Channel Estimation and Frequency Synchronization for a Multi-Antenna Wimax System

This paper develops several issues related to a multiple input multiple output - orthogonal frequency division multiplexing (MIMO-OFDM) system based on IEEE 802.16d standard. This standard just proposes a typical SISO system, and leaves as optional the development of a multiple input - single output (MISO) 2 times 1 scheme employing Alamouti space-time codification (STC). Apart from comparing both systems in terms of data transfer rate and bit error rate (BER), the inclusion of a second antenna in the receiver is studied. Following exactly the preamble structure provided for fixed broadband wireless OFDM access (IEEE 802.16d), several scenarios are studied: single input - single output (SISO) systems, MISO systems, (both applying and not applying STC) and MIMO systems (both applying and not applying STC). Therefore this study can be considered as an extension to the wireless metropolitan area networks (WMAN) standard, known as Wimax, which just proposes two of these five scenarios. In all of these communication schemes two algorithms are compared to obtain an accurate channel estimation. The first one is a maximum likelihood (ML) estimator in the frequency domain (Fernandez-Getino Garcia, 2004) and the second one is a least squares (LS) estimator in the time domain (Balamurali, 2004). Both of them are studied in terms of mean squared error (MSE) of the estimation and BER at the receiver. Moreover, algorithms for frequency offset estimation are also developed and analyzed both for SISO and MIMO systems based on IEEE 802.16d standard.