Traffic navigation using positioning information and channel quality map for system-wide load balancing

Dense small cell networks are expected to be deployed in the next generation wireless system to provide better coverage and throughput to meet the ever-increasing requirements of high data rate applications. As the trend toward densification calls for more and more wireless links to forward a massive backhaul traffic into the core network, it is critically important to take into account the presence of a wireless backhaul for the energy-efficient design of small cell networks. In this chapter, we develop a general framework to analyze the energy efficiency of a two-tier small cell network with massive MIMO macro base stations and wireless backhaul. Our analysis reveal that under spatial multiplexing, the energy efficiency of a small cell network is sensitive to the network load, and it should be taken into account when controlling the number of users served by each base station. We also demonstrate that a two-tier small cell network with wireless backhaul can be significantly more energy efficient than a one-tier cellular network. However, this requires the bandwidth division between radio access links and wireless backhaul to be optimally designed according to the load conditions.

Small cell network strategies are applied for providing enhanced coverage and maximizing system capacity in the network. In such an environment, substantial growth of signalling load on the Core Network (CN) can be caused by reduced cell size, increased user density and increased user velocity. In this paper, in order to reduce the signalling load incurred by path switching operations in the small cell network, a new mobility control function, termed the Small Cell Controller (SCC) is introduced to the existing Base Station (BS) on the Radio-Access-Network(RAN)-side. Within a cluster, a designated SCC controls and manages a group of small cells and maintains associated forwarding information for UEs within a localized mobility management domain. When compared to the legacy scheme in the 3GPP, our simulation results show that the proposed RAN-side SCC is able to achieve the signalling reduction gain by up to 58.1% on the CN.

New generation of mobile communication systems will focus on seamlessly integrating existing wireless technologies including 3G cellular systems, wireless LAN and Bluetooth to create a wide coverage, improved capacity and enhanced QoS heterogeneous wireless communication system. It is envisaged that the next generation of wireless communication systems will support comprehensive and personalized services, providing stable system performance and quality of service. In this paper we investigate and analyse the performance of a wireless communication system which consists of an integrated cellular communication system and a wireless LAN radio access networks inorder to determine an optimum combination of radio access technologies in a coverage area for efficient handling of mixed traffic requests from mobile users.

Small cell networks (SCNs) have emerged as a promising solution to meet the demand for increasing data traffic for the sixth generation and beyond wireless networks. However, power consumption and two-tier interference issues are two bottlenecks that hinder further development. This paper proposes a novel reconfigurable intelligent surface (RIS)-based SCN in which an RIS serves multiple micro users as a small cell base station while assisting the macro user’s transmission. Compared to the conventional SCNs, the RIS-based SCN can achieve significant power reduction. Meanwhile, the reflected signal can be regarded as a multipath component instead of interference to the macro user. We propose two transmission schemes and formulate the design of the phase shift matrix at the RIS and the beamforming vector at the macro base station as an optimization problem. The alternating optimization algorithm is developed to optimize the phase shift matrix and the beamforming vector to minimize the total power consumption under the user rate and phase shift constraints. Simulation results show that the total power consumption can be reduced significantly by deploying the RIS in the SCN when the number of reflective elements is sufficiently large.

We consider small cell networks and study the impact of user mobility. Assuming Poisson call arrivals at random positions with random velocities, we discuss the characterization of handovers at the boundaries. We derive explicit expressions for call block and call drop probabilities using tools from spatial queuing theory. We also derive expressions for the average virtual server held up time. These expressions are used to derive optimal cell sizes for various profile of velocities in small cell networks via some numerical examples. We further discuss the performance of the optimal system.

There is a significant increase in mobile internet usage resulting in demand for traffic volume, frequency efficiency and energy and cost reduction, for which small cell networks are expected to play a key role. Due to high bandwidth requirement, mobile health applications (m-health) and medical video streaming in particular will benefit from small cell networks in terms of Quality of Service (QoS) and Quality of Experience (QoE) enhancements. This paper presents content-aware and device-aware medical Quality of Experience evaluations in terms of subjective (e.g. MOS) and objective (e.g. PSNR and SSIM) quality metrics obtained over small cell networks. Furthermore, we address the following two main research questions: (1) How significant is ultrasound video content type in determining medical QoE? (2) How much of a role does the display device play in medical experts’ diagnostic experience? The former is answered through the content classification of ultrasound video sequences based on their spatio-temporal features and validating their significance through medical experts’ subjective ratings. The latter is answered by conducting a subjective experiment of the ultrasound video sequences across multiple devices, ranging in screen size and resolution.

For the uplink of heterogeneous network composed of macro base station and small base stations, this paper proposes an access mechanism based on coalition game in small cell networks. Firstly, the time division multiplexing method is defined in each coalition to share the spectrum and reduce the interference in the coalition. Then, according to the interference characteristics of the coalition game, the achievable transmission rate of each user is calculated, and the various utility values in the coalition game are also defined. Finally, under the constraint of the threshold of the access signal-to-noise ratio, the access optimization problem is constructed to obtain the optimal system rate, and an access algorithm based on coalition game in small cell networks is proposed to solve the optimization problem. The results show that the proposed algorithm can converge to a stable value, and the system rate of this algorithm is superior to the random access algorithm and the non-cooperative game algorithm in the area with densely distributed users.

This comprehensive resource covers everything you need to know about small cell networks, from design, to analysis, optimization and deployment. Detailing fundamental concepts as well as more advanced topics, and describing emerging trends, challenges and recent research results, this book explains how you can improve performance, decision making, resource management, and energy efficiency in next generation wireless networks. Key topics covered include green small cell networks and associated trade-offs, optimized design and performance analysis, backhauling and traffic overloading, context-aware self-organizing networks, deployment strategies and mobility management in large scale HetNets. Written by leading experts in academia and industry and including tools and techniques for small cell network design and deployment, this is an ideal resource for graduate students, researchers and industry practitioners working in communications and networking.

Content caching is a promising way to overcome backhaul limitations in small cell networks. However, in such type of networks, small base stations (SBSs) are always deployed with limited cache storages. Thus, it is necessary for SBSs to adjust their contents for better caching efficiency, so as to reduce backhaul traffic. In this paper, we study the content replacement problem to minimize the traffic flowing into the costly backhaul links. However, in small cell networks where SBSs make up backhaul mesh networks, the effectiveness of reducing backhaul traffic depends on the hop distance from the content location to the requesting user. On this basis, we formulate a hop minimization problem that is inherently combinatorial. Through log-sum-exp approximation, we can solve the problem and arrive at a close-form solution with guaranteed performance gap to the optimal solution. By exploiting the properties of continuous-time Markov chain (CTMC), the solution can be implemented by designing a CTMC that can instruct the content replacement process. As a consequence, a concise, efficient, and flexible content replacement strategy is proposed. Simulation results verify our analysis and show that our proposed strategy outperforms the conventional strategies.

The increasing demand for multimedia communication over wireless platform necessitates the QoS-aware packet scheduling schemes in Broadband Wireless Access (BWA) networks. This paper deals with the analysis of queue size of QoS-aware Weighted Hybrid Packet Scheduling Schemes (WHPSS) for heterogeneous traffic classes in BWA networks. By categorizing the heterogeneous traffics of BWA networks into several classes (i.e. Class-1, Class-2, Class-3) depending upon their QoS requirement, we analyze the effect of queue size in WHPSS using three dimensional Continuous Time Markov Chain (CTMC) model. The analysis has been carried out with respect to the several performance parameters such as queuing delay, packet loss rate and throughput. This paper aims to observe the effect of queue size for each traffic flow to maximize the throughput of the network under the specified constraint of queuing delay and packet loss rate. Thus, the analysis helps to determine suitable queue size in the BWA network under varied traffic condition satisfying the required QoS constraints.

Wireless content caching in small cell networks has recently been considered as a promising way to alleviate the congestion of the backhaul in emerging heterogenous cellular network. However, how to select files which are cached in SBSs and how to make SBSs work together is an important issue for cooperative cache research for the propose of reducing file download time. In this paper, a Cooperative-Greedy strategy (CGS) among cache-enabled small base stations (SBSs) in small cell network is proposed, in order to minimize the download time of files. This problem is formulated as a Chinese restaurant game.Using this game model, we can configure file caching schemes based on file popularity and the spectrum resources allocated to several adjacent SBSs. Both the existence and uniquencess of a Nash equilibrium are proved. In the theoretical analysis section, SBSs cooperate with each other in order to cache popular files as many as possible near UEs. Simulation results show that the CGS scheme outperforms other schemes in terms of the file-download time.

With the deployment of small cell networks, low-cost backhaul schemes for small cell base stations (SBSs) have attracted great attentions. Self-backhaul using cellular communication technology is considered as a promising solution. Although some excellent works have been done on self-backhaul in small cell networks, most existing works do not consider the recent advances of full-duplex (FD) and massive multiple-input and multiple-output (MIMO) technologies. By jointly considering them, we propose a novel self-backhaul scheme for small cell networks in this paper, where the macro base station is equipped with massive MIMO antennas, and the SBSs have the FD communication capability. Then, we can achieve the simultaneous transmissions of the access link of users and the backhaul link of SBSs in the same frequency and then spectrum efficiency is improved. Furthermore, we formulate the power allocation problem of the MBS and SBSs as an optimization problem. Because the formulated power allocation problem is a non-convex problem, we transfer the original problem into a difference of convex program by using successive convex approximation method and variable substitution, and then solve it using a constrained concave convex procedure based iterative algorithm. Finally, extensive simulations are conducted to verify the effectiveness of the proposed scheme.

This paper proposes a heterogeneous wireless network with handover in the application layer. The proposed network requires no upgrade of wireless infrastructure and mobile terminals to convert the present homogeneous networks to the proposed heterogeneous network. Only installing application programs on the content server side and the mobile terminal side is required. The performance of the proposed network has been evaluated in a field trial using a mobile broadband wireless access (MBWA) air interface with wide coverage and a wireless local area network (WLAN) air interface with high throughput. The field trial results show that the maximum value of the handover outage time is only 170ms. The proposed heterogeneous wireless network is promising since both high throughput and wide coverage area are attained by a combination of the proposed handover scheme with the present homogeneous wireless networks.

Dynamic time-division duplex (D-TDD) has emerged as an effective solution to accommodate the unaligned downlink and uplink traffic in small cell networks. However, the flexibility of traffic configuration also introduces additional inter-cell interference. In this letter, we study the effectiveness of applying fractional frequency reuse (FFR) as an interference coordination technique for D-TDD small cell networks. We derive the analytical expressions of downlink and uplink mean packet throughput (MPT), then study a network parameter optimization problem to maximize MPT while guaranteeing each user's throughput. Numerical results corroborate the benefits of the proposed FFR-based D-TDD in terms of improving throughput.

In this paper, we discuss the experimental results of application-layer delay reduction methods, which can reduce the delay during TCP applications. Due to the popularization of smart phones, Wireless Local Area Network (WLAN) access such as WLAN hot spot or WLAN tethering is increasing. This increase leads to a WLAN channel being shared by multiple data flows, resulting in the degradation of the communication performance. Specifically, the delay of the real time applications that communicate over TCP can be made longer. To reduce the delay, we developed three methods: reducing the amount of data to send, triggering TCP’s fast retransmission earlier, and returning TCP’s acknowledgment immediately. In our experiments, we measured the delay during the real time TCP applications connected with each other over WLAN and commercial fixed network and analyzed the effectiveness of our methods in the case of WLAN performance being degraded by the file transfer flow. Results indicate that our methods can reduce the 95th percentile of the delay by as much as 84%.