Abstract :
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Wireless systems are expected to require high data rates with low delay and low bit-error-rate (BER).In such situations, the performance of wireless communication systems is mainly governed by the wireless channel environment. In addition, high data rate transmission and high mobility of transmitters and/or receivers usually result in frequency-selective and time-selective, i.e., doubly selective, fading channels for future mobile broadband wireless systems. Therefore, mitigating such doubly selective fading effects is critical for efficient data transmission. Moreover, perfect channel state information (CSI) is not available at the receiver. Thus in practise, accurate estimate of the CSI has a major impact on the whole system performance. It is also because, in contrast to the typically static and predictable characteristics of a wired channel, the wireless channel is rather dynamic and unpredictable, which makes an exact analysis of the wireless communication system often difficult. Channel state information (CSI) is required for the OFDM receiver to perform coherent detection or diversity combining, if multiple transmit and receive antennas are deployed. In practice, CSI can be reliably estimated at the receiver by transmitting pilots along with data symbols. This paper presents the channel estimation techniques in OFDM.
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