Method of communicating and associated transmitter using coded orthogonal frequency division multiplexing (COFDM)

• US 7,860,147 B2
• Filed: 08/16/2006
• Issued: 12/28/2010
• 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:
  US11/464,868
• Publication Number:
  US 20080043814A1
• Time in Patent Office: 1,595 Days
• Field of Search: 375/132, 375/260, 375/261, 375/268, 375/297, 375/298, 375/300, 375/324, 375/248, 375/349
• US Class Current: 375/132
• 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 changing subcarrier constellation amplitude and phase values and frequency hopping each subcarrier at an OFDM symbol rate using an encryption algorithm and changing subcarrier center frequencies at OFDM symbol times using the same encryption algorithm used to change subcarrier constellation amplitude and phase values, and further comprising spreading the selected ON subcarriers over the frequency domain based on a fixed or variable sample rate to reduce average power 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 transmitting subcarriers such that any OFDM symbols do not transmit subcarriers on adjacent frequencies.

10. The method according to claim 1, which further comprises 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 modulation and mapping circuit and pseudo-random signal generator cooperating with the modulation and mapping circuit and configured to generate pseudo-random signals to the modulation and mapping circuit to turn ON and OFF selected subcarriers while also changing subcarrier constellation amplitude and phase values and frequency hopping each subcarrier at an OFDM symbol rate using an encryption algorithm and changing subcarrier center frequencies at OFDM symbol times using the same encryption algorithm used to change subcarrier constellation amplitude and phase values, and further comprising spreading the selected ON subcarriers over the frequency domain based on a fixed or variable sample rate to reduce average power 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 bandwidth adjust circuit for increasing a sample 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 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 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, wherein said modulation and mapping circuit reduces PAPR.

23. 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 changing subcarrier constellation amplitude and phase values and frequency hopping each subcarrier at an OFDM symbol rate using an encryption algorithm and changing subcarrier center frequencies at OFDM symbol times using the same encryption algorithm used to change subcarrier constellation amplitude and phase values and applying a spreading function followed by an Inverse Fast Fourier Transform (IFFT) for spreading the selected ON subcarriers over the frequency domain based on a fixed or variable sample rate to reduce average power and also allow for more transmit power within a spectral mask; and

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.

24. A transmitter, comprising:

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

a modulation and mapping circuit and pseudo-random signal generator cooperating with the modulation and mapping circuit and configured to generate pseudo-random signals to the modulation and mapping circuit to turn ON and OFF selected subcarriers while also changing subcarrier constellation amplitude and phase values and frequency hopping each subcarrier at an OFDM symbol rate using an encryption algorithm and changing subcarrier center frequencies at OFDM symbol times using the same encryption algorithm used to change subcarrier constellation and phase values and applying a spreading function followed by an Inverse Fast Fourier Transform (IFFT) for spreading the selected ON subcarriers over the frequency domain based on a fixed or variable sample rate to reduce average power and also allow for more transmit power within a spectral mask; and

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.