Data transmission system with automatic repeat request

PCT No. PCT/GB87/00821 Sec. 371 Date Sep. 29, 1988 Sec. 102(e) Date Sep. 29, 1988 PCT Filed Nov. 19, 1987 PCT Pub. No. WO88/04496 PCT Pub. Date Jun. 16, 1988.A data transmission system comprising a plurality of radio stations, each station including a transceiver with associated encoding/decoding means for transmitting/receiving data, wherein data signals are transmitted as packets including one or more blocks of data encoded with an error correcting code, wherein each station is arranged automatically to issue a request for repeat of a packet of data should it receive a packet containing errors which cannot be corrected, and wherein should the error rate in received packets be more than a predetermined amount over a predetermined interval of data transmission, the system is arranged automatically to reduce the rate of data transmission within each packet and/or change the channel frequency.