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A novel low-profile wideband antenna is proposed with high-gain, high-isolated, and dual-polarized properties. It consists of two mutually-orthogonal bowtie-shaped dipole radiators, four rectangular parasitic elements, and a cylindrical artificial magnetic conductor (AMC) cavity. By introducing parasitic elements, additional resonance is generated, and the bandwidth is widened. The gain is mainly improved by the cylindrical metallic wall and wideband AMC of the cavity. The AMC operates in ±90o reflection phase band-gap bandwidth of 2.35-4.25 GHz, and its equivalent circuit model is developed to understand the working mechanism. The orthogonal placement of two dipole radiators ensures polarization diversity and high isolation. The impacts of various environmental conditions on antenna performance are investigated. To verify the concept of design and demonstrate its excellent performance features, a prototype is fabricated and measured. The proposed wideband antenna has a height of 0.18 wavelength at the center frequency. The measured -10-dB impedance bandwidth is from 2.16 to 3.96 GHz, where the realized gain is 8.34-10.96 dBi and the radiation efficiency is more than 81.8%. High isolation of > 28.65 dB and low envelop correlation coefficient (ECC) of < 2.74 × 10-3 are also achieved between antenna elements. It can be used in the base station for intelligent Internet of Vehicle (IoV) applications, covering the bands of WLAN, WiMAX, Bluetooth, LTE, and 5G sub-6 GHz. [ABSTRACT FROM AUTHOR]

The relevance of vehicle communications in next-generation networks entails the necessity of studying their performance in the framework of upcoming massive architectures. In this regard, a study of the wireless channel between a hybrid massive MIMO BS and a vehicular platform is proposed. Adequate metrics and methodology are provided for the assessment of such scenarios. The impact of different multi-antenna geometries and MIMO architectures in both vehicle and BS is modeled based on a numerical simulation of a realistic urban area. We compare several massive hybrid BS configurations with distinct multi-antenna vehicular rooftop solutions. This paper studies the channel eigenvalues and capacities for sub-6 GHz (3.6 GHz) and millimeter-wave (mmWave) (26 GHz) bands under different propagation conditions. The results suggest that the use of hybrid massive configurations increase the channel capacity by subdividing the massive BS into two or four logical radio channels. It is also shown that the greater available bandwidth at mmWave band can compensate the larger attenuation of radio channels in small size cells. The use of adequate metrics to measure the temporal coherence of the channel is also discussed for the beam switching update. [ABSTRACT FROM AUTHOR]

Recent developments and the ubiquitous availability of wireless technologies and inter-vehicle communication systems are anticipated to lead to the evolution of heterogeneous wireless networks. Based on standards such as the IEEE 802.11, 5G and WiMax, coupled with mobile IP for the content delivery of road safety and infotainment services to drivers over the new generation of vehicular networks. However, the performance of traditional mobility management protocols over vehicular networks is affected by network topology changes and vehicles’ high mobility. Therefore, efficient mobility management solution that mitigates the challenges of vehicles’ mobility is needed. In this paper, we present an adaptive mobility management protocol for predictive hierarchical mobile IPv6 in vehicular networks. We develop a dynamic Mobility Anchor Point (MAP) discovery and selection scheme that adjusts the network topology structure to fit the vehicles’ mobility environment better. Moreover, the predictive handover scheme is based on a multi-observation hidden Markov model, which utilizes the vehicles’ movement projections to estimate the subsequent point of access. The performance of our proposed protocol has been tested using NS-2 and several real and synthetic mobility traces. The results indicate that our protocol exhibits better performance results when compared to well-known handover protocols in reducing the handover latency and packet loss. [ABSTRACT FROM AUTHOR]

Safe and reliable operation of future autonomous vehicles requires ultra-low latency vehicle-to-vehicle (V2V) networking. However, due to scalability issues of purely ad hoc network, vehicle-to-infrastructure (V2I) communication is still in demand. To avoid interference between V2V and V2I communications, conventional network association such as handover may generate a large amount of control and signaling overhead, especially in environments with high-speed mobility and small-coverage access points. Taking the additional latency caused by the overhead into consideration, a vehicle-centric approach is proposed to guarantee the low-latency requirements of the V2V networks. Different from solely optimizing the latency performance, the proposed approach focuses on effectively operating the network association and resources re-allocation. This avoids the massive exchange of control information and signaling and reduces its impact on latency. The proposed framework for V2V networking can underlay different virtual cells with a constrained network association rate and we can derive the corresponding upper bound of the latency performance. Analysis and simulation results indicate that our scheme successfully guarantees the upper bound of the latency and simultaneously constrains the network association rate, thus limiting the additional control exchange and signaling overhead. [ABSTRACT FROM AUTHOR]

The Cucker–Smale flocking model is designed to analyze the velocity and position-control mechanisms in a group of living individuals, such as a flock of birds. In this model, each agent (a bird or fish) adjusts its velocity according to its own velocity and the weighted mean of the relative velocities of the other members of the flock. We herein focus on the simple, distributed, and autonomous nature of the flocking model and apply its operating principles to fair resource allocation for vehicle-mounted mobile relays (VMRs) by considering their need for distributed fair resource allocation in various network topologies. By adaptively adjusting the VMR transmission power, the proposed method effectively alleviates the interference between users in vehicles and users directly connected to the base station. We evaluate the performance of the proposed method in the context of the IEEE 802.16j based system. The achievable bandwidth performance of the proposed method is evaluated relative to that of both the fixed power allocation (FPA) method and the signal-to-interference plus noise ratio (SINR)-based transmit power control method. The result shows that the proposed method adjusts to various network topologies and provides better achievable bandwidth than both the SINR-based method and the FPA method. [ABSTRACT FROM AUTHOR]

Scalable video coding, together with adaptive modulation and coding, is a promising technique for providing real-time video multicast services on mobile stations (MSs) in heterogeneous channel conditions. On the other hand, since MSs are often powered by batteries, reducing the energy consumption of mobile devices is an important concern. In this paper, we study the problem of scalable video multicast scheduling in a mobile worldwide interoperability for microwave access (WiMAX) network with the objective of maximizing the multicast energy throughput. This problem has never been seriously studied when the assumption that different multicast groups may partially overlap is made. We prove that this problem is NP-complete. Our proposed solution, which is called energy-efficient multicast scheduling with adaptive modulation and coding (EEMS-AMC), consists of three modules, namely, online admission control, base-layer data scheduling, and enhancement-layer data scheduling. The admission control rules not only help the base station to admit the maximum number of video streams but ensure that the video data can be delivered to mobile users within the timeliness requirement as well. Moreover, EEMS-AMC adopts the greedy strategy to schedule base-layer data such that even in the worst-case scenario, the average duty cycle of admitted MSs can be within a bounded factor from the theoretical minimum. Finally, EEMS-AMC employs the metric “expected multicast throughput” to derive the proper modulation and coding scheme for each enhancement-layer data and employs the metric “marginal multicast energy throughput” to efficiently derive near-optimal enhancement-layer data scheduling. Simulation results exhibit that EEMS-AMC achieves relatively good performances in terms of multicast energy throughput and normalized total utility. [ABSTRACT FROM AUTHOR]

Small cell networks offer a promising and viable approach to meeting the increasing demand for high-data-rate wireless applications. With the expected increase in the number of small cell deployments, energy efficiency (EE) is a crucial system design parameter that demands consideration from an eco-sustainability perspective. One way to improve EE is to switch off small cell base stations (BSs) or to keep them in energy-saving mode while preserving the quality of service (QoS) experienced by users. With “bits/joule” as the metric, we aim to optimize EE with the introduction of several levels of sleep depths. Using a stochastic geometry-based heterogeneous cellular network (HCN) model, we derive coverage probability, average achievable rate, and EE in heterogeneous $K$-tier wireless networks with different sleep modes for small cells. Then, we try to maximize EE under 1) a random sleeping policy and 2) a strategic sleeping policy, with constraints on both coverage probability and wake-up times. Due to the nonconvexity of EE, we propose an alternative low-complexity near-optimal solution by maximizing the lower bound of EE. We use an alternating iterative approach to solve the resulting multivariable optimization problem. Simulation results confirm the effectiveness of the scheme. With improvements of approximately 30% in EE with random sleeping policy, simulation indicates that instantaneous EE can be further improved by 15% with a strategic sleeping policy. [ABSTRACT FROM AUTHOR]

The heterogeneous network (HetNet) is an important concept for next-generation wireless Internet architecture and Internet of Things, where several wireless technologies can coexist, and the users should have the flexibility to select the connectivity based on the environmental condition and application demands. IEEE 802.11 (or WiFi) and IEEE 802.16 (or WiMAX) are the two primary building block technologies for HetNets because of their sustainability, cost effectiveness, well-deployed architectures, and ability to support high-data-rate wireless communications. The existing literature has extensively studied the interoperability between these two technologies, and seamless handover schemes are designed to support WiFi-WiMAX integration in a HetNet environment. However, effective utilization of these two technologies from the end users' point of view is another important research area. We have the following question: When should a user migrate between these two technologies in a HetNet environment? This paper proposes a handover decision mechanism in a WiFi-WiMAX integrated HetNet environment, which supports the “quality of service” and “quality of experience” requirements of the end users. The effectiveness of the proposed scheme is analyzed using simulation results. [ABSTRACT FROM PUBLISHER]

End users increasingly expect ubiquitous connectivity while on the move. With a variety of wireless access technologies available, we expect to always be connected to the technology that best matches our performance goals and price points. Meanwhile, sophisticated onboard units (OBUs) enable geolocation and complex computation in support of handover. In this paper, we present an overview of vertical handover techniques and propose an algorithm empowered by the IEEE 802.21 standard, which considers the particularities of the vehicular networks (VNs), the surrounding context, the application requirements, the user preferences, and the different available wireless networks [i.e., Wireless Fidelity (Wi-Fi), Worldwide Interoperability for Microwave Access (WiMAX), and Universal Mobile Telecommunications System (UMTS)] to improve users' quality of experience (QoE). Our results demonstrate that our approach, under the considered scenario, is able to meet application requirements while ensuring user preferences are also met. [ABSTRACT FROM PUBLISHER]

Peak-to-average power ratio (PAPR) of orthogonal frequency-division multiplexing (OFDM) may be reduced by reserving several tones to generate a peak-canceling signal (PCS). However, this method suffers from high computational complexity. To address this problem, this paper proposes an algorithm based on peak-windowing residual noise, which is generated by windowing the signal samples that exceed the predetermined threshold. Filtering the residual noise to satisfy tone reservation (TR) constraints and scaling with a scaling factor determined to minimize the out-of-range power generates the PCS. Simulation results show that the proposed algorithm can achieve 6.9-dB PAPR reduction with much lower complexity than other schemes. [ABSTRACT FROM AUTHOR]

Downlink broadcast in LTE-Advanced-(LTE-A) and WiMAX-based relay networks is a crucial service for multimedia delivery. Currently, most research effort goes into devising efficient resource allocation mechanisms to achieve more efficient resource utilization. However, spatial reuse, which is an important technique in improving transmission capacity, has received little attention in the literature. Thus, in this work, we investigate ways of achieving more efficient resource allocation in wireless relay networks via spatial reuse. We first formulate a joint spatial reuse and resource allocation problem as an integer linear programming (ILP) model. We then consider a grouping mechanism in which relay stations (RSs) are grouped together if they do not interfere with each other's transmission signal. RSs in the same group can thus utilize spatial reuse by using the same set of resources to broadcast data. Because of the high computational complexity of the ILP model, we propose a two-phase heuristic solution. In the first phase, the enhanced-resource diminishing principle approach is employed to determine the number of resources required by the base station and a set of selected RSs. In the second phase, a max-coloring algorithm is employed to organize the selected RSs into broadcast groups and then assign the required resources to each group by exploring the maximum advantage of spatial reuse. The simulation results show that the proposed solution improves system performance up to 61%, as compared with two existing mechanisms. [ABSTRACT FROM AUTHOR]

Leveraging multiple wireless technologies and radio access networks (RANs), vehicles on the move have the potential to get robust connectivity and continuous service. To support the demands of as many vehicles as possible, an efficient and fast network selection scheme is critically important to achieve high performance and efficiency. So far, prior works have primarily focused on design of optimization algorithms and utility functions for either user or network performance. Most such studies do not address the complexities involved in the acquisition of needed information and the execution of algorithms, making them unsuitable for practical implementations in vehicles. This paper proposes a fast cloud-based network selection scheme for vehicular networks. By leveraging a compute cloud's abundant computing and data storage resources, vehicles can leverage wider scope network information for decision-making. Vehicles select best access networks through a coalition formation game approach. A one-iteration fast convergence algorithm is proposed to achieve the final state of coalition structure in the game. Through extensive simulation, the proposed network selection scheme was shown to balance system throughput and fairness with a built-in utility division rule of the framework. The algorithm efficiency showed eightfold enhancement over a conventional coalition formation algorithm. Such features validate the potential of implementation in practice. [ABSTRACT FROM AUTHOR]

This paper proposes an effective real-time video uplink (UL) framework for mobile wireless camera networks (WCN) over an orthogonal frequency-division multiple access (OFDMA), based infrastructure. Mobile wireless camera stations (CSs) transmit their videos in real time to a base station (BS) so that these live video streams can be archived or fed to subscribers to facilitate real-time video monitoring. Based on the utility function driven by video quality, the target bit rate resulting in the highest possible utility is quickly set for each UL video. To optimize system performance, a real-time video packet scheduler and a spectral-efficient resource-allocation policy are derived. This scheduler is also capable of exploiting the inherent diversity gain due to channel variations. Using fourth-generation (4G) mobile network protocols and a realistic wireless channel model, it is demonstrated through our extensive simulations that our proposed method can significantly enhance utility, boost spectral efficiency, and stabilize video quality. [ABSTRACT FROM PUBLISHER]

A generalized and autonomous discontinuous reception (DRX) scheme, which is applicable to both Third-Generation Partnership Project (3GPP) and IEEE 802.16e standards, is analyzed by two-level Markov chain modeling, along with the European Telecommunications Standards Institute (ETSI) packet traffic model. Numerical analysis showed that this scheme is capable of autonomously adjusting the DRX cycle to keep up with changing user equipment activity level with no signaling overhead increase, thus producing a better tuned DRX operation. Quantitative comparison with the power-saving schemes of 3GPP and 802.16e standards demonstrated that the autonomous DRX scheme is advantageous over these power-saving schemes. [ABSTRACT FROM PUBLISHER]

In recent years, application-layer forward error correction (AL-FEC), particularly rateless AL-FEC, has received much attention due to its superior performance in both transmissional and computational efficiency. Rateless AL-FEC (e.g., Raptor code or Luby transform (LT) code) can protect a large data block with an overhead somewhat close to ideal codes. In the meantime, its data processing rates of both encoding and decoding are quite efficient even in software implementations. However, we found that conventional rateless AL-FEC schemes may not be the best candidates when considering streaming over Worldwide Interoperability for Microwave Access (WiMAX) networks for high-speed rail reception in Taiwan. In this paper, we propose a new ideal AL-FEC scheme based on the Chinese remainder theorem (CRT) to facilitate streaming service delivery for high-speed rail reception. The proposed scheme can support the rateless property, but it requires less transmission overhead than conventional rateless codes. Although it requires higher computational cost than conventional rateless codes, the cost is affordable for commodity laptops. In addition to measuring the FEC computation, storage, and decoder overhead, we also evaluate its performance in an emulation environment for simulating high-speed rail reception over WiMAX networks. The emulation result shows that the proposed scheme can achieve the same error protection as Raptor codes, but it requires less transmission overhead, which is suitable for protecting data transmission over bandwidth-limited high-mobility erasure channels. [ABSTRACT FROM PUBLISHER]

Vehicular communications have received a great deal of attention in recent years due to the demand for multimedia applications during travel and for improvements in safety. Safety applications often require fast message exchanges but do not use much bandwidth. On the other hand, multimedia services require high bandwidth for vehicular users. Hence, to provide mobile broadband services at a vehicular speed of up to 350 km/h, Worldwide interoperable for Microwave Access (WiMAX) and Long-Term Evolution (LTE) are considered the best technologies for vehicular networks. WiMAX and LTE are Fourth-Generation (4G) wireless technologies that have well-defined quality of service (QoS) and security architectures. However, some security threats, such as denial of service (DoS), an introduction of rogue node, etc., still exist in WiMAX and LTE networks, particularly in multihop networks. Therefore, strong security architecture and hasty authentication methods are needed to mitigate the existing security threats in 4G multihop wireless networks. Conversely, the network QoS should not be degraded while enhancing security. Thus, we propose QoS-aware distributed security architecture using the elliptic curve Diffie–Hellman (ECDH) protocol that has proven security strength and low overhead for 4G wireless networks. In this paper, we first describe the current security standards and security threats in WiMAX and LTE networks. Then, the proposed distributed security architecture for 4G multihop wireless networks is presented. Finally, we compare and analyze the proposed solution using testbed implementation and simulation approaches for WiMAX. From the simulation and testbed results for WiMAX networks, it is evident that the proposed scheme provides strong security and hasty authentication for handover users without affecting the QoS performance. For LTE networks, we present the theoretical analysis of the proposed scheme to show that similar performance can also be achieved. [ABSTRACT FROM PUBLISHER]