Hybrid reference signal multiplexing using combination of block spread and cyclic shift CDMA for uplink control signals in DFT-precoded OFDMA

This paper proposes a hybrid reference signal (RS) multiplexing scheme that employs a block spread (BS) and cyclic shift (CS) combination for the physical uplink control channel (PUCCH) in the Long-Term Evolution (LTE) uplink. In the proposed scheme, we give higher priority to BS multiplexing over the FFT blocks assigned to a RS within a slot than CS multiplexing. Hence, accurate channel estimation for coherent detection is achieved by shortening the despread interval in the frequency domain compared to the original multiplexing scheme using only CS to extract the channel estimate of each code channel. Computer simulation results show that, assuming the use of channel quality indicator (CQI) bits, the average received signal-to-noise power ratio (SNR) satisfying the required average block error rate when employing the proposed hybrid RS multiplexing is decreased compared to that for conventional RS multiplexing using only CS when the root mean square delay spread is longer than approximately 0.5 μsec particularly for a large number of multiplexed PUCCHs such as 12.