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Today, many wireless networks are single-channel systems. However, as the interest in wireless services increases, the contention by nodes to occupy the medium is more intense and interference worsens. One direction with the potential to increase system throughput is multi-channel systems. Multi-channel systems have been shown to reduce collisions and increase concurrency thus producing better bandwidth usage. However, the well-known hidden- and exposed-terminal problems inherited from single-channel systems remain, and a new channel selection problem is introduced. In this dissertation, Multi-channel medium access control (MAC) protocols are proposed for mobile ad hoc networks (MANETs) for nodes equipped with a single half-duplex transceiver, using more sophisticated physical layer technologies. These include code division multiple access (CDMA), orthogonal frequency division multiple access (OFDMA), and diversity. CDMA increases channel reuse, while OFDMA enables communication by multiple users in parallel. There is a challenge to using each technology in MANETs, where there is no fixed infrastructure or centralized control. CDMA suffers from the near-far problem, while OFDMA requires channel synchronization to decode the signal. As a result CDMA and OFDMA are not yet widely used. Cooperative (diversity) mechanisms provide vital information to facilitate communication set-up between source-destination node pairs and help overcome limitations of physical layer technologies in MANETs. In this dissertation, the Cooperative CDMA-based Multi-channel MAC (CCM-MAC) protocol uses CDMA to enable concurrent transmissions on each channel. The Power-controlled CDMA-based Multi-channel MAC (PCC-MAC) protocol uses transmission power control at each node and mitigates collisions of control packets on the control channel by using different sizes of the spreading factor to have different processing gains for the control signals. The Cooperative Dual-access Multi-channel MAC (CDM-MAC) protocol combines the use of OFDMA and CDMA and minimizes channel interference by a resolvable balanced incomplete block design (BIBD). In each protocol, cooperating nodes help reduce the incidence of the multi-channel hidden- and exposed-terminal and help address the near-far problem of CDMA by supplying information. Simulation results show that each of the proposed protocols achieve significantly better system performance when compared to IEEE 802.11, other multi-channel protocols, and another protocol CDMA-based.
A mobile ad hoc network is a collection of mobile terminals equipped with wireless transceivers that form an autonomous network without any pre-planned infrastructure or centralized administration. Wireless hosts in an ad hoc network typically share a single common channel for communication. The Medium Access Control (MAC) allows the hosts to resolve contention while randomly accessing the channel and plays a key role in determining the efficiency of channel usage in the network. Usage of multiple channels improves the throughput of the MAC protocol in ad hoc networks by allowing multiple nodes to transmit concurrently on different non-overlapping channels. Efficient channel selection schemes can reduce the contention in each channel leading to smaller number of collisions, backoffs, and retransmissions. This research explores a new channel selection scheme that is based on maximizing the signal to interference ratio at the receiver as well as minimizing the interference caused to all other active receivers in the vicinity of the sender. An implementation of this "cooperative" channel selection technique is proposed employing receiver-initiated busy-tones and signal power measurements at the sending and receiving nodes respectively. Simulation based performance results are presented.
The unrelenting growth of wireless communications continues to raise new research and development problems that require unprecedented interactions among communication engineers. In particular, specialists in transmission and specialists in networks must often cross each other's boundaries. This is especially true for CDMA, an access technique that is being widely accepted as a system solution for next-generation mobile cellular systems, but it extends to other system aspects as well. Major challenges lie ahead, from the design of physical and radio access to network architecture, resource management, mobility management, and capacity and performance aspects. Several of these aspects are addressed in this volume, the fourth in the edited series on Multiaccess, Mobility and Teletraffic for Wireless Communications. It contains papers selected from MMT'99, the fifth Workshop held on these topics in October 1999 in Venezia, Italy. The focus of this workshop series is on identifying, presenting, and discussing the theoretical and implementation issues critical to the design of wireless communication networks. More specifically, these issues are examined from the viewpoint of the impact each one of them can have on the others. Specific emphasis is given to the evolutionary trends of universal wireless access and software radio. Performance improvements achieved by spectrally efficient codes and smart antennas in experimental GSM testbeds are presented. Several contributions address critical issues regarding multimedia services for Third-Generation Mobile Radio Networks ranging from high rate data transmission with CDMA technology to resource allocation for integrated Voice/WWW traffic.
This book constitutes the refereed proceedings of the 6th International Conference on Ad-Hoc Networks and Wireless, ADHOC-NOW 2007, held in Morelia, Mexico, in September 2007. The 21 revised full papers were carefully reviewed and selected from 50 submissions. The papers are organized in topical sections on routing, topology control, security and privacy, protocols, as well as quality of service and performance.
Although IEEE 802.11a/b/g standards allow use of multiple channels, only a single channel is popularly used, due to the lack of efficient protocols that enable use of Multiple Channels. There are some papers challenging this problem. Some of them have requirements that will increase the cost, like requirement of multiple transceivers. Some others address the problem with single transceivers, but are very hard to be employed in highly mobile Ad Hoc networks due to network-wide synchronization requirements. In this Thesis, multiple channel use in a wireless network with single transceiver nodes is addressed, and attempted to be solved with a new efficient Ad Hoc network MAC protocol, which intends to remove the requirement of network-wide synchronization.
Cooperative diversity is proposed to combat the detrimental effects of channel fading. In this thesis, we investigate the effectiveness of cooperative diversity in interference limited ad hoc networks. The throughput performance of ad hoc networks that employ cooperative diversity techniques is examined. The negative effects of relay transmission blocking and extra time delay due to using the relay node, on the network throughput are investigated. We show that cooperative diversity based ad hoc networks inherits relay blocking problem which causes net network throughput degradation. To solve the relay blocking problem, we propose a new cooperative medium-access-control (MAC) protocol where each relay is equipped with directive antennas and the transmitter-relay-receiver transmission mode is designed using two frequency channels. Furthermore, we discuss the throughput performance considering single and multiple relay scenarios and analyze the effect of interference on the throughput. Then we investigate the throughput performance of the proposed cooperative MAC protocol in the presence of position estimation errors. In the literature, a perfect position estimation of all nodes is commonly assumed. Here, we focus on the throughput performance of the cooperative network when taking into consideration the effect of directional-of-arrival (DOA) error caused by imperfect global-positioning system (GPS) position estimation. Our results show that using adaptive antennas at the relay becomes advantageous when the DOA error is less than 20 degrees. We noted that increasing the number of antennas (at the relay station) can improve the throughput performance but, on the other hand, the effect of node position error becomes more substantial.
One of the factors that significantly affects the performance of wireless networks is fading. There are several techniques to overcome the detrimental effects of multipath fading, the most common being to provide diversity, i.e. statistically independent channels from the source to the destination.
The 8th International Conference on Ad-Hoc Networks and Wireless (ADHOC-NOW 2009) was held September 22–25, 2009 in Murcia, Spain. Since ADHOCNOW started as a workshop in 2002, it has become a well-established and well-known international conference dedicated to wireless and mobile c- puting. During the last few years it has been held in Toronto, Canada (2002), Montreal, Canada (2003), Vancouver, Canada (2004), Cancun, Mexico (2005), Ottawa, Canada (2006), Morelia, Mexico (2007) and Sophia Antipolis, France (2008). The conference serves as a forum for interesting discussions on ongoing research and new contributions addressing both experimental and theoretical research in the area of ad hoc networks, mesh networks, sensor networks and vehicular networks. In 2009, we recived 92 submissions from 28 di?erent countries around the globe: Algeria, Australia, Brazil, Canada, China, Egypt, Finland, France, G- many, Greece, India, Iran, Ireland, Italy, Japan, Korea, Luxembourg, Malaysia, Mexico,Norway,Poland,Portugal,Serbia,SouthAfrica,Spain,Tunisia,UKand USA. Of the submitted papers, we selected 24 full papers and 10 short papers for publication in the proceedings and presentation in the conference.
Wireless multi-hop ad hoc and sensor networks provide a promising solution to ensure ubiquitous connectivity for the Future Internet. Good network connectivity requires designing a reliable Medium Access Control (MAC) protocol, which is a challenging task in the ad hoc and sensor environments. The broadcast and shared nature of the wireless channel renders the bandwidth resources limited and expose the transmissions to relatively high collisions and loss rates. The necessity to provide guaranteed Quality of Service (QoS) to the upper layers triggered the design of conflict-free MAC protocols. The TDMA synchronization constraint is basically behind the rush of MAC protocol design based on a fixed frame size. This design shows inflexibility towards network variations and creates a network dimensioning issue that leads to a famine risk in case the network is under-dimensioned, and to a waste of resources, otherwise. Moreover, the alternative dynamic protocols provide more adaptive solutions to network topology variations at the expense of a fair access to the channel. Alongside with the efficient channel usage and the fair medium access, reducing the energy consumption represents another challenge for ad hoc and sensor networks. Solutions like node activity scheduling tend to increase the network lifetime while fulfilling the application requirements in terms of throughput and delay, for instance. Our contributions, named OSTR and S-OSTR, address the shortcomings of the medium access control protocol design in the challenging environment of wireless multi-hop ad hoc and sensor networks, respectively. For OSTR the idea consists in adopting a dynamic TDMA frame size that increases slot-by-slot according to the nodes arrival/departure to/from the network, and aiming to achieve a minimum frame size. For this end, OSTR couples three major attributes: (1) performing slot-by-slot frame size increase, (2) providing a spatial reuse scheme that favors the reuse of the same slot if possible, (3) and ensuring an on-demand frame size increase only according to the node requirements in terms of throughput. To tackle different frame sizes co-existence in the network, OSTR brings a cooperative solution that consists in fixing an appointment, a date when the frame size in the network is increased. Concerning S-OSTR, it is an amendment of OSTR for wireless sensor networks. It brings the idea of a dynamic active period, since it deploys a dynamic frame size that is built slot-by-slot according to nodes arrival to the network. S-OSTR enforces the slot-by-slot frame size increase by a node activity scheduling to prolong the inactivity period in the network, and hence prolong the overall network lifetime for wireless sensor networks. Our contributions are both based on the new dynamic TDMA frame size increase that consists in increasing the frame size slot-by-slot aiming to achieve a shorter frame size, and hence improve the channel utilization, and reduce the energy consumption. The performance analysis of OSTR and S-OSTR shows that they present good potentials to support QoS requirements, to provide energy-efficiency, to ensure fair medium access, to accommodate network topology changes and finally, to enhance robustness against scalability. The impact of this new TDMA frame size increase technique on the medium access control protocol performance is highlighted through multiple simulations of OSTR and S-OSTR. Multiple comparative studies are also handled to point out the effectiveness of this new technique and the soundness of our contributions.