Method of Communicating and Associated Transmitter Using Coded Orthogonal Frequency Division Multiplexing (COFDM)

• US 20080043814A1
• 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 7,860,147 B2
• Time in Patent Office: Days
• US Class Current: 375/135
• CPC Class Codes: H04B 1/7103 the interference being multiple access interference
• CPC Class Codes: H04L 27/2614 Peak power aspects
• CPC Class Codes: H04L 27/26362 Subcarrier weighting equivalent to time domain filtering, e.g. weighting per subcarrier multiplication arrangements for removing intersymbol interference at the transmitter end H04L25/03343
• CPC Class Codes: H04L 27/26534 Pulse-shaped multi-carrier, i.e. not using rectangular window

Abstract

A system and method communicates and generates a Coded Orthogonal Frequency Division Multiplexed (COFDM) communications signal as a plurality of subcarriers. Selected subcarriers are turned ON and OFF while also frequency hopping and spreading the selected ON subcarriers over the frequency domain based on a fixed or variable sample rate to reduce average power for enhanced Low Probability of Interception/Low Probability of Detection (LPI/LPD) and also allow for more transmit power within a spectral mask.

Claims

1. A method of communicating, which comprises:

generating a coded orthogonal frequency division multiplexed (COFDM) communications signal as a plurality of subcarriers; and

turning ON and OFF selected subcarriers while also frequency hopping and spreading the selected ON subcarriers over the frequency domain based on a fixed or variable sample rate to reduce average power for enhanced Low Probability of Interception/Low Probability of Detection (LPI/LPD) and also allow for more transmit power within a spectral mask.

2. The method according to claim 1, which further comprises applying a selective channel system for enhancing Channel-State Information (CSI) techniques.

3. The method according to claim 1, which further comprises applying a spreading function followed by an Inverse Fast Fourier Transform (IFFT) to spread the subcarriers over the frequency domain.

4. The method according to claim 3, which further comprises applying a Walsh Transform as a spreading function.

5. The method according to claim 3, which further comprises reducing the number of subcarriers as compared to the IFFT size and a spreading sequence length for increased processing gain and reduced average power per frequency.

6. The method according to claim 1, which further comprises increasing a sample rate to increase bandwidth and data rate.

7. The method according to claim 1, which further comprises reducing or eliminating a guard interval.

8. The method according to claim 1, which further comprises generating a pseudo-random signal based on an encryption algorithm for frequency hopping any subcarriers.

9. The method according to claim 1, which further comprises reducing Inter-Carrier Interference (ICI) by transmitting subcarriers such that any OFDM symbols do not transmit subcarriers on adjacent frequencies.

10. The method according to claim 1, which further comprises reducing Inter-Symbol Interference (ISI) by transmitting subcarriers such that consecutive OFDM symbols do not transmit subcarriers on the same frequencies.

11. A transmitter, comprising:

a circuit for generating a Coded Orthogonal Frequency Division Multiplexed (COFDM) communications signal as a plurality of subcarriers; and

a circuit for turning ON and OFF selected subcarriers while also frequency hopping and spreading the selected ON subcarriers over the frequency domain based on a fixed or variable sample rate to reduce average power for enhanced Low Probability of Interception/Low Probability of Detection (LPI/LPD) and also allow for more transmit power within a spectral mask.

12. The transmitter according to claim 11, which further comprises a circuit for applying a selective channel system for enhancing Channel-State Information (CSI) techniques.

13. The transmitter according to claim 11, which further comprises a circuit for applying a spreading function followed by an Inverse Fast Fourier Transform (IFFT) to spread the subcarriers over the frequency domain.

14. The transmitter according to claim 13, which further comprises a circuit for applying a Walsh Transform as a spreading function.

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

16. The transmitter according to claim 11, which further comprises a circuit for increasing a sample rate to increase bandwidth and data rate.

17. The transmitter according to claim 11, which further comprises a circuit for reducing or eliminating a guard interval.

18. The transmitter according to claim 11, which further comprises a circuit for generating a pseudo-random signal based on an encryption algorithm for frequency hopping any subcarriers.

19. The transmitter according to claim 11, which further comprises a circuit for reducing Inter-Carrier Interference (ICI) by transmitting subcarriers such that OFDM symbols do not transmit subcarriers on adjacent frequencies.

20. The transmitter according to claim 11, which further comprises a circuit for reducing Inter-Symbol Interference (ISI) by transmitting subcarriers such that consecutive OFDM symbols do not transmit subcarriers on same frequencies.

21. The transmitter according to claim 11, which further comprises a circuit for reducing Peak-to-Average Power Ratio (PAPR).

22. The transmitter according to claim 21, which further comprises applying a hybrid PN scrambler and soft clipping circuit for PAPR reduction.