Multiple Directional Antennas Research Articles

Robust Connectivity With Multiple Directional Antennas for Vehicular Communications

For critical vehicular communication services, such as traffic safety and traffic efficiency, it is advisable to design systems with robustness as the main criteria, possibly at the price of reduced peak performance and efficiency. We describe a simple, low-cost method for combining the output of L directional (i.e., not omnidirectional) antennas to the input of a single-port receiver with the aim to guarantee robustness, i.e., to minimize the probability that K consecutive packets arriving from the worst-case angle-of-arrival are decoded incorrectly. To minimize complexity, the combining network does not estimate or use channel state information. The combining network consists of L - 1 analog phase shifters whose phases are affine functions of time. For a general L ≤ K and when the packet error probability decays exponentially with the received SNR, the optimum slopes of the affine functions can be computed by solving an optimization problem that depends on the antenna far-field functions. We provide analytical solutions for the special case of L = 2 and 3 antennas, which turns out to be independent of the antenna far-field functions and placement on a vehicle. In an experimental setup consisting of two monopole antennas mounted on the roof of a Volvo XC90, the proposed combining method is shown to give significant performance gains, compared to using any one of the antennas.

Adaptive Direction Control for UAV Full-Duplex Relay Networks Using Multiple Directional Antennas

We consider a UAV (Unmanned Aerial Vehicle) relay network whereby each UAV senses data and forwards it to dedicated ground stations by means of multi-hop relaying. In particular, we focus on a UAV relay network with a simple yet realistic linear topology for which we propose an adaptive direction control scheme to achieve a high throughput performance. In the proposed scheme, each UAV, equipped with multiple directional antennas, selects either the Decode-and-Forward (DF) straight relaying method or the orthogonal relaying method, for full-duplex data transfer, i.e., data is transmitted and received simultaneously on the same frequency, but at different antennas. The originality of our proposed method is to make each UAV rotate relatively to the position of its neighbouring UAVs, in order to optimize its antenna radiation direction, according to the selected relaying method. The key advantage of the proposed method is that signal direction can be controlled without the need of heavy adaptive signal processing as in conventional beamforming techniques. In order to clarify the decision parameters for selecting a relaying method, we first evaluate the throughput performance of the two-hop relay network under the severe interference conditions of UAV networks, and next, propose a procedure for selecting a multihop relaying method. Numerical experiments show that the proposed scheme enables to achieve a high throughput performance, with low computational costs.

A Novel Distributed Pseudo-TDMA Channel Access Protocol for Multi-Transmit-Receive Wireless Mesh Networks

Wireless Mesh Networks (WMNs) technology has been used in recent years for broadband access in both cities and rural areas. A key development is to equip routers with multiple directional antennas so that these routers can transmit to, or receive from multiple neighbors simultaneously. The Multi-Transmit-Receive (MTR) feature can boost network capacity significantly if suitable scheduling policy is applied. In this paper, we propose a distributed link scheduler called PCP-TDMA that fully utilizes the MTR capability. In particular, it activates every link at least once within the shortest period of time. We evaluated the performance of PCP-TDMA in various network topologies, and compared it against a centralized algorithm called ALGO-2, and two distributed approaches: JazzyMAC and ROMA. The results show that PCP-TDMA achieves similar performance with the centralized algorithm in all scenarios, and outperforms the distributed approaches significantly. Specifically, in a fully connected network, the resulting superframe length of PCP-TDMA is less than 1/3 and 1/2 of JazzyMAC and ROMA, respectively.

Channel assignment, link scheduling, routing, and rate control for multi-channel wireless mesh networks with directional antennas

The wireless mesh network (WMN) has attracted significant interests as a broadband wireless network to provide ubiquitous wireless access for broadband services. Especially with incorporating multiple orthogonal channels and multiple directional antennas into the WMN, each node can communicate with its neighbor nodes simultaneously without interference between them. However, as we allow more freedom, we need a more sophisticated algorithm to fully utilize it and developing such an algorithm is not easy in general. In this paper, we study a joint channel assignment, link scheduling, routing, and rate control problem for the WMN with multiple orthogonal channels and multiple directional antennas. This problem is inherently hard to solve, since the problem is formulated as a mixed integer nonlinear problem (MINLP). However, despite of its inherent difficulty, we develop an algorithm to solve the problem by using the generalized Benders decomposition approach [2]. The simulation results show the proposed algorithm provides the optimal solution to maximize the network utility, which is defined as the sum of utilities of all sessions.

An efficient multi-channel MAC protocol for wireless ad hoc networks

IEEE 802.11 MAC is designed for single channel and based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA). The throughput of network is limited by the bandwidth of the single channel and the CSMA-based MAC protocol with omnidirectional antennas can cause the serious unfairness or flow starvation. By exploiting the multiple channels and using the directional antennas, nodes located in each other’s vicinity may communicate simultaneously. This helps to increase the spatial reuse of the wireless channel and thus increase the network performance. In this paper, we propose a Multi-channel MAC protocol with Directional Antennas (MMAC-DA) that adopts IEEE 802.11 Power Saving Mechanism (PSM) and exploits multiple channel resources and directional antennas. Nodes have to exchange control packets during the Announcement Traffic Indication Message (ATIM) window to select data channels and determine the beam directions which are used to exchange data packets during the data window. The simulation results show that MMAC-DA can improve the network performance in terms of aggregate throughput, packet delivery ratio, energy efficiency and fairness index.

English

In wireless telecommunication, the network consists of a broadcast server with a set of clients. It sends a group of information to the clients in a desired closed loop path. According to the information send by the broadcasting server the clients access it this should be happen in a cyclic path. In olden days we use fixed directional antennas for transmitting the signal from one place to another. Due to some drawback over the existing one we use multiple directional antennas at the Broadcast Server has been shown to increase performance. In many cases however, such broadcasting systems fail to exploit the full potential of the multiple antennas as they do not take into account the geographical distribution of clients within the coverage area of the system. In this project we are proposes an adaptive smart antenna based wireless push system where the beam width of each smart antenna is altered based on the current placement of clients within the system area. Coupled with a modification of the broadcast schedule, the proposed approach significantly increases the performance observed by the system clients..

A Novel Multi-channel MAC Protocol for Directional Antennas in Ad Hoc Networks

In recent years, the employment of directional antennas in ad hoc networks has increased significantly. In this paper, we propose a multi-channel MAC protocol for directional antennas (MCMDA) for IEEE 802.11 based ad hoc networks. To improve the network performance, the so-called hidden terminals and deafness should be decreased as much as possible. In MCMDA, not only multiple channels are effectively utilized but also vertically opposite clear-to-send is employed to minimize the effects of hidden terminals and deafness. Each node is equipped with multiple interfaces for multiple directional antennas such that concurrent transmissions and receptions take place in a node at the same time, resulting in further improvement of the network capacity. The performance study based on extensive computer simulation shows that the proposed MCMDA achieves significant performance improvement in comparison to the conventional directional MAC as well as IEEE 802.11 distributed coordination function in terms of network throughput and end-to-end delay.

A Geometric Deployment and Routing Scheme for Directional Wireless Mesh Networks

This paper first envisions the advent of the wireless mesh networks with multiple radios and directional antennas in future. Then, based on the observation that simplicity induces efficiency and scalability, the paper proposes a joint geometric deployment and routing strategy for such mesh networks, and also gives a concrete approach under this strategy. The main idea of this strategy is to deploy mesh networks in certain kind of geometric graph, and then design a geometric routing protocol by exploiting the routing properties of this graph. The proposed concrete approach comprises two parts: (1) a topology generation algorithm based on Delaunay triangulations and (2) a geometric routing protocol based on the greedy forwarding algorithm. Both parts are characterized by simplicity and appealing properties, with formal proofs provided when possible. The simulation results validate our proposed approach.

On Capacity of Wireless Networks Using Practical Directional Antennas

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.

On Performance Improvement of Wireless Push Systems via Smart Antennas

In environments with locality of client demands, the use of multiple directional antennas at the Broadcast Server has been shown to increase performance. In many cases however, such broadcasting systems fail to exploit the full potential of the multiple antennas as they do not take into account the geographical distribution of clients within the coverage area of the system. This letter proposes an adaptive smart antenna-based wireless push system where the beamwidth of each smart antenna is altered based on the current placement of clients within the system area. Coupled with a modification of the broadcast schedule, the proposed approach significantly increases the performance observed by the system clients.

Transmission scheduling for wireless mesh network systems equipped with multiple directional antennas

All existing broadcast scheduling algorithms (BSAs) were designed for omnidirectional antenna (OA) packet radio (PR) nodes of a wireless mesh network (WMN). However, when WMN nodes are equipped with multiple directional antennas (DAs), a signal sent from a neighboring node may be received by more than one DA of the receiving node, and some nodes may receive signals from multiple DAs sent from the same node. When existing OA BSAs are used for scheduling transmission time-slots in time division multiple access (TDMA), due to the multiple DA signal detection phenomenon a weak performance in average time delay and channel utilization is obtained. Therefore, a novel transmission scheduling algorithm (TSA) for WMN nodes equipped with multiple DAs is proposed. Simulation results demonstrate that a significant performance gain can be obtained from using the proposed DA-TSA scheme.

Multi‐channel power‐controlled directional MAC for wireless mesh networks

AbstractWireless Mesh Networks (WMNs) have emerged recently as a technology for providing high‐speed last mile connectivity in next‐generation wireless networks. Several MAC protocols that exploit multiple channels and directional antennas have been proposed in the literature to increase the performance of WMNs. However, while these techniques can improve the wireless medium utilization by reducing radio interference and the impact of the exposed nodes problem, they can also exacerbate the hidden nodes problem. Therefore, efficient MAC protocols need to be carefully designed to fully exploit the features offered by multiple channels and directional antennas.In this paper we propose a novel Multi‐Channel Power‐Controlled Directional MAC protocol (MPCD‐MAC) for nodes equipped with multiple network interfaces and directional antennas. MPCD‐MAC uses the standard RTS‐CTS‐DATA‐ACK exchange procedure. The novel difference is the transmission of the RTS and CTS packets in all directions on a separate control channel, while the DATA and ACK packets are transmitted only directionally on an available data channel at the minimum required power, taking into account the interference generated on already active connections.This solution spreads the information on wireless medium reservation (RTS/CTS) to the largest set of neighbors, while data transfers take place directionally on separate channels to increase spatial reuse. Furthermore, power control is used to limit the interference produced over active nodes.We measure the performance of MPCD‐MAC by simulation of several realistic network scenarios, and we compare it with other approaches proposed in the literature. The results show that our scheme increases considerably both the total traffic accepted by the network and the fairness among competing connections. Copyright © 2010 John Wiley & Sons, Ltd.

Multiple-Antenna Data Broadcasting for Environments With Locality of Demand

Data broadcasting is an efficient way of delivering data to mobile clients having a high degree of commonality in their demand patterns. This paper proposes the use of multiple directional antennas to increase the performance of an adaptive wireless push system in environments that are characterized by the locality of client demands. Simulation results reveal that using up to three antennas suffices for a significant performance increase over the single-antenna adaptive wireless push system.

Uplink analysis with mobile devices using directional-smart antennas

ne of the main challenges of today's networking is how to increase the capacity of wireless data networks. Given the inherent limitations of radio frequency (RF) transmission capacity, a promising approach is to divide the 2D/3D space into multiple subspaces and to apply spatial channel reuse, which has the potential: (1) to increase aggregate system capacity, (2) to increase the wireless transmission range, (3) to reduce signal-to-noise and signal-to-interference ratio (SNR/SIR), (4) to reduce fading and (5) to reduce power consumption. This paper focuses on how using switched-beam antenna, on mobile devices (stations), can improve wireless communications. Specifically, we study the potential benefit of using a selected one of a multiple flat panel directional antennas, where the antenna selection is performed dynamically packet-by-packet. The initial results are promising and show significant improvements of various aspects of the wireless system performance.

Design algorithms for multihop packet radio networks with multiple directional antennas stations

A protocol called the simple tone sense (STS) protocol is designed for multihop packet radio networks (PRNs) with multiple directional antennas stations. The protocol can minimize transmission interference by using a group of tones to identify the active neighbors. A variation of the STS protocol called the variable power tone sense (VPTS) protocol is also designed to further reduce interference. Algorithms for assigning tones and for determining the orientation and broadcasting angles of the directional antennas are designed. Design examples are given. Simulation result shows that the STS protocol gives better throughput-delay performance than the busy-tone multiple access protocol, especially when the traffic is heavy. The VPTS protocol gives still better throughput-delay performance than the STS protocol. >

A slotted ALOHA packet radio system with multiple antennas and receivers

The problem of data transmission in a mobile packet radio system with one central base station and a number of mobile terminals is addressed. A method using multiple directional antennas and receivers at the base station to improve the efficiency of transmission on the inbound channel (from the terminals to the base station) is proposed. A number of channel models are considered, including flat terrestrial propagation loss, Rayleigh fading, and noise. A finite population Markov model is used to obtain the throughput of a multiantenna and multireceiver slotted ALOHA system. Numerical results indicate that substantial gains are possible with the use of several antennas and receivers. The dynamic behavior of the system is also improved. >

Slotted ALOHA for multihop packet radio networks with multiple-directional-antenna stations

The slotted ALOHA protocol is modified to accommodate stations with multiple directional antennas in a multihop packet radio network environment. The one-hop throughput is derived for both the Poisson station distribution and the deterministic lattice station distribution. Numerical results show that the throughput values are very close for the two distributions. If the number of stations in the transmission circle is fairly large, say 50, the throughput gain using directional antennas could be as large as the number of directional antennas used.