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We propose a pure 0-1 formulation for the wireless network design problem, i.e., the problem of configuring a set of transmitters to provide service coverage to a set of receivers. In contrast with classical mixed-integer formulations, where power emissions are represented by continuous variables, we consider only a finite set of power values. This has two major advantages: it better fits the usual practice and eliminates the sources of numerical problems that heavily affect continuous models. A crucial ingredient of our approach is an effective basic formulation for the single knapsack problem representing the coverage condition of a receiver. This formulation is based on the generalized upper bound (GUB) cover inequalities introduced by Wolsey [Wolsey L (1990) Valid inequalities for 0-1 knapsacks and mips with generalised upper bound constraints. Discrete Appl. Math. 29(2-3):251-261]; and its core is an extension of the exact formulation of the GUB knapsack polytope with two GUB constraints. This special case corresponds to the very common practical situation where only one major interferer is present. We assess the effectiveness of our formulation by comprehensive computational results over realistic instances of two typical technologies, namely, WiMAX and DVB-T. Key words: wireless network design; power discretization; 0-1 linear programming; GUB cover inequalities; strong formulation History: Received August 1, 2011; accepted March 2, 2012, by Dimitris Bertsimas, optimization. Published online in Articles in Advance August 20, 2012., 1. Introduction Wireless communication systems constitute one of the most pervasive phenomena of everyday life. Television and radio programs are distributed through broadcasting networks (both terrestrial and satellite), mobile communication [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jbusres.2009.04.008 Byline: Feng-Shang Wu, Wen-Lin Chu Abstract: Growth models are applicable to mobile telephony diffusion. Although cross-sectional performance comparisons of models are numerous, varying stages of the S-shaped diffusion curve have not been analyzed by longitudinal studies. This study determines whether the best model applies to an entire diffusion life span. Mobile telephone subscriber data for Taiwan during 1988-2007 are analyzed to compare the performance of three popular diffusion models and one well-known forecasting model -- the Gompertz, Logistic, Bass, and time-series autoregressive moving average (ARMA) models, respectively. Empirical results indicate that the Gompertz model outperforms the other models before diffusion take-off, and the Logistic model is superior after inflection and over the aggregate range of the diffusion. Network externalities are the dynamics of the Logistic model and account for its excellence. This longitudinal study is the first to present empirical evidence indicating that the appropriate diffusion model for mobile telephony is stage-dependent, complementing the case dependency of the appropriate diffusion model demonstrated by cross-sectional studies. Author Affiliation: National Chengchi University, Graduate Institute of Technology and Innovation Management, 64 ZhiNan Rd. Sec. 2, Taipei 11605, Taiwan Article History: Received 1 April 2008; Revised 1 March 2009; Accepted 1 April 2009 Article Note: (footnote) [star]The authors thank Show-Ling Jang and two anonymous reviewers for their invaluable feedback on an earlier draft of this paper.

Fading phenomena impact the performance of wireless communication systems. We propose the modified hidden semi-Markov model (MHSMM) for modeling the flat fading envelope process. The properties of the envelope process are dominated by the physical fading processes and speeds of the mobile terminal. Thus, the statistics of the fading process may be non-stationary, due to different fading conditions over some time durations. The MHSMM incorporate these time-variant statistics of the envelope process in a single model, which facilitates computations of the envelope probability density function and the autocorrelation function. We provide a parameter estimation scheme to estimate the MHSMM parameters. We demonstrate the proposed parameter estimation scheme by using simulated and experimental data. The simulation is based on the GSM system parameters often encountered in practical conditions. We conducted two experiments, including cooperating and non-cooperating channel disturbances. Based on these data, the MHSMM is compared with the amplitude-based finite-state Markov chains model and the hidden Markov model. The results verify the advantages of the MHSMM and the effectiveness of the associated parameter estimation schemes. Index Terms--Fading channel model, modified hidden semi-Markov model, envelope probability density function, autocorrelation function, flat fading.

In this paper, we propose a hybrid location-update scheme, which combines the time- and movement-based location-update approaches. In the proposed scheme, a mobile user updates its location after the following two events have occurred: First, the mobile crossed n cell boundaries, and then, a time interval T elapsed. We also examine the inverse scheme, where an update is performed after the n boundary crossings occur subsequent to the time interval T. We evaluate our scheme by applying it to various mobility models, such as exponential cell-residence times with a constant mobility pattern, exponential cell-residence times with a gamma-distributed mobility pattern, hyperexponential cell-residence times, and cell-residence times with a small coefficient of variation. From our numerical analysis and simulation results, we learn that the movement-based-only method (i.e., T = 0) performs well when the coefficient of variation of the cell-residence time is relatively small. However, when the coefficient of variation is large, the proposed hybrid scheme (i.e., T > 0, n > 0) outperforms each of the two approaches, namely, the time- and movement-based location-update schemes, when these schemes are individually applied. Index Terms--Hybrid-location update, mobile networks, movement-based location update, time-base location update.

For purposes of simulating contemporary communication systems, it is, in many cases, useful to apply error models for specific levels of abstraction. Such models should approximate the packet error behavior of a given system at a specific protocol layer, thus incorporating the possible detrimental effects of lower protocol layers. Packet error models can efficiently be realized using finite-state models; for example, there exists a wide range of studies on using Markov models to simulate communication channels. In this paper, we consider aggregated Markov processes, which are a subclass of hidden Markov models (HMMs). Artificial limitations are set on the state transition probabilities of the models to find efficient methods of parameter estimation. We apply these models to the simulation of the performance of Digital Video Broadcasting-Handheld (DVB-H). The parameters of the packet error models are approximated as functions of the time-variant received signal strength and speed of a mobile vehicular DVB-H receiver, and it is shown that useful results may be achieved with the described packet error models, particularly when simulating mobile reception in field conditions. Index Terms--Broadcasting, communication channels, Markov processes, mobile communication, simulation.

Ad hoc networks are characterized by multihop wireless connectivity, frequently changing network topology and the need for efficient dynamic routing protocols plays an important role. We compare the performance of two prominent on-demand routing protocols for mobile ad hoc networks: Dynamic Source Routing (DSR), Ad Hoc On-demand distance Vector Routing (AODV). A detailed simulation model with MAC and physical layer models is used to study the interlayer interactions and their performance implications. We demonstrate that even though DSR and AODV share similar on-demand behavior, the differences in the protocol mechanisms can lead to significant performance differentials. In this paper we examine two on demand routing protocols AODV and DSR based on packet delivery ratio, normalized routing load, normalized MAC load, average end to end delay by varying the number of sources, speed and pause time. Keywords: MANET, routing protocol, on-demand, DSR, AODV, random way point model, INTRODUCTION A network is a collection of two or more computing devices, which is connected by a communication medium. There are two types of network wired network and wireless network. [...]

A wireless communication system in which multiple users cooperate to transmit information to a common destination is considered. The traffic generated by the users is subject to a stringent quality of service requirement, which is defined in terms of the asymptotic decay-rate of buffer occupancy. The performance of this communication system is analyzed, and the corresponding achievable rate-region for the two-user scenario is identified. A simple user-cooperation scheme that improves performance is proposed. This cooperative scheme is shown to significantly enlarge the achievable rate-region of the service constrained communication system, provided that the quality of the wireless link between cooperating users is better than the individual connections from the users to the intended destination. Numerical results further indicate that the gains of cooperative strategies can be substantial. This suggests that cooperation allows for a fair distribution of the wireless resources among active users. Index Terms--Communication systems, effective bandwidth, effective capacity, fluid models, quality of service (QoS), user cooperation, wireless networks.

Modeling wireless channels is essential to wireless communication systems. An autoregressive (AR) process of order one for wireless channel has long been assumed, but without a rigorous mathematical/physical basis. In this paper, we derive a first-order stochastic AR model for a flat stationary wireless channel, which comes from stochastic differential equation (SDE) theory concerning the nature of multipath fading channels. The resulting AR model describes more of the origin of multipath fading channels than previous AR models, and it can efficiently model and generate Rayleigh-distributed stationary fading channels. The Markovian property of the AR model is inherited through the SDE approach. Index Terms--Autoregressive (AR) process, multipath channels, Rayleigh, stochastic differential equation (SDE).

A deterministic model for propagation in outdoor urban environments based on the Fresnel-Kirchhoff integral is presented. Both two-dimensional (2-D) and three-dimensional (3-D) formulations considering reflection and diffraction are given. The theoretical predictions are compared with 2-D and 3-D measurements and good agreement is achieved. The 3-D experiments, conducted in an anechoic chamber with scaled models representing buildings, are described in detail and provide a benchmark for comparisons with other methods. Index Terms--Fresnel-Kirchhoff integral, measurements, radio propagation, urban environment, wireless communications.

The numerical dispersion relations of finite-difference time-domain (FDTD) methods have been analyzed extensively in lossless media. This paper investigates numerical dispersion and loss for Yee's FDTD in lossy media. It is shown that: the numerical velocity can be smaller or larger than the physical velocity; there is no 'magic time step size' in lossy media; and the numerical loss is smallest at the Courant limit. It is shown that the numerical loss is always larger than its physical value, and so Yee's FDTD over-estimates the absorption of electromagnetic energy in lossy media. The numerical velocity anisotropy can be positive or negative, but the numerical loss anisotropy is always positive. The anisotropies in the three-dimensional (3-D) case are usually larger than those in the 2-D case. Numerical experiments in 1-D are shown to agree with the theoretical prediction. Index Terms--Computational electromagnetics, finite-difference time-domain method (FDTD), numerical anisotropy, numerical dispersion, numerical loss.

Mobile-to-mobile channels find increasing applications in futuristic intelligent transport systems, ad hoc mobile wireless networks, and relay-based cellular networks. Their statistical properties are quite different from typical cellular radio channels, thereby requiring new methods for their simulation. This paper proposes a "double-ring" model to simulate the mobile-to-mobile local scattering environment, and develops sum-of-sinusoids (SoS)-based models for simulating such channels. The proposed models produce waveforms having desired statistical properties with good accuracy, and also remove some drawbacks of an existing model derived by using the discrete line spectrum simulation method. Index Terms--Fading channel simulator, mobile-to-mobile channels, Rayleigh fading, sum-of-sinusoids (SOS).

A model is constructed that examines the effect of the three factors on the diffusion of wireless communication in 64 countries. The role of culture in diffusion seems to be two-fold, and the country effect was found to explain the adoption year and the market potential, and the time effect was the most important predictor for the rate of diffusion.

Byline: Aymen I. Zreikat (1), Khalid Al-Begain (2), Kevin Smith (3) Keywords: UMTS networks; interference; power control; propagation models; queueing models; capacity bounds; Hata model Abstract: In the design of cells in mobile communication systems, path loss prediction models play an important role and have been the subject of the study for some time (M.F. Ibrahim and J.D. Parsons, IEE Proceedings, Vol. 130, No. 5, 1983). This paper presents the analysis of two main factors that affect the capacity bounds in a UMTS cell for different propagation models. These are the (i) interference levels at Node B, which increases with the number of active users, and (ii) the limited sending power of the user equipment (UE) which may not be able to send signals with enough power to reach Node B with the required received power level due to path loss. The aim of this paper is to analyse the capacity/coverage of the uplink of UMTS system in different propagation environments (free space, suburban, urban, dense urban, rural) and derive the capacity bounds for the UMTS cell. The capacity bounds have been extracted based on the extended COST-231 Hata model (http://cost.cordis.lu/src/whatiscost.cfm). COST-231 Hata is an extension of the Okumura--Hata model which covers the higher frequencies (G.L. Stuber, 'Principles of Mobile Communications,' Kluwer, 1996) necessary for WCDMA. The basic model describes the propagation loss in an urban environment, but a number of correction factors can be applied to extend its application to a broader range of environments. The analysis takes into account a number of capacity influencing factors such as the CDMA code non-orthogonality, the inter-cell interference, imperfect power control, and different service specific factors. The simulation results show the effect of different system and varying environmental parameters upon the system's capacity in different environments. The results clearly demonstrate that it is too optimistic to rely on studies based on free space assumptions. Author Affiliation: (1) Department of Information Technology, Mutah University, P.O. Box 7, Mutah, Jordan (2) School of Computing, University of Glamorgan, CF37 1DL, Pontypridd, Wales, UK (3) Department of Computing, University of Bradford, BD7 1DP, Bradford, UK Article History: Registration Date: 04/10/2004

Byline: Sebastien Roy (1), David D. Falconer (2) Keywords: array signal processing; equalizers; MIMO systems; mean square error methods; broadband communication Abstract: We present an investigation of space-time receiver architectures in multi-user wireless systems where optimal idealized (infinite-length) space-time filtering is applied to minimize the mean-square error (MSE). Feedforward, decision-feedback and cross-decision feedbackfilters are employed hence, the system eliminates the post-cursor ISI (intersymbol interference) and CCI (co-channelinterference). While this is a form of MIMO-DFE (Multi-Input Multi-OutputDecision-Feedback Equalization), no joint transmitter-receiver optimizationis performed since the transmit sources are assumed to be individual users.Our analysis leads to an entirely novel closed-form expression for the minimum achievableMSE for any single user in both fully- and partially-connected cross-decision feedback systems (XDF). This differs from previous results onMIMO-DFE obtained in a CDMA context which rely on the Gaussian assumption.Numerical results compare the performance of XDF systems with standard space-time DF and linear processing as well as the MIMO matched-filter bound in both a generic Rayleigh-fading system context and a broadband wireless context with fixed, highly directional subscriber antennas and correlatedfading based on a 3D channel model parameterized according to measurements at29.5 GHz. Results indicate that generally, an N-element array with fully-connected XDFprocessingprovides the same performance as an N+1-element array with standard linearspace-time processing. Author Affiliation: (1) Departement de genie electrique et de genie informatique, Universite Laval, Quebec, QC, Canada, G1K 7P4 (2) Department of Systems and Computer Engineering, Carleton University, 1125 Colonel By Drive, Ottawa, Canada, K1S 5B6 Article History: Registration Date: 11/10/2004