Methods and apparatus for detecting the presence of a prescribed signal in a channel of a communications system

• US 5,854,808 A
• Filed: 03/12/1996
• Issued: 12/29/1998
• Est. Priority Date: 09/14/1993
• Status: Expired due to Term

• Current Assignee: Cirrus Logic Incorporated
• Original Assignee: Pacific Communication Sciences , Inc. (Cirrus Logic Incorporated)
• Inventors: Balachandran, Kumar, Peponides, George
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): GLUCK, JEFFREY WILLIAM
• Application Number:
  US08/614,327
• Time in Patent Office: 1,022 Days
• Field of Search: 375/224, 370/241, 370/252, 370/527, 370/529, 455/434, 455/466
• US Class Current: 375/224
• CPC Class Codes: G10L 25/78 Detection of presence or absence of voice signals switching of direction of transmission by voice frequency in two-way loud-speaking telephone systems H04M9/10
• CPC Class Codes: H04L 27/0012 arrangements for identifying the type of modulation
• CPC Class Codes: H04L 27/18 Phase-modulated carrier systems, i.e. using phase-shift keying H04L27/32 takes precedence
• CPC Class Codes: H04W 48/18 Selecting a network or a communication service

Abstract

Methods and apparatus for detecting the presence of a particular signal among all the channels of interest in a cellular or similar type system are disclosed. A first method detects CDPD signals, and a second method detects DQPSK signals used in digital control channels in accordance with the IS-136 standard. These methods include the steps of sampling a received signal in at least one channel to obtain a predetermined number of samples for the at least one channel; computing an error value for each sample; determining a minimum error value; determining a ratio of the minimum error value to a reference value; and making a decision as to whether the received signal is the prescribed signal on the basis of at least the ratio, wherein the decision is made by comparing the ratio to a threshold value.

Claims

1. A method for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the method comprising the steps of:

(a) sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;

(b) computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;

(c) determining a minimum error value;

(d) comparing a function of the minimum error value to a reference value; and

(e) making a decision as to whether the received signal is said prescribed signal on the basis of the comparison.

2. A method as recited in claim 1, wherein said communications system is a cellular system.

3. A method as recited in claim 1, wherein said prescribed signal is a Cellular Digital Packet Data (CDPD) signal.

4. A method as recited in claim 1, wherein said error values are mean-squared error (MSE) values.

5. A method as recited in claim 1, wherein said reference value comprises an average of at least two error values.

6. A method as recited in claim 1, wherein said reference value comprises an ideal expected value.

7. A method as recited in claim 1, wherein said communications system is a cellular system, said prescribed signal is a Cellular Digital Packet Data (CDPD) signal, said error values are mean-squared error (MSE) values, and said reference value comprises an average of at least two error values.

8. A method for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the method comprising the steps of:

(a) sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;

(b) computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;

(c) determining a minimum error value;

(d) comparing a function of the minimum error value to a reference value; and

(e) making a decision as to whether the received signal is said prescribed signal on the basis of the comparison, wherein said prescribed signal is a DQPSK signal.

9. A method as recited in claim 8, wherein said prescribed signal is a π

/4 DQPSK signal.

10. A method as recited in claim 8, wherein said error values are mean-squared error (MSE) values.

11. A method as recited in claim 10, wherein a first of said MSE values (MSE₁) is computed over a plurality of symbols with respect to a first sample of each of said symbols, and a second of said MSE values (MSE₂) is computed over said plurality of symbols with respect to a second sample of each of said symbols.

12. A method as recited in claim 11, wherein a third of said MSE values (MSE₃) is computed over said plurality of symbols with respect to a third sample of each of said symbols, and a fourth of said MSE values (MSE₄) is computed over said plurality of symbols with respect to a fourth sample of each of said symbols.

13. A method for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the method comprising the steps of:

(a) sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;

(b) computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;

(c) determining a minimum error value;

(d) comparing a function of the minimum error value to a reference value; and

(e) making a decision as to whether the received signal is said prescribed signal on the basis of the comparison,

wherein said prescribed signal is a DQPSK signal;

wherein said error values are mean-squared error (MSE) values; and

wherein a first of said MSE values (MSE₁) is computed over a plurality of symbols with respect to a first sample of each of said symbols, a second of said MSE values (MSE₂) is computed over said plurality of symbols with respect to a second sample of each of said symbols, a third of said MSE values (MSE₃) is computed over said plurality of symbols with respect to a third sample of each of said symbols, and a fourth of said MSE values (MSE₄) is computed over said plurality of symbols with respect to a fourth sample of each of said symbols.

14. A system for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the system comprising:

(a) means for sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;

(b) means for computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;

(c) means for determining a minimum error value;

(d) means for comparing a function of the minimum error value to a reference value; and

(e) means for making a decision as to whether the received signal is said prescribed signal on the basis of the comparison.

15. A system as recited in claim 14, wherein said communications system is a cellular system.

16. A system as recited in claim 14, wherein said prescribed signal is a Cellular Digital Packet Data (CDPD) signal.

17. A system as recited in claim 14, wherein said error values are mean-squared error (MSE) values.

18. A system as recited in claim 14, wherein said reference value comprises an average of at least two error values.

19. A system as recited in claim 14, wherein said communications system is a cellular system, said prescribed signal is a Cellular Digital Packet Data (CDPD) signal, said error values are mean-squared error (MSE) values, and said reference value comprises an average of at least two error values.

20. A system for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the system comprising:

(a) means for sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;

(b) means for computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;

(c) means for determining a minimum error value;

(d) means for comparing a function of the minimum error value to a reference value; and

(e) means for making a decision as to whether the received signal is said prescribed signal on the basis of the comparison, wherein said prescribed signal is a DQPSK signal.

21. A system as recited in claim 20, wherein said prescribed signal is a π

/4 DQPSK signal.

22. A system as recited in claim 20, wherein said error values are mean-squared error (MSE) values.

23. A system as recited in claim 22, wherein a first of said MSE values (MSE₁) is computed over a plurality of symbols with respect to a first sample of each of said symbols, and a second of said MSE values (MSE₂) is computed over said plurality of symbols with respect to a second sample of each of said symbols.

24. A system as recited in claim 23, wherein a third of said MSE values (MSE₃) is computed over said plurality of symbols with respect to a third sample of each of said symbols, and a fourth of said MSE values (MSE₄) is computed over said plurality of symbols with respect to a fourth sample of each of said symbols.

25. A system for detecting the presence of a prescribed signal type in a channel of a communications system having a plurality of channels in which the prescribed signal might be present at any given time, the system comprising:

(a) means for sampling a received signal in at least one channel to obtain a predetermined number of sampling sequences for said at least one channel;

(b) means for computing an error value for each sampling sequence, each said error value based on differences, if any, between each sample value of the sampling sequence and a predetermined value;

(c) means for determining a minimum error value;

(d) means for comparing a function of the minimum error value to a reference value; and

(e) means for making a decision as to whether the received signal is said prescribed signal on the basis of the comparison, wherein said prescribed signal is a DQPSK signal;

wherein said error values are mean-squared error (MSE) values; and

wherein a first of said MSE values (MSE₁) is computed over a plurality of symbols with respect to a first sample of each of said symbols, a second of said MSE values (MSE₂) is computed over said plurality of symbols with respect to a second sample of each of said symbols, a third of said MSE values (MSE₃) is computed over said plurality of symbols with respect to a third sample of each of said symbols, and a fourth of said MSE values (MSE₄) is computed over said plurality of symbols with respect to a fourth sample of each of said symbols.

26. A mobile cellular subscriber unit, comprising:

an identification block for detecting or identifying an IS-136 digital channel carrying DQPSK signals, said identification block comprising means for (a) obtaining a predetermined number of samples of a received signal in at least one channel, (b) estimating, on the basis of said samples, a match parameter indicative of a Noise-to-Signal (NSR) ratio, and (c) making a decision as to whether said received signal is a DQPSK signal on the basis of said NSR.

27. A mobile cellular subscriber unit as recited in claim 26, and wherein said means includes means for:

computing an error value for each sample, said error value based on a difference, if any, between a sample value and a predetermined value;

determining a minimum error value;

determining a ratio of said minimum error value to a reference value; and

making a decision as to whether the received signal is a DQPSK signal on the basis of at least said ratio, wherein said decision is made by comparing said ratio to a threshold value.

28. A mobile cellular subscriber unit as recited in claim 27, wherein said error values are mean-squared error (MSE) values.

29. A mobile cellular subscriber unit as recited in claim 28, wherein a first of said MSE values (MSE₁) is computed over a plurality of symbols with respect to a first sample of each of said symbols, and a second of said MSE values (MSE₂) is computed over said plurality of symbols with respect to a second sample of each of said symbols.

30. A mobile cellular subscriber unit as recited in claim 29, wherein a third of said MSE values (MSE₃) is computed over said plurality of symbols with respect to a third sample of each of said symbols, and a fourth of said MSE values (MSE₄) is computed over said plurality of symbols with respect to a fourth sample of each of said symbols.