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The connected facility location (ConFL) problem arises in a number of applications that relate to the design of telecommunication networks as well as data distribution and management problems on networks. [...]

A study was conducted to examine a smart grid communication network architecture that supports grid applications and new applications necessitated by the introduction of smart metering. It is believed that definitions of smart grid communications architecture pay little attention to implementation challenges.

A study was conducted to explain the energy saving potential of network adaptations to traffic demands. Networks are usually designed for maximum expected throughput, and are optimized for operation at full load. The challenge is to maintain reliable service coverage while consuming the lowest energy.

The aim of the discrete simulation framework is to deal with issues of the next generation of wireless cellular networks (e.g., multimedia traffic, radio resource management and mobility ... etc) and to provide a platform for current and future investigations involving wireless cellular networks. The simulator is built from the scratch to enable customization requirements of any research and to provide the freedom to understand, configure protocol modules, draw desired topologies and specifies the movement paths of the mobile users and to plot the necessary performance graphs. In order to evaluate and validate the performance of the designed simulator, a simulation model for the wireless cellular network and mobile environment deployed. The performance of the developed simulator compared with the performance characteristics of existing algorithms. Simulation results verify the developed simulator is able to recapture the results of both the numerical result and simulation results of the comparative system utilizing an idealistic platform. In addition the simulator incorporates detail algorithms for the correlated components between the entities of the cellular networks and the development of the discrete simulator. Key words: Discrete simulation, wireless cellular network, performance modeling, INTRODUCTION The growth in complexity of communication systems increases the time and effort required for analysis and design, the need to insert new technologies into commercial products quickly requires that [...]

The 3rd Generation Partnership Project (3GPP) Technical Specification 23.246 proposed the Multimedia Broadcast Multicast Service (MBMS) that efficiently multicasts multimedia content. During MBMS content transmission, data may be lost. Three file repair schemes were proposed to retransmit the corrupted MBMS data. However, these schemes may introduce extra data traffic or signaling overheads. This paper proposes the Reuse Bearer Service (RBS) file repair scheme to resolve this issue. We analyze the four file repair schemes by analytical models and simulation experiments. This paper shows that the proposed RBS scheme may significantly outperform the previously proposed schemes. Index Terms--File repair, mobile core network, Multimedia Broadcast Multicast Service (MBMS), retransmission scoping, Universal Mobile Telecommunications System (UMTS).

In this paper, we present a silent positioning scheme termed UPS for underwater acoustic sensor networks. UPS relies on the time difference of arrivals locally measured at a sensor to detect range differences from the sensor to four anchor nodes. These range differences are averaged over multiple beacon intervals before they are combined to estimate the 3-D sensor location through trilateration. UPS requires no time synchronization and provides location privacy at underwater vehicles/sensors whose locations need to be determined. To study the performance of UPS, we model the underwater acoustic channel as a modified ultrawideband Saleh-Valenzuela model: The arrival of each path cluster and the paths within each cluster follow double Poisson distributions, and the multipath channel gain follows a Rician distribution. Based on this channel model, we perform both theoretical analysis and simulation study on the position error of UPS under acoustic fading channels. The obtained results indicate that UPS is an effective scheme for underwater vehicle/sensor serf-positioning. Index Terms--Localization, navigation, UnderWater Acoustic Sensor Networks (UWA-SNs), underwater Global Positioning System (GPS), underwater positioning, ultrawideband (UWB) Saleh-Valenzuela (S-V) model.

The Grassmann manifold [g.sub.n,p] (L) is the set of all p-dimensional planes (through the origin) in the n-dimensional Euclidean space [L.sup.n], where L is either R or C. This paper considers the quantization problem in which a source in [g.sub.n,p] (L) is quantized through a code in [g.sub.n,q] (L), with p and q not necessarily the same. The analysis is based on the volume of a metric ball in [g.sub.n,p] (L) with center in [g.sub.n,q] (L), and our chief result is a closed-form expression for the volume of a metric ball of radius at most one. This volume formula holds for arbitrary n, p, q, and L, while previous results pertained only to some special cases. Based on this volume formula, several bounds are derived for the rate--distortion tradeoff assuming that the quantization rate is sufficiently high. The lower and upper bounds on the distortion rate function are asymptotically identical, and therefore precisely quantify the asymptotic rate--distortion tradeoff. We also show that random codes are asymptotically optimal in the sense that they achieve the minimum possible distortion in probability as n and the code rate approach infinity linearly. Finally, as an application of the derived results to communication theory, we quantify the effect of beamforming matrix selection in multiple-antenna communication systems with finite rate channel state feedback. Index Terms--Finite-rate feedback, Grassmann manifolds, limited feedback, multiple-input multiple-output (MIMO) communications, quantization, rate distortion function.

The description of resonance frequency and damping evolution with the help of classic differential equations for injection-locked lasers is discussed. Results suggest a record resonance frequency of 72 GHz and a broadband response of 44 GHz.

A best practice guide for building empirical models for predicting performance variables of computing systems is presented. The practice guide assists in configuring modeling approaches systematically for best estimation, and prediction results.

The article examines the effect of transmitter and receiver in-phase/quadrature-phase (IQ) imbalance under carrier frequency offset in an orthogonal frequency division multiplexing (OFDM) system.

It is shown that there exist information networks where messages can be sent (utilizing Network Coding) more easily in one direction than in the opposite direction. This is valid even though each channel is assumed to have the same capacity in both directions. It is shown that irreversible information networks only have solutions that use nonlinear Network Coding. This correspondence argues that this result is more surprising than it might appear at first sight and that it follows using ideas resembling the path integral in Quantum Mechanics. Index Terms--Information networks, linear algebra, network coding, multiple unicast networks, nonlinear network coding, path integral.

We consider communication through a cascade of discrete memoryless channels (DMCs). The source and destination node of this cascade are allowed to use coding schemes of arbitrary complexity, but the intermediate relay nodes are restricted to process only blocks of a fixed length. We investigate how the processing at the relays must be chosen in order to maximize the capacity of the cascade, that is, the maximum achievable end-to-end rate between the source and the destination. For infinite cascades with fixed intermediate processing length at the relays, we prove that this intermediate processing can be chosen to be identical without loss of optimality, and that the capacity of the cascade coincides with the rate of the best zero-error code of length equal to the block length of the intermediate processing. We further show that for fixed and identical intermediate processing at all relays, convergence of capacity as the length of the cascade goes to infinity is exponentially fast. Finally, we characterize how the block length of the intermediate processing must scale with the length of the cascade to guarantee a constant end-to-end rate. We prove that it is sufficient that the block length scales logarithmically with the network length in order to achieve any rate above the zero-error capacity. We show that in many cases of interest logarithmic growth is also necessary. Index Terms--Capacity, network coding, zero-error capacity.

We consider a unified framework comprising both multicarrier code-division multiple-access (MC-CDMA) and orthogonal frequency-division multiple-access (OFDMA), and discuss nonlinear prefiltering for downlink transmissions based on Tomlinson-Harashima precoding. The base station (BS) is equipped with multiple transmitting antennas and channel state information is assumed to be available at the transmit side. We design the prefiltering matrices so as to minimize the sum of the mean square errors at all mobile terminals when a conventional single-user data detector is employed at the receiver side. In this way, most of the computational burden is moved to the BS, where power consumption and computational resources are not critical requirements. Computer simulations are used to assess the performance of the proposed scheme under different operating scenarios. It turns out that OFDMA outperforms MC-CDMA when the system resources (subcarriers and/or spreading codes) are optimally assigned to the active nsers according to the channel quality. Index Terms--Minimum mean square error (MMSE) prefiltering, multicarrier code-division multiple-access (CDMA), orthogonal frequency-division multiple-access (OFDMA), Tomlinson-Harashima precoding (THP).

In this paper, we develop capacity-approaching turbo-coding schemes for half-duplex relay systems as an extension of our previous work on coding for full-duplex relays. We consider the use of specific signal constellations (e.g., binary phase-shift keying) in transmission, develop practical coding schemes to be used at the source and the relay nodes, and describe a suitable information combining technique at the destination node. Unlike the full-duplex relay systems, the destination node does not perform joint decoding of multiple consecutive blocks; instead, it works with one frame at a time. Furthermore, for the half-duplex relaying scheme, the optimization of the length of the listening period for the relay node is an issue. By utilizing information theoretical tools, we perform this optimization and use it in the development of our capacity-approaching coding/decoding schemes. Specifically, when the fraction of time turns out to be less than the transmission rate, the relay node is unable to decode all the information bits transmitted, and a partial decoding approach has to be used. Through a comprehensive set of examples, we observe that the proposed scheme is promising to approach the corresponding information theoretical limits (bounds). In particular, for all the cases studied, we have obtained bit error rates of [10.sup.-5] or lower within 1-1.5 dB (in most cases, almost within 1.2 dB) of the constrained capacity under a variety of channel conditions. Extensions of the proposed scheme to coded modulation and to multiple-input multiple-output systems are also described. Index Terms--Channel capacity, cooperative diversity, hall duplex, information rates, iterative decoding, multihop, multiple-input multiple-output (MIMO), relay, turbo coding.

Ultra-wideband wireless transmission has attracted considerable attention both in academia and industry. For high-rate and short-range transmission, direct sequence based ultra-wideband (DS-UWB) systems are a strong contender for consumer market applications. Due to the large transmission bandwidth, the UWB channel is characterized by a long root-mean-square delay spread and the RAKE receiver cannot always overcome the resulting intersymbol interference. We therefore study equalization for DS-UWB systems. This paper is comprised of two parts. In this first part, we consider DS-UWB with binary phase-shift keying (BPSK) modulation, which is the mandatory transmission mode for DS-UWB systems promoted by the UWB Forum industry alliance. We derive matched filter bounds for optimum equalization taking into account practical constraints like receiver filtering, sampling, and the number of RAKE fingers when RAKE preprocessing is applied at the receiver. Our results show that chip-rate sampling is sufficient for close-to-optimum performance. For analysis of suboptimum equalization strategies we further study the distribution of the zeros of the channel transfer function including RAKE combining. Our findings suggest that linear equalization is well suited for the lower data rate modes of DS-UWB systems, whereas nonlinear equalization is preferable for high-data rate modes. Moreover, we devise equalization schemes with widely linear processing, which improves performance while not increasing equalizer complexity. Simulation and numerical results confirm the significance of our analysis and equalizer designs and show that low-complexity (widely) linear and nonlinear equalizers perform close to the pertinent matched filter bound limit. Index Terms--Direct sequence UWB, equalization, RAKE receiver, statistical channel characterization, ultra wideband (UWB), widely linear processing.

This paper considers semiblind channel estimation and data detection for orthogonal frequency-division multiplexing (OFDM) over frequency-selective fading channels. We show that the samples of an OFDM symbol are jointly complex Gaussian distributed, where the mean and covariance are determined by the locations and values of fixed pilot symbols. We exploit this distribution to derive a novel maximum-likelihood (ML) semiblind gradient-descent channel estimator. By exploiting the channel impulse response (CIR) statistics, we also derive a semiblind data detector for both Rayleigh and Ricean fading channels. Furthermore, we develop an enhanced data detector, which uses the estimator error statistics to mitigate the effect of channel estimation errors. Efficient implementation of both the semiblind and the improved data detectors is provided via sphere decoding and nulling-canceling detection. We also derive the Cramer-Rao bound (CRB) and design optimal pilots by minimizing the CRB. Our proposed channel estimator and data detector exhibit high bandwidth efficiency (requiring only a few pilot symbols), achieve the CRB, and also nearly reach the performance of an ideal reference receiver. Index Terms--Channel estimation, data detection, orthogonal frequency-division multiplexing (OFDM).

The application of the Lagrange relaxation theory to perform integer programming, during the design of wireless telecommunications networks for capacity expansion of broadband wireless access, is described.

The achievement of 7-nines availability telecommunications systems in the field requires taking a 5-nines telecommunications system and providing extremely responsive and technically excellent customer support. The theme 'respond, restore, resolve' is an important customer reliability pattern that is meant to help remind field support engineers of the best-in-class overall strategy for responding to customer issues.

A mathematical model is presented which results in an algorithm to determine the optimal fail-over scheme by taking the interactions between the software applications into account that make up the system. This model can be employed to reasonably quantify the overall reliability of a system in terms of measurements that can be obtained during a product development phase.

ABSTRACT A new approach for the solution and analysis of mixed integer programs is presented and applied to a difficult optimization problem found in robust telecommunications network design. This new […]

The performances of dual-branch postdetection switch-and-stay combining (SSC) for noncoherent orthogonai binary frequency-shift keying and noncoherent orthogonal M-ary frequency-shift keying operating over slow, flat Rician fading channels are a topic of current interest. It is shown that recently published analyses obtain incorrect final results because some incorrect probability distribution parameters are used in the analyses. The previous results are corrected, and it is seen that the final results change significantly. The revised results are used to obtain optimum switching thresholds that minimize the average bit-error rate (BER) performance of these systems. Monte Carlo simulations are presented to verify the results, and it is shown that for a given BER, the signal-to-noise ratio difference of postdetection SSC and predetection SSC is much less than previously reported. Index Terms--Diversity combining, fading channels, postdetection diversity, Rician, switch-and-stay combining (SSC).

Reflective phase compensator (RPC) filters provide a solution to the phase-dispersion problem of narrow bandpass (NBP) filters when the data rate is 40 Gbits/s or greater. By use of an RPC filter to compensate for the excessive group-delay (GD) ripple of an NBP filter, the GD ripple of the combined NBP+RPC filter is well under the required 2.5 ps. OCIS codes: 310.0310, 230.4170, 060.2340.

A design for omnidirectional high reflectors with quarter-wave dielectric stacks in the optical telecommunication band that uses conventional optical thin-film design theory is described. The omnidirectional bandwidth is derived in units of wavelength and investigated as a function of its high- and low-refractive-index values in the near infrared. The results show that the high refractive index should be larger than 2.26 for an omnidirectional high reflector and that the low refractive index for maximum omnidirectional bandwidth should be ~1.5. It is shown that one can design broad-bandwidth omnidirectional high reflectors for S, C, and L bands for optical telecommunication simply by connecting the band edges of omnidirectional high reflectors. OCIS codes: 060.4510, 230.4040, 230.4170, 240.0310, 310.6860.

This work is focused on the analysis of the survivable capacitated network design problem. This problem can be stated as follows: Given a supply network with point-to-point traffic demands, specific survivability requirements, a set of available capacity ranges and their corresponding discrete costs for each arc, find minimum cost capacity expansions such that these demands can be met even if a network component fails. Solving this problem consists of selecting the links and their capacity, as well as the routings for each demand in every failure situation. This type of problem can be shown to be NP-hard. A new linear mixed-integer mathematical programming formulation is presented. An effective solution procedure based on Lagrangean relaxation is developed. Comparison heuristics and improvement heuristics are also described. Computational results using these procedures on different sizes of randomly generated networks are reported.