Method for increased location receiver sensitivity

• US 20030043941A1
• Filed: 09/06/2001
• Published: 03/06/2003
• Est. Priority Date: 09/06/2001
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: DʼSouza, Ralph, Johnson, Mark J.
• Granted Patent: US 7,239,876 B2
• Time in Patent Office: Days
• US Class Current: 375/345
• CPC Class Codes: H04B 7/005 Control of transmission; Equalising
• CPC Class Codes: H04L 27/38 Demodulator circuits; Receiver circuits

Abstract

A first image (200) of a transmitted signal is detected within a received signal containing a plurality of images of the transmitted signal. This is accomplished by detecting a second image (210) of the transmitted signal. A set of characteristics of the second image of the transmitted signal is determined, and subsequently used to detect the first image (200) of the transmitted signal.

Claims

1. A method for detecting a first image of a transmitted signal within a received signal containing a plurality of images of the transmitted signal, the method comprising the steps of:

detecting a second image of the transmitted signal;

determining a set of characteristics of the second image of the transmitted signal; and

using the set of characteristics to detect the first image of the transmitted signal.

2. The method of claim 1 wherein the first image is a direct-path image and the second image is a secondary image.

3. The method of claim 1 wherein the set of characteristics is at least one characteristic of the transmitted signal selected from a group consisting of:

a sequence of bits, a sequence of symbols, a waveform, phase, amplitude, frequency offset, frequency variation, envelope variation, symbol skew, axis skew, and inter-symbol interference.

4. The method of claim 1 wherein the first image and the second image are distinct images of the transmitted signal.

5. The method of claim 1 wherein the step of using the set of characteristics comprises the step of performing coherent averaging over a length of time to detect the first image of the transmitted signal.

6. The method of claim 1 further comprising the step of converting the received signal to a received waveform.

7. The method of claim 6 wherein the received waveform is used as a characteristic of the transmitted signal.

8. The method of claim 6 further comprising the steps of:

applying signal processing to the received waveform to obtain a processed received waveform; and

using the processed received waveform as a characteristic of the transmitted signal.

9. The method of claim 8 wherein the signal processing comprises at least one of the following techniques:

limiting, companding, and filtering

10. The method of claim 6 further comprising the step of applying an error correction to the received waveform.

11. The method of claim 1 further comprising the steps of:

demodulating the second image of the transmitted signal to determine at least a portion of information content modulated onto the signal image by a transmitter; and

using the information content as a characteristic of the transmitted signal to detect the first image of the transmitted signal.

12. The method of claim 11 further comprising the steps of:

remodulating the information content; and

using the remodulated information content as a characteristic of the transmitted signal.

13. The method of claim 11 further comprising the steps of:

characterizing at least one error in the second image of the transmitted signal; and

using at least one characterized error as a characteristic of the transmitted signal.

14. The method of claim 1 wherein the second image of the transmitted signal arrives at a receiver at a later time than the first image of the transmitted signal.

16. The method of claim 1 wherein the step of determining a set of characteristics comprises the step of decoding at least a portion of information that is modulated on the transmitted signal prior to detecting the first image of the transmitted signal.

17. The method of claim 1 further comprising the step of converting the second image to a waveform, wherein the waveform is assumed to substantially represent a dominant image of the transmitted signal.

18. The method of claim 17 further comprising the steps of:

comparing the waveform with a second waveform that has been delayed; and

performing an operation for values of delays in a range of zero to at least a maximum delay spread expected between the first image and he second image of the transmitted signal.

19. The method of claim 1 wherein information content of the first image is reduced after the set of characteristics of the second image is determined.

20. The method of claim 1 wherein a coding gain of the first image is increased after the set of characteristics of the second image is determined.

15. The method of clam 1 wherein the second image of the transmitted signal has a higher amplitude than the first image of the transmitted signal.