Media Access Control (MAC) is critical to guarantee different Quality of Service (QoS) requirements for Unmanned Aerial Vehicle (UAV) networks, such as high reliability for safety packets and high throughput for service packets. Meanwhile, due to their ability to provide lower delay and higher data rates, more UAVs are using frequently directional antennas. However, it is challenging to support different QoS in UAV networks with directional antennas, because of the high mobility of UAV which causes serious channel resource loss. In this paper, we propose CU-MAC which is a MAC protocol for Centralized UAV networks with directional antennas. First, we design a mobility prediction based time-frame optimization scheme to provide reliable broadcast service for safety packets. Then, a traffic prediction based channel allocation scheme is proposed to guarantee the priority of video packets which are the most common service packets nowadays. Simulation results show that compared with other representative protocols, CU-MAC achieves higher reliability for safety packets and improves the throughput of service packets, especially video packets.

Urban area suffers severe multipath effects due to its complex infrastructure environment and sector antenna is a popular choice as a base station antenna in those areas. Within sector antennas, omni cell antenna is utilized as supporting antenna to cover low reception areas between them. This paper proposes a slant 45° dual polarized omnidirectional antenna to operate as the omni cell antenna in those environments. The frequency band covers the IMT band, ranging from 1920MHz to 2170MHz with directivity focusing in horizontal plane. The antenna structure consists of a loop slot antenna array as excitation element which is placed inside a cylindrical slot antenna as parasitic element. Good performance is achieved in both S-parameter and directivity results, with a gain of more than 4 dBi and a gain difference of less than 1.5dB. The measurement results also agree well with the simulation results and the final design confirms that the proposed antenna works effectively as a slant ±45 ° dual polarized omnidirectional antenna.

Sharing perceptual data (e.g., camera and LiDAR data) with other vehicles enhances the traffic safety of autonomous vehicles because it helps vehicles locate other vehicles and pedestrians in their blind spots. Such safety applications require high throughput and short delay, which cannot be achieved by conventional microwave vehicular communication systems. Therefore, millimeter-wave (mmWave) communications are considered to be a key technology for sharing perceptual data because of their wide bandwidth. One of the challenges of data sharing in mmWave communications is broadcasting because narrow-beam directional antennas are used to obtain high gain. Because many vehicles should share their perceptual data to others within a short time frame in order to enlarge the areas that can be perceived based on shared perceptual data, an efficient scheduling for concurrent transmission that improves spatial reuse is required for perceptual data sharing. This paper proposes a data sharing algorithm that employs a graph-based concurrent transmission scheduling. The proposed algorithm realizes concurrent transmission to improve spatial reuse by designing a rule that is utilized to determine if the two pairs of transmitters and receivers interfere with each other by considering the radio propagation characteristics of narrow-beam antennas. A prioritization method that considers the geographical information in perceptual data is also designed to enlarge perceivable areas in situations where data sharing time is limited and not all data can be shared. Simulation results demonstrate that the proposed algorithm doubles the area of the cooperatively perceivable region compared with a conventional algorithm that does not consider mmWave communications because the proposed algorithm achieves high-throughput transmission by improving spatial reuse. The prioritization also enlarges the perceivable region by a maximum of 20%.

This paper improves radiation patterns and impedance matching of a broadband sleeve dipole antenna. A broadband sleeve dipole antenna is designed and the effect of the structure parameters on the |S11| characteristics is calculated. Current distributions of the resonance frequencies are calculated. A broadband sleeve dipole antenna with plate element is proposed. Better impedance matching is obtained by adjusting the size of the plate element. The nulls of the radiation patterns are reduced at high frequencies and the gain in the horizontal direction is improved.

In this paper, we propose a technique to improve the gain of ultra wide-band (UWB) planar antennas by using low profile reflectors based on frequency selective surfaces (FSS). This technique not only enhances the gain of the planar UWB antennas but also guarantees a constant gain with weak variation across the entire UWB while keeping their attractive merits such as planar structure and easy fabrication. An UWB coplanar waveguide (CPW) fed antenna is installed above the proposed reflectors, to prove the effectiveness of the proposed technique. As a result, a constant gain is achieved across a very large bandwidth.

This paper analyzes the impact of directional antennas in improving the transmission capacity, defined as the maximum allowable spatial node density of successful transmissions multiplied by their data rate with a given outage constraint, in wireless networks. We consider the case where the gain Gm for the mainlobe of beamwidth can scale at an arbitrarily large rate. Under the beamwidth scaling model, the transmission capacity is analyzed for all path-loss attenuation regimes for the following two network configurations. In dense networks, in which the spatial node density increases with the antenna gain Gm, the transmission capacity scales as Gm4/α, where α denotes the path-loss exponent. On the other hand, in extended networks of fixed node density, the transmission capacity scales logarithmically in Gm. For comparison, we also show an ideal antenna model where there is no sidelobe beam. In addition, computer simulations are performed, which show trends consistent with our analytical behaviors. Our analysis sheds light on a new understanding of the fundamental limit of outage-constrained ad hoc networks operating in the directional mode.

Directional communications have been considered as a feasible alternative to improve spatial division and throughput in mobile communication environments. In general, directional MAC protocols proposed in the literature rely on channel reservation based on control frames, such as RTS/CTS. Notwithstanding, channel reservation based on control frames increases latency and has an impact on the network throughput. The main contribution of this paper is to propose a channel reservation technique based on pulse/tone signals. The proposed scheme, termed directional pulse/tone channel reservation (DPTCR), allows for efficient channel reservation without resorting to control frames such as RTS and CTS. Theoretical and empirical results show that the proposed scheme has a low probability of failure while providing significant throughput gains. The results show that DPTCR is able to provide throughput improvement up to 158% higher as compared to traditional channel reservation employing RTS/CTS frames.

This letter considers problems with an efficient link layer multicasting technique in a wireless personal area network environment using a directional antenna. First, we propose an adaptive directional multicast scheme (ADMS) for delay-sensitive applications in mmWave WPAN with directional antenna. Second, the proposed ADMS aims to improve throughput as well as satisfy the application-specific delay requirements. We evaluate the performances of legacy Medium Access Control, Life Centric Approach, and adaptive directional multicast schemes via QualNet 5.0. Our results show that the proposed scheme provides better performance in terms of total network throughput, average transmission time, packet delivery ratio and decodable frame ratio.

Wireless sensor networks are comprised of several sensor nodes that communicate via wireless technology. Locating the sensor nodes is a fundamental problem in developing applications for wireless sensor networks. In this paper, we introduce a distributed localization scheme, called the Rectangle Overlapping Approach (ROA), using a mobile beacon with GPS and a directional antenna. The node locations are computed by performing simple operations that rely on the rotation angle and position of the mobile beacon. Simulation results show that the proposed scheme is very efficient and that the node positions can be determined accurately when the beacon follows a random waypoint movement model.

This paper discusses the possibility of deploying a short-range cognitive radio (secondary communication system) within the service area of a primary system. Although the secondary system interferes with the primary system, there are certain locations in the service area of the primary system where the cognitive radio can reuse the frequency of the primary system without causing harmful interference to it and being disturbed by the primary system. These locations are referred to as having a spatial opportunity for communications in the secondary system, since it can reuse the frequency of the primary system. Simulation results indicate that the antenna gain, beamwidth, and propagation path loss greatly affect the spatial opportunity of frequency reuse for the secondary users. The results show that spatial spectrum reuse can be significantly increased when the primary system users are equipped with directional antennas. An important component in this study is the heterogeneous path loss model, i.e., the path loss model within the primary system is different from the model used to calculate the interference between the primary and the secondary systems. Our results show that the propagation models corresponding to the actual antenna heights in the primary/secondary system can largely impact the possibilities for spectrum reuse by the cognitive radios.

Utilizing available channels to improve the network performance is one of the most important targets for the cognitive MAC protocol design. Using antenna technologies is an efficient way to reach this target. Therefore, in this paper, we propose a novel cognitive MAC protocol, called Polarization-based Long-range Communication Directional MAC Protocol (PLRC-DMAC), for Cognitive Ad Hoc Networks (CAHNs). The proposed protocol uses directional antennas to acquire better spatial reuse and establish long-range communication links, which can support more nodes to access the same channel simultaneously. Moreover, the PLRC-DMAC also uses polarization diversity to allow nodes in the CAHN to share the same channel with Primary Users (PUs). Furthermore, we also propose a Long-range Orientation (LRO) algorithm to orient the long-range nodes. Simulation results show that the LRO algorithm can accurately orient the long-range nodes, and the PLRC-DMAC can significantly increase the network throughput as well as reduce the end-to-end delay.

This letter considers power-controlled transmission from directional antennas in mmWave wireless personal area network (WPAN) systems. The attributes of these systems are studied; these include the number of concurrent transmissions and the power consumption with different system parameters, such as the antenna's beamwidth and radiating efficiency. Numerical results are presented to show that the power controlled transmission enables more concurrent transmissions than the non-power controlled transmission. The results also show that the number of concurrent transmissions increases as the beamwidth and the path loss component become smaller and the antenna's radiating efficiency increases. In addition, the power controlled system generally uses less power than the non-power controlled transmission set up; the overall analysis is verified by simulation.

In this paper we analyze the characteristics of vehicle mobility and propose a novel Mobility Prediction Progressive Routing (MP2R) protocol for Inter-Vehicle Communication (IVC) that is based on cross-layer design. MP2R utilizes the additional gain provided by the directional antennas to improve link quality and connectivity; interference is reduced by the directional transmission. Each node learns its own position and speed and that of other nodes, and performs position prediction. (i) With the predicted progress and link quality, the forwarding decision of a packet is locally made, just before the packet is actually transmitted. In addition the load at the forwarder is considered in order to avoid congestion. (ii) The predicted geographic direction is used to control the beam of the directional antenna. The proposed MP2R protocol is especially suitable for forwarding burst traffic in highly mobile environments. Simulation results show that MP2R effectively reduces Packet Error Ratio (PER) compared with both topology-based routing (AODV [1], FSR [2]) and normal progressive routing (NADV [18]) in the IVC scenarios.

The directional MAC protocols improve spatial reuse, but require the exact location of destination and have the problem of deafness. In this paper, we propose a dual-channel MAC protocol with directional antennas for mobile ad-hoc networks. In the proposed MAC protocol, RTS/CTS are sent omnidirectionally as nodes do not have the exact location of the destination in mobile environments. Omnidirectional transmissions on control channel overcome deafness, but have low spatial reuse. We propose a new blocking algorithm to improve spatial reuse on control channel. We use the negative CTS (NCTS) to solve the exposed terminal problem. We confirm throughput of the proposed MAC protocol by simulations using Qualnet ver. 3.8 simulator.

This paper addresses the issue of deafness in MAC (Medium Access Control) protocols for wireless ad hoc networks using directional antennas. Directional antennas are expected to provide significant improvements over omni-directional antennas in ad hoc networks, such as high spatial reuse and range extension. Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for ad hoc networks. However, directional MAC protocols inherently introduce new kinds of problems arising from directivity. One major problem is deafness, caused by a lack of state information of neighbor nodes, whether idle or busy. This paper proposes DMAC/DA (Directional MAC with Deafness Avoidance) to overcome the deafness problem. DMAC/DA modifies the previously proposed MAC protocol, MDA (MAC protocol for Directional Antennas), to reduce the number of control messages and also maintain the ability to handle deafness. In DMAC/DA, WTS (Wait To Send) frames are simultaneously transmitted by the transmitter and the receiver after the successful exchange of directional RTS (Request To Send) and CTS (Clear To Send) to notify the on-going communication to potential transmitters that may experience deafness. The experimental results show that DMAC/DA outperforms existing directional MAC protocols, such as DMAC (Directional MAC) and MDA, in terms of throughput, control overhead and packet drop ratio under the different values of parameters such as the number of flows and the number of beams. In addition, qualitative evaluation of 9 MAC protocols is presented to highlight the difference between DMAC/DA and existing MAC protocols.

Ad hoc DMAC protocols have been proposed to improve spatial reuse, but directional transmissions have the problem of deafness. In the ToneDMAC protocol [9], an omnidirectional out-of-band tone after transmitting DATA or ACK mitigates deafness, but cannot prevent the interference packets caused by retransmissions to node in deafness. In this paper, we propose a dual-tone DMAC protocol with the out-of-band start-tone and stop-tone. In the proposed MAC protocol, a start-tone prevents retransmissions to node in deafness and decreases the packet collision probability. Throughput performance of the proposed MAC protocol is confirmed by simulations using Qualnet ver. 3.8 simulator.

The three beam-switched top-loaded antenna is suited to be applied to a wireless local area network to switch the radiation pattern by arranging several unidirectional antennas. In this paper, a three beam switched top loaded monopole antenna is proposed to realize its small size and planar structure. Three top loaded monopole antennas are arranged around a parasitic hexagonal patch at intervals of 120 degrees. The feed element is selected by the switching device to switch the radiation pattern. This antenna allows for reduction in the number of elements as well as downsizing. The front to back ratio (F/B) becomes 23 dB by selecting suitable parameters.

Use of directional antenna in the context of ad hoc wireless networks can largely reduce radio interference, thereby improving the utilization of wireless medium. Our major contribution in this paper is to devise a MAC protocol that exploits the advantages of directional antenna in ad hoc networks for improved system performance. In this paper, we have illustrated a MAC protocol for ad hoc networks using directional antenna with the objective of effective utilization of the shared wireless medium. In order to implement effective MAC protocol in this context, a node should know how to set its transmission direction to transmit a packet to its neighbors and to avoid transmission in other directions where data communications are already in progress. In this paper, we are proposing a receiver-centric approach for location tracking and MAC protocol, so that, nodes become aware of its neighborhood and also the direction of the nodes for communicating directionally. A node develops its location-awareness from these neighborhood-awareness and direction-awareness. In this context, researchers usually assume that the gain of directional antennas is equal to the gain of corresponding omni-directional antenna. However, for a given amount of input power, the range R with directional antenna will be much larger than that using omni-directional antenna. In this paper, we also propose a two level transmit power control mechanism in order to approximately equalize the transmission range R of an antenna operating at omni-directional and directional mode. This will not only improve medium utilization but also help to conserve the power of the transmitting node during directional transmission. Our proposed directional MAC protocol can be effective in both ITS (Intelligent Transportation System), which we simulate in String and Parallel Topology, and in any community network, which we simulate in Random Topology. The performance evaluation on QualNet network simulator clearly indicates the efficiency of our protocol.

Quality of Service (QoS) provisioning is a new but challenging research area in the field of Mobile Ad hoc Network (MANET) to support multimedia data communication. However, the existing QoS routing protocols in ad hoc network did not consider a major aspect of wireless environment, i.e., mutual interference. Interference between nodes belonging to two or more routes within the proximity of one another causes Route Coupling. This can be avoided by using zone-disjoint routes. Two routes are said to be zone disjoint if data communication over one path does not interfere with the data communication along the other path. In this paper, we have proposed a scheme for supporting priority-based QoS in MANET by classifying the traffic flows in the network into different priority classes and giving different treatment to the flows belonging to different classes during routing so that the high priority flows will achieve best possible throughput. Our objective is to reduce the effect of coupling between routes used by high and low priority traffic by reserving zone of communication. The part of the network, used for high priority data communication, i.e, high priority zone, will be avoided by low priority data through the selection of a different route that is maximally zone-disjoint with respect to high priority zones and which consequently allows contention-free transmission of high priority traffic. The suggested protocol in our paper selects shortest path for high priority traffic and diverse routes for low priority traffic that will minimally interfere with high priority flows, thus reducing the effect of coupling between high and low priority routes. This adaptive, priority-based routing protocol is implemented on Qualnet Simulator using directional antenna to prove the effectiveness of our proposal. The use of directional antenna in our protocol largely reduces the probability of radio interference between communicating hosts compared to omni-directional antenna and improves the overall utilization of the wireless medium in the context of ad hoc wireless network through Space Division Multiple Access (SDMA).

In a wireless home network, shadowing is frequently caused by human bodies or furniture. Therefore, relay transmission function is considered for the hub station in Wireless Homelink when the direct communication of terminals is obstructed. However, in relaying high rate isochronous data such as video streams, the bandwidth resource of Wireless Homelink may be crammed with those data. In this paper, we propose an efficient relay scheme--"Pipeline Repeater" for Wireless Homelink. The proposed scheme spatially multiplexes the relay transfer of the isochronous data using antenna directivity. The Pipeline Repeater can relay the isochronous packets as an efficient use of the limited frequency band, and it can be achieved to repeat the high rate data with delay of only one frame. To verify the proposed scheme, we conduct measurements in some actual home environments, and perform the numerical analyses and computer simulations based on the measurements. Our results confirm the efficiency of the Pipeline Repeater scheme.