基于MSINR的上行多用户MIMO多址干扰抑制算法

针对多用户多输入多输出技术上行传输系统,以最大信干噪比作为多址干扰(MAI)抑制的准则提出了一种新算法。该算法充分利用基站接收端所能获知的信道状态信息构造滤波矩阵,以抑制 MAI以及噪声带来的影响。与广泛关注的块对角化 MAI抑制算法相比,该算法考虑了噪声的影响,性能有较大提升。针对非理想信道环境,给出了本文算法的改进,仿真结果表明该算法具有优异的性能。     

基于新型故障搜寻策略的检测系统设计

为了达到复杂系统快速故障搜寻的目的,设计了一种基于二元决策图优化的新型故障搜寻策略的检测系统设计。通过对基于二元决策图优化的故障搜寻方法研究和实际的硬件电路设计,最终实现了检测系统的软硬件设计。使用这种方法能够很好的实现故障诊断系统在嵌入式平台的开发,并能够取得较好的诊断效果。     

Fair deterministic packet access protocol: F-RAMA (fair resourceassignment multiple access)

The RAMA (resource auction multiple access) protocol uses a scheme where the access procedure is divided into fixed length cycles. A variation of RAMA, the tree-search resource auction multiple access (TRAMA) protocol, was proposed to reduce the length cycle. Both protocols present disadvantages, although different ones. The authors propose and evaluate another variation of RAMA, fair resource assignment multiple access (F-RAMA). Simulation methods were used to calculate packet dropping probability, access delay and statistics of speech clipping in voice transmission     

Adaptive group-blind multiuser detection based on a new subspacetracking algorithm

Wang and Host-Madsen (see IEEE J. Select. Areas Commun., vol.17, p.1971-84, 1999) developed group-blind multiuser detectors for use in code-division multiple-access (CDMA) uplink environments in which the base station receiver has the knowledge of the spreading sequences of all the users within the cell, but not that of the users from other cells. Yu and Host-Madsen (see Proc. IEEE Vehicular Technology Conf. (VTC99), Houston, TX, p.1042-46, 1999) later developed an adaptive version of this detector for synchronous CDMA channels. We develop a new low-complexity, high-performance subspace tracking algorithm and apply it to adaptive group-blind multiuser detection in asynchronous multipath CDMA channels. The detector can track changes in the number of users and their composite signature waveforms. We present steady-state performance as well as the ability of the receiver to track changes in the signal subspace. We also address the performance gain of the group-blind detector over its blind counterpart for this application     

AQM controller design for TCP networks based on a new control strategy

When the network suffers from congestion, the core or edge routers signal the incidence of congestion through the active queue management (AQM) to the sources. The time-varying nature of the network dynamics and the complex process of retuning the current AQM algorithms for different operating points necessitate the development of a new AQM algorithm. Since the non-minimum phase characteristics of the network dynamics restrict direct application of the proportional-integral-derivative (PID) controller, we propose a compensated PID controller based on a new control strategy addressing the phase-lag and restrictions caused by the delay. Based on the unstable internal dynamics caused by the non-minimum phase characteristics, a dynamic compensator is designed and a PID controller is then allowed to meet the desired performance objectives by specifying appropriate dynamics for the tracking error. Since the controller gains are obtained directly from the dynamic model, the designed controller does not require to be tuned over the system operating envelop. Moreover, simulation results using ns2 show improvements over previous works especially when the range of variation of delay and model parameters are drastic. Simplicity, low computational cost, self-tuning structure and yet considerable improvement in performance are exclusive features of the proposed AQM for the edge or core routers.     

Dynamic Reservation Multiple Access (DRMA): A new multiple access scheme for Personal Communication System (PCS)

To improve the spectrum efficiency of integrated voice and data services in Personal Communication System (PCS), several reservation-type multiple access schemes, such as Packet Reservation Multiple Access (PRMA), Dynamic Time Division Multiple Access (D-TDMA), Resource Auction Multiple Access (RAMA), etc., have been proposed. PRMA uses the data packet itself to make a channel reservation, and is inefficient in that each unsuccessful reservation wastes one slot. However, it does not have a fixed reservation overhead and offers shorter access delay. On the other hand, fixed reservation overhead is unavoidable in both RAMA and D-TDMA. Compared to D-TDMA and PRMA, RAMA is superior in the sense that its slot assignment is independent of the traffic load. But its implementation is difficult. With these observations, a new reservation protocol, called Dynamic Reservation Multiple Access (DRMA), is proposed in this paper. With this new protocol, the success probability of channel access is greatly improved at the expense of slightly increased system complexity. It solves the problem of inefficiency in PRMA, but without introducing the fixed reservation overhead as in D-TDMA and RAMA. In addition, it is more suited to the dynamic behavior of the integrated traffic because there is no fixed boundary between voice and data slots (which is mandatory in D-TDMA and RAMA). Our numerical results indicate that its performance is superior to the existing reservation protocols, especially in the integrated traffic scenario. Moreover, the soft capacity feature is exhibited when the traffic load increases.     

Plane cover multiple access: a new approach to maximizing cellularsystem capacity

We develop a new media access control strategy, called plane cover multiple access (PCMA), that provides a means of allocating wireless bandwidth in a packet-based cellular system. PCMA seeks to maximize the number of parallel transmissions among cells by defining virtual cells in which users transmit using a given reuse factor. By keeping the reuse factors low, system throughput can be maximized. We show that the throughput of a simple system designed using PCMA is up to 82% more efficient than capture division packet access (CDPA), the best known alternative for the cellular mobile environment     

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.     

基于XML授权策略的访问控制模型的设计与实现

在安全实现身份认证的前提下,特权管理基础设施PMI同基于角色的访问控制RBAC相结合可以有效地建立一个基于角色的统一访问控制体系。本文使用基于XML的授权策略建立角色与访问权限之间的关系,同时提出并实现了一个采用该策略描述体系的基于角色的访问控制模型。     

Dual busy tone multiple access (DBTMA)-a multiple access controlscheme for ad hoc networks

In ad hoc networks, the hidden- and the exposed-terminal problems can severely reduce the network capacity on the MAC layer. To address these problems, the ready-to-send and clear-to-send (RTS/CTS) dialogue has been proposed in the literature. However, MAC schemes using only the RTS/CTS dialogue cannot completely solve the hidden and the exposed terminal problems, as pure "packet sensing" MAC schemes are not safe even in fully connected networks. We propose a new MAC protocol, termed the dual busy tone multiple access (DBTMA) scheme. The operation of the DBTMA protocol is based on the RTS packet and two narrow-bandwidth, out-of-band busy tones. With the use of the RTS packet and the receive busy tone, which is set up by the receiver, our scheme completely solves the hidden- and the exposed-terminal problems. The busy tone, which is set up by the transmitter, provides protection for the RTS packets, increasing the probability of successful RTS reception and, consequently, increasing the throughput. This paper outlines the operation rules of the DBTMA scheme and analyzes its performance. Simulation results are also provided to support the analytical results. It is concluded that the DBTMA protocol is superior to other schemes that rely on the RTS/CTS dialogue on a single channel or to those that rely on a single busy tone. As a point of reference, the DBTMA scheme out-performs FAMA-NCS by 20-40% in our simulations using the network topologies borrowed from the FAMA-NCS paper. In an ad hoc network with a large coverage area, DBTMA achieves performance gain of 140% over FAMA-NCS and performance gain of 20% over RI-BTMA     

A novel hybrid spreading and scrambling based multiple access (SSMA) technique for capacity improvement

Telecommunication Systems - Future wireless networks and 5G communication technology aims to provide seamless connectivity for geographical areas having thousands of users within hundreds of meter...     

The Cholesky-iterative detector: a new multiuser detector forsynchronous CDMA systems

The decorrelating decision-feedback (DDF) multiuser detector based on Cholesky factorization has been shown to alleviate the performance degradation of the users in the detection process, especially for relatively low cross-correlation values between user signals. A new detection concept for multiple users described in this paper employs two triangular matrices (upper and lower) and soft output information to improve the data estimates. Simulation results show that significant performance gains can be achieved over the DDF. Also, the users tend to have their bit error probabilities clustered. Thus, the performance of a given user is less dependent on its position in the detection process than for the DDF detector     

基于光纤布拉格步进啁啾光栅的OCDMA频域编/解码器的探索

依据频域编码的理论,分析和论证了基于光纤布拉格步进啁啾光纤光栅的 OCDMA 频域编/解码器的原理。通过对地址码做一映射变换,在步进啁啾光纤光栅上以相移的方式嵌入相应的多址码,实现了基于步进啁啾光纤光栅的光码分复用频域相位编/解码;文章给出了编/解码器的等效模型;对该编/解码器的仿真结果得到了很好的相关输出,证明了这种编/解码方法的可行性;并对影响基于此编解码器系统性能的参数进行了分析。     

Power-domain non orthogonal multiple access (PD-NOMA) in cooperative networks: an overview

Wireless Networks - Non-orthogonal multiple access (NOMA) scheme is emerging as a favourable multiple access scheme for future 5G networks. Compared to orthogonal multiple access techniques, NOMA...     

Blind array channel division multiple access (AChDMA) for mobilecommunications

The paper introduces array channel division multiple access (AChDMA), which is a new blind algorithm for advanced SDMA in mobile communications systems. As an SDMA technique, AChDMA increases the system capacity by improving its time and frequency reuse. Being a blind algorithm, it requires no training sequences, previously known directions of arrival, or user codes, AChDMA separates the moving sources by tracking their multipath configuration and resolving their distinct generalized steering vectors. It maximizes a finite mixture log-likelihood function, combining an efficient initialization procedure with an EM-based algorithm that provides fast convergence to the global maximum. AChDMA reconstructs the mobile data sequences using only internal variables of the EM algorithm. These characteristics and its parallel structure make AChDMA suitable for real-time mobile communications. We test AChDMA with synthetic data in a number of different scenarios, illustrating the ability of the blind algorithm to separate and track in time the moving sources, and showing its good performance in a variety of practical situations     

Power domain cyclic spread multiple access: An interference‐resistant mixed NOMA strategy

The next generation wireless access technology highly relies on nonorthogonal multiple access (NOMA) technique. This paper proposes a novel power domain cyclic spread multiple access (PDCSMA) scheme for the design of NOMA system with power domain superposition coding (SC) and cyclic spreading at the transmitter concurrent with symbol level successive interference cancellation (SL‐SIC) at the receiver. Based on acceptable difference in channel gain, the users are grouped together to form PDCSMA clusters, and the unique power is allotted to each user in a cluster. The user with good channel condition is allotted less power, and the user with poor channel condition is allotted more power. Each PDCSMA cluster has its own spreading code, and the data of every user in a cluster are cyclic spread with the same code. Each cluster supports the number of multipath components equivalent to the length of the spreading code. The use of cyclic spreading makes the signal suffered by multipath fading less prone to intra cluster interference. The user signal is decoded by minimum mean square error‐frequency domain equalization (MMSE‐FDE) or maximal ratio combining (MRC)–based receiver in which weak user is detected with hard decision, and strong user is detected with SIC. Compared with conventional power domain NOMA (PDNOMA) and interleaved NOMA, the proposed PDCSMA achieves better bit error rate (BER) performance and assures guaranteed detection.     

Further results on a new combined strategy based on theSRPT-principle

The method used for analyzing the combined shortest remaining processing time first/round robin (SRPT/RR) strategy is briefly introduced, and it is shown that this combined strategy preserves the essential advantages of the SRPT principle. In data communications, this strategy potentially may be applied to the packet switching process. The packet length corresponds to the time slice, and overhead corresponds mainly to the packet frame because most of the operations needed to organize the queue can be performed in parallel. In networks with virtual or static routing, this strategy selects the next packet of the message with the least number of remaining packets; for an equal number of remaining packets, the message with the shortest last packet is chosen. The first in, first out (FIFO) rule is used to resolve any remaining ambiguity. Local area networks are a special area of application for this strategy     

HORNET: a packet-over-WDM multiple access metropolitan area ring network

Current metropolitan area networks (MANs) based on the SONET transport are not developing at the rate required to support the phenomenal increase in data traffic. To address the needs of future MANs, the Optical Communications Research Laboratory at Stanford University and Sprint Advanced Technology Laboratories are building HORNET (Hybrid Optoelectronic Ring NETwork). HORNET has a multiple access architecture, in which nodes access any WDM channel using a novel media access control protocol and fast tunable laser transmitters. HORNET transports data packets directly over the WDM ring, eliminating the SONET transport. This paper presents the HORNET architecture, the node design consisting of novel packet-over-WDM components, and the experimental testbed with results.     

Analytical model of busy channel multiple access (BCMA) for packetradio networks in a local environment

The performance obtainable with busy-channel multiple access (BCMA) techniques is analytically defined in the context of multichannel local radio networks. Network behavior is characterized in terms of throughput and transmission delay when a single radiofrequency channel is shared among many users, thought to be within the range of a central station, suitably located in the local area. The analytical model is based on a suitable Markov model for the generic terminal, and it is assumed that the traffic presented to the common channel conforms to a Poisson distribution. An analytical evaluation of throughput as a function of offered traffic and average transmission delay is presented. The numerical results obtained are for a particular case of BCMA, the well-known busy-tone multiple access (BTMA). In this example, the analytical model proposed allows fast performance evaluation and suitable comparison with CSMA and ALOHA protocol techniques and evaluation of the capture effect     

TFAS (a tophat for all species): design and computer optimizationof a new electrostatic analyzer

TFAS (tophat for all species) is discussed. It is a 360° field-of-view electrostatic analyzer that can process particles of either charge simultaneously. The TFAS analyzer resembles two tophat analyzers placed hat to hat, but with the tophat plates removed and the tophat region shared in common by both analyzers. In the tophat region, deflection is by parallel plates, one with potential +V and the other with potential -V. A collimator allows particles to enter this parallel plate region and the particles are then deflected into the spherical deflection region of the analyzer. The TFAS has characteristics comparable to the spherical tophat analyzer. A mathematical analysis is presented showing the optimal dimensions selection for the TFAS analyzer, given a particular tophat angle. Raytracing simulations have been performed. Design curves showing various analyzer characteristics as a function of tophat angle are presented. The design curves are compared to similar curves already in the literature for the spherical tophat analyzer. Differences between the TFAS analyzer and the spherical tophat analyzer are summarized