Methods and apparatus for detecting a cellular digital packet data (CDPD) carrier

• US 5,574,750 A
• Filed: 09/14/1993
• Issued: 11/12/1996
• 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): Coles, Edward
• Assistant Examiner(s): Esposo, Allan A.
• Application Number:
  US08/121,339
• Time in Patent Office: 1,155 Days
• Field of Search: 375/224, 375/340, 375/341, 375/354, 375/355, 455/132, 455/133
• 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

Disclosed herein are methods and apparatus for detecting the presence of a CDPD carrier in a channel of a cellular system (although the invention is broadly applicable to detecting a specific kind of carrier associated with an "overlay" system, wherein an "overlay" system is one that shares the frequency allocation of another system on a non-cooperating basis). This specification describes a spectral estimation technique for detection of a CDPD carrier. In addition, this specification describes an MMSE (minimum mean-squared error) method that improves on the spectral estimation method.

Claims

1. A method for detecting an overlay signal in a channel of a primary system, wherein said overlay signal is associated with an overlay system that shares a frequency allocation with the primary system, wherein the primary system has a plurality of channels in which the overlay signal might be present at any given time, and wherein the overlay signal is characterized by a predetermined expected value, the method comprising the steps of:

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

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

(c) determining a minimum error value;

(d) determining a reference value;

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

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

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

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

4. A method as recited in claim 3, wherein said primary system is a cellular telephone system.

5. A method as recited in claim 1, wherein said primary system is a cellular telephone system.

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

7. A system for detecting an overlay signal in a channel of a primary system, wherein said overlay signal is associated with an overlay system that shares a frequency allocation with the primary system, wherein the primary system has a plurality of channels in which the overlay signal might be present at any given time, and wherein the overlay signal is characterized by a predetermined expected value, the system comprising:

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

(b) means for computing an error value for each sample, said error value based on a difference, if any, between the sample value and said predetermined expected value;

(c) means for determining a minimum error value;

(d) means for determining an average of at least two error values;

(e) means for determining a ratio of said minimum error value to said average; and

(f) means for making a decision as to whether the received signal is an overlay signal on the basis of at least said ratio, wherein said decision is made by comparing said ratio to a threshold value.

8. A system as recited in claim 7, wherein said error values are mean-squared error (mse) values.

9. A system as recited in claim 7, wherein said overlay signal is a Cellular Digital Packet Data (CDPD) signal.

10. A system as recited in claim 9, wherein said primary system is a cellular telephone system.

11. A system as recited in claim 7, wherein said primary system is a cellular telephone system.