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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.
This book focuses on the design and analysis of protocols for cooperative wireless networks, especially at the medium access control (MAC) layer and for crosslayer design between the MAC layer and the physical layer. It highlights two main points that are often neglected in other books: energy-efficiency and spatial random distribution of wireless devices. Effective methods in stochastic geometry for the design and analysis of wireless networks are also explored. After providing a comprehensive review of existing studies in the literature, the authors point out the challenges that are worth further investigation. Then, they introduce several novel solutions for cooperative wireless network protocols that reduce energy consumption and address spatial random distribution of wireless nodes. For each solution, the book offers a clear system model and problem formulation, details of the proposed cooperative schemes, comprehensive performance analysis, and extensive numerical and simulation results that validate the analysis and examine the performance under various conditions. The last section of this book reveals several potential directions for the research on cooperative wireless networks that deserve future exploration. Researchers, professionals, engineers, and consultants in wireless communication and mobile networks will find this book valuable. It is also helpful for technical staff in mobile network operations, wireless equipment manufacturers, wireless communication standardization bodies, and governmental regulation agencies.
Use of directional antennas in wireless networks has been widely studied in recent years. Since the Medium Access Control (MAC) protocol of the IEEE 802.11 standard is designed for the use of omnidirectional antennas, it cannot work properly when directional antennas are used. To maximize the system throughput in mobile ad hoc networks, one needs to design new MAC protocols that work well with directional antennas. In this thesis, we propose a new MAC protocol that can efficiently utilize the large throughput offered by directional antennas in ad hoc networks. The proposed MAC protocol makes use of two main modes; (i) omnidirectional mode where one antenna is used for the transmission of users' control frames, and (ii) directional mode where antenna arrays are used for the transmission of data frames. We define two separate channels, one for control information and the second for data transmission. We incorporate a simple routing protocol to deal with the out-of-range problem encountered in practical scenarios. The proposed protocol takes into consideration the effect of interference arising from the side-lobes of different stations. Using a practical ad hoc network model, we present performance comparisons with different MAC protocols (including the IEEE 802.11) where we show the large throughput gains achieved using the proposed MAC protocol.
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.
Pulse-position modulation (PPM) is a well-known digital modulation scheme that when used in UWB radios can achieve simple low-cost architectures and more importantly a very low-power operation while offering relatively good data rates and bit-error rate (BER) performance. The DCF function described by the IEEE 802.11 WLAN standard is used quite often as the MAC protocol when implementing wireless networks in general and has proven to be efficient for many applications. This doctoral dissertation presents a new cognitive and cooperative protocol between the physical (PHY) layer and the MAC sublayer for wireless ad-hoc networks using PPM UWB radios. By a cognitive estimation of the wireless channel and the cooperation between the MAC and PHY layers, the cognitive protocol can dynamically adjust the transmission data rate between two nodes optimizing their communication. Simulations show that the protocol improves the overall network performance in terms of message delivery ratio and average transmission delay.
Wireless transmission medium suffers from channel impairments like fading and path loss leading to performance degradations in terms of reduced throughput and increased latency. Medium access control protocols designed for wireless networking today provide multiple retransmissions as a way to account for frame losses caused by the channel. By retransmitting in the same channel, effectiveness of retransmissions can be reduced due to prolonged periods of channel impairments like obstacles in the line of sight of communication. Spatial diversity provides statistically different channels that can compensate for frame losses. Wireless medium being broadcast in nature paves way to achieve spatial diversity by asking neighboring nodes that can overhear transmissions to retransmit the frames. This procedure is termed cooperation. The nodes that help in successful communication between two other nodes are called relays. Medium access control protocols that are designed to account for cooperation are called cooperative medium access control protocols. This thesis presents one such cooperative protocol. The cooperative protocol presented in this thesis is unique in that the relays are opportunistic in nature. Relays here only help the source that is transmitting frames to a destination when a transmission failure occurs. A metric to find a suitable relay is presented and heurisitic algorithms to find transmission rate pairs for links in the cooperative setup are also presented. The thesis also shows that the cooperative protocol proposed can also be used in multi-hop networks. A cross layer routing metric to jointly perform route and relay selection in multi-hop networks is also presented. Simulation and analytical studies were carried out and results are presented in this thesis comparing the performance of the cooperative protocol presented here and the standard protocol it is based on. Performance improvements in terms of throughput and latency are brought about by using opportunistic cooperation. The performance improvements depend on careful selection of relays and transmission rates used for the links in the cooperative setup. The gains perceived in single hop networks were also seen in multi-hop networks but the magnitude of gains in multi-hop scenarios were dependent on network topology.
Cooperative devices and mechanisms are increasingly important to enhance the performance of wireless communications and networks, with their ability to decrease power consumption and packet loss rate and increase system capacity, computation, and network resilience. Considering the wide range of applications, strategies, and benefits associated wit
Cooperative diversity has emerged as a promising technique to combat fading and improve reliability in a wireless environment. In cooperative diversity protocols, neighboring nodes act as virtual multiple-input-multiple-output (VMIMO) systems, where they cooperate with the transmitter-receiver pair to deliver multiple copies of a packet to the receiver via spatially independent fading channels. These multiple copies of the same packet can be combined at the receiver to recover the original packet. Medium Access Control (MAC) protocols play an important part in realizing this concept by effectively coordinating handshake and transmissions between source, partner and destination nodes. In this thesis, we investigate opportunities for improving reliability in Wireless Sensor Networks using cooperative MAC protocols. First, a Medium Access Control protocol, called CPS-MAC, is proposed. Design challenges such as efficiently waking up neighborhood nodes, minimizing energy overhead, and partner selection are also addressed. Then, Reliable Cooperative Transmission-MAC (RCT-MAC) is proposed which extends the functionality of Cooperative Preamble Sampling-MAC (CPS-MAC) by implementing the Cooperation on Demand concept: nodes cooperate only when needed. Furthermore, RCT-MAC is one of the first attempts to compare the performance of a cooperative Wireless Sensor Network (WSN) MAC protocol against conventional protocols for WSNs namely B-MAC, L-MAC, and IEEE 802.15.4. The reliability vs energy efficiency tradeoff is analyzed for both CPS-MAC and RCT-MAC. Lastly, we evaluate a Packet Error Prediction scheme particularly envisioned for preamble sampling cooperative protocols and meant to supplement traditional partner selection schemes. The correlation between the handshake packets and data packets is analyzed using empirical data. ; eng
Fundamentals of 5G Mobile Networks provides an overview of the key features of the 5th Generation (5G) mobile networks, discussing the motivation for 5G and the main challenges in developing this new technology. This book provides an insight into the key areas of research that will define this new system technology paving the path towards future research and development. The book is multi-disciplinary in nature, and aims to cover a whole host of intertwined subjects that will predominantly influence the 5G landscape, including the future Internet, cloud computing, small cells and self-organizing networks (SONs), cooperative communications, dynamic spectrum management and cognitive radio, Broadcast-Broadband convergence , 5G security challenge, and green RF. This book aims to be the first of its kind towards painting a holistic perspective on 5G Mobile, allowing 5G stakeholders to capture key technology trends on different layering domains and to identify potential inter-disciplinary design aspects that need to be solved in order to deliver a 5G Mobile system that operates seamlessly.