Methods and apparatus for transmitting non-contiguous spread spectrum signals for communications and navigation

• US 7,366,243 B1
• Filed: 10/29/2003
• Issued: 04/29/2008
• Est. Priority Date: 10/29/2003
• Status: Active Grant

• Current Assignee: Harris Global Communications, Inc. (L3Harris Technologies, Inc.)
• Original Assignee: ITT Manufacturing Enterprises, Inc. (ITT, Inc.)
• Inventors: McCrady, Dennis D.
• Primary Examiner(s): Corrielus; Jean B.
• Application Number:
  US10/695,484
• Time in Patent Office: 1,644 Days
• Field of Search: 370/210, 370/203, 375/130, 375/259, 375/285, 375/296, 375/350, 375/346, 375/260, 375/222, 375/219
• US Class Current: 375/259
• CPC Class Codes: G01S 1/20 using a comparison of transit time of synchronised signals transmitted from non-directional antennas or antenna systems spaced apart, i.e. path-difference systems
• CPC Class Codes: G01S 19/25 involving aiding data received from a cooperating element, e.g. assisted GPS
• CPC Class Codes: G01S 5/0226 Transmitters
• CPC Class Codes: H04L 25/03834 using pulse shaping
• CPC Class Codes: H04Q 2213/13294 CDMA, code division multiplexing, i.e. combinations of H04Q2213/13291 and/or H04Q2213/13292 with space division

Abstract

A technique for transmitting a spread spectrum signal using plural non-contiguous frequency bands separated by segments of frequency spectrum excluded from use involves: generating a digital time-domain spread spectrum signal; converting the time-domain signal to a frequency-domain signal via an FFT; excising a portion of the frequency-domain signal by selectively removing frequency bins of the frequency-domain signal to cause spectral nulling of the transmit signal at the frequencies of the excluded segments; and converting the excised frequency-domain signal to an excised time-domain signal via an inverse FFT, which is then converted to an analog signal for transmission. The non-contiguous spectrum selection technique is implemented in a transmitter that transmits data communication signals or navigation signals, and permits use of plural, non-contiguous frequency bands to transmit a wide bandwidth signals that cannot be transmitted in a continuous frequency band due to constrains in the allocated frequency spectrum available for transmission.

Claims

1. A system for generating a single-carrier wideband signal for transmission in non-contiguous frequency bands that are separated by at least one segment of frequency spectrum excluded from use in transmitting the signal, comprising:

a processor that generates a digital time-domain signal;

a non-contiguous spectrum selector that converts the digital time-domain signal to a frequency-domain signal that includes the non-contiguous frequency bands and the at least one segment of frequency spectrum, excises a portion of the frequency-domain signal corresponding to the at least one segment of frequency spectrum, and converts the excised frequency-domain signal to an excised time-domain signal that includes signal components in the non-contiguous frequency bands, wherein the excised time-domain signal is a single-carrier wideband signal having a bandwidth comprising a collective bandwidth of the non-contiguous frequency bands used for transmission.

2. The system of claim 1, wherein the non-contiguous spectrum selector comprises:

a discrete Fourier transform module that converts the digital time-domain signal to the frequency-domain signal, wherein the frequency-domain signal comprises a plurality of frequency-domain samples corresponding to respective frequency bins;

an excision module that selectively removes frequency bins to cause spectral nulling at the at least one segment of frequency spectrum excluded from signal transmission; and

an inverse discrete Fourier transform module that converts the excised frequency-domain signal to the excised time-domain signal.

3. The system of claim 2, wherein the discrete Fourier transform module comprises a fast Fourier transform (FFT) and the inverse discrete Fourier transform module comprises an inverse FFT.

4. The system of claim 3, wherein the discrete Fourier transform module includes windowing to shape the frequency response of the frequency bins.

5. The system of claim 1, wherein digital time-domain signal is a baseband signal.

6. The system of claim 5, further comprising:

a digital mixer that up-converts the excised time-domain signal to an intermediate frequency signal; and

a digital-to-analog converter configured to convert the intermediate frequency signal to an analog signal for transmission.

7. The system of claim 6, further comprising a reconstruction filter that receives the analog signal from the digital-to-analog converter and supplies a filtered intermediate signal to an RF transmission module.

8. The system of claim 1, wherein the signal is a single, direct sequence spread spectrum signal.

9. The system of claim 8, wherein the digital time-domain signal comprises a sequence of samples of chips.

10. The system of claim 1, wherein the signal includes data for transmission to a communication device.

11. The system of claim 1, wherein the signal is a ranging waveform for determining a range between two communication devices.

12. The system of claim 1, further comprising a receiver comprising:

an analog-to-digital converter that converts a received signal to a received digital time-domain signal; and

a receiver spectrum selector that converts the received digital time-domain signal to a received frequency-domain signal, excises a portion of the received frequency-domain signal corresponding to the at least one segment of frequency spectrum, and converts the excised received frequency-domain signal to an excised, received time-domain signal.

13. The system of claim 12, further comprising a time of arrival processor that determines a time of arrival of the received signal from the excised, received time-domain signal.

14. The system of claim 12, further comprising a communications acquisition processor that acquires the received signal from the excised, received time-domain signal.

15. The system of claim 12, wherein the receiver spectrum selector performs interference excision.

16. The system of claim 1, wherein the system comprises a modem including a transmitter and a receiver, wherein the transmitter includes the non-contiguous spectrum selector.

17. The system of claim 1, wherein the system comprises a communication device that includes the processor and the non-contiguous spectrum selector.

18. The system of claim 17, wherein the communication device is a mobile communication device.

19. The system of claim 1, wherein the system comprises a plurality of communication devices communicating in a network.

20. The system of claim 1, wherein the non-contiguous spectrum selector excises the portion of the frequency-domain signal corresponding to the at least one segment of the frequency spectrum, independent of a signal level of the digital time-domain signal or frequency-domain signal.

21. The system of claim 1, wherein a bandwidth of the frequency domain signal generated by the non-contiguous spectrum selector corresponds to an overall band that extends from a lowest frequency of a lowest of the non-contiguous frequency bands to a highest frequency of a highest of the non-contiguous frequency bands.

22. The system of claim 1, wherein a pulse shape of the single-carrier wideband signal is changed by excision of the portion of the frequency-domain signal.

23. A method for generating a single-carrier wideband signal for transmission in non-contiguous frequency bands that are separated by at least one segment of frequency spectrum excluded from use in transmitting the signal, comprising:

(a) generating a digital time-domain signal;

(b) converting the digital time-domain signal to a frequency-domain signal that includes the non-contiguous frequency bands and the at least one segment of frequency spectrum;

(c) excising a portion of the frequency-domain signal corresponding to the at least one segment of frequency spectrum to produce an excised frequency-domain signal that includes signal components corresponding to the non-contiguous frequency bands;

(d) converting the excised frequency-domain signal to an excised time-domain signal, wherein the excised time-domain signal is a single-carrier wideband signal having a bandwidth comprising a collective bandwidth of the non-contiguous frequency bands used for transmission; and

(e) converting the excised time-domain signal to an analog signal for transmission.

24. The method of claim 23, wherein:

(b) includes converting the digital time-domain signal to the frequency-domain signal via a windowed fast Fourier transform (FFT), wherein the frequency-domain signal comprises a plurality of frequency-domain samples corresponding to respective frequency bins;

(c) selectively removing frequency bins to cause spectral nulling at the at least one segment of frequency spectrum excluded from signal transmission; and

(d) includes converting the excised frequency-domain signal to the excised time-domain signal via an inverse FFT.

25. The method of claim 23, wherein digital time-domain signal is a baseband signal.

26. The method of claim 25, further comprising:

(f) up-converting the excised time-domain signal to an intermediate frequency signal.

27. The method of claim 23, wherein the signal is a single, direct sequence spread spectrum signal, and the digital time-domain signal comprises a sequence of samples of chips.

28. The method of claim 23, wherein the signal includes data for transmission to a communication device.

29. The method of claim 23, wherein the signal is a ranging waveform for determining a range between two communication devices.

30. The method of claim 23, further comprising:

(f) converting a received signal to a received digital time-domain signal;

(g) converting the received digital time-domain signal to a received frequency-domain signal;

(h) excising a portion of the received frequency-domain signal corresponding to the at least one segment of frequency spectrum; and

(i) converting the excised received frequency-domain signal to an excised, received time-domain signal.

31. The method of claim 30, further comprising:

(j) determining a time of arrival of the received signal from the excised, received time-domain signal.

32. The method of claim 23, wherein (c) includes excising the portion of the frequency-domain signal corresponding to the at least one segment of the frequency spectrum, independent of a signal level of the digital time-domain signal or frequency-domain signal.

33. The method of claim 23, wherein a bandwidth of the frequency domain signal corresponds to an overall band that extends from a lowest frequency of a lowest of the non-contiguous frequency bands to a highest frequency of a highest of the non-contiguous frequency bands.

34. The method of claim 23, wherein a pulse shape of the single-carrier wideband signal is changed by excision of the portion of the frequency-domain signal.