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.     

基于Turbo-TCM与时空分组码的级联系统的次优译码算法

针对瑞利信道中存在的严重的多径衰落,本文实现了Turbo-TCM方案与时空分组码的级联系统,以期利用空间分集改善系统的误码率性能。针对级联系统的译码,本文给出了一种具有低译码时延的次优译码算法,该算法的特点是各模块独立译码,先算比特对数似然比再进行二进制Turbo码译码。最后通过计算机仿真给出了使用该次优译码算法的Turbo－TCM方案与时空分组码的级联系统的译码性能。仿真结果说明,当发射天线数目一定时,随着接收天线数目的增加,译码性能的增益随之增加而帧长对译码性能的影响则随之减小。     

Turbo编译码在3G中的应用及前景

Turbo码是一种接近Shannon编码理论极限性能的并行级联码。介绍了Turbo码的编、译码原理,并对它的性能进行分析。然后,详述了Turbo码在第三代移动通信中的应用。     

3G系统中AMR语音业务的链路配置和模式切换的研究

本文针对3G系统中自适应多比特率(AMR)语音业务的各种语音编码模式,设计了采用Turbo码的不等保护信道编码为基础的链路配置方案.为了研究AMR的链路适配,提出了针对3G系统多业务、多接入速率特征的不等功率分配策略,并在此基础上分析了AMR的不同编码模式对小区的接入容量的影响.基于链路级的仿真和对系统容量的分析,本文归纳了3G系统中AMR语音业务的链路配置和模式切换准则,对实际系统中的无线资源管理具有参考价值.     

A new architecture for 3G and WLAN integration and inter-system handover management

WLAN has strong potential to provide a perfect broadband complement to the 3G wireless systems. This has raised much interest in their integration. In this paper, a novel architecture using the Network Inter-operating Agent (NIA), and Integration Gateway (IG) is proposed to integrate the 3G systems and WLANs of various providers that may not necessarily have direct service level agreement (SLA) among them. The proposed architecture is scalable as it eliminates the need for the creation of bilateral SLA among the 3G and WLAN operators. In addition, inter-system handover (ISHO) protocols using the concept of the dynamic boundary area is proposed to support seamless roaming between 3G and WLAN. The dynamic boundary area is determined based on the speed of the user and WLAN cell size. The ISHO procedures are initiated when a mobile user enters the boundary area of the WLAN and are completed before the user leaves the coverage area of the serving WLAN. This ensures that the roaming from WLAN to 3G is transparent to the applications. The performance evaluation shows that the proposed boundary area based ISHO algorithm outperforms the existing 3G/WLAN ISHO algorithms. Shantidev Mohanty (SM’04) received his B. Tech. (Hons.) degree from the Indian Institute of Technology, Kharagpur, India and the M.S. degree from the Georgia Institute of Technology, Atlanta, Georgia, in 2000 and 2003, respectively, both in electrical engineering. He is currently a graduate research assistant with the Broadband and Wireless Networking Laboratory and a Ph.D. candidate at the School of Electrical and Computer Engineering, Georgia Institute of Technology. His current research interests include wireless networks, mobile communications, mobility management, ad-hoc and sensor networks, and cross-layer protocol design. From 2000 to 2001 he worked as a mixed signal design engineer for Texas Instruments, Bangalore, India. He worked as a summer intern for Bell Labs, Lucent Technologies, Holmdel, New Jersey, during the summers of 2002 and 2003 and for Applied Research, Telcordia Technologies, Piscataway, New Jersey, uring the summer of 2004.