Please use this identifier to cite or link to this item: http://hdl.handle.net/10266/2865
Title: Analysis and Performance Evaluation of Reception Schemes for Correlated MIMO System
Authors: Singh, Simranjit
Supervisor: Khanna, Rajesh
Patterh, Manjeet Singh
Keywords: MIMO, FrFT, Correlated channels
Issue Date: 11-Aug-2014
Abstract: The rapid advancement in wireless communications has led to an increasing demand on the data rates for applications such as seamless high definition video streaming, video conferencing etc. As the bandwidth/frequency spectrum available for wireless systems is limited, all the demands have to be fulfilled within this spectrum only. This entails the development of bandwidth efficient wireless systems which can deliver higher data rates without requiring additional bandwidth. A very promising solution to this problem is the use of Multiple-Input Multiple-Output (MIMO) systems incorporating multiple antennas at the transmitter and receiver. MIMO systems effectively enable the use of spatial dimension in order to increase the data rate without imposing any bandwidth penalty on the system. Transmitting different data streams from different antennas enables the use of same spectrum for transmitting different data, i.e. the number of antennas is directly proportional to the data rate that can be achieved. This technique of increasing the data rate is called Spatial Multiplexing (SM) because it exploits the multiplexing gain. To achieve this, variety of receivers such as Zero Forcing (ZF), Minimum Mean Squared Error (MMSE), Vertical Bell Labs Layered Space Time (VBLAST) etc. have been developed for spatial multiplexing. The increase in capacity is true for a channel with rich scattering and antennas with sufficient spacing amongst them. However, with the size of wireless devices becoming smaller by the day, it is becoming difficult for the system designers to incorporate independent multiple antennas on the same device. This leads to correlation between different antennas, taking away the advantage of spatial dimension. Spatial correlation may significantly degrade the performance of a MIMO system. Firstly, the existing spatial multiplexing techniques are studied in detail. The error performance of these techniques is evaluated in uncorrelated and correlated fading channels. To complete the study, a brief analysis of computational complexity of various receivers is also done. Based on the error rate performance and complexity parameters, the MMSE receiver is selected. Secondly, a Fractional Fourier Transform (FRFT) based generic MMSE receiver is proposed for multiple antenna systems. Based on a recently proposed novel method for filtering signals in the fractional Fourier domains, the proposed receiver gives a lower mean square error (MSE) as compared to the conventional MMSE receiver. The proposed receiver is generic in the sense that it can be used with all systems irrespective of the antenna configuration. Since this dissertation is focused on the receiver side of wireless systems, first a receiver is proposed for Single-Input Multiple-Output (SIMO) systems as a fractional optimum combining diversity technique. Then a generalized receiver is proposed for MIMO systems as a fractional MMSE receiver. The bit error rate performance of the proposed receiver is studied in uncorrelated and correlated fading channels. Based on fractional domain filtering, improved channel estimation schemes are proposed for rapidly fading channels and block fading channels. To estimate a rapidly fading channel, an interpolation technique is used where pilot symbols are transmitted at equally spaced intervals. With the channel estimate known at pilot positions, the rest of the channel is estimated using interpolation. For block fading channels, pilot symbols are prefixed to the transmitted block. The channel estimated using prefixed pilots remains constant throughout the transmission block. Both the proposed techniques are shown to give better quality channel estimates than their respective conventional counterparts. In the last part of the dissertation, the error rate performance of the proposed fractional MMSE receiver is considered with Low Density Parity Check Coding (LDPC). Channel coding is often viewed as a smart way to reduce the errors in transmission and improving the link reliability. The reason for selecting LDPC codes is that they are powerful channel codes with excellent error performance but a low decoding complexity. There have been simulations that perform within 0.0045 dB of the Shannon limit using LDPC codes for an Additive White Gaussian Noise (AWGN) channel. The use of LDPC codes along with fractional MMSE improves the error performance of the fractional MMSE considerably.
Description: PHD, ECED
URI: http://hdl.handle.net/10266/2865
Appears in Collections:Electronic Theses & Dissertations @ TIET
Electronic Theses & Dissertations @ TIET

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