System and method for communicating data using symbol-based randomized orthogonal frequency division multiplexing (OFDM)

• US 7,751,488 B2
• Filed: 08/16/2006
• Issued: 07/06/2010
• 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.
• Primary Examiner(s): Liu, Shuwang
• Assistant Examiner(s): Timory, Kabir A
• Application Number:
  US11/464,877
• Publication Number:
  US 20080043861A1
• Time in Patent Office: 1,420 Days
• Field of Search: 375/260, 375/261, 375/268, 375/297, 375/298, 375/300, 375/324, 375/348, 375/349
• US Class Current: 375/260
• CPC Class Codes: H04L 27/2618 Reduction thereof using auxiliary subcarriers
• CPC Class Codes: H04L 27/2634 Inverse fast Fourier transform [IFFT] or inverse discrete Fourier transform [IDFT] modulators in combination with other circuits for modulation

Abstract

A system and device communicates data. A modulation and mapping circuit 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 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, reduced power per frequency (dB/Hz/sec), and lower any required transmission power while maintaining an instantaneous signal-to-noise ratio.

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 comprising a modulator and a subcarrier mapper circuit for mapping carriers to an Inverse Fast Fourier Transform (IFFT) in a matrix operation; and

a pseudo-random signal generator comprising a pseudorandom amplitude and phase signal generator operative with the modulator for generating pseudo-random signals to the modulator using an encryption algorithm for changing subcarrier constellation amplitude and phase values, and a pseudo-random subcarrier location circuit operative with the subcarrier mapper circuit and generating pseudo-random signals to the subcarrier mapper circuit using the same encryption algorithm used to change subcarrier constellation amplitude and phase values such that each subcarrier is frequency hopped at an OFDM symbol rate and subcarrier center frequencies are changed at OFDM symbol times according to the encryption algorithm.

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

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

4. The device according to claim 1, and further comprising an Inverse Fast Fourier Transform (IFFT) circuit that applies the Inverse Fast Fourier Transform for modulating subcarriers orthogonal to each other.

5. 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).

6. The device according to claim 1, wherein said modulator maps communications data into modulated symbols based on a specific mapping algorithm.

7. The device according to claim 1, and further comprising a Forward Error Correction circuit for adding a FEC code.

8. 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 comprising a modulator and a subcarrier mapper circuit for mapping carriers to an Inverse Fast Fourier Transform (IFFT) in a matrix operation, and a pseudo-random signal generator comprising a pseudo-random amplitude and phase generator operative with the modulator for generating pseudo-random signals to the modulator using an encryption algorithm for changing subcarrier constellation amplitude and phase values, and a pseudo-random subcarrier location circuit operative with the subcarrier mapper circuit and generating pseudo-random signals to the subcarrier mapper circuit using the same encryption algorithm used to change subcarrier constellation amplitude and phase values such that each subcarrier is frequency hopped at an OFDM symbol rate and subcarrier center frequencies are changed at OFDM symbol times according to the encryption algorithm; and

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

9. A system according to claim 8, wherein said transmitter is operative for modulating a main carrier signal.

10. The system according to claim 9, wherein said pseudo-random signal generator is operative for generating a pseudo-random signal using said encryption algorithm such that consecutive OFDM symbols do not transmit subcarriers on the same frequency.

11. The system according to claim 9, wherein said pseudo-random signal generator is operative for generating a pseudo-random signal using said encryption algorithm such that a Guard Interval is reduced or eliminated.

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

13. The system according to claim 9, wherein said transmitter further comprises an Inverse Fast Fourier Transform (IFFT) circuit that applies the Inverse Fast Fourier Transform for modulating subcarriers orthogonal to each other.

14. The system according to claim 9, wherein said transmitter further comprises a circuit for inserting signals for reducing peak-to-average-power ratio (PAPR).

15. The system according to claim 9, wherein said transmitter is operative for adding a Forward Error Correction (FEC) code.

16. A method for communicating data, which comprises:

distributing communications data over multiple subcarrier frequencies that are orthogonal to each other within a modulator circuit and subcarrier mapper circuit that maps carriers to an Inverse Fast Fourier Transform (IFFT) in a matrix operation 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 while also generating pseudo-random signals from a pseudo-random amplitude and phase signal generator to the modulator using an encryption algorithm for changing subcarrier constellation amplitude and phase values and generating pseudo-random signals from a pseudo-random subcarrier location circuit to the subcarrier mapper circuit using the same encryption algorithm used to change subcarrier constellation amplitude and phase values such that each subcarrier is frequency hopped at an OFDM symbol rate and subcarrier center frequencies are changed at OFDM symbol times according to the encryption algorithm; and

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

17. The method according to claim 16, which further comprises generating a pseudo-random signal using said encryption algorithm such that consecutive OFDM symbols do not transmit subcarriers on the same frequency.

18. The method according to claim 16, which further comprises generating a pseudo-random signal using said encryption algorithm such that a Guard Interval is reduced or eliminated.

19. The method according to claim 16, which further comprises inserting signals for reducing peak-to-average-power ratio (PAPR).

20. The method according to claim 16, which further comprises modulating a main carrier signal on which the multiple subcarrier frequencies are transmitted.

21. The method according to claim 16, which further comprises varying pseudo-randomly a subcarrier constellation amplitude and phase value.

22. The method according to claim 16, which further comprises applying an Inverse Fast Fourier Transform (IFFT) for distributing the communications data over multiple subcarriers that are orthogonal to each other.