Abstract: A TDMA cellular mobile radio system has at least one network control unit, at least one radio transceiver, and at least one multiplexor for multiplexing and demultiplexing digitally encoded and compressed speech data transmitted between the network control unit and radio transceiver. The bandwidth of the speech data is reduced through compression. The bandwidth of the speech data required on a radio transceiver side of the multiplexor is further reduced by buffering the speech data arriving at the multiplexor at a relatively high modulation rate, retransmitting the buffered speech data at a relatively lower modulation rate, buffering the speech data arriving from the multiplexor at a relatively lower modulation rate, and retransmitting the buffered speech data at a relatively higher modulation rate.

Abstract: In a base station of a mobile cellular telephone system of the type having time division multiple access (TDMA) channels, a radio frequency test loop is established between a predetermined downlink channel of a base station transmitter and a predetermined uplink channel of a base station receiver. The test loop is in real time, thereby eliminating the time offset of the radio channels used for communications. The radio frequency test loop includes a circuit for transposing the frequency of the carrier signal from the transmitter to a frequency that can be received by the receiver. The signal having the transposed frequency is used in tests for determining values such as bit error rate (BER), transmission signal level, or reception sensitivity.