Adaptive distribution‐based handover scheme for cellular communication networks

In this paper, we propose a new Generalized Distribution‐Based Handover (DBHO) to deal with the inefficient utilization of spectral resources due to the non‐uniform cell loads. The DBHO scheme is different from the existing adaptive schemes since it uses a new criterion to initiate handover when moving from/to a congested cell. Two risk factors are used to dynamically change handover boundaries according to the distribution of traffic loads. This controls the handover initiation process such that a user in a congested cell that is moving to a free cell is allowed to initiate a handover to a new cell earlier, as long as the signal received from the target cell is higher than a certain threshold. While delaying the handover initiation process for a user moving in the opposite direction, as long as the signal received from the serving cell is not lower than a certain threshold. Our results show a substantial reduction in the handover and call dropouts rates. Our scheme is complementary to the existing adaptive schemes proposed in the literature. The proposed scheme also gives cellular system designers a new tool to optimize the overall network performance by initiating handovers based on the traffic intensities. Frequent handovers increase the load on switching networks, which consequently degrades the Quality of Service (QoS). Existing handover schemes usually use parameters such as the received signal strength for initiating a handover with some additional measurements to reduce unnecessary handovers and call dropouts. These schemes perform well when cell loads are somewhat evenly distributed, but fail to account for nonuniform traffic, as is often the case in microcells. Hence, it is desirable to design efficient handover schemes to avoid unnecessary handovers, reduce call dropouts and yet dynamically adapt to the variation of traffic among cells. In this paper, we present a new adaptive handover scheme that dynamically changes the handover boundaries to balance cell loads and to effectively reduce the average number of handovers. Copyright © 2004 John Wiley & Sons, Ltd.     

适于蜂窝网的高效机器类通信业务调度机制

Cellular-based Machine-Type Communication (MTC) will become more and more important in the near future for the advantage of the long-distance wireless communication. However, a large number of MTC applications introduce heavy load to cellular network. MTC traffic scheduling schemes are proposed to avoid congestion in this paper. Our approaches are based on the delay-tolerance of MTC traffic. Some MTC traffic is postponed until the network load becomes light. Moreover, our scheme efficiently utilizes the bandwidth resources reserved for handover in traditional cellular network. Simulation results show that the utility usage of radio resources is improved and the congestion probability is reduced.     

Congestion‐Aware Handover in LTE Systems for Load Balancing in Transport Network

Long‐Term Evolution employs a hard handover procedure. To reduce the interruption of data flow, downlink data is forwarded from the serving eNodeB (eNB) to the target eNB during handover. In cellular networks, unbalanced loads may lead to congestion in both the radio network and the backhaul network, resulting in bad end‐to‐end performance as well as causing unfairness among the users sharing the bottleneck link. This work focuses on congestion in the transport network. Handovers toward less loaded cells can help redistribute the load of the bottleneck link; such a mechanism is known as load balancing. The results show that the introduction of such a handover mechanism into the simulation environment positively influences the system performance. This is because terminals spend more time in the cell; hence, a better reception is offered. The utilization of load balancing can be used to further improve the performance of cellular systems that are experiencing congestion on a bottleneck link due to an uneven load.     

Efficient and adaptive congestion control for heterogeneous delay-tolerant networks

Detecting and dealing with congestion in delay-tolerant networks (DTNs) is an important and challenging problem. Current DTN forwarding algorithms typically direct traffic towards more central nodes in order to maximise delivery ratios and minimise delays, but as traffic demands increase these nodes may become saturated and unusable. We propose CafRep, an adaptive congestion aware protocol that detects and reacts to congested nodes and congested parts of the network by using implicit hybrid contact and resources congestion heuristics. CafRep exploits localised relative utility based approach to offload the traffic from more to less congested parts of the network, and to replicate at adaptively lower rate in different parts of the network with non-uniform congestion levels. We extensively evaluate our work against benchmark and competitive protocols across a range of metrics over three real connectivity and GPS traces such as Sassy [44], San Francisco Cabs [45] and Infocom 2006 [33]. We show that CafRep performs well, independent of network connectivity and mobility patterns, and consistently outperforms the state-of-the-art DTN forwarding algorithms in the face of increasing rates of congestion. CafRep maintains higher availability and success ratios while keeping low delays, packet loss rates and delivery cost. We test CafRep in the presence of two application scenarios, with fixed rate traffic and with real world Facebook application traffic demands, showing that regardless of the type of traffic CafRep aims to deliver, it reduces congestion and improves forwarding performance.     

An algorithm for combined cell-site selection and power control tomaximize cellular spread spectrum capacity

There is much current interest in spread spectrum wireless mobile communications and in particular the issue of spread spectrum wireless capacity. We characterize spread spectrum cellular capacity and provide a combined power control, cell-site selection algorithm that enables this capacity to be achieved. The algorithm adapts users' transmitter power levels and switches them between cell-sites, and it is shown that the algorithm converges to an allocation of users to cells that is optimal in the sense that interference is minimized. The algorithm is decentralized, and can be considered as a mechanism for cell-site diversity and handover. We provide numerical examples to show how effectively the algorithm relieves local network congestion, by switching users in a heavily congested cell to adjacent, less congested cells     

最小化路径代价和流量均衡模型及算法

流量均衡是流量工程中为避免网络拥塞经常采用的路由优化目标,如何选择路径以使流量达到均衡分布是流量路由的研究热点和难点.为了最小化网络拥塞,该文在指出网络拥塞决定于流量路由时所选路径的拥塞特征后,建立了流量分布的最小化路径代价和模型.在流量路由选择路径时,提出基于瓶颈链路的最小代价路径路由算法.在实际的网络拓扑和流量矩阵数据基础上对所提模型及算法进行了实验验证,结果显示:在网络负载较大时最大链路利用率相对于已有模型可降低近20%.     

Local area network characteristics, with implications for broadbandnetwork congestion management

The authors examine the phenomenon of congestion to better understand the congestion management techniques that will be needed in high-speed, cell-based networks. The first step of this study is to use high time-resolution local area network (LAN) traffic data to explore the nature of LAN traffic variability. Then the data are used for a trace-driven simulation of a connectionless service that provides LAN interconnection. The simulation allows one to characterize what congestion might look like in a high-speed, cell-based network. When realistic data are applied to simple models of LAN interconnection, it is observed that during periods, congestion persists and losses can be significant; congestion losses cannot be avoided by modest increases in buffer capacity; consequences of misengineering can be serious; and, fortunately, most congested periods are preceded by signs of impending danger     

Congestion control in a wireless network

This article proposes a congestion control model for a wireless network. Wireless communications can cause congestion in a high‐speed switching network depending on the volume of calls, their origination and the network architecture. In congested areas where wireless services are extensively used, the switching network can become congested. The proposed congestion control model allows for evaluation of these limitations and for choosing the best possible solution. Copyright © 1999 John Wiley & Sons, Ltd.     

A model for the handover traffic in low earth-orbiting (LEO) satellite networks for personal communications

The spectacular growth of cellular telephone networks has demonstrated the demand for personal communications. Communication systems based on low earth orbit (LEO) constellations of satellites seem to be an adequate approach to achieve a world-wide network. When defining the capacity in terms of satellite circuits, the network designer has to take into account the handover traffic. Unfortunately, in a LEO communication network where handover is most often due to the network nodes motion, handover traffic models for terrestrial cellular networks cannot be used. Hence specific models must be developed. This paper proposes an analytical model for the handover in LEO satellite networks. This model is applied to different network configurations and compared to discrete-time simulations. Simulation results agree with those obtained from the analytical model.     

Traffic balancing‐based path recommendation mechanisms in vehicular networks

In this paper, we propose both reactive and proactive balancing traffic path recommendation mechanisms, which we refer to as Bal‐Traf and Abs‐Bal, respectively. Bal‐Traf is initiated when a certain output road segment located at any road intersection is detected in an overloaded situation. In the event that the existing traffic density of any output road exceeds its optimal capacity, Bal‐Traf recommends that those vehicles that plan to pass over this road segment as next hop choose another, less congested output road segment. On the other hand, Abs‐Bal is a proactive balancing traffic mechanism. Its main purpose is to distribute input traffic completely even among all output road segments at intersections. Moreover, Abs‐Bal considers the best travel time of vehicles in addition to the goal of balancing traffic. From the experimental results, we can see that Bal‐Traf eliminates the number of overwhelmed road segments over the road network in scenarios with only partial network congestion. It also decreases the number of congested road segments in scenarios with complete network congestion. However, it increases the density drastically over the remaining congested road segments in these scenarios. Abs‐Bal performs well in decreasing the percentage of congested road segments and balancing traffic among road segments located throughout the road network, in the event of complete network congestion.     

Congested Banyan network analysis using congested-queue states andneighboring-queue effects

A Banyan network analysis technique is presented which more accurately models a congested network than other reported techniques. The analysis is based on the observation that a full queue (within the switching modules making up the network) causes traffic to back up. For a short time after becoming full, the free space in the queue is limited to no more than one slot. A queue in such a condition is called congested. Because of blocking the arrival rate to a congested queue is higher; this tends to maintain congestion. The arrival rate to a congested queue's dual is lower, as is the service rate for queues feeding the congested queue. These effects are captured in the analysis by using a state model that codes the condition of a queue and its neighbors. From a queue's state it can be determined if the queue, its dual, or a next-stage queue to which it connects is congested, as well as the number of items in the queue. Network throughput computed with the model is closer to that obtained from simulations than other Banyan analyses appearing in literature, including those designed to model congestion. Further, the queue-occupancy distributions are much closer than other analyses, suggesting that the analysis better models conditions in congested Banyan networks     

Predicting Properties of Congestion Events for a Queueing System With fBm Traffic

In packet networks, congestion events tend to persist, producing large delays and long bursts of consecutive packet loss resulting in perceived performance degradations. The length and rate of these events have a significant effect on network quality of service (QoS). The packet delay resulting from these congestion events also influences QoS. In this paper a technique for predicting these properties of congestion events in the presence of fractional Brownian motion (fBm) traffic is developed.     

User’s mobility effect on the performance of wireless cellular networks serving elastic traffic

The objective of the present paper is to give an analytic approximation of the performance of elastic traffic in wireless cellular networks accounting for user’s mobility. To do so we build a Markovian model for users arrivals, departures and mobility in such networks; which we call WET model. We firstly consider intracell mobility where each user is confined to remain within its serving cell. Then we consider the complete mobility where users may either move within each cell or make a handover (i.e. change to another cell). We propose to approximate the WET model by a Whittle one for which the performance is expressed analytically. We validate the approximation by simulating an OFDMA cellular network. We observe that the Whittle approximation underestimates the throughput per user of the WET model. Thus it may be used for a conservative dimensioning of the cellular networks. Moreover, when the traffic demand and the user speed are moderate, the Whittle approximation is good and thus leads to a precise dimensioning.     

Infrastructure‐based vehicular congestion detection scheme for V2I

With the increasing number of vehicles, traffic jam becomes one of the major problems of the fast‐growing world. Intelligent transportation system (ITS) communicates perilous warnings and information on forthcoming traffic jams to all vehicles within its coverage region. Real‐time traffic information is the prerequisite for ITS applications development. In this paper, on the basis of the vehicle‐to‐infrastructure (V2I) communication, a novel infrastructure‐based vehicular congestion detection (IVCD) scheme is proposed to support vehicular congestion detection and speed estimation. The proposed IVCD derives the safety time (time headway) between vehicles by using iterative content‐oriented communication (COC) contents. Meanwhile, the roadside sensor (RSS) provides an infrastructure framework to integrate macroscopic traffic properties into the estimation of both the traffic congestion and vehicle safety speed. The main responsibilities of RSS in IVCD are to preserve privacy, aggregate data, store information, broadcast routing table, estimate safety speed, detect traffic jam, and generate session ID (S‐ID) for vehicles. Monte Carlo simulations in four typical Chinese highway settings are presented to show the advantage of the proposed IVCD scheme over the existing Greenshield's and Greenberg's macroscopic congestion detection schemes in terms of the realized congestion detection performance. Real road traces generated by Simulation of Urban Mobility (SUMO) over NS‐3.29 are utilized to demonstrate that the proposed IVCD scheme is capable of effectively controlling congestion in both single and multilane roads in terms of density and speed health with previous schemes in this field.     

网络流量的混乱控制

This paper presents a chaotic control method on network traffic. By this method, the chaotic network traffic can be controlled to pre-assigned equilibrium point according to chaotic prediction and the Largest Lyapunov Exponent (LLE) of the traffic on congested link is reduced, thereby the probability of traffic burst and network congestion can be reduced. Numerical examples show that this method is effective.     

A cause of self‐similarity in TCP traffic

We analyse the statistical properties of aggregated traffic flows generated by TCP, in order to clarify a possible cause of self‐similarity in Internet traffic. Using ns‐2 simulation, we first show that aggregated traffic flows by TCP can be characterized by phase transition phenomena between non‐congested and congested phases in statistical physics. Interestingly, although the traffic exhibits self‐similarity with the Hurst parameter H ≈ 1.0 at the critical point between them, it is close to Poissonian away from the critical point. This result is consistent with results from real WAN traffic measurement. The main contribution of our work is to show that TCP itself contains a mechanism for generating self‐similarity, without assuming self‐similarity or long‐range dependency (LRD) in the application layer (e.g. packet inter‐arrival, connection arrival, and file size distribution). Moreover, we find that the value of the Hurst parameter at the critical point is determined by the simple feedback control called stop‐and‐wait flow control. Namely, it appears even without any packet retransmission events and is independent of the explicit rate increment algorithm such as slow‐start and congestion avoidance. Additionally, we demonstrate that the value of the Hurst parameter at the critical point depends on the constant bit rate algorithm and topology of network. Finally, we indicate that the time series of the round trip time follow the same statistics at the critical state. Copyright © 2005 John Wiley & Sons, Ltd.     

一种动态寻路中的机会转发模型

动态寻路（Dynamic Routing）是一项用以解决城市交通拥堵的智能交通技术.通过让一些车辆产生和转发路况拥堵消息,另一些车辆能够避开拥堵路段,从而缓解交通状况.以“存储-携带-转发”为通信模式的机会网络被广泛运用于动态寻路研究.文中提出了一种新型路况信息的机会转发算法,算法综合考虑车辆的位置和行驶方向.仿真实验表明,算法在保持信息散布效果的前提下,显著降低了网络负载,提升了效率.     

ACC: using active networking to enhance feedback congestion controlmechanisms

Active congestion control (ACC) uses active networking (AN) technology to make feedback congestion control more responsive to network congestion. Current end-to-end feedback congestion control systems detect and relieve congestion only at endpoints. ACC includes programs in each data packet that tell routers how to react to congestion without incurring the round-trip delay that reduces feedback effectiveness in wide area networks. The congested router also sends the new state of the congestion control algorithm to the endpoints to ensure that the distributed state becomes consistent. We present a model for extending feedback congestion control into an active network, apply that model to TCP congestion control, and present simulations that show that the resulting system exhibits up to 18 percent better throughput than TCP under bursty traffic. In simulations without bursty traffic, the systems behaved comparably     

互联网重要用户和重要服务的优先服务策略

互联网带宽不足时导致网络流量拥塞,保障重要客户重要服务业务流的服务质量,转化国际、国内出口拥塞问题,在网络拥塞和受攻击情况下,通过QoS策略来保证重点业务的服务质量,保障高级别用户拥塞时的服务质量。据策略实施后的客户感知度调查和时延测试分析,能总体控制时延过大的问题,同时用户感知度提升明显。     

Timely Effective Handover Mechanism in Heterogeneous Wireless Networks

Next-generation wireless networks should be able to coordinate and integrate different communication systems. It has been a challenging problem to support a seamless handover in these diverse wireless network environments. Link level triggers can provide information about events which can help handover decision and layer 3 entities better streamline their handover related activities. In most conventional layer 2 triggering approaches, a pre-defined threshold for a specific perspective such as the received signal strength is used. This may cause too late or too early handover executions. In this paper we propose a new predictive handover framework that uses the neighbor network information to generate timely the link triggers so that the required handover procedures can appropriately finish before the current link goes down. First we estimate a required handover time for the given neighbor network conditions, then using a predictive link triggering mechanism the handover start time is dynamically determined to minimize handover costs. The handover costs are analyzed in terms of the total required handover time and the service disruption time. The numerical analysis and simulation results show that the proposed method significantly enhances the handover performance in heterogeneous wireless networks.