Implementation Issues in Turbo Decoding for 3GPP FDD Receiver

In the Frequency Division Duplex (FDD) mode of the Third Generation Partnership Project (3GPP) standard, implementation of the turbo decoder, especially for the mobile equipments, faces design decisions related to computational complexity, power efficiency, and memory requirements. In this paper we compare different approaches of low complexity implementation of the turbo decoder, with emphasis on the issues of signal scaling and quantization, the sliding window operation for memory size reduction and the iteration stopping algorithms. The demodulated signal at the output of the RAKE receiver may have a wide dynamic range and it may require many bits of precision. In order to overcome the numerical precision problem and to prevent Log Likelihood ratio (LLR) metric overflow, a scaling algorithm must be used. Our simulation results indicate that the Average Absolute (AA) algorithm using dynamic scaling outperforms other scaling schemes and it is less sensitive to the channel conditions. One of the major challenges in the implementation of a practical turbo decoder is optimization of memory requirements. In this paper we evaluate the performance of the sliding window algorithm using different main and guard window sizes. We show that the bit and block error rate performance of the sliding window scheme mainly depend on the guard window size rather than the main window size. The simulation results indicate that small guard window sizes can significantly decrease the iteration gain for large frames in fast fading channels. Iteration stopping algorithms reduce the power consumption and the latency of the decoder and help to dedicate more resources to other functions of the receiver. The block error distribution in the fading channels makes it even more essential to use an iteration stopping rule. Our simulations conclude that a rule called the minimum absolute value appears to be a very effective, low complexity and robust algorithm. Mohamadreza Marandian Hagh was born in Tabriz, Iran on January 1974. He received the B.S. and the M.S. degrees in electrical engineering from Tehran University with honors in 1996 and 1999, respectively. He is pursuing the Ph.D. degree in electrical engineering at Northeastern University, Boston. His research interests includes information theory, channel coding and iterative techniques for wireless communication systems. His current research is focused on low complexity designs for iterative receivers using Space-Time coding in time-dispersive channels. He is also interested in Exit-Chart analysis of iterative receivers. From 1996 to 1999, he was with Sana Pro Inc. as a system engineer, developing simulation tools for OFDM, WCDMA, CDMA2000. He is currently with Airvana Inc. in Chelmsford, MA and working on 1xEVDO wireless systems. Masoud Salehi received BS degree (Summa Cum Laude) from Tehran University and MS and Ph.D. degrees from Stanford University all in Electrical Engineering. Before joining Northeastern, he was with the Departments of Electrical and Computer Engineering, Isfahan University of Technology and Tehran University. From February 1988 to May 1989 Dr. Salehi was a visiting professor at the Information Theory Research Group, Department of Electrical Engineering, Eindhoven University of Technology, The Netherlands, where he did research in network information theory and coding for storage media.In 1989 Dr. Salehi joined Department of Electrical and Computer Engineering, Northeastern University. Professor Salehi is a member of the CDSP (Communication and Digital Signal Processing) Center. His main areas of research interest are network information theory, source-channel matching problems in single and multiple user systems, data compression, turbo coding, coding for fading channels, and digital watermarking. Professor Salehi’s research has been supported by research grants from the National Science Foundation (NSF), GTE, NUWC, CenSSIS, and Analog Devices. Professor Salehi has also done consulting to the industry including Teleco Oilfield Services and AT&T. Professor Salehi is currently a member of the Editorial Board of The International Journal of Electronics and Communications.Professor Salehi is the coauthor of the textbooks “Communication Systems Engineering”, Prentice-Hall 1994, 2002, “Contemporary Communication Systems Using MATLAB and Simulink” Thomson 1998, 2000, 2004, and “Fundamentals of Communication Systems”, Prentice-Hall 2005. Abhay Sharma received B.E. (Hons) Electrical and Electronics Engineering degree from Birla Institute of Technology and Science, Pilani, India in 1996 and M.S. Electrical Engineering degree from Ohio State University, Columbus in 2000. From 2000 to 2005 he was working with Analog Devices, RF and Wireless Systems Group, Wilmington, USA, where he was working on design and implementation of algorithms for the emerging cellular communication standards. Currently he is working with Allgo Embedded Systems, Bangalore, India, in the area of wireless networks and systems based on the emerging W-PAN wireless technologies. Zoran Zvonar received the Dipl. Ing. degree in 1986 and the M.S. degree in 1989, both from the Department of Electrical Engineering, University of Belgrade, Yugoslavia, and the Ph.D. degree in Electrical Engineering from the Northeastern University, Boston, in 1993.From 1986 to 1989 he was with the Department of Electrical Engineering, University of Belgrade, Belgrade, Yugoslavia, where he conducted research in the area of telecommunications. 1993 to 1994 he was a Post-Doctoral investigator at the Woods Hole Oceanographic Institution, Woods Hole, MA, anconducted research on multiple-access communications for underwater acoustic networks. Since 1994 he has been with the Analog Devices, Communications Division, Wilmington, USA. He is the Manager of the Systems Engineering Group focusing on the design of algorithms and architectures for wireless communications, with emphasis on integrated solutions and real-time software.He was a Guest Editor of the IEEE Transactions on Vehicular Technology, the International Journal of Wireless Information Networks and the ACM/Baltzer Wireless Networks, Associate Editor of the IEEE Communications Letters and a co-editor of the books GSM: Evolution Towards Third Generation Systems, Kluwer Academic Publishers, 1998, Wireless Multimedia Networks Technologies, Kluwer Academic Publishers, 1999 and Software Radio Technologies: Selected Reading, IEEE Press, 2001. Dr. Zvonar is currently Co-Editor of the Radio Communication Series in the IEEE Communications Magazine.     

A New Signature Scheme with Shared Verification

1Introduction Withthedevelopmentofcomputerandnetworkcom municationtechnology,andwiththedifferenceofuser s demands,digitalsignaturetechniquesarebeingexpand edgreatly,fromthesinglesignature,singleverification modetothemulti user sone.Forexample,adocument sy…     

Channel modeling based on multilayer artificial neural network in metro tunnel environments

Traditional deterministic channel modeling is accurate in prediction, but due to its complexity, improving computational efficiency remains a challenge. In an alternative approach, we investigated a multilayer artificial neural network (ANN) to predict large-scale and small-scale channel characteristics in metro tunnels. Simulated high-precision training datasets were obtained by combining measurement campaign with a ray tracing (RT) method in a metro tunnel. Performance on the training data was used to determine the number of hidden layers and neurons of the multilayer ANN. The proposed multilayer ANN performed efficiently (10 s for training; 0.19 ms for prediction), and accurately, with better approximation of the RT data than the single-layer ANN. The root mean square errors (RMSE) of path loss (2.82 dB), root mean square delay spread (0.61 ns), azimuth angle spread (3.06°), and elevation angle spread (1.22°) were impressive. These results demonstrate the superior computing efficiency and model complexity of ANNs.     

Adaptive blind receivers for MC‐CDMA communication systems

In this paper, we propose three adaptive blind algorithms for multiuser multicarrier code division multiple‐access systems in multipath fading channels. The proposed adaptive blind receivers are based on the property of the discreteness of the input data symbol and are updated in every symbol interval. We also use the concept that the variance of the output signal approaches to the variance of the desired signal to get the cost function. The three proposed receiver structures are the traditional finite impulse response (FIR) structure, the despreading (DES) filter structure and the generalized sidelobe canceller (GSC) structure. The advantage of the FIR filter is that the length of the filter weights does not have to be the same length as the spreading code. For the DES filter, the combination of the adaptive weight and the despreading code has the simplest structure than the other two proposed receiver structures. The constrained GSC filter is superior to the other two proposed receiver structures in the environments dominated by multiple‐access interference. By this constraint, the blind GSC filter can guarantee to converge to the desired solution. Simulation results are given to show the effectiveness and comparison of the proposed adaptive blind receivers. Copyright © 2012 John Wiley & Sons, Ltd.     

An Orthogonal Wavelet Transform Fractionally Spaced Blind Equalization Algorithm Based on the Optimization of Genetic Algorithm

An orthogonal wavelet transform fractionally spaced blind equalization algorithm based on the optimization of genetic algorithm(WTFSE-GA) is proposed in viewof the lowconvergence rate,large steady-state mean square error and local convergence of traditional constant modulus blind equalization algorithm(CMA).The proposed algorithm can reduce the signal autocorrelation through the orthogonal wavelet transform of input signal of fractionally spaced blind equalizer,and decrease the possibility of CMA local convergence by using the global random search characteristics of genetic algorithm to optimize the equalizer weight vector.The proposed algorithm has the faster convergence rate and smaller mean square error compared with FSE and WT-FSE.The efficiency of the proposed algorithm is proved by computer simulation of underwater acoustic channels.     

一个完善的秘密分享方案

可验证秘密分享在实用密码学领域内是一个非常重要的工具,它在密钥管理协议、门限或分布式签名协议、电子商务、多方安全计算及团体式密码系统等许多方面都有极为广泛的应用。针对一类突发事务须及时、安全解决的特点, 利用离散对数问题的难解性,在假设初始化阶段和秘密恢复阶段始终有一位值得信赖的分发者参与的情况下,提出了一个可公开验证的门限秘密分享方案。     

基于MIMO的可见光通信中的信道均衡

针对基于多输入多输出(MIMO)的室内可见光通信(Visible-Light Communication,VLC)系统中存在的码间串扰(ISI)问题进行了分析,并提出了适用于MIMO可见光通信系统的信道均衡方案及实现方法.仿真实验结果表明,该方法可以有效降低MIMO可见光通信系统中的码间串扰的影响.     

Multi-factor cheating prevention in visual secret sharing by hybrid codebooks

Visual secret sharing, or the so-called visual cryptography, is a well-known scheme that encrypts a secret image into several meaningless share images, usually printed on transparencies, and decrypts as stacking some or all share images by the human visual system. More and more researches about visual secret sharing and its applications have been recently proposed. Unfortunately, the cheating attack in which malicious participants cheat the honest one(s) by forging a fake share image has existed. Since 2006, some cheating prevention schemes have been proposed but suffered from one or more disadvantages as follows: (1) maintaining extra share images used to verify the integrity of a share image prior to stacking, (2) introducing extra pixel expansion, (3) raising heavy computation cost, and (4) giving ambiguous cheating detection. In this paper, a multi-factor cheating–preventing scheme, aiming at exploiting the hybrid codebook to hide the additional verification images into the share images, has been proposed without suffering the above-mentioned deficiencies. Two-factor cheating–detection exploits the design of verification to both share images and stacked results to deter attackers’ cheating. The experimental results demonstrate the proposed scheme is feasible.     

Spectral Efficiency Evaluation for MRC Diversity Schemes Over Generalized Rician Fading Channels

In this paper, closed-form expressions for the capacities per unit bandwidth for generalized Rician fading channels are derived for power and rate adaptation, constant transmit power, channel inversion with fixed rate, and truncated channel inversion adaptation policies. The closed-form solutions are derived for the single antenna reception (without diversity combining) and maximal-ratio combining (MRC) diversity cases. Truncated channel inversion adaptation policy is the best policy for the single antenna reception case, while the channel inversion with fixed rate policy is the best policy for the MRC diversity case. Constant transmit power policy provides the lowest spectral efficiency as compared to the other policies with and without diversity.     

几种发射分集OFDM系统信道估计方法性能评估

给出了3种基于发射分集的OFDM系统信道估计方法,分别从训练序列对算法的影响、估计准确度、算法复杂度和算法适用性等方面对各自性能作了分析比较,并进行了仿真.分析比较和仿真结果表明,训练序列对3种算法的影响很大,通过训练序列的正交化设计,LS和EM算法可以得到很大程度的简化;EM算法与LS算法估计精度相当,信噪比较大时,多项式模型算法估计精度要远远高于LS和EM算法;总体上来说,多项式模型算法复杂度最高,EM算法复杂度最低.