Single Carrier Frequency Domain Equalization In MIMO System

As the data rate has been continuously growing, along with the introduction of multiple-input multiple-output (MIMO) for broadband wireless communication systems, the impact brought by multi-path propagation in wireless channel is increasing. The dispersion encountered by data symbols in time domain causes significant inter-symbol interference, which is also indicated in frequency domain as more severe frequency-selective fading, and these characteristics of transmission channel largely determines system performances. Channel equalization is an effective technology that can be utilized to combat those negative features of radio channel. Since higher data rates would lead to higher complexity of implementation due to the increasing number of taps in time-domain equalization, frequency-domain equalization is proposed. With the help of more advanced digital signal processing techniques, equalization operation can be performed in frequency-domain instead of time-domain, which dramatically decreases the implementation complexity and gains enhanced system performances.Chapter 1 reviews MIMO system and space-time coding, besides some analysis on wireless channel characteristics. Chapter 2 studies the basic principles of channel equalization and investigates its implementation in time-domain and frequency-domain, with typical equalization algorithms being introduced.In chapter 3, a novel effective low-complexity single carrier frequency-domain equalization (SC-FDE) scheme in multiple-input multiple-output (MIMO) system is introduced under frequency selective channel. It contains the advantages of SC-FDE and the complexity decreasing in MMSE algorithm by frequency-domain QR (FD-QR) decomposition. Also a rearrangement is implemented according to signal to noise (SNR). So performance gain can be obtained from rearrangement, demodulation after detection and equalization on specific antenna. Simulation result shows that the proposed scheme can obtain a significant performance gain to the conventional MMSE algorithm.In chapter 4, a novel Frequency Domain Turbo Equalization (FD-TE) is proposed in multiple input multiple output (MIMO) systems, in which equalization is executed on Single Frequency Tone (SFT). It is proposed that received data from all receive antennas on one frequency tone are considered jointly, and then minimum mean square error (MMSE) equalization is implemented. This algorithm can reduce the calculation complexity greatly, and has the same performance as the conventional algorithms. After equalization, data from one transmit antenna on all frequency tones are processed together and transformed into time domain. Later, extrinsic Log-likelihood ratio (LLR) is calculated and sent to Soft-In Soft-Out (SISO) decoder. Theory and simulation prove that it can obtain the same performance with a low complexity.In chapter 5, An efficient frequency domain soft interference cancellation (FD-SIC) scheme is proposed for turbo frequency domain equalization (FDE) in multiple-input multiple-output (MIMO) system. At the transmitter, vertical-bell laboratory layered space-time (VBLAST) is suitable for multiple modulation and coding scheme (MCS) on different antennas, which can also enhance channel capacity. At the receiver, inter-antenna interference (IAI) is cancelled by prior information of data on other antennas from Soft-In Soft-Out (SISO) decoder at each iteration, which can improve the input signal to interference and noise ratio (SINR) of equalizer. Also conventional frequency domain Turbo equalization in MIMO system is derived. Then block (data of one transmit antenna) wise frequency domain minimum mean square error (MMSE) equalization is implemented, which utilizes prior information of all blocks. Symbol Log-likelihood ratio (LLR) is calculated from the output of equalizer. Simulation results show that the proposed scheme has better link performance than traditional algorithms.