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.