Conventional Cellular Networks Research Articles

Fairness Guaranteed Cooperative Resource Allocation in Femtocell Networks

User-deployed low-power femtocell access points (FAPs) can provide better indoor coverage and higher data rates than conventional cellular networks. However, a major problem in this uncoordinated frequency reuse scenario is the inter-cell interference. In this paper, we propose a graph based distributed algorithm called fairness guaranteed cooperative resource allocation (FGCRA) to manage interference among femtocells. Since the optimal resource allocation is a NP-hard problem, which is difficult to get global optimization in femtocell networks, our proposed FGCRA algorithm provides sub-optimal resource allocation via cooperation among interfering neighbors. First, we propose a specific fairness factor obtained from two-hop interference relations, to determine the lower bound amount of subchannels that each FAP can use and guarantee the fairness among femtocells. Second, we propose scalable rules for distributed resource allocation and the solution to avoid the conflicts among interfering neighbors. Simulation results show that our proposed FGCRA significantly enhances both average user throughput and cell edge user throughput, and provides better fairness.

Multicell cooperation [Guest Editorial

It is well recognized that the conventional cellular networks can no longer meet the user performance requirements in terms of throughput and coverage, which is due to the significant increase in the number of mobile users along with their traffic demands and the limited spectrum resource. This has stimulated the search for new approaches to alleviate this problem. Recently, cooperative communications at both the base station (BS) and mobile station (MS) levels has been proposed as a key technology to address this problem. Multicell cooperation is a new and emerging communication paradigm promising significant improvement in system capacity by mitigating intercell interference. It has been shown that, with the aid of multicell cooperation, a significant improvement of cellular system performance can be achieved, and the increase in throughput can be as large as an order of magnitude. Although the advantages of multicell cooperation have been demonstrated, many problems related to the research and development of practical and effective schemes for multicell cooperation exist. They have attracted considerable research attention in both academia and industry. This special issue of IEEE Wireless Communications puts together some recent results in the area of multicell cooperation for the next generation cellular wireless networks. It includes 11 articles, a brief account for each of which is provided below.

Optimal trade-off between power saving and QoS provisioning for multicell cooperation networks

Multicell cooperation is emerging as a promising wireless communication technique to significantly improve the performance of cellular networks in terms of the coverage of high-datarate services and the system throughput for the next generation wireless networks. On the other hand, multicell cooperation also imposes the new challenges associated with the two mutually conflicting constraints between the power/energy efficiency/saving and the QoS provisioning required by mobile users, which differ from the conventional cellular networks. To overcome the above problem, we propose the semi-Markov decision process model-based stochastic optimization scheme for the optimal trade-off between power saving and QoS provisioning over multicell cooperation networks. Our objective is to efficiently minimize the power consumption at base stations while guaranteeing diverse QoS provisioning for mobile users through multicell cooperation power scheduling. To achieve this goal, we apply finite-state Markov chains to model the mobile users' density, mobility, multicell cooperation power-profile scheduling, and QoS provisioning. Using these models, we formulate the SMDP-based stochastic optimization problem and develop an efficient iteration algorithm to implement our SMDP-based scheme. We evaluate our proposed schemes through numerical analyses, which show that our proposed schemes significantly outperform the other schemes in terms of minimizing power consumption while guaranteeing the required QoS provisioning.

Throughput-Aware and Interference-Aware RRM Techniques for OFDMA-Based Networks

This paper presents techniques for performing radio resource allocation in orthogonal frequency-division multiple-access networks. They are throughput-aware and interference-aware adaptive water-filling schemes for conventional (non-relay) cellular networks and threshold-based distributed radio resources management scheme for relay-based networks. The strategy is to exploit (a) the coarse granularity of the practical throughput curve for the non-relay-based networks and (b) the system interference dynamics in relay networks. Firstly, the numerical results show a significant improvement in throughput using the proposed schemes. Secondly, they provide insight into the potential performance improvements from a two-hop relaying scheme with a simple distributed resource management policy. And thirdly, they demonstrate that some simple but moderately interference-smart algorithms are enough to provide sufficiently good results for future broadband wireless networks.

Optimal resource allocation in fetmocell networks based on Markov modeling of interferers’ activity

Femtocell networks offer a series of advantages with respect to conventional cellular networks. However, a potential massive deployment of femto-access points (FAPs) poses a big challenge in terms of interference management, which requires proper radio resource allocation techniques. In this article, we propose alternative optimal power/bit allocation strategies over a time-frequency frame based on a statistical modeling of the interference activity. Given the lack of knowledge of the interference activity, we assume a Bayesian approach that provides the optimal allocation, conditioned to periodic spectrum sensing, and estimation of the interference activity statistical parameters. We consider first a single FAP accessing the radio channel in the presence of a dynamical interference environment. Then, we extend the formulation to a multi-FAP scenario, where nearby FAP’s react to the strategies of the other FAP’s, still within a dynamical interference scenario. The multi-user case is first approached using a strategic non-cooperative game formulation. Then, we propose a coordination game based on the introduction of a pricing mechanism that exploits the backhaul link to enable the exchange of parameters (prices) among FAP’s.

Fairness-aware resource partition and routing in relay-enhanced orthogonal-frequency-division-multiple-accessing cellular networks

Unlike conventional cellular networks where the evolved Node B (eNB) performs centralised scheduling, future relay-enhanced cellular (REC) networks allow relay nodes (RNs) to schedule users independently. This decentralised nature of the REC networks brings about challenges to maintain fairness. In this study, we formulate the generalised proportional fair (GPF) resource allocation problem, where resource partition and routing are included as part of the overall radio resource management aiming to provide fairness across all users served by the eNB and its subordinate RNs. Although the traditional proportional fair scheduling algorithm is executed independently at the eNB and each RN to maintain local fairness, we propose efficient resource partition and routing algorithms to maintain global fairness by optimising the GPF objective for the whole relay-enhanced cell. Through system level simulations, the proposed algorithms are evaluated and compared with both non-relaying and relaying systems with benchmark resource partition and routing algorithms. The simulation results show that the proposed algorithms outperform the existing algorithms in providing a better trade-off between system throughput and fairness performance.

Improving Quality of Experience of Subscribers through Post Deployment Network Planning in UMTS Cellular Networks

It is an established fact that cost of churning is a common concern for being profitable in the cellular network service provider’s space. Service providers can view this problem as a service management problem and can have a solution to enhance the stickiness of subscribers by managing the quality of user experience. Quality of Experience (QoE) is important in contrast to Quality of Service (QoS). Three basic components of service management are stage, prop, and user experience. In this cellular network service context, network infrastructure acts as prop. Prop needs to be flexible to enable the personalization in providing the service. In reality the major challenge for a service provider is keep the fitment between prop and the dynamic changes in subscriber profile in a cost effective manner. To define the problem more precisely, the authors take the conventional UMTS cellular network. Here, operators have considered single-homing of RNCs to MSCs/SGSNs (i.e., many-to-one mapping) with an objective to generate service at lower cost over a fixed period of time. However, a single-homing network does not remain cost-effective and flexible anymore when subscribers later begin to show specific inter-MSC/SGSN mobility patterns over time. This necessitates post-deployment topological extension of the network in which some specific RNCs are connected to two MSCs/SGSNs via direct links resulting in a more complex many-to-two mapping structure in parts of the network. The authors formulate the scenario as a combinatorial optimization problem and solve the NP-Complete problem using three meta-heuristic techniques, namely Simulated Annealing (SA), Tabu search (TS), and Ant colony optimization (ACO). They then compare these techniques with a novel optimal heuristic search method that the authors propose typically to solve the problem. The comparative results reveal that the search-based method is more efficient than meta-heuristic techniques in finding optimal solutions quickly.

Application of MIH for the lightweight deployment of LTE-advanced systems through mobile relaying

In a conventional cellular network end users connect directly to a Base Station (BS). Mobile relaying allows establishing an indirect two-hop link between the end user, called Mobile Node (MN), and the BS through a Mobile Relay (MR). This spreads out the cell coverage and increases the cell-edge throughput hence improving fairness among nodes. This article is focused on a Long Term Evolution Advanced (LTE-A) cellular network where MNs and MRs are connected through a Wireless Fidelity (WiFi) ad-hoc connection. It is proposed the use of Media Independent Handover (MIH) signaling to define an efficient dynamic routing mechanism for MR in this framework. The proposed mechanism, called MIH-Driven Relay Selection Mechanism (MIDRES), detects which is the best direct or indirect link with the BS based on information collected using MIH messages. The MNs or MRs send MIH messages when experiencing bad channel conditions, that is detected thanks to predefined thresholds. Then, the BS starts a polling process, again supported by MIH signaling, and performs optimal route selection either through the LTE-A radio interface or through a WiFi ad-hoc interface. This article examines the implementation of this mechanism and obtains the optimal thresholds that maximize operational performance. Moreover, the potential benefit of this LTE-compliant mobile relaying solution is evaluated using a calibrated simulation tool. The results show significant savings in cost of network deployment.

Inter-Cell Interference Coordination Based on Shared Relay

Abstract Introducing Relay Nodes (RNs) to conventional cellular networks in 3GPP LTE-A, the interference coordination in cellular networks will be more complex. The resource allocation of cellular networks with RNs should be taken seriously. The following aspects should be considered in the process of resource allocation with RNs 1) Interference mitigation, 2) Performance improvement brought by Relay. This paper proposes an Inter-Cell Interference Coordination (ICIC) scheme based on Shared Relay (ISR), which is utilized in cellular networks with RNs. The proposed scheme can either mitigates inter-cell interference or enhance throughput of cell edge users (CEUs) through intra cell frequency reuse. Simulation results show that the throughput and blocking rate of CEUs in proposed scheme is better than that in existing scheme.

Handoff Management in Green FEMTOCELL Network

Integrated femtocell/macrocell networks, comprising a conventional cellular network overlaid with femtocells, offer an economically appealing way to improve coverage, quality of service, and access network capacity. The key element to successful femtocells/macrocell integration lies in its selforganizing capability. Provisioning of quality of service is the main technical challenge of the femtocell/macrocell integrated networks, while the main administrative challenge is the choice of the proper evolutionary path from the existing macrocellular networks to the integrated network. In this paper, we propose a new Autonomic Architecture with self organizing capabilities based on the election of a Femtocell cluster Head (FH) for each group of Femtocell APs. The FH will be responsible to dynamically adjust the network overall coverage to save FAP energy and provide better QoS to users. Further it uses an advanced decision algorithm for intelligent handovers. General Terms Wireless Networking, Algorithms.

Network Evolution and QOS Provisioning For Integrated Femtocell/Macrocell Networks

Integrated femtocell/macrocell networks, comprising a conventional cellular network overlaid with femtocells, offer an economically appealing way to improve coverage, quality of service, and access network capacity. The key element to successful femtocells/macrocell integration lies in its self- organizing capability. Provisioning of quality of service is the main technical challenge of the femtocell/macrocell integrated networks, while the main administrative challenge is the choice of the proper evolutionary path from the existing macrocellular networks to the integrated network. In this article, we introduce three integrated network architectures which, while increasing the access capacity, they also reduce the deployment and operational costs. Then, we discuss a number of technical issues, which are key to making such integration a reality, and we offer possible approaches to their solution. These issues include efficient frequency and interference management, quality of service provisioning of the xDSL-based backhaul networks, and intelligent handover control.

Spectrum allocation in tiered cellular networks

Two-tier networks, comprising a conventional cellular network overlaid with shorter range hotspots (e.g. femtocells, distributed antennas, or wired relays), offer an economically viable way to improve cellular system capacity. The capacity-limiting factor in such networks is interference. The cross-tier interference between macrocells and femtocells can suffocate the capacity due to the near-far problem, so in practice hotspots should use a different frequency channel than the potentially nearby high-power macrocell users. Centralized or coordinated frequency planning, which is difficult and inefficient even in conventional cellular networks, is all but impossible in a two-tier network. This paper proposes and analyzes an optimum decentralized spectrum allocation policy for two-tier networks that employ frequency division multiple access (including OFDMA). The proposed allocation is optimal in terms of area spectral efficiency (ASE), and is subjected to a sensible quality of service (QoS) requirement, which guarantees that both macrocell and femtocell users attain at least a prescribed data rate. Results show the dependence of this allocation on the QoS requirement, hotspot density and the co-channel interference from the macrocell and femtocells. Design interpretations are provided.

Uplink capacity and interference avoidance for two-tier femtocell networks

Two-tier femtocell networks- comprising a conventional cellular network plus embedded femtocell hotspots- offer an economically viable solution to achieving high cellular user capacity and improved coverage. With universal frequency reuse and DS-CDMA transmission however, the ensuing cross-tier interference causes unacceptable outage probability. This paper develops an uplink capacity analysis and interference avoidance strategy in such a two-tier CDMA network. We evaluate a network-wide area spectral efficiency metric called the operating contour (OC) defined as the feasible combinations of the average number of active macrocell users and femtocell base stations (BS) per cell-site that satisfy a target outage constraint. The capacity analysis provides an accurate characterization of the uplink outage probability, accounting for power control, path loss and shadowing effects. Considering worst case interference at a corner femtocell, results reveal that interference avoidance through a time-hopped CDMA physical layer and sectorized antennas allows about a 7x higher femtocell density, relative to a split spectrum two-tier network with omnidirectional femtocell antennas. A femtocell exclusion region and a tier selection based handoff policy offers modest improvements in the OCs. These results provide guidelines for the design of robust shared spectrum two-tier networks.

Coverage in multi-antenna two-tier networks

In two-tier networks comprising a conventional cellular network overlaid with shorter range hotspots (e.g. femtocells, distributed antennas, or wired relays) with universal frequency reuse, the near-far effect from cross-tier interference creates dead spots where reliable coverage cannot be guaranteed to users in either tier. Equipping the macrocell and femtocells with multiple antennas enhances robustness against the near-far problem. This work derives the maximum number of simultaneously transmitting multiple antenna femtocells meeting a per-tier outage probability constraint. Coverage dead zones are presented wherein cross-tier interference bottlenecks cellular and femtocell coverage. Two operating regimes are shown namely 1) a cellular-limited regime in which femtocell users experience unacceptable cross-tier interference and 2) a hotspot-limited regime wherein both femtocell users and cellular users are limited by hotspot interference. Our analysis accounts for the per-tier transmit powers, the number of transmit antennas (single antenna transmission being a special case) and terrestrial propagation such as the Rayleigh fading and the path loss exponents. Single-user (SU) multiple antenna transmission at each tier is shown to provide significantly superior coverage and spatial reuse relative to multiuser (MU) transmission. We propose a decentralized carrier-sensing approach to regulate femtocell transmission powers based on their location. Considering a worst-case cell-edge location, simulations using typical path loss scenarios show that our interference management strategy provides reliable cellular coverage with about 60 femtocells per cell-site.

A medium access control scheme for TDD-CDMA cellular networks with two-hop relay architecture

In this paper, we propose a multihop medium access control (mMAC) scheme for time division duplexing-code division multiple access (TDD-CDMA) cellular networks with two-hop relay architecture to support packet data transmission. The proposed mMAC is based on joint CDMA/PRMA (packet reservation multiple access) protocol and it includes BCH code selection, power control and multihop relaying. Simulation results reveal that cellular networks with two-hop relay architecture with the proposed mMAC scheme can substantially provide a good performance as well as larger cell coverage as compared to conventional TDD-CDMA single-hop cellular networks.

Media handling for multimedia conferencing in multihop cellular networks

This article addresses the media-handling aspects of multimedia conferencing in multihop cellular networks. Participation in multimedia conferences in MCNs may be confined to either the conventional cellular network or the MANET. Participation also can span both networks. However, neither the media-handling architectures currently in use in conventional cellular networks, nor the ones in use in MANETs are appropriate. When they are used, either the participants in the conventional cellular network, or the ones in the MANETs, might experience long and potentially unacceptable end-to-end stream delays. Furthermore, these architectures are the antipodes of each other. Reconciling them is not an easy task. We evaluate the architectures currently in use in cellular networks and MANETs, show that none is suitable, and propose a new architecture that bridges the two worlds. The new architecture uses the MANET media-handling architectures as a starting point. It is based on media mediators. A media mediator is composed of two functional entities: the media gateway controller mediator and the media gateway mediator. A proof-of-concept prototype was implemented, and extensive simulations were conducted to evaluate performance.

Any Resource Sharing via HWN* Routing

In this paper we present an adaptive distributed cross-layer routing algorithm (ADCR) for hybrid wireless network with dedicated relay stations (HWN*). To support versatile multimedia communication for Mobile Terminals (MTs), the HWN* integrates a cellular network, an ad hoc network and fixed relay nodes (RNs). A MT may borrow cellular data channels that are available thousands mile away via secure multi-hop RNs, where RNs are placed at flexible locations in the network. The MT can also communicate with each other or access internet ubiquitously. We discuss cross media access and network layers routing issues. The ADCR establishes routing paths across RNs or cellular network while providing appropriate QoS (quality of service). Through simulation, we verify the routing performance benefits of HWN* over conventional cellular systems and other hybrid network frameworks. It is anticipated that the simulation results reported in this paper will serve as a guideline for research based on distributed source routing involving heterogeneous wireless technologies.

Comparison of symmetric and asymmetric routing for fixed two-hop cellular relaying network

In this paper, routing strategies for fixed two-hop cellular relaying networks are discussed in terms of area spectral efficiency. We consider symmetric and asymmetric routing in uplink and downlink. Simulation results show that relaying increases the average throughput in comparison with conventional cellular networks and the area spectral efficiency of asymmetric routing is slightly better than that of the symmetric

Performance comparison of cellular and multi-hop wireless networks

In this paper we study the performance trade-offs between conventional cellular and multi-hop ad-hoc wireless networks. We compare through simulations the performance of the two network models in terms of raw network capacity, end-to-end throughput, end-to-end delay, power consumption, per-node fairness (for throughput, delay, and power), and impact of mobility on the network performance. The simulation results show that while adhoc networks perform better in terms of throughput, delay, and power, they suffer from unfairness and poor network performance in the event of mobility.We discuss the trade-offs involved in the performance of the two network models, identify the specific reasons behind them, and argue that the trade-offs preclude the adoption of either network model as a clear solution for future wireless communication systems. Finally, we present a simple hybrid wireless network model that has the combined advantages of cellular and ad-hoc wireless networks but does not suffer from the disadvantages of either.

High-Quality and High-Speed Wireless Multimedia Transmission Technologyfor Personal Handy Phone System

The Personal Handy-phone System (PHS), developed as a PCS, has been very widely accepted. This system offers many benefits as the infrastructure of the mobile data communication services that are expected to be available soon with the popularity of nomadic computing. Data communication systems based on PHS and some applications are proposed in this paper. One of the key technologies, an error control scheme, is also introduced. Three kinds of possible system configurations are discussed as a data communication platform for PHS. One of them has an ARQ function which corrects all errors that occur in the propagation path. Conventional application software on nomadic computers can be used in the mobile environment because this ARQ function is installed as a lower layer protocol. The introduced system connects all mobile computers to all servers that are on the networks which include ISDN, the conventional analog PSTN, cellular networks and PHS networks.