Use Of Directional Antennas Research Articles

Antenna selection and deployment strategies for indoor wireless communication systems

Effective antenna selection and deployment strategies are important for reducing co-channel interference in indoor wireless systems. Low-cost solutions are essential, and strategies that utilise simple (passive) antennas (such as directional patches) are advantageous from this perspective. However, performance is always an issue and the improvements achievable through clever antenna deployment (both placement and orientation) need to be quantified. An experimental investigation of indoor propagation comparing the performance of directional and omni-directional antennas is reported. In the case study of a voice-based indoor communication system employing DS-CDMA radio access technique with BPSK modulation, the outage probability for base stations fitted with directional antennas was observed to change in the −54% to +66% range relative to the omni-directional case. The effective change in the distribution of carrier-to-interference ratios by the use of directional antennas is well established in outdoor micro cellular deployment scenarios; however, the magnitude of the influence is quantified for an indoor environment in this case study. It is also shown that obstacles in the environment can amplify the effectiveness of the antenna deployment by acting as physical cell boundaries that restrict interference. External interference has been shown to cause a significant degradation to the performance of an indoor system when the carrier-to-external-interference ratio. This performance degradation can be minimised by appropriate deployment of directional antennas at the base stations, although the optimum antenna orientations depends on the strength of external interference.

Capacity improvement of wireless ad hoc networks with directional antennae

Network Capacity, which is limited by interference between simultaneous transmissions of neighboring links, is a fundamental performance metric for wireless ad hoc networks. Ref. [1] showed that the capacity of wireless ad hoc networks with omnidirectional antennae does not scale well as the node density increases. Other related work ([2], [3], [4], etc.) demonstrated that the network capacity scales better with the use of directional antennae. Most previous investigations, however, were based on simplified but unrealizable models of antenna patterns. So far, there has not been a general framework for the analysis of network capacity when directional antennae of realizable generic patterns are used. Also, few papers have derived explicitly the impact of nulls and null-width in antenna pattern on network scalability. Specifically, the scale law of network capacity with general directional antennae has not yet been investigated. This paper addresses these issues. We study arbitrary and random networks (corresponding to the best case and random case respectively), where nodes with smart antennae are assumed to be located in a planar disk without mobility. We also point out how to generalize the result to that of generic directional antenna pattern. To conserve space here, we defer detailed analysis of the impact of null-width to the full paper.

Joint optimization of energy consumption and antenna orientation for multicasting in static ad hoc wireless networks

To explore the energy saving advantage offered by the use of directional antennas, we consider the case of source initiated multicast traffic in static ad hoc wireless networks that use switched antennas and have limited energy resources. We present a constraint formulation for the joint optimization problem MEM-AO (minimum-energy multicast and antenna orientation) in terms of MTLP (mixed integer linear programming). The optimal solution can be obtained using an MILP solver in a timely manner for moderately sized networks with switched antennas. In addition to the theoretical effort, we also provide two heuristic algorithms and a general post-process operation TR (tree reconstruction) for handling larger networks. The experimental results show that our TR operation significantly improves the performance of both heuristic algorithms

ACR: an adaptive communication‐aware routing through maximally zone‐disjoint shortest paths in ad hoc wireless networks with directional antenna

AbstractA fundamental problem that distinguishes wireless networks from wired networks is the mutual interference between routes within the proximity of each other. This phenomenon is known as route coupling and it restricts the possibility of occurrence of simultaneous communications along the coupled routes. In this context, the use of directional antenna, having smaller transmission beam‐width compared to omni‐directional antenna, helps to easily decouple interfering routes, and improves network performance through space division multiple access (SDMA). However, even if we have an efficient directional MAC protocol, it alone would not be able to guarantee good system performance, unless we have a proper routing strategy in place that exploits the advantages of directional antenna. So, in this paper, an adaptive routing strategy is proposed that exploits the advantages of directional antenna in ad hoc networks through the selection of maximally zone‐disjoint shortest routes. Zone‐disjoint routes would minimize the effect of route coupling and improve the overall network performance. The proposed strategy ensures effective load balancing and is applied to design and implement both single path and multipath routing protocols in ad hoc networks with directional antennas. Simulation results obtained on QualNet network simulator shows the effectiveness of the proposed routing protocols. Copyright © 2006 John Wiley & Sons, Ltd.

Location-Aware Power-Efficient Directional MAC Protocol in Ad Hoc Networks Using Directional Antenna

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.

Performance analysis for indoor wireless systems employing directional antennas

Using indoor propagation measurements, an investigation of the influence of antenna directivity on the performance of an indoor wireless system is presented. By comparing the path loss data measured from collocated omnidirectional and directional antennas (at different orientations), it is shown that the 'effective' directivity of a directional antenna is heavily dependent on the surrounding environment. Antenna directivity and orientation are shown to influence the level of interference within a system and, therefore, affect overall system performance. Analysis of a simple indoor system with two cochannel base stations showed that the use of directional antennas could either enhance or degrade system performance, relative to a system using omnidirectional antennas. In the best case the use of directional antennas decreased outage probability by 56%, while in the worst case the outage probability increased by 66%.

Near-ground channel measurements over line-of-sight and forested paths

Near-ground radio-wave propagation is of interest for emerging military applications such as battlefield sensor networks and for wireless communication between dismounted soldiers. Narrowband and wideband channel measurement results at 300 and 1900 MHz are presented for near-ground propagation, characterising the effect of antenna heights, radiation patterns and foliage environments. An additional set of channel measurements was performed to study the effect of rain on near-ground propagation at 1900 MHz in a forest environment. Measured power–delay profiles indicate significant multipath propagation with the multipath components becoming stronger relative to the direct path for decreasing antenna heights. In the LOS measurements, the RMS delay spread decreased with the use of directional antennas and increasing antenna heights, and increased with distance. This effect was not evident in the forest measurements, suggesting a larger angle spread of the multipaths. Measurement results indicate that leaves and wet foliage do not contribute significantly to the scattering of radio waves. Foliage effects are more significant at 1900 MHz than 300 MHz. Results from near-ground sensor measurements demonstrate that path-loss varies inversely with the square of the receiving antenna height, as in the plane-Earth and Egli models.

Energy-aware wireless networking with directional antennas: the case of session-based broadcasting and multicasting

We consider ad hoc wireless networks that use directional antennas and have limited energy resources. To explore quantitatively the advantage offered by the use of directional antennas over the case of omnidirectional antennas, we consider the case of connection-oriented multicast traffic. Building upon our prior work on multicasting algorithms, we introduce two protocols that exploit the use of directional antennas and evaluate their performance, We observe significant improvement with respect to the omnidirectional case, in terms of both energy efficiency and network lifetime. Additionally, we show that further substantial increase in the network's lifetime can be achieved by incorporating a simple measure of a node's residual energy into the node's cost function.

A switched dual antenna array for mobile computing networks

The 2.4GHz licence-free ISM band is used extensively for hosting high performance mobile computing networks. The demand for wireless mobile computing networks with high aggregate throughput and channel quality is countered by the high levels of multipath noise in indoor environments. Although the use of directive antennas has shown good results in overcoming the multipath effect, antennas with large directivity cannot be used in a mobile computing network without affecting the functionality of the wireless protocol used. This paper presents a solution to this problem, introducing a dual antenna diversity scheme for the 2.4GHz ISM band and its beam selector circuit for controlling the diversity scheme. The proposed antenna produces an omnidirectional pattern and two directional patterns with very large nulls in their azimuth pattern, while its low complexity and low cost allows easy integration into consumer products.

Calibration of directional antennas and limitations in their use

An error due to a directional antenna calibration on an open area test site (OATS) is discussed with an example of a log-periodic (LP) antenna and the substitution method. It is shown that the accuracy of the calibration may be improved by the distance choice, a directional transmitting antenna (TA) use, calibration on a site of reduced reflection coefficient, and the use of calculated or measured correction factors. The approach may be applied to arbitrary directional antennas. Then, limitations in the use of directional antennas for electromagnetic field (EMF) measurements in the conditions of multipath propagation are discussed, and the concept of an omnidirectional set is presented.

Do phototactic ciliates make use of directional antennas to track the direction of light?

Summary Phototaxis describes the directed movement of motile microorganisms with respect to the direction of light. In ciliates, phototactic orientation has been reported for more than a dozen species. Some, like Stentor and Blepharisma , arc brightly coloured due to their numerous pigment granules. In Chlamydodon , a stigma appears in conjunction with a behavioural change from negative to positive phototaxis. The histophagous ciliates Ophryoglena and Porpostoma , which either possess a watchglass organelle or a composed crystalline organelle, display different phototactic behaviour at different stages of their life cycles. It has been suggested that the characteristic pigments and cell organelles of phototactic ciliates play important roles in the detection of the light direction. Bleached cells with a reduced number of pigment granules, transparent cells without a stigma, and cells that lacked a watchglass organelle due to micromanipulation were found to be little sensitive to light, or showed inaccurate or no phototactic orientation. While the pigment granules of the heterotrichs presumedly contain the photoreceptor molecules mediating photo-orientation, the stigma of Chlamydodon , the watchglass organelle of Ophryoglena , and the composed crystalline organelle of Porpostoma are suspected shading or light reflecting structures. Interacting with the sites of sensory transduction, which should be located in the cell membrane nearby, but are unidentified, conspicuous organelles could be used by the cells as direction-sensitive light detectors.

Slotted ALOHA multihop packet radio networks with directional antennas

The use of directional antennas in multihop packet radio networks using slotted ALOHA access is considered. Tractable approximations to the network performance in terms of expected forward progress are derived. Results show that packet collisions can be strongly reduced already with moderate gain antennas to allow for a substantial increase in network performance.

Throughput of slotted ALOHA channel with multiple antennas and receivers

The performance improvement which can be obtained in a slotted ALOHA channel by the use of directional antennas and multiple receivers is analysed in the letter.