A terminal‐controlled vertical handover decision scheme in IEEE 802.21‐enabled heterogeneous wireless networks

The seamless internetworking among heterogeneous networks is in great demand to provide ‘always‐on’ connectivity services with quality of service (QoS) provision, anywhere at anytime. The integration of wireless‐fidelity (Wi‐Fi) and wireless metropolitan area networks (WiMAX) networks can combine their best features to provide ubiquitous access, while mediating the weakness of both networks. While it is challenging to obtain optimized handover decision‐based dynamic QoS information, users can improve their perceived QoS by using the terminal‐controlled handover decision in a single device equipped with multiple radio interfaces. The IEEE 802.21 aims at providing a framework that defines media‐independent handover (MIH) mechanism that supports seamless handover across heterogeneous networks. In this paper, an multiple attributes decision making‐based terminal‐controlled vertical handover decision scheme using MIH services is proposed in the integrated Wi‐Fi and WiMAX networks to provide ‘always‐on’ connectivity QoS services. The simulation results show that the proposed scheme provides smaller handover times and lower dropping rate than the RSS‐based and cost function‐based vertical handover schemes. Copyright © 2009 John Wiley & Sons, Ltd.     

A handover-aware seamless video streaming scheme in heterogeneous wireless networks

With the development of wireless technologies, video streaming services over heterogeneous wireless networks have become more popular in recent years. Video streaming schemes for heterogeneous networks should consider vertical handover in which the link capacity is varied significantly, because the quality experienced for a video streaming service is affected by the network status. When a vertical handover occurs, an abrupt bandwidth change and substantial handover latency lead to bursty packet loss and discontinuity of the video playback. In this paper, we propose a handover-aware video streaming scheme to provide seamless video streaming services over heterogeneous wireless networks. The proposed scheme adjusts its sending rate and the quality level of the transmitted video streams according to the significant bandwidth variation that occurs in a vertical handover. To expedite the response to the bandwidth variation due to a handover, our scheme uses an explicit notification message that informs the streaming server of a client's handover occurrence. In order to evaluate the performance, we use a simulation environment for a vertical handover between wireless local area networks and cellular networks. Through the simulation results, we prove that our scheme improves the experienced quality of video streaming in vertical handovers.     

Impact of L2 Triggering Time on Handover Performance for 4G Wireless Networks

4G wireless networks are based on All-IP architecture integrating cellular networks, Wireless local area networks, Worldwide Interoperability for Microwave Access, Wireless ad hoc networks, and Wireless Personal Area Networks etc. This makes seamless handover an important issue for users roaming among these networks. Anticipation of future events based on layer 2 (L2) trigger information is the basic principle of fast handover. It incurs higher signaling costs compared with the other protocols like Mobile IPv6 and Hierarchical Mobile IPv6. L2 trigger is based on fluctuating wireless channel states. Therefore, the handover anticipation using L2 trigger may sometimes be incorrect. Unnecessary buffer space is used for providing a smooth handover in the case of incorrect anticipation. Therefore, it is very important to analyze overhead costs and compare the performance of IP based handover protocols. This paper investigates the impact of L2 triggering time on the signaling cost, packet delivery cost, total overhead cost, and buffer space. Results show that Session to mobility ratio, L2 trigger time and number of subnets are determining parameters for optimizing handover performance.     

基于媒体独立切换并提供QoS保证的跨UMTS和WiMAX无线异构网络的网络切换方案

The rapid growth and innovation of the various mobile communication technologies have caused a change in the paradigm of internet access. Wireless technologies such as WiMAX, WiFi and UMTS/LTE networks have shown great potential in dominating the wireless access markets. The existence of various access technologies requires a means for seamless internetworking to provide anywhere, anytime services without interruption in the ongoing session, especially in multimedia applications with rigid Quality of Services (QoS) requirements. The IEEE 802.21 Media Independent Handover (MIH) working group was formed to develop a set of mechanisms under a standard framework with the capability to support migration of mobile users across heterogeneous networks. Therefore, the implementation of handover is extremely important in the heterogeneous network environment. In order to guarantee various QoS requirements during handover execution especially in multimedia applications, in this paper we propose a novel MIH-based capacity estimation algorithm to execute handover with QoS provision supporting both horizontal and vertical handovers across UMTS and WiMAX networks. Simulation shows that the proposed mechanism achieves lower call dropping rate (highest approximate 3% ) and higher system throughput (average 92% ) than the basic handover method does.     

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.     

New efficient cross‐layer and multihoming mechanisms at layer 2 for inter‐radio access technology handover between UMTS and WiMAX

Next generation mobile networks will provide seamless mobility between existing cellular systems and other wireless access technologies. To realize a seamless vertical handover (inter‐radio access technology handover) among these different access technologies, a multi‐interfaced mobile station (i.e., multihomed) is a good approach to provide better handover performance in terms of packet loss rate and handover latency. In this article, we propose a novel layer 2 multihoming approach for inter‐radio access technology handover between Universal Mobile Telecommunications System (UMTS) and Worldwide Interoperability for Microwave Access (WiMAX) in both integrated and tight coupling architectures. This layer 2 multihoming approach has the ability of enabling either soft handover or make‐before‐break handover to adapt to mobility scenarios for the sake of a lossless and short latency handover procedure. Our simulation results show that, in case of handover from UMTS to WiMAX for transmission control protocol (TCP) traffics, the layer 2 multihoming approach can achieve a lossless and zero latency handover procedure by enabling soft handover. In case of handover from WiMAX to UMTS, because of the fact that the performance gain of soft handover is more affected by the differences of bandwidth and transmission delay between these wireless links, the make‐before‐break handover is preferred to achieve lossless and short latency handover procedure. Copyright © 2012 John Wiley & Sons, Ltd.     

A novel media independent handover‐based approach for vertical handover over heterogeneous wireless networks

The key purpose for seamless mobility and service continuity between heterogeneous wireless networks is the handover. Vertical handover management is one of key challenges in such environment. To deal with some of these challenges, an IEEE 802.21 media independent handover (MIH) framework has been standardized. The main purpose of this standard is to offer a general interface for the handover by abstracting the link layer intelligence to higher layers. However, there still exist a number of limitations in MIH architecture. In this paper, a new architecture of improved MIH is presented to perform vertical handover between wireless heterogeneous networks. We focused on interworking architecture between wireless local area network and long term evolution advanced network with the use of MIH signaling to define an efficient vertical handover. A performance analysis model for the proposed MIH‐based vertical handover is derived. Analysis results show that the proposed method can be easily deployed in present multimedia service networks. Copyright © 2013 John Wiley & Sons, Ltd.     

WLAN-GPRS integration for next-generation mobile data networks

The ongoing wireless LAN standardization and R&D activities worldwide, which target bit rates higher than 100 Mb/s, combined with the successful deployment of WLANs in numerous hotspots justify the fact that WLAN technology will play a key role in wireless data transmission. Cellular network operators have recognized this fact, and strive to exploit WLAN technology and integrate this technology into their cellular data networks. For this reason, there is currently a strong need for interworking mechanisms between WLANs and cellular data networks. We focus on these interworking mechanisms, which effectively combine WLANs and cellular data networks into integrated wireless data environments capable of ubiquitous data services and very high data rates in hotspot locations. We discuss the general aspects of integrated WLANs and cellular data networks, and we examine the generic interworking architectures that have been proposed in the technical literature. In addition, we review the current standardization activities in the area of WLAN-cellular data network integration. Moreover, we propose and explain two different interworking architectures, which feature different coupling mechanisms. Finally, we compare the proposed interworking architectures, and discuss their advantages and drawbacks.     

Effective session key distribution for secure fast handover in mobile networks

In this paper, we introduce a session key distribution mechanism for fast secure handover in wireless mobile networks. The proposed mechanism is based on the stream control transmission protocol in where a mobile node actively changes its IP address without its connection loss. When a mobile node moves between different access routers, the required session key at a new access router is distributed previously through the tunnel established between the previous access router and the new access router. Due to the reduced key distribution time, the mobile node achieves its secure seamless handover. The provided performance analysis proves that the proposed mechanism provides the reduced signaling cost compared to existing mobility protocols. In addition, the proposed mechanism reduces the handover latency so that the reduced amount of packet loss provides the stable handover performance for real-time applications.     

Predictive link trigger mechanism for seamless handovers in heterogeneous wireless networks

Effective and timely link‐layer trigger mechanisms can significantly influence the handover performance. The handover process will not perform the correct decision and execution unless adequate and timely link‐layer trigger information is delivered. In this paper, a predictive link trigger mechanism for seamless horizontal and vertical handovers in heterogeneous wireless networks is proposed. Unlike previous link trigger algorithms based on pre‐defined signal level thresholds, the link layer triggers in this study are adaptively and timely fired in accordance with the network conditions. Firstly, the time required to perform a handover is estimated based on the neighboring network conditions. Secondly, the time to trigger a Link_Going_Down to initiate a handover is determined using a least mean square linear prediction in which the prediction interval (k_h) is dynamically determined based on the estimated handover time. An upper bound for the packet loss rate during a handover is derived for a Gaussian shadowing channel. A manner in which this approach can be applied to IEEE 802.21 is shown in media independent handover scenarios. Simulation results of the proposed predictive link triggering mechanism show that it provides a timely proactive handover. The packet loss rate observed in a Gaussian shadowing channel remains low during a handover. Copyright © 2008 John Wiley & Sons, Ltd.     

An efficient handover decision in heterogeneous LTE-A networks under the assistance of users’ profile

The increasing demand for wireless networks calls for the use of heterogeneous networks in order to fulfil user requirements. Mobility management is considered one of the important entities for such networks. The handover is one of the main features of mobility management in regard to the long term evolution advanced (LTE-A) system, which depends purely on the hard handover. The vertical handover decision is a significant component of heterogeneous networks; it authorizes the user equipment (UE) to migrate between the two-tier LTE-A wireless networks. Femtocell, or also known as the home-evolved nodeB (HeNB), has turned out to be a promising arrangement, as it enhances the coverage and the quality of service for users on one hand, and offloads the eNB on the other hand. In this paper, an advanced handover technique is presented, in terms of adding new and critical parameters, as well as combining between the present UE trajectory and the HeNB cell location. A polynomial function is used to predict the future UE position while the cosine function along with distance are used for the selection of an appropriate target cell. The proposed algorithm is evaluated and then compared to the present work based on the handover number, number of signaling measurements, packet delay ratio, packet loss ratio, and system throughput. Simulation of the LTE-Sim demonstrates that the proposed algorithm significantly reduces the number of handovers, the transmission measurement number, the packet delay ratio, and the packet loss ratio and increases system throughput.     

Performance Improvements of Mobile SCTP in Integrated Heterogeneous Wireless Networks

The complementary characteristics of cellular networks and wireless local area networks (WLANs) make it attractive to integrate these two technologies. In this integrated heterogeneous environment, mobile stream control transmission protocol (MSCTP) is ideal to support vertical handover (VHO) between them by enabling a mobile client to freely switch between IP addresses acquired in different networks. In this paper, we show that the MSCTP-based VHO scheme suffers from poor throughput performance during WLAN to cellular forced VHOs. We propose a novel error recovery scheme called Sending-buffer Multicast-Aided Retransmission with Fast Retransmission (SMART-FRX) to improve performance during VHO by multicasting the buffered and new data over both WLAN and cellular links when handover losses occur. In addition, we propose a new analytical model for SCTP that takes into account the congestion window, the round trip time, the slow-start and congestion avoidance processes. By comparing numerical results from the proposed analytical model with simulation results, we demonstrate that our analytical model is able to predict the SCTP throughput accurately, with or without the SMART-FRX scheme. The analytical model provides a useful tool that can be extended to study the performance of SCTP in other applications. Analytical and simulation results show that the proposed SMART-FRX scheme can improve the SCTP throughput performance significantly in WLAN to cellular forced VHO situations.     

Seamless session mobility scheme in heterogeneous wireless networks

The next generation wireless communication system will likely be heterogeneous networks, as various technologies can be integrated on heterogeneous networks. A mobile multiple‐mode device can easily access the Internet through different wireless interfaces. The mobile multiple‐mode device thus could switch to different access points to maintain the robustness of the connection when it can acquire more resources from other heterogeneous wireless networks. The mobile multiple‐mode device therefore needs to face the handover problem in such environment. This work introduces Session Initiation Protocol (SIP)‐based cross‐layer scheme to support seamless handover scheme over heterogeneous networks. The proposed scheme consists of a battery lifetime‐based handover policy and cross‐layer fast handover scheme, called the SIP‐based mobile stream control transmission protocol (SmSCTP). This work describes the major idea of the proposed scheme and infrastructure. The proposed scheme has been implemented in Linux system. The simulation and numerical results demonstrate that the proposed SmSCTP scheme yields better signaling cost, hand‐off delay time, packet loss and delay jitter than SIP and mSCTP protocols. Copyright © 2010 John Wiley & Sons, Ltd.     

Handover management in integrated WLAN and mobile WiMAX networks [recent advances and evolution of WLAN and WMAN standards]

Recently there has been much effort, in both academia and industry, to integrate a plethora of wireless technologies in order to provide ubiquitous broadband access to mobile users. Handover management is still one of the most challenging issues to be solved for seamless integration of wireless networks. This article addresses the integration of IEEE 802.11 WLANs and IEEE 802.16 WMANs, focusing mainly on the handover management aspects. First, we describe architectures, futuristic application scenarios such as the envisioned heterogeneous multihop wireless networks (HMWNs) and moving networks, as well as the related research issues. Second, we present IEEE 802.21, a new emerging standard aimed at providing a framework for media-independent handover (MIH) among heterogeneous networks. Finally, we discuss how the MIH framework can help handover management for the integrated network.     

An Intelligent Vertical Handover Scheme for Audio and Video Streaming in Heterogeneous Vehicular Networks

In heterogeneous vehicular networks, the most challenging issue is obtaining an efficient vertical handover during the vehicle roaming process. Efficient network selection process can achieve satisfactory Quality-of-Service for ongoing applications. In this paper, we propose an Intelligent Network Selection (INS) scheme based on maximization scoring function to efficiently rank available wireless network candidates. Three input parameters were utilized to develop a maximization scoring function that collected data from each network candidate during the selection process. These parameters are: Faded Signal-to-Noise Ratio, Residual Channel Capacity, and Connection Life Time. The results show that the proposed INS scheme is more efficient at decreasing handover delays, End-to-End delays for VoIP and Video applications, packet loss ratios as well as increasing the efficiency of network selection processes in comparison with the state of the arts.     

Interworking techniques and architectures for WLAN/3G integration toward 4G mobile data networks

The intense wireless LAN standardization and R&D activities worldwide, combines with the recent successful deployment of WLANs, provide prime evidence that WLAN technology will play a key role in the fourth generation of mobile data networks. In this context, there is a strong need to integrate WLANs with 3G mobile data networks and develop hybrid mobile data networks capable of ubiquitous data services and very high data rates in strategic locations. This article addresses this need by proposing and discussing some novel architectures able to provide internetworking between WLAN and 3G networks, and meet the requirements of the most common internetworking scenarios. These architectures can enable 3G subscribers to benefit from high-throughput IP connectivity in hotspots and also to attain service roaming across several radio access technologies, such as IEEE 802.11, HiperLan/2, ULTRAN, and GERAN.     

Achieving performance enhancement in IEEE 802.11 WLANs by using the DIDD backoff mechanism

Wireless local area networks (WLANs) based on the IEEE 802.11 standards have been widely implemented mainly because of their easy deployment and low cost. The IEEE 802.11 collision avoidance procedures utilize the binary exponential backoff (BEB) scheme that reduces the collision probability by doubling the contention window after a packet collision. In this paper, we propose an easy‐to‐implement and effective contention window‐resetting scheme, called double increment double decrement (DIDD), in order to enhance the performance of IEEE 802.11 WLANs. DIDD is simple, fully compatible with IEEE 802.11 and does not require any estimation of the number of contending wireless stations. We develop an alternative mathematical analysis for the proposed DIDD scheme that is based on elementary conditional probability arguments rather than bi‐dimensional Markov chains that have been extensively utilized in the literature. We carry out a detailed performance study and we identify the improvement of DIDD comparing to the legacy BEB for both basic access and request‐to‐send/clear‐to‐send (RTS/CTS) medium access mechanisms. Copyright © 2006 John Wiley & Sons, Ltd.     

Control of the Interworking Between Packet Reservation Multiple Access and Dynamic Carrier Allocation

This work deals with an enhanced frequency division multiplex/packet reservation multiple access (FDM/PRMA) technique for cellular systems also suitable for wireless local area networks (WLANs); such enhancements consist of an efficient control of the interworking between dynamic carrier allocation (DCA) strategies, which guarantee a real-time rearrangement of the carriers-to-cells assignment and PRMA techniques. This allows a higher carrier exploitation. In this respect, the novelties introduced in this paper are: (i) the definition of a short-term packet dropping probability which permits the real-time assessment of the link quality of a PRMA carrier; (ii) the determination of a procedure the base station (BS) can follow in order to perform a real-time estimation of the above-mentioned short-term parameter; (iii) an efficient carrier management and interworking between the DCA mechanism and the PRMA technique realized by means of such parameter. The paper also shows simulation results highlighting a remarkable improvement of the carrier utilization, obtained by the proposed interworking of the DCA and PRMA techniques.     

Improving TCP performance for vertical handover in heterogeneous wireless networks

The incorporation of wireless local area networks (WLANs) into existing cellular networks as supplementary access technologies has become an issue of great interest. However, vertical handover (VHO), which allows users to roam between a WLAN and a cellular network, causes an abrupt change in certain link characteristics such as the round trip time and data rate. Owing to such changes, reordering problem and premature timeout occur and trigger unnecessarily fast retransmission during VHO, causing throughput degradation. Thus, we propose a new transmission control protocol (TCP) mechanism, which resolves the reordering problem by suppressing unnecessary retransmission caused by spurious duplicate acknowledgments (dupacks) incurred because of the reordering problem, and prevents premature timeout by employing an adaptive retransmission timer. We analytically investigate the throughput of our proposed TCP scheme. The numerical and simulation results show that our proposed TCP performs better in terms of throughput than other schemes appearing in the literature. Copyright © 2009 John Wiley & Sons, Ltd.