Wireless multimedia networks: cross-layer access protocols based on sequential opportunistic decoding (SOD)

Spread spectrum (SS) solutions offer well understood advantages to wireless networking, e.g., robustness to noise and interference, concurrent asynchronous transmissions, effective power and transmission rate control mechanisms. One of the authors' recent advances in this field makes it possible to take SS solutions to the next performance level, i.e., sequential opportunistic decoding, or SOD for short. SOD is based on transmitting data symbols multiple times within the frame using non-orthogonal partial signature waveforms or mini-frames. Depending on the received instantaneous signal-to-interference-plus-noise ratio (SINR), a given subset of such mini-frames may suffice to reliably decode the data symbols. The best performing subset contains mini-frames that are received under better-than-average SINR channel conditions - i.e., these are referred to as the opportunistic mini-frames. By instantaneously controlling the number of mini-frames transmitted, SOD also offers distributed adaptable processing gain. The objective of this report is to propose cross-layer medium access control (MAC) protocols based on SOD. These protocols are especially suited to operate in a crowded radio spectrum, e.g., when multiple WLANs and/or wireless sensor networks coexist in the same radio space, possibly supporting multimedia applications. This unique advantage originates from the integration of two sub-layers. The lower sub-layer (SOD-MAC) applies the SOD adaptable processing gain to contain both the level of interference in the radio channel and network latency. It also minimizes the power consumption at the node and supports multiple c1asses of service. The upper sub-layer (ARQ-MAC) enables statistical multiplexing of an unbounded number of attempts of frame transmission generated by uncoordinated active nodes and it provides the automatic retransmission request (ARQ) capabilities. In essence, the uniqueness of these cross-layer access protocols is their ability to achieve efficient statistical multiplexing of traffic generated by uncoordinated nodes while containing the level of interference in the radio channel. The challenge is to combine frame retransmission schemes and SOD adaptable processing gain strategies in the most effective way, while keeping the access protocols in the stable region. The payoff is the ability to: increase the radio channel utilization, contain network latency, reduce energy consumption at the wireless node, and provide a QoS platform for both real-time and datagram traffic.