Various retransmission schemes for wireless communication systems have been used to improve performance such as reliability and throughput. Each retransmission scheme is designed to improve the performance according to characteristics of each layer of protocol stacks, such as delay components and error control. Recently, related works exploit the concept of cross-layered design to improve the data transmission performance. The cross-layered retransmission scheme is designed for performance improvement at the wireless access networks. Especially, a cross-layered retransmission scheme has been proposed to maximize the spectral efficiency by combining a retransmission scheme and adaptive modulation and coding (AMC). However, the previous works have not account the end-to-end performance between end-terminals such as user equipment (UE) and application server. Therefore, this dissertation presents advanced cross-layered retransmission schemes considering the end-to-end performance for improving user-perceived performance and wireless resource efficiency.
The first proposed cross-layered retransmission scheme is an application-aware modulation and coding scheme (MCS) level selection method. The application-aware MCS level selection method selects an MCS level depending on the service characteristics. The proposed method adjusts a target PER according to the type of application. To adopt different target PER according to service type, the target PER is derived by using the target packet loss rate (PLR) at the application layer. Simulation results show that the proposed method improves the efficiency of the wireless channel resource in comparison with an existing cross-layered retransmission scheme.
The second proposed cross-layered retransmission scheme is novel MCS level selection method considering the throughput at the transport layer to improve the end-to-end performance. To obtain the end-to-end performance, the analytical model of the delay and the throughput at the transport layer are derived when a system uses a cross-layered retransmission scheme and the TCP as the reliable transmission protocols. The proposed method adopts new criteria for MCS level selection by considering the end-to-end performance. The results of numerical simulations show that the proposed method improves the throughput at the transport layer as compared with existing ones. This verifies that the existing methods for maximizing wireless channel utilization may be inefficient in terms of the throughput at the transport layer.
