SC-FDMA User Pairing and Frequency Allocation with Imperfect Channel State Information

We consider user pairing for singe-carrier frequency-division multiple-access (SC-FDMA) transmission in the uplink of a Long Term Evolution (LTE) system. Two users, equipped with one antenna each, are multiplexed to the same time and frequency resource within one cell. A virtual multiple-input multiple-output (V-MIMO) system arises for each user pair if multiple receive antennas are employed at the base station. For user pairing and frequency allocation, knowledge about the channel state is necessary. According to the LTE standard sounding reference signals are used and transmitted with interleaved frequency-division multiple-access (I-FDMA). In channel state acquisition, first, the subcarriers not included in channel sounding should be interpolated in frequency direction. Then a prediction in time domain for the point in time of the considered subframe is required. Channel interpolation and prediction is revisited in this paper. Then the influence of channel interpolation and prediction errors on the capacity of the system with user pairing and frequency resource allocation is studied. Simulation results show that joint user pairing and frequency allocation combined with channel interpolation and prediction is beneficial for low speed and medium-to-high signal-to-noise ratio (SNR). For medium-to-high speed or low SNR, random pairing and frequency allocation is a better choice.