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Title: Adaptive resource allocation with packet retransmissions in OFDMA systems
Author: Liu, Xiaoyan
Awarding Body: University of Kent
Current Institution: University of Kent
Date of Award: 2011
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In orthogonal frequency division multiple access (OFDMA) systems, the delay of packets has a great impact on quality of service (QoS), especially for real-time transmission. The basic concept of resource allocation in an OFDMA system is to allocate a subcarrier to the user with the best channel condition in that sub carrier. However, when a retransmission technique is used, the packet delay of successfully transmitting failed packets may be quite large in conventional retransmission schemes. In this paper, the packet combining technique in the downlink OFDMA system is introduced in conjunction with frequency diversity to enhance the reliability of retransmissions and thus reduce the large time delay caused by retransmissions. The novel retransmission technique aims to reduce the maximum number of retransmissions for failed packets, while maximizing the throughput. Bit error rate (BER) and transmit power are constraints in the throughput maximization formulation. A suboptimal algorithm is proposed, in which the retransmitted packets have higher priorities to be given resources than new packets. At the receiver, failed and retransmitted packets are combined before detection by using maximal ratio combining (MRC). It is shown that the proposed retransmission scheme can reduce the maximum packet delay significantly, while maintaining the maximum throughput of the conventional retransmission schemes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available