Ad hoc self-healing of OFDMA networks using UAV-based relays

Due to the demand for constantly increasing data rates, especially within LTE (Long Term Evolution) and LTE-Advanced networks, today’s mobile radio systems are operating more and more at their capacity limits. Consequently, techniques to compensate cell outage and cell overload situations are needed. Existing approaches to address these problems are typically static solutions and are accompanied by Inter-Cell Interference (ICI), like the introduction of femtocells. In this paper we propose an UAV-based (Unmanned Aerial Vehicle) approach in order to provide ad hoc self-healing of cellular networks. Thereby, the UAVs are acting as mobile relays and offload traffic to surrounding cells with free resources. We introduce the genetic Interference-aware Positioning of Aerial Relays (IPAR) algorithm which is able to find suitable positions for the UAVs that maximize the downlink throughput of the cellular network. The algorithm is evaluated for hexagonal as well as irregular cellular network layouts and is based on an analytical model for deriving the key performance indicators throughput, system loss and free remaining resources in the cells for the downlink. In order to decrease the introduced interference between the UAVs and surrounding base stations, a random frequency allocation scheme is applied. Based on an exact analytical model for the SINR (Signal to Interference and Noise Ratio) of users served by UAVs, it is shown that by different hopping distributions a reduction of the SINR up to 11.6 dB can be achieved compared to the worst case performance of systems without resource planning.     

AORS: adaptive mobile data offloading based on attractor selection in heterogeneous wireless networks

The unforeseen mobile data explosion poses a major challenge to the performance of today’s cellular networks, and is in urgent need of novel solutions to handle such voluminous mobile data. Obviously, data offloading through third-party WiFi access points (APs) can effectively alleviate the data load in the cellular networks with a low operational and capital expenditure. In this paper, we propose and analyze an attractor-aware offloading ratio selection (AORS) algorithm, which can adaptive select an optimum offloading ratio based on attractor selection for the current networks environment. In the proposed algorithm, the throughput of AP and the cellular load corresponding to the coverage area of the AP, are mapped into the cell activity, which is the reflector of the current network environment. When the current attractor activity is low, the network is dominated by the noise. Then, the noise triggers the controller to select adaptive attractor for each users, the optimal offloading ratio \(\phi \), to adapt to the dynamic network environment. Hence, according to the offloading ratio \(\phi \), the part of the cellular traffic will be transmitted via WiFi networks. Through simulation, we show that the proposed AORS algorithm outperforms the existing ones with 42 % higher heterogeneous network throughput in a dense traffic environment.     

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.     

SDN Based Mobile Networks: Concepts and Benefits

Mobile Internet traffic is expected to grow faster than the fixed Internet traffic in a near future. Since, today’s broadband networks are approaching theoretical limits in terms of spectral efficiency per link, mobile operators are compelled to seek for new solutions that will be able to accommodate the expected traffic growth and improve their position in the competitive market. Addressing those challenges with current inflexible, not scalable and complex architecture is very hard, if possible at all. Software defined networking (SDN) is a new networking architecture paradigm that holds great promise to overcome many of mentioned limitations and provides required improvements in performance by decoupling control functions from underlying physical infrastructure. In this paper, we explain key reasons for transition to SDN based mobile networks and briefly describe several proposals of design scenario. Special emphasis is placed on SDN’s contribution to more efficient inter-cell interference management, traffic control and network virtualization.     

Handoff traffic characterization in cellular networks undernonclassical arrivals and service time distributions

The phenomenal growth in the subscriber population has necessitated the accurate dimensioning and performance analysis of cellular networks. Classically, cellular networks have been analyzed using Poisson call arrivals and negative exponential channel holding times. However, these assumptions may not be valid for modern networks providing heterogeneous services and serving users with highly varied mobility. In this paper, we propose a moment-based approach for analyzing cellular networks under more generalized arrival processes and more generalized channel holding-time distributions. We present a model for accurately characterizing the handoff traffic offered by a cell to its neighbor in a simple two-cell scenario. We derive this handoff traffic for two different channel holding-time distributions. Our two-cell model easily lends itself to being used as a building block for analyzing more general cellular network layouts. We illustrate the accuracy of our analysis using comparison with simulation results     

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.     

Energy efficiency analysis of heterogeneous cellular network based on Thomas cluster process

In the existing heterogeneous cellular networks (HCN),the rapid increasing of small cells caused a problem that the hotspots where users were clustered generated a huge amount of energy consumption.To improve the energy efficiency of the networks,the spatial model was researched.The users in hotspots in the HCN were modeled as the Thomas cluster process,combined with the max mean bias received signal power (max-BRP) strategy to achieve base station load balancing,and the user’s association probability,coverage probability and the network’s energy efficiency were derived using tool from stochastic geometry.The simulation shows that the derived formulas are accurate,and the network’s energy efficiency can be greatly improved by setting appropriate bias factors.     

Tracking Traffic Peaks in Mobile Networks Using Statistics of Performance Metrics

In recent years, there has been an increasing awareness to tracking traffic peaks reflecting the presence of mass events or permanent traffic hotspots. This trend is driven by dominant themes for wireless evolution towards 5G networks such as the problematic of hotspot offloading solutions, the emergence of heterogeneous networks with small cells’ deployment and the development of green networks’ concept. Actually, tracking traffic peaks with a high accuracy is of great interest to know how the congested zones can be offloaded, where small cells should be deployed and how they could be managed for sleep mode concept or even controlled according to traffic mobility if they are moving. In this paper, we propose a method for tracking peaks of traffic using performance metrics extracted from the operation and maintenance database of the network. These metrics are the timing advance, the angle of arrival, the neighboring cell level, the cell load and two mean throughputs: arithmetic (AMT) and harmonic (HMT). The combined use of these performance metrics, projected over a coverage map, yields a promising traffic localization precision even with considering imperfections of coverage prediction and mobile equipment capabilities in handling measurements. The proposed solution can be easily implemented in the network at an appreciable low cost.     

A novel antenna allocation technique for green single cell MIMO and MIMO-CoMP downlink transmission

To meet the increasing traffic and energy consumption demands of wireless networks, energy efficiency and energy efficient transmission techniques have become an urgent need for cellular networks. In this work, the problem of base station (BS) power consumption reduction for increased network energy efficiency of downlink TDMA-based transmission is considered. To meet network’s high traffic demand due to high data rates required by large numbers of users, multiple-input multiple-output (MIMO) and coordinated multi-point (CoMP) transmission have been considered. By adopting realistic power consumption models for single cell MIMO and multi-cell MIMO-CoMP networks, enhanced antenna allocation techniques are proposed and their energy efficiency is compared to the conventional power allocation schemes. It is shown that for a target signal to interference plus noise ratio (SINR), the proposed techniques consume less total power compared to traditional schemes, which leads to higher energy efficiency. In addition, for same power level, the symbol error rate (SER) is reduced and system’s sum rate increases, which leads to higher spectral efficiency.     

Performance Comparison of Time Slot Allocation Schemes in TDD-CDMA Multihop Cellular Networks

Today, high-speed multimedia services are becoming one of the most challenging demands of cellular subscribers. Many approaches have been proposed during last decade and still there are many ongoing researches aiming to provide higher speed and higher quality services for users. Multihop cellular network (MCN) is a promising solution to this problem. MCNs offer high-speed communication to mobile stations which are far from their base stations by relaying their data in a multihop connection. Moreover, TDD-CDMA networks are proven to be able to accommodate the asymmetric traffic generated by applications such as Internet browsers or multimedia applications. These types of traffic are most of the time biased towards uplink or downlink. In this paper we deploy multihop relaying in TDD-CDMA networks in order to provide high data rate connections targeting for multimedia applications. We propose time slot allocation schemes for TDD-CDMA MCNs and compare them with conventional schemes used in TDD-CDMA single-hop cellular networks in terms of users’ data rate and maximum capacity in different symmetric and asymmetric traffic scenarios. Results of this study show that our proposed schemes can provide higher data rate as well as capacity and outperform other conventional schemes.     

Nonclassical traffic modeling and performance analysis of cellularmobile networks with and without channel reservation

We present a two-moment performance analysis of cellular mobile networks with and without channel reservation. Unlike classical analysis where handoff traffic is modeled as Poisson, we characterize handoff traffic as a general traffic process and represent it using the first two moments of its offered traffic. We empirically show that handoff traffic is a smooth process under negative exponential channel holding times. We also show how one may determine customer-oriented grade-of-service parameters such as new-call blocking, handoff call blocking, and forced termination probability under the two-moment representation of traffic offered to each cell. We present extensive results validating our analysis. We compare the performance of the proposed two-moment analysis with classical single-moment analysis and simulation results. Our simulation employs five different mobility models. We show that our proposed model outperforms the existing analytical method when compared to simulation results employing all five mobility models     

User-Centric Offloading to WLAN in WLAN/3G Vehicular Networks

In recent years, there has been a growing demand in 3G data services, leading to deteriorating 3G service quality. Noting that Wireless Local Area Networks (WLANs) as well as 3G cellular networks are widely available today, WLANs could be effectively utilized to relieve the overload in the 3G networks. On the other hand, use of IEEE 802.11 WLAN Access Points (APs) has proliferated tremendously, resulting in a communication device inside a mobile vehicle to access the Internet. However, using Internet through APs in moving vehicles is challenging since WLAN APs have a short range and are typically not deployed to cover all roads. Several studies have investigated the performance of using intermittently available WLAN connectivity from moving vehicles for data transfers and predictive offloading in WLAN/3G networks. However, these works have not addressed mobility pattern from the viewpoint that drivers’ mobility is generally known to have a daily routine. Therefore, in this paper, we consider the user’s historical mobility to decide to offload data to WLAN instead of switching to 3G network. The user’s application usage pattern is also considered into predicting available WLANs. To evaluate the performance of our offloading algorithm, we analyze the prediction error and conduct simulations. The simulation results show that the proposed algorithm achieves shorter transmission time than the existing schemes that do not consider user’s mobility pattern by delivering more data to the WLANs.     

Performance Analysis of D2D-Aided Underlaying Cellular Networks Based on Poisson Hole Cluster Process

D2D (Device-to-Device) communication has become a crucial part of 4G and 5G networks. It can not only decrease the transmit power of user equipments (UEs) and increase area spectral efficiency of cellular networks, but also offload traffic from cellular networks and alleviate scarcity of spectrum resources by using in-band communication. In this paper, we consider a real tele-communication scenario in which the mobile UEs are primarily located in hotspots and cell edges. By integrating Poisson Hole Process with Thomas Cluster Process, a kind of D2D-Aided Underlaying Cellular Networks (D2D-UCNs) is built. In the D2D-UCNs, we first investigate the aggregation interference of the typical UE and D2D user by using stochastic geometry. Subsequently we analyze their coverage probability and area spectral efficiency. The simulation results show that the coverage probability of D2D users and UEs can be effectively guaranteed by establishing exclusion zone, whilst the area spectral efficiency of the D2D-UCNs can be maximized by optimizing the number of simultaneously active D2D links.

     

软件无线电应用趋势展望——网络设计：用于软件无线电系统的虚级联模块设计、性能分析及实现

软件无线电（Software Radio）是通信系统中极具发展前途的技术。随着高速数字信号处理器的发展以及大规模可编程门阵（FPGA）的普及,软件无线电把诸多与具体信号类型紧密相关的处理任务软件化,从而使通信中的硬件设备更为通用。但是待传输的数据或已被接收的数据都需要通过局域网或其他类型的骨干网络与数据中心交换数据。多协议传输平台（MSTP）是一种融合数据业务与实时业务在SDH网络中传输的规范,是目前流行宽带数据接入形式,它为软件无线电提供了多种灵活的接入形式。作为MSTP,其关键技术之一是虚级联。与传统的连续级联相比,虚级联减小了带宽分配的颗粒度,使SDH传输管理更为灵活,提高了整体网络的资源利用率。本文介绍我们在MSTP芯片中VC-12虚级联模块的设计和理论分析过程。经过软件仿真和FPGA验证,这部分电路设计正确合理,可以稳定工作在预定工作速率。应用该设计的MSTP芯片目前已经完成加工,并被成功应用于MSTP网络设备中。相信我们的工作对软件无线电技术的未来发展有着积极的作用。     

Load-balance cell association for improving network capacity in heterogeneous cellular networks

Heterogeneous cellular networks improve the spectrum efficiency and coverage of wireless communication networks by deploying low power base station （BS） overlapping the conventional macro cell. But due to the disparity between the transmit powers of the macro BS and the low power BS, cell association strategy developed for the conventional homogeneous networks may lead to a highly unbalanced traffic loading with most of the traffic concentrated on the macro BS. In this paper, we propose a load-balance cell association scheme for heterogeneous cellular network aiming to maximize the network capacity. By relaxing the association constraints, we can get the upper bound of optimal solution and convert the primal problem into a convex optimization problem. Furthermore we propose a Lagrange multipliers based distributed algorithm by using Lagrange dual theory to solve the convex optimization, which converges to an optimal solution with a theoretical performance guarantee. With the proposed algorithm, mobile terminals （MTs） need to jointly consider their traffic type, received signal-to-interference-noise-ratios （SINRs） from BSs, and the load of BSs when they choose server BS. Simulation results show that the load balance between macro and pico BS is achieved and network capacity is improved significantly by our proposed cell association algorithm.     

Adaptive Beam-Centric Admission Control for WCDMA Multicell/Multiservice Scenarios with Non-Uniform Traffic

The goal of the study presented in this paper is the accurate performance evaluation of adaptive beam-centric admission control (AC) for wideband code-division multiple access (WCDMA) multicell networks with non-uniform traffic requirements. Each NodeB employs antenna arrays (AAs), used either to form fixed grids of beams (FGoBs), or to steer and shape multiple beams towards directions of increased traffic, in an adaptive manner. The adaptive beam-centric AC maximizes the cell throughput in a multirate/multicell environment by grouping as many users as possible under a common beam formed by the AA, taking into account their spatial distribution and overall interference. Due to the increased complexity of the Monte Carlo (MC) simulations, a novel grid-enabled problem solving environment has been developed in order to reduce execution times considerably and make feasible full scale extensive simulations of complex operational scenarios (up to 4 tiers of cells, multiple beams per cell, non-uniform traffic distributions with different spatial characteristics). Results show that the network with the adaptive beam-centric AC can achieve significantly higher throughput per beam in multirate/multicell environments with hotspots. In particular, it is shown that the throughput per beam gain depends exponentially on the number of hotspots per cell and their angular width, and gains up to 200/350/700% can be achieved with 1/2/3 hotspots, respectively. Moreover, it is shown that the adaptive beam-centric AC provides significant reduction in interbeam handovers, which leads to more available resources in downlink, reduced signaling requirements and easier network planning.     

Optimal resource allocation and adaptive call admission control for voice/data integrated cellular networks

Resource allocation and call admission control (CAC) are key management functions in future cellular networks, in order to provide multimedia applications to mobiles users with quality of service (QoS) guarantees and efficient resource utilization. In this paper, we propose and analyze a priority based resource sharing scheme for voice/data integrated cellular networks. The unique features of the proposed scheme are that 1) the maximum resource utilization can be achieved, since all the leftover capacity after serving the high priority voice traffic can be utilized by the data traffic; 2) a Markovian model for the proposed scheme is established, which takes account of the complex interaction of voice and data traffic sharing the total resources; 3) optimal CAC parameters for both voice and data calls are determined, from the perspective of minimizing resource requirement and maximizing new call admission rate, respectively; 4) load adaption and bandwidth allocation adjustment policies are proposed for adaptive CAC to cope with traffic load variations in a wireless mobile environment. Numerical results demonstrate that the proposed CAC scheme is able to simultaneously provide satisfactory QoS to both voice and data users and maintain a relatively high resource utilization in a dynamic traffic load environment. The recent measurement-based modeling shows that the Internet data file size follows a lognormal distribution, instead of the exponential distribution used in our analysis. We use computer simulations to demonstrate that the impact of the lognormal distribution can be compensated for by conservatively applying the Markovian analysis results.     

User’s mobility effect on the performance of wireless cellular networks serving elastic traffic

The objective of the present paper is to give an analytic approximation of the performance of elastic traffic in wireless cellular networks accounting for user’s mobility. To do so we build a Markovian model for users arrivals, departures and mobility in such networks; which we call WET model. We firstly consider intracell mobility where each user is confined to remain within its serving cell. Then we consider the complete mobility where users may either move within each cell or make a handover (i.e. change to another cell). We propose to approximate the WET model by a Whittle one for which the performance is expressed analytically. We validate the approximation by simulating an OFDMA cellular network. We observe that the Whittle approximation underestimates the throughput per user of the WET model. Thus it may be used for a conservative dimensioning of the cellular networks. Moreover, when the traffic demand and the user speed are moderate, the Whittle approximation is good and thus leads to a precise dimensioning.     

Key Management in Secure Satellite Multicast Using Key Hypergraphs

Satellite networks play an important role in today’s information age because they can provide the global coverage services. Information security is an important concern in satellite multicast communications, where eavesdropping can be performed much easier than the fixed terrestrial networks. In this work, a novel multicast key management scheme based on key hypergraph for satellite networks on a predefined communication scenario is proposed. We use logical key hierarchy and distributed-logical key hierarchy as reference models for performance comparisons. It is shown that the proposed multicast key management scheme is scalable to large dynamic groups and minimizes satellite bandwidth usage.     

SBT (Sense Before Transmit) Based LTE Licenced Assisted Access for 5 GHz Unlicensed Spectrum

Utilization of unlicensed spectrum under licensed assisted access ensuring fair co-existence with Wi-Fi networks is a good solution to address immense usage of mobile data. Radio communication operation of LTE in unlicensed frequency band is referred as LTE-unlicensed (LTE-U) or LTE-licensed assisted access. In this paper, we consider a HGNW in which coverage area of Wireless-Fidelity (Wi-Fi)’s Access Point is integrated within the LTE-U small base station’s cellular network coverage area. To overcome the disadvantages of existing LTE-U technics like carrier sense adaptive transmission and listen before talk, we proposed a new methodology i.e., sense before transmit in this paper by adopting a transmit power control mechanisms using reciprocity theorem based on the channel state information to assign the secondary carriers in the uplink as well as in the downlink directions in the unlicensed spectrum to carry the traffic. In our proposal, LTE-U users are allowed to use the unlicensed spectrum provided that the interference produced at Wi-Fi users due to LTE-U activities is remained below a certain threshold. We evaluated the performance of proposed network model in terms of outage probability and achievable throughputs.