Information-Theoretic Methods for the Design and Evaluation of Adaptive Protocols for Direct-Sequence Spread-Spectrum Transmissions

Adaptation of the code rate and spreading factor for direct-sequence spread-spectrum packet radio transmissions provides much higher throughput than if the code rate and spreading factor are fixed. A low-complexity protocol for packet-by-packet adaptation can be obtained if receiver statistics that are developed during the demodulation of a packet are used to choose the code rate and spreading factor for the next packet. The design and evaluation of the protocol typically requires extensive simulations, especially for modern packet radio receivers that employ iterative decoding. We show that analytical methods based on Shannon capacity results greatly simplify the design of the adaptive protocol and provide good estimates of its throughput performance.