Tone Dual‐Channel MAC Protocol with Directional Antennas for Mobile Ad Hoc Networks

The directional medium access control (MAC) protocol improves the throughput of mobile ad hoc networks but has a deafness problem and requires location information for neighboring nodes. In the dual‐channel directional MAC protocol [12], the use of omnidirectional packets does not require the exact location of destination node. In this letter, we propose a tone dual‐channel MAC protocol with directional antennas to improve the throughput of mobile ad hoc networks. In the proposed MAC protocol, we use a directional CTS and an out‐of‐band directional DATA tone with a new blocking algorithm to improve the spatial reuse. We confirm the throughput performance of the proposed MAC protocol by computer simulations using the Qualnet simulator.     

Ad hoc networking with directional antennas: a complete system solution

Directional antennas offer tremendous potential for improving the performance of ad hoc networks. Harnessing this potential, however, requires new mechanisms at the medium access and network layers for intelligently and adaptively exploiting the antenna system. While recent years have seen a surge of research into such mechanisms, the problem of developing a complete ad hoc networking system, including the unique challenge of real-life prototype development and experimentation has not been addressed. In this paper, we present utilizing directional antennas for ad hoc networking (UDAAN). UDAAN is an interacting suite of modular network- and medium access control (MAC)-layer mechanisms for adaptive control of steered or switched antenna systems in an ad hoc network. UDAAN consists of several new mechanisms-a directional power-controlled MAC, neighbor discovery with beamforming, link characterization for directional antennas, proactive routing and forwarding-all working cohesively to provide the first complete systems solution. We also describe the development of a real-life ad hoc network testbed using UDAAN with switched directional antennas, and we discuss the lessons learned during field trials. High fidelity simulation results, using the same networking code as in the prototype, are also presented both for a specific scenario and using random mobility models. For the range of parameters studied, our results show that UDAAN can produce a very significant improvement in throughput over omnidirectional communications.     

Distributed cooperative MAC for multihop wireless networks

This article investigates distributed cooperative medium access control protocol design for multihop wireless networks. Cooperative communication has been proposed recently as an effective way to mitigate channel impairments. With cooperation, single-antenna mobile terminals in a multi-user environment share antennas from other mobiles to generate a virtual multipleantenna system that achieves more reliable communication with a higher diversity gain. However, more mobiles conscribed for one communication inevitably induces complex medium access interactions, especially in multihop wireless ad hoc networks. To improve the network throughput and diversity gain simultaneously, we investigate the issues and challenges in designing an efficient MAC scheme for such networks. Furthermore, based on the IEEE 802.11 DCF, a cross-layer designed cooperative MAC protocol is proposed. The MAC scheme adapts to the channel condition and payload length.     

A Shoelace-Based QoS Routing Protocol for Mobile Ad Hoc Networks Using Directional Antenna

In this paper, we propose a new quality-of-service (QoS) routing protocol for mobile ad hoc network (MANET) using directional antennas. The proposed scheme offers a bandwidth-based routing protocol for QoS support in MANET using the concept of multi-path. Our MAC sub-layer adopts the CDMA-over-TDMA channel model. The on-demand QoS routing protocol calculates the end-to-end bandwidth and allocates bandwidth from the source node to the destination node. The paths are combined with multiple cross links, called shoelace, when the network bandwidth is strictly limited. Due to the property of the directional antenna, these cross links can transmit data simultaneously without any data interference. We develop a shoelace-based on-demand QoS routing protocol by identifying shoelaces in a MANET so as to construct a QoS route, which satisfied the bandwidth requirement, more easily. The shoelace-based route from the source to the destination is a route whose sub-path is constructed by shoelace structure. With the identified shoelaces, our shoelace-based scheme offers a higher success rate to construct a QoS route. Finally, simulation results demonstrate that the proposed routing protocol outperform existing QoS routing protocols in terms of success rate, throughput, and average latency.     

On Busy-Tone Based MAC Protocol for Wireless Networks with Directional Antennas

The application of directional antennas in wireless ad hoc networks offers numerous benefits, such as the extended communication range, the increased spatial reuse, the improved capacity and the suppressed interference. However, directional antennas can cause new location-dependent carrier sensing problems, such as new hidden terminal and deafness problems, which can severely degrade the network performance. Recently, a few schemes have been proposed to address these problems. However, most of these existing methods can only partially solve the hidden terminal and deafness problems. Some of them even bring significant performance overhead. In this paper, we propose a novel MAC protocol, in terms of the busy-tone based directional medium access control (BT-DMAC) protocol. In BT-DMAC, when the transmission is in progress, the sender and the receiver will turn on their omni-directional busy tones to protect the on-going transmission. Integrating with the directional network allocation vector (DNAV), the scheme can almost mitigate the hidden terminal problem and the deafness problem completely. We then propose an analytical model to investigate the throughput performance of BT-DMAC. The numerical results show that BT-DMAC outperforms other existing directional MAC schemes. We next evaluate the performance of BT-DMAC through extensive simulation experiments. The results show that our proposed BT-DMAC scheme has superior performance to other existing solutions, in terms of higher throughput.     

The design of a channel-access protocol for a wireless ad hoc network with sectored directional antennas

A packet scheduler and a medium access control (MAC) protocol are presented for a direct-sequence spread-spectrum, wireless ad hoc network that contains a mix of nodes with directional antennas and nodes with omnidirectional antennas. The scheduler and MAC protocol are designed to prevent the co-site interference problem that arises in some types of nodes employing directional antennas. It is shown that the presence of nodes with directional antennas exacerbates the vulnerability of the network to the receiver blocking problem. A modification of the MAC protocol is presented that mitigates the receiver blocking problem, and it is shown to improve the performance of a network that includes nodes with directional antennas.     

Power-controlled medium access for ad hoc networks with directional antennas

Directional antennas have the potential to significantly improve the throughput of a wireless ad hoc network. At the same time, energy consumption can be considerably reduced if the network implements per-packet transmission power control. Typical MAC protocols for ad hoc networks (e.g., the IEEE 802.11 Ad Hoc mode) were designed for wireless devices with omnidirectional antennas. When used with directional antennas, such protocols suffer from several medium access problems, including interference from minor lobes and hidden-terminal problems, which prevent full exploitation of the potential of directional antennas. In this paper, we propose a power-controlled MAC protocol for directional antennas that ameliorates these problems. Our protocol allows for dynamic adjustment of the transmission power for both data and clear-to-send (CTS) packets to optimize energy consumption. It provides a mechanism for permitting interference-limited concurrent transmissions and choosing the appropriate tradeoff between throughput and energy consumption. The protocol enables nodes to implement load control in a distributed manner, whereby the total interference in the neighborhood of a receiver is upper-bounded. Simulation results demonstrate that the combined gain from concurrent transmissions using directional antennas and power control results in significant improvement in network throughput and considerable reduction in energy consumption.     

Enhancing the performance of medium access control for WLANs with multi-beam access point

Wireless LANs with multi-beam directional antennas have received intensive attention lately due to the potential gain in throughput performance. However, when the multi-beam directional antennas are introduced in this system, the ever popular contention-based medium access control protocol such as IEEE 802.11 MAC is no longer effective, and many challenging problems, such as beam-synchronization problem, beam-overlapping problem, mobility and receiver blocking problem (deafness problem), need to be resolved. In this paper, we propose a novel MAC protocol to carefully address these problems. In addition to improving communication efficiency, we also consider the backward compatibility in our design, whereby an IEEE 802.11 terminal can transparently access a multi-beam access point. Furthermore, we present an analytical model to evaluate the performance of multi-beam wireless LANs. Extensive simulation studies are used to validate the analytical model and show that our scheme can significantly improve the throughput performance     

A multiple relay‐based medium access control protocol in multirate wireless ad hoc networks with multiple beam antennas

The advanced technique of multiple beam antennas is recently considered in wireless networks to improve the system throughput by increasing spatial reuse, reducing collisions, and avoiding co‐channel interference. The usage of multiple beam antennas is similar to the concept of Space Division Multiple Access (SDMA), while each beam can be treated as a data channel. Wireless networks can increase the total throughput and decrease the transmission latency if the physical layer of a mobile node can support multirate capability. Multirate wireless networks incurs the anomaly problem, because low data rate hosts may influence the original performance of high data rate hosts. In this work, each node fits out multiple beam antennas with multirate capability, and a node can either simultaneously transmit or receive multiple data on multiple beams. Observe that the transmitting or receiving operation does not happen at the same time. In this paper, we propose a multiple relay‐based medium access control (MAC) protocol to improve the throughput for low data rate hosts. Our MAC protocol exploits multiple relay nodes and helps the source and the destination to create more than one data channel to significantly reduce the transmission latency. Observe that low data rate links with long‐distance transmission latencies are distributed by multiple relay nodes, hence the anomaly problem can be significantly alleviated. In addition, the ACK synchronization problem is solved to avoid the condition that source nodes do not receive ACKs from destination nodes. An adjustment operation is presented to reduce unnecessary relay nodes during the fragment burst period. Finally, simulation results illustrate that our multiple relay‐based MAC protocol can achieve high throughput and low transmission latency. Copyright © 2009 John Wiley & Sons, Ltd.     

MAC protocols using directional antennas in IEEE 802.11 based ad hoc networks

Using directional antennas can be beneficial for wireless ad hoc networks consisting of a collection of wireless hosts. The most important benefit includes a reduction of the radio interference. Thus, it can significantly increase the spatial reuse, thereby improving the network throughput. To best utilize directional antennas, a suitable Medium Access Control (MAC) protocol must be designed. Current MAC protocols, such as the IEEE 802.11 standard, do not benefit when using directional antennas, because these protocols have been designed for omnidirectional antennas. In this paper, we present modified MAC protocols suitable for 802.11 based ad hoc networks using directional antennas. Our comprehensive simulation results demonstrate the performance improvement obtained with the proposed protocols. Copyright © 2007 John Wiley & Sons, Ltd.     

System evaluation of optimal downlink beamforming with congestion control in wireless communication

We investigate the use of congestion control and joint optimal downlink beamforming, power control, and access point allocation, in a multi-cell wireless communication system. The access points of the system employ smart antennas and single antennas are used at the terminals. The possibility to send messages to multiple terminals at the same frequency in the same time slot is exploited. We show how previously proposed algorithms for optimal downlink beamforming easily can be extended to determine also the optimal access point for each mobile terminal. In order to assign resources, optimal beamforming requires a feasible set of mobiles, i.e. that all admitted users can be offered the required signal-to-interference-and-noise ratio. Therefore, an algorithm for deciding which mobile terminals to admit or reject from a congested system is proposed and evaluated. Using the proposed congestion algorithm, joint optimal downlink beamforming is evaluated and the throughput increase as compared to decentralized beamforming algorithms and other congestion control strategies is assessed from a system point of view. The results show that the proposed strategy can almost double the throughput compared to decentralized beamforming algorithms and give a fivefold increase in throughput compared to conventional beamforming without any interference suppression.     

Angular MAC: a framework for directional antennas in wireless mesh networks

Capacity of wireless mesh networks can be enhanced through the use of smart directional antennas, which not only enable nodes to have high quality links but also increase network throughput by allowing spatial reuse. This paper proposes a new MAC protocol and framework, called Angular MAC (ANMAC) that enables directional antennas in wireless mesh networks. The protocols and algorithms of the ANMAC framework fit well with the requirements of mesh networks such as neighbor discovery and self-configuration, while providing significant throughput enhancements. The throughput enhancements are proven by comprehensive simulations with realistic antenna patterns, including performance comparisons of ANMAC with directional schemes using a similar node architecture and omni 802.11. Also, the effect of contention window size is analyzed and a dynamic contention window adaptation algorithm is proposed to maximize the throughput of the self-configuring mesh network, by taking instantaneous traffic conditions into account.     

Energy-Efficient Routing Algorithms Using Directional Antennas for Mobile Ad Hoc Networks

Power consumption is an important issue in the wireless ad hoc networking environment. In this paper, we present several energy-efficient routing algorithms using directional antennas for wireless ad hoc networks. These algorithms are simple to implement and are distributed and can be applied to mobile environments. We evaluate how directional antennas improve system throughput. We study the influence of the battery recovery effect and mobility on the network throughput during a network lifetime. We also present an algorithm that exploits the broadcast nature of the wireless communication environment to improve end-to-end bit error performance for a Rayleigh fading channel.     

CRDMAC的设计与评价: 基于循环RTR的无线自组网络的定向MAC协议

Using directional antennas in Wireless Ad hoc Networks (WANETs) offers great potential of reducing the radio interference, and improving the communication throughput. Directional antennas, however, introduces new problems in the wireless Media Access Control (MAC), that is, the deafness and new hidden terminal problem, which may cause severe performance degradation. To solve the problems, we propose an effective Circular RTR Directional MAC (CRDMAC) protocol for WANETs by using a sub-transmission channel and Ready to Receive (RTR) packets, which modifies the IEEE 802. 11 Distributed Coordinated Function (DCF). The sub-channel avoids collisions to other ongoing transmission, and the RTR packets notify the neighbor nodes that the mutual transmission has been finished. We evaluate the CRDMAC protocol through simulations and the results show that the proposed protocol outperforms existing DMAC (directional MAC) protocol and the CRCM (Circular RTS and CTS MAC) protocol in terms of throughput and packet drop rate.     

MANETs中智能天线和功率控制的应用

分析了MANETs中基于CDMA的MAC协议存在的问题,提出在协议中引入智能天线和功率控制技术来解决多址干扰和远-近效应等问题.对采用智能天线和功率控制技术的MAC协议的工作原理进行了阐述,并通过仿真评估了智能天线与功率控制技术结合后对网络吞吐量和节点耗能的影响.研究结果表明,在MANETs中使用智能天线和功率控制技术可以有效地提高网络的吞吐量,降低节点的能耗.     

On designing MAC protocols for wireless networks using directional antennas

We investigate the possibility of using directional antennas for medium access control in wireless ad hoc networks. Previous research in ad hoc networks typically assumes the use of omnidirectional antennas at all nodes. With omnidirectional antennas, while two nodes are communicating using a given channel, MAC protocols such as IEEE 802.11 require all other nodes in the vicinity to remain silent. With directional antennas, two pairs of nodes located in each other's vicinity may potentially communicate simultaneously, increasing spatial reuse of the wireless channel. Range extension due to higher gain of directional antennas can also be useful in discovering fewer hop routes. However, new problems arise when using directional beams that simple modifications to 802.11 may not be able to mitigate. This paper identifies these problems and evaluates the tradeoffs associated with them. We also design a directional MAC protocol (MMAC) that uses multihop RTSs to establish links between distant nodes and then transmits CTS, DATA, and ACK over a single hop. While MMAC does not address all the problems identified with directional communication, it is an attempt to exploit the primary benefits of beamforming in the presence of some of these problems. Results show that MMAC can perform better than IEEE 802.11, although we find that the performance is dependent on the topology and flow patterns in the system.     

DTRA: directional transmission and reception algorithms in WLANs with directional antennas for QoS support

Recent research results show that there are significant gains in throughput to be realized with directional transmission and directional reception compared to using omnidirectional; however, no specific reservation/scheduling algorithms are presented (Su Yi et al., 2003). In this article we propose a novel directional transmit and receive algorithm (DTRA) in wireless local area networks with directional antennas for quality of service support. To the best of our knowledge, all the previous work assumes omnidirectional reception at certain stages of the algorithms. However, the omnireceive requirement makes the protocol vulnerable to jamming. In this article no omniantennas or omnidirectional reception capability is assumed at all. The proposed algorithm exploits 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, we present a TDMA-based MAC algorithm for load-dependent negotiation of slot reservations. Our new protocol offers four significant advantages: it assumes directional transmission/reception, it is distributed (i.e., it relies on local information only), it allocates slots to different links dynamically based on demand, and power control is easily carried out during neighbor discovery, reservation, and data transmission with very little overhead. We believe this is the first work on pure directional transmission and reception in wireless ad hoc networks. The algorithm can be used in many commercial and military applications. Preliminary simulation results indicate that DTRA performs much better than IEEE 802.11 for the network considered.     

Directional MAC and routing schemes for power controlled Wireless Mesh Networks with adaptive antennas

Wireless Mesh Networks (WMNs) have emerged recently as a technology for next-generation wireless networking. Several approaches that exploit directional and adaptive antennas have been proposed in the literature to increase the performance of WMNs. However, while adaptive antennas 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 are needed to fully exploit the features offered by adaptive antennas. Furthermore, routing protocols that were designed for omnidirectional communications can be redesigned to exploit directional transmissions and the cross-layer interaction between the MAC and the network layer.In this paper we first propose a novel Power-Controlled Directional MAC protocol (PCD-MAC) for adaptive antennas. PCD-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 with a tunable power while the DATA and ACK are transmitted directionally at the minimal required power.We then propose the Directional Deflection Routing (DDR), a routing algorithm that exploits multiple paths towards the destination based on the MAC layer indication on channel availability in different directions.We measure the performance of PCD-MAC and DDR by simulation of several realistic network scenarios, and we compare them with other approaches proposed in the literature. The results show that our schemes increase considerably both the total traffic accepted by the network and the fairness among competing connections.     

Design and analysis of low‐power access protocols for wireless and mobile ATM networks

This paper describes the design and analysis of a low‐power medium access control (MAC) protocol for wireless/mobile ATM networks. The protocol – denoted EC‐MAC (energy conserving medium access control) – is designed to support different traffic types with quality‐of‐service (QoS) provisions. The network is based on the infrastructure model where a base station (BS) serves all the mobiles currently in its cell. A reservation‐based approach is proposed, with appropriate scheduling of the requests from the mobiles. This strategy is utilized to accomplish the dual goals of reduced energy consumption and quality of service provision over wireless links. A priority round robin with dynamic reservation update and error compensation scheduling algorithm is used to schedule the transmission requests of the mobiles. Discrete‐event simulation has been used to study the performance of the protocol. A comparison of energy consumption of the EC‐MAC to a number of other protocols is provided. This comparison indicates the EC‐MAC has, in general, better energy consumption characteristics. Performance analysis of the proposed protocol with respect to different quality‐of‐service parameters using video, audio and data traffic models is provided. This revised version was published online in August 2006 with corrections to the Cover Date.     

Mobility–capacity–delay trade-off in wireless ad hoc networks

We show that there is a trade-off among mobility, capacity, and delay in ad hoc networks. More specifically, we consider two schemes for node mobility in ad hoc networks. We divide the entire network by cells whose sizes can vary with the total number of nodes n, or whose size is independent of the number of nodes. We restrict the movement of nodes within these cells, calculate throughput and delay for randomly chosen pairs of source–destination nodes, and show that mobility is an entity that can be exchanged with capacity and delay. We also investigate the effect of directional antennas in a static network in which packet relaying is done through the closest neighbor and verify that this approach attains better throughput than static networks employing omnidirectional antennas.