Adaptive Channel Estimation and Equalization in Frequency Domain Based on Superimposed Pilot Technique for Vehicular OFDM Communications

Abstract

OFDM is consider a promise immune system against the Inter-Symbol Interference (ISI). However, in vehicular scenario it will be no longer robust against to the fast variation of the channel response within the time, these variation as result of the certain movement between transmitter and receiver with a certain speed and Doppler frequency that mainly degrade the system performance. In this paper we present a low computational complexity channel estimation and equalization implemented in frequency domain for lessening the effect of (ISI) in multipath fast fading channel environment. The proposed technique was successive in fast tracking the channel variation and adjust the coefficient of adaptive algorithm recursively by using Recursive Least Square (RLS) adaptive algorithm and a Superimposed Training Sequence (STS) for channel estimation purpose. The implementing OFDM with (STS) instead of the conventional pilot sequence avoids the use of frequency multiplex training pilots with the transmitted data symbols that reflect positively in saving system bandwidth. System were simulated over high vehicular speed starts from 50 km/h (31 mph) to 100 km/h (62 mph).