ARQ schemes for data transmission in mobile radio systems

The problem of providing data communications over a land mobile radio channel is considered, taking into account error detection combined with retransmission on request as a means of obtaining reliability in digital data transmission. The considered systems are referred to as automatic RQ (repeat-request) or ARQ. It is pointed out that the distinguishing features of a land mobile radio (LMR) system, as far as the ARQ protocol is concerned, are a frequency or pair of frequencies shared by a large population of half-duplex users which cannot transmit and receive simultaneously. A description is presented of those variations of ARQ which are adaptable to an LMR system. A new channel model for a fading LMR channel is developed, and several ARQ protocols and some new protocol combinations are described. The relationships are developed for a description of the various protocols in terms of channel failure probabilities. Undetected error probabilities are developed and compared.