Vol. 63, n° 5-6, May-June 2008
Content available on Springerlink

Guest editors
Michel Terré, CNAM, Paris, France
Bernhard Walke, RWTH Aachen University, Aachen, Germany
Luis Correia, Instituto Superior Tecnico, Lisbon, Portugal
Alain Sibille, ENSTA, Paris, France

Foreword

Michel Terré, Bernhard Walke, Luis Correia, Alain Sibille

Kumar’s, Zipf’s and other laws: how to structure a large-scale wireless network?

M. Dohler¹ · T. Watteyne^2,3 · F. Valois ³ · J.-L. Lu³

¹Centre Tecnologic de Telecomunicacions de Catalunya (CTTC), Parc Mediterrani de la Tecnologia, Av. Canal Olimpic S/N, 08860, Castelldefels, Barcelona, Spain
²France Télécom R&D, Meylan Cedex, 38243, France
³ARES INRIA / CITI, INSA-Lyon, 69621, France

Abstract Networks with a very large number of nodes are known to suffer from scalability problems, influencing throughput, delay, and other quality-ofservice parameters. Mainly applicable to wireless sensor networks, this paper extends prior work and aims to give some fundamental indications on a scalable and optimum (or near-optimum) structuring approach for large-scale wireless networks. Scalability and optimality will be defined with relation to various performance criteria, an example of which is the throughput per node in the network. Various laws known from different domains will be invoked to quantify the performance of a given topology; most notably, we will make use of the well-known Kumar’s law, as well as less-known Zipf’s and other scaling laws. Optimum network structures are derived and discussed for a plethora of different scenarios, facilitating knowledgeable design guidelines for these types of networks.

Keywords Large-scale wireless network · Asymptotic behaviour · Scaling laws

On multicell cooperative transmission in backhaul-constrained cellular systems

Patrick Marsch  and Gerhard Fettweis

Vodafone Chair Mobile Communications Systems, Technische Universität Dresden, Dresden, Germany

Abstract Recent work has shown that multicell cooperative signal processing in cellular networks can significantly increase system capacity and fairness. For example, multicell joint transmission and joint detection can be performed to combat intercell interference, often mentioned in the context of distributed antenna systems. Most publications in this field assume that an infinite amount of information can be exchanged between the cooperating base stations, neglecting the main downside of such systems, namely, the need for an additional network backhaul. In recent publications, we have thus proposed an optimization framework and algorithm that applies multicell signal processing to only a carefully selected subset of users for cellular systems with a strongly constrained backhaul. In this paper, we consider the cellular downlink and provide a comprehensive summary and extension of our previous and current work. We compare the performance obtained through centralized or decentralized optimization approaches, or through optimal or suboptimal calculation of precoding matrices, and identify reasonable performance-complexity trade-offs. It is shown that even low-complexity optimization approaches for cellular systems with a strongly constrained backhaul can yield major performance improvements over conventional systems.

Keywords Network MIMO · Joint transmission · Beamforming · Constrained backhaul

Performance impact of flexible power arrangement in OFDMA based cellular communication networks

Yikang Xiang¹, Jijun Luo¹, Egon Schulz¹ and Carmelita Görg²

¹Nokia Siemens Network GmbH & Co.KG, Munich, Germany
²ComNets, University of Bremen, Bremen, Germany

Abstract In the OFDMA-based downlink of wireless cellular communication networks, the intercell interference would be a key performance-limiting factor, especially for the cell edge users. To enhance the cell edge user performance, several flexible power allocation schemes have been proposed, e.g., the so-called soft frequency reuse scheme and the partial frequency reuse scheme. This paper analyzes those schemes in a very realistic multicell setting, investigates the layer 2 resource allocation algorithms that are associated to the physical layer setting, and finally gives results of the performance evaluation.

Keywords OFDMA · Frequency reuse · Multicell · Power allocation

Decentralized spectrum and radio resource management enabled by an on-demand Cognitive Pilot Channel

O. Sallent, R. Agustí, J. Pérez-Romero, L. Giupponi

Department of Signal Theory and Communications, Universitat Politècnica de Catalunya (UPC), c/ Jordi Girona, 1-3, Campus Nord UPC, D4 Building, 08034 Barcelona, Spain

Abstract This paper presents a framework to achieve an efficient dynamic and decentralized spectrum and radio resource usage in heterogeneous wireless network scenarios. The envisaged technical solution follows a layered approach, where joint radio resource management (JRRM) and advanced spectrum management mechanisms are identified at both the intra- and inter-operator levels. The importance of cognitive network functionalities is highlighted. An ondemand Cognitive Pilot Channel (CPC) is proposed as radio enabler solution for decentralized operation with decision making processes executed at the mobile terminal side. The suitability of the proposed solution is shown by comparison with a broadcast CPC approach. Finally, the paper presents and evaluates decentralized JRRM algorithms both at the intra- and inter-operator levels using the proposed framework.

Keywords Advanced spectrum management . Joint radio resource management . Decentralized algorithms . Cognitive Pilot Channel . Cognitive networks

Performance evaluation of multicast MISO-OFDM systems

Berna Özbek¹, Didier Le Ruyet² and Hajer Khanfir ²

¹ Electrical and Electronics Engineering Department, Izmir Institute of Technology, Urla 35430, Izmir, Turkey
² Electronics and Communications Laboratory, Conservatoire National des Arts et Métiers (CNAM), 292 rue Saint Martin, 75141, Paris, France

Abstract In this paper, we analyze the performance of multicast orthogonal frequency division multiplexing (OFDM) systems with single and multiple transmit antennas. We show that the resource allocation that includes the subcarrier allocation, bit loading, and the precoding vector selection in the multiple-input singleoutput (MISO) case is a difficult optimization problem. Consequently, we propose suboptimal algorithms based on the maximization of the sum data rate and the maximization of the minimum user data rate criteria. For practical application, we consider a complete transmission chain by combining powerful erasure codes with the proposed algorithms. Using this scheme, we guarantee that each user receives the same amount of information to decode the same data. Simulation results show that, for both single-input single-output (SISO)-OFDM andMISO-OFDM cases, the proposed multicast OFDM systems achieve gains over the worst user case algorithm.

Keywords Multicast OFDM · Adaptive resource allocation · Multiple transmit antennas · Precoding vector optimization · Subcarrier and bit allocation · Erasure codes

Analytical investigation of intersection based range-free localization

Michel Sortais¹, Sven D. Hermann², Adam Wolisz²

¹ MAP5, UMR CNRS 8145, Université Paris Descartes, 45 rue des Saints-Pères, 75006 Paris, France
² Telecommunications Networks Group, Technische Universität Berlin, Einsteinufer 25, 10587 Berlin, Germany

Abstract The localization of mobile devices is essential for the provisioning of location-based services, e.g., to locate people facing an accident or to provide relevant information to device users, depending on their current whereabouts. Several localization mechanisms have been developed using estimates of absolute distances or angles between the devices and the base stations of the networks. These mechanisms often require expensive enhancements of the existing base stations or mobile devices. In recent years, so-called range-free approaches have been proposed, which limit the possible positions of a device to the coverage areas of radio network cells, without relying on precise distances or angles. The accuracy of the corresponding information can be refined by computing the intersection area of all cells that cover the current position of the device. However, the computation of this intersection area, e.g., by the location server of a network carrier, can be a complex task. To avoid unnecessary workload, one would like to preestimate the possible reduction of location uncertainty, i.e., the information gain that can be achieved. The contribution of this paper is an analytical and numerical investigation of the problem. Several approaches are presented for the computation of the information gain, based on stochastic geometry and on a Monte-Carlo method. We show that simple scaling arguments can be used to estimate the order of magnitude of the average information gain, while more complex approximations based on Voronoi cells lead to relatively good results.

Keywords Range-free localization · Location information gain · Stochastic geometry · Poisson point processes · Voronoi tessellation

Open Topics

Evaluating voice traffic requirements on IEEE 802.11 ad hoc networks

Pedro Braconnot Velloso¹, Marcelo G. Rubinstein², Otto Carlos M. B. Duarte³

¹ LIP6/CNRS, Université Pierre et Marie Curie, 8, rue du Capitaine Scott, 75015 Paris, France
² PEL/DETEL-FEN, Universidade do Estado do Rio de Janeiro, R. São Fco. Xavier, 524, 20550-013 Rio de Janeiro, RJ, Brazil
³ GTA/COPPE/Poli, Universidade Federal do Rio de Janeiro, P.O. Box 68504, 21945-970 Rio de Janeiro, RJ, Brazil

Abstract This paper analyzes voice transmission capacity on IEEE 802.11 ad hoc networks by performing simulations related to delay, jitter, loss rate, and consecutive losses. We evaluate the influence of mobility on the number of sources transmitting voice. Another issue addressed in this paper is the effect of node density on voice transmission. Our simulation model has allowed us to identify the main reasons for voice degradation in ad hoc networks. Results show that voice transmission capacity degrades with mobility and network load, being more sensitive to high mobility due to link failures. The network capacity can easily experience a decrease of up to 60% on the number of voice transmissions on a multi-hop environment. We also show that node density is also relevant when considering voice transmission on multi-hop networks.

Keywords Wireless ad hoc networks . IEEE 802.11 . Voice transmission . Mobility

Super-quasiorthogonal space-time trellis codes for four transmit antennas with rectangular signal constellations

Corneliu Eugen D. Sterian¹, Yi Wu² and Matthias Pätzold²

¹ Polytechnic University of Bucharest, Bucharest, Romania
² University of Agder, Grimstad, Norway

Abstract In this paper, we present the first superquasiorthogonal space-time trellis codes (SQOSTTCs) for systems with four transmit antennas using various types of rectangular signal constellations to increase the spectral efficiency up to 5 bits/s/Hz. In our wireless communications system, we define an eightdimensional (8D) signal constellation as Cartesian product of four two-dimensional (2D) rectangular signal sets. The transmission of an 8D point from the first antenna is achieved by transmitting four concatenated 2D points in four consecutive channel uses. The 2D symbols transmitted from the other three antennas are not independent but so chosen as to form, together with the symbols transmitted from the first antenna, the entries of a 4 × 4 quasiorthogonal transmission matrix. The union of two sets of quasiorthogonal transmission matrices forms a so-called super-quasiorthogonal signal set. With the 4 × 4 quasiorthogonal transmission matrices, we then label the state transitions of a trellis diagram describing the operation of the encoder. The simulation results of the frame error rate and the bit error rate demonstrate the excellent performance of our proposed SQOSTTCs.

Keywords MIMO wireless systems · Quadrature-amplitude modulation · Space-time coding · Super-quasiorthogonal space-time codes · Transmit antenna diversity · Trellis-coded modulation