A protocol for adaptive multicast transmission in packet radio networks

Adaptation is required for efficient transmission in a wireless communications network because of the fluctuations in propagation conditions that occur on the links. In a half-duplex packet radio network, the use of unicast transmission typically permits the receiving radio to send packet-by-packet acknowledgments and include a small amount of feedback information in each acknowledgment. For multicast transmission in such a network, it is usually not feasible for all receiving radios to send packet-by-packet acknowledgments, so a receiving radio has fewer opportunities to provide feedback. We present a low-complexity adaptive multicast transmission protocol that compensates for time-varying propagation losses in a packet radio network by adjusting the modulation and coding. Simple receiver statistics furnish the necessary control information for the adaptive protocol; no channel estimation, training, or pilot symbols are needed. The protocol's throughput performance is evaluated for dynamic channels and compared with the throughput of hypothetical ideal protocols that are given perfect channel-state information. We demonstrate that our protocol performs nearly as well as the ideal protocols.