Abstract: A local area network system using a code division multiple access method is provided. The system includes a repeater for generating a reference synchronizing signal to synchronize the system, transceivers, connected to the repeater via a sending line and a receiving line, and subscriber units, connected to each transceiver. Each transceiver includes a common synchronizing circuit section for replicating and regenerating a synchronizing signal, as a reference signal, which is equal to the reference synchronizing signal generated by the repeater. Each transceiver also has a transmitter for delaying the synchronizing signal in accordance with the specific number of each subscriber unit and the delay time attributed to the sending and the receiving lines, multiplying the delayed synchronizing signal by the signal obtained by level coding the data sent by the transmitter into M-ary data, and then transmitting multiplied data to the sending line.

Abstract: A hybrid companding delta modulation system is an improvement of adaptive delta modulation and is particularly suitable for coding a speech signal. It employs both syllabic and instantaneous companding schemes. The syllabic compandor provides a long term step size of the quantizer which varies relatively slowly by estimating either the envelope of slope or amplitude variation of the input signal. On the other hand, the instantaneous compandor adjusts the step size instantaneously according to a predetermined control logic in response to variations of the input signal. With the hybrid companding delta modulation system the dynamic range of the system can be made as large as the range of the input signal level. The signal-to-quantization noise ratio is improved over presently known adaptive delta modulation systems. Finally, the effect of channel errors is minimized.