We revisit the pilot contamination problem using the LTE pilot frame structure, and perform channel estimation in the time domain using Zadoff–Chu pilot sequences. Sequences in each cell occupy the same time slot, multiple subcarrier frequencies, and are orthogonal in time via properly chosen cyclic shifts. Sequences in multiple cells are chosen from a pool of non-orthogonal yet distinguishable sequences through their root indices. Exchanging root indices among cells allows a given cell to reconstruct sequences used in neighboring cells and to estimate interfering channels as the number of channel taps is usually limited, thus mitigating pilot contamination. Furthermore, we propose a greedy selection algorithm to find combinations of sequences that further reduce the channel estimation mean-square-error. The greedy algorithm exhibits increasing gains with increasing signal-to-noise-ratios and sequence lengths.
['Samer Bazzi', 'Wen Xu']
Mitigating Inter-Cell Pilot Interference via Network-Based Greedy Sequence Selection and Exchange