宽带GEO卫星网络媒体接入控制协议

宽带地球同步轨道（GEO）卫星通信网络中对媒体接入控制协议设计的目的就是在保障用户服务质量的同时提高系统资源利用率。概述了宽带GEO卫星网络的特点,总结了影响媒体接入控制协议性能的主要因素,重点对两种多址接入方案进行分析：基于混合式自适应分配机制的媒体接入控制协议和基于地面请求策略的动态分配多址接入协议。结果表明,提高网络性能的最佳方法是将有效的地面请求策略与合理的资源分配方式相结合。最后,对下一步的研究方向提出了建议。     

Channel assignment problem in cellular systems: a new model and atabu search algorithm

The channel assignment in cellular systems has the task of planning the reuse of available frequencies in a spectrum efficient way. A classical approach to frequency assignment problems, when applied to the frequency planning of cellular networks, does not enable this task to be performed in an efficient way, since it does not consider the cumulative effect of interferers. We propose a new model for the channel assignment problem in narrow-band cellular networks, which accounts for the cumulative effect of interferers. In this model, the service area is partitioned into regions and the propagation characteristics are assigned by means of the levels received in each region by the considered base stations (BSs). The objective is to maximize the sum of traffic loads offered by regions in which the ratio between the received power and the sum of powers received from interfering transmissions is above a threshold value. We also present an algorithm, based on tabu search (TS) techniques, to solve this problem. This algorithm has been tested on some instances obtained by using a simple radio channel model and on a real world instance     

The end of spectrum scarcity [spectrum allocation and utilization]

This article discusses the issues of spectrum allocation and the effect of new technologies on spectrum utilization. To understand the impact new radio technologies are having on spectrum availability, it is helpful first to address a common misconception: that spectrum is a concrete and finite resource. Not so. Radio waves do not pass through some ethereal medium called "spectrum"; they are the medium. What is licensed by governments is not a piece of a finite pie but simply the right to deploy transmitters and receivers that operate in particular ways. Moreover, interference is not some inherent property of spectrum. It is a property of devices. A better receiver will pick up a transmission where an earlier one heard only static. Whether a new radio system "interferes" with existing ones is entirely dependent on the equipment involved. Consequently, the extent to which there appears to be a spectrum shortage largely depends not on how many frequencies are available but on the technologies that can be deployed.     

Channel assignment scheme in clustered multichannel cognitive radio networks with outdated CSI over Rayleigh fading channels

This work investigates channel assignment for cooperative spectrum sensing in multichannel cognitive radio networks, where the heterogeneity of primary user (PU) activity and the effect of varying channel condition on the received signal‐to‐noise ratio during cluster formation are considered. With the objective to minimize interference to the PU while enhancing multiple spectrum utilization of the secondary user (SU), an overlapping cluster‐based assignment is formulated into a nonlinear integer optimization problem. To obtain an efficient solution, the nonlinear integer problem is transformed into a mixed integer linear problem, based on which, this paper proposes an exact solution and then two new heuristic algorithms for suboptimal solutions, respectively. Furthermore, a comparative study of four different cluster head selection schemes with respect to their performance in cooperative spectrum sensing, under cluster's heterogeneity in terms of SUs distribution relative to PU transmitter location is presented. Based on the study, a robust cluster head selection scheme is proposed. Simulation results show that good sensing performance and increased opportunistic spectrum utilization in multichannel cognitive radio networks are two sides of a coin that depend on the ratio of the SUs to the number of PU channels. How far away the PU is from the cluster center is also seen to be key in the optimal selection of cluster heads in cooperative spectrum sensing.     

Capacity allocation and channel assignment in cellular radio systems using reuse partitioning

Reuse partitioning is a technique for providing more efficient spectrum reuse in cellular radio systems. A cell in such a system is divided into concentric zones, each associated with an overlaid cell plan. For these schemes an optimum channel assignment strategy is proposed. Numeric examples show capacity improvements of about 50% compared to conventional systems.<>     

A compact dynamic channel assignment scheme based on Hopfield networks for cellular radio systems

In this paper, a new channel assignment strategy named compact dynamic channel assignment (CDCA) is proposed. The CDCA differs from other strategies by consistently keeping the system in the utmost optimal state, and thus the scheme allows to determine a call succeeding or failing by local information instead of that of the whole network. It employs Hopfield neural networks for optimization which avoids the complicated assessment of channel compactness and guarantees optimum solutions for every assignment. A scheme based on Hopfield neural network is considered before; however, unlike others, in this algorithm an energy function is derived in such a way that for a neuron, the more a channel is currently being allocated in other cells, the more excitation the neuron will acquire, so as to guarantee each cluster using channels as few as possible. Performance measures in terms of the blocking probability, convergence rate and convergence time are obtained to assess the viability of the proposed scheme. Results presented show that the approach significantly reduces stringent requirements of searching space and convergence time. The algorithm is simple and straightforward, hence the efficient algorithm makes the real‐time implementation of channel assignment based on neural network feasibility. Copyright © 2008 John Wiley & Sons, Ltd.     

Exploiting context, profiles, and policies in dynamic sub-carrier assignment algorithms for efficient radio resource management in OFDMA networks

Dynamic sub-carrier assignment (DSA) is considered as one of the most important aspects for achieving efficient spectrum utilization in orthogonal frequency division multiple access (OFDMA) based networks. Most of well-known DSA algorithms operate in a best effort manner, where the full set of sub-carriers is used in order to achieve the maximum possible quality of service level per user. However, in a real network environment, there are several management aspects to be considered such as context information (users, services, and radio environment conditions), user profiles, and network operator policies. In the context of OFDMA networks management, DSA algorithms should be extended incorporating such aspects in order to introduce fairness in the assignment of sub-carriers as well as to improve the overall system performance. In this paper, an efficient radio resource management scheme that incorporates a new DSA algorithm which exploits context profiles and policies information is presented. Results showcase the benefits that the proposed approach brings in terms of fairness on sub-carriers assignment and overall system performance.     

Improving the capacity in wireless networks through integratedchannel base station and power assignment

The limited availability of radio frequency spectrum will require future wireless systems to use more efficient and sophisticated resource allocation methods to increase network capacity. In this work, we propose a joint resource allocation algorithm (JRAA) that makes the channel base station and power assignment in a wireless network with an arbitrary number of base stations and mobiles attempting to minimize the number of channels needed to provide each user in the system with an acceptable radio connection. We compare the performance of the JRAA for both the forward (downstream) and reverse (upstream) directions, in terms of the achievable traffic capacity, with some bounds on the performance of the maximum packing (MP), clique packing (CP), and reuse partitioning (RP) techniques, which are usually used as benchmarks on the capacity that can be achieved by any traffic-adaptive dynamic channel assignment strategy, where the quality is guaranteed by the reuse distance. Those performance results verify the improvement that can be achieved by the integration of the channel base station and power assignment. Finally, several versions of the two-way channel assignment problem are studied and evaluated     

基于遗传算法的光电干扰资源优化分配研究

结合光电信息系统作战运筹中目标分配原则，及军事运筹理论，建立了干扰资源优化分配模型。给出了基于遗传算法的模型求解方法及步骤，阐述了遗传算法在光电干扰资源分配中的应用，并进行了实例仿真，得出了最佳干扰资源分配方案。仿真结果证明，该方法对于约束条件复杂的优化模型求解是有效、可行的，为光电信息系统指挥控制决策提供了有力支持。     

Channel assignment for cellular radio using extended dynamic programming

The channel assignment is an important aspect of cellular radio networks. Because of the limitations on the frequency spectrum, the optimal or near-optimal channel assignment has become an essential part of the network operations of wireless personal communication systems. We formulate a new strategy for the channel assignment problem in agreement with the electromagnetic compatibility constraints. We introduce and formulate the extended dynamic programming (EDP), as an extension of dynamic programming for solving the channel assignment problem in a cellular system. Using EDP an algorithm is developed for fixed channel assignment problem and it is tested and compared with other existing methods by solving different problems. In agreement with electromagnetic compatibility constraints, solution strategy based on EDP algorithm finds many valid solutions with minimum possible bandwidth.     

认知无线电及其关键技术

认知无线电能感知频谱环境,并通过学习实时调整传输参数,实现频谱再利用,是一种能有效提高频谱利用率的新型通信模式。在介绍了认知无线电的基本概念及国内外的研究概况后,着重讨论了认知无线电研究中碰到的几个关键技术：无线电参数智能优化技术、宽带频谱感知技术、宽带数据传输技术等。提出了这些关键技术应着重研究的方向。     

Dynamic Channel Assignment with Flexible Reuse Partitioning in Cellular Systems

In cellular communications, one of the main research issues is how to achieve optimum system capacity with limited frequency spectrum. For many years, researchers have proposed and studied many dynamic channel assignment (DCA) schemes to increase the capacity of cellular systems. Another proposed technique, Reuse Partitioning (RP), is used to achieve higher capacity by reducing the overall reuse distance. In convention, when RP is exploited in network-based DCA, a portion of channels will be assigned permanently to each partitioned region. However, the number of channels assigned to each region may not be~optimum due to factors like the uneven and time-varying traffics. In this paper, a new network-based DCA scheme is proposed with the flexible use of RP technique, named as flexible dynamic reuse partitioning with interference information (FDRP-WI). In this scheme, channels are open to all incoming calls and no channel pre-allocation for each region is required. As long as the channel assignment satisfies the co-channel interference constraints, any user from any region can use any channel. The scheme aims to minimize the effect of assigned channels on the availability of channels for use in the interfering cells and to reduce overall reuse distance. Both FDRP-WI with stationary users and mobile users are investigated. Simulation results have confirmed the effectiveness of FDRP-WI scheme. In the case with stationary users, FDRP-WI exhibits outstanding performance in improving the system capacity under both uniform and non-uniform traffic distributions. Under the uniform traffic case, the scheme can provide over 100% capacity improvement as compared to conventional fixed channel assignment scheme with 70 system channels at 1% blocking probability. In the case with mobile users, the impact of mobility on the new call probability, P _b, and the call dropping probability, P _d, is evaluated. The effect on system capacity of reserving some channels for handoff calls is first studied. Then, we propose a new handoff scheme, called “Reverse Overflow” (RO), to improve the utilization of channels with smaller reuse distances under mobile environment. Simulation results show that, with RO handoff, the system capacity of FDRP-WI is effectively improved at the expense of higher handoff rates in the cellular system.     

A Class of Decentralized Routing Algorithms Using Relaxation

An important problem in packet-switched communication networks is the optimal assignment of routes to the message packets. An optimal routing assignment is one which chooses network paths for the packets in a way that minimizes some cost function, typically average message delay. A class of optimal routing algorithms is described which utilize a type of iterative computation known as relaxation. Computation is decentralized in the sense that each node computes its routing strategy using only information supplied from adjacent nodes. Being iterative, the algorithms are inherently adaptive. The routing computation is based conceptually on an electrical network analog for the optimization problem. We show that a simple, convergent relaxation procedure can be used to "solve" the analog network, thereby yielding the optimal routing strategy. A simple example is presented to illustrate the method. In general, the computational load compares favorably with other (centralized) methods, although further work is needed to obtain quantitive comparisons in specific cases.     

光子晶体光纤中频率啁啾对超连续谱的影响

基于光子晶体光纤(PCF)中脉冲演变遵循的非线性演化方程,用数值方法研究了反常色散情形下PCF中脉冲初始啁啾对超连续谱产生的影响,探讨了利用脉冲啁啾控制超连续谱产生的方法。结果表明：正、负啁啾均使谱展宽的速率变小,尤其是负啁啾情形,展宽速率更小,说明啁啾对谱展宽是不利的;在一定的初始条件下,光谱展宽存在一个最佳光纤长度,在这个长度处,光谱展宽最大,进一步增加光纤长度,谱宽基本保持不变;相对于变换极限脉冲来说,初始正、负啁啾脉冲对应的最佳光纤长度分别缩短和延长。     

An optimum step-size assignment for incremental LMS adaptive networks based on average convergence rate constraint

This paper presents an optimum step-size assignment for incremental least-mean square adaptive networks in order to improve its robustness against the spatial variation of observation noise statistics over the network. We show that when the quality of measurement information (in terms of observation noise variances) is available, we can exploit it to adjust the step-size parameter in an adaptive network to obtain better performance. We formulate the optimum step-size assignment as a constrained optimization problem and then solve it via the Lagrange multipliers approach. The derived optimum step-size for each node requires information from other nodes, thus with some justifiable assumptions, near-optimum solutions are derived that depend only on local information. We show that the incremental LMS adaptive network with near-optimal step sizes has improved robustness and steady-state performance. Simulation results are also presented to support the theoretical results.     

Survivable routing,spectrum and waveband assignment strategy in cloud Optical and Data Center Network

These years, data centers are developing quickly and cloud Optical and Data Center Network (ODCN) has been shown to be the most viable solution for inter-data-center network implementation with less energy consumption and higher transmit rate. At the same time, elastic optical networks and waveband switching can address the problems caused by dramatic increase in network scale. In cloud hierarchical ODCN with flexible spectrum and waveband switching, survivability is an important and complex issue which is needed to be researched. So, we study the survivable routing, spectrum and waveband assignment strategy in cloud hierarchical ODCN, and in this paper, a novel hierarchical shared-protection (HSP) strategy is proposed. We consider spectrum fragmentation, waveband and shared-protection simultaneously. By quantifying the influence of spectrum assignment and the emergence of fragmentation, slots are assigned to the optimal paths. In order to share protection resource or wavebands, a heuristics algorithm named HSPGA is proposed for optimally picking out the two protection paths. Simulation results show that the proposed HSP strategy decreased the amount of employed ports significantly. In addition, the spectrum efficiency is improved.     

基于竞争双深度Q网络的频谱感知和接入

认知用户通过频谱感知和接入过程识别频谱状态并占用空闲频谱,可有效利用频谱资源。针对频谱感知中存在感知错误和频谱接入中存在用户碰撞的问题,首先建立多用户多信道模型,设计频谱感知和频谱接入过程;然后通过结合双深度Q网络和竞争Q网络,设计竞争双深度Q网络,解决过估计问题的同时优化网络结构;最后通过智能体与所设计模型中状态、观测、回报和策略的交互,完成使用竞争双深度Q网络解决频谱感知和接入问题的一体化研究。仿真结果表明,相比于已有深度强化学习方法,使用竞争双深度Q网络得到的数值结果更稳定且感知正确率和信道利用率都提高了4%。     

Call Admission for MPEG Video Streams

In modern visual communications, transmitted data may be discarded because of network congestion. With the constraint on transmission delay, the lost data cannot be retransmitted and therefore may cause a fatal degradation on the visual quality. In this paper, we discuss some topics of delivering MPEG video over networks for robust transmission. Not only are relevant techniques introduced, but we also present an empirical bandwidth allocation strategy. The essential motivation of the proposed strategy is to eliminate the burst of MPEG video streams and thereby retain the quality of visual service. The experimental results indicate that the proposed strategy can allocate an effective bandwidth for MPEG video streams. Moreover, the proposed strategy can still maintain the same level of network utilization that compares to the optimum solution, which is found based on an exhaustive search.     

A new frequency channel assignment algorithm in high capacity mobile communication systems

A new algorithm for frequency channel assignment in mobile radio communication is proposed. The algorithm uses flexible fixed channel assignment which enables the calls having all their nominal channels busy to borrow channels from the neighboring cells provided that co-channel interference will not result. The borrowed channel cannot be used in three interfering cells; therefore reassignment strategy is used when a call is terminated on a nominal channel to switch a call in progress in a borrowed channel to that nominal one and set free the borrowed channel in the three interfering cells. Thus the traffic carried on borrowed channels is minimized. Also different call switching strategies are proposed to give priority to some channels to be used by the nominal cells and other channels to be borrowed by neighboring cells. These strategies considerably reduce the blocking probability. A simulation study of the algorithm was carried out on 49 hexagonal zones having uniform traffic density. Also a combined telephone and dispatch traffic was included in the simulation study. The results showed that the new algorithm is better than the other channel assignment schemes. This can be applied in high capacity mobile communications systems to utilize the spectrum efficiently.     

认知无线电中基于频谱聚合的频谱分配算法

为了使认知用户可成功接入分配的频谱,进一步提高频谱利用率,提出了一种基于频谱聚合的分布式频谱分配算法(SADSA),该算法以图论着色为模型,算法过程考虑了认知用户的带宽需求和认知设备的最大聚合范围,仿真结果表明了该算法在认知用户接入率方面的优越性.