Multi-radio Access Technology Research Articles

Adaptive bearer split control for 5G multi-RAT scenarios with dual connectivity

The Dual Connectivity (DC) technology has gained a lot of momentum as an underlying fundamental concept for the deployment of multi-Radio Access Technology (RAT) 5G mobile networks based on the tight interworking between the Long Term Evolution (LTE) and 5th Generation (5G) standards. In the so-called bearer split configuration of the DC technology, a flow control mechanism executed at a Master Node (MN) controls the bearer split ratios such that the correct amount of data is transmitted from the MN and Secondary Nodes (SNs) to enhance the Quality of Service (QoS) provision. In this context, the present work proposes a flow control algorithm that maximizes the user satisfaction by dynamically orchestrating the bearer split ratios based on the adaptation of utility functions. The adaptation is performed according to a predefined network operator goal, such as maintaining a certain QoS level at a given network node. Furthermore, the proposed solution tracks the channel and QoS metrics variations such that the best split ratios are employed. Simulations conducted in 5G multi-RAT scenarios show that the adaptability of the proposed algorithm effectively maximizes the user satisfaction as well as enhances the users and system throughput when compared to state-of-the-art algorithms from the literature.

Simple Multi-RAT RoF System With $2\times2$ MIMO Wireless Transmission

A simple multi-radio access technology (multi-RAT) capable radio over fiber (RoF) system with 2 × 2 multiple-inputmultiple-output (MIMO) wireless transmission is proposed and experimentally demonstrated. The transmission of sub-6 GHz and 60 GHz millimeter-wave (MMW) services is enabled by a dual-drive Mach-Zehnder modulator (DDMZM) and an optical interleaver. In the central office (CO), sub-6 GHz and 30 GHz signals are applied to the dual branches of the DDMZM which is biased at the quadrature point. After transmission over singlemode fiber (SMF), the two services are separated by the optical interleaver. One output port of the interleaver is used for delivering the sub-6 GHz signal while the other one is used for the generation and transmission of the 60 GHz MMW signal. Furthermore, we also demonstrate the MIMO technology can be used in the proposed architecture to improve the capacity. A proofof-concept experiment is performed to verify the feasibility of the proposed scheme. In the experiment, a 1.3 Gb/s orthogonal frequency division multiplexing (OFDM) signal at 55 GHz is transmitted over 25 km of SMF and 1 m 2 × 2 MIMO wireless distance while a 675 Mb/s OFDM signal at 0.375 GHz is delivered over 25 km of SMF at the same time.

An Optimized Load Balance Solution for Multi-homed Host in Heterogeneous Wireless Networks.

The imminent wireless technologies are demanding fusion of several networks with diverse technologies. A convenient user device for such an environment is the multihomed host, which is capable of making use of simultaneous multiple connections of heterogeneous networks and smartly distributing/receiving data among them. The aim of this work is to develop a mechanism for assessing the multihoming concept and to propose a system model for increasing its applicability. The proposed model provided a novel user-centric scheme for multihoming for multi-radio access technologies (multi-RAT). It is considered an evolution of traffic offloading for gaining more capacity, higher data rates, and real-time services. This work assumes data classifications, evaluates and ranks the available connections, and utilizes the application data in an unequal load balance scheme. This is achieved by analyzing the performance of three of the most widely used alternative-choice for multiple attributes decision making (MADM) methods. The analytical hierarchy process (AHP), along with a utility equation, is applied to the system model for unequal load balance solution. The proposed model is targeting an energy efficient mechanism which satisfies application needs. Moreover, it reveals an efficient transmission mechanism for a better quality of service, traffic management, and availability solutions. The simulation results show that the proposed system surpassed its former counterparts.

Small Cell Deployment Along Roads: Coverage Analysis and Slice-Aware RAT Selection

We characterize a multi-tier wireless network consisting of multi-radio access technology (RAT) small cells, operating in both sub-6GHz and millimeter wave (mm-wave) bands, overlaid on top of traditional macro cells. To realistically characterize the user equipment (UE) performance, we model the position of the small cells along roads. First, we provide tractable, yet realistic models to characterize the mm-wave interference and the effect of vehicular blockages on the mm-wave signals. Then, we introduce an association policy, where an UE selects the serving tier using the powers measured on the sub-6GHz band, and then, using the biased power of the mm-wave band, selects the RAT. Based on this, we derive the signal to interference plus noise ratio (SINR) coverage probabilities of pedestrian UEs. We investigate the effect of the RAT selection bias on the vehicular blockage, SINR coverage, and rate coverage experienced by the UEs. Leveraging the results of our analysis, we propose to use a varied range of RAT selection biases to support the diverse applications of the fifth generation (5G) mobile networks. Accordingly, we provide a slice-aware RAT selection strategy to support three types of services, characterized by different requirements in terms of reliability, coverage, and data rates.

A survey of mmWave user association mechanisms and spectrum sharing approaches: an overview, open issues and challenges, future research trends

Fifth generation (5G) cellular networks promise to support multi-radio access technologies (multi-RATs) with low and high frequencies aiming at delivering good coverage, several gigabits data rate, and ultra-reliable services. In this context, user-association and resource allocation appear to be a huge challenge due to the variety of specifications and varied propagation environments. In this treatise, the focus is on the technical and administrative difficulties of the adoption of user association (UA) mechanism and spectrum sharing approach (SSA) in millimeter wave (mmWave) systems, for example, the technical design considerations and their underlying options, as well as their impact on users and network performance. In addition, details on the importance of the rules and regulations of SSA are presented. This study also identified a few possible design solutions and potential promising technologies in both UA and SSA. In the context of UA, several mechanisms are identified, such as backhaul-, caching-, and hybrid multi-criteria-aware UA to achieve seamless connectivity and to enhance the network utility. In the context of SSA, this study pinpoints varied subjects that need to be explored, such as joint efficient rules and regulations enactment, assessment of fairness and independence in multi-independent mobile network operators (multi-IMNOs) that support SSA, as well as the implementation of hybrid-SSA via Virtualized Cloud Radio Access Network. Finally, attention is drawn to several key conclusions to enable readers and interested researchers to learn about the most controversial points of mmWave 5G cellular networks.

Distributed RRM for 5G Multi-RAT Multiconnectivity Networks

A tight interworking between the next generation of wireless cellular networks, the fifth generation (5G), and legacy standards, e.g., long term evaluation (LTE), is being envisioned in order to support a wide range of service requirements. Aiming at addressing the challenge of coordinating resources across different technologies, centralized processing units are being considered. However, they have practical issues, e.g., processing costs and increased signaling overhead. In this context, this work formulates an optimization problem in order to manage resources in a multi radio access technology (RAT) scenario. Its objective is to maximize the minimum user throughput in the system subject to the constraint that for each user, his throughput must be higher than a requirement. One of the differences from previous works is that the users may connect to more than one RAT at the same time, the so-called dual connectivity. The referred problem is nonlinear and hard to solve. However, we get to transform it into a simpler form, a mixed integer linear programming, which can be optimally solved using standard optimization methods. This solution is categorized as a centralized solution. Thus, we propose a distributed framework to overcome the drawbacks of centralized processing. This framework is divided into two parts: a base station (BS) selection procedure (performed by the users) and a resource assignment algorithm (performed by the BSs). Besides, a performance evaluation is conducted, considering fourth generation LTE and 5G new radio parameters.

On Optimal Resource Allocation in Multi-RAT Wireless Networks With Receiver Characteristic Awareness

Next-generation wireless systems are expected to use multiple coexisting radio access technologies with different receive and transmit characteristics. This will make the radio frequency front-ends susceptible to unprecedented adjacent-channel interference (ACI), which can jeopardize communication performance. In this paper, we propose a novel ACI-aware joint channel and power allocation framework that takes into account the receiver imperfections arising due to: 1) imperfect image frequency rejection and 2) analog-to-digital converter aliasing. The objective is to minimize the number of allocated channels and the aggregate power transmitted while satisfying the rate demands of different links in a multi-radio access technology environment. As the overall problem is NP-hard, we develop an efficient algorithm to solve it through decomposing the problem into two subproblems: channel allocation and power assignment. Then, it solves the decomposed problem by iteration using a two-phase structure. In Phase I, a particle swarm optimization-based algorithm is tailored to obtain good solutions for the channel allocation subproblem. Phase II solves the power allocation subproblem optimally given the channel allocation solution obtained in Phase I. The results demonstrate: 1) the criticality of receiver-characteristic awareness when designing resource allocation schemes and 2) the superiority of the proposed algorithm in solving the overall problem efficiently.

Multipath TCP for V2I communication in SDN controlled small cell deployment of smart city

Vehicle-to-infrastructure (V2I) connectivity enables a variety of safety, infotainment, and mobility applications in smart cities. However, these applications require “always best and seamless connectivity”, which constitutes a key challenge in the context of available radio access and core network technologies. Multipath TCP (MPTCP) in multi-radio access technologies can be an emerging solution to meet the requirements of TCP-based services. Since MPTCP enables a vehicle to use multiple network interfaces and IP paths simultaneously, MPTCP seems a better option than legacy TCP in heterogeneous networks (HetNets). Software Defined Networking (SDN) with its unique features such as its centralized control, programmability, and flexibility, can be beneficial for mobility management and performance requirements for vehicular communication. Although studies exist, that explore the performance of MPTCP and SDN separately for V2I context, a combination of these two are unexplored. In this article, we evaluate the performance of MPTCP for V2I connectivity in SDN controlled small cells of DSRC and Wi-Fi using the Mininet-WiFi emulator. Our experimental study reveals that issues related to Layer-2 handover in Wi-Fi and flow installation by the SDN controller play a key role. If these two issues can be handled wisely in SDN, MPTCP can offer benefits to V2I connectivity in small cells, such as Wi-Fi and DSRC. We also propose an approach for rule installation to V2I connectivity in the software-defined vehicular network.

Dynamic Spectrum Management through Resource Virtualization with M2M Communications

Wireless spectrum licensing has increased due to the continuous evolution and use of cellular technology. The increase in the number of mobile-connected devices and global data traffic demand has led to a significant increase in demand for spectrum access with studies showing that there is unexploited capacity in the spectrum. This is especially critical for 5G networks where the service requirements are extremely stringent. To that end, this article proposes dynamic spectrum management through the combination of two innovative architectures, wireless resource virtualization (WRV) and machine-to-machine (M2M) communications. WRV allows for better utilization of the spectrum, while reducing both the capital and operational expenditures. On the other hand, M2M communications can help boost capacity and improve quality of service by leveraging spectrum access across multiple radio technologies. In this article, a brief discussion of multi-radio access technology heterogeneous networks is given. Then the problem of dynamic spectrum management through resource virtualization with M2M communications is described. To the best of our knowledge, such a combined framework has not been previously proposed. Two different algorithms are proposed to evaluate the performance of the considered architecture, namely a decomposition- based algorithm and a greedy-based algorithm. Simulation results show that such architecture can boost the overall capacity of the system by achieving higher data rates. Moreover, it is shown that the number of possibly supported M2M pairs is increased while using the same spectrum.

Coverage Analysis and Load Balancing in HetNets With Millimeter Wave Multi-RAT Small Cells

We characterize a two tier heterogeneous network, consisting of classical sub-6 GHz macro cells, and multi radio access technology (RAT) small cells able to operate in sub-6 GHz and millimeter-wave (mm-wave) bands. For optimizing coverage and to balance loads, we propose a two-step mechanism based on two biases for tuning the tier and RAT selection, where the sub-6 GHz band is used to speed-up the initial access procedure in the mm-wave RAT. First, we investigate the effect of the biases in terms of signal-to-interference-plus-noise ratio (SINR) distribution, cell load, and user throughput. More specifically, we obtain the optimal biases that maximize either the SINR coverage or the user downlink throughput. Then, we characterize the cell load using the mean cell approach and derive upper bounds on the overloading probabilities. Finally, for a given traffic density, we provide the small cell density required to satisfy system constraints in terms of overloading and outage probabilities. Our analysis highlights the importance of deploying dual-band small cells, in particular, when small cells are sparsely deployed or in case of heavy traffic.

MuMAB: A Multi-Armed Bandit Model for Wireless Network Selection

Multi-armed bandit (MAB) models are a viable approach to describe the problem of best wireless network selection by a multi-Radio Access Technology (multi-RAT) device, with the goal of maximizing the quality perceived by the final user. The classical MAB model does not allow, however, to properly describe the problem of wireless network selection by a multi-RAT device, in which a device typically performs a set of measurements in order to collect information on available networks, before a selection takes place. The MAB model foresees in fact only one possible action for the player, which is the selection of one among different arms at each time step; existing arm selection algorithms thus mainly differ in the rule according to which a specific arm is selected. This work proposes a new MAB model, named measure-use-MAB (muMAB), aiming at providing a higher flexibility, and thus a better accuracy in describing the network selection problem. The muMAB model extends the classical MAB model in a twofold manner; first, it foresees two different actions: to measure and to use; second, it allows actions to span over multiple time steps. Two new algorithms designed to take advantage of the higher flexibility provided by the muMAB model are also introduced. The first one, referred to as measure-use-UCB1 (muUCB1) is derived from the well known UCB1 algorithm, while the second one, referred to as Measure with Logarithmic Interval (MLI), is appositely designed for the new model so to take advantage of the new measure action, while aggressively using the best arm. The new algorithms are compared against existing ones from the literature in the context of the muMAB model, by means of computer simulations using both synthetic and captured data. Results show that the performance of the algorithms heavily depends on the Probability Density Function (PDF) of the reward received on each arm, with different algorithms leading to the best performance depending on the PDF. Results highlight, however, that as the ratio between the time required for using an arm and the time required to measure increases, the proposed algorithms guarantee the best performance, with muUCB1 emerging as the best candidate when the arms are characterized by similar mean rewards, and MLI prevailing when an arm is significantly more rewarding than others. This calls thus for the introduction of an adaptive approach capable of adjusting the behavior of the algorithm or of switching algorithm altogether, depending on the acquired knowledge on the PDF of the reward on each arm.

Signal to Noise Ratio Based Wi-Fi Offloading Decision Algorithm in Vehicular Networks

Nowadays, the rapid increase in mobile data demand is faced by the existing mobile networks. It becomes clear that the existing cellular infrastructure, along with its next generation upgrades is unable to meet the requirements of the users to provide them a required level of throughput for their services. This paper provides an overview of the different standards and requirements in Wi-Fi offloading system. In Het-Nets, multi Radio Access Technology may be operating jointly with the cellular network. This scheme is aimed at evaluating the performance of incorporating Wi-Fi Access Points (APs) along with the cellular network. The decision is based on the selection of best Wi-Fi AP for offloading the data, for which the Signal to Noise Ratio value at the user location is more than the threshold value in vehicular environment. At the end, the numerical results evaluate the performance of presented scheme which justify its application in vehicular networks.

Dual Connectivity for LTE-NR Cellular Networks: Challenges and Open Issues

The Dual Connectivity (DC) technology has gained a lot of momentum in the LTE Release 12 as a means to enhance the per-user throughput and provide mobility robustness. Some studies in the literature have discussed the interworking between the LTE and the air interface of the upcoming Fifth Generation (5G) in a DC scenario. That integration may provide some benefits to meet the high throughput, reliability and availability requirements of the 5G networks. This work firstly presents a brief overview of the DC technology considering the integration between 4G e 5G. Then, we highlight some open issues and challenges for future investigation involving Radio Resource Management (RRM) in such a scenario, which includes: (i) user-cell association, (ii) interaction between base stations and (iii) resource allocation. After that, we propose an extension of a utility-based resource allocation algorithm for DC scenarios. Finally, a performance evaluation is conducted in multi-Radio Access Technology (RAT) LTE-NR scenarios considering the bearer split configuration of the DC technology, where the gains provided by the proposed algorithm are demonstrated.

Applying Multiradio Access Technologies for Reliability Enhancement in Vehicle-to-Everything Communication

The design of the 5G cellular network should take account of the emerging services with divergent quality of service requirements. For instance, a vehicle-to-everything (V2X) communication is required to facilitate the local data exchange and therefore improve the automation level in automated driving applications. In this paper, we inspect the performance of two different air interfaces (i.e., LTE-Uu and PC5) which are proposed by the third generation partnership project to enable the V2X communication. With these two air interfaces, the V2X communication can be realized by transmitting data packets either over the network infrastructure or directly among traffic participants. In addition, the ultra-high reliability requirement in some V2X communication scenarios cannot be fulfilled with any single transmission technology (i.e., either LTE-Uu or PC5). Therefore, we discuss how to efficiently apply multi-radio access technologies (multi-RAT) to improve the communication reliability. In order to exploit the multi-RAT in an efficient manner, both the independent and the coordinated transmission schemes are designed and inspected. Subsequently, the conventional uplink is also extended to the case where a base station can receive data packets through both the LTE-Uu and PC5 interfaces. Moreover, different multicast-broadcast single-frequency network area mapping approaches are also proposed to improve the communication reliability in the LTE downlink. Last but not least, a system level simulator is implemented in this paper. The simulation results do not only provide us insights on the performances of different technologies but also validate the effectiveness of the proposed multi-RAT scheme.

Towards Harmonious Coexistence in the Unlicensed Spectrum: Rational Cooperation of Operators.

5G New Radio (NR) operating in the unlicensed spectrum is accelerating the Fourth Industrial Revolution by supporting Internet of Things (IoT) networks or Industrial IoT deployments. Specifically, LTE-Advanced (LTE-A) is looking to achieve spectrum integration through coexistence with multi-radio access technology (RAT) systems in the same unlicensed bands with both licensed-assisted and stand-alone access. The listen-before-talk (LBT) mechanism is mainly considered to enable an LTE operator to protect other incumbent unlicensed systems. In this article, we investigate the behaviors of multiple LTE operators along with the deployment of WiFi networks in the unlicensed spectrum from both short- and long-term points of view. In countries without mandatory LBT requirements, we show that an LTE operator is susceptible to collusion with another LTE operator, thus exploiting scarce spectrum resources by deceiving other wireless networks into thinking that channels are always busy; hence, mandatory usage of LTE with LBT is highly recommended at national level to achieve harmonious coexistence in the unlicensed spectrum. We discuss several possible coexistence scenarios to resolve the operator’s dilemmaas well as to improve unlicensed spectrum efficiency among multi-RAT systems, which is viable in the near future.

A 5G virtualized RAN based on NO Stack

The virtualized radio access network (vRAN) could implement virtualized baseband functions on general-purpose platforms and expand the processing capacity of the radio access network (RAN) significantly. In this paper, a Not Only Stack (NO Stack) based vRAN is proposed to be employed in the fifth generation (5G) mobile communication system. It adopts advanced virtualization technologies to maintain flexible and sustainable. The baseband processing and storage resources should be sliced and orchestrated agilely to support multi radio access technology (multi-RAT). Also it is analyzed and demonstrated by different use cases to validate the benefits. The proposed vRAN reduces signaling overheads and service response time in the bearer establishment procedure. Concluded from the analyses and demonstrations, the NO Stack based vRAN could support multi-RAT convergence and flexible networking effectively.

Intelligent cooperation management of multi-radio access technology towards the green cellular networks for the twenty-twenty information society

An unprecedented increase in subscribers and demand for high-speed data are considered a critical step towards the new era of mobile wireless networks, i.e., Fifth Generation (5G), where the legacy mobile communication system will still be operational for a long time in the future. This has subsequently increased the overall energy consumption, operational costs and carbon footprint of cellular networks, due to increase the number of base stations (BSs), which consume the most energy. Switching BSs off/on in accordance with the traffic pattern variations is considered an effective method for improving energy efficiency. However, the main concerns from the network operators are the requirements to switched on/off the BSs, coverage issues and secured the radio service for the affected area. Hence, the main focus of this study is to develop an intelligent cooperation management (switch BSs on/off) within a multi-radio access technology (RAT) environment between a future generation 5G into the existing LTE and UMTS cellular network towards green cellular networks, while guaranteeing maximum cells coverage area during a switch off session. Particle swarm optimisation has been adopted in this study to maximize the cell coverage area under the constraints of the transmission power of the BS $$(P_{tx})$$(Ptx), the total antenna gain (G), the bandwidth (BW), the signal-to-interference-plus-noise ratio (SINR), and shadow fading $$(\sigma )$$(ź). Moreover, the modulation and coding scheme, the data rate, and the energy efficiency are considered. The results have shown that by applying the proposed a dynamic multi-RAT BSs switching off$$\backslash $$\on strategy according to the traffic load variations, the daily energy savings of up to 42.3% can be achieved, with guaranteed maximum cells coverage area.

5G Technology : A Survey of Architecture and Emerging Technologies

Research on 5G mobile wireless technologies has been very active in both academia and industry in the past few years. While there has been certain consensus on the overall requirements of 5G wireless systems (e.g., in data rate, network capacity, delay), various enabling wireless technologies have been considered and studied to achieve these performance targets. It has been quite clear, however, that there would be no single enabling technology that can achieve all diverse and even conflicting 5G requirements. In the near future, i.e., beyond 4G, some of the prime objectives or demands that need to be addressed are increased capacity, improved data rate, decreased latency, and better quality of service. To meet these demands, drastic improvements need to be made in cellular network architecture. This paper presents the results of a detailed survey on the fifth generation (5G) cellular network architecture and some of the key emerging technologies that are helpful in improving the architecture and fulfil the demands. In this detailed survey, the prime focus is on the 5G cellular network architecture, massive multiple input multiple output technology, and device-to-device communication (D2D). Along with this, some of the emerging technologies that are addressed in this paper include interference management, spectrum sharing with cognitive radio, ultra-dense networks, multi-radio access technology association, full duplex radios, milli-meter wave solutions for 5G cellular networks, and cloud technologies for 5G radio access networks and software defined networks. In this paper, a general probable 5G cellular network architecture is proposed, which shows that D2D, small cell access points, network cloud, and the Internet of Things can be a part of5G cellular network architecture. A detailed survey is included regarding current research projects being conducted in different countries by research groups and institutions that are working on 5G technologies.

Energy‐efficiency resource allocation for cognitive heterogeneous networks with imperfect channel state information

In this study, the authors focus on the downlink resource allocation to optimise energy-efficiency (EE) of orthogonal frequency division multiplexing-based cognitive heterogeneous network (HetNet), where network service providers operate multi-radio access technologies. A more practical case is considered, in which imperfect channel state information (CSI) is available for wireless channels between secondary base stations and secondary users (SUs), primary users (PUs). Since imperfect CSI may result in outage in secondary networks and make collision occur in primary networks, a joint subcarrier and power allocation scheme for the cognitive HetNet is proposed to guarantee quality of service requirements for both SUs and PUs in probabilistic manners. Then the probabilistic EE optimisation scheme is approximated into a deterministic convex form, and the optimal solutions for the scheme are derived by double-loop iteration method. Afterwards, the authors develop a low-complexity algorithm in the presence of imperfect CSI with a small reduction of system performance. Simulation results are provided to show the impact of channel estimation error on the EE optimisation problem and to highlight the performance improvement from considering channel estimation error in the joint subcarrier and power allocation scheme for the cognitive HetNet system.

A unified traffic steering framework for LTE radio access network coordination

This article presents an overview of recent 3GPP developments in the area of traffic steering that are shaping the road toward the approaching 5G systems. Due to the increasing availability of RAN features addressing mobile data delivery over a variety of spectrum access techniques, a new traffic steering design is required for the evolving LTE-Advanced Pro standard. LTE evolution toward 5G brings an opportunity to introduce a native and unified approach to the coordination of radio access mechanisms in multi-radio access technology networks for efficient data delivery in mobile networks. This leads to a design of a unified traffic steering framework, aiming at the orchestration of traffic steering related features for optimal radio resource utilization. Load-based radio access network coordination is presented and accompanied by illustrative examples to visualize how the multitude of LTE-Advanced Pro features can be handled in a holistic manner. Based on the proposed solution, potential evolution directions of mobile networks are discussed as an initial step toward the standardization of 5G.