Multiple directional antennas in suburban ad-hoc networks

Proposing a centralized algorithm to minimize message broadcasting energy in wireless sensor networks using directional antennas

Interference optimization for multicast and broadcast traffics in multi-radio multi-channel WMNs equipped with directional antennas

Exploring the effects of directional antennas on the secure connectivity and hop count of secure multi-hop ad-hoc wireless networks

In this paper, we present simulation results of an all directional transmission and reception algorithm, proposed in Z. Zhang (2005), (named as LiSL/d for a link scheduler) in mobile wireless ad hoc networks with directional antennas. The all-directional algorithms are designed mainly for military applications and exploit the beamforming capabilities of smart antennas to tailor resource access according to the services desired for individual traffic flows while limiting interference, probability of detection and jamming in the network. Specifically, the newly proposed protocol offers four significant advantages: (1) it assumes only directional transmission/reception (no omni-directional or omni-capability is assumed at all), (2) it is distributed, that is, it relies on local information only, (3) it allocates slots to different links dynamically based on demand, (4) power control is easily carried out during neighbor discovery, reservation as well as data transmission period with very little overhead. To evaluate the performance of the proposed algorithms against with IEEE 802.11 omni protocol and the directional virtual carrier sensing (DVCS) protocol, extensive simulations have been conducted in QualNet for the Lakehurst scenario and some random network topologies. Simulation results show that without jamming, both LiSL/d and DVCS improve the network performance by about 3 times and LiSL/d also outperforms DVCS. When there is jamming, depending on the power level of jamming nodes, the percentage of packet received under LiSL/d can be 7 times higher than that of DVCS and IEEE 802.11 with omni-directional antennas

Although directional antennas have been used in mobile communications systems for quite a long time, realistic applications of directional or smart antennas in wireless ad hoc network have emerged just in recent years. Directional antennas provide numerous benefits, such as higher gains, increased transmission range and low interferences. Wireless medium access schemes play a crucial role in ensuring the efficient and fair sharing of wireless resources. Therefore there are many research work on mechanisms at the wireless medium access layer by using directional antennas. The new features of MAC with directional antennas can cause not only location dependent carrier sensing problems, which have appeared in omnidirectional wireless networks, but also novel issues related to directional antennas. In this paper, an introduction of directional antennas is given. We give a classification of the current wireless MAC protocols using directional antennas. We also present different MAC protocols and compare them. This survey discusses the challenges in the design of these MAC protocols.

Directional antennas have numerous advantages over traditional omnidirectional antennas, which include more spatial reuse, extended range, less interference, and less energy consumption. Directional antennas introduce deafness and new hidden terminal problems. Deafness may cause more collisions, and hidden terminal problems may result in more retransmissions, poor quality of service, more energy consumption, and less packet delivery ratio. Hence, it is important to design of an effective medium access protocol specifically for directional antennas in order to reap the benefits of directional antennas while managing deafness and hidden terminal problems, otherwise the challenges can adversely affect system performance. In wireless sensor networks, the sensors are battery powered with limited supply of energy. Therefore, energy efficient protocols and solutions are immensely important with the desired goal of extending the network lifetime longer than what is possible through the omnidirectional antennas. In this thesis, I have proposed an energy efficient scheduled directional medium access control protocol (DTRAMA) which is specially designed for the wireless sensor nodes which use directional antennas in wireless sensor networks. It is a traffic adaptive scheduled medium access protocol in which nodes create their transmission and sleep schedules on the basis of their traffic. Scheduled medium access for packet transmission is used to address the deafness and hidden terminal problems caused by the use of directional communication in contention based MAC protocols. Use of directional antenna reduces interference which indirectly improves packet delivery ratio by improving the signal to noise ratio and by reducing the packet error rate. DTRAMA is energy efficient: firstly because the nodes use directional data communication which requires lower node transmit power than the omnidirectional data communication for the same transmission range; and secondly, because the nodes schedule their sleep period to reduce idle listening and overhearing which improves energy efficiency. In DTRAMA, sleep schedule of the node is traffic adaptive which is essential to maximize the sleep period. The node, by using spatial reuse checks, reuses the wireless medium to the maximum extent to reap the spatial reuse benefits of the directional antenna. The nodes reduce their packet latency through spatial reuse. Through simulation and by using different topologies, I have compared the performance of DTRAMA with those of omnidirectional schedule MAC protocol (TRAMA) and contention based directional MAC protocol (DMAC), which clearly shows that DTRAMA outperforms TRAMA and DMAC in packet delivery ratio and outperforms TRAMA in terms of packet latency.

Directional antennas have numerous advantages over traditional omnidirectional antennas, which include more spatial reuse, extended range, less interference, and less energy consumption. Directional antennas introduce deafness and new hidden terminal problems. Deafness may cause more collisions, and hidden terminal problems may result in more retransmissions, poor quality of service, more energy consumption, and less packet delivery ratio. Hence, it is important to design of an effective medium access protocol specifically for directional antennas in order to reap the benefits of directional antennas while managing deafness and hidden terminal problems, otherwise the challenges can adversely affect system performance. In wireless sensor networks, the sensors are battery powered with limited supply of energy. Therefore, energy efficient protocols and solutions are immensely important with the desired goal of extending the network lifetime longer than what is possible through the omnidirectional antennas. In this thesis, I have proposed an energy efficient scheduled directional medium access control protocol (DTRAMA) which is specially designed for the wireless sensor nodes which use directional antennas in wireless sensor networks. It is a traffic adaptive scheduled medium access protocol in which nodes create their transmission and sleep schedules on the basis of their traffic. Scheduled medium access for packet transmission is used to address the deafness and hidden terminal problems caused by the use of directional communication in contention based MAC protocols. Use of directional antenna reduces interference which indirectly improves packet delivery ratio by improving the signal to noise ratio and by reducing the packet error rate. DTRAMA is energy efficient: firstly because the nodes use directional data communication which requires lower node transmit power than the omnidirectional data communication for the same transmission range; and secondly, because the nodes schedule their sleep period to reduce idle listening and overhearing which improves energy efficiency. In DTRAMA, sleep schedule of the node is traffic adaptive which is essential to maximize the sleep period. The node, by using spatial reuse checks, reuses the wireless medium to the maximum extent to reap the spatial reuse benefits of the directional antenna. The nodes reduce their packet latency through spatial reuse. Through simulation and by using different topologies, I have compared the performance of DTRAMA with those of omnidirectional schedule MAC protocol (TRAMA) and contention based directional MAC protocol (DMAC), which clearly shows that DTRAMA outperforms TRAMA and DMAC in packet delivery ratio and outperforms TRAMA in terms of packet latency.

In cognitive radio ad hoc networks, omni-directional antennas are typically used at both primary users (PUs) and secondary users (SUs), which can cause high interference. We name such cognitive radio ad hoc networks with omni-directional antennas as OMN-CRAHNs. Different from omni-directional antennas, directional antennas can concentrate the transmission on desired directions and can consequently reduce interference in undesired directions. In this paper, we investigate both the local connectivity and the overall connectivity of cognitive radio ad hoc networks with directional antennas (DIR-CRAHNs), in which both PUs and SUs are equipped with directional antennas. In particular, we establish a theoretical framework to analyze both the probability of node isolation and the probability of connectivity of DIR-CRAHNs and OMN-CRAHNs. Our analytical results show that DIR-CRAHNs can have higher connectivity than OMN-CRAHNs.

The objective of this paper is to study the effect and suitability of directionality in near-field microwave head imaging system. To that end, the near-field performances of directional and omnidirectional antennas are compared. The imaging performance comparison is carried out through experimental validation of a realistic artificial head phantom with an emulated brain injury. The results conclude that the directional antenna yields more focused images with low artifacts than the omnidirectional antenna.

Using directional antennas to reduce interference and improve throughput in multihop wireless networks has attracted much attention from the research community in recent years. In this paper, we consider the issue of minimum delay broadcast in multirate wireless mesh networks using directional antennas. We are given a set of mesh routers equipped with directional antennas, one of which is the gateway node and the source of the broadcast. Our objective is to minimize the total transmission delay for all the other nodes to receive a broadcast packet from the source, by determining the set of relay nodes and computing the number and orientations of beams formed by each relay node. We propose a heuristic solution with two steps. Firstly, we construct a broadcast routing tree by defining a new routing metric to select the relay nodes and compute the optimal antenna beams for each relay node. Then, we use a greedy method to make scheduling of concurrent transmissions without causing beam interference. Extensive simulations have demonstrated that our proposed method can reduce the broadcast delay significantly compared with the methods using omnidirectional antennas and single-rate transmission. In addition, the results also show that our method performs better than the method with fixed antenna beams. Copyright © 2012 John Wiley & Sons, Ltd.

Capacity is one fundamental problem in wireless Ad hoc networks. Deploying directional antennas to wireless networks can reduce interference among concurrent transmissions and increase spatial reuse, while the technology of multi-channel can separate concurrent transmissions. Therefore, combining these two technologies into one wireless network is capable of great improvement on the network capacity. Recent studies proposed a multi-channel network architecture that equips each wireless node with multiple directional antennas, which is called MC-MDA network. The capacity in MC-MDA network is derived under arbitrary and random placements. However, they only used a simplified directional antenna model. For approaching the more accurate capacity in real scenario, we consider a hybrid antenna model, which takes the effect of side lobe into account. We derive the capacity upper-bounds of MC-MDA networks in arbitrary and random network with the hybrid model to find the effect of side lobe. We show that the network capacity is closely related to the ratio of the radiuses of side lobe to main lobe. The capacity decreases when the ratio increases. Moreover, we compare the network capacity of MC-MDA using the simplified antenna model with our results.

In this paper, the physical layer for a multi-antenna vehicular communication channel has been investigated considering the effects of antenna types, antennas' orientation and position through a ray-tracing simulation. The simulation software utilized is Wireless InSite® from Remcom Inc. Both static and dynamic scenarios are considered. Multiple transmitters and receivers were spread on the rear, center and front of two vehicles separated by 10m distance. A car with a height more than transmitting and receiving end car was placed in between them to study the vehicular channel behavior in complete Non-Line of Sight (N-LOS) scenarios. To simulate the dynamic scenarios, the response of each receiver with respect to each transmitter was analyzed at a static situation. Then, the entire set up (transmitting, receiving and blocking cars) was moved to a new position, to examine the variation in the Signal to Noise Ratio (SNR) as well as multipath contributions in the changes in channel capacity. Both Omni directional and directional antennas were studied. Different antenna orientations were adopted in the case of directive horn antennas to analyze the effect of antenna directivity on improving the channel efficiency. Furthermore, incorporating the concept of Multiple Input and Multiple Output (MIMO), antenna selection both at the transmitter and receiver sides were used to evaluate the channel capacity of a Vehicle to Vehicle (V2V) communication system in respect to antenna position and car locations.

Directional antennas in wireless sensor networks (WSNs) have several advantages including the enhanced capacity of the network, longer range of transmission, better spatial reuse and lower interference. By enhancing the alleviating contention and the range of communication, the directional antennas improve the performance of WSNs. In common, various methods like localisation, power management, data aggregation and optimisation obtain these advantages in WSNs; however, the reliability requirements and the energy concerns make the antenna technology more advantageous. When compared with methods, in which the directional antennas provide advantages like the extended range of transmission, energy savings, better prevention of wormhole attack, long coverage and high interference tolerance. This review provides a detailed study of recent improvements and open research problems on directional antennas in WSN applications. First, the introduction and the background of directional antennas briefly based on their classification radiation patterns and advantages in directional communication in WSNs. During the past years, a number of directional antennas are designed for the applications of WSNs. In this study, recently developed directional antennas and their applications in WSNs are reviewed. The applications of directional antenna in WSNs are classified into security benefits, localisation, convergecast, contention reduction and energy efficiency.

Device-Free Localization (DfL) exploits the radio signal irregularities, hence can be used as an assistive technology to detect the moving entities, e.g. people, without the need for wearable devices. However, most of DfL systems employ omni-directional antennas, where the localization accuracy of these systems experienced the complex multipath propagation behavior. The directional micro-strip patch antennas have been implemented into the existing DfL system to observe the quality of radio link behavior and its effect to the human indoor localization accuracy. The performance of the proposed system has been evaluated and compared to the existing omni-directional attenuation-based DfL, which usually experienced the complex multipath propagation problem. Result shows that the proposed system was able to accurately detect a human presence in both static and moving scenarios, with a significant improvement in the quality of radio links behavior.

Since the unlicensed 60 GHz band has the extensively wide continuous spectrum and its corresponding millimeter-wave signal has high directivity gain, the 60 GHz band is a good option for the broadband wireless mesh networks. This paper focuses on link scheduling and routing over the 60 GHz multi-channel wireless mesh networks, where each mesh router has multiple radios and multiple directional antennas. We formulate a linear programming based framework, which incorporates multi-channel and multi-radio, directional antenna, and 60 GHz millimeter-wave communications, to model the network throughput of the directional antenna based 60 GHz mesh networks. Under this framework, we derive the solution to the problem of maximizing the network throughput subject to the fairness constraint and the directional-antenna based wireless channel interference constraint. Then, we design a heuristic joint link scheduling and routing scheme which aims at approximately attaining the optimal solution to the joint optimization problem under our proposed framework. We conduct extensive simulations to validate and evaluate our proposed scheme.