System and method for fast acquisition of ultra wideband signals

• US 20050089083A1
• Filed: 09/30/2004
• Published: 04/28/2005
• Est. Priority Date: 11/15/2002
• Status: Active Grant

• Current Assignee: Humatics Corporation
• Original Assignee: Time Domain Corporation (Humatics Corporation)
• Inventors: Roberts, Mark D., Richards, James, Dodoukh, Irina, Brethour, Vernon R., Fisher, Teresa E., Rolin, Jennifer P.
• Granted Patent: US 7,436,876 B2
• Time in Patent Office: Days
• US Class Current: 375/130
• CPC Class Codes: H04B 1/7075 with code phase acquisition
• CPC Class Codes: H04B 1/7183 Synchronisation
• CPC Class Codes: H04B 1/719 Interference-related aspects
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation

Abstract

An ultra wideband system employing a threshold to detect signal quality during acquisition wherein the threshold is adjusted based on signal characteristics such as packet traffic rate, packet loss rate, and packet loss fraction. In one embodiment, the threshold is adjusted by adjusting the gain of a variable gain stage ahead of the threshold. In another embodiment, gain and threshold are adjusted in a coordinated manner wherein gain is adjusted for low signal levels and threshold is adjusted for high signal levels. In one embodiment, packet traffic rate is evaluated over an interval based on maximum packet length, number of monitor packets, and inter-packet delay. In a further embodiment, multiple ramp builders are operated in parallel at multiple code offset values to generate signal statistics to compare with the threshold. Embodiments are disclosed wherein the thresholds are adaptively adjusted based on signal performance characteristics or the multipath environment.

Claims

1. An ultra wideband transceiver system comprising:

an ultra wideband transmitter;

an ultra wideband antenna coupled to the uwb transmitter;

an ultra wideband receiver coupled to the uwb antenna for receiving an input signal, said ultra wideband receiver further comprising;

a sampling stage for sampling the input signal and generating a sampled signal;

a summation stage for summing a plurality of sampled signals and generating a sum signal;

an evaluation stage for evaluating one or more sum signals to generate an evaluation result;

a threshold comparator to compare the evaluation result with a threshold;

wherein the threshold is varied based on a performance criterion.

2. The system of claim 1 wherein the timing is adjusted to receive signals synchronous with a different frame offset value and a new set of sampled signals is generated and evaluated.

3. The system of claim 1 further including multiple parallel ramp builders to generate a plurality of concurrently generated sum signals wherein said plurality of concurrently generated sum signals is evaluated to generate the evaluation result.

4. The system of claim 1 wherein the input signal includes packet sequence information and the receiver utilizes said packet sequence information for setting said threshold.

5. A network of UWB transceivers having a protocol, said protocol including packet count information, said network comprising;

at least one transmitter sending a plurality of packets;

at least one receiver receiving a portion of said plurality of packets;

wherein said at least one transmitter includes said packet count information in at least one packet and said receiver uses said packet count information to adjust at least one threshold.

6. The network of claim 5 wherein said packet count information is a packet sequence number.

7. An ultra wideband receiver comprising:

an ultra wideband antenna;

an ultra wideband receiver coupled to the uwb antenna for receiving an input signal, said ultra wideband receiver further comprising;

a sampling stage for sampling the input signal and generating a sampled signal;

a summation stage for summing a plurality of sampled signals and generating a sum signal;

an evaluation stage for evaluating one or more sum signals to generate an evaluation result;

a threshold comparator to compare the evaluation result with a threshold;

wherein the threshold is varied based on a performance criterion.

8. The receiver of claim 7 wherein the timing is adjusted to receive signals synchronous with a different frame offset value and a new set of sampled signals is generated and evaluated.

9. The receiver of claim 7 wherein the receiver includes a single correlator.

10. The receiver of claim 7 wherein the evaluation stage and threshold comparator utilize a plurality of ramps in accordance with one or more of the following relationships:

Number Threshold Equation 0 MaxR >

C 1 N * MaxR / MA_meanV >

C 2 MaxR / NextR >

C 3. Logic AND of equation 1 and 2 4 Logic OR of equation 1 and 2 5 N * MaxR / MaxV >

C 6 N * (MaxR / MA_meanV) * (MinV / MaxV) >

C 7 N * (MaxR / MA_meanV) * [FORCE_ZERO(MinV −

MA_MinV) / FORCE_ONE(MaxV −

MA_MinV)] >

C 8 N * (MaxR −

NextR) / MA_meanV >

C 9 N * [(MaxR −

NextR) / MA_meanV] * (MinV / MaxV) >

C

11. The receiver of claim 10 wherein two or more of the relationships are combined by a logical AND.

12. The receiver of claim 10 wherein two or more of the relationships are combined by a logical OR.

13. The receiver of claim 10 wherein the selection of the one or more relationship is made in response to a criterion of the received signal.

14. The receiver of claim 13 wherein the criterion comprises a performance measure.

15. The receiver of claim 13 wherein the criterion comprises an application characteristic.

16. The receiver of claim 10 wherein the selection of the one or more relationship is made in response to the success or failure rates of the threshold decision.

17. The receiver of claim 10 wherein at least two of the plurality of ramps are generated serially.

18. The receiver of claim 17 wherein at least two of the plurality of ramps are generated in sequence.

19. The receiver of claim 10 wherein the plurality of ramps is generated in parallel.

20. The receiver of claim 7 further including a memory, wherein the receiver receives the signal from a given transmitter a plurality of times, the threshold parameters associated with the given transmitter are stored and retrieved from the memory and utilized to search for the given transmitter.

21. The receiver of claim 7 wherein said receiver receives a plurality of packets wherein the number of missed packets can be estimated;

wherein said receiver adjusts at least one threshold based on said number of missed packets

22. The receiver of claim 21 wherein said plurality of packets have a known traffic rate over a time period;

wherein said receiver estimates said number of missed packets by comparing the number of received packets with said known traffic rate over said time period.

23. The receiver of claim 22 wherein said known traffic rate is based on packet length, number of monitor packets, and inter packet delay.

24. The receiver of claim 21 wherein at least one packet of said plurality of packets includes packet count information and wherein said number of missed packets is estimated by comparing said packet count information with the number of received packets.

25. The receiver of claim 24 wherein the packet count information is a packet sequence number.

26. An ultra wideband receiver comprising:

an ultra wideband antenna;

an ultra wideband receiver coupled to the uwb antenna for receiving an input signal, said ultra wideband receiver further comprising;

a sampling stage for sampling the input signal and generating a sampled signal;

a summation stage for summing a plurality of sampled signals and generating a sum signal;

a first evaluation stage for evaluating one or more sum signals to generate an evaluation result;

a threshold comparator to compare the first evaluation result with a threshold;

a plurality of subsequent evaluation stages for comparing one or more sum signals to generate a evaluation results;

wherein data is demodulated after all of the thresholds are satisfied.

27. The receiver of claim 26 wherein the threshold of the first evaluation stage is varied based on the success or failure rates of the evaluations in the subsequent stages.

28. The receiver of claim 26 wherein a plurality of the thresholds are adjusted based on the success rates of one or more of the evaluation stages.

29. The receiver of claim 26 further including a memory, wherein the receiver receives the signal from a given transmitter a plurality of times, the threshold parameters associated with the given transmitter are stored and retrieved from the memory and utilized to search for the given transmitter.

30. An ultra wideband receiver comprising:

an ultra wideband antenna;

an ultra wideband receiver coupled to the uwb antenna for receiving an input signal, said ultra wideband receiver further comprising;

a sampling stage for sampling the input signal and generating a sampled signal;

a summation stage for summing a plurality of sampled signals and generating a sum signal;

a gain control loop having a gain setting, said gain control loop for compressing the dynamic range of the sum signal;

an evaluation stage for evaluating one or more sum signals to generate an evaluation result;

a threshold comparator to compare the evaluation result with a threshold;

wherein the threshold is adjusted based on said gain setting.

wherein data is demodulated after the threshold is satisfied.

31. The receiver of claim 30 wherein gain is varied based on a long term average of the maximum ramp value.

32. The receiver of claim 31 wherein the gain control loop has a gain limit and the threshold is varied when the gain limit is reached.

33. A method for receiving an ultra wideband signal, said method comprising:

sampling said ultra wideband signal to generate a sampled signal;

summing a plurality of sampled signals to generate a sum signal;

generating an evaluation criteria based on at least one said sum signal;

comparing said evaluation criteria with a predetermined threshold value;

proceeding with further processing when the threshold is met;

generating a performance criterion relating to the threshold value;

adjusting the threshold value based on the performance criteria;

34. The method of claim 33 wherein the receiving includes a short code receiving process and the threshold value relates to receiving short code signals.

35. The method of claim 33 wherein the receiving includes a long code receiving process and the threshold value relates to receiving long code signals.

36. The method of claim 33 wherein the receiving includes a quick check process and the threshold value relates to receiving quick check signals.

37. The method of claim 33 wherein the receiving includes a delimiter receiving process and the threshold value relates to receiving delimiter signals.

38. The method of claim 33 wherein the receiver includes a memory, wherein the ultrawideband signal is from a particular transmitter among a plurality of transmitters, said method further including the steps of:

associating at least one threshold value with said particular transmitter;

storing said at least one threshold value in memory;

restoring from memory said at least one threshold value for comparing with signals relating to said particular transmitter.

39. The method of claim 33 wherein the sampling step includes sampling by multiple correlators.

40. The method of claim 33 wherein the summing step includes summing by multiple parallel ramp builders.

41. The method of claim 33 wherein the generating step is based on multiple sum signals.

42. The method of claim 33 wherein the performance criterion is based on packet received rate.

43. The method of claim 33 further including the step of determining at least one threshold value based on optimization information received from a remote unit.

44. The method of claim 33 wherein threshold criteria peaks are observed as signal space is scanned over a range of frame offset values and the threshold is set to receive the strongest signal and reject the next strongest signal

45. The method of claim 33 wherein the threshold is set to receive the strongest signal and reject the next strongest reflection based on a prior scan of the multipath environment.

46. The method of claim 33 wherein the performance criterion is based on a packet loss rate.

47. The method of claim 46 wherein the packet loss rate is derived, at least in part, from packet size, or monitor packet rate, or inter packet delay.

48. The method of claim 33 further including an initial detection stage and a quick check stage wherein the quick check false alarm rate is used to adjust the initial detection threshold.

49. The method of claim 33 further including a quick check stage and wherein the receiver scans a frame offset modulo;

wherein the quick check threshold is adjusted based on the time required to scan the frame offset modulo.

50. A method of acquiring an ultra wideband signal, comprising the steps of:

(a) establishing an acquisition threshold;

(b) obtaining a template signal;

(c) receiving the ultra wideband signal;

(d) comparing the received ultra wideband signal and the template signal to produce a comparison result;

(e) determining whether the comparison result satisfies the acquisition threshold; and

(f) if the comparison result fails to satisfy the acquisition threshold, varying the acquisition threshold based on a performance criteria and returning to step (b), and if the comparison result satisfies the acquisition threshold, locking on the received ultra wideband signal.

51. A method of acquiring an ultra wideband signal, comprising:

varying the timing of a generated template signal until a comparison of the template signal and the ultra wideband produces a comparison result that satisfies an acquisition threshold, wherein the acquisition threshold is varied in accordance with a performance criteria.

52. A method of acquiring an ultra wideband signal, comprising:

satisfying each of a plurality of thresholds wherein at least one of said plurality of thresholds is adjusted based on a performance criteria.