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

Modeling and Link Quality Assessment of THz Network Within Data Center

Terahertz band has gained enormous interest recently due to its wide bandwidth availability, and the data rate is reaching 100 Gbps are nowadays achievable. The current advancement in Terahertz technology is aiming to achieve the data rate up to 1 Terabit per second. However, the unique band characteristics introduce some issues related to the propagation channel like high path and absorption loss which increases with distance. Such limitations at one hand can limit the coverage and throughput. But, on the other hand, suits indoor environment such as data center, a data center geometry is used in this paper to design and model a network of THz nodes placed on the top of the data center racks, to increase network connectivity, THz reflectors are positioned on ceiling and walls. Through simulations, we show that it is possible to reduce the average number of interferers in the system and minimize bit error probability by using specific waveforms and planar antenna array with active variable elements

Impact of channel errors and data aggregation on throughput in THz communications

In Terahertz communications, the throughput can be affected by incoming packet rate from upper layers and channel bit error probability. The techniques like block aggregation and retransmission can be used to mitigate these effects. The impact of data aggregation and forward error control on the overall throughput of Terahertz communications is shown and modeled in this paper. The throughput is also analyzed based on buffer status. The results suggest that using block aggregation with forwarding error control can enhance the useful throughput and reduce the buffer load

Experimental evaluation of a software defined radio-based prototype for a disaster response cellular network

In post disaster situations it is vital to restore voice and data communication services quickly. Currently, portable wireless systems are used as a temporary solution. However, these solutions have a lengthy setup, limited coverage, and typically require the use of expensive satellite backhaul. Solutions based on cognitive radio mesh networks have been proposed, to exploit self-configuration and spectrum agility. To evaluate their potential, we build a software-radio-based prototype for a multi-cell network that uses an IEEE 802.11's unlicensed wireless communication band for backhaul, and an open-source GSM stack for access. The prototype provides voice communication services. We evaluate the prototype in an open environment. We demonstrate that under the right conditions, the system can support large numbers of simultaneous calls with acceptable quality. However, when the unlicensed band is heavily used, call quality quickly degrades because of interference on the backhaul link. We conclude that in order to provide acceptable quality of service it is desirable to exploit idle licensed spectrum for backhaul communication between base stations

Cognitive radio policy-based adaptive blind rendezvous protocols for disaster response

In disaster scenarios, with damaged network infrastructure, cognitive radio (CR) can be used to provide temporary network access in the first few hours. Since spectrum occupancy will be unknown, the radios must rely on spectrum sensing and opportunistic access. An initial goal is to establish rendezvous between CR nodes to set up the network. The unknown primary radio (PR) activity and CR node topology makes this a challenging task. Existing blind rendezvous strategies provide guarantees on time to rendezvous, but assume channels with no PR activity and no external interferers. To handle this problem of blind multi-node rendezvous in the presence of primary users, we propose an Extended Modular Clock Algorithm which abandons the guarantee on time to rendezvous, an information exchange mechanism for the multi-node problem, and various cognitive radio operating policies. We show that the adapted protocols can achieve up to 80% improvement in the expected time to rendezvous and reduce the harmful interference caused to the primary radio

A cognitive radio-based fully blind multihop rendezvous protocol for unknown environments

In Cognitive Radio networking, the blind rendezvous problem is when two or more nodes must establish a link, but where they have no predefined schedule or common control channel for doing so. The problem becomes more challenging when the information about the existence of other nodes in the network, their topology, and primary user activity are also unknown, identified here as a fully blind rendezvous problem. In this paper, a novel and fully blind multihop (FBM) rendezvous framework is proposed with an extended modular clock algorithm (EMCA). The EMCA-FBM is a fully blind multihop rendezvous protocol as it assumes the number of nodes, primary radio activity and topology information as unknown. It is shown to work with different Cognitive Radio operating policies to achieve adaptiveness towards the unknown primary radio activity, and self-organization for autonomously handling the rendezvous process by using transmission schedules. It is capable of working without any information of neighbor nodes and terminating the rendezvous process whenever all or sufficient nodes are discovered. The proposed FBM is also shown to work as a general framework to extend existing single hop rendezvous protocols to work as a multihop rendezvous protocol. In comparison with other modified blind rendezvous strategies for multihop network, the combination of the proposed EMCA-FBM protocol and operating policies is shown to be effective in improving the average time to rendezvous (up to 70%) and neighbor discovery accuracy (almost 100%) while reducing harmful interference

Cognitive radio for disaster response networks: survey, potential, and challenges

In the wake of a natural or man-made disaster, restoration of telecommunications is essential. First responders must coordinate their responses, immediate casualties require assistance, and all affected citizens may need to access information and contact friends and relatives. Existing access and core infrastructure may be damaged or destroyed, so to support the required services, new infrastructure must be rapidly deployed and integrated with undamaged resources still in place. This new equipment should be flexible enough to interoperate with legacy systems and heterogeneous technologies. The ability to selforganize is essential in order to minimize any delays associated with manual configuration. Finally, it must be robust and reliable enough to support mission-critical applications. Wireless systems can be more easily reconfigured than wired solutions to adapt to the various changes in the operating environment that can occur in a disaster scenario. A cognitive radio is one that can observe its operating environment, make decisions and reconfigure in response to these observations, and learn from experience. This article examines the use of cognitive radio technologies for disaster response networks and shows that they are ideally suited to fulfill the unique requirements of these networks. Key enabling technologies for realizing real-world cognitive radio networks for disaster response are discussed and core challenges are examined

Integrating THz Wireless Communication Links in a Data Centre Network

Modern data centre networks are increasingly made up of optical fibre connections and controlled by software defined networking. Recent advances in THz wireless technologies have paved the way for ultra-high bandwidth wireless communication, reaching the point where these wireless links can begin to compete with optical fibre links. This work investigates the feasibility of integrating wireless THz links in a data centre network, reporting on the performance that can be achieved at the physical layer, proposing an architecture for the data link layer and illustrating, through network emulation, how these wireless links could be used to reduce congestion in a network