Self‐optimization of handover parameters for dynamic small‐cell networks

Seamless handover is an essential feature of cellular networks. For small‐cell networks, effective handover becomes particularly challenging. If some cells may be activated and deactivated dynamically, effective handover handling will become even more difficult. A key factor of good handover performance is “handover timing,” that is, making handover decision at a right time. If handover is executed too early or too late, users will experience temporary link disconnection, called radio link failure (RLF). Handover timing is controlled by handover parameters, which are set by the network. RLF prevention is directly related to the proper configuration of these parameters. In this paper, we propose a self‐optimization scheme that adjusts the handover parameters to minimize RLFs for dynamic small‐cell networks. Our scheme first detects the types of RLF and then adjusts the handover parameters according to the types of RLF. Unlike most existing schemes, our scheme adjusts both system common parameters and cell‐specific parameters together. In certain situations, such as when two adjacent cells do not have sufficient coverage overlap, RLFs may not be reduced to a satisfactory level by the handover parameter adjustment alone. To deal with such a case, our scheme adjusts the cell coverage in conjunction with the handover parameter optimization. The simulation results show that the proposed scheme can virtually eliminate RLFs. Copyright © 2013 John Wiley & Sons, Ltd.     

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.     

Self‐optimizing neighbor cell list with dynamic threshold for handover purposes in networks with small cells

To select a proper target cell for handover of mobile users, signal level of cells in user's neighborhood is scanned by a user equipment (UE). Cells assumed to be scanned are included in the so‐called neighbor cell list (NCL). Conventionally, the NCL is managed according to the probability of handover of users to a target cell with fixed threshold. Nevertheless, the size of NCL could be significant if this approach is applied to networks with small cells. In this paper, we exploit knowledge of handover probability among cells derived from a handover history to reduce the amount of scanned cells. We introduce dynamic adaptation of the amount of cells to be scanned according to the quality of signal of a serving cell, measured by the UE. We also investigate impact of relation between the handover probability and the signal level to maximize efficiency of this approach. Further, the NCL management considering either summarized handover history of all UE or individual history of each user is compared in our evaluations. As the results show, both methods notably reduce the amount of cells to be scanned, while call drop rate and outage of the users are still negligible as in the conventional way. Copyright © 2013 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.     

Optimized handover and resource management: an 802.21‐based scheme to optimize handover and resource management in hybrid satellite‐terrestrial networks

Satellite communications can provide fourth generation (4G) networks with large‐scale coverage. However, their integration to 4G is challenging because satellite networks have not been designed with handover in mind. The setup of satellite links takes time, and so, handovers must be anticipated long before. This paper proposes a generic scheme based on the Institute of Electrical and Electronics Engineers 802.21 standard to optimize handover and resource management in hybrid satellite‐terrestrial networks. Our solution, namely optimized handover and resource management (OHRM), uses the terrestrial interface to prepare handover, which greatly speeds up the establishment of the satellite link. We propose two mechanisms to minimize the waste of bandwidth due to wrong handover predictions. First, we leverage the support of 802.21 in the terrestrial access network to shorten the path of the signaling messages towards the satellite resource manager. Second, we cancel the restoration of the satellite resources when the terrestrial link rolls back. We use OHRM to interconnect a digital video broadcasting and a wireless 4G terrestrial network. However for the simulation tool, we use a WiMAX as the terrestrial technology to illustrate the schemes. The simulation results show that OHRM minimizes the handover delay and the signaling overhead in the terrestrial and satellite networks. Copyright © 2013 John Wiley & Sons, Ltd.     

SRGH: A secure and robust group‐based handover AKA protocol for MTC in LTE‐A networks

Machine‐type communication (MTC) is defined as an automatic aggregation, processing, and exchange of information among intelligent devices without humans intervention. With the development of immense embedded devices, MTC is emerging as the leading communication technology for a wide range of applications and services in the Internet of Things (IoT). For achieving the reliability and to fulfill the security requirements of IoT‐based applications, researchers have proposed some group‐based handover authentication and key agreement (AKA) protocols for mass MTCDs in LTE‐A networks. However, the realization of secure handover authentication for the group of MTCDs in IoT enabled LTE‐A network is an imminent issue. Whenever mass MTCDs enter into the coverage area of target base‐station simultaneously, the protocols incur high signaling congestion. In addition, the existing group‐based handover protocols suffer from the huge network overhead and numerous identified problems such as lack of key forward/backward secrecy, privacy‐preservation. Moreover, the protocols fail to avoid the key escrow problem and vulnerable to malicious attacks. To overcome these issues, we propose a secure and robust group‐based handover (SRGH) AKA protocol for mass MTCDs in LTE‐A network. The protocol establishes the group key update mechanism with forward/backward secrecy. The formal security proof demonstrates that the protocol achieves all the security properties including session key secrecy and data integrity. Furthermore, the formal verification using the AVISPA tool shows the correctness and informal analysis discusses the resistance from various security problems. The performance evaluation illustrates that the proposed protocol obtains substantial efficiency compared with the existing group‐based handover AKA protocols.     

Inter‐cell coordinated beamforming with opportunistic scheduling

This paper proposes a distributed coordination framework with opportunistic scheduling among multiple users as opposed to the existing works on the multiple‐cell cooperative beamforming problem that deals with a single active user in each cell. In this cross‐layer design framework that deals with the beamforming in the physical layer and multiuser scheduling in the upper layer, radio resource management and inter‐cell coordination issues are jointly considered to improve the cell‐edge throughput performance by trading off their individual benefit in an optimal manner. Our simulation results demonstrated that its performance can reach up to 85% of its upper bound at the cell boundary. Copyright © 2015 John Wiley & Sons, Ltd.     

Clock synchronization for packet networks using a weighted least‐squares error filtering technique and enabling circuit emulation service

Circuit emulation service (CES) allows time‐division multiplexing (TDM) services (T1/E1 and T3/E3 circuits) to be transparently extended across a packet network. With circuit emulation over IP, for instance, TDM data received from an external device at the edge of an IP network is converted to IP packets, sent through the IP network, passed out of the IP network to its destination, and reassembled into TDM bit stream. Clock synchronization is very important for CES. This paper presents a clock synchronization scheme based on a double exponential filtering technique and a linear process model. The linear process model is used to describe the behaviour of clock synchronization errors between a transmitter and a receiver. In the clock synchronization scheme, the transmitter periodically sends explicit time indications or timestamps to a receiver to enable the receiver to synchronize its local clock to the transmitter's clock. A phase‐locked loop (PLL) at the receiver processes the transmitted timestamps to generate timing signal for the receiver. The PLL has a simple implementation and provides both fast responsiveness (i.e. fast acquisition of transmitter frequency at a receiver) and significant jitter reduction in the locked state. Copyright © 2006 John Wiley & Sons, Ltd.     

Implementing virtual platform for global‐scale cyber physical system networks

The need for global‐scale cyber physical system (CPS) is increasing with the evolution of CPS research. A global‐scale CPS requires additional considerations beyond the well‐known CPS requirements, such as security, reliability, and timely delivery, which cannot be easily satisfied when a CPS becomes global scale. Building an entire dedicated network for a global‐scale CPS cannot be a solution, because it requires a large capital outlay in order to be actualized. To overcome these obstacles, we implement a virtual platform named Xebra that includes effective CPS middleware for realizing a global‐scale CPS and isolation techniques based on virtualization. In this paper, we discuss the requirements for realizing global‐scale CPS network, and also, we introduce our implementation as a virtual platform with its performance evaluation. Copyright © 2014 John Wiley & Sons, Ltd.     

Admission control and handover management for high‐speed trains in vehicular geostationary satellite networks with terrestrial gap‐filling

Following a recent upgrade, the Digital Video Broadcasting—Return Channel Satellite (DVB‐RCS) standard sets up to support terminal mobility. In this scenario, integration with terrestrial systems becomes a primary concern to ensure network connectivity in urban areas. This article proposes an integrated satellite–terrestrial architecture for the provision of broadband services onboard high‐speed trains, in which terrestrial cellular networks are seen as viable gap‐fillers for discontinuous satellite coverage. We derive an analytical model of the hybrid DVB‐RCS‐cellular system by exploiting analogies between the mobility pattern predictability of LEO constellations and that of high‐speed trains. Terminals whose QoS cannot be guaranteed by the satellite segment are proposed to temporarily divert the connections towards the terrestrial infrastructure, where available. Using an iterative approach based on the Erlang fixed‐point approximation, we show performance improvements with respect to stand‐alone satellite systems in terms of handover failure probability and overall resource utilization. The analytical model is also validated via our ns2‐based DVB‐RCS packet‐level simulator. Detailed modelling of synchronization and signalling mechanisms confirms the accuracy of the analytical results, and shows that topology and mobility information can contribute to refine radio resource utilization optimality when used jointly. Copyright © 2009 John Wiley & Sons, Ltd.     

Optimization and efficient detection of primary synchronization signal for multi‐beam satellite‐LTE systems

A new design of primary synchronization signal (PSS) sequences and an efficient detection algorithm for multi‐beam satellite long‐term evolution (LTE) systems are investigated in this paper. First, a transmit‐timing adjustment method is proposed to reduce the large time difference of arrival of received signals from different satellites. Then, using the particular subcarrier mapping scheme of LTE, original Zadoff–Chu sequences are generalized to obtain more candidate sequences with good correlation properties. Later on, choosing an optimal subset from these candidate sequences, new PSS sequences for seamless global coverage multi‐beam satellite‐LTE systems are obtained. Subsequently, an efficient synchronization and low complexity PSS detection algorithm using interference cancellation method is presented. Finally, simulation results verify the effectiveness of the proposed scheme. Copyright © 2015 John Wiley & Sons, Ltd.     

Opportunistic distributed channel access for a dense wireless small‐cell zone

This paper considers uplink channel access in a zone of closed‐access small‐cells that is deployed in a macrocell service area. All small‐cell user equipments (SUEs) have access to a common orthogonal set of channels, leading to intercell interference. In addition, each channel forms a separate collision domain in each cell, thus can be successfully used only by one SUE of that cell. This paper proposes two non‐cooperative Bayesian games, G ₁ and G ₂, that are played among the SUEs. G ₁ assumes the availability of channel state information at the transmitters, while G ₂ assumes the availability of only the distribution of the channel state information. Each SUE can choose to transmit over one of the channels or not to transmit. The emphasis of the paper is on the set of symmetric threshold strategies where the Nash equilibrium is fully determined by a single parameter. The existence and uniqueness of pure Bayesian–Nash symmetric equilibrium of G ₁ in threshold strategies and mixed Bayesian–Nash symmetric equilibrium of G ₂ in uniformly distributed threshold strategies are proven. Numerical results corroborate the theoretical findings and benchmark against another decentralized scheme. Copyright © 2015 John Wiley & Sons, Ltd.     

Semi‐distributed dynamic inter‐cell interference coordination scheme for interference avoidance in heterogeneous networks

Inter‐cell interference (ICI) is a major problem in heterogeneous networks, such as two‐tier femtocell (FC) networks, because it leads to poor cell‐edge throughput and system capacity. Dynamic ICI coordination (ICIC) schemes, which do not require prior frequency planning, must be employed for interference avoidance in such networks. In contrast to existing dynamic ICIC schemes that focus on homogeneous network scenarios, we propose a novel semi‐distributed dynamic ICIC scheme to mitigate interference in heterogeneous network scenarios. With the goal of maximizing the utility of individual users, two separate algorithms, namely the FC base station (FBS)‐level algorithm and FC management system (FMS)‐level algorithm, are employed to restrict resource usage by dominant interference‐creating cells. The distributed functionality of the FBS‐level algorithm and low computational complexity of the FMS‐level algorithm are the main advantages of the proposed scheme. Simulation results demonstrate improvement in cell‐edge performance with no impact on system capacity or user fairness, which confirms the effectiveness of the proposed scheme compared to static and semi‐static ICIC schemes.     

基于时延补偿的小小区多跳空口同步

在密集蜂窝异构网络中,小小区之间的时频同步是发挥小小区技术优势的重要条件以及网络系统正常运转的前提。传统的小区同步技术包括同步卫星辅助同步及IEEE 1588协议同步。为克服传统小区同步技术的不足,空口同步技术成为研究热点。在此基础上,提出了一种基于时延补偿的多跳空口同步机制,通过源小区空口同步信号(RISS)所在时帧位置来确定其同步等级,同时对源小区RISS的传播时延进行补偿,从而提高目标小小区同步精度。仿真表明,该方案在同步跳数为4时,定时同步误差仍可维持在1 μs以内,从而有效地提高了网络同步精度,并突破了同步跳数对空口同步技术的限制,扩大了空口同步范围。     

On cell range extension in LTE‐Advanced Type 1 inband relay networks

Relay node cell area is limited by low transmission power and limited antenna capabilities, which may not allow it to carry a significant share of the traffic load, thus reducing its efficiency. Cell range extension is thus expected to better balance the load in the network, hence, improving the performance of relay deployments. Herein, we investigate two relay cell range extension techniques, introducing a bias to cell selection and handover thresholds along with reduction in donor enhanced Node B transmission power. The study focuses on inband half‐duplex relaying where resource partitioning among the two relay hops is jointly considered with cell range extension. As opposed to picocell deployments, extending the relay cell range offloads only partially the macrocell as newly admitted users increase the resource demand of the relay on its wireless backhaul link from its donor enhanced Node B. Hence, joint optimization of the decisive parameters for different key performance metrics is performed. Comprehensive analysis was carried out for both the downlink and the uplink in urban and suburban scenarios within the LTE‐ Advanced framework. Results reveal that the investigated solution yields significant gains. Finally, we discuss on the realization of cell range extension as part of network planning and offline optimization.Copyright © 2013 John Wiley & Sons, Ltd.     

Green optical backbone networks: virtual topology adaptation using a page rank‐based rating system

An energy‐aware virtual topology rating system is proposed in this work, which can be utilized as a tool during the virtual topology reconfiguration procedure in an optical backbone network in order to reduce its energy consumption. It is well known that maintaining a static virtual topology in Internet Protocol (IP)‐over‐Wavelength Division Multiplexing (WDM) networks is not energy‐efficient. To that end, virtual topology adaptation algorithms have been developed to adjust the virtual topology to the constantly fluctuating traffic load. While these algorithms achieve significant energy savings, further reduction on the total network energy consumption can be achieved through the proposed rating system. The proposed rating system is a modified version of the page rank algorithm, which ranks websites in the Internet based on their importance. The proposed rating system attributes ratings to lightpaths, which indicate the relative significance of a lightpath in the virtual topology in terms of energy consumption. The rating can be used during the routing procedure as an energy efficiency indicator, in order to increase the number of lightpaths that are deactivated from the reconfiguration mechanism and increase the utilization per lightpath. The proposed reconfiguration scheme (page rank‐based virtual topology reconfiguration) achieves up to 12% additional energy savings in comparison to an existing virtual topology reconfiguration algorithm at the cost of slightly increased average hop distance. Copyright © 2015 John Wiley & Sons, Ltd.     

An efficient network‐coding based back‐pressure scheduling algorithm for wireless multi‐hop networks

Back‐pressure scheduling has been considered as a promising strategy for resource allocation in wireless multi‐hop networks. However, there still exist some problems preventing its wide deployment in practice. One of the problems is its poor end‐to‐end (E2E) delay performance. In this paper, we study how to effectively use inter‐flow network coding to improve E2E delay and also throughput performance of back‐pressure scheduling. For this purpose, we propose an efficient network coding based back‐pressure algorithm (NBP), and accordingly design detailed procedure regarding how to consider coding gain in back‐pressure based weight calculation and how to integrate it into next hop decision making in the NBP algorithm. We theoretically prove that NBP can stabilize the networks. Simulation results demonstrate that NBP can not only improve the delay performance of back‐pressure algorithm, but also achieve higher network throughput. Copyright © 2016 John Wiley & Sons, Ltd.     

Design of a preamble signal for synchronization in ultra‐wideband noncoherent energy detection receivers

We present an effective preamble design scheme that can improve synchronization performance in ultra‐wideband noncoherent energy detection receivers. Focusing on the effect of the nonuniform energy allocation of a preamble in energy detection‐based synchronization, we propose a preamble energy allocation scheme. This scheme determines the energy distribution of a preamble by using a constrained optimization method. Through the proposed scheme, we promise that we can provide a generalized solution to design preambles for energy detection‐based synchronization, in that it is possible to design the power distribution of preamble pattern in various shapes according to the system's specification. In addition, we also suggest two preamble design scheme that finally decides the practical shape of a preamble from the determined energy distribution of a preamble. By providing preamble design examples, we show that preambles based on nonuniform energy distribution provide improved synchronization performance without any additional increase in receiver complexity in ultra‐wideband channel environments. Copyright © 2011 John Wiley & Sons, Ltd.     

Inter‐cell interference mitigation based on joint beamforming

In cellular networks, global channel state information (CSI) shall be shared among neighboring cells to mitigate various inter‐cell interference (ICI). In this paper, we propose that comparable ICI is mitigated while weak ICI is treated as noise. The amount of shared CSI is highly reduced, because of that only the CSI corresponding to comparable ICI is shared among neighboring cells. In the case of single user equipment in each cell, a joint singular value decomposition and interference alignment method is proposed along with the analysis of its approximate sum rate. Some nodes select singular value decomposition method, while others choose interference alignment method. The method at each node is determined by global selection principle or user classification principle. In the case of multiple UEs in each cell, all nodes utilize minimum mean square error method, but ICI is neglected at cell center users. Copyright © 2014 John Wiley & Sons, Ltd.