In Chapter I, we introduced and motivated the problems. In Chapter II, we proposed the cross-layer based opportunistic MAC protocols, which integrate the cooperative spectrum sensing at PHY layer and the packets scheduling at MAC layer, for the syn- chronous cognitive radio networks. Specifically, the MAC protocols enable the SUs to identify and utilize the vacant frequency spectrum in a way that constrains the level of interference to the PUs. In our proposed protocols, each SU is equipped with two transceivers. One transceiver is tuned to the dedicated control channel, while the other is used as a cognitive radio that can periodically sense and dynamically use the identified vacant channels. To obtain the channel status accurately, we proposed two collaborative channel spectrum-sensing policies, namely, the random sensing policy and the negotiation-based sensing policy, to help the MAC protocols detect the avail- ability of vacant channels. Under the random sensing policy, each SU just randomly selects one of the channels for sensing. On the other hand, under the negotiation- based sensing policy, different SUs attempt to select the distinct channels to sense by overhearing the control packets over the control channel. We developed the Markov
chain model and the M/GY/1-based queueing model to characterize the performance
of our proposed multi-channel MAC protocols under the two types of channel-sensing policies for the saturation network and the non-saturation network scenarios, respec- tively. In the non-saturation network case, we quantitatively identified the tradeoff between the aggregate traffic throughput and the packet transmission delay, which can provide the insightful guidelines to improve the delay-QoS provisionings over cognitive radio wireless networks.
In Chapter III, we proposed a channel-hopping based cognitive radio MAC pro- tocol for synchronized wireless networks with hardware constraints, which can enable the SUs to opportunistically utilize the unused licensed-spectrum without interfering with the PUs. In our proposed scheme, the SUs switch across the licensed channels with their distinct channel-hopping sequences. In particular, when an SU sender wants to send packets to its intended SU receiver, the SU sender changes its hopping schedule and follows the hopping sequence of the intended receiver to conduct the negotiation and then transmit data packets if the channel is not currently used by PUs. The main advantages of our proposed scheme include the followings: 1) no extra control channel is needed; 2) it overcomes the single control channel bottle- neck problem; and 3) one transceiver is sufficient. We developed an Markov chain based analytical model to analyze the performance of our proposed scheme in terms of throughputs. We also identified the tradeoff between the channel utilization and the packet transmission delay.
Chapter IV proposed an efficient Cognitive Radio-EnAbled Multi-channel MAC (CREAM-MAC) protocol, which integrates the sequential spectrum sensing at phys- ical layer and the packet scheduling at MAC layer, over the wireless DSA networks. Under the proposed CREAM-MAC protocol, each SU is equipped with a cognitive radio-enabled transceiver and multiple channel sensors. Our cooperative sequential
spectrum sensing scheme improves the accuracy of spectrum sensing and further pro- tects the PUs. The proposed CREAM-MAC enables the SUs to best utilize the unused frequency spectrum while avoiding the collisions among SUs and between SUs and PUs. We developed the Markov chain model and M/GY/1 queueing model
to rigourously study our proposed CREAM-MAC protocol for both the saturation networks and the non-saturation networks. We also conducted extensive simulations to validate our developed protocol and analytical models.
In Chapter V, we considered a cognitive radio wireless network in which a set of SUs opportunistically utilize the wireless spectrum licensed to the PUs to transmit packets to the secondary base station. It is challenging to maximize the spectrum utilization while limiting the interference imposed to PUs due to SUs. To achieve the optimal tradeoff between the spectrum utilization and the interference caused by SUs, we proposed the adaptive spectrum sharing schemes for code division multiple access (CDMA) based cognitive medium access control (MAC) in the uplink communications over the cognitive radio networks. Our proposed schemes address the joint problems of channel sensing, data transmission, and power and rate allocations. Under our pro- posed schemes, the SUs can adaptively select between the intrusive spectrum sharing and the non-intrusive spectrum sharing operations to transmit data to secondary base station based on the channel utilization, traffic load, and interference constraints. Our proposed schemes enable the SUs to efficiently utilize the available frequency spec- trum which is licensed to the PUs while stringently limiting the interference to the PUs. We also conducted extensive simulations to validate and evaluate our proposed schemes, which show the superiority of our proposed schemes as compared with the other schemes.
In Chapter VI, instead of focusing on the SUs, we concentrate on the PU net- works. By exploiting the unique property of the wireless fading channel and cross-
layer design technique, we developed a packet scheduling scheme for the PUs in the context of wireless TDMA networks, which is set up to operate friendly towards the SUs in terms of vacant-channel probability. Our proposed scheme can be imple- mented with just slight modification on the traditional TDMA scheduling algorithm. We developed a rigorous queuing model, and then quantitatively analyze the tradeoff among multiple performance metrics to identify when and where the cost for favoring the SUs is worthy. The analytical results show that our proposed scheme can gen- erate more vacant-channel opportunities for SUs, at the expense of little increasing packet delay for PUs, as compared with the traditional wireless TDMA scheduling algorithm. In addition, since the implementation of our proposed scheme only needs little modification on the existing TDMA scheduling algorithm, our proposed scheme is a practical and cost-effective approach to increase the wireless spectrum utilization.