EFFICIENCY OF PACKET RESERVATION MULTIPLE ACCESS

Packet reservation multiple access (PRMA) can be viewed as a merger of the slotted ALOHA protocol 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. This paper examines the influence of several variables on PRMA efficiency, defined as the number of conversations per channel. The number of channels is the ratio of transmission rate to speech coding rate. For example, we find 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 conversations per channel. The number of conservations 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 greater-than-or-equal-to 512 kb/s, with 32 kb/s speech coding). Other factors studied in this paper 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.