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

• US 5,719,902 A
• Filed: 04/18/1995
• Issued: 02/17/1998
• 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: Smith, Keith, Quick, R. Franklin, Balachandran, Kumar
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): PHAN, HAI
• Application Number:
  US08/424,706
• Time in Patent Office: 1,036 Days
• Field of Search: 375/224, 375/216, 375/316, 375/340, 370/110.1, 370/171, 370/94.1, 370/94.2, 370/95.1, 455/54.1, 455/34.1, 455/34.2, 455/67.1, 455/334, 455/269, 455/33.1
• 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 spectral estimation method for detecting an overlay signal in a channel of a 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 clock frequency, the method comprising the steps of:

(a) determining which of the plurality of channel of said primary system are occupied by a signal by computing a ratio of spectral components within a prescribed spectral band to spectral components outside the prescribed spectral band for each of the plurality of channels;

(b) asychronously enhancing a spectral component at said clock frequency by performing a non-linear operation on each of the plurality of channels determined to be occupied by a signal in step (a); and

(c) deciding whether each of the plurality of channels is occupied by an overlay signal as a function of the enhanced spectral component.

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

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

4. A method as recited in claim 2, wherein said primary system is a cellular telephone system.

5. A method as recited in claim 1, wherein step (a) of claim 1 further comprises, with respect to each channel, the substeps:

(1) receiving signal and noise components in said channel;

(2) processing the received components to enhance noise components outside a prescribed spectral band relative to noise components within said prescribed spectral band;

(3) computing the ratio of spectral components within said prescribed spectral band to the enhanced spectral components outside said prescribed spectral band;

(4) comparing said ratio to a prescribed threshold value; and

(5) identifying the channel as carrying a signal if said ratio exceeds said threshold.

6. A method as recited in claim 4, wherein step (a) further comprises, with respect to each channel, the substeps:

(1) receiving signal and noise components in said channel;

(2) processing the received components to enhance noise components without a prescribed spectral band relative to noise components within said prescribed spectral band;

(3) computing the ratio of spectral components within said prescribed spectral band to the enhanced spectral components without said prescribed spectral band;

(4) comparing said ratio to a prescribed threshold value; and

(5) identifying the channel as carrying a signal if said ratio exceeds said threshold.

7. A system for detecting an overlay signal in a channel of a 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 prescribed clock frequency, the system comprising:

means for determining which of the plurality of channel of said primary system are occupied by a signal by computing a ratio of spectral components within a prescribed spectral band to spectral components outside the prescribed spectral band for each of the plurality of channels;

means for asynchronously enhancing a spectral component at said clock frequency by performing a non-linear operation on each of the plurality of channels determined to be occupied by a signal; and

means for deciding whether each of the plurality of channels is occupied by an overlay signal as a function of the enhanced spectral component.

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

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

10. A system as recited in claim 8, wherein said primary system is a cellular telephone system.

11. A system as recited in claim 7, wherein said means for determining which, if any, channel(s) of said primary system are occupied by a signal further comprises:

(1) means for receiving signal and noise components in said channels;

(2) means for processing the received components to enhance noise components without a prescribed spectral band relative to noise components within said prescribed spectral band;

(3) means for computing the ratio of spectral components within said prescribed spectral band to the enhanced spectral components without said prescribed spectral band;

(4) means for comparing said ratio to a prescribed threshold value; and

(5) means for identifying a channel as carrying a signal if said ratio exceeds said threshold.

12. A system as recited in claim 10, wherein said means for determining which, if any, channel(s) of said primary system are occupied by a signal further comprises:

(1) means for receiving signal and noise components in said channels;

(2) means for processing the received components to enhance noise components without a prescribed spectral band relative to noise components within said prescribed spectral band;

(3) means for computing the ratio of spectral components within said prescribed spectral band to the enhanced spectral components without said prescribed spectral band;

(4) means for comparing said ratio to a prescribed threshold value; and

(5) means for identifying a channel as carrying a signal if said ratio exceeds said threshold.