Ultra-wideband communications system

• US 6,810,087 B2
• Filed: 01/03/2001
• Issued: 10/26/2004
• Est. Priority Date: 01/04/2000
• Status: Expired due to Fees

• Current Assignee: General Electric Company
• Original Assignee: General Electric Company
• Inventors: Hershey, John Erik, Hoctor, Ralph Thomas, Tomlinson, Harold Woodruff Jr., Welles, Kenneth Brakeley II
• Primary Examiner(s): Corrielus, Jean B.
• Application Number:
  US09/753,443
• Publication Number:
  US 20010053175A1
• Time in Patent Office: 1,392 Days
• Field of Search: 375/259, 375/219, 375/295, 375/316, 375/256, 375/342, 375/343, 375/377, 327/1, 327/18, 327/28, 332/185
• US Class Current: 375/259
• CPC Class Codes: H04B 1/71632 Signal aspects H04B1/7172 and H04B1/7176 take precedence
• CPC Class Codes: H04B 1/71637 Receiver aspects H04B1/7183 takes precedence
• CPC Class Codes: H04B 1/7172 Pulse shape in general H04L25/03834
• CPC Class Codes: H04B 2001/6908 using time hopping
• CPC Class Codes: H04B 2201/71636 Transmitted reference
• CPC Class Codes: H04L 25/4902 Pulse width modulation; Pulse position modulation
• CPC Class Codes: H04L 27/0004 using wavelets

Abstract

An ultra-wideband (UWB) communications system combines the techniques of a transmitted reference (TR) and a multiple access scheme called delay hopping (DH). Combining these two techniques using UWB signaling results in a penalty in signal-to-noise ratio (SNR) over conventional pulse position modulation (PPM) techniques but avoids the synchronization difficulties associated with conventional approaches. The signaling pulse waveforms are designed to insure that their power spectral densities, after any frequency translation to the center of an operating band, are essentially spectrally disjoint with frequencies that must be protected. This TR technique is combined with the DH multiple access technique to create a UWB communications scheme that has a greater multiple access capacity than does the UWB TR technique by itself.

Claims

1. An ultra-wideband (UWB) radio communication system comprising:

a transmitter far generating pairs of pulses separated by a time interval, D, wherein transmitted data is encoded by a relative polarity of two pulses of a pair of pulses; and

a receiver having a pulse-pair correlator (132), the pulse-pair correlator including a delay (21) for delaying a received signal by the time interval, D, a signal multiplier (22) for multiplying delayed and undelayed versions of the received signal, and a finite impulse response integrator (23) for integrating a product signal output by the signal multiplier (22), wherein said delay is varied in a fixed pattern known to both of the transmitter and the receiver.

2. The UWS radio communication system of claim 1, wherein the time interval D is selected to correspond to a specific value of an autocorrelation function of an additive noise that obscures the signal, to thereby reduce the effect of the additive noise.

3. The UWB radio communication system of claim 1, wherein a known value of an autocorrelation function at a lag, given by the time interval D, is subtracted from an output of the finite impulse response integrator prior to bit decisions being made.

4. The UWB radio communication system of claim 1, wherein the pairs of pulses generated by the transmitter have waveforms designed so that their power spectral densities are such that, after any frequency translation to the center of an operating band, they are essentially spectrally disjoint with frequencies that must be protected.

5. The UWB radio communication system of claim 1, wherein the transmitter is adapted to transmit pairs of pulses at a pulse repetition rate (PRT) which is varied in order to shape a spectrum of transmission.

6. The UWB radio communication system of claim 1, wherein more than one pair of pulses is associated with each information bit, the pairs of pulses which are associated with a common information bit having a fixed time interval between pulses and the integration time of the finite impulse response integrator (23) being determined by a time required to transmit a number of pairs of pulses associated with an information bit.

7. The UWS radio communication system of claim 1, wherein the transmitter is adapted to generate three or more pulses separated by a known sot of delays with controlled polarities for representing one or more information bits.

8. The UWS radio communication system of claim 7, wherein the receiver is adapted to perform N−

1 correlations to recover encoded information, where N is the number of pulses generated by the transmitter to represent one or more information bits.

9. The UWB radio communication system of claim 1, wherein the transmitter is adapted to transmit a code word consisting of Nc chips, transmitted sequentially, each chip being composed of Np pairs of pulses separated by a same time interval.

10. The UWS radio communication system of claim 9, wherein the receiver comprises a bank of pulse-pair correlators (132), each correlator in the bank being tuned to a different delay (21), and further comprising a code word correlator for receiving outputs of the bank of pulse-pair correlators (132) and generating information bits as an output.

11. The UWS radio communication system of claim 10, wherein the code word correlation is adapted to be implemented as software running on a digital signal processor (134), further comprising a plurality of analog-to-digital converters (133) each connected to sample a corresponding output of the bank of pulse-pair correlators (132) and provide digital inputs to the digital signal processor (134).

12. The UWS radio communication system of claim 1, wherein the receiver further Comprises a baseband demodulator (101) for converting a the received signal to real and imaginary parts of a complex output, the delay (21) being adapted to delay both the real and imaginary parts of the complex output and the signal multiplier (22) being adapted to perform a complex multiplication of a direct path by a complex conjugate of a delayed path, the finite impulse response integrator (23) comprising two integrators, one for the real part and another for the imaginary part of the product signal output by the signal multiplier (22).

13. The UWO radio communication system of claim 12, further comprising means for taking a modulus of a complex quantity connected to the output of the finite impulse response integrator (23).

14. The UWB radio communication system of claim 12, further comprising:

phase estimating means for estimating a phase of an output of the finite impulse response integrator (23); and

a phase correction multiplier for performing a multiplication of the output of the finite impulse response integrator (23) and a complex conjugate of a phasor having the estimated phase to correct the phase of the output of the integrator (23), thereby allowing both positive and negative transmitted pulses to be received and detected.

15. The UWB radio communication system of claim 1, wherein the delay time interval D comprises a plurality of delays where the plurality of delays have nominal values spread around a nominal value of the transmitter'"'"'s delay, a delay actually used for demodulation being selected from among existing delays as that one whose output has the highest energy in response to a transmission at the nominal delay.

16. The UWB radio communication system of claim 15, wherein the selected delay is adapted to be varied to account for drift in a delay value at the transmitter or receiver caused by temperature variations.

17. The UWB radio communication system of claim 15, wherein the selected delay comprises different delays for different transmitters.

18. A method of ultra-wideband (UWB) radio communication comprising the steps of:

generating pairs of pulses separated by a time interval, D in a transmitter;

encoding data by a relative polarity of two pulses of a pair of pulses;

transmitting the data encoded as pairs of pulses;

receiving the data encoded in a receiver;

delaying received encoded data by the time interval, D; and

correlating the received encoded data by the steps of complex conjugate multiplying delayed and undelayed versions of the received encoded data and integrating a signal produced by the complex conjugate multiplication;

wherein said delaying is varied in a fixed pattern known to both of the transmitter and the receiver.

19. The method of UWB radio communication of claim 18, further comprising the step of selecting the time interval D to correspond to a specific value of an autocorrelation function of the an additive noise that obscures the signal, thereby reducing the effect of the additive noise.

20. The method of UWB radio communication of claim 18, further comprising the step of subtracting a known value of an autocorrelation function at a lag, given by the time interval D, from an output of the step of integrating prior to bit decisions being made.

21. The method of UWB radio communication of claim 18, wherein the step of generating pairs of pulses is performed by generating pulses which have waveforms designed so that their power spectral densities are such that, after any frequency translation to the center of an operating band, the generated pulses are essentially spectrally disjoint with frequencies that must be protected.

22. The method of UWS radio communication of claim 18, wherein the step of transmitting pairs of pulses is performed by transmitting the pairs of pulses at a pulse repetition rate (PRT) which is varied in order to shape a spectrum of transmission.

23. The method of UWB radio communication of claim 18, wherein in the step of encoding, more than one pair of pulses is associated with each information bit, the pairs of pulses which are associated with a common information bit having a fixed time interval between pulses and the integration time in the step of correlating being determined by a time required to transmit a number of pairs of pulses associated with an information bit.

24. The method of UWB radio communication of claim 18, wherein the step of generating is performed by generating three or more pulses separated by a known set of delays with controlled polarities for representing one or mare information bits.

25. The method of UWB radio communication of claim 24, wherein the step of correlating performs N−

1 correlations to recover encoded information, where N is the number of pulses generated by the transmitter to represent one or more information bits.

26. The method of UWB radio communication of claim 18, wherein the step of transmitting is performed by transmitting a code word consisting of Nc chips, transmitted sequentially, each chip being composed of Np pairs of pulses separated by a same time interval.

27. The method of UWB radio communication of claim 26, wherein the step of correlating is performed for each pulse-pair, each correlation being tuned to a different delay, and further comprising the steps of:

receiving correlation signals generated by correlating each pulse-pair;

correlating a code word from the received correlation signals; and

generating information bits as an output.

28. The method of UWB radio communication of claim 27, wherein the step of correlating a code word is performed on a digital signal processor, further comprising the step of performing analog-to-digital conversions of the received correlation signals and providing digital inputs to the digital signal processor.

29. The method of UWB radio communication of claim 18, wherein the step of receiving further comprises the step of baseband demodulating a received signal to convert the received signal to real and Imaginary parts of a complex output, the delay delaying both the real and imaginary parts of the complex output, the step of multiplying performing a complex multiplication of a direct path by a complex conjugate of a delayed path, and the step of integrating performing an integration for the real part and another for the imaginary part of the product signal output produced by the step of multiplying.

30. The method of UWB radio communication of claim 29, further comprising the step of taking a modulus of a complex quantity output by the step of integrating.

31. The method of UWB radio communication of claim 29, further comprising the steps of:

estimating a phase of an output of the step of integrating; and

performing a multiplication of the output of the step of integrating and a complex conjugate of a phasor having the estimated phase to correct the phase of the output of the step of integrating, allowing both positive and negative transmitted pulses to be received and detected.

32. The method of UWB radio communication of claim 18, wherein the delay time interval D comprises a plurality of delays where the plurality of delays have nominal values spread around a nominal value of the transmitters delay, a delay actually used for demodulation being selected from among existing delays as that one whose output has the highest energy in response to a transmission at the nominal delay.

33. The method of UWB radio communication of claim 32, wherein the selected delay is varied to account for drift in a delay value at the transmitter or receiver caused by temperature variations.

34. The method of UWS radio communication of claim 32, wherein the selected delay comprises different delays for different transmitters.