Performance analysis of an optimal file transfer protocol for integrated mobile satellite services

A file-transfer protocol based on the selective-repeat automatic-retransmission-request (ARQ) scheme has been developed for the Mobile Satellite Experiment (MSAT-X). In this protocol, each file is divided into packets, which are error-detected and acknowledge individually. A file can be transferred in either the open- or closed-end connection. In the open-end connection, the file is transmitted continuously according to the selective-repeat scheme until all packets are positively acknowledged; in the closed-end connection, each retransmission will initiate its own connection request. The relationship between the packet size and the average end-to-end delay in the mobile fading environment is investigated. The communications channel uses trellis-coded modulation with symbol interleaving, packet replication, and error detection. The packet error performance in such a channel is evaluated by simulation, and the optimal packet size for various operating conditions is derived, using the simulated results. It is shown that for a symbol-energy-to-noise ratio of 12 dB, each file should be divided into packets of length between 256 bits and 512 bits (excluding the overhead) to minimize the average end-to-end delay.