An adaptive-transmission protocol for direct-sequence spread-spectrum packet radio networks

Wireless communication channels may change greatly from one transmission to the next due to variations in propagation loss and interference. The use of fixed transmission parameters for such channels results in wasted energy when channel conditions are good. Adaptation of the power, code rate, and symbol rate reduces energy consumption and interference caused to other systems. Such adaptation requires information about the characteristics of the channel, which is more difficult to obtain in a packet radio network or other mobile ad hoc network than in a typical cellular communication system. We present techniques to provide partial information about the channel state, and we describe and evaluate a protocol that uses this information to adapt the transmission parameters in a direct-sequence spread-spectrum packet radio network. The channel-state information consists of three statistics that are derived in different subsystems of the receiver. From these statistics, the receiver extracts information about the channel conditions which is provided to the transmitter in an acknowledgment packet or control packet. The performance of the adaptive-transmission protocol is compared to a system with fixed transmission parameters and to an adaptive protocol that is furnished with perfect knowledge of the channel state at the completion of each transmission.