Abstract: A spread spectrum communications system includes an encoder for differentially encoding a spread spectrum spreading code sequence in accordance with an input data signal. Each chip of the spreading code sequence is inverted, or not inverted, relative to the polarity of a corresponding chip of the spreading code sequence a fixed time delay previously, depending on whether the input data is a logic one or zero, respectively. At the receiver, the data is recovered in a differential data decoder wherein the presently received chip of the spread spectrum signal and a corresponding previously received chip of spread spectrum signal, received a fixed time delay previously, are compared one chip at a time. Since it is the spreading code sequence that is differentially encoded and differentially decoded, there is no need for a synchronized code sequence generator at the receiver, and data synchronization is achieved after one cycle time of the received spread spectrum spreading code sequence has elapsed.
Abstract: A multiple phase PSK demodulator for use in a spread spectrum communication system includes a plurality of baseband frequency converters coupled to a corresponding plurality of differential decoders in order to directly recover the encoded PSK data. The logic outputs of the plurality of differential data decoders are coupled to a majority vote logic circuit for determining the correct logic level output signal of the plurality of differential data decoders. In another embodiment, a three phase resistive network is used to convert the two phase quadrature output of two baseband frequency converters to plural phase outputs coupled to the inputs of a corresponding plurality of differential data decoders.
Abstract: A code division multiplex system for use in a spread spectrum communication system utilizes selectable length spread spectrum spreading code sequences. At the encoder, one of a pluraluty of a spread spectrum spreading code sequences having a given fixed length is selected for differential encoding in accordance with the input data to be transmitted. At the receiver correlator, a selectable length differential decoder is set to be responsive to a spread spectrum spreading code sequence having a length substantially equal to the length of the encoded spread spectrum spreading code sequence.