Efficiency of packet reservation multiple access

Packet-reservation multiple access (PRMA) is viewed as a merger of slotted ALOHA and time-division multiple access (TDMA). Dispersed terminals transmit packets of speech information to a central base station. When its speech activity detector indicates the beginning of a talkspurt, a terminal contends with other terminals for access to an available time slot. After the base station detects the first packet in the talkspurt, the terminal reserves future time slots for transmission of subsequent speech packets. The influence of several variables on PRMA efficiency, defined as the number of conversations per channel, is examined. The number of channels is the ratio of transmission rate to speech coding rate. It is found that with 32-kb/s speech coding and 720-kb/s transmission (22.5 channels), PRMA supports up to 37 simultaneous conversations, or 1.64 conservations per channel. The number of conversations per channel is at least 1.5 over a wide range of packet sizes (8 ms of speech per packet to 34 ms) and for all systems with 16 or more channels (transmission rate >or=512 kb/s, with 32-kb/s speech coding). Other factors studied are the sensitivity of the speech activity detector, the retransmission probability of the contention scheme, and the maximum time delay for the transmission of speech packets.<
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