Channel estimation algorithms and their implementationsfor mobile receivers are considered in this paper.The 3GPP long term evolution (LTE) based pilot structureis used as a benchmark in a multiple-input multiple-output(MIMO) orthogonal frequency division multiplexing(OFDM) receiver. The decision directed (DD) space alternatinggeneralized expectation-maximization (SAGE)algorithm is used to improve the performance from that ofthe pilot symbol based least-squares (LS) channel estimator.The performance is improved with high user velocities,where the pilot symbol density is not sufficient. Minimummean square error (MMSE) filtering is also usedin estimating the channel in between pilot symbols. Thepilot overhead can be reduced to a third of the LTE pilot overhead with DD channel estimation, obtaining a ten percentincrease in data throughput. Complexity reduction andlatency issues are considered in the architecture design.The pilot based LS, MMSE and the SAGE channel estimatorsare implemented with a high level synthesis tool,synthesized with the UMC 0.18 μm CMOS technologyand the performance-complexity trade-offs are studied. TheMMSE estimator improves the performance from the simpleLS estimator with LTE pilot structure and has low powerconsumption. The SAGE estimator has high power consumptionbut can be used with reduced pilot density toincrease the data rate.
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