OFDM Channel Estimation in Radio over Fiber Distributed Antenna System

The radio over fiber (RoF) distributed antenna system (DAS) has been chosen as one of the candidate technologies for next generation communication system. In RoF, the radio remote unit (RRU) utilizes orthogonal frequency division multiplexing (OFDM) transmission, because of its increased data rate and its resilience to multipath fading. Also in optical fiber system, the optical components cannot be operated at high power, so their power needs to be reduced before inputting over the fiber. In OFDM transmission, it is necessary to estimate the channel to overcome the distortion caused by channel fading. The widely used channel estimation techniques are least square (LS) method and minimum mean square error (MMSE) method. However, they are preferred one over another for different scenarios. In this paper, we analyze and present modification in LS and MMSE method compromising between their complexity and performance for OFDM transmission in RoF distributed antenna system. We evaluate their performance through mean square error and bit error rate. We find that depending upon the estimator complexity, there can be considerable gain in signal to noise ratio (SNR) over the LS estimator. This considerable gain adds to the advantage of sending the signal with low power over the fiber before transmitting from RRU antenna.