674 research outputs found

    Multihop Rendezvous Algorithm for Frequency Hopping Cognitive Radio Networks

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    Cognitive radios allow the possibility of increasing utilization of the wireless spectrum, but because of their dynamic access nature require new techniques for establishing and joining networks, these are known as rendezvous. Existing rendezvous algorithms assume that rendezvous can be completed in a single round or hop of time. However, cognitive radio networks utilizing frequency hopping that is too fast for synchronization packets to be exchanged in a single hop require a rendezvous algorithm that supports multiple hop rendezvous. We propose the Multiple Hop (MH) rendezvous algorithm based on a pre-shared sequence of random numbers, bounded timing differences, and similar channel lists to successfully match a percentage of hops. It is tested in simulation against other well known rendezvous algorithms and implemented in GNU Radio for the HackRF One. We found from the results of our simulation testing that at 100 hops per second the MH algorithm is faster than other tested algorithms at 50 or more channels with timing ±50 milliseconds, at 250 or more channels with timing ±500 milliseconds, and at 2000 channels with timing ±5000 milliseconds. In an asymmetric environment with 100 hops per second, a 500 millisecond timing difference, and 1000 channels the MH algorithm was faster than other tested algorithms as long as the channel overlap was 35% or higher for a 50% required packet success to complete rendezvous. We recommend the Multihop algorithm for use cases with a fast frequency hop rate and a slow data transmission rate requiring multiple hops to rendezvous or use cases where the channel count equals or exceeds 250 channels, as long as timing data is available and all of the radios to be connected to the network can be pre-loaded with a shared seed

    Defining the gap between research and practice in public relations programme evaluation - towards a new research agenda

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    The current situation in public relations programme evaluation is neatly summarized by McCoy who commented that 'probably the most common buzzwords in public relations in the last ten years have been evaluation and accountability' (McCoy 2005, 3). This paper examines the academic and practitioner-based literature and research on programme evaluation and it detects different priorities and approaches that may partly explain why the debate on acceptable and agreed evaluation methods continues. It analyses those differences and proposes a research agenda to bridge the gap and move the debate forward