Optimum Pilot Placement for Chunk-Based OFDMA Uplink: Time Direction Scenario

In this paper, we investigate the optimum pilot placement along time direction for the chunk-based OFDMA uplink. The proposed optimization is performed within a single chunk, where the channel estimation is based on the least-square linear interpolation. Unlike the state-of-the-art optimum pilot placements, the proposed scheme takes into account the impact of interpolation error in addition to the noise. It is established that in the presence of the large Doppler shift, the impact of interpolation error shows the dominative effect in the large SNR range, the optimum pilot spacing should be 1/radic3 of the chunk length regardless of the channel realization. However, in the most practical scenarios, the impact of the interpolation error is too small to affect the overall performance compared to the noise. Therefore, the optimization of pilot placement should be focused on minimizing the noise.