OFDM Baseband Receiver Design for Wireless Communications

6

Channel Estimation and Equalization

Channel estimation provides information about distortion of the transmission signal when it propagates through the channel. This information is then used by equalizers so that the fading effect and/or co-channel interference can be removed and the original transmitted signal can be restored.

6.1 Introduction

Channel estimation plays an important role in a communication receiver. In order to mitigate hostile channel effects on the received signal, precise channel estimation is required to provide information for further processing of the received signal. Channel estimators can be categorized as non-data-aided or data-aided. Non-data-aided or blind channel estimators estimate channel response by statistics of the received signals. No specialized reference (training) signals are needed and the transmission efficiency is retained for systems using such channel estimation schemes. However, without precise knowledge of the transmitted signals, a large number of data must be collected in order to obtain reliable estimation. On the other hand, the data-aided channel estimators require known reference (training) signals to be transmitted. Rapid and accurate channel estimation can be achieved by comparing the received and transmitted reference signals. A sufficient number of such reference signals must be inserted according to the degree of channel variation, namely coherence time and coherence bandwidth of the channel under estimation.

OFDM has been ...