Half-duplex modem without turnaround delay

Claim 1

A modem for transmitting and receiving data signals over a data channel in a half-duplex mode comprising: (a) a transmitter section having: (1) preamble means for generating preamble bits; (2) input means for receiving data bits in successive data streams from a data source, each data stream being separated from a succeeding data stream by a time period T D ; (3) encoding means for encoding one of said preamble bits and data bits into encoded signals; (4) transmitter timer means for measuring said time period T D ; (5) switch means for feeding said preamble bits to said encoding means only when a time period T D preceding a particular data stream as measured by said transmitter timer exceeds a preset level, said encoding means generating encoded preamble signals prior to generating encoded data signals corresponding to bits of said particular data stream; and (6) modulating means for modulating said encoded signals in signal stream corresponding to said data streams; and (b) a receiver section for receiving data from said channel in signal streams having: (1) demodulating means for demodulating received signals to generate domodulated signals; (2) decoding means for decoding said demodulated signals; and (3) receiver timing means for determining a time interval between said received signal streams, and for generating a retrain signal when said time interval exceeds said preset level for retraining said demodulator.