Frequency Domain Link Adaptation for OFDM-based Cellular Packet Data

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In order to be competitive with emerging mobile systemsand to satisfy the ever growing request for higher data rates, the3G consortium, 3rd Generation Partnership Project (3GPP), iscurrently developing concepts for a long term evolution (LTE) ofthe 3G standard. The LTE-concept at Ericsson is based onOrthogonal Frequency Division Multiplexing (OFDM) as downlink airinterface. OFDM enables the use of frequency domain linkadaptation to select the most appropriate transmission parametersaccording to current channel conditions, in order to maximize thethroughput and maintain the delay at a desired level.The purpose of this thesis work is to study, implement andevaluate different link adaptation algorithms. The main focus ison modulation adaptation, where the differences in performancebetween time domain and frequency domain adaptation areinvestigated. The simulations made in this thesis are made with asimulator developed at Ericsson.Simulations show in general that the cell throughput is enhancedby an average of 3% when using frequency domain modulationadaptation. When using the implemented frequency domain powerallocation algorithm, a gain of 23-36% in average is seen in theusers 5th percentile throughput. It should be noted that thesimulations use a realistic web traffic model, which makes thechannel quality estimation (CQE) difficult. The CQE has greatimpact on the performance of frequency domain adaptation.Throughput improvements are expected when using an improved CQE orinterference avoidance schemes.The gains with frequency domain adaptation shown in this thesiswork may be too small to motivat...