SC-FDMA user pairing and frequency allocation with imperfect channel state information

We consider user pairing for a single-carrier frequency-division multiple-access (SC-FDMA) transmission in the uplink of a Long Term Evolution (LTE) system. Two single-antenna users 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 for channel acquisition and transmitted with interleaved frequency-division multiple-access (I-FDMA). In channel state acquisition, the subcarriers not included in the channel sounding procedure should be taken into account by interpolation in frequency direction in a first step. Then a prediction in time direction for the time instant of the considered subframe is required. Channel interpolation and prediction are revisited in this paper, and the influence of channel interpolation and prediction errors on the achievable data rate 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 always beneficial for static or slowly moving users. However, for high user velocity the performance approaches that of random pairing and frequency allocation or becomes even worse.