BLIND CHANNEL ESTIMATION ENHANCEMENT FOR MIMO-OFDM SYSTEMS UNDER HIGH MOBILITY CONDITIONS

ABSTRACT In this paper, we propose an enhancement of a blind channel estimator based on a subspace approach in a MIMO OFDM context (Multi Input Multi Output Orthogonal Frequency Division Multiplexing

[[alternative]]System Evaluation, Simulation Platform Set Up and Baseband Circuit Implementation for Wireless Sensor Network

計畫編號：NSC93-2213-E032-023研究期間：200408~200507研究經費：515,000[[abstract]]本計畫分三年以實現無線感測網路之系統評估模擬平台建置與基頻電路研製。本計劃研 究子題如下： (A) IEEE 802.15.4 系統之分析及設計 1. 媒介擷取控制層與實體層間之介面設計 2. 系統架構的確定，系統規格及各子方塊之間之介面規格之訂定 3. 低功率基頻電路的設計及探討 4. 接收機技術研究(同步、通道等化、信號偵測等) 5. 利用 ADS 與 Matlab 以建立模擬平台 6. 傳送端與接收端低功率基頻電路之硬體實現 (B) IEEE 802.15.4a 系統之分析及設計 1. UWB 基本原理之研究與探討 2. UWB 傳送與接收基本技術之研究 3. 利用 ADS 及 Matlab 建立模擬平台，對 UWB 之架構模擬 4. UWB 基本方塊規格之訂定 5. 精確定位之研究 (C) IEEE 802.15.4 之MIMO 架構設計 1. MIMO 架構之演算法與架構之研究 2. MIMO 架構之用於IEEE 802.15.4 之通道效應之探討與研究 3. 利用MIMO 架構傳送MPEG-4 之效能探討 4. MIMO 架構之接收技術之研究 5. 利用 ADS 及 Matlab 建立性模擬平台以研究多頻帶的傳輸特性 6. 探討如何利用基頻電路的切換以達低功率而高速的信號傳送 (D) 通道分析及模型的建立 1. 通道傳送損失特性之分析 2. 路徑衰減及多重路徑之分析 3. 路徑衰減之經驗公式推導 4. 通道模型之建立 5. 通道等化器演算法之推導及分析(E) 模擬平台的建立 1. 利用 ADS 程式以建立基頻及 RF 端之模擬平台 2. 利用 Matlab 程式以建立基頻及 RF 端之模擬平台 3. 基頻及 RF 端 ADS 模擬平台的介面設計 4. 基頻及 RF 端 Matlab 模擬平台的介面設計 5. 系統特性的模擬及數據分析 (F) 測試平台的建立 1. IEEE 802.15.4 實體層各子方塊之 Verilog 程式燒錄至 FPGA 並測試 2. IEEE 802.15.4 實體層整合電路之 Verilog 程式燒錄至 FPGA 並測試 3. Mulit-Band 實體層之 Verilog 程式燒錄至 FPGA 並測試 4. IEEE 802.15.4 實體層 ASIC 之測試 5. IEEE 802.15.4 實體層 ASIC 與 RF 之整合測試 6. IEEE 802.15.4 實體層 ASIC 與 MAC 之整合測試 7. IEEE 802.15.4 實體層 ASIC , MAC 及 RF 之整合測試[[sponsorship]]行政院國家科學委員

Blind channel estimation and signal retrieving for MIMO relay systems

In this paper, we propose a blind channel estimation and signal retrieving algorithm for two-hop multiple-input multiple-output (MIMO) relay systems. This new algorithm integrates two blind source separation (BSS) methods to estimate the individual channel state information (CSI) of the source-relay and relay-destination links. In particular, a first-order Z-domain precoding technique is developed for the blind estimation of the relay-destination channel matrix, where the signals received at the relay node are pre-processed by a set of precoders before being transmitted to the destination node. With the estimated signals at the relay node, we propose an algorithm based on the constant modulus and signal mutual information properties to estimate the source-relay channel matrix. Compared with training-based MIMO relay channel estimation approaches, the proposed algorithm has a better bandwidth efficiency as no bandwidth is wasted for sending the training sequences. Numerical examples are shown to demonstrate the performance of the proposed algorithm

Performance analysis of channel codes in multiple antenna OFDM systems

Multiple antenna techniques are used to increase the robustness and performance of wireless networks. Multiple antenna techniques can achieve diversity and increase bandwidth efficiency when specially designed channel codes are used at the scheme’s transmitter. These channel codes can be designed in the space, time and frequency domain. These specially designed channel codes in the space and time domain are actually designed for flat fading channels and in frequency selective fading channel, their performance may be degraded. To counteract this possible performance degradation in frequency selective fading channel, two main approaches can be applied to mitigate the effect of the symbol interference due to the frequency selective fading channel. These approaches are multichannel equalisation and orthogonal frequency division multiplexing (OFDM). In this thesis, a multichannel equalisation technique and OFDM were applied to channel codes specially designed for multiple antenna systems. An optimum receiver was proposed for super-orthogonal space-time trellis codes in a multichannel equalised frequency selective environment. Although the proposed receiver had increased complexity, the diversity order is still the same as compared to the code in a flat fading channel. To take advantage of the multipath diversity possible in a frequency selective fading channel, super-orthogonal block codes were employed in an OFDM environment. A new kind of super-orthogonal block code was proposed in this thesis. Super-orthogonal space-frequency trellis-coded OFDM was proposed to take advantage of not only the possible multipath diversity but also the spatial diversity for coded OFDM schemes. Based on simulation results in this thesis, the proposed coded OFDM scheme performs better than all other coded OFDM schemes (i.e. space time trellis-coded OFDM, space-time block coded OFDM, space-frequency block coded OFDM and super-orthogonal space-time trellis-coded OFDM). A simplified channel estimation algorithm was proposed for two of the coded OFDM schemes, which form a broad-based classification of coded OFDM schemes, i.e. trelliscoded schemes and block-coded schemes. Finally in this thesis performance analysis using the Gauss Chebychev quadrature technique as a way of validating simulation results was done for super-orthogonal block coded OFDM schemes when channel state information is known and when it is estimated. The results obtained show that results obtained via simulation and analysis are asymptotic and therefore the proposed analysis technique can be use to obtain error rate values for different SNR region instead of time consuming simulation.Thesis (PhD)--University of Pretoria, 2012.Electrical, Electronic and Computer Engineeringunrestricte

FGPA Implementation of Low-Complexity ICA Based Blind Multiple-Input-Multiple-Output OFDM Receivers

In this thesis Independent Component Analysis (ICA) based methods are used for blind detection in MIMO systems. ICA relies on higher order statistics (HOS) to recover the transmitted streams from the received mixture. Blind separation of the mixture is achieved based on the assumption of mutual statistical independence of the source streams. The use of HOS makes ICA methods less sensitive to Gaussian noise. ICA increase the spectral efficiency compared to conventional systems, without any training/pilot data required. ICA is usually used for blind source separation (BSS) from their mixtures by measuring non-Gaussianity using Kurtosis. Many scientific problems require FP arithmetic with high precision in their calculations. Moreover a large dynamic range of numbers is necessary for signal processing. FP arithmetic has the ability to automatically scale numbers and allows numbers to be represented in a wider range than fixed-point arithmetic. Nevertheless, FP algorithm is difficult to implement on the FPGA, because the algorithm is so complex that the area (logic elements) of FPGA leads to excessive consumption when implemented. A simplified 32-bit FP implementation includes adder, Subtractor, multiplier, divider, and square rooter The FPGA design is based on a hierarchical concept, and the experimental results of the design are presented

Blind channel estimation for MIMO OFDM communication systems

Ph.DDOCTOR OF PHILOSOPH

Channel estimation for SISO and MIMO OFDM communications systems.

Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2010.Telecommunications in the current information age is increasingly relying on the wireless link. This is because wireless communication has made possible a variety of services ranging from voice to data and now to multimedia. Consequently, demand for new wireless capacity is growing rapidly at a very alarming rate. In a bid to cope with challenges of increasing demand for higher data rate, better quality of service, and higher network capacity, there is a migration from Single Input Single Output (SISO) antenna technology to a more promising Multiple Input Multiple Output (MIMO) antenna technology. On the other hand, Orthogonal Frequency Division Multiplexing (OFDM) technique has emerged as a very popular multi-carrier modulation technique to combat the problems associated with physical properties of the wireless channels such as multipath fading, dispersion, and interference. The combination of MIMO technology with OFDM techniques, known as MIMO-OFDM Systems, is considered as a promising solution to enhance the data rate of future broadband wireless communication Systems. This thesis addresses a major area of challenge to both SISO-OFDM and MIMO-OFDM Systems; estimation of accurate channel state information (CSI) in order to make possible coherent detection of the transmitted signal at the receiver end of the system. Hence, the first novel contribution of this thesis is the development of a low complexity adaptive algorithm that is robust against both slow and fast fading channel scenarios, in comparison with other algorithms employed in literature, to implement soft iterative channel estimator for turbo equalizer-based receiver for single antenna communication Systems. Subsequently, a Fast Data Projection Method (FDPM) subspace tracking algorithm is adapted to derive Channel Impulse Response Estimator for implementation of Decision Directed Channel Estimation (DDCE) for Single Input Single Output - Orthogonal Frequency Division Multiplexing (SISO-OFDM) Systems. This is implemented in the context of a more realistic Fractionally Spaced-Channel Impulse Response (FS-CIR) channel model, as against the channel characterized by a Sample Spaced-Channel Impulse Response (SS)-CIR widely assumed by other authors. In addition, a fast convergence Variable Step Size Normalized Least Mean Square (VSSNLMS)-based predictor, with low computational complexity in comparison with others in literatures, is derived for the implementation of the CIR predictor module of the DDCE scheme. A novel iterative receiver structure for the FDPM-based Decision Directed Channel Estimation scheme is also designed for SISO-OFDM Systems. The iterative idea is based on Turbo iterative principle. It is shown that improvement in the performance can be achieved with the iterative DDCE scheme for OFDM system in comparison with the non iterative scheme. Lastly, an iterative receiver structure for FDPM-based DDCE scheme earlier designed for SISO OFDM is extended to MIMO-OFDM Systems. In addition, Variable Step Size Normalized Least Mean Square (VSSNLMS)-based channel transfer function estimator is derived in the context of MIMO Channel for the implementation of the CTF estimator module of the iterative Decision Directed Channel Estimation scheme for MIMO-OFDM Systems in place of linear minimum mean square error (MMSE) criterion. The VSSNLMS-based channel transfer function estimator is found to show improved MSE performance of about -4 MSE (dB) at SNR of 5dB in comparison with linear MMSE-based channel transfer function estimator