This work proposes a distributed dynamic channel assignment of multi-channel MAC protocol in Ad-Hoc networks. Major characteristics of the proposed protocol are: (a) each mobile node is equipped with two network interfaces, (b) no time synchronization is needed, (c) distribution channel assignment. The proposed protocol reduces the cost of channel negotiation by considering the property that a connection generates multiple frames for transmitting and can assign channel information faster. Compared with other multi-channel MAC protocols, the proposed algorithm allows the whole network channel allotment be stable quickly. The performance evaluation is conducted on NS-2. Simulation results show that the proposed protocol can reduce the cost of channel negotiation significantly, increase the network throughput.

Embedded systems have become more complex and it is hard to predict the behavior of networkdue to its dynamic nature. Several devices can interact to perform highly sophisticated real-timetasks while having the demand of interaction and sharing of resources. The interactingcomponents in these systems have strict timing constraints which require time criticalcommunication.We have designed the DCC-EDF protocol for wireless communication using the motivation fromthe research done in optical communication. We have chosen dedicated control channel protocolbecause it does not require time synchronization. To provide real-time services, we will use theEarly Deadline First scheduling algorithm (EDF) because of its optimality and efficiency. Theperformance for the soft real-time traffic is analyzed through simulation.

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Recent research has shown that several spectrum bands are mostly underutilised. To resolve the issue of underutilisation of spectrum bands across the networks, the concept of Cognitive Radio (CR) technology was envisaged. The CR technology allows Secondary Users (SUs) to acquire opportunistic access to large parts of the underutilised spectrum bands on wireless networks. In CR networks, SUs may scan and identify the vacant channels in the wireless spectrum bands and then dynamically tune their receivers to identify vacant channels and transmitters, and commence communication among themselves without causing interference to Primary/Licensed Users (PUs). Despite the developments in the eld of CR technology, recent research shows that still there are many challenges unaddressed in the eld. Thus, there is a need to reduce additional handshaking over control and data channels, to minimise large sized control frames and to introduce reliable channel selection process and maintenance of SUs' communication when PUs return to a licensed channel. A fundamental challenge a ecting this technology is the identi cation of reliable Data Channels (DCHs) for SUs communication among available channels and the continuation of communication when the PU returns. This doctoral research investigates in detail how to resolve issues related to the protocol design for Cognitive Radio Networks (CRNs) on Medium Access Layers (MAC) for Ad-Hoc networks. As a result, a novel Reliable and Energy e cient Cognitive Radio multi-channel MAC protocol (RECR-MAC) for Ad-Hoc networks is proposed to overcome the shortcomings mentioned. After discussing the background, operation and architecture of CR technology, this research proposes numerous platforms and testbeds for the deployment of personal and commercial applications of the CRNs. Side by side, optimised control frames and a reduced number of handshakes over the CCH are suggested to extend the transmitting time for data communication. In addition, the reliable channel selection process is introduced instead of random selection of DCHs for successful data communication among the SUs. In RECR-MAC, the objective of every SU is to select reliable DCHs, thereby ensuring high connectivity and exchanging the successful data frames across the cognitive network. Moreover, the selection criteria of the DCHs are based on multiple factors, such as an initial selection based on the maximum free time recorded by the SUs over the DCH channel ranking, which is proportional to the number of positive/negative acknowledgements, and the past history of DCHs. If more than two DCHs have an equal value during the second, third and following iterations, then the DCHs are selected based upon the maximum free time. The priorities of the DCHs are then assigned based on Reliable Data Channels, that is, RDCH 1, RDCH 2, RDCH 3, and RDCH 4 respectively (where RDCH 1 and RDCH 2 have the highest priority, DRCH 3 and RDCH 4 have the next priority, and so on). The impacts of channel selection process and Backup Data Channel (BDC) over the proposed RECR-MAC protocol are analysed in combination with comparative benchmark CR-MAC protocols based on the timing diagrams proposed. Finally, the RECR-MAC protocol is validated by using a MATLAB simulator with PU impact over the DCHs, both with and without BDC, and by comparing results, such as communication time, transmitting energy and throughput, with benchmark CR-MAC protocols.

In this thesis, research is described which leads to the proposal of a link-directionality-based dual channel MAC (Medium Access Control) protocol (DCP) for carrier sense wireless ad hoc networks. It attempts to double the capacities of such networks using an industrial standard (the single-channel IEEE 802.11 protocol) as a benchmark. Simulations show that the proposed scheme can increase the capacities to more than 1.7 times of the single-channel IEEE 802.11 protocol in large-scale random network topologies. The algorithm, however, requires extra radio spectrum resource which could be costly. In addition to DCP, a signal-to-interference ratio comparison algorithm (SCA) is proposed to further release the protocol constraints imposed by the virtual carrier-sensing mechanism. Interestingly, while the capacity of the pure DCP decreases when link lengths are short, the capacity of the pure SCA increases when link lengths are short. The two algorithms compensate for the downside of each other to bring about a more uniform capacity improvement. Simulations show that the integrated scheme can further increase the network throughputs to more than 2.13 times in random topologies. This thesis also clarifies inter-link interference in wireless ad-hoc networks by using link-directional interference graphs (l-graph). By colouring the l-graphs, independent data streams obtained by Multi-Carrier Code Division Multiple Access (MC-CDMA) are assigned for transmitting up-link and down-link traffic separately in order to eliminate the hidden-node and exposed-node problems in wireless local area networks (WLAN). Finally, a generic approach for capacity analysis is proposed to show that the concept of link-directionality can also be adopted with other network models, protocols and parameter settings. However, in certain scenarios where links are densely packed together, the advantage of using link-directionality could be diminished. Therefore, the proposed generic approach for capacity analysis allows one to determine whether channel allocations according to link-directionalities should be applied to a given network.

As more and more wireless applications/services emerge in the market, the already heavily crowded radio spectrum becomes much scarcer. Meanwhile, however,as it is reported in the recent literature, there is a large amount of radio spectrum that is under-utilized. This motivates the concept of cognitive radio wireless networks that allow the unlicensed secondary-users (SUs) to dynamically use the vacant radio spectrum which is not being used by the licensed primary-users (PUs). In this dissertation, we investigate protocol design for both the synchronous and asynchronous cognitive radio networks with emphasis on the medium access control (MAC) layer. We propose various spectrum sharing schemes, opportunistic packet scheduling schemes, and spectrum sensing schemes in the MAC and physical (PHY) layers for different types of cognitive radio networks, allowing the SUs to opportunistically utilize the licensed spectrum while confining the level of interference to the range the PUs can tolerate. First, we propose the cross-layer based multi-channel MAC protocol, which integrates the cooperative spectrum sensing at PHY layer and the interweave-based spectrum access at MAC layer, for the synchronous cognitive radio networks. Second, we propose the channel-hopping based single-transceiver MAC protocol for the hardware-constrained synchronous cognitive radio networks, under which the SUs can identify and exploit the vacant channels by dynamically switching across the licensed channels with their distinct channel-hopping sequences. Third, we propose the opportunistic multi-channel MAC protocol with the two-threshold sequential spectrum sensing algorithm for asynchronous cognitive radio networks. Fourth, by combining the interweave and underlay spectrum sharing modes, we propose the adaptive spectrum sharing scheme for code division multiple access (CDMA) based cognitive MAC in the uplink communications over the asynchronous cognitive radio networks, where the PUs may have different types of channel usage patterns. Finally, we develop a packet scheduling scheme for the PU MAC protocol in the context of time division multiple access (TDMA)-based cognitive radio wireless networks, which is designed to operate friendly towards the SUs in terms of the vacant-channel probability. We also develop various analytical models, including the Markov chain models, M=GY =1 queuing models, cross-layer optimization models, etc., to rigorously analyze the performance of our proposed MAC protocols in terms of aggregate throughput, access delay, and packet drop rate for both the saturation network case and non-saturation network case. In addition, we conducted extensive simulations to validate our analytical models and evaluate our proposed MAC protocols/schemes. Both the numerical and simulation results show that our proposed MAC protocols/schemes can significantly improve the spectrum utilization efficiency of wireless networks.