一种用于MIMO系统的快速天线选择算法

在多径衰落环境中, MIMO系统的信道容量随天线数的增加呈线性增加,发射/接收天线选择方法能以很小的性能损失换取射频成本的大幅度降低,使MIMO系统不完全受射频成本的限制。为快速选择出使系统容量最优的发射/接收天线子集,该文提出一种快速天线选择算法的改进算法。该算法通过实时更新优化参数,大大降低计算复杂度。仿真结果表明,该算法在不影响系统容量的情况下大大减少了计算时间。     

大跨度天基数据链的TDD时隙调度分析与优化

针对天基数据链系统卫星间的传播时延较大且节点间距离变化较大等特点，提出了一种提高时频资源利用率、提升系统容量、减小时延的方法。在时分多址与空分多址相结合的接入方式下，进行了时隙调度的分析与优化，利用卫星星座的空间复用与大跨度传播时延特性，采用时隙编排、收发状态调整、帧格式优化等手段，将信道利用率和系统容量提升了1倍，将卫星节点在某一方向获得服务的平均等待时间缩短为原来的1/4，提高了天基数据链系统的服务质量。     

速率调整对系统容量的影响

本文是在cdma2000移动通信系统容量分析的基础上,对调整数据业务的数据速率来增加系统的容量进行了理论分析,首次把服务时间的影响引入到系统容量中,同时考虑到业务速率的大小和业务服务时间的长短对系统容量的影响,从理论上给出了速率调整的依据和范围,依照此结论,可以最大系统化的容量.此理论证明了降低速率不一定能够增加系统的容量,改变了传统的观念.仿真结果表明了按照本文给出的理论结论,系统具有最小的中断概率,因此具有最大的容量.     

Capacity analysis of the MEO satellite constellation

Aiming to calculate the system capacity of a given satellite constellation,a time-varying traffic model based on varying traffic with varying time zone was proposed.Focusing on a MEO satellite constellation with global coverage,using a load balanced routing algorithm,the system capacity in different time slices was analyzed and the effect of inter-satellite link (ISL) capacity on the system capacity was investigated.The time-varying traffic model makes analysis more reliable and effective via comparison with equal traffic model.Application of time slices reduces complexity of calculation.     

TTT System (50 Mbits/s PCM-TDMA System With Time Preassignment and TASI) and Its Satellite Test Results

An experimental 50 Mbits/s pulse-code modulation-time-division multiple access (PCM-TDMA) system with time preassignment and time-assignment speech interpolation (TASI) features (called the TTT system) was built for use in a satellite test. This system was designed for application in the INTELSAT IV network and has the channel capacity of more than 700 telephone channels. This capacity can be increased up to twice when pulse-code modulation-time-assignment speech interpolation (PCM-TASI) is adopted. The field test was conducted via INTELSAT III in 1970 and satisfactory results were obtained, which encourages the introduction of the TDMA system for commercial use.     

MPC/OOC二维地址码的构造及性能分析

基于光正交跳频码构造原理,用改进素数码作为时域扩频模式,光正交码为频域跳频模式,构造了适用于光码分多址(OCDMA)系统的MPC／OOC二维地址码。和现有二维地址码相比,该MPC／OOC二维组合码容量更大,通过有规律地分组,每组内码字具有良好的自相关和互相关性能,同时每组内具有较大的码容量。     

Scalability of Web-based electronic commerce systems

In a Web-based electronic commerce system, users browse product information offered by an online store and submit requests to purchase selected items. From the user's perspective, response time is a factor that could impact the acceptability of electronic commerce. This article is concerned with system architectures for online stores. Emphasis is placed on techniques to improve a system's capacity to support more users without suffering a noticeable degradation in response time performance. Such techniques have been investigated as part of a Canadian Institute for Telecommunications Research major project entitled Enabling Technology for Electronic Commerce Applications, developed in close collaboration with the IBM/sup /spl reg// Centre for Advanced Studies. The basic architecture of a Web-based electronic commerce system is first described along with the types of data that need to be managed. Next, an overview of existing techniques for improving system capacity is presented. Finally, highlights of research results obtained as part of the CITR electronic commerce major project are discussed.     

Bandwidth and rise time calculations for digital multimodefiber-optic data links

The use of multimode fiber in digital fiber-optic data links requires simple and accurate procedures for the calculation of data line component bandwidth and rise time responses. The author investigates source/fiber/detector interactions, to develop a simple model for multimode fiber system information capacity. Simplified expressions for the baseband impulse and frequency responses of each component are given along with relationships between the theoretical impulse response root mean square (RMS) width and the component rise time or bandwidth. The application of the central limit theorem to the system yields expressions for the composite system rise time and bandwidth which contain correction factors to those that would be obtained using the normal Gaussian assumptions     

Spatial-multiplexing phase-sweep transmit diversity (SM-PSTD) for multiantenna base stations with mobile-assisted scheduling and incremental rate feedback

Phase-sweep transmit diversity (PSTD) has been widely studied in 3G1X and Universal Mobile Telecommunications Systems (UMTS) for its performance gain and simplicity. However, conventional PSTD systems are designed based on asingle-sweeping beam, and only one user is selected for transmission at any time. Therefore, it fails to fully exploit the available spatial degree of freedom. In this study, a novel spatial-multiplexing phase-sweep transmit diversity (SM-PSTD) scheme with partial feedback mobile-assisted scheduling is being proposed. The downlink performance (system capacity and proportional fairness) of a multiantenna base station has been its focus. The spatial-channel sweeping facilitates the multiuser selection diversity between users, while the spatial multiplexing significantly enhances the system capacity. As the number of transmit antennas n/sub T/ is increased, the SM-PSTD system performance is gradually limited by the multiuser interference because it is more and more difficult to find a set of users perfectly orthogonal within the n/sub T/ spatial channels. Yet, the multiuser interference could be reduced by increasing the number of active users K in the system. Asymptotically, at large n/sub T/ and K, it shows that the system capacity scales linearly instead of logarithmically with respect to the transmitted power.     

A Partially-Blocking Queueing System with CBR/VBR and ABR/UBR Arrival Streams

In this paper we consider an ATM transmission link, to which CBR or VBR and ABR or UBR calls arrive according to independent Poisson processes. CBR/VBR calls (characterized by their equivalent bandwidth) are blocked and leave the system if the available link capacity is less than required at the time of arrival. ABR/UBR calls, however, accept partial blocking, meaning that they may enter service even if the available capacity is less than the specified required peak bandwidth, but greater than the so called minimal accepted bandwidth. Partially blocked ABR/UBR calls instead experience longer service time, since smaller given bandwidth entails proportionally longer time spent in the system, as first suggested in [3] and analyzed in details herein. Throughout the life time of an ABR/UBR connection, its bandwidth consumption fluctuates in accordance with the current load on the link but always at the highest possible value up to their peak bandwidth (greedy sources). Additionally, if this minimal accepted bandwidth is unavailable at the time of arrival, ABR/UBR calls are allowed to wait in a finite queue. This system is modeled by a Continuous Time Markov Chain (CTMC) and the CBR/VBR and ABR/UBR blocking probabilities and the mean ABR/UBR waiting- and service times are derived.     

一种高速数据采集／重放系统的实现

介绍了一种高速数据采集／重放系统。该系统采用工业控制计算机作为主控设备，在主控计算机内部配置了大容量内存作为高速海量存储介质。系统采用一块基于FPGA的高速信号采集／回放PCI卡来实现。该卡以FPGA为采集／回放的核心控制芯片，并在FPGA内部实现了64位/33MHz的PCI接口逻辑。系统有实时和非实时两种模式，其采集／回放速度高达240MHz，存储容量能扩展至3GB，它可供电磁信号环境仿真及复杂信号分析用。     

Feeders-TDMA: a distributed-control algorithm for satellite channel capacity assignment in a mixed traffic and faded environment

This paper presents Faded Environments Effective Distributed Engineering Redundant Signalling (FEEDERS), an access scheme for sharing, in time division multiple access (TDMA) mode, the capacity of a satellite channel among a number of stations, on the basis of user demand. This scheme and its companion Distributed Allocation with Request In Fixed Slots (DRIFS), result from a study carried out by the authors on distributed-control protocols for geostationary satellite access. Both protocols derive from the Fifo Ordered Demand Assignment/Information Bit Energy Adapter (FODA/IBEA) centralized-control system and have the same features. The distributed technique to compute the capacity allocation adopted by FEEDERS improves some performance in FODA/IBEA, but raises a problem about system stability. Techniques to solve this problem are presented, together with system performance. A comparison is also made with the FODA/IBEA system. © 1997 John Wiley & Sons, Ltd.     

Comparison of time slot allocation strategies for CDMA/TDD systems

The traffic (load) asymmetry between uplink and downlink is a remarkable traffic characteristic in cellular mobile multimedia communications. The code division multiple access system with time division duplex mode (CDMA/TDD system), adopting unbalanced slot allocation between uplink and downlink, is a good solution for this traffic asymmetry. However, the level of traffic asymmetry may be significantly different from cell to cell. In this paper, we investigate a slot allocation strategy (DA strategy), by which each cell has its own slot allocation according to the level of traffic asymmetry. We compute the system capacity with DA strategy and find out the optimal slot allocation for the system. We also compare the maximum capacity to that with another strategy (SA strategy), by which all cells have the same slot allocation. As a result, this paper shows that the system with DA strategy outperforms the system with SA strategy in the aspect of capacity     

一种适合时分双工环境的分组预约多址协议

对数字式蜂窝移动通信网络,本文提出了时分双工环境下的冲突削弱分组预约多址（CR－PRMA／TDD）协议,并使用平衡点法推导出给定同时通话终端数时的分组丢弃率。计算机仿真结果表明,CR－PRMA／TDD协议可以极大地提高系统的容量。     

Two-stage voltage control strategy for PV plants based on variable droop control

ABSTRACT

Voltage violation is an important factor that restricts grid-connected photovoltaic system. The utilization of PV plant’s reactive power capability is an effective measure to mitigate voltage violation. This paper proposes two-stage voltage control strategy to enhance the voltage support capability of photovoltaic grid-connected system. In first stage, adaptive gains are set according to the maximum reactive capacity of each PV plant in order to distribute reactive power among PV plants more reasonably, avoiding certain PV plants operating in the limit state for a long time. In second stage, when the reactive power capacity is insufficient, the priority of active power curtailment for each PV plant is calculated in real time. Active power curtailment control will be performed in PV plants with high priority to released more reactive power capacity for voltage support. The simulation results carried out by PSCAD/EMTDC software demonstrated that this strategy can effectively solve the voltage violation problem. Meanwhile, the proposed strategy not only can exploit reactive capacity of each PV plant as much as possible to avoid certain PV plants operating in the limit state for a long time, but also can reduce the amount of active power curtailment when reactive power adequacy is insufficient.     

Low rate encoding: A means of increasing system capacity in a TDMA/DSI system

The satellite capacity required in a TDMA/DSI system for a certain amount of traffic can be substantially reduced when using associated LRE techniques. An analysis based on the future EUTELSAT TDMA/DSI traffic forecast has been made in this respect, by using the computer program presently in use at EUTELSAT for the generation of burst time plans. The analysis considers different operational modes (single destination, multidestination and multiclique) and presents also some considerations on the problem of transition from a 64 kb/s TDMA/DSI system to a 32 kb/s TDMA/DSI system.     

Optical video/audio signal distribution network for a broadcastcenter using WD/TD/SD hybrid multiplexing

Today's TV broadcast centers require large capacity and flexible routing networks for handling uncompressed serial digital video signals. Fuji Television's new broadcast center employs a newly developed optical video/audio signal distribution network This paper describes the design concept, the system structure, and the performance of the optical network. A wavelength-division and time division hybrid multiplexed (WD/TD) optical network has been applied to the broadcast center. This type of optical network is attractive for a broadcast center application, because of its large capacity, multiple format handling, and flexible operation capabilities     

Optimal control of a removable server in an M/Ek/1 queueing system with finite capacity

This paper deals with the economic behavior of a removable server in the N policy M/E_k/1 queueing system with finite capacity. Expressions for the probability mass functions of the number of customers in the system are derived and taken in closed-form. As special cases, the probability mass functions of the number of customers for the N policy M/M/1 queueing system, the ordinary M/K_k/1 queueing system, and the ordinary M/M/1 queueing system are obtained. The cost structure includes a holding cost per unit time spent in the system for each customer, costs per unit time for keeping the server on or off, a server start-up cost, a server shut-down cost, and fixed cost for every lost customer. Following the construction of the total expected cost per unit time, we determine the optimal operating policy at minimum cost.     

Performance of a cellular hybrid C/TDMA mobile radio systemapplying joint detection and coherent receiver antenna diversity

For future mobile radio systems, an appropriately chosen multiple access technique is a critical issue. Multiple access techniques presently under discussion are code division multiple access (CDMA), time division multiple access (TDMA), and hybrids of both. In the paper, a hybrid C/TDMA system using joint detection (JD-C/TDMA) with coherent receiver antenna diversity (CRAD) at the base station (BS) receiver is proposed. Some attractive features of the JD-C/TDMA system are the possibility to flexibly offer voice and data services with different bit rates, soft capacity, inherent frequency and interferer diversity, and high system capacity due to JD. Furthermore, due to JD, a cluster size equal to 1 can be realized without needing soft handover. The single cell E_b/N₀ performance and the interference situation in a cellular environment of the uplink of a JD-C/TDMA mobile radio system with CRAD is investigated in detail. It is shown that the cellular spectrum efficiency is remarkably high, taking values up to 0.2 bit/s/Hz/BS in the uplink, depending on the actual transmission conditions     

A Custom Image Convolution DSP with a Sustained Calculation Capacity of >1 GMAC/s and Low I/O Bandwidth

A customized processor for real time image convolution has been designed to increase the performance of an instrument for automated cereal grain quality assessment. Image convolution requires an extensive amount of calculation capacity and a corresponding amount of data transfers, hard to achieve with standard processors in real time. Therefore, a tailored architecture with a streamlined dataflow has been developed with emphasis on a system design perspective. The designed processor has a sustained calculation capacity of >1 GMAC/s and on-chip line buffers reduce the amount of external data transfers. Hence, the complexity of the designed processor has been increased to gain a lower complexity of the complete system. To achieve powerful and versatile filtering the size of the programmable kernel functions have been maximized to 15 × 15.