Decentralised Learning MACs for Collision-free Access in WLANs

By combining the features of CSMA and TDMA, fully decentralised WLAN MAC schemes have recently been proposed that converge to collision-free schedules. In this paper we describe a MAC with optimal long-run throughput that is almost decentralised. We then design two \changed{schemes} that are practically realisable, decentralised approximations of this optimal scheme and operate with different amounts of sensing information. We achieve this by (1) introducing learning algorithms that can substantially speed up convergence to collision free operation; (2) developing a decentralised schedule length adaptation scheme that provides long-run fair (uniform) access to the medium while maintaining collision-free access for arbitrary numbers of stations

Random Access Game and Medium Access Control Design

Motivated partially by a control-theoretic viewpoint, we propose a game-theoretic model, called random access game, for contention control. We characterize Nash equilibria of random access games, study their dynamics, and propose distributed algorithms (strategy evolutions) to achieve Nash equilibria. This provides a general analytical framework that is capable of modeling a large class of system-wide quality-of-service (QoS) models via the specification of per-node utility functions, in which system-wide fairness or service differentiation can be achieved in a distributed manner as long as each node executes a contention resolution algorithm that is designed to achieve the Nash equilibrium. We thus propose a novel medium access method derived from carrier sense multiple access/collision avoidance (CSMA/CA) according to distributed strategy update mechanism achieving the Nash equilibrium of random access game. We present a concrete medium access method that adapts to a continuous contention measure called conditional collision probability, stabilizes the network into a steady state that achieves optimal throughput with targeted fairness (or service differentiation), and can decouple contention control from handling failed transmissions. In addition to guiding medium access control design, the random access game model also provides an analytical framework to understand equilibrium and dynamic properties of different medium access protocols

A Media Access Control Protocol for Wireless Adhoc Networks with Misbehaviour Avoidance

The most common wireless Medium Access Control (MAC) protocol is IEEE 802.11. Currently IEEE 802.11 standard protocol is not resilient for many identified MAC layer attacks, because the protocol is designed without intention for providing security and with the assumption that all the nodes in the wireless network adhere to the protocol. However, nodes may purposefully show misbehaviours at the MAC layer in order to obtain extra bandwidth con-serve resources and degrade or disrupt the network performance. This research proposes a secure MAC protocol for MAC layer which has integrated with a novel misbehaviour detection and avoidance mechanism for Mobile Ad Hoc Networks (MANETs). The proposed secure MAC protocol the sender and receiver work collaboratively together to handshakes prior to deciding the back-off values. Common neighbours of the sender and receiver contributes effectively to misbehaviours detection and avoidance process at MAC layer. In addition the proposed solution introduces a new trust distribution model in the network by assuming none of the wireless nodes need to trust each other. The secure MAC protocol also assumes that misbehaving nodes have significant levels of intelligence to avoid the detectio

Exploiting programmable architectures for WiFi/ZigBee inter-technology cooperation

The increasing complexity of wireless standards has shown that protocols cannot be designed once for all possible deployments, especially when unpredictable and mutating interference situations are present due to the coexistence of heterogeneous technologies. As such, flexibility and (re)programmability of wireless devices is crucial in the emerging scenarios of technology proliferation and unpredictable interference conditions. In this paper, we focus on the possibility to improve coexistence performance of WiFi and ZigBee networks by exploiting novel programmable architectures of wireless devices able to support run-time modifications of medium access operations. Differently from software-defined radio (SDR) platforms, in which every function is programmed from scratch, our programmable architectures are based on a clear decoupling between elementary commands (hard-coded into the devices) and programmable protocol logic (injected into the devices) according to which the commands execution is scheduled. Our contribution is two-fold: first, we designed and implemented a cross-technology time division multiple access (TDMA) scheme devised to provide a global synchronization signal and allocate alternating channel intervals to WiFi and ZigBee programmable nodes; second, we used the OMF control framework to define an interference detection and adaptation strategy that in principle could work in independent and autonomous networks. Experimental results prove the benefits of the envisioned solution

A Resilient MAC Protocol for Wireless Networks

Paper presented at the IMA Conference on Game Theory and its Applications, Oxford, 8/12/2014Peer reviewe

Counting Is Not Enough: Investing in Qualitative Case Reviews for Practice Improvement in Child Welfare

Outlines the value of quality case service reviews in child welfare systems, requirements for building and sustaining a robust process and adapting it under limited state budgets, and recommendations for jurisdictions, initiators, and national leadership