Analytical framework for simultaneous MAC packet transmission (SMPT) in a multicode CDMA wireless system

Stabilizing the throughput over wireless links is one of the key challenges in providing high-quality wireless multimedia services. Wireless links are typically stabilized by a combination of link-layer automatic repeat request (ARQ) mechanisms in conjunction with forward error correction and other physical layer techniques. In this paper, we focus on the ARQ component and study a novel class of ARQ mechanisms, referred to as simultaneous MAC packet transmission (SMPT). In contrast to the conventional ARQ mechanisms that transmit one packet at a time over the wireless air interface, SMPT exploits the parallel code channels provided by multicode code-division multiple access. SMPT stabilizes the wireless link by transmitting multiple packets in parallel in response to packet drops due to wireless link errors. While these parallel packet transmissions stabilize the link layer throughput, they also increase the interference level in a given cell of a cellular network or cluster of an ad hoc network. This increased interference reduces the number of traffic flows that can be simultaneously supported in a cell/cluster. We develop an analytical framework for the class of SMPT mechanisms and analyze the link-layer buffer occupancy and the code usage in a wireless system running some form of SMPT. Our analysis quantifies the tradeoff between increased link-layer quality of service and reduced number of supported flows in SMPT with good accuracy, as verified by simulations. In a typical scenario, SMPT reduces the probability of link-layer buffer overflow by over two orders of magnitude (thus enabling high-quality multimedia services, such as real-time video streaming) while supporting roughly 20% fewer flows than conventional ARQ. Our analytical framework provides a basis for resource management in wireless systems running some form of SMPT and optimizing SMPT mechanisms.