The rendezvous process allows cognitive users to find an available channel and establish a communication link. The implementation of rendezvous strategies to minimize the time to rendezvous (TTR) is a major challenge in this context. In this paper we present a comprehensive analysis of the benefits of periodic channel hopping sequences in the rendezvous process. We also introduce a novel short-sequence-based (SSB) rendezvous algorithm which works under symmetric and asymmetric channel models. Theoretical analysis and simulations show that the proposed SSB outperforms other recently developed rendezvous protocols in terms of expected TTR and maximum TTR.

Cognitive radio networks (CRNs) have emerged as a promising paradigm that can solve the shortage of spectrum resources, providing the ability to adapt and opportunistically exploit the spectrum holes. The rendezvous process allows cognitive users to find a common channel and establish a communication link. In this paper, we focus on the design of fast blind rendezvous algorithms to guarantee that every node should be able to rendezvous in all common available channels. We follow a systematic approach by first proposing a role-based algorithm that ensures maximum rendezvous diversity and then extending it to a common strategy through the use of multiples radios. Both proposals guarantee rendezvous under symmetric and asymmetric models. Simulation results show that our proposals outperform other recently developed rendezvous protocols with similar approaches in terms of expected time to rendezvous and maximum time to rendezvous.

It has been demonstrated that LoRa-based wide area networks (WANs) can cover extended areas under harsh propagation conditions. Traditional LoRaWAN solutions based on single-hop access face important drawbacks related to the presence of blind spots. This paper aims to tackle blind spots and performance issues by using a relaying approach. Many researchers investigating multi-hop solutions consider a fixed spreading factor (SF). This simplifies synchronization and association processes, but does not take advantage of the orthogonality between the virtual channels (i.e., frequency, SF) that help to mitigate blind spots. This paper proposes a time-slotted spreading factor hopping (TSSFH) mechanism that combines virtual channels and time slots into a frame structure. Pseudo-random scheduling is used inside blind spots, which simplifies the end-devices’ communication process and network organization. The results show how collisions decrease inside blind spots when more communication opportunities become available as more relaying nodes can be listening in different cells (i.e., frequency, SF-offset, time-offset). This has a direct impact on the collision-free packet delivery ratio (PDR) metric, which improves when more listening windows are opened, at the expense of faster battery depletion.

Rendezvous is the process in which two users attempt to meet on a common channel and it is of fundamental importance in cognitive ad hoc radio networks. A cognitive radio blind rendezvous algorithm named simple role‐based is proposed that exploits the common channel labelling inherent to wireless networks. The scheme guarantees the simultaneous rendezvous of multiple cognitive users. Analytical expressions are derived for the expected time to rendezvous and maximum time to rendezvous. Numerical results show that the proposed method outperforms the other well‐known rendezvous algorithms.

Blind rendezvous strategies for dynamic spectrum access in multi-channel ad-hoc networks have recently attracted the attention of many researchers. Their work has mostly focused on the design of rendezvous strategies between two network devices which actively try to establish communication. In this paper, we extend the analysis of pair-wise strategies to multi-hop ad-hoc networks and propose strategies to implement rendezvous process in these scenarios. The upper bound of time to rendezvous for multiple users is computationally derived for different network topologies. Analytic results are validated through extensive simulations using state-of-the-art channel hopping sequences.