Results 11 - 20 of 105

Effect of Antenna Placement and Diversity on Vehicular Network Communications

by S. Kaul, K. Ramachandran, P. Shankar, S. Oh, M. Gruteser, I. Seskar, T. Nadeem
"... In this paper we present empirical results from a study examining the effects of antenna diversity and placement on vehicle-to-vehicle link performance in vehicular ad hoc networks. The experiments use roofand in-vehicle mounted omni-directional antennas and IEEE 802.11a radios operating in the 5GH ..."
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In this paper we present empirical results from a study examining the effects of antenna diversity and placement on vehicle-to-vehicle link performance in vehicular ad hoc networks. The experiments use roofand in-vehicle mounted omni-directional antennas and IEEE 802.11a radios operating in the 5GHz band, which is of interest for planned inter-vehicular communication standards. Our main findings are two-fold. First, we show that radio reception performance is sensitive to antenna placement in the 5Ghz band. Second, our results show that, surprisingly, a packet level selection diversity scheme using multiple antennas and radios, Multi-Radio Packet Selection (MRPS), improves performance not only in a fading channel but also in line-of-sight conditions. This is due to propagation being affected by car geometry, leading to the highly non-uniform antenna patterns. These patterns are very sensitive to the exact antenna position on the roof, for example at a transmit power of 40mW the line-of-sight communication range varied between 50 and 250m depending on the orientation of the cars. These findings have implications for vehicular MAC protocol design. Protocols may have to cope with an increased number of hidden nodes due to the directional antenna patterns. However, car makers can reduce these effects through careful antenna placement and diversity.

1 Interference analysis for highly directional 60 GHz mesh networks: the case for rethinking medium

by Sumit Singh, Raghuraman Mudumbai, Upamanyu Madhow , 2010
"... access control ..."
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access control
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A survey on mac protocols for ad hoc networks with directional antennas

by Robert Vilzmann, Christian Bettstetter - In EUNICE Open European Summer School , 2005
"... Abstract — The application of directional antennas in the mobile devices of wireless ad hoc networks has the potential to increase the network connectivity and capacity. However, new solutions for medium access control (MAC) are needed. This paper provides a survey and overview of recently proposed ..."
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Abstract — The application of directional antennas in the mobile devices of wireless ad hoc networks has the potential to increase the network connectivity and capacity. However, new solutions for medium access control (MAC) are needed. This paper provides a survey and overview of recently proposed MAC protocols for this scenario. We summarize problems specific to this setup and categorize proposed protocols. Index Terms — Ad hoc networking, medium access, directional antennas, beamforming I.
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1 Blockage and Directivity in 60 GHz Wireless Personal Area Networks: From Cross-Layer Model to Multihop MAC

by Sumit Singh, Student Member, Federico Ziliotto, Upamanyu Madhow, Elizabeth M. Belding, Senior Member, Mark Rodwell
"... Abstract—We present a cross-layer modeling and design approach for multiGigabit indoor wireless personal area networks (WPANs) utilizing the unlicensed millimeter (mm) wave spectrum in the 60 GHz band. Our approach accounts for the following two characteristics that sharply distinguish mm wave netwo ..."
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Abstract—We present a cross-layer modeling and design approach for multiGigabit indoor wireless personal area networks (WPANs) utilizing the unlicensed millimeter (mm) wave spectrum in the 60 GHz band. Our approach accounts for the following two characteristics that sharply distinguish mm wave networking from that at lower carrier frequencies. First, mm wave links are inherently directional: directivity is required to overcome the higher path loss at smaller wavelengths, and it is feasible with compact, low-cost circuit board antenna arrays. Second, indoor mm wave links are highly susceptible to blockage because of the limited ability to diffract around obstacles such as the human body and furniture. We develop a diffraction-based model to determine network link connectivity as a function of the locations of stationary and moving obstacles. For a centralized WPAN controlled by an access point, it is shown that multihop communication, with the introduction of a small number of relay nodes, is effective in maintaining network connectivity in scenarios where single-hop communication would suffer unacceptable outages. The proposed multihop MAC protocol accounts for the fact that every link in the WPAN is highly directional, and is shown, using packet level simulations, to maintain high network utilization with low overhead. Index Terms—Wireless personal area networks (WPAN), Millimeter wave WPANs, Millimeter wave propagation, 60 GHz networks, Medium Access Control (MAC). I.
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A Reliable Wireless Network Architecture

by Chaegwon Lim, Haiyun Luo, Chong-ho Choi - in Proc. IEEE ICNP’06 , 2006
"... Abstract — Despite years of research and development, pioneering deployments of multihop wireless networks have not proven successful. The performance of routing and transport is often unstable due to contention-induced packet losses, especially when the network is large and the offered load is high ..."
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Abstract — Despite years of research and development, pioneering deployments of multihop wireless networks have not proven successful. The performance of routing and transport is often unstable due to contention-induced packet losses, especially when the network is large and the offered load is high. In this paper we propose RAIN, a reliable wireless network architecture for large-scale multihop wireless networks. A RAIN network enforces contention control by limiting the queue length at intermediate wireless routers to the minimum. To keep the queue short a RAIN network enforces congestion control through in-network implicit back-pressure. RAIN congestion control is built on wireless datalink layer mechanisms, e.g., mandatory per-frame acknowledgement and inter-frame backoff in popular CSMA/CA wireless transceivers, therefore very efficient and effective compared with those defined at the network or transport layer for the wired Internet. As a result of the built-in contention and congestion control, RAIN presents the end hosts a highly reliable network service model, even more reliable than that of the wired Internet. The end hosts only need to deal with packet losses due to router or routing failures. Therefore, the transport protocol can be significantly simplified. This is in stark contrast to the existing approach of adding more and more complexity to adapt TCP for multihop wireless networks. We propose the details of RAIN datalink layer protocol, and a simple transport protocol at the end hosts. Performance evaluation through intensive simulations shows that RAIN improves the throughput by up to 92 % and fairness by up to 48%, with packet losses due to contention and congestion significantly reduced. I.
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Modeling Wireless Ad Hoc Networks with Directional Antennas

by Marcelo M. Carvalho, J. J. Garcia-Luna-Aceves - Proc. IEEE INFOCOM , 2006
"... This paper presents the first analytical model of wireless ad hoc networks that considers the impact of realistic antenna-gain patterns on network performance. As such, our modeling approach allows the study of ad hoc networks in which nodes are equipped with directional antennas. This modeling capa ..."
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This paper presents the first analytical model of wireless ad hoc networks that considers the impact of realistic antenna-gain patterns on network performance. As such, our modeling approach allows the study of ad hoc networks in which nodes are equipped with directional antennas. This modeling capability stands out from all previous analytical models, which have only dealt with omnidirectional or over-simplified antenna gain patterns, and which have not addressed the specific mechanisms of the medium access control (MAC) protocols used (e.g., the backoff mechanism). A new analytical model for the IEEE 802.11 DCF MAC is introduced that allows the study of different carrier-sensing mechanisms, such as the directional virtual carrier sensing (DVCS) protocol that we use to validate our analytical model and show its applicability. Our numerical results show that our new analytical model predicts the results obtained by discrete-event simulations very accurately, and does it with a processing time that is orders of magnitude faster than the time required by simulations.

SYN-DMAC: A Directional MAC Protocol for Ad Hoc Networks with Synchronization

by Jianfeng Wang, Yuguang Fang, Dapeng Wu
"... Abstract — Directional antenna has received intensive research interests in recent years due to its potential to increase communication efficiency and resilience to interference and jamming. In this paper, we provide a novel directional MAC protocol termed SYN-DMAC for ad hoc networks with synchroni ..."
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Abstract — Directional antenna has received intensive research interests in recent years due to its potential to increase communication efficiency and resilience to interference and jamming. In this paper, we provide a novel directional MAC protocol termed SYN-DMAC for ad hoc networks with synchronization. We demonstrate our proposed SYN-DMAC can efficiently address the major open problems in the directional MAC design such as the deafness problem, the hidden terminal problem, the exposed terminal problem and the Head-of-Line(HOL) blocking problem. Preliminary simulation results show that our scheme significantly improves throughput in comparison with IEEE 802.11 MAC protocol. I.
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A Busy-Tone based MAC Scheme for Wireless Ad Hoc Networks using Directional Antennas

by Hong-ning Dai, Kam-wing Ng, Min-you Wu
"... Applying directional antennas in wireless ad hoc networks offers numerous benefits, such as extended communication range, increased spatial reuse, improved capacity and suppressed interference. However, directional antennas can cause new location-dependent carrier sensing problems, such as new hidde ..."
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Applying directional antennas in wireless ad hoc networks offers numerous benefits, such as extended communication range, increased spatial reuse, improved capacity and suppressed interference. However, directional antennas can cause new location-dependent carrier sensing problems, such as new hidden terminal and deafness problems, which can cause severe penalties to the performance. Recently, a few schemes have been proposed to tackle these problems. However, these methods can provide limited solutions on the hidden terminal and deafness problems. We propose a new MAC protocol, termed the busy-tone based directional medium access control (BT-DMAC) protocol. When the transmission is in progress, the sender and the receiver will turn on their omnidirectional busy tone to protect the transmission. By combining with directional network allocation vector (DNAV), the scheme almost mitigates the hidden and the deafness problems completely. The mechanism increases the probability of successful data transmission and consequently improves the network throughput. This paper describes the BT-DMAC scheme and analyzes its performance. The simulation results also demonstrate the effectiveness of the protocol.
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A receiver-initiated directional MAC protocol for handling deafness in Ad Hoc networks

by Masanori Takata, Masaki B, Takashi Watanabe - in Proceedings of the IEEE International Conference on Communications (ICC ’06 , 2006
"... Abstract — Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for wireless ad hoc networks. Although directional transmissions are expected to provide significant improvements, directional MAC protocols introduce new kin ..."
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Abstract — Recently, several MAC protocols using directional antennas, typically referred to as directional MAC protocols, have been proposed for wireless ad hoc networks. Although directional transmissions are expected to provide significant improvements, directional MAC protocols introduce new kinds of problems. One such problem is deafness. Deafness is caused when a transmitter repeatedly attempts to communicate with its intended receiver, but it fails because the receiver has its beam pointed towards a direction away from the transmitter. This paper proposes RI-DMAC (Receiver-Initiated Directional MAC) to address the issue of deafness in directional MAC protocols. RI-DMAC is a combination of sender- initiated and receiver-initiated operations. The sender-initiated mode is the default mode and the receiver-initiated mode is triggered when the transmitter experiences deafness. In RI-DMAC, each node maintains a polling table and polls a potential deafness node using the RTR (Ready To Receive) frame after the completion of every dialog. The experimental results show that RI-DMAC improves throughput and fairness performance compared to existing directional MAC protocols. I.
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Link Layer Multicasting with Smart Antennas: No Client Left Behind

by Souvik Sen, Jie Xiong, Rahul Ghosh, Romit Roy Choudhury
"... Abstract—Wireless link layer multicast is an important service primitive for emerging applications, such as live video, streaming audio, and other content telecasts. The broadcast nature of the wireless channel is amenable to multicast because a single packet transmission may be received by all clie ..."
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Abstract—Wireless link layer multicast is an important service primitive for emerging applications, such as live video, streaming audio, and other content telecasts. The broadcast nature of the wireless channel is amenable to multicast because a single packet transmission may be received by all clients in the multicast group. However, in view of diverse channel conditions at different clients, the rate of such a transmission is bottlenecked by the rate of the weakest client. Multicast throughput degrades severely. Attempts to increase the data rate result in lower reliability and higher unfairness. This paper utilizes smart beamforming antennas to improve multicast performance in wireless LANs. The main idea is to satisfy the stronger clients with a high-rate omnidirectional transmission, followed by highrate directional transmission(s) to cover the weaker ones. By selecting an optimal transmission strategy (using dynamic programming), we show that the multicast throughput can be maximized while achieving a desired delivery ratio at all the clients. We use testbed measurements to verify our main assumptions. We simulate our protocol in Qualnet, and observe consistent performance improvements over a range of client topologies and time-varying channel conditions. bottleneck identification may not be trivial. (3) Even if bottleneck rate is suitably identified, packet losses are still possible due to fading and interference. The protocol will need to recover from such losses so that clients achieve an application-specified reliability. This paper aims to design a link layer multicast service that addresses these challenges in the context of WiFi networks. A practical solution is of interest that can accomplish high multicast throughput, while meeting a required per-node delivery ratio. Increasing transmission rates does not resolve the challenges, since some weak clients will fail to receive transmissions at higher data rates, and thus, be “left behind”. We believe smart antennas offer new opportunities to augment the state of the art in link layer multicast. We motivate the applicability of smart antennas, and present our main ideas next.
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