Tree-based backward pilot generation for sparse channel estimation

A scheme of tree-based backward pilot generation for sparse channel estimation in orthogonal frequency division multiplexing (OFDM) systems is proposed. Instead of straightforward searching for the best from all possible pilot subsets, the scheme iteratively removes a subcarrier from all OFDM subcarriers in a backward manner. At each time, every subcarrier is tested by deleting it and calculating the coherence of the resulting matrix, where the subcarrier with the smallest coherence is picked up. Finally the subcarriers left make up the optimal pilot subset. Considering the greedy essence of the scheme, a tree structure is also incorporated to avoid the locally-optimal but globally-incorrect selections. Simulation results demonstrate that the proposed scheme can obtain substantial improvement for sparse channel estimation.