LTE-Advanced radio access enhancements: A survey

Long Term Evolution Advanced (LTE-Advanced) is the next step in LTE evolution and allows operators to improve network performance and service capabilities through smooth deployment of new techniques and technologies. LTE-Advanced uses some new features on top of the existing LTE standards to provide better user experience and higher throughputs. Some of the most significant features introduced in LTE-Advanced are carrier aggregation, enhancements in heterogeneous networks, coordinated multipoint transmission and reception, enhanced multiple input multiple output usage and deployment of relay nodes in the radio network. Mentioned features are mainly aimed to enhance the radio access part of the cellular networks. This survey article presents an overview of the key radio access features and functionalities of the LTE-Advanced radio access network, supported by the simulation results. We also provide a detailed review of the literature together with a very rich list of the references for each of the features. An LTE-Advanced roadmap and the latest updates and trends in LTE markets are also presented

Self organization of tilts in relay enhanced networks: a distributed solution

Despite years of physical-layer research, the capacity enhancement potential of relays is limited by the additional spectrum required for Base Station (BS)-Relay Station (RS) links. This paper presents a novel distributed solution by exploiting a system level perspective instead. Building on a realistic system model with impromptu RS deployments, we develop an analytical framework for tilt optimization that can dynamically maximize spectral efficiency of both the BS-RS and BS-user links in an online manner. To obtain a distributed self-organizing solution, the large scale system-wide optimization problem is decomposed into local small scale subproblems by applying the design principles of self-organization in biological systems. The local subproblems are non-convex, but having a very small scale, can be solved via standard nonlinear optimization techniques such as sequential quadratic programming. The performance of the developed solution is evaluated through extensive simulations for an LTE-A type system and compared against a number of benchmarks including a centralized solution obtained via brute force, that also gives an upper bound to assess the optimality gap. Results show that the proposed solution can enhance average spectral efficiency by up to 50% compared to fixed tilting, with negligible signaling overheads. The key advantage of the proposed solution is its potential for autonomous and distributed implementation

Inband Relaying in Long Term Evolution-Advanced Networks

The set of stringent requirements for 4G radio access networks has triggered the embodiment of new small low-power nodes, e.g. relay, Femto and Pico access nodes, as part of the network infrastructure. Various types of relay nodes are currently supported in IEEE 802.16m and 3GPP LTE-Advanced, e.g. inband Layer 2 or Layer 3 nodes and outband nodes, considering different functional capabilities and backhauling characteristics. In general, relay nodes are characterized by compact physical characteristics, low power consumption, a wireless backhaul link to the core network, and relaxed installation guidelines with respect to radiation and planning regulation. In specific, inband relay nodes, the matter of this study, are Layer 3 access nodes with time-multiplexed transmission and reception on their wireless backhaul and access links, which operate on the same frequency band. These characteristics impose serious challenges on one hand, but allow for significant improvements on the other hand. In this context, the deployment flexibility of relay nodes simplifies the network planning procedure and reduces deployment costs. On the other hand, low power transmission and limited antenna capabilities result in small relay cell coverage areas which will lead to load imbalances. Besides, multiplexing backhaul and access communications on different subframes implies the need for suitable two-hop resource allocation and scheduling. Further challenges are attributed to increased interference levels compared to macrocell deployments, as well as the introduction of a new interference type known as relay-to-relay interference resulting from the misalignment of access and backhaul link dedicated subframes at different relay nodes. The research towards this thesis has addressed these challenges within 3GPP LTE-Advanced context. A feasibility study of different relaying modes is provided and the performance of relay deployments is evaluated in different propagation environments. Thereafter, simple network planning techniques are proposed to alleviate the limitations of the inband backhaul link. Further, novel techniques are investigated to address resource allocation and scheduling, load balancing and interference coordination. The performance of proposed techniques along with the energy efficiency of relay nodes is evaluated. Results show in general significant gains and validate relaying as an efficient enhancement technology

Design of a Quality of Service-Based Load Balancing Relay Selection Mechanism for Long Term Evolution-Advanced Systems

Serving as the fourth generation mobile communication standard, Long Term Evolution-Advanced provides various technical support to achieve high transmission speed. In particular, relays are an essential technology supported by the standard. Because a relay uses the resources within a communication system, user devices adopt the optimal relay method as the transmission pathway to optimize resource utilization. According to the quality of service required by various user applications, this paper fabricates a method for selecting the optimal load-balancing transmission pathway for user devices

Backhaul Link Enhancement and Radio Resource Management for Relay Deployments

Mobile networks are experiencing a dramatic increase in the data traffic. Besides, a continuously growing number of users expect mobile broadband access with the utmost in quality and ubiquitous connectivity. In this regard, multi-hop decode-and-forward relaying is a promising enhancement to existing radio access networks to fulfill the challenging requirements in a cost-efficient way and, thus, is an integral part of the Fourth Generation (4G) standards. Nevertheless, in order to fully exploit the potential benefits of relay deployments, proper radio resource management (RRM) is necessary. The research in this thesis has contributed to cellular relay deployments for future mobile networks. Concretely, we have developed key RRM concepts with a particular focus on the uplink (UL) system performance to complement the existing literature. We have demonstrated the performance of these concepts by taking Third Generation Partnership Project (3GPP) Long-Term Evolution (LTE) Release 10 and beyond (LTE-Advanced) Type 1 inband relaying as a practical framework, and by considering urban and suburban scenarios. First, by performing relay site planning (RSP) we aim at improving the quality of the wireless backhaul which is crucial for the end-to-end user performance. Then, we analyze UL power control (PC) and verify its importance and applicability in relay deployments. In this context, we propose manual and automated optimizations to tune PC parameters on all links to further enhance the system performance. Moreover, we study the energy efficiency by taking into account throughput (TP) per power consumption. Further, we investigate various resource sharing strategies among and within the links. Via proposed approaches, performance enhancement is targeted along with higher system fairness and more flexible resource allocation. In addition, we address a key issue regarding the small coverage area of an RN cell in the overlaying macrocell, which results in load imbalances, inefficient resource utilization, and increased UL inter-cell interference. Specifically, we apply practical cell range extension (CRE) techniques to cope with these drawbacks. Performance evaluations reveal that relay deployments clearly outperform macrocell-only deployments in terms of TP as well as TP per power consumption provided that proper RRM is performed. Our results also verify that the use of RSP yields substantial improvements. Furthermore, our results show that the proposed RRM concepts and the associated joint optimization strategies can fulfill the aforementioned goals while achieving significant system performance enhancements

Scalable base station switching framework for green cellular networks

With the recent unprecedented growth in the wireless market, network operators are obliged not only to find new techniques including dense deployment of base stations (BSs) in order to support high data rate services and high user density, but also to reduce the operating costs and energy consumption of various network elements. To solve these challenges, powering down certain BSs during low-traffic periods, so-called BS sleeping, has emerged as an effective green communications paradigm. While BS sleeping offers the potential to significantly lower energy consumption, it also raises many challenges, since when a BS is switched off, this can lead to, for example, coverage holes, sudden degradation in quality of service (QoS), higher transmit power dissipation in off-cell mobile stations (MSs), an inability to rapidly power up/down equipment and finally, a failure to uphold regulatory requirements. In order to realise greener network designs which both maximise energy savings whilst guaranteeing QoS, innovative BS switching mechanisms need to be developed. This thesis presents a novel BS switching framework which improves energy efficiency (EE) in comparison with existing approaches, while guaranteeing the minimum QoS and seamless services. The major technical contributions in this framework are: i) a new BS to relay station (RS) switching model where certain BSs are switched to RS mode rather than being turned off, firstly using a fixed threshold based switching algorithm utilizing temporal traffic diversity, and ii) then subsequently by means of an adaptive threshold by exploiting the inherently asymmetric traffic profile between cells, i.e., by exploiting both the temporal and spatial traffic diversity; iii) a traffic-and-interference-aware BS switching strategy that considers the impact of inter-cell interference in the decision making process to dynamically determine the best BS set to be kept active for improved EE; and finally iv) a novel scalable multimode BS switching model which enables each BS to operate in different power modes i.e., macro/micro/sleep to explore energy savings potential even at higher traffic conditions. The thesis findings conclusively confirm this new BS switching framework provides significant EE improvements from both BS and MS perspectives, under diverse network conditions and represents a notable step towards greener communications