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In the Long Term Evolution (LTE) Time Division Duplex (TDD) systems, base stations use uplink Sounding Reference Signals (SRSs) to estimate downlink Channel State Information (CSI) for downlink beamforming transmissions. Because SRSs sent by up to 8 users are multiplexed on the same time-frequency resources, there exist mutual interferences among these SRSs over fading channels. Thus this scheme inevitably impacts the estimation accuracy of CSI and thereby degrades the beamforming performance. In recent years, wireless communication systems are evolving toward the cellular systems based on Multiple-Input Multiple-Output (MIMO) and Orthogonal Frequency Division Multiplexing (OFDM) techniques due to the strong demand of broadband mobile services.
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