Guaranteed Rendezvous for Cognitive Radio Networks Based on Cycle Length

Rendezvous is a fundamental process establishing a communication link on common channel between a pair of nodes in the cognitive radio networks. How to reach rendezvous efficiently and effectively is still an open problem. In this work, we propose a guaranteed cycle lengths based rendezvous (CLR) algorithm for cognitive radio networks. When the cycle lengths of the two nodes are coprime, the rendezvous is guaranteed within one rendezvous period considering the time skew between the two nodes. When Ti and Tj are not coprime, i.e., Ti=Tj, the deadlock checking and node IDs are combined to decide the time point and the way to independently change the cycle length on each node to guarantee rendezvous. In detail, as long as the deadlock situation is detected based on the threshold, each node can independently change its cycle length be based on the current checking bit of the node ID. The threshold used for deadlock checking is defined as the length of the maximum possible rendezvous period between the two nodes. As long as the current checking bits between the two nodes are different, the rendezvous will be reached in the following rendezvous period, The theoretical analysis also proves the guarantee of the CLR algorithm under both the two cases. We use three metrics: success rate of rendezvous, expected time to rendezvous and channel load to conduct simulation studies. The simulation results show that the CLR algorithm always has higher successful rendezvous rate of 100%, and stable and low expected time to rendezvous compared to the HH algorithm. In addition, the channel loads are smoothly distributed on all channels with CLR, while HH algorithm depends on the channels with smaller IDs

A Reinforcement Learning Approach for the Multichannel Rendezvous Problem

In this paper, we consider the multichannel rendezvous problem in cognitive radio networks (CRNs) where the probability that two users hopping on the same channel have a successful rendezvous is a function of channel states. The channel states are modelled by two-state Markov chains that have a good state and a bad state. These channel states are not observable by the users. For such a multichannel rendezvous problem, we are interested in finding the optimal policy to minimize the expected time-to-rendezvous (ETTR) among the class of {\em dynamic blind rendezvous policies}, i.e., at the $t^{th}$ time slot each user selects channel $i$ independently with probability $p_i(t)$, $i=1,2, \ldots, N$. By formulating such a multichannel rendezvous problem as an adversarial bandit problem, we propose using a reinforcement learning approach to learn the channel selection probabilities $p_i(t)$, $i=1,2, \ldots, N$. Our experimental results show that the reinforcement learning approach is very effective and yields comparable ETTRs when comparing to various approximation policies in the literature.Comment: 5 pages, 9 figures. arXiv admin note: text overlap with arXiv:1906.1042

Cognitive radio adaptive rendezvous protocols to establish network services for a disaster response

Disasters are catastrophic events that cause great damage or loss of life. In disasters, communication services might be disrupted due to damage to the existing network infrastructure. Temporary systems are required for victims and first responders, but installing them requires information about the radio environment and available spectrum. A cognitive radio (CR) can be used to provide a flexible and rapidly deployable temporary system due to its sensing, learning and decision-making capabilities. This thesis initially examines the potential of CR technology for disaster response networks (DRN) and shows that they are ideally suited to fulfill the requirements of a DRN. A software defined radio based prototype for multiple base transceiver stations based cellular network is proposed and developed. It is demonstrated that system can support a large number of simultaneous calls with sufficient call quality, but only when the background interference is low. It is concluded that to provide call quality with acceptable latency and packet losses, the spectrum should be used dynamically for backhaul connectivity. The deployment challenges for such a system in a disaster include the discovery of the available spectrum, existing networks, and neighbours. Furthermore, to set up a network and to establish network services, initially CR nodes are required to establish a rendezvous. However, this can be challenging due to unknown spectrum information, primary radio (PR) activity, nodes, and topology. The existing rendezvous strategies do not fulfill the DRN requirements and their time to rendezvous (TTR) is long. Therefore, we propose an extended modular clock algorithm (EMCA) which is a multiuser blind rendezvous protocol, considers the DRN requirements and has short TTR. For unknown nodes and topologies, a general framework for self-organizing multihop cooperative fully blind rendezvous protocol is also proposed, which works in different phases, can terminate when sufficient nodes are discovered, and is capable of disseminating the information of nodes which enter or leave a network. A synchronization mechanism is presented for periodic update of rendezvous information. An information exchange mechanism is also proposed which expedites the rendezvous process. In both single and multihop networks, EMCA provides up to 80% improvement in terms of TTR over the existing blind rendezvous strategies while considering the PR activity. A simple Random strategy, while being poorer than EMCA, is also shown to outperform existing strategies on average. To achieve adaptability in the presence of unknown PR activity, different CR operating policies are proposed which avoid the channels detected with PR activity to reduce the harmful interference, provide free channels to reduce the TTR, and can work with any rendezvous strategy. These policies are evaluated over different PR activities and shown to reduce the TTR and harmful interference significantly over the basic Listen before Talk approach. A proactive policy, which prefers to return to channels with recent lower PR activity, is shown to be best, and to improve the performance of all studied rendezvous strategies

MAC Protocol Design for Parallel Link Rendezvous in Ad Hoc Cognitive Radio Networks

The most significant challenge for next wireless generation is to work opportunistically on the spectrum without a fixed spectrum allocation. Cognitive Radio (CR) is the candidate technology to utilize spectrum white space, which requires the CR to change its operating channel as the white space moves. In a CR ad-hoc network, each node could tune to a different channel; as a result, it cannot communicate with other nodes. This different tuning is due to the difficulty of maintaining Common Control Channel (CCC) in opportunistic spectrum network, and keeping the nodes synchronized in ad-hoc network. The CR ad-hoc network requires a protocol to match tuning channels between ad-hoc nodes, namely, rendezvous channels. In this thesis, two distributed Medium Access Control (MAC) protocols are designed that provide proper rendezvous channel without CCC or synchronization. The Balanced Incomplete Block Design (BIBD) is used in both protocols to provide our protocols a method of rendezvous between CR ad-hoc nodes. In fact, the BIBD guarantees there is at least one common element between any two blocks. If the channels are assigned to the BIBD elements and the searching sequence to the BIBD block, there is a guarantee of a rendezvous at least in one channel for each searching sequence. The first protocol uses a single-BIBD sequence and a multi-channel sensing. Alternatively, the second protocol uses a multi-BIBD sequence and a single-channel sensing. The single-sequence protocol analysis is based on the discrete Markov Chain. At the same time, the sequence structure of the BIBD in a multi-sequence protocol is used to define the Maximum Time to Rendezvous (MTTR). The simulation results confirm that the protocols outperform other existing protocols with respect to Time to Rendezvous (TTR), channel utilization, and network throughput. In addition, both protocols fairly distribute the network load on channels, and share the channels fairly among network nodes. This thesis provides straight forward and efficiently distributed MAC protocols for the CR ad-hoc networks