ORTHOGONAL FREQUENCY DIVISION MULTIPLEXING (OFDM) COMMUNICATIONS DEVICE AND METHOD THAT INCORPORATES LOW PAPR PREAMBLE AND FREQUENCY HOPPING

• US 20100080265A1
• Filed: 10/01/2008
• Published: 04/01/2010
• Est. Priority Date: 10/01/2008
• Status: Active Grant

• Current Assignee: Smartsky Networks Llc
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: MOFFATT, Christopher D., HOFFMANN, John E.
• Granted Patent: US 8,160,165 B2
• Time in Patent Office: Days
• US Class Current: 375/135
• CPC Class Codes: H04L 27/2602 Signal structure
• CPC Class Codes: H04L 5/0007 the frequencies being orthogonal, e.g. OFDM(A), DMT

Abstract

A communications device includes communication data and a training sequence corresponding to a preamble. A modulation and mapping circuit modulates the communications data and training sequence into a plurality of multiple subcarriers that are orthogonal to each other to form an OFDM communications signal having modulated subcarriers carrying the communications data forming a data payload and modulated subcarriers forming the preamble. A pseudo-random signal generator is operative with the modulation and mapping circuit and generates pseudo-random signals based on an encryption algorithm for frequency hopping each subcarrier at an OFDM symbol rate. The modulation and mapping circuit applies a quadratic modulation to the subcarriers carrying the training sequences to produce a low peak-to-average power ratio (PAPR) preamble with a PAPR value of approximately 2.6 decibels (dB).

Claims

1. A communications device, comprising:

a source of communications data and a training sequence corresponding to a preamble;

a modulation and mapping circuit that modulates the communications data and training sequence into a plurality of multiple subcarriers that are orthogonal to each other to form an Orthogonal Frequency Division Multiplexing (OFDM) communications signal having modulated subcarriers carrying the communications data forming a data payload and modulated subcarriers forming the preamble;

a pseudo-random signal generator operative with the modulation and mapping circuit for generating pseudo-random signals to the modulation and mapping circuit based on an encryption algorithm for frequency hopping each subcarrier at an OFDM symbol rate; and

wherein said modulation and mapping circuit applies a quadratic modulation to the subcarriers carrying the training sequences to produce a low peak-to-average power ratio (PAPR) preamble with about a PAPR value of 2.6 decibels (dB).

2. The communications device according to claim 1, and further comprising a circuit for turning OFF and ON selected subcarrier based on an encryption algorithm to increase transmit power and signal-to-noise ratio per subcarrier and reduce the Inter-Carrier Interference (ICI).

3. The communications device according to claim 1, and further comprising a circuit for spreading the selected ON subcarriers over the frequency domain to reduce average power for enhanced Low Probability of Interception/Low Probability of Detection (LPI/LPD) to allow for more transmit power within a spectral mask and reduce adverse effects of Frequency Selective Fading.

4. The communications device according to claim 3, and further comprising a circuit for reducing the number of subcarriers as compared to an IFFT size and a spreading sequence length for increased processing gain and reduced average power per frequency bin.

5. The communications device according to claim 1, wherein said modulation and mapping circuit is operative for independently amplitude modulating each subcarrier carrying the data sequences.

6. The communications device according to claim 1, wherein the low PAPR preamble is independent of the number of subcarriers forming the OFDM communications signal.

7. The communications device according to claim 1, wherein said modulation and mapping circuit is operative for setting quadratic phases of sinusoids forming the subcarriers carrying the training sequences.

8. The communications device according to claim 7, wherein said modulation and mapping circuit is operative for setting the phases of the sinusoids to a specific angle.

9. The communications device according to claim 1, wherein the preamble includes a long sync sequence for acquisition, detection, frequency and channel estimation having a guard interval (GI).

10. The communications device according to claim 1, wherein said modulation and mapping circuit is operative for forming each of the subcarriers that carries the training sequences of the OFDM communications signal to have equal amplitude.

11. A method of communicating data, comprising:

receiving communications data to be transmitted and a training sequence corresponding to a preamble;

generating an Orthogonal Frequency Division Multiplexing (OFDM) communications signal having modulated subcarriers carrying the communications data forming a data payload and subcarriers carrying the training sequences forming the preamble;

generating pseudo-random signals to a modulation and mapping circuit based on an encryption algorithm and frequency hopping each subcarrier at an OFDM symbol rate;

applying quadratic phase modulation to subcarriers carrying the training sequences to produce a low peak-to-average power ratio (PAPR) preamble with about a PAPR value of 2.6 decibels (dB); and

transmitting the OFDM communications signal along a communications channel to a receiver.

12. The method according to claim 11, which further comprises turning OFF and ON selected subcarrier based on an encryption algorithm to increase transmit power and signal-to-noise ratio per subcarrier and reduce the Inter-Carrier Interference (ICI).

13. The method according to claim 11, which further comprises spreading the selected ON subcarriers over the frequency domain to reduce average power for enhanced Low Probability of Interception/Low Probability of Detection (LPI/LPD) to allow for more transmit power within a spectral mask and reduce adverse effects of Frequency Selective Fading.

14. The method according to claim 13, which further comprises reducing the number of subcarriers as compared to an IFFT size and a spreading sequence length for increased processing gain and reduced average power per frequency bin.

15. The method according to claim 11, which further comprises equally spacing in frequency each of the subcarriers carrying the training sequences.

16. The method according to claim 11, which further comprises forming each of the subcarriers carrying the training sequences to have equal amplitude.

17. The method according to claim 11, which further comprises independently amplitude modulating each subcarrier carrying the data sequences.

18. The method according to claim 11, which further comprises measuring fluctuations within a flat-topped spectrum of the OFDM communications signal corresponding to the preamble to reflect the frequency response of the communications channel.

19. The method according to claim 11, which further comprises setting quadratic phases of sinusoids forming the subcarriers carrying the training sequences.

20. The method according to claim 19, which further comprises setting the phases of the sinusoids to a specific angle.

21. A method of communicating data, comprising:

receiving communications data to be transmitted and a training sequence corresponding to a preamble;

generating an Orthogonal Frequency Division Multiplexing (OFDM) communications signal having modulated subcarriers carrying the communications data forming a data payload and subcarriers carrying training sequences forming the preamble, wherein the preamble includes a long sync sequence for acquisition, detection, frequency and channel estimation having a guard interval (GI);

generating pseudo-random signals to a modulation and mapping circuit based on an encryption algorithm and frequency hopping each subcarrier at an OFDM symbol rate;

applying a quadratic phase modulation to subcarriers carrying the training sequences to produce a low peak-to-average power ratio (PAPR) preamble with about a PAPR value of 2.6 decibels (dB); and

splitting the guard interval from the long sync sequence and processing into values that represent the inverse low PAPR preamble as plus or minus one (+/−

1) values in a real or imaginary component as adds and subtracts for channel estimation.

22. The method according to claim 21, which further comprises turning OFF and ON selected subcarrier based on an encryption algorithm to increase transmit power and signal-to-noise ratio per subcarrier and reduce the Inter-Carrier Interference (ICI).

23. The method according to claim 21, which further comprises spreading the selected ON subcarriers over the frequency domain to reduce average power for enhanced Low Probability of Interception/Low Probability of Detection (LPI/LPD) to allow for more transmit power within a spectral mask and reduce adverse effects of Frequency Selective Fading.

24. The method according to claim 23, which further comprises reducing the number of subcarriers as compared to an IFFT size and a spreading sequence length for increased processing gain and reduced average power per frequency bin.

25. The method according to claim 21, which further comprises using the “

n”

samples of the guard interval as a normal guard interval and portions of the long sync sequence for Fast Fourier Transform (FFT) processing for channel estimation.