Methods and apparatus for transmitting non-contiguous spread spectrum signals for communications and navigation
View Patent ↗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.
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.