Uplink Channel Sounding in TDD-OFDM Cellular Systems

In this paper, we consider uplink channel sounding in time division duplex (TDD) orthogonal frequency division multiplexing (OFDM)-based cellular systems. The channel information provided by uplink sounding may be necessary to exploit closed loop transmission techniques in TDD-OFDM systems. However, conventional sounding schemes may suffer from large sounding overhead, significantly restricting the number of sounding users due to the resource shortage. To reduce the sounding overhead, the proposed scheme transmits sounding signal only through subchannels which are not highly correlated to each other. The whole channel information can be estimated from the partial one by exploiting the channel correlation in the frequency domain. Thus, the proposed scheme allows a larger number of users to transmit the sounding signal, while making the base station employ closed loop transmission techniques with the use of whole channel information. Finally, simulation results show that the proposed scheme noticeably improves the performance over conventional schemes in the presence of channel correlation.