Method and apparatus for demodulating trellis coded direct sequence spread spectrum communication signals
First Claim
1. A method for spread spectrum communication, the method comprising the steps of:
- performing binary phase-shift keyed (BPSK) despreading on a received quadrature phase-shift keyed (QPSK) signal;
demultiplexing the despread signal to form a BPSK data signal; and
recovering a pilot signal from the BPSK data signal.
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Abstract
A method and an apparatus for demodulating trellis coded direct sequence spread spectrum communication signals are provided. A transmitted QPSK signal is received. Binary phase-shift keyed (BPSK) despreading is performed on the QPSK signal. The BPSK despreading includes correlating the in-phase and the quadrature components of the received QPSK signal with independent PN sequences for the each of the in-phase and the quadrature components. The despread signal is then demultiplexed, and the pilot signal and the BPSK data signal are recovered. The recovered pilot signal is used to provide a channel phase estimate and a channel magnitude estimate. The recovered BPSK data signal is demodulated, despread, and decoded. The despreading and decoding includes determining a number of cross-correlation terms of the received signal using a number of transmitted biorthogonal Walsh sequences. The cross-correlation terms are used as the branch metrics in a maximum likelihood decoding algorithm. The branch metrics may be computed with a Fast Walsh Transform scaled in response to the channel phase estimate from the recovered pilot signal. The maximum likelihood decoding algorithm may be a Viterbi algorithm in which the optimum path is the path with the maximum accumulated branch metric. The decoding algorithm recovers and outputs a transmitted data bit sequence.
39 Citations
31 Claims
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1. A method for spread spectrum communication, the method comprising the steps of:
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performing binary phase-shift keyed (BPSK) despreading on a received quadrature phase-shift keyed (QPSK) signal; demultiplexing the despread signal to form a BPSK data signal; and recovering a pilot signal from the BPSK data signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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- 12. A receiver for use in spread spectrum communications, the receiver comprising a despreading device performing BPSK despreading on a received QPSK signal to generate a BPSK signal, wherein the received QPSK signal comprises a multiplexed BPSK data signal with an embedded pilot signal.
- 20. A spread spectrum communications system comprising a phase coherent receiver, wherein the receiver comprises a despreading device performing BPSK despreading on a received QPSK signal to generate a BPSK signal, wherein the received QPSK signal comprises a BPSK data signal and an embedded pilot signal.
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27. A computer readable medium containing executable instruction which, when executed in a processing system, causes the system to perform the steps for communicating signals comprising:
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performing binary phase-shift keyed (BPSK) despreading on a received quadrature phase-shift keyed (QPSK) signal; demultiplexing the despread signal to form a BPSK data signal; and recovering a pilot signal from the BPSK data signal. - View Dependent Claims (28, 29, 30, 31)
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Specification