System and Method for Communicating Data Using Symbol-Based Randomized Orthogonal Frequency Division Multiplexing (OFDM) With Selected Subcarriers Turned ON or OFF

• US 20080043860A1
• Filed: 08/16/2006
• Published: 02/21/2008
• Est. Priority Date: 08/16/2006
• Status: Active Grant

• Current Assignee: Smartsky Networks Llc
• Original Assignee: Harris Corporation (L3Harris Technologies, Inc.)
• Inventors: Moffatt, Christopher D.
• Granted Patent: US 7,813,433 B2
• Time in Patent Office: Days
• US Class Current: 375/260
• CPC Class Codes: H04B 1/707 using direct sequence modulation
• CPC Class Codes: H04B 1/713 using frequency hopping
• CPC Class Codes: H04L 5/0044 allocation of payload

Abstract

A device and system communicates data and includes a modulation and mapping circuit that modulates and maps data symbols into a plurality of multiple subcarrier frequencies that are orthogonal to each other to form an Orthogonal Frequency Division Multiplexed (OFDM) communications signal based on a fixed or variable OFDM symbol rate. A pseudo-random signal generator is operative with the modulation and mapping circuit and generates pseudo-random signals to the modulation and mapping circuit based on an encryption algorithm for frequency hopping each subcarrier at an OFDM symbol rate to lower any probability of interception and detection, reduce power per frequency (dB/Hz/sec), and lower any required transmission power while maintaining an instantaneous signal-to-noise ratio, wherein selected subcarriers are turned ON or OFF to increase the transmit power and signal-to-noise ratio and reduce the Inter-Carrier Interference (ICI) and adverse effects of frequency selective fading.

Claims

1. A device for communicating data, comprising:

a modulation and mapping circuit that modulates and maps data symbols into a plurality of multiple subcarrier frequencies that are orthogonal to each other to form an Orthogonal Frequency Division Multiplexed (OFDM) communications signal based on a fixed or variable OFDM symbol rate; and

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 to lower any probability of interception and detection, reduce power per frequency (dB/Hz/sec), and lower any required transmission power while maintaining an instantaneous signal-to-noise ratio, wherein selected subcarriers are turned ON or OFF to increase the transmit power and signal-to-noise ratio and reduce the Intercarrier Interference (ICI) and adverse effects of Frequency Selective Fading.

2. The device according to claim 1, wherein selected subcarriers are turned ON or OFF depending on the required data rate to be transmitted.

3. The device according to claim 1, wherein selected subcarriers are turned ON or OFF relative to the number of subcarriers and desired transmit power for allowing a trade-off for data rate and distance within the same spectral mask.

4. The device according to claim 1, wherein said pseudo-random generator comprises a dead-time pseudo-random generator for decreasing the ON time of subcarriers and increasing the output spacing of symbols to reduce continuous transmission time.

5. The device according to claim 1, wherein the spacing between symbols is varied to prevent spectral lines and reduce cyclostationary statistics of the signal.

6. The device according to claim 1, wherein selected subcarriers are turned ON or OFF based on one of least received signal-to-noise ratio, location of interferers, channel impairments, negotiated channel mask with a receiver, desired data rate, desired signal range, and transmit power requirements.

7. The device according to claim 1, and further comprising a frequency domain spreader circuit for spreading any ON subcarriers over the frequency domain.

8. The device according to claim 1, wherein said pseudo-random signal generator is operative for generating a pseudo-random signal based on said encryption algorithm such that consecutive OFDM symbols do not transmit subcarriers on the same frequency.

9. The device according to claim 1, wherein said pseudo-random signal generator is operative for generating a pseudo-random signal based on said encryption algorithm such that OFDM symbols do not transmit subcarriers on adjacent frequencies for reduced Inter-Carrier Interference (ICI).

10. The device according to claim 1, wherein said pseudo-random signal generator is operative for generating a pseudo-random signal based on said encryption algorithm such that a Guard Interval is reduced or eliminated.

11. The device according to claim 1, wherein said modulation and mapping circuit is operative for inserting signals for reducing peak-to-average-power ratio (PAPR).

12. The device according to claim 1, wherein said pseudo-random signal generator is operatively connected to said modulator for varying amplitude and phase values using an encryption algorithm.

13. The device according to claim 1, and further comprising an encoder for adding a Forward Error Correction (FEC) code.

14. A system for communicating data, comprising:

a transmitter for transmitting a communications signal that carries communications data and comprises a modulation and mapping circuit that maps data symbols into a plurality of multiple subcarrier frequencies that are orthogonal to each other to form an Orthogonal Frequency Division Multiplexed (OFDM) communications signal based on a fixed or variable OFDM symbol rate, and 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 to lower any probability of interception and detection, reduce power per frequency (dB/Hz/sec), and lower any required transmission power while maintaining an instantaneous signal-to-noise ratio, wherein selected subcarriers are turned ON or OFF to increase the transmit power and signal-to-noise ratio and reduce the Intercarrier Interference (ICI) and adverse effects of Frequency Selective Fading; and

a receiver for receiving the communications signal and includes a demapping and demodulation circuit for processing the communications signal to obtain the communications data.

15. The system according to claim 14, wherein said receiver is operative for transmitting a signal back to said transmitter for varying the transmitted signal by selectively turning ON or OFF subcarriers.

16. The system according to claim 14, wherein subcarriers are turned ON or OFF depending on the required data rate to be transmitted.

17. The system according to claim 14, wherein selected subcarriers are turned ON or OFF relative to the number of subcarriers and desired transmit power for allowing a trade-off for data rate and distance within the same spectral mask.

18. The system according to claim 14, wherein said pseudo-random generator comprises a dead-time pseudo-random generator for decreasing the ON time and increasing the output spacing of symbols to reduce continuous transmission time.

19. The system according to claim 14, wherein the spacing between symbols is varied to prevent spectral lines and reduce cyclostationary statistics of the signal.

20. The system according to claim 14, wherein selected subcarriers are turned ON or OFF based on one of least received signal-to-noise ratio, location of interferers, channel impairments, negotiated channel mask with a receiver, desired data rate, desired signal range, and transmit power requirements.

21. The system according to claim 14, and further comprising a frequency domain spreader circuit for spreading any ON subcarriers over the frequency domain.

22. The system according to claim 14, wherein said pseudo-random signal generator is operative for generating a pseudo-random signal based on said encryption algorithm such that consecutive OFDM symbols do not transmit subcarriers on the same frequency.

23. The system according to claim 14, wherein said pseudo-random signal generator is operative for generating a pseudo-random signal based on said encryption algorithm such that OFDM symbols do not transmit subcarriers on adjacent frequencies for reduced Inter-Carrier Interference (ICI).

24. The system according to claim 14, wherein said pseudo-random signal generator is operative for generating a pseudo-random signal based on said encryption algorithm such that a Guard Interval is reduced or eliminated.

25. The system according to claim 14, wherein said pseudo-random signal generator is operatively connected to said modulator for varying amplitude and phase values using an encryption algorithm.

26. The system according to claim 14, wherein said transmitter further comprises a circuit for inserting signals for reducing peak-to-average-power ratio (PAPR).

27. A method for communicating data, which comprises:

distributing communications data over multiple subcarrier frequencies that are orthogonal to each other to form an Orthogonal Frequency Division Multiplexed (OFDM) communications signal based on fixed or variable OFDM symbol rate;

frequency hopping each subcarrier at an OFDM symbol rate to lower any probability of interception and detection, reduce power per frequency (dB/Hz/sec), and lower any required transmission power while maintaining an instantaneous signal-to-noise ratio;

turning ON and OFF selected subcarriers for increasing the transmit power and signal-to-noise ratio and reducing the Intercarrier Interference (ICI) and adverse effects of Frequency Selective Fading; and

transmitting the communications data over a communications signal that includes the frequency hopping subcarriers.

28. The method according to claim 27, which further comprises receiving a signal back from the receiver, and in response, selectively turning ON or OFF subcarriers.

29. The method according to claim 27, which further comprises turning subcarriers ON or OFF depending on the required data rate to be transmitted.

30. The method according to claim 27, which further comprises turning selected subcarriers ON or OFF relative to the number of subcarriers and desired transmit power for allowing a trade-off for data rate and distance within the same spectral mask.

31. The method according to claim 27, which further comprises decreasing the ON time of subcarriers and increasing the output spacing of symbols to reduce continuous transmission time.

32. The method according to claim 27, which further comprises varying the spacing between symbols to prevent spectral lines and reduce cyclostationary statistics of the communications signal.

33. The method according to claim 27, which further comprises turning ON or OFF selected subcarriers based on of least received signal-to-noise ratio, location of interferers, channel impairments, negotiated channel mask with a receiver, desired data rate, desired signal range, and transmit power requirements.

34. The method according to claim 27, which further comprises generating a pseudo-random signal based on said encryption algorithm such that consecutive OFDM symbols do not transmit subcarriers on the same frequency.

35. The method according to claim 27, which further comprises generating a pseudo-random signal based on said encryption algorithm such that OFDM symbols do not transmit subcarriers on adjacent frequencies for reduced Inter-Carrier Interference (ICI).

36. The method according to claim 27, which further comprises generating a pseudo-random signal based on said encryption algorithm such that a Guard Interval is reduced or eliminated.

37. The method according to claim 27, which further comprises inserting signals for reducing peak-to-average-power ratio (PAPR).