Robust channel estimation for the OFDM-based WLAN systems with imperfect synchronization

As an effective technique for combating multipath fading and for high data rate transmission over wireless channels, orthogonal frequ- ency division multiplexing (OFDM) is extensively used in wireless local area network (WLAN) systems to support high-performance bandwidth- efficient multimedia services. In this paper, a robust channel estimation scheme is proposed for the OFDM-based WLAN systems with imperfect synchronization. The frame structure information, the preamble information, the pilot information are efficiently utilized in the proposed channel estimation scheme. Simulation results are used to illustrate the performance of the proposed scheme.     

基于分布式空频码的协作通信系统的信道估计及优化

该文研究了协作通信中分布式空频码系统的信道估计问题。为使信道可辨识,在中继节点处加入了循环卷积滤波器(CCF)。推导了训练模式中导频序列和中继节点处CCF的准最优设计方案,并由此得到了源节点与中继节点之间功率分配的闭合表达式。计算机仿真验证了本文工作的有效性。     

OFDM系统中面向判决的同步与信道联合估计算法

该文提出了一种新的面向判决的OFDM时间和载波频率偏差与信道的联合跟踪算法,并给出了开环和闭环两种结构,不同结构适用于不同的信道环境。该算法提取出信道估计结果所包含的同步信息用于实现同步估计,然后利用当前同步估计结果对信道估计结果进行修正,使之尽量逼近真实信道。采用闭环结构并适当地选择块长和反馈因子的取值,该算法可以有效地对时变信道进行跟踪。     

Highly Simplified and Bandwidth‐Efficient Human Body Communications Based on IEEE 802.15.6 WBAN Standard

This paper presents a transmission method for improving human body communications in terms of spectral efficiency, and the performances of bit‐error‐rate (BER) and frame synchronization, with a highly simplified structure. Compared to the conventional frequency selective digital transmission supporting IEEE standard 802.15.6 for wireless body area networks, the proposed scheme improves the spectral efficiency from 0.25 bps/Hz to 1 bps/Hz based on the 3‐dB bandwidth of the transmit spectral mask, and the signal‐to‐noise‐ratio (SNR) by 0.51 dB at a BER of with an reduction in the detection complexity of the length of the Hamming distance computation. The proposed preamble structure using its customized detection algorithm achieves perfect frame synchronization at the SNR of a BER of by applying the proposed pre‐processing to compensate for the distortions on the preamble signals due to the band‐limit effects by transmit and receive filters.     

Practical packet combining for use with cooperative and non-cooperative ARQ schemes in resource-constrained wireless sensor networks

An improved implementation of a post-detection packet combining scheme, which is especially applicable to low power, resource-constrained sensor networks, is developed and practically implemented on popular off-the-shelf wireless motes. The algorithm can be used as part of protocols such as cooperative communications and hybrid-ARQ schemes which have been shown to be of major benefit for wireless communications. Using the packet combining implementation developed in this paper more than an 85% reduction in energy costs are possible over previous, similar approaches. Both simulated and practical experiments are developed in which packet combining is shown to offer up to approximately 2.5 dB reduction in the required Signal-to-Noise Ratio (SNR) for a desired Packet Error Rate (PER). This is a welcome result as complex schemes, such as maximal-ratio combining, are not implementable on many of the resource constrained devices under consideration.     

Performance analysis of a multiple access protocol for voice and data support in multiuser broadband wireless LANs

Wireless Local Area Networks (WLANs) is one of the most promising access technologies for the upcoming fourth-generation wireless communication systems. In the last few years, several research efforts have been devoted to investigate possible multiple access schemes capable of supporting real-time traffic as well as best-effort data transmissions. In particular, the use of suitable transmission schemes allows not only to achieve higher data-rates, but also to perform resource allocation in order to guarantee specific service requirements. In this paper we propose a medium access control (MAC) scheme for a WLAN supporting real-time (voice) and best-effort (data) services, based on Orthogonal Frequency Division Multiplexing (OFDM) technique. A suitable analytical approach is proposed in order to derive the performance of the proposed MAC scheme. In particular, it is shown in the paper that a high overall network capacity in terms of simultaneously active users is achieved by effectively exploiting the multiuser capabilities offered by OFDM, together with a proper service differentiation. Work partially supported by MIUR within the WOMEN project. Romano Fantacci, (M’87,SM’91, F’05) born in Pistoia, Italy, graduated from the Engineering School of the Universit di Firenze, Florence, Italy, with a degree in electronics in 1982. He received his Ph.D. degree in telecommunications in 1987. After joining the Dipartimento di Elettronica e Telecomunicazioni as an assistant professor, he was appointed associate professor in 1991 and full professor in 1999. His current research interests are digital communications, computer communications, queuing theory, satellite communication systems, wireless broadband communication networks, ad-hoc and sensor networks. He has been involved in several European Space Agency (ESA) and INTELSAT advanced research projects. He is the author of numerous articles published in prestigious communication science journals. He guest edited special issues in IEEE Journals and magazines and served as symposium chair of several IEEE conferences, including VTC, ICC and Globecom. Professor Fantacci received the IEE IERE Benefactor premium in 1990 and IEEE COMSOC Award Distinguished Contributions to Satellite Communications in 2002. He is currently serving as Editor for Telecommunication Systems, IEEE Trans. Commun. and IEEE Transactions on Wireless Communications. Gianluca Vannuccini born in Florence, Italy, graduated in Electronics Engineering in 1999. He received his Ph.D. degree in Telematics and Information Society in 2003 from the Electronics and Telecommunications Department of the University of Florence. During 2002 he was for six months in IBM Zurich Research Laboratory, Zurich, Switzerland, working in a research project on IEEE 802.11e performance evaluation. During the Ph.D. course, he has published on several IEEE conferences and served as reviewer for several journals on the telecommunications and telematics research area. He has been IEEE student member since 1999 and IEEE member since 2004. He is now with the IT department of the Florence local government organization, where he works as a program manager on data quality and integration and e-government IT projects. Gabriele Vestri was born in Florence (Italy) in November 1976. He received his degree in telecommunications from the Universit di Firenze, Florence, Italy, in March 2002. He has been research scientist for CSO Ophthalmic (Florence) since September 2002. His current research interests include ophthalmic instruments, contact lens design, image processing, the effects of optical aberrations and of retinal architecture of the eye on visual performance.     

Using Chain of Mobile Access Gateway to Reduce Delay for PMIPv6 Protocol Applied in WLAN

Wireless LAN controller (WLC) is used to manage and control Access points (APs) in Wireless local area network (WLAN).Proxy mobile IPv6 (PMIPv6) protocol supports network-layer mobility in WLC based WLAN.However,it introduces extra delay in delivering packets from the APs to the WLC.We use Mobile access gateway (MAG) chain to reduce packet delay.The handoff delay and packet delivery delay under the proposed scheme are derived,based on which we formulate the delay minimization problem whose solution leads to the optimal MAG chain length.Numerical analysis results indicate that the proposed scheme outperforms the existing scheme in terms of delay in the case when the delay between Local mobility anchor (LMA) and WLC is relatively greater than the delay between two neighboring WLCs.The proposed scheme is able to reduce packet loss resulting from the traditional handoff procedure introduced in the PMIPv6 protocol and that due to delay limitation.     

Stability and Optimization Analysis for the PRMA Protocol for Voice and Burst Data Integration in a Personal Communication Network

Personal Communication Networks (PCNs) have become an important filed of activity and they are expected to play a fundamental role in next-generation telecommunication systems. In particular, the emerging personal communication services, such as portable computing, paging, personal e-mail, etc. have led to the need of an efficient integration of voice and data traffic in a same PCN by means of a suitable multiple-access scheme. This paper considers stability and optimization issues for the Packet Reservation Multiple Access (PRMA) protocol used for integrating voice and burst data traffic in a PCN. An important result here devised is that the optimized PRMA protocol permits to be achieved good performance even under heavy traffic load conditions.     

Cross‐Layer Resource Allocation Scheme for WLANs with Multipacket Reception

Tailored for wireless local area networks, the present paper proposes a cross‐layer resource allocation scheme for multiple‐input multiple‐output orthogonal frequency‐division multiplexing systems. Our cross‐layer resource allocation scheme consists of three stages. Firstly, the condition of sharing the subchannel by more than one user is studied. Secondly, the subchannel allocation policy which depends on the data packets’ lengths and the admissible combination of users per subchannel is proposed. Finally, the bits and corresponding power are allocated to users based on a greedy algorithm and the data packets’ lengths. The analysis and simulation results demonstrate that our proposed scheme not only achieves significant improvement in system throughput and average packet delay compared with conventional schemes but also has low computational complexity.