Sounding reference signal pattern design for time division duplex multiple-input multiple-output and orthogonal frequency division multiplexing systems

In the long-term evolution (LTE) time division duplex (TDD) systems, base stations (BSs) use uplink sounding reference signals (SRSs) to estimate downlink channel state information (CSI) for downlink beamforming transmissions. In the current SRS pattern scheme, because SRSs of up to eight users are multiplexed on the same time-frequency resources, there exist mutual interferences among these SRSs over fading channels. Thus, the current scheme impacts the estimation accuracy of CSI and degrades the beamforming performance. Based on the characteristics of TDD systems, the authors propose a SRS pattern scheme, in which each user sends SRSs only on the allocated bandwidth instead of on full bandwidth as in the current LTE TDD systems, to eliminate the interferences among SRSs. Simulations show that the proposed scheme outperforms the current scheme in the estimation accuracy for various frequency-selective and time-selective fading channels. In addition, compared with the current SRS pattern scheme, the proposed SRS pattern scheme is robust to frequency-selective channels, and does not be impacted by the timing offset, and provides the flexibility for the choice of channel estimator at the BS side.