CRC-based message detection/demodulation apparatus and method for radio frequency signals

• US 8,019,360 B2
• Filed: 04/23/2007
• Issued: 09/13/2011
• Est. Priority Date: 04/22/2006
• Status: Expired due to Fees

• Current Assignee: Locus Location Systems, LLC
• Original Assignee: Locus Location Systems, LLC
• Inventors: Qahwash, Murad
• Primary Examiner(s): Bost; Dwayne
• Assistant Examiner(s): Nair; Sowmini
• Application Number:
  US11/738,634
• Publication Number:
  US 20090075674A1
• Time in Patent Office: 1,604 Days
• Field of Search: 455/452, 455/456.1, 455/456.5, 375/259
• US Class Current: 455/456.5
• CPC Class Codes: H04B 17/27 for locating or positioning the transmitter
• CPC Class Codes: H04W 64/00 Locating users or terminals or network equipment for network management purposes, e.g. mobility management

Abstract

A method for determining a location of a wireless transmitting device transmitting a digitally modulated transmitted radio frequency signal. The method comprises, at spaced-apart receivers: generating a received radio frequency signal and including time tags therein responsive to the transmitted radio frequency signal, detecting a destination message signal responsive to the received radio frequency signal, comparing the destination message signal and the received radio frequency signal and determining a time of arrival of the destination message signal responsive to the step of comparing and responsive to the time tags. The method further comprises determining a pairwise time difference of arrival of the received radio frequency signal for two pairs of receivers and determining the location of the device responsive to the pairwise time difference of arrival.

Claims

1. A method for determining a location of a wireless transmitting device transmitting a digitally modulated transmitted radio frequency signal, the method comprising:

at spaced-apart receivers;

generating a received radio frequency signal and including time tags therein responsive to the transmitted radio frequency signal;

generating received radio frequency signal samples responsive to the received radio frequency signal;

detecting a destination message signal responsive to the received radio frequency signal;

comparing the destination message signal and the received radio frequency signal;

determining a time of arrival of the destination message signal responsive to the step of comparing and responsive to the time tags;

determining a pairwise time difference of arrival of the received radio frequency signal for two pairs of receivers;

determining the location of the device responsive to the pairwise time difference of arrival; and

wherein the step of detecting the destination message signal further comprises;

(a) incrementally loading the received radio frequency signal samples to successive memory locations of a buffer;

(b) selecting received radio frequency signal samples stored in selected memory locations;

(c) for each selected sample, determining a detected sample responsive to the selected sample;

(d) loading the detected samples into a memory device, wherein a capacity of the memory device is sufficient to store one detected sample for each symbol of the destination message signal;

(e) analyzing the detected samples to determine if the detected samples form a valid destination message signal; and

(f) repeating the steps (a) through (e) until a result at the step (e) indicates the detected samples form a valid destination message signal.

2. The method of claim 1 wherein a step (e) further comprises applying a cyclical redundancy code check to the detected samples to determine if the detected samples form a valid destination message signal.

3. The method of claim 1 wherein responsive to the detected samples forming a valid destination message signal, the method further comprises:

(j) encoding the detected samples using an error detection code to produce encoded samples;

(k) comparing the encoded samples with the detected samples;

(l) determining a bit error rate responsive to the step (k);

(m) if the bit error rate is less than a predetermined threshold, declaring the detected samples to be valid; and

(n) if the bit error rate is greater than the predetermined threshold, returning to the step (a) for loading another received radio frequency signal sample to the next successive memory location.

4. The method of claim 1 wherein responsive to incrementally loading another received radio frequency signal sample to a successive memory location according to the step (a), the selected memory locations of the step (b) are incremented to the next successive memory location.

5. The method of claim 1 wherein a number of memory locations between two consecutive memory locations comprises a number of samples in each symbol of the destination message signal.

6. The method of claim 1 wherein the buffer comprises a circular buffer.

7. The method of claim 1 wherein the buffer comprises a number of memory locations equal to 1+(N−

1)(M), where M is a number of samples in each symbol of the destination message signal and N is a number of symbols in the destination message signal.

8. The method of claim 1 wherein the detected samples will form a valid destination message signal after processing only one sample of the last symbol of the destination message signal.

9. An apparatus for determining a location of a wireless transmitting device transmitting a transmitted RF signal, the apparatus comprising:

at spaced-apart receivers;

a first module for generating a received RF signal and including time tags therein responsive to the transmitted RF signal, the time tags synchronized at the receivers;

a second module for determining a valid message responsive to the received RF signal;

a third module for comparing the valid message and the received RF signal to determine a time of arrival of the message further responsive to the time tags;

determining a pairwise time difference of arrival of the message at two pairs of receivers;

determining the location of the device responsive to the pairwise time difference of arrival; and

wherein the second module further comprises;

first memory locations for storing samples of the received RF signal, wherein successive samples of the received RF signal are incrementally input to successive first memory locations;

bit detectors, each bit detector associated with one of the first memory locations, wherein the sample stored in the one of the first memory locations is input to the associated bit detector for producing a bit value;

a memory buffer having a number of second memory locations equal to the number of bit detectors, each bit detector supplying the bit value to the associated second memory location; and

a fourth module operating on the bit values in the memory buffer for determining if the bit values present a valid message, and wherein if a valid message is not presented, a next sample of the received RF signal is input to a next one of the first memory locations, overwriting a sample previously stored therein and the bit detectors are associated with a next one of the first memory locations, the fourth module operating on bit values until a valid message is presented in the memory buffer.