Unmanned aerial vehicles (UAVs) can be deployed efficiently to provide high quality of service for Internet of Things (IoT). By using cooperative communication and relay technologies, a large swarm ...of UAVs can enlarge the effective coverage area of IoT services via multiple relay nodes. However, the low latency service requirement and the dynamic topology of UAV network bring in new challenges for the effective routing optimization among UAVs. In this paper, a layered UAV swarm network architecture is proposed and an optimal number of UAVs is analyzed. Furthermore, a low latency routing algorithm (LLRA) is designed based on the partial location information and the connectivity of the network architecture. Finally, the performance of the proposed LLRA is verified by numerical results, which can decrease the link average delay and improve the packet delivery ratio in contrast to traditional routing algorithms without layered architecture.
In face of the explosive surge of mobile data services, spectrum aggregation or carrier aggregation technology has been proposed to improve system throughput and spectrum efficiency (SE) by ...aggregating licensed and unlicensed spectrum bands. However, the system performances would be severely deteriorated by the channel access collision if the channel access and resource scheduling approaches are not coordinated among different networks in the same spectrum band. Therefore, in order to improve the system throughput and the SE, a fairness-based license-assisted access and resource scheduling scheme are designed for the coexisting systems, incorporating long term evolution-advanced and WiFi systems in the unlicensed band. The optimal sizes of the contention window in the proposed fairness-based channel access approach are obtained in terms of various density ratios between these two systems. Furthermore, a novel resource scheduling approach employing linear programming is proposed to maximize the utility function with the goal of improving the service experience of users and the SE with various spectrum qualities. The theoretical proofs and simulation results verify the enhanced performances of the proposed approaches in terms of key metrics, such as throughput, SE, delay, and packet loss ratio.
As a key sensor for Advanced Driving Assistance System (ADAS), millimeter automotive radar has been a promising candidate for fulfilling tasks including adaptive cruise control and collision ...avoidance. However, the widely deployment of millimeter automotive radars may cause serious mutual interference among vehicles, thus degrading radar ranging performance severely. In this article, we analyze the mutual interference among multiple Frequency Modulated Continuous Wave (FMCW) radars. On one hand, we model the interference precisely by employing Matern Hard-Core Process (MHCP) model to characterize the distribution of vehicle nodes in practical bidirectional two-lane and multi-lane scenarios. Besides, the interference is analyzed in terms of the channel fading, the directional antenna pattern and the fluctuation of the target Radar Cross-Section (RCS) in two-lane and multi-lane scenarios. Besides, we analyze the reflected interference in detail. On the other hand, we evaluate the interference mitigation performance of the Random Frequency Division Multiplexing (RFDM) and Frequency Hopping (FH) approaches in terms of the probability of false detection and miss detection, effective detectable density and maximum number of interference-free radar. Finally, a novel AFH-PM mitigation approach is proposed to further improve the interference mitigation performance, which combines the adaptive FH technology with the binary phase modulation. Simulation results verify the proposed framework for interference analysis by employing Monte Carlo method, and the performance improvement of RFDM, FH and AFH-PM is 6.7 dB, 7.6 dB and 8.2 dB, respectively.
A series of simulations of chemical mechanical polishing (CMP) were conducted to investigate the contact force between abrasive particles and specimens by using the finite element method (FEM). In ...this paper, a micro-contact model, which only involves the mechanical interactions, was set up to simulate the polishing process by changing the processing parameters, including the downward pressure, abrasive size, and polishing speed. Simulation results show that the contact force becomes larger when the downward pressure increases. In addition, when the downward pressure and abrasive size increase, the fluctuation of the contact force becomes large, whereas it declines with decreases in the polishing speed. In addition, corresponding CMP experiments were done to investigate the material removal rate (MRR) and polished average roughness (Ra) under different simulation conditions. Through the establishment of the contact force properties in the simulation and the MRR and Ra in the CMP experiment, qualitative research has been done on the relationship between the contact force in the simulation and experimental results. Experimental results indicate that the MRR and surface roughness are influenced by the contact force. A high MRR can be obtained by a large contact force and dramatic fluctuations can lead to poor surface-finish quality. The investigation contributes to obtaining higher polishing efficiency and lower surface roughness through optimization of the polishing parameters.
Driven by the exponential surge on high data rate services, network operators are facing the challenges of how to enhance the capacity and optimize the coverage in a cost-efficient approach. However, ...traditional network optimization technologies passively adjust the network configurations based on network's congestion ratio, drop-off rate, coverage holes, etc., leading to suboptimum user experiences. Therefore, the objective of this paper is to optimize the network configurations by obtaining the accurate network status, user demand, and application request distribution based on the real-time data. The data mining technique is introduced to predict the resource margin based on historical measurement statistics. To explore the dynamic distribution of user demand and application request, a weighted k-nearest neighbors model is proposed to predict periodic characteristics of network traffics, denoting different temporal and spatial patterns of radio resource margins. In contrast to the traditional passive network optimization approaches, the radio resources can be reconfigured actively to meet the dynamic patterns of traffic loads by using the proposed optimization algorithm. Results prove that the proposed data mining model can capture the dynamics of traffic loads to optimize the traffic load balance and increase the efficiency of radio resource utilization using the network statistic data.
To underpin the predicted growth of the Internet of Things (IoT), a highly scalable, reliable and available connectivity technology will be required. Whilst numerous technologies are available today, ...the industry trend suggests that cellular systems will play a central role in ensuring IoT connectivity globally. With spectrum generally a bottleneck for 3GPP technologies, TV white space (TVWS) approaches are a very promising means to handle the billions of connected devices in a highly flexible, reliable and scalable way. To this end, we propose a cognitive radio enabled TD-LET test-bed to realize the dynamic spectrum management over TVWS. In order to reduce the data acquisition and improve the detection performance, we propose a hybrid framework for the dynamic spectrum management of machine-to-machine networks. In the proposed framework, compressed sensing is implemented with the aim to reduce the sampling rates for wideband spectrum sensing. A noniterative reweighed compressive spectrum sensing algorithm is proposed with the weights being constructed by data from geolocation databases. Finally, the proposed hybrid framework is tested by means of simulated as well as real-world data.
In recent years, flexible sensors based on laser-induced graphene (LIG) have played an important role in areas such as smart healthcare, smart skin, and wearable devices. This paper presents the ...fabrication of flexible sensors based on LIG technology and their applications in human–computer interaction (HCI) systems. Firstly, LIG with a sheet resistance as low as 4.5 Ω per square was generated through direct laser interaction with commercial polyimide (PI) film. The flexible sensors were then fabricated through a one-step method using the as-prepared LIG. The applications of the flexible sensors were demonstrated by an HCI system, which was fabricated through the integration of the flexible sensors and a flexible glove. The as-prepared HCI system could detect the bending motions of different fingers and translate them into the movements of the mouse on the computer screen. At the end of the paper, a demonstration of the HCI system is presented in which words were typed on a computer screen through the bending motion of the fingers. The newly designed LIG-based flexible HCI system can be used by persons with limited mobility to control a virtual keyboard or mouse pointer, thus enhancing their accessibility and independence in the digital realm.
In face of the explosive service demands, solving the problem of spectrum scarcity is becoming more important than ever. To utilize the spectrum resources more thoroughly and efficiently, ...virtualization technologies have been proposed, which can be a means to mitigating resource granularity and increasing efficiency in heterogeneous network environments. In this paper, a traffic-oriented resource virtualization with demand-supply dynamic analysis is proposed for optimized resource allocation of heterogeneous networks with multiple types of services. On the supply side, i.e., the network side, a low-complexity matching game approach is introduced with the novel "Match-Degree" conception, which could be defined with the Grey relational analysis. The complexity of generating preference list can be reduced by unifying various dimensions of network parameters. On the demand side, i.e., the user side, bandwidth allocation algorithm is designed to consider the comprehensive network traffic characteristics, energy consumption, and network price factors, to maximize the overall utility. Except from theoretic analysis, simulation has also been employed to compare the proposed scheme with prior and traditional ones. To further verify the practicability, tractability, and effectiveness of the proposed demand-supply scheme, a test bed is designed and developed in this paper.
To solve the optimal bandwidth allocation problem in heterogeneous radio access networks (H-RANs), a two-level game-theoretic approach is proposed to maximize the utility of network providers and ...users by considering the network resource distributions and service demands. In the area-level game, the Nash equilibrium is achieved by using a noncooperative game for the bandwidth allocation in different areas to maximize network utility. Moreover, in each service area, the traffic-level bandwidth allocation and pricing approach is applied to allocate the appropriate portion of bandwidth for different networks and users using the Stackelberg game, with the network as the leader and the user as the follower. Furthermore, the Stackelberg equilibrium is achieved by an iterative algorithm in this paper. Simulation results prove that the proposed game-theoretic approaches can efficiently and significantly maximize the utility of networks and users.
In this paper, spectrum holes in space-time dimensions are exploited to improve the spectrum utilization of cognitive radio networks (CRNs). To achieve this goal, we design the architecture of three ...regions, which are separately known as the black region, the gray region, and the white region. Temporal spectrum holes exist in the gray region, where secondary users (SUs) can opportunistically access the licensed spectrum with interweave spectrum sharing. In the white region, SUs can exploit spatial spectrum opportunities and transmit at any time by taking advantage of their long distances from the primary users (PUs), without causing severe interference to PUs. Moreover, the existence condition of the transition zone between the gray region and the white region is theoretically analyzed, where power control should be implemented in SUs. Closed-form bounds of three regions are obtained, which can be used in space-time spectrum sensing and access in CRNs. Finally, we provide numerical results to evaluate the relations among the key parameters in the three regions.
PDF
