Decision-making models for group vertical handover in vehicular communications

In vehicular communications across composite radio environments, the one prominent feature is network heterogeneity, which means that diverse radio access networks co-exist with each other. And another particular feature is group mobility, because multiple mobile equipments in the vehicle are moving at the same time. Therefore, with movement of vehicle, many mobile terminals (MTs) in a train or bus may operate vertical handover actions almost at the same time, which is regarded as the group vertical handover (GVHO). However, the current literatures on vertical handover (VHO) mainly focus on when to trigger handover and how to select the best target network for single user, if these VHO schemes were applied in vehicular communication scenario, it may lead to system performance degradation or network congestion, because the MTs with these VHO decision-making methods selfishly select the best networks regardless of the influences from other concurrent VHO users. Therefore, in order to provide reliable QoS guarantee and keep service connectivity for group mobility in vehicular communications across heterogeneous networks, three models are proposed in this paper to deal with the decision-making problems of incomplete and inaccurate information in GVHO scenario. Two of them adopt MT controlled VHO, while another adopts network assisted VHO. The performances of these schemes are studied with regard to the average transmission delay and average packet losses rate.     

Mobile Small Cells for Further Enhanced 5G Heterogeneous Networks

A heterogeneous network (HetNet) is a network topology composed by deploying multiple HetNets under the coverage of macro cells (MCs). It can improve network throughput, extend cell coverage, and offload network traffic; for example, the network traffic of a 5G mobile communications network. A HetNet involves a mix of radio technologies and various cell types working together seamlessly. In a HetNet, coordination between MCs and small cells (SCs) has a positive impact on the performance of the networks contained within, and consequently on the overall user experience. Therefore, to improve user‐perceived service quality, HetNets require high‐efficiency network protocols and enhanced radio technologies. In this paper, we introduce a 5G HetNet comprised of MCs and both fixed and mobile SCs (mSCs). The featured mSCs can be mounted on a car, bus, or train and have different characteristics to fixed SCs (fSCs). In this paper, we address the technical challenges related to mSCs. In addition, we analyze the network performance under two HetNet scenarios — MCs and fSCs, and MCs and mSCs.     

分层异构网络中基于进化博弈的小区附着机制

相比传统的宏蜂窝网络,分层异构网络是实现系统容量增强的一种很有前景的技术。尽管如此,由于家庭基站与宏基站同频部署,且它们被随机部署,异构网络中的干扰可能会更强。为了提升网络吞吐量,本文研究了一种新型的基于进化博弈的小区附着算法,为最小化小区间干扰,提高网络吞吐量提供了理论参考。     

SDN/NFV‐based handover management approach for ultradense 5G mobile networks

With the great increase of connected devices and new types of applications, mobile networks are witnessing exponential growth of traffic volume. To meet emerging requirements, it is widely agreed that the fifth‐generation mobile network will be ultradense and heterogeneous. However, the deployment of a high number of small cells in such networks poses challenges for the mobility management, including frequent, undesired, and ping‐pong handovers, not to mention issues related to increased delay and failure of the handover process. The adoption of software‐defined networking (SDN) and network function virtualization (NFV) technologies into 5G networks offers a new way to address the above‐mentioned challenges. These technologies offer tools and mechanisms to make networks flexible, programmable, and more manageable. The SDN has global network control ability so that various functions such as the handover control can be implemented in the SDN architecture to manage the handover efficiently. In this article, we propose a Software‐Defined Handover (SDHO) solution to optimize the handover in future 5G networks. In particular, we design a Software‐Defined Handover Management Engine (SDHME) to handle the handover control mechanism in 5G ultradense networks. The SDHME is defined in the application plane of the SDN architecture, executed by the control plane to orchestrate the data plane. Simulation results demonstrate that, compared with the conventional LTE handover strategy, the proposed approach significantly reduces the handover failure ratio and handover delay.     

Distinguishing social contacts and pass-by contacts in DTN routing

Smallcells deployment in heterogeneous networks (HetNets) introduce uplink (UL) downlink (DL) asymmetry, backhaul bottleneck, cell load imbalances, increased core network signaling, interference and mobility management problems. In order to address these issues, concept of dual connectivity has been introduced in 3rd generation partnership project (3GPP) release 12. In dual connectivity, a given user equipment can consume radio resources of at least two different network points connected through non-ideal backhaul for spectrum aggregation and cooperative access mechanisms in dense 5G HetNets. Alternatively, another concept of downlink and uplink decoupling (DUDe) has also been recently introduced in 3GPP to improve uplink performance, load balancing and cell capacity. In order to take advantage of the strengths of these latest developments, this paper significantly advances prior work by analyzing K-tier 5G HetNets having dual connectivity and decoupled access (joint DUDe dual-connectivity) for spectrum aggregation in UL and DL. In the preceding works, K-tiers as per present-day heterogeneity, uplink power control and receiver noise have not been considered for joint DUDe dual-connectivity. With the use of stochastic geometry, we have developed closed form solutions for association, coverage and outage probabilities along with average throughput for joint DUDe dual-connectivity by considering uplink power control, receiver noise and K-tiers of HetNets. The resultant performance metrics are evaluated in terms of achieved gains over conventional downlink received power access policies. Results show that cell association technique based on joint DUDe dual-connectivity can significantly improve load balancing, mobility management and UL performance for forthcoming 5G HetNets.     

Robust resource allocation for NOMA-assisted heterogeneous networks

As a promising technology to improve spectrum efficiency and transmission coverage, Heterogeneous Network (HetNet) has attracted the attention of many scholars in recent years. Additionally, with the introduction of the Non-Orthogonal Multiple Access (NOMA) technology, the NOMA-assisted HetNet cannot only improve the system capacity but also allow more users to utilize the same frequency band resource, which makes the NOMA-assisted HetNet a hot topic. However, traditional resource allocation schemes assume that base stations can exactly estimate direct link gains and cross-tier link gains, which is impractical for practical HetNets due to the impact of channel delays and random perturbation. To further improve energy utilization and system robustness, in this paper, we investigate a robust resource allocation problem to maximize the total Energy Efficiency (EE) of Small-Cell Users (SCUs) in NOMA-assisted HetNets under imperfect channel state information. By considering bounded channel uncertainties, the robust resource optimization problem is formulated as a mixed-integer and nonlinear programming problem under the constraints of the cross-tier interference power of macrocell users, the maximum transmit power of small base station, the Resource Block (RB) assignment, and the quality of service requirement of each SCU. The original problem is converted into an equivalent convex optimization problem by using Dinkelbach's method and the successive convex approximation method. A robust Dinkelbach-based iteration algorithm is designed by jointly optimizing the transmit power and the RB allocation. Simulation results verify that the proposed algorithm has better EE and robustness than the existing algorithms.     

基于硬件损伤的MIMO异构网络波束成形算法

由于多输入多输出(MIMO)异构网络能够提高系统容量和实现更多的用户接入,因此受到了学术界和工业界的广泛关注,从而成为下一代通信系统的关键技术之一。然而,由于放大器非线性、相位噪声和I/Q不均衡等因素的影响,这类硬件损伤成为制约当前MIMO异构网络波束成形性能进一步提升的瓶颈。为了解决该问题,该文提前将硬件损伤考虑到MIMO异构网络波束成形算法设计当中。首先,考虑了每个基站的最大发射功率约束和每个用户的最小信干噪比约束,建立了一个含硬件损伤参数的系统总能耗最小的资源优化问题。其次,利用等价变换和半正定松弛方法,将原非凸问题转化为凸优化问题进行求解。仿真结果表明,与完美硬件条件下的波束成形算法对比,所提算法具有较好的抗硬件损伤能力和较低的中断概率。     

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.     

Software‐defined networking approach for enhanced evolved packet core network

The evolved packet core (EPC) network is the mobile network standardized by the 3rd Generation Partnership Project and represents the recent evolution of mobile networks providing high‐speed data rates and on‐demand connectivity services. Software‐defined networking (SDN) is recently gaining momentum in network research as a new generation networking technique. An SDN‐based EPC is expected to introduce gains to the EPC control plane architecture in terms of simplified, and perhaps even software‐based, vendor independent infrastructure nodes. In this paper, we propose a novel SDN‐based EPC architecture along with the protocol‐level detailed implementation and provide a mechanism for identifying information fields exchanged between SDN‐EPC entities that maintains correct functionality with minimal impact on the conventional design. Furthermore, we present the first comprehensive network performance evaluation for the SDN‐based EPC versus the conventional EPC and provide a comparative analysis of 2 networks performances identifying potential bottlenecks and performance issues. The evaluation focuses on 2 network control operations, namely, the S1‐handover and registration operations, taking into account several factors, and assessing performance metrics such as end‐to‐end delay (E2ED) for completion of the respective control operation, and EPC nodes utilization figures.     

Physical layer security performance analysis of multi-antenna full-duplex relay aided heterogeneous cellular network

To alleviate the spectrum shortage problem and security threats in heterogeneous network (HetNet),multi-antenna full-duplex relay was introduced for communication between femto base station (FBS) and legitimate user.With the aid of multi-antenna full-duplex relay in FBS network,the secrecy performance of HetNets could be improved.Under a stochastic geometry framework,the fundamental analysis model to evaluate the secrecy performance in multi-antenna full-duplex relay aided HetNet was set up.To be specific,the exact expressions for the secrecy outage probability of the typical user,serving relays and HetNet were derived respectively.Then,based on the theoretical analyses and simulation results,the influences of transmit power and antenna number of both macro base station and FBS on secrecy performance in HetNet were examined.Finally,the results show that introducing multi-antenna full-duplex relay for FBS networks improves the secrecy performance of HetNet.     

Context-aware parallel handover optimization in heterogeneous wireless networks

Annals of Telecommunications - The key idea of this paper is to a use cross-layer triggering concept in order to control the vertical handover (VHO) in heterogeneous networks. Current mobility...     

Dynamic inter-domain MDS approach with secure seamless handover based on IEEE 802.21 MIH

The accessibility of available wireless access technologies with increasing demand for real time multimedia application becomes an essential part for mobile communication. Mobile users resourcefully utilize the heterogeneous environment for best quality of service (Qos) anywhere and anytime. Efficient handover optimization and intelligent mobility management is a key requirement for designing next generation wireless networks. Therefore, a novel IEEE 802.21 media independent handover (MIH) standard is adopted to provide an associated service for intelligent handover procedures. In addition, dynamic mobility management decision server (MDS) and IEEE 802.21a security extension for MIH services are also integrated in the proposed architectures to support fast, seamless and secure handover optimization in inter-domain mobility. Simulation results prove that the presented work resourcefully minimizes the packet loss, unnecessary handover probability and vertical handover delay by avoiding time consuming scanning process for target network discovery. The system thus achieves Qos guarantee by balancing the network load and throughput improvement for different applications with Proxy MIPv6 mobility management protocol.     

Dynamic handover algorithm with interference cancellation in 5G networks for emergency communication

The integration of 5G networks with cognitive radio (CR) technology enables the software‐defined networking (SDN) infrastructure to support emergency applications. In future, CR can be integrated with 5G and many wireless networks like Wi‐Fi, WSN, and MANET for efficient spectrum utilization with higher data rate and lower latency. This CR technology allows unlicensed users to access the licensed spectrum, whenever it is free. In this paper, an efficient SDN architecture with cognitive ability for emergency network is proposed in which the SDN controller prolong communication between disaster victims and first responders and so the first responders can arrive at the spot directly and rescue the victims. The SDN controller has cognitive ability so that the victims can utilize the vacant licensed band to communicate with the first responders, thereby improving the spectrum utilization of the network. Another two main challenges during emergency are the occurrence of interference and link failure. The proposed dynamic handover algorithm with interference cancellation (DHAIC) cancels the interference between the nodes inside the network and performs dynamic handoff, whenever link failure occurs between the cluster head (CH) and the controller. An optimum throughput and minimal delay is achieved to ensure the network performance.     

Performance analysis of handover delay and buffer capacity in mobile OpenFlow‐based networks

Software‐defined networking (SDN) is a network concept that brings significant benefits for the mobile cellular operators. In an SDN‐based core network, the average service time of an OpenFlow switch is highly influenced by the total capacity and type of the output buffer, which is used for temporary storage of the incoming packets. In this work, the main goal is to model the handover delay due to the exchange of OpenFlow‐related messages in mobile SDN networks. The handover delay is defined as the overall delay experienced by the mobile node within the handover procedure, when reestablishing an ongoing session from the switch in the source eNodeB to the switch in the destination eNodeB. We propose a new analytical model, and we compare two systems with different SDN switch designs that model a continuous time Markov process by using quasi‐birth–death processes: (1) single shared buffer without priority (model SFB), used for all output ports for both control and user traffic, and (2) two isolated buffers with priority (model priority finite buffering [PFB]), one for control and the other for user plane traffic, where the control traffic is always prioritized. The two proposed systems are compared in terms of total handover delay and minimal buffer capacity needed to satisfy a certain packet error ratio imposed by the link. The mathematical modeling is verified via extensive simulations. In terms of handover delay, the results show that the model PFB outperforms the model SFB, especially for networks with high number of users and high probability of packet‐in messages. As for the buffer dimensioning analysis, for lower arrival rates, low number of users, and low probability of packet‐in messages, the model SFB has the advantage of requiring a smaller buffer size.     

A reliable quality of service aware fault tolerant gateway discovery protocol for vehicular networks

A great interest in vehicular ad‐hoc networks has been noticed by the research community. General goals of vehicular networks are to enhance safety on the road and to ensure the convenience of passengers by continuously providing them, in real time, with information and entertainment options such as routes to destinations, traffic conditions, facilities' information, and multimedia/Internet access. Indeed, time efficient systems that have high connectivity and low bandwidth usage are most needed to cope with realistic traffic mobility conditions. One foundation of such a system is the design of an efficient gateway discovery protocol that guarantees robust connectivity between vehicles, while assuring Internet access. Little work has been performed on how to concurrently integrate load balancing, quality of service (QoS), and fault tolerant mechanisms into these protocols. In this paper, we propose a reliable QoS‐aware and location aided gateway discovery protocol for vehicular networks by the name of fault tolerant location‐based gateway advertisement and discovery. One of the features of this protocol is its ability to tolerate gateway routers and/or road vehicle failure. Moreover, this protocol takes into consideration the aspects of the QoS requirements specified by the gateway requesters; furthermore, the protocol insures load balancing on the gateways as well as on the routes between gateways and gateway clients. We discuss its implementation and report on its performance in contrast with similar protocols through extensive simulation experiments using the ns‐2 simulator. Copyright © 2013 John Wiley & Sons, Ltd.     

Toward green 5G heterogeneous small-cell networks: power optimization using load balancing technique

The overwhelming demand for data by an ever-increasing number of users is a great challenge wireless cellular networks are faced with. One potential solution to this issue is deploying a massive number of small cells (SCs) in the existing macro network. As SC overlay has a big role in the future wireless networks that can overcome the data traffic upsurge at little power cost, heterogeneous network (HetNet) has been viewed as a promising technology for 5G networks that extends cell coverage, improves network capacity and offloads the network traffic from the macro cell (MC) to the SCs. However, the hyper-dense SCs and their uncorrelated operation raise an important question about the joint power consumption of the macro base station (MBS) and the small base stations (SBSs) in the HetNet since the aggregate power consumption of the dense SBSs cannot be ignored. Recently, the SC sleeping technique has become a hot topic for saving energy in HetNets. To minimize power consumption in HetNets, we propose three algorithms to dynamically adapt the operation of the SBSs to active/sleep (on/off) for non-uniform user distribution in the HetNet. We investigate the general optimal power minimization problem for HetNet that requires relatively high computational complexity. Taking into account the additional increase of the traffic load brought to the MBS, a key design principle of the proposed algorithms is to switch off the SBSs gradually based on their locations, user densities in their coverage areas or the highest power that can be saved by switching some of them off, respectively. Then, we enhance the mathematical framework to make the analysis more realistic by considering the offloading between the SCs and the MBS that occurs when the traffic load exceeds SCs’ capacity. In this paper, based on the fact that user densities of SCs and MC change with time, we model the traffic on the European traffic profile and portray the power consumption of the HetNet throughout the day. Simulation results show that by applying SC sleeping and our proposed algorithms, the HetNet can save about 20% power daily. The performances of our proposed algorithms are close to that of the optimal algorithm and their computational complexities are remarkably lower.     

Improvements to seamless vertical handover between mobile WiMAX and 3GPP UTRAN through the evolved packet core - [LTE part II: 3GPP release 8]

Recent mobile devices are integrated with multiple network interfaces. Users want their devices connected to the network anytime anywhere. It is highly feasible for a user to change connection to another network for users that leave the service area of its current serving network, where handover needs to be executed seamlessly such that ongoing service sessions are not interrupted. The handover operation not only requires switching the interfaces within a device but also involves seamless reconfiguration of the supporting networks. In this article, an improved IP-based vertical handover technology for mobile WiMAX [1, 2], 3GPP legacy systems (i.e., Global System for Mobile communications and Universal Mobile Telecommunications System) [3, 4], and 3G Long Term Evolution [5, 6] is presented, which is based on existing optimized handover techniques between mobile WiMAX and 3GPP accesses [7?9]. Formerly proposed 3GPP WiMAX optimized VHO solutions introduced new elements, such as the forward attachment function and access network discovery and selection function. The ANDSF supports the discovery of target access, and the FAF provides the functionality that authenticates the UE before the execution of VHO. However, the previous technique has limitations that result in data loss and abnormal disconnection to the source access [7?9]. This article provides a solution by introducing an additional network element called the data forwarding function (DFF) that eliminates the data loss during VHO execution. In addition, the DFF resolves the problem of abrupt disconnection to the source network. The simulation results show that the proposed VHO technique is effective in minimizing data loss during VHO execution between mobile WiMAX and 3GPP networks. As the proposed solution of this article is an IP based handover solution, it can be similarly applied to other communication networks.     

Modeling of OpenFlow-related handover messages in mobile networks

Software defined networking (SDN) and its most popular southbound implementation OpenFlow (OF) are already greatly exploited in the existing mobile cellular networks as part of data centers and mobile core networks. Due to user’s mobility, it is of upmost importance for the operators to provide the shortest possible interruption when the mobile users are performing the procedure of handover. In this work, we proposed a novel analytical approach to model the OF-related handover messages exchanged between the OF-switches and the SDN controller. We modeled two different OF-switch implementations and we compared the results: (1) single shared buffer used for the control and data plane; (2) two priority buffers, where the data plane packets are served only when there are no packets to be processed in the control plane. We numerically evaluated the two systems and we validated the model by using simulations. The obtained results clearly point that although the priority buffering increased the complexity, it effectively provided the shortest handover delay. Therefore, the priority buffering should be the preferred mechanism for mobile networks.

     

Joint load balancing and interference coordination in multi-antenna heterogeneous networks

In heterogeneous networks (HetNets), it is desirable to offload users from macro cells to small cells to achieve load balancing. However, the offloaded users suffer a strong inter-tier interference. To guarantee the performance of the offloaded users, the interference from macro cells should be carefully managed. In this paper, we jointly optimize load balancing and interference coordination in multi-antenna HetNets. Different from previous works, instead of almost blank subframes (ABS) on which the macro cells waste time resource, the macro cells suppress the interference to the offloaded users by zero-forcing beamforming (ZFBF) on interference nulling subframes (INS). Considering user association cannot be conduct frequently, we derive the long-term throughput of users over Rayleigh fading channels while previous works focused on instantaneous rate. From the perspective of the spectrum efficiency and user fairness, we formulate a long-term network-wide utility maximization problem. By decomposing the problem into two subproblems, we propose an efficient joint load balancing and interference coordination strategy. Simulation results show that our proposal can achieve good system performance gains over counterparts in term of the network utility, cell edge throughput and average throughput.     

Software‐defined networking to improve handover in mobile edge networks

Mobility management and handover for a seamless connection are among all‐time challenges of wireless networks. Software‐defined networking (SDN) has opened new horizons toward research by adding intelligence in edge networks while decoupling the control and data planes. The flexibility and centralized nature of SDN further improve the handover decision algorithms. In this paper, we have improved the network performance with respect to the number of handovers and the handover delay by applying an LTE‐SDN architecture and a novel handover decision algorithm based on predicting the future locations of a moving vehicle. The proposed algorithm decouples the handover procedure into two phases of preparation and execution. In the preparation phase, which occurs in the control plane, the handover decision and resource allocation take place, and in the execution phase, handover gets executed similar to the LTE architecture. The results of our research indicate that our proposed LTE‐SDN performance is improved with respect to the number of handovers, handover delay, and signaling overhead by 24%, 16%, and 20%, respectively. On the other hand, average Reference Signal Received Quality (RSRQ) value is decreased by 4% as a tradeoff for the improvements gained.