Analysis of joint channel estimation and joint data detection in TD-SCDMA systems

Time Division-Synchronous Code Division Multiple Access (TD-SCDMA) has several attractive characteristics that made it capable of meeting the requirements of G4 systems when applied as a platform directly. Joint detections, the unpaired spectrums with flexible sharing of resources, and some other advanced properties leads TD-SCDMA to achieve high data rate services. In this paper a comprehensive analysis is presented that involve accurate Joint Channel Estimation (JCE) for traditional and enhanced estimators based on two criterions: Least square (LS) & Minimum Mean Square Error (MMSE) at two scenarios of users' movements. In addition to a comprehensive Multi-Users Joint Detection (MUJD) is improved to mitigate Multiple Access Interference (MAI) and Inter-Symbol Interference (ISI) using the following detectors: Matched Filter (MF), Zero Forcing Block Linear Equalizer (ZF-BLE), and Minimum Mean Square Error Block Linear Equalizer (MMSE-BLE) for traditional and enhanced channel estimation criterions. Simulation results showed that equalizers fed by Channel Impulse Response (CIR) optimized according to enhanced LS or MMSE give a better performance to that ones when CIR obtained from traditional LS or MMSE criterion. The using of MMSE give the opportunity to implement adaptive equalizes to cope with fast fading and/or non stationary interference environments

Successive interference cancellation schemes for time-reversal space-time block codes

In this paper, we propose two simple signal detectors that are based on successive interference cancellation (SIC) for time-reversal space-time block codes to combat intersymbol interference in frequency-selective fading environments. The main idea is to treat undetected symbols and noise together as Gaussian noise with matching mean and variance and use the already-detected symbols to help current signal recovery. The first scheme is a simple SIC signal detector whose ordering is based on the channel powers. The second proposed SIC scheme, which is denoted parallel arbitrated SIC (PA-SIC), is a structure that concatenates in parallel a certain number of SIC detectors with different ordering sequences and then combines the soft output of each individual SIC to achieve performance gains. For the proposed PA-SIC, we describe the optimal ordering algorithm as a combinatorial problem and present a low-complexity ordering technique for signal decoding. Simulations show that the new schemes can provide a performance that is very close to maximum-likelihood sequence estimation (MLSE) decoding under time-invariant conditions. Results for frequency-selective and doubly selective fading channels show that the proposed schemes significantly outperform the conventional minimum mean square error-(MMSE) like receiver and that the new PA-SIC performs much better than the proposed conventional SIC and is not far in performance from the MLSE. The computational complexity of the SIC algorithms is only linear with the number of transmit antennas and transmission rates, which is very close to the MMSE and much lower than the MLSE. The PA-SIC also has a complexity that is linear with the number of SIC components that are in parallel, and the optimum tradeoff between performance and complexity can be easily determined according to the number of SIC detectors

TD-SCDMA Relay Networks

PhDWhen this research was started, TD-SCDMA (Time Division Synchronous Code Division Multiple Access) was still in the research/ development phase, but now, at the time of writing this thesis, it is in commercial use in 10 large cities in China including Beijing and Shang Hai. In all of these cities HSDPA is enabled. The roll-out of the commercial deployment is progressing fast with installations in another 28 cities being underway now. However, during the pre-commercial TD-SCDM trail in China, which started from year 2006, some interference problems have been noticed especially in the network planning and initialization phases. Interference is always an issue in any network and the goal of the work reported in this thesis is to improve network coverage and capacity in the presence of interference. Based on an analysis of TD-SCDMA issues and how network interference arises, this thesis proposes two enhancements to the network in addition to the standard N-frequency technique. These are (i) the introduction of the concentric circle cell concept and (ii) the addition of a relay network that makes use of other users at the cell boundary. This overall approach not only optimizes the resilience to interference but increases the network coverage without adding more Node Bs. Based on the cell planning parameters from the research, TD-SCDMA HSDPA services in dense urban area and non-HSDPA services in rural areas were simulated to investigate the network performance impact after introducing the relay network into a TD-SCDMA network. The results for HSDPA applications show significant improvement in the TDSCDMA relay network both for network capacity and network interference aspects compared to standard TD-SCDMA networks. The results for non- HSDPA service show that although the network capacity has not changed after adding in the relay network (due to the code limitation in TD-SCDMA), the TD-SCDMA relay network has better interference performance and greater coverage

Performance evaluation of the third generation TD-SCDMA system.

Firstly, a basic reverse TD-SCDMA system is setup, including a transmitter, a receiver and a channel. Within the receiver model, a specific soft Viterbi decoding algorithm is developed. Secondly, the system synchronization requirements and their impact on its performance under realistic conditions are evaluated. The need for uplink synchronization is established and the sensitivity of the system performance to time misalignment is qualified. To mitigate multipath fading, a RAKE receiver and a minimum mean-square-error (MMSE) receiver are considered. Two RAKE receivers are compared and it is observed that the MMSE-based RAKE receiver always outperforms the cross-correlation based RAKE receiver. An MMSE receiver, including fully or fractionally spaced equalizer is also considered. MMSE receivers do improve the performance for some channels, but not in others. Fractionally spaced equalizers outperform the fully spaced equalizer.Among all the third generation (3G) systems, time-division duplex synchronous code-division multiple access (TD-SCDMA) system is a unique system and has a lot advantages. The performance of the TD-SCDMA system is evaluated using both link level computer simulations and analysis. This dissertation is focused on the performance evaluation and improvement from the receiver model perspective, including Viterbi decoding algorithms, receiver structures, channel estimation algorithms, channel equalization algorithms, and smart antenna techniques.Finally, the performance of the system with an antenna array consisting of a linear array of four equally spaced omni-directional antenna elements, and a direct matrix inversion algorithm (DMI) using the MMSE criterion, was also evaluated

Application of Smart Antenna in TD - SCDMA

With the rapid development of global communications business, future personal communication wireless mobile communicationtechnology has aroused great concern. Way to eliminate the impact of co-channel interference (CCI), multiple access interference (MAI)and multipath fading becomes a major factor in improving the performance of wireless mobile communication systems. The smart antennauses the digital signal processing technology to generate the spatial directional beam so that the antenna main beam is aligned with thedirection of arrival of the user signal. The side lobe or the zero point is aligned to the direction of the interfering signal to reach the fullefficient use of the mobile subscriber signal, thus remove or suppress the interference signal purpose. Compared with other increasinglydeep and mature interference removal technology, the application of smart antenna technology in mobile communication is even more in theascendant and showing great potential. One of the key technologies of the third generation mobile communication standard TD-SCDMAsystem submitted by our country is the intelligent antenna technology. The paper introduces the history and development of the smartantenna in detail, and deeply analyzes the application of the smart antenna in TD-SCDMA. The application of smart antenna has beendeveloped

A General Framework for Analyzing, Characterizing, and Implementing Spectrally Modulated, Spectrally Encoded Signals

Fourth generation (4G) communications will support many capabilities while providing universal, high speed access. One potential enabler for these capabilities is software defined radio (SDR). When controlled by cognitive radio (CR) principles, the required waveform diversity is achieved via a synergistic union called CR-based SDR. Research is rapidly progressing in SDR hardware and software venues, but current CR-based SDR research lacks the theoretical foundation and analytic framework to permit efficient implementation. This limitation is addressed here by introducing a general framework for analyzing, characterizing, and implementing spectrally modulated, spectrally encoded (SMSE) signals within CR-based SDR architectures. Given orthogonal frequency division multiplexing (OFDM) is a 4G candidate signal, OFDM-based signals are collectively classified as SMSE since modulation and encoding are spectrally applied. The proposed framework provides analytic commonality and unification of SMSE signals. Applicability is first shown for candidate 4G signals, and resultant analytic expressions agree with published results. Implementability is then demonstrated in multiple coexistence scenarios via modeling and simulation to reinforce practical utility

Current Situation and Development Trend of Mobile Communication Systems

This paper introduces the development background of mobile communication and the development of mobilecommunication. It introduces the application principle, network structure, main technology, the advantages anddisadvantages of the three generations of mobile communication system respectively, and introduces the currentthird generation mobile communication system, including its technical support and research direction, analysis andcomparison of the European WCDMA system, the United States CDMA2000 system and China's TD-SCDMA systemtechnical characteristics. Finally, the development trend and prospect of future mobile communication system arediscussed

Design and Implementation of a Low Complexity Multiuser Detector for Hybrid CDMA Systems

In hybrid CDMA systems, multiuser detection (MUD) algorithms are adopted at the base station to reduce both multiple access and inter symbol interference by exploiting space-time (ST) signal processing techniques. Linear ST-MUD algorithms solve a linear problem where the system matrix has a block-Toeplitz shape. While exact inversion techniques impose an intolerable computational load, reduced complexity algorithms may be efficiently employed even if they show suboptimal behavior introducing performance degradation and nearfar effects. The block-Fourier MUD algorithm is generally considered the most effective one. However, the block-Bareiss MUD algorithm, that has been recently reintroduced, shows also good performance and low computational complexity comparing favorably with the block Fourier one. In this paper, both MUD algorithms will be compared, along with other well known ones, in terms of complexity, performance figures, hardware feasibility and implementation issues. Finally a short hardware description of the block-Bareiss and block Fourier algorithms will be presented along with the FPGA (Field Programmable Gate Array) implementation of the block-Fourier using standard VHDL (VHSIC Hardware Description Language) design

Towards 5th Generation Cellular Mobile Networks

Cellular mobile networks have enabled ubiquitous communications and largely changed the way we live and work. At the same time, the network itself has been undergoing significant changes in the process of meeting our ever increasing demands on data rate and quality of service. In this article, we show the path of the evolution in both standards and techniques, and provide our vision for the future of the cellular networks. We review the evolution of international standards for cellular mobile networks in the last two decades, describe how the network layout has been migrating from rigid cellular architecture to random and dense small cells, and provide an indepth discussion on potential enabling techniques for the next generation (5G) cellular networks, particularly massive MIMO and multiband base-station antennas