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Future communication networksrequire higher bandwidth, greater coverage, and better throughput. The Space-Air-Ground Integrated Network (SAGIN) has the advantage of wide-area coverage and can cover global communications. It can meet the needs of network resources for maritime activities and remote mountainous areas, which is of great significance to the realization of a new generation of communications networks. With the development of the network and the emergence of delay-sensitive applications such as the Internet of Things, improving the delay performance of the system has received extensive attention. SAGIN involves multiple networks and is more complex than other networks. If there is no reasonable management between different networks, it is easy to lead to difficult link deployment and high time delay. On the basis of research and customization of SFC technology, it can provide a wide range of services and other advantages. It has significant performance in application scenarios involving multi network integration. In order to solve the above problems, this paper studies the SAGIN architecture of SFC based on business types. A service function chain mapping method based on delays prediction is proposed. Calculate the delay of the deployment path and select the path with the lowest delay as the SFC mapping path. The service model is constructed according to the mapping path, and the network slices are divided based on the service type. The simulation results show that the SFC mapping algorithm based on time delay prediction is compared with the traditional SFC mapping scheme. The algorithm does not affect other indicators, the CPU resource utilization rate is 27.8 $\%$ higher, and the link resource utilization rate is 22.7 $\%$ higher. The service acceptance rate increased by 21.5 $\%$ , the latency performance increased by 38.2 $\%$ , and the total resource consumption is reduced by 25.2 $\%$. [ABSTRACT FROM AUTHOR]

This paper analyzes plug-in hybrid electric vehicle (PHEV) behavior, its impact on the electric grid, and possible charging opportunities using representative synthetic cycles with the consideration of daily driving schedules. The representative naturalistic cycles are synthesized through a stochastic process utilizing transition probability matrices extracted from naturalistic driving data collected in the Midwest region of the United States. The representativeness of the cycles is achieved through the subsequent statistical analysis. The distributions of the departure/arrival time and the rest time, analyzed from the real-world data at the key locations, complete the picture to analyze vehicle daily missions and the PHEV impact on the grid. PHEV simulation is used to determine the battery state of charge (SOC) distribution upon arrival. The results for typical locations such as residential, work, large business, and small business allow the assessment of the PHEV impact on the grid and possible charging opportunities during daily missions. [ABSTRACT FROM PUBLISHER]

Big data is the fuel for powering pervasive artificial intelligence (AI) applications. Aiming at promoting efficient cooperation in data market for big data, in this paper we propose a novel cooperative data purchase framework, by leveraging the power of the data user crowd and their intrinsic trustworthy collaboration relationships. For achieving efficient cooperative data purchase, we develop a comprehensive approach consisting of both data purchase group formation and selection. For the data purchase group formation, we partition the users into multiple data purchase groups for the purpose of budget pooling, by taking into account their data interest and budget levels, meanwhile respecting their underlying collaboration relationships and the maximum allowable group size for data sharing enforced by the data market platform. For the data purchase group selection, we construct a data purchase flow network formulation and devise a minimum cut based solution for selecting the proper set of data purchase groups to fully support their demands subject to the budget constraints. We extensively evaluate the performance of cooperative data purchase framework using both Erdos-Renyi and scale-free collaboration graphs. The numerical results demonstrate that the proposed framework can achieve superior performance, with more than ${40}\%$ and ${100}\%$ performance gain over the case without cooperation in terms of the total received payment and the number of satisfied users, respectively. [ABSTRACT FROM AUTHOR]

The introduction of fourth-generation wireless technologies has fueled the rapid development of cellular networks, significantly increasing the energy consumption and the expenditures of mobile network operators (MNOs). In addition, network underutilization during low-traffic periods (e.g., night zone) has motivated a new business model, namely, infrastructure sharing, which allows the MNOs to have their traffic served by other MNOs in the same geographic area, thus enabling them to switch off part of their network. In this paper, we propose a novel infrastructure-sharing algorithm for multioperator environments, which enables the deactivation of underutilized base stations during low-traffic periods. Motivated by the conflicting interests of the MNOs and the necessity for effective solutions, we introduce a game-theoretic framework that enables the MNOs to individually estimate the switching-off probabilities that reduce their expected financial cost. Our approach reaches dominant strategy equilibrium, which is the strategy that minimizes the cost of each player. Finally, we provide extensive analytical and experimental results to estimate the potential energy and cost savings that can be achieved in multioperator environments, incentivizing the MNOs to apply the proposed scheme. [ABSTRACT FROM AUTHOR]

Mobile opportunistic networks make use of node mobility to provide occasional contact opportunities for mobile devices to deliver data. In this paper, we investigate the inherent properties of data disseminations in mobile opportunistic networks by answering the question regarding how far and how fast a packet can be disseminated in mobile opportunistic networks. This problem has been overlooked by recent research, but it is very important because it reveals the potential for mobile opportunistic networks to support emerging applications such as mobile commerce and emergency services that may involve time and location sensitive information dissemination. Our investigations are taken from the perspectives of small and large scales. From the perspective of small scale, the probability distributions of the minimum time needed by the data to spread to a given region, namely, \mathcalT, are deduced for both the one-copy case and the multiple-copy case. From the perspective of large scale, by using the large deviation theory, the probability distributions of \mathcalT are deduced for both the one-copy case and the multiple-copy case when the destination region is far enough from the data origin. [ABSTRACT FROM PUBLISHER]

Location-based services (LBSs) are becoming an increasingly important component in our social and business life. All existing LBS providers support the nearest place searching via a single point of interest (POI) query. That is, in one query, a user is allowed to search for only one type of service. However, in real life, people usually need to search multiple different types of services and hope that their locations are as close as possible for convenience. For example, one user would like to search for a restaurant with a KTV nearby. To support this application scenario, we propose a novel LBS termed “ $N$ -in-One,” which is the first scheme to extend the function of single-POI LBS to multiple-POI LBS such that a single query can be employed to request multiple POIs that are geographically close. Providing “ $N$ -in-One” is challenging because: 1) serving a “ $N$ -in-One” query is not equivalent to serving $N$ queries independently due to the distance correlation among the $N$ POIs; and 2) the cask effect is getting worse in the service area mode of “ $N$ -in-one” as most of the returned results may be rendered useless when some hot POIs are blocked. To overcome these challenges, we propose several algorithms using computational geometry techniques to identify the best $K$ POIs that are geographically close and the service area (denoted by a given-sized rectangle) that can cover as many the best $Q$ clusters as possible while reducing the cask effect in the service area mode. Extensive simulations based on both synthetic and real world data demonstrate the effectiveness of the proposed algorithms. [ABSTRACT FROM AUTHOR]

In this paper, different control channel (CC) implementations for multichannel medium access control (MAC) algorithms are compared and analyzed in the context of opportunistic spectrum access (OSA) as a function of spectrum-sensing performance and licensed user activity. The analysis is based on a discrete Markov chain model of a subset of representative multichannel OSA MAC classes that incorporates physical layer effects, such as spectrum sensing and fading. The analysis is complemented with extensive simulations. The major observations are given as follows: 1) When the CC is implemented through a dedicated channel, sharing such dedicated channel with the licensed user does not significantly decrease the throughput achieved by the OSA network when the data packet sizes are sufficiently large or the number of considered data channels is small. 2) Hopping OSA MACs, where the CC is spread over all channels, are less susceptible to licensed user activity than those with a dedicated CC (in terms of both average utilization and on/off times). 3) Scanning efficiency has a large impact on the achievable performance of licensed and OSA users for all analyzed protocols. 4) The multiple rendezvous MAC class, which has yet to be proposed in OSA literature, outperforms all the multichannel MAC designs analyzed in this paper. Index Terms--Communication channels, communication systems, multiaccess communication, radio spectrum management, resource management.

This paper studies the performance of cellular mobile systems employing a signal-to-noise ratio (SNR)-based generalized selection combining (GSC) algorithm in the presence of background white noise and multiple cochannel interfering signals. Closed-form expressions are derived for the received signal-to-interference-plus-noise ratio (SINR) distribution and outage probability, considering the case when the interfering signals experience mixed Rayleigh and Nakagami-q fading conditions, and the desired-signal replicas are attenuated by flat Rayleigh fading. These expressions are obtained via the new representation of the total interference-to-noise ratio (INR) distribution for the mixed mode of fading experienced by different interferers. The derived expressions for the aforementioned statistical measures are valid for an arbitrary number of interferers and system diversity order and can be employed to investigate the impact of various system and fading parameters on the performance measures. Several case studies can be deduced from the results presented in this paper, including interference-limited systems, wherein the impact of white noise can be neglected. Index Terms--Cochannel interference, generalized selection combining (GSC), Nakagami-q fading, performance analysis, Rayleigh fading.

Source-localization techniques arc crucial in transportation applications such as navigation or Global Positioning Systems (GPS). A computationally efficient technique for multiple wideband source localization is presented in this paper using the expectation-maximization (EM) algorithm in the near field of a sensor array/area. Our basic idea is to decompose the recorded sensor data, which is a superimposition of multiple sources, into individual components in the frequency domain and then separately estimate the corresponding location parameters associated with each source. Instead of the conventional alternating projection (AP) method, we propose to adopt the EM algorithm in this paper; our method involves two steps, namely, Expectation (E-step) and Maximization (M-step). In the E-step, the individual incident source waveforms are estimated. Then, in the M-step, the maximum-likelihood (ML) estimates of the source-location parameters are obtained. These two steps arc iteratively and alternatively executed until the user's predefined convergence is reached. The computational complexity comparison between our proposed EM algorithm and the existing AP scheme is also investigated. Provably, it is shown through Monte Carlo simulations that the computational complexity of the proposed EM algorithm is significantly lower than that of the conventional AP scheme. We also derive the Cramer-Rao lower bound (CRLB) for the source-location estimates. Index Terms--Alternating projection (AP), Cramer-Rao lower bound (CRLB), expectation-maximization (EM), maximum likelihood (ML), near field, source localization, wideband sources.

This paper proposes a stochastic multipath model that is useful for generating multiple-input-multiple-output (MIMO) channel matrices in time-variant environments. The multipath model is developed by first extracting the relevant multipath cluster characteristics from measured indoor channel data and subsequently capturing these characteristics in an autoregressive stochastic model. This model is then used to generate channel matrices whose space-time characteristics closely match those of realistic scenarios, particularly when birth and death of multipath clusters are included in the stochastic representation. Computational examples reveal the applicability and the accuracy of the approach. While the current implementation is based on data taken assuming that propagation is confined to the horizontal plane, this paper also discusses the extension of the model to describe 3-D propagation, enabling its application to a wide range of physical scenarios and antenna characteristics. Index Terms--Communication channels, multiple-input-multiple-output (MIMO) systems, propagation.

This paper reexamines the problem of frequency offset estimation and signal detection of the Bell Laboratories Layered Space-Time (BLAST) scheme. Today, typical multiple-input-multiple-output (MIMO) receivers separately execute these two steps, but in succession. In this paper, we propose a joint frequency offset estimator and signal detector (JFESD). In our scheme, the frequency offset can be well compensated by utilizing the intermediate detector results. Our detector is evolved from conventional zero-forcing BLAST detectors. It is extendable to situations where the receive dimension is lower than the transmit dimension with a marginal increase of computational complexity. We evaluate the bit error probability and mean square error performance of the JFESD and compare them with other schemes. Index Terms--Carrier frequency offset (CFO), minimum mean square error (MMSE), QR-decomposition, successive interference cancellation (SIC), V-Bell Laboratories Layered Space-Time (BLAST), zero forcing (ZF).

In this paper, a modified turbo detector is proposed, which, by combining a standard turbo detector with an iterative reconstruction method, cancels multiaccess interference (MAI) and clipping distortion in uplink coded multicarrier code-division multiple-access (MC-CDMA) systems. For clipping noise cancellation, signal reconstruction methods use nondistorted samples to reconstruct distorted samples; however, in MC-CDMA systems, the MAI causes these methods to not work properly. On the other hand, because of clipping, MAI-cancellation methods do not work properly. In this paper, we propose a joint iterative MAI and clipping noise-cancellation method, which is composed of a standard turbo detection structure and a clipping error estimator in each iteration. Furthermore, we investigate the convergence of the proposed method. Simulation results show that the proposed method improves the performance of coded MC-CDMA systems in the uplink in the presence of clipping distortion. Index Terms--Interference suppression, iterative methods, signal reconstruction, turbo detection.

The opportunistic beamforming system (OBS) is currently receiving much attention in the field of downlink beamforming due to its simple random beamforming, low feedback complexity, and same throughput scaling obtained with perfect channel-state information using dirty paper coding at the transmitter. In this paper, we focus on its closed-form throughput evaluation over Rayleigh fading channels, based on the asymptotic theory of extreme order statistics. First, the throughput of a single-beam OBS is investigated, and an analytical solution tighter than the previously reported one is derived. Then, the asymptotic throughput bounds on a multibeam OBS are presented, and also, our analytical expression is shown to be very tight with the simulation results even with fewer users. After that, we argue that the reported conclusion that the single-beam OBS is much preferable to the multibeam OBS in the high-signal-to-noise-ratio (SNR) regime is inaccurate, but that, instead, it is satisfied only when the number of users is very small, due to its limited multiuser diversity gain. Finally, we show that four transmit beams is the most preferable in the multibeam OBS with a large number of users and moderate SNR, which arrives at the tradeoff between increasing spatial multiplexing gain and disappearing multiuser diversity gain. Index Terms--Multiple-input single-output (MISO), multiuser diversity, opportunistic beamforming system (OBS), spatial multiplexing, throughput.

This paper presents a numerical Bayesian approach for the direction-of-arrival (DOA) tracking of multiple targets using a linear and passive sensor array. In this paper, support vector regression (SVR) method is employed, together with particle filters (PFs), to obtain an effective proposed distribution utilizing observed phenomena to propose a new sample. Two PF algorithms are presented: One is based on SVR for a large sample set, and the other is based on sequential SVR for a small sample set. The simulation results present the superiority of the proposed method while considering a small sample set and show that it is also competitive when a large sample set is considered. Index Terms--Direction-of-arrival (DOA) tracking, particle filters (PFs), support vector regression (SVR).

In this paper, we extend the switching rate analysis of M out of N generalized selection combining (GSC) in an earlier paper of Cavers and Ho to the case of nonidentical branches. Despite the fact that nonidentical branches introduce a correlation between the difference of the Mth and the M + 1th strongest signals u(t) and its derivative u'(t), we were able to derive an analytical expression for the switching rate of the GSC receiver under this condition (independence between u(t) and u'(t) is crucial in obtaining the simple results in Cavers and Ho). Our numerical results agree with the intuition that having nonidentical branches reduces the switching rate. The more dissimilar the branches are, the larger the reduction. While this lowering of the switching rate allows the GSC receiver more time to dwell on the selected signals, hence producing more accurate channel estimates for coherent combining, the bit-error rate of GSC, unfortunately, is higher when the branches are not identical. Index Terms--Doppler frequency, generalized selection combining (GSC), nonidentical branches, Rayleigh fading, switching rate.

Power scheduling and localization play important roles in network topology management. Distributed power scheduling is an efficient way to construct a reliable and energy-efficient network topology. Localization provides geographical information for topology management. However, during the course of transmission power control, localization based on the received signal strength (RSS) is a challenging problem because of the inconsistent RSS indication (RSSI) measurements in wireless sensor networks. This paper presents an algorithm that takes advantage of the information from the ongoing wireless communication links to calculate the estimated position of sensor nodes. Considering the existing transmit-power-aware medium access control (MAC) protocols, we propose a localization algorithm based on particle filtering for sensor networks assisted by multiple transmit-power information. Therefore, the primary contribution of this paper is the elegant strategy on how to incorporate the practical multiple transmit-power information into the process of particle filtering. Furthermore, a general message-passing framework of the transmit-power-aware MAC is seamlessly integrated with the tracking service. The proposed particle-filtering-based localization algorithm uses the RSS information from the beacons or the neighboring nodes to infer the position of the concerned node without the requirement of any additional hardware instruments. Theoretical analysis and simulation results are presented to demonstrate the performance of the proposed localization method. The simulation results show that the proposed algorithm outperforms the existing algorithms that do not utilize multiple power information. Index Terms--Medical information systems, networks, wireless LAN.

Cooperative communication and orthogonal frequency-division multiplexing (OFDM) technology are both promising candidates for next-generation wireless communication systems. In this paper, we investigate cooperation strategies and resource-allocation algorithms for multiuser cooperative orthogonal frequency-division multiple-access (OFDMA) systems. There are two major contributions of this paper. First, we propose a novel cooperation strategy for the OFDMA system. When there are two users in the system, the strategy achieves the capacity region upper bound for decode-and-forward (DF) cooperation. When there are multiple users in the system, the strategy can achieve near upper-bound performance in certain network topologies. Moreover, the strategy always outperforms those that are previously proposed for cooperative OFDMA systems. The second contribution is that we develop novel centralized resource-allocation algorithms for cooperative OFDMA systems. The advantages of the algorithms are that they not only simultaneously solve relay, power, and subcarrier allocation but also have complexity that increases only linearly with the number of subcarriers in the systems. Index Terms--Cooperative communication, orthogonal frequency-division multiple access (OFDMA), resource allocation.

In this paper, we consider the uplink transmission in multicarrier code-division multiple-access (MC-CDMA) systems. As other multicarrier signals, MC-CDMA signals have high envelope fluctuations and a high peak-to-mean envelope power ratio (PMEPR), which leads to amplification difficulties. This is particularly important for the uplink transmission, since an efficient low-cost power amplification is desirable at the mobile terminals (MTs). Moreover, the transmission over time-dispersive channels destroys the orthogonality between spreading codes, which might lead to significant multiple-access interference levels. To reduce the envelope fluctuations of the transmitted signals, while maintaining the spectral efficiency, the MC-CDMA signal associated to each MT is submitted to a clipping device, followed by a frequency-domain filtering operation. However, the nonlinear distortion effects can be high when an MC-CDMA transmitter with reduced envelope fluctuations is intended (e.g., a small clipping level and/or when successive clipping and filtering operations are employed). In this paper, we define an iterative receiver that jointly performs a turbo multiuser detection and the estimation and cancellation of the nonlinear distortion effects. Our performance results show that the proposed receiver structure allows good performances, very close to the linear receiver ones, even for high system load and/or when a PMEPR as low as 1.7 dB is intended for each MT. Index Terms--Multicarrier code-division multiple access (MC-CDMA), multiuser detection (MUD), nonlinear distortion, turbo equalization.

Multiple-input-multiple-output (MIMO) receivers with direct-conversion radio-frequency (RF) architecture are investigated in this paper. Direct conversion is a low-cost RF design that requires fewer external components in chip implementation. Nevertheless, it introduces extra RF impairments such as I-Q imbalance and dc offset in addition to frequency offset that is commonly encountered in all RF architectures. This paper proposes to do the joint least squares (LS) estimation of frequency, dc offset, I-Q imbalance, and a channel in MIMO receivers to improve performance; frequency-dependent and frequency-independent I-Q imbalances are included. Previously, RF impairments were separately estimated in MIMO receivers, which leads to inferior performance. In particular, a receiver architecture that facilitates the joint estimation of the frequency, the dc offset, the I-Q imbalance, and the channel is proposed. The LS criterion is then applied to obtain the joint estimators, with a special training-sequence design to reduce complexity. Simplified estimators on the frequency and dc offset are also proposed with almost no loss in performance. Finally, the estimators are shown through analysis to be unbiased and approach the Cramer-Rao lower bound (CRLB) for signal-to-noise ratios (SNRs) of interest. The analysis is verified by computer simulations. Index Terms--Direct-conversion RF architecture, joint least squares (LS) estimations, multiple-input-multiple-output (MIMO) receiver.

In this paper, we study the problem of dynamic resource management for delay-sensitive users over wireless networks. We focus on a decentralized setting, where autonomous users make self-interested decisions to maximize their utility functions as evaluated based on information feedback. In this paper, two types of information feedback are discussed. One is the private information feedback between a transmitter-receiver pair. The other is the public information feedback among users (i.e., different transmitter-receiver pairs). Due to the informationally decentralized nature of the wireless network, a user cannot have complete information about the transmission actions of its interfering neighbors. However, the user can implicitly or explicitly model the transmission strategies of its major interference sources based on the information feedback. In this paper, we provide an interactive learning framework for distributed power control of delay-sensitive users over multicarrier wireless networks. Specifically, the user can adopt corresponding interactive learning schemes to explicitly model the other users' strategies if public information feedback is available or to implicitly model the impact of other users' actions on its utility if only private information is available. Based on these models, the user creates beliefs and is able to strategically adapt its decisions to maximize its utility. We determine the performance upper bounds for the user's utility when learning from private or public information feedback and investigate the cost-performance tradeoffs resulting from the information feedback gathered with different frequencies and from various users. The simulation results show that the proposed adaptive interactive learning approach significantly improves the energy efficiency of delay-sensitive users compared with schemes that perform myopic best response. Index Terms--Delay-sensitive applications, information feedback, interactive learning, power control.

The mobility pattern of users is one of the distinct features of vehicular ad hoc networks (VANETs) compared with other types of mobile ad hoc networks (MANETs). This is due to the higher speed and the roadmap-restricted movement of vehicles. In this paper, we propose a new analytical mobility model for VANETs based on product-form queueing networks. In this model, we map the topology of the streets and the behavior of vehicles at both intersections and different parts of the streets onto different parameters of a BCMP open queueing network comprising M/G/[infinity] nodes. This model represents a sparse situation for VANETs. To include the effect of dense situation on the mobility model, we modify the proposed queueing network as a new one comprising nodes with state-dependent service rates, i.e., M/G(n)/[infinity] nodes. With respect to the product-form solution property of the proposed queueing networks, we are able to find the spatial traffic distribution for vehicles at both sparse and dense situations. Furthermore, we are able to modify the proposed queueing network to find the lower and upper bounds for the probability of connectivity. In the last part of this paper, we show the flexibility of the proposed model by several numerical examples and confirm our modeling approach by simulation. Index Terms--Connectivity, mobility model, queueing network, spatial traffic distribution, vehicular ad hoc network (VANET).

In this paper, we analyze the queuing performance in the finite-state Markov channel (FSMC) when the single-step power control (SSPC) scheme is adopted. To start with, an SSPC model and its extended power control error (PCE) model are proposed and described in detail. Such models can emulate the behaviors of the interaction between the SSPC and an FSMC and the variation of the PCE with high accuracy. Furthermore, the packet error rate that has been recently analyzed by Lee and Chang is adopted to evaluate the service rate, the time average queuing length, and the probability mass function (PMF) of the queuing length variation. Based on these results, a queuing variation model is proposed to emulate the queuing variation in the FSMC. The flooring phenomenon of the queuing length is observed under a particular requirement of an overflow probability when the SNR value is greater than a certain value. This indicates that the trade-off among the SNR, the buffer size of the queue, and the overflow probability exists. Hence, two different approaches to select the optimal target SNR of the SSPC and the maximum buffer size of the queue under the requested queuing buffer overflow probability are proposed. The improvement of the SSPC, its impact on the system, and the validity of the proposed models are shown in this paper as well. Index Terms--Finite-state Markov channel (FSMC), queuing performance, queuing variation model, single-step power control (SSPC), SSPC model.

The aim of this paper is to investigate the vibrations in a new tram model (the 'Combino Plus') developed by Siemens Company, Germany, which was recently launched on a main Budapest road, and in an older tram model withdrawn from the same line. Comparative measurements were made from terminal to terminal (18 sections). The results of this investigation gave us information about the advances made in relation to the vibrational characteristics of trams. This paper summarizes literature concerning the physiological effects of continuous vibration exposures, as well as the standard ISO 2631, to clarify the relevance of the topic and to draw attention to the recorded parameters of the new 'Combino Plus' tram. The new 'Combino Plus' tram successfully absorbs the vibrations originating from the roughness of the tram rail. This tram produces significantly less vibration for passengers and drivers than the older model tram withdrawn from the main road traffic. The new Combino Plus satisfies the ergonomic requirements and ensures favorable working conditions. Index Terms--Acceleration sensor, environmental protection, passenger transport, spectral analysis, tram vibration.

This paper presents an analysis framework for estimating spatio-temporal distortion associated with data-gathering algorithms in sensor networks. We assume that the underlying data field being sensed is spatially and temporally correlated and that the sink node performs real-time reconstruction of the field. Unlike existing work, the proposed analysis framework assumes realistic transmission schemes and network/routing parameters, such as congestion and limited transmission range. Our simulations show that, even for a simple collision-free transmission scheme and regular deployment patterns, the distortion analyses yield starkly different results, compared with the analyses performed in the absence of these assumptions. The analytical method presented in this paper could easily be extended to consider the real-time data-reconstruction problem under different transmission schemes, node distributions, and reconstruction methods. Index Terms--Data gathering, distortion analysis, spatio-temporal correlation, wireless sensor networks.

Service discovery is a crucial operation for the usability of mobile ad hoc networks (MANETs). Traditional solutions to service discovery that were adopted on the Internet are not well suited for MANETs because of their dynamic nature. This paper presents a novel service discovery protocol based on a hierarchical grid architecture in an ad hoc network. The geographical area of a MANET is divided into a 2-D logical hierarchical grid. The proposed scheme registers the information of available services to a specific location along a predefined trajectory. To enhance resource availability and effective discovery, each grid cell selects a directory for caching available services. This paper utilizes the transmitting trajectory to improve the efficiency of registration and discovery. First, the service provider registers a service along the proposed register trajectory. The requestor then discovers the service along the discovery trajectory to acquire the service information. This paper also proposes an improved process to avoid the sparse node network topology. This paper adopts analysis and simulation to measure the protocol performance. The analytical and simulation results show that the proposed protocol can raise the discovery success ratio and reduce the discovery cost more than the existing geographical service discovery protocol. Index Terms--Grid, mobile ad hoc networks (MANETs), mobile computing, service discovery, wireless networks.

Orthogonal frequency-division multiplexing (OFDM) can be used to support high-data-rate transmissions over time-dispersive fading channels. Many OFDM-based communication systems use packet-based transmission, where channel estimation is needed for the detection of information-carrying symbols. The finite impulse response (FIR) channel model is simple and effective for some simulations of channel estimation for the OFDM-based communication systems over the time-dispersive channels; yet, it is only an approximate channel model that cannot be used in the case of accurate channel estimation. Unfortunately, many researchers have overlooked this issue and have been devising channel-estimation algorithms squarely based on the FIR channel model. While the channel estimation results from these algorithms can be impressive for the FIR channels, the algorithms can hardly be applied in real-world applications. This paper explains in detail the reason the FIR channel model is only an approximate channel model for the OFDM-based communication systems, trying to discourage the inappropriate usage of this model, which can lead to fruitless efforts. This paper also presents a realistic channel model for OFDM-based communication systems, which can be used to realistically access the channel parameter-estimation algorithms. Index Terms--Channel estimation, channel model, orthogonal frequency-division multiplexing (OFDM).

This paper considers a scheduling problem for multi-user transmissions over the downlink of a time-slotted cellular data network. For such a network, opportunistic scheduling exploits the time-varying radio channel and improves network performance. This paper presents a new scheduling solution that maximizes the aggregate user performance subject to certain minimum and maximum performance constraints. By constraining the performance experienced by individual users, who share a common radio downlink, to some upper bounds, it is possible to provide the system operator with a better control of radio resource allocations and service differentiation among different classes of users. The proposed solution, which is referred to as Throughput Constrained Opportunistic Scheduling (TCOS), offers better service differentiation among different classes of users than the existing opportunistic scheduling algorithms with only minimum performance constraints. For ideal memoryless fading channels, TCOS provides performance comparable with an existing scheme with minimum and maximum performance constraints. For realistic fading channels with memory, TCOS significantly improves system performance due to its ability to trade off feasibility with throughput. Extensive simulation results demonstrate the improved system performance and effective service differentiation of the proposed solution under realistic channel conditions. Index Terms--Land mobile radio cellular systems, resource management, scheduling, time division multi-access.

This paper introduces a novel analytical model for analyzing the performance of handoff algorithms based on absolute and relative signal strength measurements. The performance is analyzed in multicell and multisector environments where cochannel interference (CCI) is present. The model presented in this paper accounts for the distinct features of intersector handoff compared with intercell handoff. Numerical results show that the performance metrics are affected by the CCI level. The occurrence condition of unnecessary handoffs in multisector systems is also presented. Index Terms--Cochannel interference (CCI), handoff algorithm, multisector systems, signal strength measurement.

Ultrawideband (UWB) communications involve very sparse channels, because the bandwidth increase results in a better time resolution. This property is used in this paper to propose an efficient algorithm that jointly estimates the channel and the transmitted symbols. More precisely, this paper introduces an expectation-maximization (EM) algorithm within a wavelet-domain Bayesian framework for semiblind channel estimation of multiband orthogonal frequency division multiplexing based UWB communications. A prior distribution is chosen for the wavelet coefficients of the unknown channel impulse response to model a sparseness property of the wavelet representation. This prior yields, in maximum a posteriori estimation, a thresholding rule within the EM algorithm. We particularly focus on reducing the number of estimated parameters by iteratively discarding 'insignificant' wavelet coefficients from the estimation process. Simulation results using UWB channels that were issued from both models and measurements show that, under sparseness conditions, the proposed algorithm outperforms pilot-based channel estimation in terms of the mean square error (MSE) and bit error rate (BER). Moreover, the estimation accuracy is improved, whereas the computational complexity is reduced compared with traditional semiblind methods. Index Terms--Bayesian channel estimation, expectation-maximization (EM) algorithm, iterative (turbo) detection, orthogonal frequency-division multiplexing (OFDM), sparse-wavelet-domain representation, ultrawideband (UWB).

As receiver performance will be degraded by carrier frequency offset (CFO), Doppler shift, and low signal-to-noise ratio (SNR), a novel estimator that jointly considers CFO, Doppler shift, and SNR is proposed in this paper. The proposed algorithm uses the Fourier transform (FT) to calculate the power spectral density of time-varying channels through channel estimates. Then, a new periodogram technique is utilized to estimate CFO, Doppler shift, and SNR together. Unlike conventional methods in sinusoid estimation, which rely on the peak-value search of a periodogram, this paper exploits the hypothesis test to address the random frequency modulation of time-varying channels. Furthermore, to optimize estimation performance, a theoretical analysis is also provided on the influences of some key parameters, e.g., the length of the signal processed with fast FT, the amplitude threshold value, the SNR dynamic range, and the velocity dynamic range. Correspondingly, the appropriate key parameters are chosen according to this analysis and are validated by simulations. The results are consistent with our analysis and present high accuracy over a wide range of velocities and SNRs. Index Terms--Carrier frequency offset (CFO), Doppler shift, hypothesis test (HT), joint estimation, periodogram, signal-to-noise ratio (SNR).

This paper presents a system for automotive crash detection based on hidden Markov models (HMMs). The crash pulse library used for training comprises a number of head-on and oblique angular crash events involving rigid and offset deformable barriers. Stochastic distribution characteristics of crash signals are validated to ensure conformity with the modeling assumptions. This step is achieved by analyzing the quantile-quantile (Q-Q) plot of actual pulses against the assumed bivariate Gaussian distribution. HMM parameters are next induced by utilizing the expectation-maximization (EM) procedure. The search for an optimal crash pulse model proceeds using the 'leave-one-out' technique with the exploration encompassing both fully connected and left-right HMM topologies. The optimal crash pulse architecture is identified as a seven-state left-right HMM with its parameters computed using real and computer-aided engineering (CAE)-generated data. The system described in the paper has the following advantages. First, it is fast and can accurately detect crashes within 6 ms. Second, its implementation is simple and uses only two sensors, which makes it less vulnerable to failures, considering the overall simplicity of interconnects. Finally, it represents a general and modularized algorithm that can be adapted to any vehicle line and readily extended to use additional sensors. Index Terms--Automotive crash detection, computer-aided engineering (CAE), continuous-value emission hidden Markov models (HMMs), crash pulse, discrete-value emission HMM, finite-element analysis (FEA).

In this paper, we investigate the problem of multiuser resource management in multihop cognitive radio networks for delay-sensitive applications. Since tolerable delay does not allow propagating global information back and forth throughout the multihop network to a centralized decision maker, the source nodes and relays need to adapt their actions (transmission frequency channel and route selections) in a distributed manner, based on local network information. We propose a distributed resource-management algorithm that allows network nodes to exchange information and that explicitly considers the delays and cost of exchanging the network information over multihop cognitive radio networks. In this paper, the term 'cognitive' refers to both the capability of the network nodes to achieve large spectral efficiencies by dynamically exploiting available frequency channels and their ability to learn the 'environment' (the actions of interfering nodes) based on the designed information exchange. Note that the node competition is due to the mutual interference of neighboring nodes using the same frequency channel. Based on this, we adopt a multiagent-learning approach, i.e., adaptive fictitious play, which uses the available interference information. We also discuss the tradeoff between the cost of the required information exchange and the learning efficiency. The results show that our distributed resource-management approach improves the peak signal-to-noise ratio (PSNR) of multiple video streams by more than 3 dB, as opposed to the state-of-the-art dynamic frequency channel/route selection approaches without learning capability, when the network resources are limited. Index Terms--Cognitive radio networks, delay-sensitive applications, distributed resource management, multiagent learning, multihop wireless networks.

Recent advances in vehicular communications make it possible to realize vehicular sensor networks, i.e., collaborative environments where mobile vehicles that are equipped with sensors of different nature (from toxic detectors to still/video cameras) interwork to implement monitoring applications. In particular, there is an increasing interest in proactive urban monitoring, where vehicles continuously sense events from urban streets, autonomously process sensed data (e.g., recognizing license plates), and, possibly, route messages to vehicles in their vicinity to achieve a common goal (e.g., to allow police agents to track the movements of specified cars). This challenging environment requires novel solutions with respect to those of more-traditional wireless sensor nodes. In fact, unlike conventional sensor nodes, vehicles exhibit constrained mobility, have no strict limits on processing power and storage capabilities, and host sensors that may generate sheer amounts of data, thus making already-known solutions for sensor network data reporting inapplicable. This paper describes MobEyes, which is an effective middleware that was specifically designed for proactive urban monitoring and exploits node mobility to opportunistically diffuse sensed data summaries among neighbor vehicles and to create a low-cost index to query monitoring data. We have thoroughly validated the original MobEyes protocols and demonstrated their effectiveness in terms of indexing completeness, harvesting time, and overhead. In particular, this paper includes 1) analytic models for MobEyes protocol performance and their consistency with simulation-based results, 2) evaluation of performance as a function of vehicle mobility, 3) effects of concurrent exploitation of multiple harvesting agents with single/multihop communications, 4) evaluation of network overhead and overall system stability, and 5) performance validation of MobEyes in a challenging urban tracking application where the police reconstruct the movements of a suspicious driver, e.g., by specifying the license number of a car. Index Terms--Middleware, opportunistic communications, urban monitoring, vehicular communications, vehicular sensor networks.

In this paper, we propose an analytical model for the distributed reservation protocol (DRP), which is defined in the WiMedia specification for ultra-wideband (UWB)-based wireless personal area networks (WPANs). We model the tagged user as a discrete-time queue with vacations, which captures the joint behavior of a queue length variation and a time-varying UWB channel due to shadowing under a given reservation pattern. Furthermore, we consider two reservation methods: hard reservation and soft reservation. With the hard reservation, a time slot is exclusively used by the owner, whereas the unused time slots can be accessed by other users using the soft reservation. Closed-form expressions of important performance metrics such as the mean service time, the waiting time, and the throughput are derived. Through numerical results, we validate the accuracy of the proposed analytical model and investigate the interaction between the DRP and various system parameters. This paper should provide insights into the performance of the DRP and useful guidelines to further improve the protocol to support isochronous applications with a tight delay requirement in UWB-based WPANs. Index Terms--Channel model, distributed reservation protocol (DRP), matrix-geometric approach, shadowing, ultra-wideband (UWB), vacation queue, wireless personal area network (WPAN).

This paper considers the problem of selecting a subset of nodes in a two-hop wireless network to act as relays in aiding the communication between the source-destination pair. Optimal relay subset selection with the objective of maximizing the overall throughput is a difficult problem that depends on multiple factors, including node locations, queue lengths, and power consumption. A partial decode-and-forward strategy is applied in this paper to improve the tractability of the relay selection problem and the performance of the overall network. Note that the number of relays that are selected ultimately determines the performance of the network. This paper benchmarks this performance by determining the net diversity that is achieved using the relays that are selected and the partial decode-and-forward strategy. This framework is subsequently used to further transform relay selection into a simpler relay placement problem, and two proximity-based approximation algorithms are developed to determine the appropriate set of relays to be selected in the network. Other selection strategies, such as random relay selection and a greedy algorithm that relies on channel state information, are also presented. This paper concludes by showing that the proposed proximity-based relay selection strategies yield near-optimal expected rates for a small number of selected relays. Index Terms--Greedy algorithms, partial decode-and-forward, relays, superposition coding.

In this paper, the hybridization of a small passenger car equipped with a continuously variable transmission (CVT) is investigated. Designing a hybrid drive train is a multiobjective design problem. The main design objectives are fuel consumption, emissions, and performance. However, it is difficult to find a global optimal integral design solution due to the interdependence of design choices (parameters) regarding the drive-train topology, component sizes, component technologies, and control strategy, as well as the unknown sensitivity of the design objectives to the design parameters. In this paper, a parametric optimization procedure is presented to solve the design problem, where the main design objective is fuel consumption. The effects of parameter variation on fuel consumption have been investigated. Furthermore, a reduced hybrid drive-train model is introduced, with which the effects of design parameter variation is very quickly studied with an average error of less than 1.6%. Index Terms--Continuously variable transmission (CVT), energy source, hybrid electric vehicles (HEVs), vehicle simulation.

Energy conservation is essential to wireless networks, particularly for third-generation (3G) and fourth-generation (4G) wireless systems, because high-speed data transmissions would rapidly exhaust the energy of a mobile station. This paper presents the details of energy-saving mechanisms for packet data services in two major standards, namely, the Third-Generation Partnership Project (3GPP) and the Third-Generation Partnership Project 2 (3GPP2). In addition to qualitative comparison, analytic models and quantitative comparison based on the energy-saving models are provided. The proposed analytic models analyze and quantify the energy consumption for bursty and streaming traffic in cdma2000 and wideband code division multiple access (WCDMA). The impacts of an inactivity timer on energy consumption and reconnection cost are demonstrated further by simulation and analysis. The analytic results could be used to suggest proper timer lengths that can balance the energy consumption and the reconnection cost. In addition to providing insights of the energy-conservation mechanisms of 3GPP and 3GPP2, which are often difficult to directly obtain from standards specifications, results shown in this paper are also practical for 3GPP and 3GPP2 operators to determine proper parameters for energy efficiency. Index Terms--Energy efficiency, performance analysis, resource control, third-generation (3G) wireless systems, wireless communications.

Wireless platforms are becoming less expensive and more powerful, enabling the promise of widespread use for everything from health monitoring to military sensing. Like other networks, sensor networks are vulnerable to malicious attack. However, the hardware simplicity of these devices makes defense mechanisms designed for traditional networks infeasible. This paper explores the denial-of-sleep attack, in which a sensor node's power supply is targeted. Attacks of this type can reduce the sensor lifetime from years to days and have a devastating impact on a sensor network. This paper classifies sensor network denial-of-sleep attacks in terms of an attacker's knowledge of the medium access control (MAC) layer protocol and ability to bypass authentication and encryption protocols. Attacks from each classification are then modeled to show the impacts on four sensor network MAC protocols, i.e., Sensor MAC (S-MAC), Timeout MAC (T-MAC), Berkeley MAC (B-MAC), and Gateway MAC (G-MAC). Implementations of selected attacks on S-MAC, T-MAC, and B-MAC are described and analyzed in detail to validate their effectiveness and analyze their efficiency. Our analysis shows that the most efficient attack on S-MAC can keep a cluster of nodes awake 100% of the time by an attacker that sleeps 99% of the time. Attacks on T-MAC can keep victims awake 100% of the time while the attacker sleeps 92% of the time. A framework for preventing denial-of-sleep attacks in sensor networks is also introduced. With full protocol knowledge and an ability to penetrate link-layer encryption, all wireless sensor network MAC protocols are susceptible to a full domination attack, which reduces the network lifetime to the minimum possible by maximizing the power consumption of the nodes' radio subsystem. Even without the ability to penetrate encryption, subtle attacks can be launched, which reduce the network lifetime by orders of magnitude. If sensor networks are to meet current expectations, they must be robust in the face of network attacks to include denial-of-sleep. Index Terms--Medium access control (MAC), wireless security, wireless sensor networks (WSNs).

The IEEE 802.16 standard for wireless metropolitan area networks (WMANs) is defined to meet the need for wide-range broadband wireless access at low cost. The objective of this paper is to study how to exploit spectral reuse in resource allocation in an IEEE 802.16 mesh network, which includes routing tree construction (RTC), bandwidth allocation, time-slot assignment, and bandwidth guarantee of real-time flows. The proposed spectral reuse framework covers bandwidth allocation at the application layer, RTC and resource sharing at the medium access control (MAC) layer, and channel reuse at the physical layer. To the best of our knowledge, this is the first paper that formally quantifies spectral reuse in IEEE 802.16 mesh networks and exploits spectral efficiency under an integrated framework. Simulation results show that the proposed schemes significantly improve the throughput of IEEE 802.16 mesh networks. Index Terms--IEEE 802.16, mesh network, resource allocation, routing tree, WiMax, wireless network.

In this paper, we analyze spatial multiplexing techniques for the downlink of a multiple-input-multiple-output (MIMO) orthogonal frequency-division multiplexing (OFDM) system. Our study is focused on outdoor environments characterized by a moderate angular spread. We consider two techniques that are able to separate the downlink data streams associated with different users and to guarantee a fixed error probability by exploiting limited feedback from each user. The grid of beams (GoBs) and the proposed adaptive GoB (AGoB) differ in the way the precoders are designed (by adaptive or fixed processing) and in their scheduling policy. The new AGoB is able to harness partial knowledge of the downlink channel spatial structure to better select the users and adjust their precoders for downlink transmission. The performances of GoB and AGoB are compared in this paper in terms of throughput and cell coverage capability. The radio interface is adapted to fit the requirements for the adaptive modulation and coding with advanced antenna system (AMC-AAS) mode of the IEEE 802.16-2005 standard. Numerical results show that, as long as the channel exhibits a limited angular spread at the base station, the AGoB technique is able to provide significant throughput gains compared with the fixed GoB approach. On the other hand, large angular spreads are proved to have a substantial impact on system performance as the benefits of adaptation are significantly reduced. Index Terms--MIMO-OFDM systems, multiuser diversity, spatial multiplexing, zero-forcing beamforming.

On the multiantenna broadcast channel, the spatial degrees of freedom support simultaneous transmission to multiple users. The optimal multiuser transmission, which is known as dirty paper coding, is not directly realizable. Moreover, close-to-optimal solutions such as Tomlinson-Harashima precoding are sensitive to channel state information (CSI) inaccuracy. This paper considers a more practical design called per user unitary and rate control (PU2RC), which has been proposed for emerging cellular standards. PU2RC supports multiuser simultaneous transmission, enables limited feedback, and is capable of exploiting multiuser diversity. Its key feature is an orthogonal beamforming (or precoding) constraint, where each user selects a beamformer (or precoder) from a codebook of multiple orthonormal bases. In this paper, the asymptotic throughput scaling laws for PU2RC with a large user pool are derived for different regimes of the signal-to-noise ratio (SNR). In the multiuser interference-limited regime, the throughput of PU2RC is shown to logarithmically scale with the number of users. In the normal SNR and noise-limited regimes, the throughput is found to scale double logarithmically with the number of users and linearly with the number of antennas at the base station. In addition, numerical results show that PU2RC achieves higher throughput and is more robust against CSI quantization errors than the popular alternative of zero-forcing beamforming if the number of users is sufficiently large. Index Terms--Broadcast channels, feedback communication, multiuser channels, space division multiplexing.

Switched reluctance (SR) drive systems are a candidate technology for electric vehicle applications, particularly where a high degree of component integration is required within a thermally demanding environment--typical of engine-mounted power-assist solutions. This paper discusses the design, prototype realization, and test validation of an SR machine for a mild-hybrid power-assist starter/alternator application that has performance requirements of both high starting torque and a wide speed range at full power. While a number of papers on SR machine design for automotive starter/alternator applications have been published, a comprehensive case study discussing the design and application issues has not been published. This paper focuses on the impact of the performance requirements and volumetric and environmental constraints on the machine design. It is shown that a higher number of stator and rotor poles is more appropriate for the utilization of the available active volume. While various operation and fault scenarios have been presented for SR drive systems, this paper also discusses test observations that suggest the potential for the transient self-excitation of the SR generator via residual magnetization of the machine rotor--a fault scenario that has only been briefly reported on. Index Terms--Machine design, mild-hybrid electric vehicles, starter/generators, switch reluctance machines.

This paper discusses interference precancellation in digital hierarchical broadcasting (HB). In particular, we present the principles and implementation of structured dirty paper coding (SDPC) that approaches the capacity limit of dirty paper coding in multilayer broadcasting. As an alternative to Tomlinson-Harashima precoding (THP), SDPC eliminates the significant performance loss suffered by THP in the low signal-to-noise ratio (SNR) regime due to the modulo operation. The key idea behind the SDPC scheme is the exploitation of the modulation structure of interference, thereby simplifying the demodulation process in hierarchical reception. We exemplify the SDPC technique by implementing an SDPC-based HB system on a real-time test bed. The experimental results show that SDPC delivers the performance of 'superposition coding with successive interference cancellation' without extra computation or memory requirements at the receiver side. Index Terms--Dirty paper coding, hierarchical broadcasting, structured dirty paper coding, Tomlinson-Harashima precoding.

Recent trends in the telecommunication industry have been moving toward the development of ubiquitous information systems, where the provision of a plethora of advanced multimedia services should be possible, regardless of time and space limitations. An efficient and seamless delivery of multimedia services over various types of wireless networks is still a challenging task. The underlying difficulty consists of the disparity in the bandwidth availability over each network type. Indeed, the fundamental chailenge upon a handoff phenomenon in a heterogeneous wireless network consists of an efficient probing of the bandwidth availability of the new network, followed by a prompt adjustment of the data delivery rate. This paper presents a cross-layer approach that involves five layers, namely, physical, data link, application, network, and transport layers. The three former layers are used to anticipate the handoff occurrence and to locate the new point of attachment to the network. Based on their feedback, the transport layer is used then to probe the resources of the new network using low-priority dummy packets. Being the most widely used protocol for multimedia delivery, this paper addresses multimedia applications based on the Transmission Control Protocol (TCP) and the Real-time Transport Protocol (RTP). The design of the whole cross-layer architecture is discussed, and enhancements to the two protocols are proposed. The performance of the enhanced TCP and the RTP are evaluated and compared against existing schemes through extensive simulations. The obtained results are encouraging and promising for the delivery of multimedia services in heterogeneous wireless networks. Index Terms--Cross layer, heterogeneous wireless networks, next-generation wireless Internet, Real-time Transport Protocol (RTP), Transmission Control Protocol (TCP).

In this paper, we introduce a novel approach for computing the number, location, and transmission powers of wireless base stations in a 2-D urban setup. The new approach utilizes 2-D convolution to extract the supply-demand correlation. Available efficient methods for computing the convolution are then used to substantially reduce the complexity of the solution. The proposed approach enables network designers to choose arbitrary antenna propagation and radio demand patterns using a simple color-coding mechanism. Simulations of the proposed algorithm show its efficiency and flexibility in solving the placement problem. In this paper, we consider only the coverage planning. Consequently, the technique in this paper is useful in networks that operate with time-division mnltiple-access technology. However, the work can be extended to consider simultaneous coverage and frequency planning. Index Terms--Base station (BS), cell planning, convolution, placement, wireless communications.

Location management plays a central role in guaranteeing the effective operation of personal communication service (PCS) networks. In current PCS networks, a two-tier system of home location register (HLR) and visitor location register (VLR) databases is commonly used for location management. To improve the performance of PCS networks, several dynamic location management schemes have been proposed. Among the existing dynamic schemes, the movement-based location management may be the most practical due to its effectiveness and easy implementation under the framework of current PCS networks. To implement location management in PCS networks, cost analysis is a crucial aspect. However, most of the existing cost analyses for the movement-based scheme are too simple and not available for PCS networks with the HLR/VLR architecture. One reason for this is the complexity and the difficulty associated with the problem. Li et al. and Rodrlguez-Dagnino et al. challenged this task by considering the HLR/VLR architecture. However, the cost analysis developed by Li et al. was carried out under the assumption that the cell and location area (LA) residence times are exponentially distributed. Rodriguez-Dagnino et al. furthered Li et al.'s work by assuming that the LA residence time follows a hyperexponential distribution and that the cell residence time is generally distributed. However, Li et al. and Rodriguez-Dagnino et al. failed to consider VLR location updates that are caused by terminal movements between LAs. In this paper, we relax the restrictions imposed on the distributions of the cell and LA residence times and propose an analytical model to study the movement-based scheme with HLR/VLR architecture. The issue of VLR location updates that are caused by movements between LAs is addressed carefully and successfully. Analytical formulas for the costs of HLR and VLR location updates are derived using a unified approach. Numerical study suggests that the total cost is a convex function of the movement threshold and is sensitive to the variances of the cell and LA residence times. The result presented in this paper can serve as a guideline for the system design and the implementation of the movement-based scheme for PCS networks. Index Terms--Cost analysis, location management, location update, personal communication service (PCS) networks, visitor location register (VLR).

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).