A column generation and partitioning approach for multi-commodity flow problems

Multi-commodity network flow problems, prevalent in transportation, production and communication systems, can be characterized by a set of commodities and an underlying network. The objective is to flow the commodities through the network at minimum cost without exceeding arc capacities. In this paper, we present a partitioning solution procedure for large-scale multi-commodity flow problems with many commodities, such as those encountered in the telecommunications industry. Using a cycle-based multi-commodity formulation and column generation techniques, we solve a series of reduced-size linear programs in which a large number of constraints are relaxed. Each solution to a reduced-size problem is an improved basic dual feasible solution to the original problem and, after a finite number of steps, an optimal multi-commodity flow solution is determined. Computational experience is gained in solving randomly generated test problems and message routing problems in the communications industry. The tests show that the procedure solves large-scale multi-commodity flow problems significantly faster than existing linear programming or column generation solution procedures.     

Burst reduction properties of rate-control throttles: downstreamqueue behavior

Considers rate-based flow control throttles feeding a sequence of single server infinite capacity queues. Specifically, the authors consider two types of throttles, the token bank and the leaky bucket. They show that the cell waiting times at the downstream queues are increasing functions of the token buffer capacity. These results are established when the rate-based throttles have finite capacity data buffers as well as infinite capacity buffers. In the case that the data buffer has finite capacity, they require that the sum of the capacities of the data buffer and token buffer be a constant. Last, they establish similar results for the process of number of losses at the last downstream queue in the case that the waiting buffer has finite capacity     

基于二元域等效的RS码编码参数盲识别

现代数字通信中常常进行信道编码识别处理.目前RS（Reed-Solomon,RS）码盲识别需对高阶域下所有谱分量进行求取,计算较为复杂,因此提出了一种基于二元域等效的识别方法.首先根据有限域性质将RS码等效为二元域上的线性分组码,然后建立码长、信息分组长度、生成多项式和本原多项式的关联模型.通过遍历各阶本原多项式,并验证二元线性分组码的校验向量,完成各参数的联合识别.仿真结果和理论分析表明,该方法在提升抗误码性能的同时有效减少了计算量,可用于智能通信和通信侦察等系统中.     

Insufficiency of linear coding in network information flow

It is known that every solvable multicast network has a scalar linear solution over a sufficiently large finite-field alphabet. It is also known that this result does not generalize to arbitrary networks. There are several examples in the literature of solvable networks with no scalar linear solution over any finite field. However, each example has a linear solution for some vector dimension greater than one. It has been conjectured that every solvable network has a linear solution over some finite-field alphabet and some vector dimension. We provide a counterexample to this conjecture. We also show that if a network has no linear solution over any finite field, then it has no linear solution over any finite commutative ring with identity. Our counterexample network has no linear solution even in the more general algebraic context of modules, which includes as special cases all finite rings and Abelian groups. Furthermore, we show that the network coding capacity of this network is strictly greater than the maximum linear coding capacity over any finite field (exactly 10% greater), so the network is not even asymptotically linearly solvable. It follows that, even for more general versions of linearity such as convolutional coding, filter-bank coding, or linear time sharing, the network has no linear solution.     

多频带混合场景下终端直通通信用户最优用户密度与功率分配研究

该文分析了蜂窝与终端直通(Device-to-Device, D2D)混合网络中多频带资源的场景下D2D用户最佳密度和功率分配问题。在混合网络中包含一个或者多个蜂窝网络,D2D用户复用蜂窝系统上行频谱资源。通过采用随机几何理论,上述问题可以建模成一个以最大化D2D网络容量为目标并以蜂窝用户和D2D用户的中断概率为约束条件的优化问题。由于上述优化问题非凸,因此分成两步解决原问题:首先证明当D2D用户密度确定的时候原问题对于功率分配是凸问题,并通过拉格朗日对偶方法得到了最优功率分配方案;随后证明中断约束条件将D2D用户密度的定义域分成有限个子区间,在每个子区间上可以通过求导的方式得到D2D传输容量局部最优解,基于上述两个结论,文中设计了一种子区间最优值搜索算法。通过仿真验证了算法的有效性,并且反映出D2D传输容量主要由中断约束条件和来自蜂窝网络的干扰决定。     

Throughput evaluation of multichannel slotted Aloha-type protocols with receiver collisions

The problem of receiver collisions in multichannel multiaccess communication systems is studied in this paper. A rigorous method is developed for the analytic solution of throughput performance assuming receiver buffer with a capacity of one packet. We calculate the average rejection probability at the destination of a packet in order to estimate the effect of receiver collisions. The evaluations are carried out for multichannel slotted Aloha-type protocols with Poisson arrivals and finite population. Also numerical results are showing the throughput reduction as it compared with the protocol case without receiver collisions.     

A general scheme for equalization of space-time block-coded systems with unknown CSI

Recently, space-time block codes (STBCs) have gained much attention as an effective transmit diversity technique to increase the capacity of wireless communication systems. In this paper, we consider a general technique for direct equalization of space-time block-coding systems with unknown channel state information (CSI). This technique is suitable for several existing hybrid STBC schemes, such as STBC/orthogonal-frequency-division multiplexing (STBC-OFDM) and STBC/code-division multiple access (STBC-CDMA). We show that by exploiting the redundancy in the structure of STBC, a zero-forcing equalizer can be constructed without channel estimation. The conditions for the identifiability of the zero-forcing equalizer are also derived to ensure correct equalization. To further improve the performance of the proposed method, a new iterative algorithm is developed by incorporating the finite alphabet property of information symbols. Simulation results show that the proposed algorithms can outperform comparative schemes in most simulation conditions.     

Hybrid filter with predict-estimator and compensator for the linear time invariant delayed system

This paper investigates the problem of real-time estimation for one kind of linear time invariant systems which subject to limited communication capacity. The communication limitations include signal transmission delay, the out-of-sequence measurements and data packet dropout, which appear typically in a network environment. The kernel of filter design is equally to formularize the traditional Kalman filter as one linear weighted summation which is composed of the initial state es-timate and all sequential sampled measurements. For it can adapt aforementioned information limi-tatious, the linear weighted summation is then decomposed into two stages. One is a predict-estimator composed by all reached measurements, another is one compensator constructed by those time-delayed data. In the network environment, there are obvious differences between the new hybrid filter and those existing delayed Kalman filters. For example, the novel filter can be optimal in the sense of linear minimum mean square error as soon as all measurements available and has the lowest running time than these existing delayed filters. One simulation, including two cases, is utilized to illustrate the design procedures proposed in this paper.     

A fieldbus prototype for educational purposes

One of the problems with instrumentation systems is the interconnection between the multiple devices with different communication protocols. Exacerbating this problem are two typical requirements of interconnection: minimize cabling cost and avoid degradation of the signal during transmission. Cabling cost can be reduced through several multidrop communication systems: industrial local area networks or wireless communication. Reduction of signal to noise can restrict system performance and the quality of manufactured products, even if high-accuracy devices are used. Another problem in the field of manufacturing instrumentation networks is that industry uses multiple solutions to interconnect instrumentation with different communication protocols. This article presents the development of a prototype for an instrumentation network with the goal to study and analyze the characteristics of the different communication solutions. The overall system contains a large number of instrumentation devices, which is a great advantage for educational purposes and laboratory experiments. The students can configure, calibrate, and operate a large number of instruments connected to different segments of the DCS. We also connected some current-loop devices to the FF system to evaluate their performance when connected to a fully digital network. Results from the prototype DCS show that networking between different instrumentation devices and protocols can be successful and that a hybrid solution using conventional 4-20 mA current loop and fully digital instrumentation can work to leverage existing analogue systems. Future work will include the development of a fieldbus network analyzer to trace messages in the network and study the quality of FF service parameters, such as packet loss and delay measurement, as a function of network load.     

Networked Control for Singular Systems Over Unreliable Channel with Limited Capacity

This paper addresses networked control problem for discrete-time linear singular systems over unreliable channel. It is assumed that the controller can only receive the transmitted sequence of finite coded signals via unreliable channels, which may be lost due to the limited communication capacity and transmission errors. By introducing compensation terms at every update instant and auxiliary systems in each sampling interval, both state- and output-based coder–decoder–controller procedures are proposed. Then, a uniform sufficient feedback stabilization condition involving the size of coding alphabet, the sampling period and data packet dropout rate is obtained. Finally, an example is given to illustrate the design procedures and effectiveness of the proposed results.     

Design and analysis of very high-speed network architectures

Communication architectures for very-high-speed networks are dealt with. The use of high communication speed increases the ratio between the end-to-end propagation delay and the packet transmission time. This increase restricts the utilization of the high system bandwidth in broadcast channel-based systems, causing a rapid performance deterioration. A communication system architecture characterized by the use of several parallel channels and design of the nodes' channel interface is presented. The channel-division approach is introduced, showing that for a given system bandwidth the total system capacity will be increased by bandwidth division and parallel communication. An analytic model of this system is developed, from which the proposed system's performance is obtained and performance bounds determined for multichannel slotted finite systems. The results show that the architecture has a potential to improve significantly the system performance compared to conventional single-channel-based systems. Furthermore, for a given network configuration an optimal architecture can be found which simultaneously maximizes the system throughput and minimizes the average packet delay     

多信源据流的建模与分析

本文提出多信息源多种数据类型单一输出通道的数据通信系统数据流的一个Markov模型,给出有限缓冲条件下系统的稳态数据丢失率,数据传输率和输出通道利用率等性能指标的精确求解算法,并将数据流模型应用到选择性接入的控制策略的性能评价。     

智能天线非理想波束赋形对TD-SCDMA系统性能的影响

在实际的无线网络中,由于无线信道的复杂性以及DOA估计的误差,会导致智能天线系统的波束赋形出现一定程度的偏差。该文通过分析智能天线系统的原理,提出了非理想波束赋形智能天线对系统性能影响的研究方法,研究了智能天线系统的鲁棒性以及不理想波束赋形的智能天线对TD-SCDMA系统性能的影响。理论和仿真结果表明,波束赋形的准确度直接影响移动通信系统的性能,系统所能容忍的波束赋形偏差有一个固定的门限值,该门限值随着系统负载的增加而减小。     

Performance analysis of a rate-control throttle where tokens andjobs queue

A rate-control throttle is used for overload control in distributed switching systems and computer and communication networks. Typical implementations of the throttle have a token bank where an arriving job is blocked and rejected if the bank is empty of tokens. The author examines an expanded implementation where an arriving job queues in a finite buffer when the token bank is empty. It is shown that the steady-state throughput and blocking of jobs depends on the capacity of the job buffer and the capacity of the token bank only via the sum of the two capacities, not on their individual values. Thus, the job buffer per se is not needed to enhance the robustness of the throughput of the throttle to unknown exogenous job arrival rates. However, a job buffer (along with a token bank) with adjustable buffer capacities does have the potential to shape the departure process and to adapt between a delay control and a work-rejection control     

ARMA system identification based on second-order cyclostationarity

Previous work has presented novel techniques that exploit cyclostationarity for channel identification in data communication systems. The present authors investigate the identifiability of linear time-invariant (LTI) ARMA systems based on second-order cyclic statistics. They present a parametric and a nonparametric method. The parametric method directly identifies the zeros and poles of ARMA channels with a mixed phase. The nonparametric method estimates the channel phase based on the cyclic spectra alone. They analyze the phase estimation error of the nonparametric method for finite dimensional ARMA channels. For specific, finite dimensional ARMA channels, an improved method is given, which combines the parametric method with the nonparametric method. Computer simulation illustrates the effectiveness of the methods in identifying ARMA system impulse responses     

Interface optimization for concurrent systems under timingconstraints

The scope of most high-level synthesis efforts to date has been at the level of a single behavioral model represented as a control/data-flow graph. The communication between concurrently executing processes and its requirements in terms of timing and resources have largely been neglected. This restriction limits the applicability of most existing approaches for complex system designs. This paper describes a methodology for the synthesis of interfaces in concurrent systems under detailed timing constraints. The authors model interprocess communication using blocking and nonblocking messages. They show how the relationship between messages over time can be abstracted as a constraint graph that can be extracted and used during synthesis. They describe a novel technique called interface matching that minimizes the interface cost by scheduling each process with respect to timing information of other processes communicating with it. By scheduling the completion of operations, some blocking communication can be converted to nonblocking while ensuring the communication remains valid. To further reduce hardware costs, the authors describe the synthesis of interfaces on shared physical media. They show how this sharing can be increased through rescheduling and serialization of the communication. In addition to systematically reducing the interface synchronization cost, this approach permits analysis on the timing consistency of interprocess communication     

Optimal Bandwidth Assignment on Up- and Downlinks of Satellite with Buffer Capacity

This paper considers a satellite communication system with the slotted ALOHA access mode where the satellite is assumed to have on-board regeneration ability and the finite buffer capacity for storing noncollided packets from the uplink. The system is analyzed with the downlink bandwidth restricted to1/Lof the uplink bandwidth, and with the conventional slotted ALOHA system whereL = 1and the buffer size at the satellite is equal to zero. Maximum throughput and throughput-delay characteristics of this system are analytically obtained. The satellite is given an optimal buffer size to achieve maximum throughput and minimum packet transmission delay. It is shown that the constraints that lead to the downlink bandwidth being lower than the uplink bandwidth do not necessarily result in throughput penalties in a buffered satellite system. Furthermore, when the total bandwidth which can be divided between up- and downlinks is given, if two or three times that of the downlink is assigned to the uplink and if the satellite has buffer storage space only for a few packets, we show that maximum throughput of the system will be improved about 40 percent with little change in delay characteristics in comparison with that of the conventional slotted ALOHA system where the given total bandwidth is equally divided between up- and downlinks.     

Loss Probability for a Finite Buffer Multiplexer with the <Emphasis Type="Italic">M/G/∞</Emphasis> Input Process

This paper studies the impact of long-range-dependent (LRD) traffic on the performance of a network multiplexer. The network multiplexer is characterized by a multiplexing queue with a finite buffer and an M/G/∞ input process. Our analysis expresses the loss probability bounds using a simple relationship between loss probability and buffer full probability. Our analysis also derives an exact expression for the buffer full probability and consequently calculates the loss probability bounds with excellent precision. Through numerical calculations and simulation examples, we show that existing asymptotic analyses lack the precision for calculating the loss probability over realistic ranges of buffer capacity values. We also show that existing asymptotic analyses may significantly overestimate the loss probability and that designing networks using our analysis achieves efficient resource utilization.     

Capacity of interconnected ring communication systems with unique loop-free routing (Corresp.)

{em Capacity} is defined for a given distribution of offered traffic as the maximum rate with which packets can be sent with finite delay through the network by appropriate routing. It is shown how capacity depends on the traffic characteristics and on the topology of ring communication systems interconnected so as to provide unique loop-free routing. First, the traffic conditions are given under which the capacity of a {em single ring} attains its maximum and its minimum. For the case of {em uniform traffic} it is shown that the capacity is equal to twice the minimum capacity. Then it is shown that, for uniform traffic, the capacity relative to a single ring communication system can be increased by as much as33.3or80percent when the stations are split up into two or three separate rings, respectively, interconnected to give unique loop-free routing. Exact formulas are given for the capacity of systems with an arbitrary number of stations split up into an arbitrary number of separate rings interconnected to give unique loop-free routing. Finally, it is shown that connecting {em local rings} through a star network with a central switching node is particularly useful when stations can be segregated into local groups of stations which often communicate with stations from the same local group but only rarely with stations from the other groups. Exact formulas are given to calculate the capacity of such interconnected ring communication systems.