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Interference avoidance and dynamic frequency planning for WiMAX femtocells networks

Femtocells have been recently proposed as a potential good solution to increase not only indoor radio coverage, but also system capacity. In this paper, a framework for radio coverage prediction and system level simulation for WiMAX macrocell/femtocell scenarios is presented. Furthermore, the feasibility of the co-channel deployment of WiMAX femtocell in an existing WiMAX macrocell network is investigated, and a method for interference avoidance based on DFP (dynamic frequency planning) is proposed. The resulting impact of DFP in a macrocell/femtocell scenario compared with other frequency assignment strategies is analyzed. Experimental evaluations carried out using our framework show the boost in the system capacity when using DFP and femtocells.

LEMON - an Open Source C++ Graph Template Library

This paper introduces LEMON, a generic open source C++ library providing easy-to-use and efficient implementations of graph and network algorithms and related data structures. The basic design concepts, features, and performance of LEMON are compared with similar software packages, namely BGL (Boost Graph Library) and LEDA. LEMON turned out to be a viable alternative to these widely used libraries, and our benchmarks show that it typically outperforms them in efficiency.

OFDMA femtocells: A self-organizing approach for frequency assignment

This work presents 2 novel approaches for the self-organization of Orthogonal Frequency Division Multiple Access (OFDMA) femtocells, in which the femtocell is able to dynamically sense the air interface and tune its sub-channel allocation in order to reduce inter-cell interference and enhance system capacity. In the sensing phase, these techniques make use of either messages broadcast by the femtocells or measurements reported by the users, while in the tuning phase, they provide a good solution for the frequency assignment problem. Results shows that it is recommend to use information collected at the user position (measurement reports), when devising self-organization algorithms for tuning the parameters of femtocells.

Optimization method for the joint allocation of modulation schemes, coding rates, resource blocks and power in self-organizing LTE networks

This article investigates the problem of the allocation of modulation and coding, subcarriers and power to users in LTE. The proposed model achieves inter-cell interference mitigation through the dynamic and distributed self-organization of cells. Therefore, there is no need for any a prior frequency planning. Moreover, a two-level decomposition method able to find near optimal solutions is proposed to solve the optimization problem. Finally, simulation results show that compared to classic reuse schemes the proposed approach is able to pack more users into the same bandwidth, decreasing the probability of user outage.

Applying FDTD to the coverage prediction of WiMAX femtocells

Femtocells, or home base stations, are a potential future solution for operators to increase indoor coverage and reduce network cost. In a real WiMAX femtocell deployment in residential areas covered by WiMAX macrocells, interference is very likely to occur both in the streets and certain indoor regions. Propagation models that take into account both the outdoor and indoor channel characteristics are thus necessary for the purpose of WiMAX network planning in the presence of femtocells. In this paper, the finite-difference time-domain (FDTD) method is adapted for the computation of radiowave propagation predictions at WiMAX frequencies. This model is particularly suitable for the study of hybrid indoor/outdoor scenarios and thus well adapted for the case of WiMAX femtocells in residential environments. Two optimization methods are proposed for the reduction of the FDTD simulation time: the reduction of the simulation frequency for problem simplification and a parallel graphics processing units (GPUs) implementation. The calibration of the model is then thoroughly described. First, the calibration of the absorbing boundary condition, necessary for proper coverage predictions, is presented. Then a calibration of the material parameters that minimizes the error function between simulation and real measurements is proposed. Finally, some mobile WiMAX system-level simulations that make use of the presented propagation model are presented to illustrate the applicability of the model for the study of femto- to macrointerference.

Tree based broadcast in ad hoc networks

Although broadcasting using tree structure established in a network is a well known and widely used technique, it is typically claimed to be inappropriate for ad hoc networks, being the maintained tree very sensitive to network changes. On the contrary this paper presents an efficient tree based broadcasting scheme, which is reliable and stable even in case of the ever changing network structure of the ad hoc networks.To achieve this, first, a novel method is presented to maintain a spanning tree in an ad hoc network in a fully distributed, on-line and asynchronous way. Once the tree is established the broadcast itself is performed based on this tree. Some further improvements on the basic algorithm are also presented that reduce the resource requirements even more, increase the stability of the tree, enable the mobility of the nodes to be taken into account and make the method more configurable.As it is shown by simulation, the obtained broadcast scheme is stable, reliable and it uses small amount of resources: the acyclic structure of the broadcast tree ensures that the nodes get the broadcast messages only once, so the broadcast needs little bandwidth and the nodes need not store the recent broadcast messages, reducing the computational and memory requirements.As a byproduct a technique is proposed to measure the mobility of the nodes. This technique needs no additional GPS device or any geographical information but it is based on the stability of the links of the node.

Dynamic Frequency Planning Versus Frequency Reuse Schemes in OFDMA Networks

Abstract —In order to avoid inter-cell interference, OFDMAnetworks are flexible in terms of radio resource managementtechniques, supporting different frequency reuse schemes (FRSs),which in turn, may decrease inter-cell interference and increasenetwork performance. However, because most of them are basedon fix patterns, these FRSs cannot cope with the uneven distri-bution and dynamic behavior of the traffic throughout the day.This work introduces a novel approach to the frequency as-signment problem called Dynamic Frequency Planning (DFP) tai-lored to OFDMA networks. The proposed approach dynamicallyadapts the radio frequency parameters to the environment takingthe user and channel conditions into account. Moreover, a variantof DFP, called vertical DFP, based on the fractional frequencyreuse schemes (FFRSs) concept is proposed. In comparison tothe traditional FRSs, these techniques notably mitigate inter-cellinterference and enhance network performance. I. I NTRODUCTION Interference has been proven to be the major problem ofwireless communication systems across the years, because:

Minimizing re-routing in MPLS networks with preemption-aware constraint-based routing

In this paper, we study the effect of distributed constrained shortest path first (CSPF)-based path selection on the dynamics of label switched path (LSP) preemption. We propose new CSPF algorithms for minimizing preemption of lower priority LSPs without requiring any enhancements to the recently proposed link-state parameters. The difference between priority-based path selection methods and previously proposed CSPF methods lies in the way the selection is done among equal cost shortest paths. Our priority-aware CSPF algorithms decrease the number of preempted lower priority LSPs while the LSP setup success ratio is basically the same for all methods.

Distributed resource allocation for femtocell interference coordination via power minimisation

This paper proposes a decentralized model for the allocation of modulation and coding schemes, subchannels and transmit power to users in OFDMA femtocell deployments. The proposed model does not rely on any exchanged information between cells, which is especially useful for femtocell networks. Coordination between femtocells is achieved through the intrinsic properties of minimising transmit power independently at each cell, which leads the network to self-organize into an efficient frequency reuse pattern. This paper also provides a two-level decomposition approach for solving this intricate resource assignment problem that is able to find optimal solutions at cell level in reduced periods of time. System-level simulations show a significant performance improvement in terms of user outages and network capacity when using the proposed distributed resource allocation in comparison with scheduling techniques based on uniform power distributions among subcarriers.

OFDMA Femtocells: Intracell Handover for Interference and Handover Mitigation in Two-Tier Networks

This work presents a novel approach for the avoidance of cross-tier interference in two-tier networks comprised of Orthogonal Frequency Division Multiple Access (OFDMA) macrocells and femtocells. This new technique is based on the use of Intracell HandOvers (IHOs), and it makes possible that either a macrocell or a femtocell can reassign its sub-channel or power allocation upon the detection of cross-tier interference. Simulation results show that this approach is able to cope with the cross-tier interference issues intrinsic to closed access femtocells, and the increased number of HandOvers (HOs) resulting from open access femtocells.