The Effect of Pilot Bit Arrangement on OFDM System Performance in Pilot Based Channel Estimation

Abstract

In this study, the effect of pilot bit placement on an OFDM system performance with comb-type based channel estimation was investigated. For this, OFDM simulator was created by using the MATLAB programming language. The estimation of the three different frequency selective channels at pilot frequencies is based on LS (Least Square) while the channel interpolation is done using low-pass interpolation. The pilot ratio (ratio of pilot bits to data bits, PR) that gives the lowest bit error rate (BER) is determined as the Optimum Pilot Ratio (OPR) through the simulator for the three different frequency selective channels. Unlike the previous studies, we observe that the change in OPR dependent on channel profile and number of subcarriers. When number of subcarriers decreased, OPR increased while the distance between pilot bits remained the same. Therefore it was concluded that OPR is expressed best with (Delta f) (OPR) (optimum pilot spacing). Since (Delta f) (OPR) related to interval that channel experience flat fading, the relationship between the channel coherence bandwidth (BC) and (Delta f) (OPR) was investigated. Simulation results show that, there is a linear relationship [(Delta f) (OPR)congruent to 0.65B(C, 0.9)] between the coherence bandwidth with 0.9 (B-C,B- 0.9) correlation coefficient and (Delta f) (OPR). Using such a relationship, OPR can be set easily by a single variable channel parameter for different frequency selective channels.