SPREAD-SPECTRUM RECEIVER WITH FAST M-SEQUENCE TRANSFORM

• US 20070195862A1
• Filed: 03/03/2007
• Published: 08/23/2007
• Est. Priority Date: 02/28/2000
• Status: Active Grant

• Current Assignee: Comtech Mobile Datacom Corporation (Comtech Telecommunications Corporation)
• Original Assignee: AeroAstro, Inc.
• Inventors: McDermott, Scott, Stafford, James, Seng, William
• Granted Patent: US 7,433,391 B2
• Time in Patent Office: Days
• US Class Current: 375/147
• CPC Class Codes: H04B 1/7093 Matched filter type
• CPC Class Codes: H04B 2001/70935 using a bank of matched fileters, e.g. Fast Hadamard Transform

Abstract

A receiving system dynamically searches a communications band for transmissions of messages having the same nominal communications parameters, including the use of the same spreading code, but having potentially different specific frequencies and code-phases. The receiver samples the communications band at each code-phase of the spreading code over a span of down-converted transmission frequencies. When a message element is detected at a particular code-phase and frequency, it is forwarded to a demodulator that demodulates the message and sends it to its intended destination. This technique allows each transmitter to be independent of the receiver. In a preferred embodiment of this invention, a Fast M-Sequence Transform (a Walsh-Hadamard Transform) is used to determine the power level at multiple code-phases at a given frequency in parallel, thereby substantially reducing the time required to search for transmissions at each discrete code-phase.

Claims

1. A receiving system comprising:

a receiver that is configured to receive a composite signal from a plurality of transmitters, each transmitter providing a transmitted signal at a different code-phase of a plurality of code-phases of a spreading code,

a down-converter that is configured to provide a baseband signal from the composite signal, and

a phase detector that is configured to identify the code-phase corresponding to each transmitter of the plurality of transmitters,

wherein the phase detector is configured to identify the plurality of code-phases by applying a plurality of samples of the baseband signal to a Fast M-Series transform that is configured based on the spreading code.

2. The system of claim 1, including

a plurality of demodulators that are each configured to demodulate the baseband signal to provide a decoded data item based on each code-phase of the plurality of code-phases, and

a plurality of queues, each queue of the plurality of queues being configured to receive the decoded data-item from a corresponding demodulator of the plurality of demodulators.

3. The system of claim 2, including

a queue controller that is configured to:

receive identification of the code-phases from the plurality of phase detectors,

allocate a demodulator to each identified code-phase, and

control the demodulator to use the identified code-phase for demodulating the baseband or further baseband signal.

4. The system of claim 3, wherein

the queue controller is configured to:

detect a drift of the identified code-phase, and

control the demodulator to use a modified code-phase based on the drift.

5. The system of claim 2, including

a plurality of down-converters that are configured to provide a plurality of further baseband signals based on a variance about a nominal transmission frequency common to the plurality of transmitters, and

a plurality of phase detectors, each phase detector being configured to identify further pluralities of code-phases corresponding to a plurality of further transmitters by applying a plurality of samples of each corresponding further baseband signal from a corresponding demodulator of the plurality of demodulators to a Fast M-Series transform that is configured based on the spreading code.

6. The system of claim 5, wherein

the plurality of demodulators is configured to demodulate the plurality of further baseband signals to provide a plurality of further decoded data items based on each code-phase of the further pluralities of code-phases, and

the plurality of queues is configured to receive the further decoded data-items from a corresponding further demodulator of the plurality of demodulators.

7. The system of claim 6, including

a queue controller that is configured to:

receive identification of the code-phases and further code-phases from the plurality of phase detectors,

allocate a demodulator to each identified code-phase and further code-phase, and

control the demodulator to use the identified code-phase or further code-phase for demodulating the baseband or further baseband signal.

8. The system of claim 1, including

a plurality of down-converters that are configured to provide a plurality of further baseband signals based on a variance about a nominal transmission frequency common to the plurality of transmitters, and

a plurality of phase detectors, each phase detector being configured to identify further pluralities of code-phases corresponding to a plurality of further transmitters by applying a plurality of samples of each corresponding further baseband signal from a corresponding demodulator of the plurality of demodulators to a Fast M-Series transform that is configured based on the spreading code.

9. The system of claim 8, including

a plurality of demodulators that is configured to demodulate the baseband signal and the plurality of further baseband signals to provide a plurality of decoded data items based on each identified code-phase of the plurality of code-phases and further pluralities of code-phases, and

a plurality of queues that is configured to receive the decoded data-items from a corresponding demodulator of the plurality of demodulators.

10. The system of claim 9, including

a queue controller that is configured to:

receive the identified code-phases from the plurality of phase detectors,

allocate a demodulator to each identified code-phase and further code-phase, and

control the demodulator to use the identified code-phase for demodulating the corresponding baseband or further baseband signal.

11. The system of claim 1, wherein

the composite signal is received from a satellite system that receives the transmitted signals from the plurality of transmitters.

12. The system of claim 11, wherein

the plurality of transmitters are configured to provide data from at least one of:

a biological sensor, a chemical sensor, and a nuclear sensor.

13. The system of claim 12, wherein

the plurality of transmitters are distributed over a geographic area.

14. The system of claim 1, wherein

the receiver is common to the plurality of transmitters, and operates independent of each transmitter.

15. The system of claim 14, wherein

the demodulator operates independent of each transmitter.

16. The system of claim 1, wherein

each of the plurality of transmitters is configured to operate autonomously.

17. The system of claim 16, including the plurality of transmitters.

18. The system of claim 1, including

a satellite system that receives the transmitted signals from the plurality of transmitters and provides the composite signal to the receiver.

19. The system of claim 18, wherein

the satellite system is configured to operate in at least one of:

a bent-pipe configuration, and a store-and-forward configuration.

20. The system of claim 1, including

a transform that is configured to identify a time of transition of data within an epoch of the spreading code.

21. A method comprising:

receiving a composite signal that includes a plurality of transmission signals from a plurality of transmitters, each transmitter of the plurality of transmitters being configured to operate at a common nominal transmit frequency using a common spreading code,

down-converting the composite signal to form one or more baseband signals,

processing the one or more baseband signals to provide a plurality of identified code-phases corresponding to the plurality of transmission signals, and

demodulating the one or more baseband signals using each identified code-phase of the plurality of identified code-phases to form a plurality of messages corresponding to the plurality of transmission signals,

wherein the processing of the one or more baseband signals includes

providing a plurality of samples of each of the one or more baseband signals to one or more Fast M-Series transforms that are configured based on the spreading code.

22. The method of claim 21, including

detecting at least one of a frequency drift and code-phase drift of at least one of the transmission signals, and

adjusting the demodulating of the one or more baseband signals to maintain a correspondence between the message and the transmission signal.

23. The method of claim 21, wherein

the one or more baseband signals are formed based on an estimated variance of frequencies among the plurality of transmission signals.

24. The method of claim 21, wherein

receiving the composite signal includes receiving the composite signal from a satellite system.

25. The method of claim 21, wherein

the plurality of messages correspond to messages related to detection of at least one of:

biological agent, a chemical agent, and a nuclear emission.

26. The method of claim 21, wherein

the receiving of the composite is independent of each of the plurality of transmissions.

27. The method of claim 21, wherein

the processing of the one or more baseband signals is independent of each of the plurality of transmissions.