Spread-Spectrum Access to Mixed Voice-Data Local Area Networks

The various issues relating to the use of direct-sequence (DS) spread-spectrum (SS) modulation as access protocols for a local computer network are investigated. Voice and data messages having different traffic characteristics are packetized and the information bits DPSK modulated, after which spreading by the DS gives the waveform to be transmitted. Each node within the network will have a SS modem, to which all kinds of voice and data sources of different rates can be connected. Each node will be characterized by a certain DS code, thus getting security as a fringe benefit. Except for the code circuit, all SS modems will look the same; moreover, all the DS signals transmitted will have the same spectral properties, thus achieving uniformity and modularity of signals and equipments throughout the network. Among the performance criteria, we choose the signal-to-noise ratio (SNR) at the demodulator, the packet delay, the probability of correct packet detection, and the useful throughput. A new definition is suggested for the network efficiency and all performance criteria for the proposed network are compared to those of a classic FDMA/ALOHA-type network under the same circumstances.