Search

In a Fog Radio Access Network (F-RAN), fog access points (F-APs) are equipped with caches that can store popular files during off-peak hours. Besides, they are densely deployed to have overlapping radio coverage so that requested files can be delivered cooperatively using beamforming. The bottleneck of the network is typically in the bandwidth-limited wireless fronthaul, which connects a cloud server to the F-APs. This work studies index coding design for cooperative caching and delivery in F-RAN to minimize fronthaul traffic and transmit energy. Index coding algorithms are designed considering the cached content at the F-APs and the possibility of beamforming in the access network under coded and uncoded caching schemes. An optimal polynomial-time index coding algorithm for uncoded and repetition caching and an efficient heuristic for Maximum Distance Separable (MDS) coded caching are designed, and their superior performance is verified by simulations. The study is further extended to consider the tradeoff between the traffic load of the fronthaul link and the transmit energy consumed in the access network. At the expense of more fronthaul traffic, beamforming opportunities can be increased, significantly reducing energy consumption. Algorithms to achieve the tradeoff are crafted, and simulation results show that uncoded caching well balances the tradeoff. [ABSTRACT FROM AUTHOR]

Social media traffic constitutes the highest percentage of Internet traffic. Such traffic is largely facilitated by mobile devices, which imposes a huge traffic load on backhaul links in 5G networks, and can in turn affect the quality of service. This traffic load can be alleviated by using vehicular networks as a traffic offloading platform. In particular, vehicles can act as a resourceful asset for edge caching, thus enabling data acquisition from nearby caching nodes rather than the remote backhaul servers. In this paper, we propose the Predictive Proactive Caching Framework (PPCF), which exploits the daily driving routine and predictable behavior of users to pre-cache the data at parked vehicles for the requesters to proactively acquire as they pass by. PPCF is composed of a cache placement module and a prediction module. The former aims at maximizing cache hits by assigning replicas to caching spots that yield maximum certainty in their spatiotemporal availability for requesters. To estimate such availability, the prediction module aims at making accurate travel time predictions by proposing the use of a Long Short-Term Memory (LSTM) network trained using particle swarm optimization (PSO-LSTM). The predicted average travel time is then used to estimate a personalized travel time for users by considering their different driving behaviors. Extensive simulations demonstrate the ability of the proposed framework to achieve significant improvements in its targeted objectives compared to other prominent caching and prediction schemes in vehicular networks. [ABSTRACT FROM AUTHOR]

In a multihop wireless network, the traffic at each node and the channel over each link may fluctuate with time. Thus, traditional optimal resource allocation needs to be computed for each moment with instantaneous information of channel states over all links and the traffic rates at all nodes, leading to huge communication overhead and computation cost. To solve this challenge, in this correspondence, we propose to use robust resource allocation, in which the only needed information is the mean and variance of the wireless channels and the traffic rates. In the formulated problem, there are probabilistic constraints, which are difficult to handle. Effective methods are provided that can transform the probabilistic constraints to convex constraints. As the resource allocation does not need instantaneous channel state information or instantaneous traffic rate information, it is robust to channel and traffic variations, with very little communication and computation overhead. [ABSTRACT FROM AUTHOR]

The explosion of mobile applications and phenomenal adoption of mobile connectivity by end users have generated increasing amounts of mobile data traffic. Recognizing the need of increasing network capacity, cooperative device-to-device (D2D) communications and efficient power allocation have been proposed to address the imperative problem. Existing works mainly focus on relay selection and power control at physical layer. The social connections between mobile users, however, are omitted in consideration of improving the cooperative D2D communication quality. Leveraging social trust, we propose an innovative social-aware energy-efficient relay selection (SERS) mechanism that considers the hidden social ties among mobile users to ensure that more users are willing to participate in the cooperative communications. The proposed SERS takes both social and physical constraints into account to determine the best choice of relay devices. In SERS, we further develop an optimization problem based on game theory, aiming at reducing energy consumption and interference. In the game, social distance is treated as a penalty coefficient and performs distributed control of the transmission power for D2D communications. Simulations based on real-world social network data traces show that SERS achieves a significant performance gain, compared with other relay selection approaches. [ABSTRACT FROM AUTHOR]

In this paper, we propose an efficient analytical method for admission control of wireless virtual networks (VNs), with heterogeneous traffic profiles, and various quality-of-experience (QoE) requirements, in the future software-defined radio access networks. We present a novel methodology for the admission control process that includes feedback information to the VN customers to improve their traffic profile accuracy, and consequently, their QoE. We formulate the virtual network admission control problem as a convex optimization problem which allows general multiple association between user equipment and base stations. Consequently, we propose an algorithm for solving this problem. The proposed method is applicable on heterogeneous networks with heterogeneous traffic distributions. We also propose a number of extensions to the problem including mechanisms that consider minimization of the network and service cost, and optimization according to the backhaul limitations. The simulation results show that our proposed methods are accurate and result in significant improvement in network resource utilization and customer satisfaction. [ABSTRACT FROM PUBLISHER]

Heterogeneous cellular networks (HCNs) are capable of meeting the explosive mobile-traffic demands. However, the conventional base station (BS) deployment strategy is unsuitable for supporting the often unpredictable nonuniform mobile-traffic demands, as governed by the large-scale user behavior (LUB). This results in the inefficient exploitation of the system's resources. In this paper, we develop an analytical framework for characterizing the achievable energy-spectral-efficiency (ESE) of HCNs, which explicitly quantifies the relationship between the network's ESE and the randomly time-varying LUBs as well as other network deployment parameters. Specifically, we model the quantitative impact of the geographical mobile-traffic intensity, the load migration factor, the users’ required service rate and the per-tier BS densities on the achievable ESE of the network, while considering the area-spectral-efficiency requirements. Importantly, a closed-form ESE expression is derived, which enables us to explicitly analyze the properties of the network's ESE. Furthermore, the optimal LUB-aware BS deployment strategy is proposed for maximizing the ESE under specific outage constraints. Using numerical simulations, we verify the accuracy of the analytical ESE expression and quantify the impact of several relevant system parameters on the achievable ESE. Furthermore, we evaluate the achievable ESE performance of the network under diverse time-varying LUB scenarios. Our work, therefore, provides valuable insights for designing future ultradense HCNs. [ABSTRACT FROM PUBLISHER]

Multiuser multiple-input and multiple-output (MU-MIMO) technology is regarded as one of the most promising technologies to cope with the enormous amount of network traffic in wireless local area networks. However, combining uplink and downlink MU-MIMO on the basis of a distributed coordination function causes serious channel resource loss because of collisions between uplink and downlink transmissions. In this paper, we propose a phase-divided medium access control (PD-MAC) protocol, in which a novel integrated frame structure is introduced that allocates two phases for uplink and downlink in a periodic cycle to remove contentions between uplink and downlink transmissions. PD-MAC also adopts an overhead mitigation scheme to reduce control overhead in user selection and employs an algorithm to balance uplink and downlink throughputs. An analytical model is developed to characterize the PD-MAC network throughput. Simulation results show that PD-MAC outperforms the previous unified MAC with regard to network throughput by 21.2%, and that the overhead mitigation scheme improves PD-MAC network throughput by 47.3%. [ABSTRACT FROM PUBLISHER]

For real-time traffic, the link quality and call blocking probability (both derived from coverage probability) are realized to be poor for cell edge users (CEUs) compared to cell center users (CCUs) as the signal reception in the cell center region is better compared to the cell edge region. In heterogeneous networks (HetNets), the uncoordinated channel access by different types of base stations determine the interference statistics that further arbitrates the coverage probability. Thus, the spectrum allocation techniques have major impact on the performance of CCU and CEU. In this paper, the performance of CCUs and CEUs in a random two-tier network is studied for two spectrum allocation techniques namely: 1) co-channel (CSA) and 2) shared (SSA). For performance analysis, the widely accepted conception of modeling the tiers of HetNet using independent homogeneous Poisson point process (PPP) is considered to accommodate the spatial randomness in location of base stations. To incorporate the spatial randomness in the arrival of service and to aid the load-aware analysis, the cellular traffic is modeled using spatio-temporal PPP. Under this scenario, we have developed an analytical framework to evaluate the load-aware performance, including coverage and blocking probabilities, of CCUs and CEUs under both spectrum allocation techniques. Furthermore, we provide insight into achievable area energy efficiency for SSA and CSA. The developed analytical framework is validated through extensive simulations. Next, we demonstrate the impact of traffic load and femto access points density on the performance of CCUs/CEUs under CSA and SSA. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the resource allocation problem in two-tier heterogenous networks (HetNets) with massive MIMO, where two frequency bands, cellular frequency band and millimeter wave frequency band, are used for wireless backhaul links. To coordinate the interference among small cells (SCs), SCs are grouped into multiple SC clusters (SCCs), where SC users are jointly served by SC base stations (BSs) (SBSs) belonging to the same SCC. To eliminate the multi-user and inter-tier interference, we propose a block diagonalization based precoding scheme at macro-BS and each SCC, where the transmit precoding matrix for users is projected onto the null space of interference channels. Following this, we formulate a power allocation optimization problem to maximize the downlink sum rate of the system subject to per-SCC power and users’ quality of service requirements. Since the formulated problem is nonconvex, we transform it into a convex one by appropriate approximation, and a constrained concave convex procedure based iterative algorithm is proposed to obtain the solution. Furthermore, we prove that the obtained solution converges to the local optimum. Meanwhile, according to the structure of the original formulated problem, we divide it into multiple subproblems and propose an optimal iterative water-filling algorithm. Next, we extend the original problem with per-SBS power constraint, which results in that the precoding of each SCC has to be redesigned. On this basis, we propose an iterative water-filling algorithm to obtain the optimal power allocation and precoding. Numerical results are presented to verify the performance of our proposed algorithms. [ABSTRACT FROM PUBLISHER]

Sleep-mode operation of base stations aims to switch OFF some hardware modules to reduce power consumption while not degrading the quality of service. In this paper, novel hotspot-oriented green frameworks based on sleep-mode operation of remote radio heads (RRHs) are proposed for cloud radio access networks (C-RANs). The tradeoff between the reduction in power consumption of RRHs and the increase in transmission power at user equipment (UE) is first analyzed based on realistic models for ultrasmall cell C-RANs. In the proposed energy-efficient frameworks, corresponding clustering strategies are adopted to ensure that active RRHs are located as near as possible to hotspot areas for different infrastructure conditions and information availabilities. This reduces the increase in the uplink transmission power while maximizing the overall RRH power reduction. The green frameworks are modeled using C-RANs based on random topologies. It is shown that area power consumption can be reduced by more than 79% at a low traffic level compared with no sleep-mode operation. One of the frameworks is also compared with a baseline strategy that deals with hotspot areas and shows a 70% reduction in UE transmission power. The pros and cons of applying different frameworks are also investigated and analyzed. [ABSTRACT FROM PUBLISHER]

This paper studies the issues on wireless networks virtualization in terms of two important performance metrics, i.e., energy efficiency (EE) and delay. Different from existing works on physical layer, we aim to achieve a good tradeoff between EE and delay in wireless networks virtualization using cross-layer stochastic optimization approach. In particular, we formulate a cross-layer problem using fractional programming and Lyapunov optimization method. The EE and delay tradeoff solution is given explicitly by deriving their analytical bounds that are verified by simulation results. [ABSTRACT FROM PUBLISHER]

In 3GPP LTE-A releases v.8 and beyond, the plug and play nature of the eNodeBs lets a dense deployment of eNodeBs, thus, causing over-provisioned network infrastructure. Here, while most of the recent studies aim to optimize power consumption on a single traffic type, we provide a novel framework that corresponds both power adjustment and quality of users (QoS) requirements of end-users with multitraffic types. In this manner, we propose a novel energy efficiency coefficient (EEC) considering QoS and channel utilization while reducing power consumption. Moreover, our proposed resource auction module assigns resource blocks to low-utilized cellular networks. Furthermore, the traffic types are modeled with a queuing theoretic approach. We also define an optimization problem that employs novel EEC parameters to determine new power levels (8-levels) for eNodeBs’ configurations with less power consumption. To solve this optimization problem, we introduce a novel heuristic called “Multi Level Branch and Bound Algorithm” (MLBB). MLBB algorithm contains two nested branch and bound algorithms that manipulates end-users differently. Consequently, our proposed methodology serves end-users with 67% better QoS than the conventional mechanisms. [ABSTRACT FROM PUBLISHER]

A heterogeneous network (HetNet) can actively utilize the spectrum reuse with low power consumption, and thus is promising for the next-generation cellular networks. However, there are some technical challenges to be overcome in order for HetNets to be practical, and we address the following two in this paper. One is how to formulate the association and resource scheduling problem in a way that an optimal solution can be found in a reasonable amount of time, and the other is how to accommodate varying users’ demand. In order to minimize the power consumption and to satisfy varying users’ quality of service requirements, we propose a low-complex, distributed association and resource allocation scheme. By taking a cost-based approach, we first separate a nonconvex joint association and resource allocation problem into two subproblems. The channel allocation and base station assignment problem is then relaxed so that the problem becomes tractable. For the power allocation problem, we introduce a low-complex iterative algorithm by using the decomposition theory. The evaluation results show that the proposed solution can maintain the overall power consumption minimized while satisfying the QoS requirements. [ABSTRACT FROM PUBLISHER]

Coordinated multipoint transmission (CoMP) with the joint transmission (JT) scheme is employed in cellular networks to improve data rate and cell-edge throughput and/or to increase system throughput. In CoMP-JT, since the user equipment (UE) is capable of receiving the desired signal from an adjacent cell, as well as from its serving cell, it can achieve an improved signal-to-interference ratio (SIR). However, this scheme entails exhaustion of resources in serving base stations. In this paper, we propose a call admission control scheme (CAC) to improve the performance of CoMP-JT-based cellular systems. In this CAC scheme, the CoMP-JT technique is applied to UEs located near the edge of a cell. To establish an analytical model for CoMP-JT-based cellular systems, we introduce a model for traffic analysis using a 2-D Markov chain and approximate the computation of the power sum of multiple lognormal random components in a multicell environment. Performances of CoMP-JT-based cellular systems are evaluated with respect to two quality-of-service (QoS) constraints pertaining to call-blocking and outage probabilities, respectively, from the network-layer and the physical-layer perspectives. We first measure the resource utilization and call blocking probability for the downlink resources for various offered loads in the cell. Based on that, we obtain the outage probability and effective throughput of the system. The analytical results are compared with computer simulations. Finally, we consider the dynamic point selection (DPS) scheme that is a modified version of the JT scheme, in which some resources of adjacent cells are muted. [ABSTRACT FROM PUBLISHER]

With encounter-based communication introduced in intermittently connected mobile networks (ICMNs), the message dissemination in mobile Internet subscriber/publisher services can be augmented through near-distance communication of mobile nodes. Specifically, mobile nodes with Internet connectivity can help those without to obtain messages once stored and currently carried by the former. We model such a system, particularly considering the time-critical property of messages, the limited communication bandwidth, and the existence of multiple sources. Based on the model, we propose analytical methods for obtaining the performance of message delivery ratio and average delay under the 1-hop or the 2-hop relaying mode specified in this paper, respectively. Through extensive simulations, we validate the proposed methods and discuss system performance under different parameter settings and relaying schemes. [ABSTRACT FROM PUBLISHER]

In this paper, we study the impact of imperfect small-cell positioning with respect to traffic hotspots in cellular networks. To derive the throughput distribution in macrocells and small cells, we first perform static-level analysis of the system considering a nonuniform distribution of user locations. Second, we introduce the dynamics of the system, which is characterized by random arrivals and departures of users after finite service duration, with the service rates and distribution of radio conditions outfitted from the first part of the work. When dealing with the dynamics of the system, macrocells and small cells are modeled by multiclass processor sharing (PS) queues. Macrocells and small cells are assumed to operate in the same bandwidth. Consequently, they are coupled due to the mutual interference generated by each cell to the other. We derive several performance metrics such as the mean flow throughput and the gain, if any, generated from deploying small cells to manage traffic hotspots. Our results show that in the case that the hotspot is near the macro base station (BS), even a perfect positioning of the small cell will not yield improved performance due to the high interference experienced at macro- and small-cell users. However, in case the hotspot is located far enough from the macro-BS, performing errors in small-cell positioning is tolerated (since related results show positive gains), and it is still beneficial in offloading traffic from the congested macrocell. The best performance metrics also depend on several other important factors such as the users' arrival intensity, the capacity of the cell, and the size of the traffic hotspot. [ABSTRACT FROM PUBLISHER]

This paper addresses the power minimization problem subject to a target quality-of-service (QoS) constraint of two-way relay systems with asymmetric traffic requirements using an amplify-and-forward (AF) relaying mode. By transforming the power minimization problem into a two-stage problem and by using the traffic information together with the short-term channel knowledge, an optimum power control (OPC) technique is first proposed, leading to closed-form solutions for individual transmit power at the relay and the sources. Then, by making use of the available diversity of the multiple-relay channel, the joint design of OPC and relay selection (RS) is investigated, eventually resulting in a joint power control and RS (JPCRS) algorithm with two decentralized RS policies for transmit power minimization. Simulation results are provided to validate the derived expressions and confirm the efficiency of the proposed strategies. It is shown that our proposed strategies can significantly reduce the system transmit power, while ensuring the target QoS of the system, and that the proposed RS algorithm is superior to the conventional max–min and max-sum methods in any traffic and/or channel conditions in terms of energy saving. [ABSTRACT FROM PUBLISHER]

To support a tremendous amount of traffic demands via wireless access in 2020 and beyond, limited bandwidth of the licensed bands has been a major obstacle to boosting further the capacity of wireless services. To fundamentally break through this predicament, an emerging technology known as heterogeneous carrier communications has been launched into standardization in the form of licensed-assisted access (LAA) to the unlicensed bands. Integrating the heterogeneous cloud radio access networks and carrier aggregation, and although LAA-empowered cellular networks gain wider bandwidth from the unlicensed bands, communications may suffer from intersystem interference. To avoid interference, listen-before-talk has been designated as a mandatory function; however, it leads to significant challenges of the hidden-terminal problem. To address this open issue in LAA, in this paper, we consequently propose a resource-optimal scheme using a minimum amount of replicated radio resources to achieve the most essential latency guarantees for real-time applications. To further support non-real-time applications, a new resource control as well as the mathematical architecture inspired by so-called political communications is proposed to further maximize the throughput of packet delivery. Our scheme not only optimizes resource utilization in time and spatial domains but also suggests optimum energy efficiency and computation efficiency, to successfully deploy cellular networks on the unlicensed bands. [ABSTRACT FROM PUBLISHER]

Device-to-device (D2D) communication has been recently proposed to reduce cellular traffic by directly connecting the local nodes. In this paper, we consider a cellular-based primary network coexisting with a cognitive D2D pair. The primary network consists of a base station and multiple cellular users, which can sell their spectrum to the D2D user. Additionally, under low-interference conditions, the spectrum can be simultaneously shared between cellular users and D2D-capable users, which is called the nonorthogonal sharing mode. We introduce a double-sided bandwidth-auction game for cognitive D2D communication. In the auction, the D2D transmitter has three types of service providers (SPs) or sharing modes. The SPs operate on different frequency spectra, and a D2D-capable pair intends to share these spectra. This situation is formulated as an auction game, where a D2D transmitter bids a demand price–bandwidth curve, and each SP offers a price–bandwidth supply curve. The Nash equilibrium point of the auction game is analytically obtained. Then, a learning method is proposed for the decision making of the players in an incomplete-information repeated game. Moreover, the convergence of the proposed learning method to the Nash equilibrium point is studied through the converse Lyapunov theorem. Finally, the proposed auction game is extended to the multiple-D2D case, and the optimal bandwidth allocation strategy to maximize the sum rate is derived. [ABSTRACT FROM PUBLISHER]

Bridging between two cognitive personal area networks (CPANs) is a fundamental step toward a reliable and efficient routing protocol. In this paper, we describe a bridging protocol for two-hop cognitive networks that use the transmission tax-based medium access control and propose ways to prioritize bridge traffic over that of ordinary nodes in both CPANs. We develop an analytical model based on probabilistic modeling and queueing theory to evaluate the performance of the bridging protocol. We validate the network performance by analyzing the waiting time of local and nonlocal packets and how the node or bridge transmission is affected by the collision with primary-source activity. Our results provide insights into the impact of various traffic and network parameters on the performance of two-hop bridging. The results indicate that the proposed protocol is effective and efficient when the bridge transfers a moderate amount of traffic. [ABSTRACT FROM PUBLISHER]

With the advances in wireless communication and mobile computing, a future infrastructureless self-organizing traffic information system, where vehicles can form a network for exchanging traffic information among themselves, will soon be realized. In an infrastructureless traffic information system, vehicles will act as mobile sensors and collect the traffic data as they travel. Smartphones are a great choice for traffic sensing devices as they are now equipped with a variety of sensors such as global positioning system (GPS) receivers, accelerometers, gyroscopes, cameras, and microphones. These sensors can be exploited to collect traffic data. Although there are many types of sensors available for traffic sensing, past studies have mainly focused on a GPS receiver. However, a GPS receiver consumes a lot of power; hence, it can significantly shorten the battery life. In this paper, we explore a possibility of using other types of sensors on a smartphone for traffic sensing. In particular, we investigate whether it is possible and how accurate it is to estimate the average speed of a vehicle from the data sensed by an accelerometer. Two estimation methods will be introduced, and their accuracy will be evaluated. [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]

Blocking probability is widely used as a performance measure for dimensioning a variety of networks, including wireless communication systems. However, the performance of the system may be affected by factors other than traffic and resources, i.e., the primary ingredients in blocking. Such factors include interference, energy consumption, service delay restriction, and others. In this case, blocking by itself does not fully convey the extent of the system quality of service (QoS). Those other phenomena may lead the system to experience an outage, in which case resources, even if available, cannot be used because of the performance degradation that this may incur. In this paper, we propose a performance measure, i.e., BlockOut probability, that combines blocking and outage in one parameter. Exact, closed-form, and recursive forms of this parameter are presented, and a simple example of application is shown. The BlockOut probability encompasses the well-known Erlang-B formula as a special case. Although the application example focuses on wireless systems, BlockOut may find use in a variety of other networks. [ABSTRACT FROM PUBLISHER]

Due to the tremendous increase in mobile data traffic, there is a general trend toward the decentralization of mobile operator networks, at least to a certain extent. This shall be further facilitated with the virtualization of mobile network functions and the enabling of mobile cloud networking, whereby mobile networks are created on demand and in a flexible manner. Mobile network decentralization will not be efficient without rethinking mobility management schemes, particularly for users moving for a long distance and/or at a high speed (e.g., vehicles and bullet trains). To support such highly mobile users, this paper introduces: 1) a data anchor gateway (GW) relocation method based on user mobility, history information, and user activity patterns, and 2) a handover management policy that selects a target base station or evolved Node B (eNB) in a way to minimize mobility anchor GW relocation. The performance of the proposed schemes is evaluated via Markov model-based analysis and through simulations. Encouraging results are obtained, validating the design objectives of the scheme. [ABSTRACT FROM PUBLISHER]

Recently, the energy efficiency of a relay network has become a hot research topic in the wireless communication society. In this paper, we investigate the energy efficiency of three basic bidirectional relay transmission schemes [i.e., the four time-slot (4TS), three time-slot (3TS), and two time-slot (2TS) schemes] from the angle of relay deployment. Since a realistic power consumption model is very important in analyzing energy efficiency, and a power amplifier (PA) consumes up to 70% of the total power, we consider a realistic nonideal PA model. The derived closed-form expressions for the optimal relay deployment and the simulation results reveal the following important conclusions. First, it is possible to achieve the optimal energy efficiency and enlarge the cell coverage simultaneously in bad channel conditions, but it may be very challenging in good channel conditions. Second, under asymmetric traffic conditions, particularly when the downlink rate is larger than the uplink rate, all the aforementioned three schemes have almost the same optimal relay deployment, but the 2TS scheme has the highest energy efficiency when the spectral efficiency is large. Third, the relay node should be deployed closer to the base station with the nonideal PA than that with the ideal PA, and the optimal energy efficiency with the nonideal PA is much higher than that with the ideal PA. Moreover, the impact of small-scale fading depends on the value of path loss. To overcome the small-scale fading, the relay network needs to consume more energy. [ABSTRACT FROM PUBLISHER]

Wireless Access in Vehicular Environment (WAVE) dictates primitives for intelligent transportation system (ITS) applications and services. The medium access control (MAC) layer in WAVE facilitates service differentiation. This offers quality of service (QoS) by prioritizing traffic through different access categories (ACs), which are based on application-requested priorities. However, it is oblivious to network load, to delay requirements for ITS safety applications, and to the “severity” of vehicles. In this paper, we propose a novel opportunistic service differentiation (OSD) scheme as an enhancement to WAVE. We define a fuzzy inference system (FIS) to deduce a context severity metric (CSM) that relates the driving behavior of a vehicle to its environment. Our OSD traffic distribution heuristic prioritizes vehicle traffic, with respect to CSM, and accounts for network load and link layer bounds. Furthermore, the OSD scheme guarantees that ACs do not exceed maximum allowable delay for ITS applications. Our methodology entails defining and designing a linear programming (LP) model for verification and validation of the OSD scheme. We perform a comparative study of OSD-enhanced WAVE and classical WAVE analytically and in a vehicular ad hoc network (VANET) simulator. We show that both simulation and analytical results substantiate our claim of improvement in performance of OSD-enhanced WAVE over classical WAVE. [ABSTRACT FROM PUBLISHER]

The 802.11p/WAVE standard relies on the presence of onboard units (OBUs) and roadside units (RSUs) for communications in vehicular networks. In this paper, we study the benefits of deploying RSUs to improve communications in highway scenarios. We develop an analytical model to analyze communication delay in a highway scenario with bidirectional traffic, considering both connected and disconnected RSUs, and validate our model via simulations and experimental measurements with 802.11p equipment. Contrary to conventional wisdom, our results show that significant benefits of RSUs in terms of connectivity and message dissemination can only be achieved when the deployed RSUs are interconnected. Conversely, deploying a large number of disconnected RSUs will lead to little or no benefit in message dissemination delay. [ABSTRACT FROM PUBLISHER]

Multichannel medium-access-control (MAC) protocols have attracted much attention because they possess the ability to boost the capacity of wireless networks. In the literature, a staggered channel model has been proposed to handle the rendezvous problem and improve the bandwidth usage. However, it might cause a channel traffic unbalance (CTU) problem in which certain channels are busy whereas others are idle. It is a great challenge to balance the traffic of each channel because each station finds it difficult to manage the incoming slots in a distributed manner. To cope with the CTU problem, a novel MAC protocol the staggered multichannel traffic-balanced MAC (STB-MAC) protocol, is proposed, which applies the staggered channel model that migrates traffic from busy channels to idle channels. Performance evaluation reveals that the proposed STB-MAC achieves superior performance in network throughput and packet delay. [ABSTRACT FROM PUBLISHER]

A multi-layered satellite network (MLSN) appears to be a promising network for providing global ubiquitous broadband communication. To utilize the abundant network resources of the MLSNs, fair traffic distribution among its satellite layers is, indeed, important. In this paper, we propose a routing method to optimally distribute traffic load among the layers (i.e., the satellite layers in the MLSN). The load balancing scheme of the proposed routing method is developed by adopting a traffic distribution model, which is based upon network capacity estimation and theoretical analysis of the congestion rate in each layer. The performance of the proposed routing method has been validated through extensive computer simulations, which demonstrate that our traffic distribution model is reliable enough to characterize the traffic behavior in the MLSN. Furthermore, in contrast with the basic routing approach, our proposed routing method is more effective in terms of improved throughput and lower packet drops, which are optimized by the theoretical parameter setting. [ABSTRACT FROM PUBLISHER]

The worldwide popularity of wireless local area networks (WLANs) calls for efficient solutions in scheduling multimedia (voice, data, and video) traffic transmissions. Enhanced distributed channel access (EDCA), which is the contention-based channel access function of IEEE 802.11e, is unable to guarantee priority access to higher priority traffic in the presence of significant traffic loads from low-priority users. In this paper, we propose the use of a token- and self-policing-based scheduling scheme, which not only addresses this problem but also prevents bursty video nodes from overusing the medium and tackles the problem of idle time due to large transmission opportunities (TXOPs). [ABSTRACT FROM PUBLISHER]

Telemedicine traffic carries critical information with regard to a patients' condition; hence, it requires the highest transmission priority compared with all other types of traffic in the cellular network. The need for expedited errorless transmission of multimedia telemedicine traffic calls for a guaranteed bandwidth to telemedicine users. This condition, however, creates a tradeoff between the satisfaction of the very strict quality-of-service (QoS) requirements of telemedicine traffic and the loss of this guaranteed bandwidth in the numerous cases when it is left unused due to the infrequent nature of telemedicine traffic. To resolve this complex problem, in this paper, we propose and combine the following two techniques: 1) an adaptive bandwidth reservation scheme based on road map information and on user mobility and 2) a fair scheduling scheme for telemedicine traffic transmission over wireless cellular networks. [ABSTRACT FROM PUBLISHER]

Wireless mesh networking (WMN) is regarded as a low-cost technology for rapid wireless network deployment. However, in a single-channel WMN, the overlapped transmission ranges between relaying mesh points could introduce serious interference. Using multiple radios over multiple channels can decrease the interference and improve the capacity of a WMN, but it increases the cost of a mesh point. One possible solution to balance between interference, hence performance, and cost is utilizing fewer radios that switch among multiple channels instead of using per-channel radios. In this paper, we propose a channel-switching method, called the traffic-aware switching scheme (TRASS), for a mesh point with a limited number of radios. TRASS utilizes the existing IEEE 802.11 mechanisms, i.e., hybrid-coordination-function-controlled channel access and power saving, to avoid packet loss during channel switching. A TRASS mesh point monitors the occupied channel time to schedule radios that switch among channels. The implemented TRASS demonstrates 75% throughput improvement by (2, 1), i.e., two-channel single-radio, over (1, 1). (3, 2) and (3, 1) achieve 69.8% and 39.7%, respectively, of the throughput of (3, 3) in the simulated TRASS. [ABSTRACT FROM PUBLISHER]

The IEEE 802.16 standard adopts a centralized resource-allocation mechanism to poll nodes with three polling modes, i.e., the unicast, multicast, and broadcast polling modes, depending on the residual bandwidth of the base station (BS). In the multicast and broadcast polling modes, the BS uses the truncated binary exponential backoff (TBEB) algorithm as the contention-resolution process (CRP) for mobile nodes to access the wireless network while the traffic load increases up to saturation. The random contention-based TBEB used in the initial ranging and bandwidth request suffers from high collision probability under a high traffic load. TBEB thus significantly degrades the grade of service (GoS), particularly while performing handoff in the mobile (IEEE 802.16e) or multihop relay WiMAX (IEEE 802.16j) networks. Additionally, WiMAX's TBEB exhibits two critical problems. First, TBEB neglects the node priority (i.e., the new or handoff node) and the service flow class (i.e., the real-time or nonreal-time service class); thus, it cannot achieve the optimal network revenue. Second, all different-priority connections immediately transit to the same minimum contention windows (CWs) after winning contentions and then easily lead to high collision probability at succeeding contentions. Therefore, this paper first proposes an efficient contention-resolution algorithm that consists of three key contributions: 1) providing the adaptive minimum–maximum backoff-value algorithm (\AM^2) to partition collision domains; 2) supporting a dynamic waiting-penalty algorithm (DWP) for successful contentions; and 3) differentiating the decrements of CWs (DDW) to avoid collisions, even though the contentions randomly choose the same CW value. Second, we model the proposed approach as a discrete-time Markov chain model and then mathematically analyze several important metrics, i.e., the collision probability, access delay, GoS, and throughput. Numerical results indicate that the analytical results are very close to the simulation results, which justify the accuracy of the analytical model. Additionally, the proposed approach outperforms IEEE 802.16 and all compared approaches in collision probability, delay, GoS, and network throughput. [ABSTRACT FROM PUBLISHER]

Wireless communication has emerged as the most promising and one of the leading sectors of the telecommunications industry in the 21st century. To appreciate the expansion of the wireless sector, in 1990, there were only ten million cellular phone subscribers worldwide that frequently use first-generation technology. Today, there are more than one billion subscribers, and it is expected to increase to more than three billion subscribers during 2007-2010. Attempting to more efficiently use the limited frequency bands available for mobile communications, the idea of overlaying a code-division multiple-access (CDMA) system on an existing narrowband system has been proposed and explored. The basic idea of a CDMA overlay is to allow wideband CDMA waveforms to share a common spectrum with narrowband conventional waveforms to take advantage of the unexploited bandwidth available in the narrowband systems. Theoretically, the separation of CDMA and narrowband waveforms can be accomplished through notch filters. However, the filtering techniques are not sufficient for eliminating the multicross interference problem. In this paper, as a means of reducing the interference that cannot be eliminated by the use of filters, we have introduced a new proposal of an overlaid system in which we reduce the coverage area of the time-division multiple-access (TDMA) interference slots (slots inside the CDMA bandwidth are henceforth cited as cochannel slots). With this new strategy, we significantly reduce the effect of TDMA interference over the CDMA system. [ABSTRACT FROM AUTHOR]

We propose new models for characterizing the cell residence time in a mobile low-Earth-orbit (LEO) satellite cellular network, which, unlike previous models, can accommodate the effect of the Earth's rotation in the teletraffic analysis. The speed of the satellite is typically much higher than that of the mobile; as such, the duration of a cell residence time is finite. Therefore, we use distributions with finite support to model the cell residence time. In particular, we model the residence time in the first (origination) cell with a right-truncated gamma distribution and the residence time in all the other cells with a generalized beta distribution. These distributions have finite support and are sufficiently flexible to accommodate the effects of different system conditions, including the Earth's rotation. To illustrate the use of the proposed models, we study the performance of a mobile LEO satellite cellular network based on the assumption that the residence time in the first cell follows the right-truncated gamma distribution, the residence times in all the other cells follow the generalized beta distribution, and the call duration is gamma distributed. The goodness of the proposed models is validated by computer simulation. [ABSTRACT FROM AUTHOR]

A linear group-wise successive interference canceller in a synchronous code-division multiple-access system (CDMA) is considered in this paper. The proposed hybrid detector that combines successive and parallel cancellation techniques makes use of advantages offered by the two techniques. The convergence of the hybrid interference cancellation (HIC) detector is guaranteed by an adjustable parameter that depends upon the largest eigenvalue of the system's transition matrix. Since the largest eigenvalue is difficult to estimate, an upper bound is necessary for successful convergence. For this reason, a new upper bound for the maximum eigenvalue of the system's transition matrix was developed. Moreover, a new ordering and grouping algorithm that results in a higher convergence speed is proposed. Simulation results show that a significant improvement in performance is obtained using this technique. [ABSTRACT FROM AUTHOR]

The stall of delivering medium access control (MAC) layer data to the upper layer is a serious problem when a negative acknowledgement (NACK) control signal becomes an acknowledgement (ACK) signal, especially for a high-speed mobile terminal during handoff. Stall avoidance mechanisms aim to reduce such the transmission delay and keep in-sequence delivery of the MAC layer data to the upper layer. Recently, for providing high- speed downlink packet access (HSDPA) in the wideband code-division multiple access system, an indicator-based stall avoidance (ISA) mechanism was proposed to remove the nonrecoverable gap in the received out-of-sequence packets. In this paper, we derive the closed-form expression for the gap-processing time of the ISA mechanism when applying the multiprocess stop-and-wait (SAW) hybrid automatic repeat request (HARQ) mechanism. The derived analytical formulas can be used to understand performance tradeoffs between the gap-processing time and throughput in terms of various numbers of users and parallel processes when implementing the multiprocess SAW HARQ mechanism in the HSDPA system. [ABSTRACT FROM AUTHOR]

Multipath transport provides higher usable band- width for a session. It has also been shown to provide load balancing and error resilience for end-to-end multimedia sessions. Two key issues in the use of multiple paths are 1) how to minimize the end-to-end delay, which now includes the delay along the paths and the resequencing delay at the receiver, and 2) how to select paths. This paper presents an analytical framework for the optimal partitioning of real-time multimedia traffic that minimizes the total end-to-end delay. Specifically, it formulates optimal traffic partitioning as a constrained optimization problem using deterministic network calculus and derives its closed-form solution. Compared with previous work, the proposed scheme is simpler to implement and enforce. This analysis also greatly simplifies the solution to the path selection problem as compared to previous efforts. Analytical results show that for a given flow and a set of paths, a minimal subset can be chosen to achieve the minimum end-to-end delay with O(N) time, where N is the number of available paths. The selected path set is optimal in the sense that adding any rejected path to the set will only increase the end-to-end delay. [ABSTRACT FROM AUTHOR]

Resource allocation and call admission control (CAC) are key management functions in future cellular networks, in order to provide multimedia applications to mobiles users with quality of service (QoS) guarantees and efficient resource utilization. In this paper, we propose and analyze a priority based resource sharing scheme for voice/data integrated cellular networks. The unique features of the proposed scheme are that 1) the maximum resource utilization can be achieved, since all the leftover capacity after serving the high priority voice traffic can be utilized by the data traffic; 2) a Markovian model for the proposed scheme is established, which takes account of the complex interaction of voice and data traffic sharing the total resources; 3) optimal CAC parameters for both voice and data calls are determined, from the perspective of minimizing resource requirement and maximizing new call admission rate, respectively; 4) load adaption and bandwidth allocation adjustment policies are proposed for adaptive CAC to cope with traffic load variations in a wireless mobile environment. Numerical results demonstrate that the proposed CAC scheme is able to simultaneously provide satisfactory QOS to both voice and data users and maintain a relatively high resource utilization in a dynamic traffic load environment. The recent measurement-based modeling shows that the Internet data file size follows a lognormal distribution, instead of the exponential distribution used in our analysis. We use computer simulations to demonstrate that the impact of the lognormal distribution can be compensated for by conservatively applying the Markovian analysis results. [ABSTRACT FROM AUTHOR]

In this paper, the authors develop an analytical model to study the performance of a mobile low earth orbiting (LEO) satellite cellular network. The model assumes that the call duration has a gamma distribution and considers the effect of system parameters such as the number of channels per cell, the number of channels reserved for the handoff, and the cell residence time, on the teletraffic performance of the system. The quality of service (QoS) measures studied in this paper include new call blocking probability, handoff failure probability, premature call-termination probability (CTP), and call dropping probability (CDP). Based on the causal central limit theorem, the authors use a two-parameter gamma distribution to approximate the distribution of the sum of the residence times in the cells. The analytical model presented in this paper may be used with any call-holding-time distribution. The analytical results are validated by a computer simulation. [ABSTRACT FROM AUTHOR]

Presents a model describing the mobility of vehicle-borne terminals under realistic urban traffic conditions. Information on the mobility model; Mobility-model validation; Mobility and teletraffic model integration; Conclusion.

Presents proofs for some conjectures on the peakedness of handoff traffic. Variance of the output traffic; Uniqueness of a solution; Conclusion.

Presents teletraffic analysis of hierarchical cellular communication networks. System architecture and multiclass mobility modeling; Description of cell modeling; Performance parameters; Numerical examples and related results; Conclusion.

Presents the location of the mobile traffic distribution by comparing measured field strength samples with predicted field strength values from a radio network planning tool. Relation of the reliability of field strength predictions to the accuracy of mobile traffic distribution; Methods for mobile position detection; Results and discussion.

Examines the teletraffic behavior of code division multiple access (CDMA) cellular networks taking into account CDMA soft capacity and the use of soft handoff between cells. Description of CDMA; Examination of interference; Analysis of call admission control scheme.

Proposes a flexible wireless multimedia communications system where time-division multiple-access (TDMA) and direct sequence code-division multiple access schemes are flexibly selectable according to user's quality of services and channel conditions. Traffic performance of the proposed system; Impact of the access scheme selectability on the traffic performance; Element of the proposed system; Diagram of a TDMA system.

Presents information on a study which focused on the teletraffic behavior of code-division multiple access cellular networks. System and propagation issues; Interference characterization; Outage probability; Numerical examples; Conclusions.

Presents information on a study which evaluated the teletraffic performance of four different handoff priority-oriented channel allocation schemes of personal communication networks. Simulation model; Performance evaluation criteria; Description of the rigid division-based guard channel priority schemes; Results and discussion; Conclusions.