group u.

22. A Code Shift Keying (CSK) communication system receiver comprising:

two correlators for generating two correlation signals from a received signal;

a carrier detecting means for receiving signals from said two correlators and accepting signals from and providing signals to a synchronization control circuit;

the synchronization control circuit including

first monitoring means for periodically monitoring two correlation signals,

means for generating timing pulses partly based on outputs from the first monitoring means, and on outputs from said carrier detecting means; and

a demodulator including

first monitoring means for periodically monitoring two correlation signals,

means for generating a sequence of data bits based on outputs from the first monitoring means and based on the periodic timing pulses.

23. A Code Shift Keying (CSK) communication method for transmitting and receiving digital data each of which is a bit having a value of either "1" or "0," the method comprising the steps of:

transmitting, comprising the steps of;

processing each of its input bits,

continuously generating two M-series codes, a first M-series code being identical to a second M-series code except in its phase,

selecting one of said two M-series codes depending on the value of a particular bit being processed, and

outputting as a transmitted signal the selected code in a period of time spanning the duration of the particular bit; and

receiving, comprising the steps of;

recapturing the transmitted signal as a received signal,

obtaining two correlation signals by correlating the received signal with each copy of the two M-series codes,

partitioning each correlation signal into a sequence of consecutive periods,

comparing during each period the largest peak of one correlation signal with the largest peak of the other correlation signal,

deciding during each period whether the received signal spanning the period has value of "1" or "0" depending on the result of comparing the sizes of the peaks, and

generating a sequence of bits each of which has value of either "1" or "0."

24. A communication method as in claim 23, wherein said receiving step comprises the steps of:

generating periodic pulses each of whose center is synchronized to each peak of a signal formed by performing an operation on two correlation signals; and

detecting and storing the location and size of said each peak within a duration of time spanned by one of said periodic pulses.

25. A Code Shift Keying (CSK) communication transmitting method for processing and transmitting digital data each of which is a bit having a value of either "1" or "0," the transmitting method comprising the steps of:

continuously generating a first and a second M-series codes in a period of time spanning the duration of a particular bit, the first M-series code being identical to the second M-series code in its sequence of 1'"'"'s and 0'"'"'s but different in its phase;

selecting one of said two M-series codes depending on the value of said particular bit;

outputting, as transmitted signal, the selected code in a period of time spanning the duration of the particular bit.

26. A transmitting method as in claim 25, wherein the step of generating said M-series code comprises the steps of:

generating said first M-series code;

generating said second M-series code identical to the first code; and

setting the phase of the second M-series code so that the phase of the second code is different from that of the first M-series code.

27. A transmitting method as in claim 25, wherein the step of generating said M-series code comprises:

generating said first M-series code; and

generating said second M-series code by delaying the first M-series code; and

producing the delayed first M-series code as said second M-series code.

28. A Code Shift Keying (CSK) communication receiving method for capturing a signal and processing the captured signal which is capable of including series of a first and a second M-series codes which is identical to the first code except in its phase, the receiving method comprising the steps of:

generating a first correlation signal by correlating a local of the first code and the captured signal;

generating a second correlation signal by correlating a local replica of the second code and the captured signal; and

demodulating, including the steps of;

periodically monitoring the first and the second correlation signals,

comparing during each monitoring period the largest peak of the first correlation signal with the largest peak of the second correlation signal,

deciding during each monitoring period whether the captured signal spanning the monitoring period has the value of "1" or "0" depending on the result of comparing sizes of said largest peaks, and

generating sequence of bits each of which has value of either "1" or "0."

29. A receiving method as in claim 28, wherein said demodulating step comprises the steps of:

generating periodic pulses each of whose center is synchronized to a main peak of a signal formed by performing an operation on two correlation signals during a period of time spanning one of said bits; and

detecting one of said largest peaks within a duration of time spanned by one of the periodic pulses.

30. A Code Shift Keying (CSK) communication receiving method comprising steps of generating two correlation signals from a received signal, demodulating a sequence of data bits based on two correlation signals and periodic timing pulses, producing synchronization signals based on timing pulses and two correlation signals, and generating the timing pulses partly based on synchronization signals, wherein the step of producing synchronization signals comprises the steps of:

(1) peak position detecting, including the steps of;

processing two correlation signals,

generating peaks of a signal resulting from the processing,

detecting each position of said peaks, each peak within a single period of time spanned by one bit, and outputting a peak position detection signal;

(2) storing detected peak positions over a duration of time spanned by N data bits;

(3) assigning, for each of N periods of time, M number of subintervals, each subinterval within one period having corresponding N-1 subintervals in other N-1 periods, all corresponding subintervals forming a single subinterval group, and all subintervals forming M subinterval groups;

(4) determining, for each duration of time spanning one period, which of M subintervals contain one of stored detected peaks;

(5) counting, for each subinterval group, the total number of correlation peaks contained within each subinterval group based on the intermediate and final results of step (4);

(6) generating each of M counts resulting from the counting (5);

(7) determining if any of M counts is equal to or greater than a prescribed number m, deciding that a carrier has been detected if one of the counts is not less than m, and thereafter producing various synchronization signals.

31. A receiving method as in claim 30, wherein said carrier detecting further comprises allowing steps (2) through (7) which depends m and N to switch their dependency from numbers m and N to numbers m'"'"' and N'"'"'.

32. A receiving method as in claim 30, wherein the processing of two correlation signals in (1) comprises the steps of:

adding said two correlation signals;

evaluating and producing the absolute value of added signals.

33. A receiving method as in claim 30, wherein the processing of two correlation signals in (1) comprises:

evaluating the absolute value of each of two said correlation signals;

producing larger one of the two absolute values.

34. A receiving method as in claim 30, wherein step (3) includes a step of preventing any one subinterval within one period from overlapping any other subintervals within the same period.

35. A receiving method as in claim 30, wherein step (3) includes a step of causing any one subinterval within one period to partially overlap its adjacent subintervals within the same period.

36. A Code Shift Keying (CSK) communication receiving method comprising steps of generating two correlation signals from a received signal, demodulating a sequence of data bits based on two correlation signals and periodic timing pulses, producing synchronization signals based on timing pulses and two correlation signals, and generating the timing pulses partly based on synchronization signals, wherein the producing synchronization signals comprises the steps of:

(1) peak position detecting including the steps of;

processing two correlation signals,

generating peaks of a signal resulting from the processing,

detecting each position of said peaks, each peak within a single period of time spanned by one bit, and

outputting a peak position detection signal;

(2) peak position determining, comprising the steps of;

assigning, for each of N periods of time, M number of subintervals, each subinterval within one period having corresponding N-1 subintervals in other N-1 periods, all corresponding subintervals forming a single subinterval group, and all subintervals forming M subinterval groups, and

determining, for each duration of time spanning one period, which of M subintervals contain one of stored detected peaks;

(3) counting, for each subinterval group, the total number of correlation peaks contained within each subinterval group based on the intermediate and final results of step (2);

(4) generating each of M counts resulting from the counting in step (3); and

(5) determining if any of M counts from step (4) is equal to or greater than a prescribed number m, deciding that a carrier has been detected if one of the counts is not less than m, and thereafter producing various synchronization signals.

37. A receiving method as in claim 36, wherein the generating of timing pulses comprises a step of synchronizing said timing pulses to said peaks depending on a number of said synchronization signals.

38. A receiving method as in claim 36, wherein the generating of timing pulses comprises:

(1) extracting information from said synchronization signals;

(2) abstracting from extracted signals

the number of subinterval groups each of which contains greater than or equal to m peaks,

the number of subinterval groups,

a numeric label of each of subinterval groups,

the starting position of each subinterval group,

the end position of each subinterval group,

a numeric label of each subinterval group which does not contain m peaks,

the number of occurrences of peaks in each subinterval group,

the total number of occurrences of peaks in all subinterval groups, and

the sum of every peak amplitude in each subinterval group,

(3) computing, using the result of (2), a weighted mean peak position every N periods; and

(4) generating timing pulses synchronized to said peaks, each position of timing pulses depending on the weighted mean peak position and said synchronization signals.

39. A receiving method as in claim 38, wherein computing the weighted mean peak position P₀ comprises carrying out steps of an algorithm according to the following equation, ##EQU9## wherein r denotes the number of subinterval groups each of which contains greater than or equal to m peaks,

j denotes the number of subinterval groups,

u denotes a numeric label of each of subinterval groups,

LSu denotes the starting position of each subinterval group u,

LEu denotes the end position of each subinterval group u, and

v denotse a numeric label of each subinterval group which does not contain m peaks.

40. A receiving method as in claim 38, wherein computing the weighted mean peak position P₀ comprises carrying out steps of an algorithm according to the following equation, ##EQU10## wherein j denotes the number of subinterval groups,

u denotes a numeric label of each of subinterval groups,

LSu denotes the starting position of each subinterval group u,

LEu denotes the end position of each subinterval group u,

Vu denotes the number of occurrences of peaks in each subinterval group u, and

V denotes the total number of occurrences of peaks in all subinterval groups.

41. A receiving method as in claim 38, wherein computing the weighted mean peak position P₀ comprises carrying out steps of an algorithm according to the following equation, ##EQU11## wherein r denotes the number of subinterval groups each of which contains greater than or equal to m peaks,

j denotes the number of subinterval groups,

u denotes a numeric label of each of subinterval groups,

LSu denotes the starting position of each subinterval group u,

LEu denotes the end position of each subinterval group u,

v denotse a numeric label of each subinterval group which does not contain m peaks,

Vu denotes the number of occurrences of peaks in each subinterval group u,

V denotes the total number of occurrences of peaks in all subinterval groups, and

Xu denotes the sum of every peak amplitude in each subinterval group u.

42. A receiving method as in claim 38, wherein computing the weighted mean peak position P₀ comprises carrying out steps of an algorithm according to the following equation, ##EQU12## wherein r denotes the number of subinterval groups each of which contains greater than or equal to m peaks,

j denotes the number of subinterval groups,

u denotes a numeric label of each of subinterval groups,

LSu denotes the starting position of each subinterval group u,

LEu denotes the end position of each subinterval group u,

v denotse a numeric label of each subinterval group which does not contain m peaks,

Vu denotes the number of occurrences of peaks in each subinterval group u,

V denotes the total number of occurrences of peaks in all subinterval groups, and

Xu denotes the sum of every peak amplitude in each subinterval group u.

43. A Code Shift Keying (CSK) communication receiving method comprising the steps of:

generating two correlation signals from a received signal;

processing two correlation signals and timing signals to produce synchronization signals;

pulse generating, comprising the steps of;

(1) periodically monitoring two correlation signals,

(2) generating timing pulses partly based on the result of (1), and on synchronization signals; and

demodulating, comprising the steps of;

(3) periodically monitoring two correlation signals independently from (1),

(4) generating a sequence of data bits based on the result of (3) and on the periodic timing pulses.