Pilot Insertion Rate for SC-FDE Systems Employing Subspace-Based Channel Estimation

Blind or semi-blind channel estimation techniques, such as subspace decomposition, often use second order statistics which can provide channel estimates that are multiplied by an unknown complex constant, known as the ambiguity. Determination of this ambiguity can be achieved by the insertion of a small number of pilot symbols within a data block. The goal of this paper is to investigate the bit error rate performance of single carrier frequency domain equalization (SC-FDE) based transmissions using different pilot insertion rates, with the goal of determining the ambiguity without sacrificing spectral efficiency. Using Monte Carlo simulation, our results show, for the conditions presented in this paper, the insertion of 4 pilot symbols per 64 symbol block (or a ratio of 1 pilot per 15 information symbols) achieves a BER of 10^-3 with a power loss of 1dB or 1.5 dB (depending on the channel order) compared to a system with perfect ambiguity resolution.