A Low-Cost Spread-Spectrum Packet Radio

Abstract

The goal of the Low Cost Packet Radio (LPR) Program funded by DARPA, via a contract through CECOM, Contract No. DAAK80-81-C-0213, and being developed by Hazeltine Corporation, is a packet radio unit with low cost, low weight, low volume, low power, and high reliability. The LPR consists of a digitally controlled spread spectrum radio and a microprocessor acting as a packet switch. It is to be used in support of experiments with large packet radio networks. The radio utilizes direct-sequence, spread-spectrum techniques using MSK modulation. A code-changeable, SAW matched filter is employed. It is followed by a decision-directed, SAW fading memory filter to provide synchronization, multipath accumulation, and demodulation reference functions. Two data transmission rates are provided at 100 kbps or 400 kbps. In order to improve the reliability of the network links, a convolutional encoder/sequential decoder with forward-error correction capability at three code rates has been incorporated. To achieve an undetected BER of 10-12, CRC is employed for both encoded and uncoded modes of operation. Besides the RF data link, the LPR provides an input/output data link at either low or high speed. The microprocessor system architecture has been optimized to maximize its bus bandwidth.