Fast frequency hopping spread spectrum for code division multiple access communication networks (FFH-CDMA)

• US 6,381,053 B1
• Filed: 10/08/1998
• Issued: 04/30/2002
• Est. Priority Date: 10/08/1998
• Status: Expired due to Fees

• Current Assignee: Universite Laval
• Original Assignee: Universite Laval
• Inventors: Fathallah, Habib, Rusch, Leslie Ann, La Rochelle, Sophie
• Primary Examiner(s): MULLEN, THOMAS J
• Application Number:
  US09/192,180
• Time in Patent Office: 1,300 Days
• Field of Search: 359/136, 359/130, 359/138, 359/140, 375/132, 370/320, 370/335, 370/337, 370/342, 370/347
• US Class Current: 398/99
• CPC Class Codes: H04B 1/7136 Arrangements for generation of hop frequencies, e.g. using a bank of frequency sources, using continuous tuning or using a transform
• CPC Class Codes: H04B 2001/71365 using continuous tuning of a single frequency source
• CPC Class Codes: H04J 14/005 Optical Code Multiplex

Abstract

An improved method and apparatus for optical and radio frequency implementation of a fast frequency hopping spread spectrum communication for code division multiple access systems is disclosed. The method avoids the frequency hopping synthesizer requirements in the transmitter as well as in the receiver. In a system where a pool of CDMA users share a channel characterized by a number of F available frequencies (or frequency bands), each user is assigned a subset of M (M less than or equal to F) frequencies from the F available frequencies, selected and ordered in time as prescribed by his own code (or address). In the transmitter, the information bit sequence modulates a broadband source so that the energy assigned to a data bit is concentrated on just a short interval of the bit period which is less than or equal to the so-called chip interval. The data modulated signal enters equipment which simultaneously or sequentially performs three functions: 1) spectral slicing of the input signal into chip pulses, 2) a chip-pulse modulation and 3) a chip-pulse delaying. The output is an FFHSS signal composed from M sub-pulses (or chip-pulses), each of which is centered at different frequency and ordered in time as fixed by the FFH code. In an optical implementation, a broadband source and a set of in-line fiber Bragg gratings performs the FFHSS encoding and decoding operations with ASK chip-modulation. The gratings can be tuned to allow the programmability of the encoding/decoding system.

Claims

1. A method of optical signal transmission comprising the steps of:

generating a multi-wavelength optical signal modulated to encode data and occupy a predetermined fraction of a bit time slot;

selecting a plurality of wavelength division slots within a wavelength range of said multi-wavelength signal;

introducing, according to a code, a predetermined time delay in spectral components of said multi-wavelength optical signal corresponding to each of said plurality of wavelength division slots to displace said spectral components within said bit time slot; and

feeding said spectral components delayed according to said code into a waveguide transmission medium shared by at least one other transmitter using said wavelength division slots and a different code.

2. The method as claimed in claim 1, wherein said step of introducing said predetermined time delay comprises providing an in-waveguide Bragg grating device having a plurality of spaced Bragg grating reflectors for reflecting said spectral component time delayed according to said code.

3. The method as claimed in claim 2, wherein said step of introducing further comprises providing an optical circulator, coupling said optical signal to a first port of said circulator, coupling said in-waveguide Bragg grating device to a second port of said circulator, and coupling a third port of said circulator to said waveguide transmission medium.

4. The method as claimed in claim 3, wherein said in-waveguide Bragg grating device comprises an in-fiber Bragg grating.

5. The method as claimed in claim 4, wherein said code utilizes fewer than all of said wavelength division slots and a bit time slot is used which is shorter than a bit time slot used when all of said wavelength division slots are utilized, whereby a shorter code length may be used to achieve a higher bit rate.

6. The method as claimed in claim 1, wherein said code utilizes fewer than all of said wavelength division slots and a bit time slot is used which is shorter than a bit time slot used when all of said wavelength division slots are utilized, whereby a shorter code length may be used to achieve a higher bit rate.

7. The method as claimed in claim 1, wherein said step of introducing said predetermined time delay comprises providing a programmable in-waveguide Bragg grating device having a plurality of tunable spaced Bragg grating reflectors for reflecting said spectral component time delayed according to said code, and tuning said Bragg grating reflectors according to said code.

8. The method as claimed in claim 7, wherein said tuning comprises adjusting a temperature control of a temperature control device for each of said Bragg grating reflectors.

9. The method as claimed in claim 7, wherein said tuning comprises adjusting a voltage control of a piezoelectric element for each of said Bragg grating reflectors.

10. A method of optical communication comprising the steps of:

generating a multi-wavelength optical signal modulated to encode data and occupy a predetermined fraction of a bit time slot at a transmitter end;

selecting a plurality of wavelength division slots within a wavelength range of said multi-wavelength signal;

introducing, according to a code, a predetermined time delay in spectral components of said multi-wavelength optical signal corresponding to each of said plurality of wavelength division slots to displace said spectral components within said bit time slot;

feeding said spectral components delayed according to said code into a waveguide transmission medium shared by at least one other transmitter using said wavelength division slots and a different code;

receiving said optical signal from said transmission medium; and

detecting said displaced spectral components according to said code to recover said data.

11. The method as claimed in claim 10, wherein said step of detecting comprises:

introducing, according to a reverse code complementary to said code, a predetermined time delay in spectral components of said multi-wavelength optical signal corresponding to each of said plurality of wavelength division slots to displace said spectral components within said bit time slot; and

detecting only within said predetermined fraction of said bit time slot signal energy of said received optical signal.

12. The method as claimed in claim 11, wherein said step of receiving comprises compensating for chromatic dispersion caused by said transmission medium.

13. The method as claimed in claim 11, wherein said transmitter end is subject to temperature variations affecting a wavelength of said spectral components, said step of detecting comprises providing a programmable in-waveguide Bragg grating device having a plurality of tunable spaced Bragg grating reflectors for reflecting said spectral component time delayed according to said code, and tuning said Bragg grating reflectors to compensate for said temperature variations.

14. The method as claimed in claim 13, wherein said tuning comprises adjusting a temperature control of a temperature control device for each of said Bragg grating reflectors.

15. The method as claimed in claim 13, wherein said tuning comprises adjusting a voltage control of a piezoelectric element for each of said Bragg grating reflectors.

16. The method as claimed in claim 11, wherein said code utilizes fewer than all of said wavelength division slots and a bit time slot is used which is shorter than a bit time slot used when all of said wavelength division slots are utilized, whereby a shorter code length may be used to achieve a higher bit rate, said step of detecting including steps of:

detecting any signal present in at least one unused ones of said wavelength division slots at predetermined time delays; and

subtracting said signal detected in the previous step from said displaced spectral components according to said code in order to recover said data.

17. The method as claimed in claim 10, wherein said step of receiving comprises compensating for chromatic dispersion caused by said transmission medium.

18. The method as claimed in claim 10, wherein said code utilizes fewer than all of said wavelength division slots and a bit time slot is used which is shorter than a bit time slot used when all of said wavelength division slots are utilized, whereby a shorter code length may be used to achieve a higher bit rate, said step of detecting including steps of:

detecting any signal present in at least one unused ones of said wavelength division slots at predetermined time delays; and

subtracting said signal detected in the previous step from said displaced spectral components according to said code in order to recover said data.

19. The method as claimed in claim 10, wherein said code utilizes fewer than all of said wavelength division slots and a bit time slot is used which is shorter than a bit time slot used when all of said wavelength division slots are utilized, whereby a shorter code length may be used to achieve a higher bit rate.

20. A method of fast frequency hopping spread spectrum communication comprising the steps of:

generating a multi-frequency source signal occupying a wide frequency band;

modulating said source signal to encode data and occupy a predetermined fraction of a bit time slot at a transmitter end;

selecting a plurality of frequency division slots within said wide frequency band;

introducing, according to a code, a predetermined time delay in spectral components of said modulated source signal corresponding to each of said plurality of frequency division slots to displace said spectral components within said bit time slot;

transmitting said spectral components delayed according to said code over a medium shared by at least one other transmitter using said frequency division slots and a different code;

receiving said transmitted spectral components from said transmission medium, and detecting said temporally displaced spectral components according to said code to recover said data.