Retransmission optimization in DS-CDMA random access networks

Multimedia wireless services demand sophisticated signal processing to improve quality, and to reduce transmission cycle time. With more users everyday, the system limits capacity due to increased number of packet collisions that require retransmissions. An extensive research has been performed on optimizing system capacity by analyzing retransmission diversity in DS-CDMA random access based wireless systems. In this dissertation, we propose a retransmission optimization technique that uses adaptive retransmission control (ARC) with packet error control or diversity packet combining scheme. The benefit of using such system is the cost savings by reducing the retransmission cycle time and producing more capacity in the high traffic region. This dissertation has developed a theoretical background with simulation proofs that will allow wireless industries to plan and design such systems for deployment.; In ARC, we determine a backlog user threshold at which the system throughput for a given retransmission probability is maximum. At the threshold, the retransmission probability is adaptively changed according to the system state so that the throughput can be maintained at its maximum in the higher states. A packet error control scheme is added to perform a joint adaptation processing on ARC and block error correction coding (ECC) with code rate boundaries. ECC with optimal code rate increases the maximum peak conditional throughput for a given number of users and then ARC maintains the achieved highest throughput as much as possible during the higher system states. A diversity packet combining with ARC scheme is also analyzed to reduce the number of retransmissions required by exploiting the memory data of collided packets. Reducing the number of retransmissions reduces system response time and increases normalized system throughput. The proposed protocol utilizes the instantaneous received signal-to-interference-and-noise ratio (SINR) to control both the packet combining and ARC schemes. Numerical results show that ARC, joint control of ARC and ECC, and joint control of packet combining and ARC schemes can significantly increase the system capacity and maintain the performance very close to its optimum in the high traffic region.; The ARC scheme blocks backlog users to receive new packets from higher layers. Since the proposed system assumes unbuffered user terminals, any new arrival to backlog user terminals can not be transmitted. While blocking new transmissions from backlog users the system tries to clear out the backlog congestion by controlling packet retransmission probability. (Abstract shortened by UMI.)...