Performance Analysis of Channel Estimation and Adaptive Equalization in Slow Fading Channel

Performance Analysis of Channel Estimation and Adaptive Equalization in Slow Fading Channel
Authors:R. VENKATA NARASIMULU, BRAHMADESAM. T. MADAV

Abstract: In this project we are going to mainly focus on the issue of optimal RS preamble design using the Cramer-Rao bound (CRB) averaged over the channel, which is assumed to be Rayleigh. We show that the optimal value of J is a trade-off between the multipath diversity gain and the number of unknowns to be estimated. In the case of correlated channel taps, we also show that uniform power loading of the active sub carriers is not optimal (in contrast with the uncorrelated case) and better power loading schemes are proposed. The proposed power loading schemes consist of allocating more power to activated carriers with higher signal-to-noise ratios. Simulation-based performance results of the maximum likelihood estimator support the CRBbased theoretical results. Carrier frequency offset (CFO) estimation is a key challenge in wireless systems employing OFDM modulation. Often, CFO estimation is carried out using a preamble made of a number, say J, of repetitive slots (RS). 

Keywords: Cramer-Rao Bound (CRB), Carrier Frequency Offset (CFO), Repetitive Slots (RS).

INTRODUCTION 

      Orthogonal frequency division multiplexing (OFDM) has become the standard of choice for wireless LAN’s such as IEEE 802.11a, and is being considered for several IEEE 802.11 and 802.16 standards. The popularity of OFDM arises from the balanced transceiver complexity, and the time-frequency granularity that it offers. However, synchronization continues to be a critical challenge. This work focuses on carrier frequency offset (CFO) synchronization, assuming perfect frame and timing synchronization. Data-aided CFO estimation in current OFDM systems employs a preamble made of a number, say J, of repetitive slots (RS). This preamble is obtained using one OFDM symbol after deactivating all sub carriers except those whose frequencies are integer multiples of J. It has been shown that the RS-based CFO maximum likelihood (ML) estimator is identical to the null-sub carrier(NSC-)- based ML estimator in the absence of virtual sub carriers, which are the sub carriers at the edges of the allocated frequency band that are deactivated in order to avoid interference with adjacent systems. 

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