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Abstract

Apparatus and a method for transmitting a direct sequence, spread spectrum communication system signal. A transmitter (10) that receives a variable data rate information bearing input signal from a digital data source (12) includes a forward error correction encoder (80) that provides redundancy and an interleaver (82) that rearranges the input data. The forward error correction encoder and interleaver minimize the effect of errors that arise in the propagation of the transmitted signal. The output of the interleaver is applied to the input of a Hadamard encoder (84), which converts data words from the interleaver into one of N orthogonal codes, producing a Hadamard signal that varies at a bit rate that changes as the data rate of the information bearing signal varies. A pseudorandom number code generator (16) produces a code signal comprising a pseudorandom sequence of chips supplied at a constant chip rate. The Hadamard signal is input to a direct sequence (DS) modulator that modulates the information bearing signal with the code signal, using an integer number (greater than one) of chips to modulate each bit of the Hadamard signal. As the data rate of the information bearing signal varies, the number of chips per bit of the Hadamard signal is varied so as to minimize variations in the chip rate of the DS modulated signal. The transmitter is preferably combined with a receiver (29) in a transceiver. The receiver demodulates a received signal, and correlates it with a code signal from a pseudorandom number code generator (40) corresponding to the pseudorandom number code generator in the transmitter. The receiver also includes a Hadamard decoder (94), deinterleaver (96), and forward error correction decoder (98). A frequency hopping capability is optionally provided.

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