Mobile ad hoc relaying for upward vertical handoff in hybrid WLAN/cellular systems

One of the main issues in hybrid wireless networks is vertical handoff. Dropping probability is one of the important parameters that must be considered in planning the wireless communication systems. However, there has not been much effort in dropping rate reduction in loosely coupled hybrid wireless networks. In loosely coupled WLAN/cellular systems the system administrator of the WLAN is different from the cellular one. Therefore, in these situations, reducing the dropping probability based on classical methods such as using reserved guard channels is difficult. A handoff from a WLAN to a cellular system occurs when a multi-mode device moves out of the WLANs coverage area. This is an upward vertical handoff in a hybrid network. In this paper, we propose to employ ad hoc relaying during the upward vertical handoff in a hybrid WLAN/cellular system. Two-hop and multi-hop relaying approaches, which we propose in this paper, improve the dropping probability regardless of the number of reserved channels. Simulation results support the effectiveness of the proposed methods. Also, practical routing protocols are proposed in order to implement the suggested relaying methods.     

Hotspot wireless LANs to enhance the performance of 3G and beyond cellular networks

At present, WLANs supporting broadband multimedia communications are being developed and deployed around the world. Standards include HIPERLAN/2 defined by ETSI BRAN and the 802.11 family defined by the IEEE. These systems provide channel adaptive data rates up to 54 Mb/s (in a 20 MHz channel spacing) over short ranges up to 200 m. The HIPERLAN/2 standard also specifies a flexible radio access network that can be used with a variety of core networks, including UMTS. It is likely that WLANs will become an important complementary technology to 3G cellular systems and will typically be used to provide hotspot coverage. In this article the complementary use of WLANs in conjunction with UMTS is presented. In order to quantify the capacity enhancement and benefits of cellular/hotspot interworking we have combined novel ray tracing, software-simulated physical layer performance results, and optimal base station deployment analysis. The study focuses on an example deployment using key lamppost mounted WLAN access points to increase the performance (in terms of capacity) of a cellular network.     

Intelligent Vertical Handoffs between Heterogeneous Communication Networks

1IntroductionWith the increasing demand for mobile access ,theInternet has to provide not only li mited mobility,suchas WLAN[1 ~3]access ,but also worldwide mobility,asexemplified by Mobile IP[4 ~7]to meet the user require-ments in terms of data rate and mobility.In particular ,it is desired that when a user stays in the hotspot cov-ered by WLAN, he can access the Internet throughWLAN,and when he goes out of the hotspot ,the on-going connection should not be dropped,but is insteadhanded …     

Immune optimization algorithm for solving vertical handoff decision problem in heterogeneous wireless network

In heterogeneous wireless network environment, wireless local area network (WLAN) is usually deployed within the coverage of a cellular network to provide users with the convenience of seamless roaming among heterogeneous wireless access networks. Vertical handoffs between the WLAN and the cellular network maybe occur frequently. As for the vertical handoff performance, there is a critical requirement for developing algorithms for connection management and optimal resource allocation for seamless mobility. In this paper, we develop a mathematical model for vertical handoff decision problem, and propose a multi-objective optimization immune algorithm-based vertical handoff decision scheme. The proposed scheme can enable a wireless access network not only to balance the overall load among all base stations and access points but also maximize the collective battery lifetime of mobile terminals. Results based on a detailed performance evaluation study are also presented here to demonstrate the efficacy of the proposed scheme.     

An efficient cross layer based channel reservation method for vehicular networks

The swift growth of the mobile users and limited availability of bandwidth lead to the requirement of effective channel allocation process. Channel allocation becomes tedious in vehicular ad hoc network, as the mobility of the nodes is high. So, in this paper, we propose a method called as cross layer based channel reservation with preemption (CCRP) method that performs channel allocation process by estimating the handoffs in vehicular ad hoc networks. The time estimated is communicated from physical layer to medium access control layer using a cross‐layer design. The reusability concept is used, and the channels are divided into three groups. The different cells acquire different groups based on the database status and exclusively to avoid interference. Preemption is incorporated to give the highest priority to real time originating calls and real time handoff calls. The performance of the proposed method, CCRP, is compared with the legacy systems such as cooperative reservation of service channels and very fast handover scheme in terms of dropping probability, blocking probability, and handoff latency. The results show that the proposed algorithm, CCRP, performs better in comparison. Copyright © 2013 John Wiley & Sons, Ltd.     

Improving Voice and Data Services in Cellular/WLAN Integrated Networks by Admission Control

In this paper, we study voice and data service provisioning in an integrated system of cellular and wireless local area networks (WLANs). With the ubiquitous coverage of the cellular network and the disjoint deployment of WLANs in hot-spot areas, the integrated system has a two-tier overlaying structure. As an essential resource allocation aspect, admission control can be used to properly admit voice and data calls to the overlaying cells and WLANs. A simple admission scheme is proposed in this study to analyze the dependence of resource utilization and the impact of user mobility and traffic characteristics on admission parameters. Both admission control and rate control are considered to limit the input traffic to the WLAN, so that the WLAN operates in its most efficient states and effectively complements the cellular network. The call blocking/dropping probabilities and data call throughput are evaluated for effective and accurate derivation of the admission parameters. It is observed that the utilization varies with the configuration of admission parameters, which properly distributes the voice and data traffic load to the cells and WLANs. Mobility and traffic variability have a significant impact on the selection of the admission parameters.     

车联网中基于贝叶斯决策的垂直切换方法研究

车辆需要在车联网的异构无线网络环境下进行垂直切换,针对垂直切换技术普遍不能支持 WAVE, WiMAX和3G cellular间的垂直切换这一问题,提出了一种基于贝叶斯决策的垂直切换算法。首先,根据接入网络的信号强度、传输速率、误码率和网络阻塞率以及车辆终端的速度和运动趋势建立多条件相关的切换概率分布,计算出切换先验概率;然后通过贝叶斯决策算法计算后验概率并进行决策分类,从而选取最优网络接入。仿真实验结果表明,该算法不仅有效地实现WAVE,WiMAX和3G cellular无线接入技术之间的垂直切换,而且避免了乒乓效应,保证了网络及时更新。     

An adaptive channel preemption model for small‐cell embedded large‐cellular networks

In this paper, we present an analytical model of adaptive channel preemption (ACP) for small‐cell embedded large‐cellular (SCELC) networks. An SCELC network consists of a fixed base station (FBS) with large coverage and many embedded base stations (EBS) with relatively small coverage. Channel capacity in an FBS cell may become insufficient when traffic is unexpectedly increased particularly in some special occasion. This paper considers two aspects of dynamically allocating channels for an SCELC network. First, by increasing one or more EBS cells within an FBS cell, the proposed ACP can reduce blocking probability of new calls. Second, to reduce dropping probability of handoff calls, the proposed ACP allows a handoff call to preempt an on‐going call, when the latter is located in an EBS cell or in the overlapping area of two adjacent FBS cells. For the purpose of performance evaluation, we build an analytical model with 4‐tuple Markov chains. Numerical results reveal that embedding one or more EBS cells inside an FBS cell needs to be done carefully since it results in a tradeoff between the reduction of new‐call blocking probability and the increase of handoff‐call dropping probability. Copyright © 2011 John Wiley & Sons, Ltd.     

An efficient handover decision method based on frame retransmission and data rate for multi-rate WLANs

To enhance the communication performance at handover between multi-rate WLANs, we propose a new handover decision method that can be applied to our previously reported handover management scheme, which handled a handover by utilizing two WLAN interfaces (IFs) through cross-layer collaboration between layer 2 and layer 4. It should be noted that we here propose a new handover decision scheme for traversing between multi-rate WLANs, while our previous decision scheme works only in fixed-rate WLANs. In this paper, to treat a handover between multi-rate WLANs, we employ two kinds of information: (1) the most frequently used data rate (MFDR) for assessing the stable communication performance of a multi-rate WLAN, and (2) the frame retransmission ratio (FRR) for assessing its exact communication performance. The MFDR enables us to estimate the area where we should start handover. If the MFDRs of two interfaces are same in the area, the FRR allows us to compare the wireless condition on the two interfaces precisely to give an optimal handover point. Through simulation experiments, we show that our proposed scheme certainly estimates an appropriate handover point as a result of multi-path transmission (s), thereby providing handover successfully. That is, the proposed method can determine handover at an optimal point depending on the various distances between access points, the mobile node (MN) velocity, and the MN moving pattern. Moreover, our proposed scheme prevents the redundant network load caused by multi-path transmission as much as possible, thereby providing the ideal TCP communication performance.     

On Improving the Performance of IEEE 802.11 with Relay-Enabled PCF

Integrating wireless LAN (WLAN) techniques with the third generation cellular networks has become a promising way to improve the performance of wireless systems. As WLANs play an important role in such heterogeneous systems, the performance of WLANs becomes important to the whole system. It is well known that WLANs provide a physical layer multi-rate capability, and hence MAC layer mechanisms are needed to exploit this capability. In this paper, we propose a novel MAC layer relay-enabled point coordination function (PCF) protocol, called rPCF, to exploit the physical layer multi-rate capability. Since WLAN supports multiple data rates in response to different channel conditions, data packets may be delivered faster through a relay node than through the direct link if the direct link has low quality and low rate. To enable MAC layer relay, the access point needs to collect information about the channel conditions, and notify the mobile nodes which data rate to use and whether to transmit the data through a relay station. We design protocols to achieve this goal and refine these protocols to minimize the control overhead. Simulation results show that rPCF can significantly improve the system performance in terms of system throughput and transmission delay by adding only a negligible control overhead.     

影响无线局域网系统吞吐率的因素分析

无线局域网(WLAN)技术的发展,使得 WLAN 成为重要的无线系统组网方式。在衡量系统性能的诸多指标中,系统吞吐率是其中最重要的考察指标。在实际环境中,许多因素影响着系统吞吐率。尤其在多小区 WLAN 中,通过对覆盖交叠方式、非对称抑制现象、频率分配方案进行分析与研究,有助于更好地完成 WLAN 系统的规划与设计。     

Adaptive resource allocation for prioritized call admission over anATM-based wireless PCN

In future personal communications networks (PCNs) supporting network-wide handoffs, new and handoff requests will compete for connection resources in both the mobile and backbone networks. Forced call terminations due to handoff call blocking are generally more objectionable than new call blocking. The previously proposed guard channel scheme for radio channel allocation in cellular networks reduces handoff call blocking probability substantially at the expense of slight increases in new call blocking probability by giving resource access priority to handoff calls over new calls in call admission control. While the effectiveness of a fixed number of guard channels has been demonstrated under stationary traffic conditions, with nonstationary call arrival rates in a practical system, the achieved handoff call blocking probability may deviate significantly from the desired objective. We propose a novel dynamic guard channel scheme which adapts the number of guard channels in each cell according to the current estimate of the handoff call arrival rate derived from the current number of ongoing calls in neighboring cells and the mobility pattern, so as to keep the handoff call blocking probability close to the targeted objective while constraining the new call blocking probability to be below a given level. The proposed scheme is applicable to channel allocation over cellular mobile networks, and is extended to bandwidth allocation over the backbone network to enable a unified approach to prioritized call admission control over the ATM-based PCN     

An enhanced TCP for upward vertical handoff in integrated WLAN and cellular networks

The integration of wireless local area networks (WLANs) and third generation (3G) cellular networks has been recently a subject of great interest, mainly aimed at augmenting cellular networks with high‐rate data services by WLANs in hotspots. The complementary characteristics of 3G cellular networks and 802.11 WLANs are expected to offer the best of both technologies. On the other hand, the drastically different characteristics of both networks could be a serious obstacle to providing seamless mobility in the integrated WLAN and cellular networks. In particular, mobile users suffer from a drastic decrease in data rate after a vertical handoff from a WLAN to a 3G cellular network. However, current TCP congestion control cannot adapt to the change in the data rate after the vertical handoff, resulting in significant throughput degradation. Thus, we propose a novel TCP scheme to enhance the throughput when a vertical handoff occurs from a WLAN to a cellular network. For the proposed scheme, the throughput performance is investigated via analytic modeling and simulation. Copyright © 2008 John Wiley & Sons, Ltd.     

A movable safety zone scheme in urban fiber-optic microcellularsystems

We consider an urban fiber-optic microcellular system in which a cigar-shaped cell consists of several microzones with their own antenna sites connected to a central station through optical fibers. To increase the efficiency of radio resources and reduce unnecessary handoffs between microzones, we propose a movable safety zone scheme. A safety zone is a virtually guarded area that does not permit cochannel interference. Outside the safety zone, cochannels can be reused. The safety zone can move under the condition that its user does not meet cochannel interference as he moves to an adjacent microzone. Considering user mobility characteristics in the cigar-shaped cell, we analyze and evaluate the proposed system in terms of intracell and intercell handoff rates, blocking probability, intracell call-dropping probability, and channel reuse parameter. The proposed system can handle a traffic capacity of about 12 Erlangs for seven traffic channels under a call blocking probability of 1% and generates a negligible number of intracell handoffs compared with those of intercell handoffs     

Load balancing for cellular/WLAN integrated networks

The interworking between heterogeneous third-generation cellular networks and wireless local area networks is one promising evolution approach to fourth-generation wireless networks, which can exploit the complementary advantages of the cellular network and WLANs. Resource management for the 4G-oriented cellular/WLAN integrated network is an important open issue that deserves more research efforts. In this article we present a policy framework for resource management in a loosely coupled cellular/WLAN integrated network, where load balancing policies are designed to efficiently utilize the pooled resources of the network. A two-phase control strategy is adopted in the load balancing policies, in which call assignment is used to provide a statistical quality of service guarantee during the admission phase, and dynamic vertical handoff during the traffic service phase is used to minimize the performance variations. Numerical results are presented to demonstrate that the proposed load balancing solution achieves significant performance improvement over two other reference schemes     

Heterogeneous Wireless Networks: Configuration and Vertical Handoff Management

Vertical handoff is one of the most important issues for the next generation heterogeneous wireless networks. However, in many situations, unbeneficial vertical handoffs occur across intersystem heterogeneous networks cause network performance degradation. Therefore, we propose a novel configuration architecture that can be deployed in the next generation of wireless networks. Second, we propose a predictive and adaptive Vertical Handoff Decision Scheme that optimizes the handoff initiation time as well as selection of the most optimal network. The proposed vertical handoff decision algorithm considers the technology type as well as the Signal to Interference Ratio (SIR), the Mobile Station (MS) velocity, the user preferences, the applications requirements and the terminal capabilities as the most important factors to make vertical handoff decision. In order to minimize handoff costs, the proposed decision algorithm uses the dwell timer concept. The handoff costs are analyzed in terms of unnecessary and unbeneficial handoffs rate.The simulation results show that the reduction of unnecessary handoffs proposed in our vertical handoff decision scheme reduces the handoff blocking probability, the packets loss rate and the handoff overhead     

Joint Optimal Access Point Selection and Channel Assignment in Wireless Networks

In wireless cellular networks or in other networks with single-hop communication, the fundamental access control problem pertains to access point (AP) selection and channel allocation for each user. For users in the coverage area of one AP, this involves only channel allocation. However, users that belong in the intersection of coverage areas of more than one AP can select the appropriate AP to establish connection and implicitly affect the channel assignment procedure. We address the joint problem of AP selection and channel assignment with the objective to satisfy a given user load vector with the minimum number of channels. Our major finding is that the joint problem reduces to plain channel allocation in a cellular network that emerges from the original one after executing an iterative and provably convergent clique load balancing algorithm. For linear cellular networks, our approach leads to minimum number of required channels to serve a given load vector. For 2D cellular networks, the same approach leads to a heuristic algorithm with a suboptimal solution due to the fact that clique loads cannot be balanced. Numerical results demonstrate the performance benefits of our approach in terms of blocking probability in a dynamic scenario with time-varying number of connection requests. The presented approach constitutes the basis for addressing more composite resource allocation problems in different context.     

Self‐adaptive routing protocols for integrating cellular networks,WLANs, and MANETs

A growing need to have ubiquitous connectivity has motivated our research to provide continuous connection between various wireless platforms such as cellular networks, wireless local area networks (WLANs), and mobile ad hoc networks (MANETs). In this paper, we consider integration at the routing layer and propose two adaptable routing protocols (IRP‐RD and IRP‐PD) that exploit topology information stored at the fixed network components (cellular base stations and WLAN access points) for the route discovery and maintenance processes. Our proposed protocols can provide connectivity to the cellular network and/or WLAN hotspots through multihop routing, while differ in the gateway discovery approach used. In IRP‐RD, multihop routes to gateways to the cellular network or WLAN hot spots are discovered on demand, while in IRP‐PD out of coverage users proactively maintain routes to the gateways. Furthermore, proposed protocols can be used in any heterogeneous scenario, combining a cellular network and WLANs operating in infrastructure or ad hoc (MANET) mode. We provide simulation results that demonstrate the effectiveness of the proposed integrated routing protocols and show the advantages and drawbacks of each gateway discovery approach in different heterogeneous scenarios. Copyright © 2006 John Wiley & Sons, Ltd.     

PERFORMANCE STUDY OF AN INTEGRATED SATELLITE/TERRESTRIAL MOBILE COMMUNICATION SYSTEM

Terrestrial cellular networks and mobile satellite systems are expected to converge towards a future integrated satellite/terrestrial mobile communication network. Besides a system globalization, the integration of terrestrial and satellite mobile systems will lead to the unloading of the fixed part of the mobile network. This paper proposes an integrated satellite/terrestrial mobile communication system and evaluates its performance in terms of the blocking probability for new call attempts, the call dropping probability and the probability of unsuccessful call. This communication system was simulated and its performence compared with that of a stand-alone terrestrial mobile system. In the terrestrial part of the system we have considered fixed channel allocation (FCA) and dynamic channel allocation (DCA) techniques. Satellite channels can have equal or lower priority compared to terrestrial channels. The improvement of the system performance by means of satellite-to-terrestrial handovers was also estimated.     

Improving DL-MU-MIMO performance in IEEE 802.11ac networks through decoupled scheduling

The IEEE 802.11ac standard introduces new downlink multi-user MIMO (DL-MU-MIMO) transmissions to up to four users in order to increase spatial reuse in wireless local area networks (WLANs). We argue that even better WLAN performance can be achieved by slightly modifying the DL-MU-MIMO scheduling. To this end we propose a new queuing mechanism based on the decoupling of EDCA and DL-MU-MIMO scheduling (DEMS) to avoid head-of-line blocking. We show that DEMS outperforms traditional 802.11ac scheduling based on first in, first out transmission queues. The improvement is shown in terms throughput achieved with: (a) more efficient channel usage, (b) increased probability of transmission of high priority traffic, and (c) decreased competition between frames destined to distinct users.