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Offloading Spectrum Sensing Enabled by Blockchain

Lupe

Group Members: Nadiya Romanova, Joel Stenkvist, Pratik Walvekar, Jakob Wiren

Supervisors: Suzan Bayhan and Anatolij Zubow

The growth of internet traffic is exploding with an exponential growth in the number of connected devices and more data-consuming traffic for example video. As radio spectrum is naturally limited resource and cannot be expanded, new ways to use the existing spectrum more efficiently is necessary. Cognitive radio (CR) allows unlicensed- / secondary users (SU) to use licensed spectrums when idle.The first rule of cognitive spectrum access is to make sure that the primary user (PU) of the spectrum must not be interrupted if the spectrum is used for an SU. Currently this is solved by sensing the spectrum for PU activity with some arbitrary interval. During sensing, transmission is paused and hence, the overall performance may be affected. A suggested solution to this issue, is to offload the sensing to a helper which offers to sense the spectrum in exchange for some payment. To handle the setup of a contract and exchange of payments between an SU and a helper, smart contracts and blockchain may be a solution. The goal with this project was to analyse a spectrum sensing system consisting of a PU, an SU and several helpers and investigate how offloading the sensing would affect both the SU and PU in terms of network performance such as throughput and collision probability. More specifically, a payment system to handle the contracts and exchange of payments was desired to be built on an ethereum blockchain. Since an exchange of payments is present, this might attract cheating helpers that send faulty data to earn money or users that send faulty data with purpose to make the SU collide with the PU, for example. Hence, cheating helpers were taken into consideration. An endless number of cheating types may appear in such a system. To limit our scope, two types of cheaters were taken into consideration.

 

  1. The first type of cheater will simply generate a random sequence of data without sensing the
    spectrum which is sent to the SU. This type of cheating may be used by a cheater with
    initiative to earn money by minimal work.
  2. The second type of cheater senses the spectrum and acts dichotomously to the sensed spectrum. If the spectrum is busy, the cheater would tell the SU the spectrum is free. This type of cheater may be a malware or similar.

Based on an Ethereum blockchain, a smart payment system was successfully built. The smart payment system was written in Javascript and Solidity – a contract-oriented programming language for writing smart contracts. The contracts were hosted on an Ethereum blockchain. This means, that all transactions and storage of assets were run on an Ethereum network. By using these components, a smart payment system that can initiate contracts, store assets and transfer assets was successfully built. By building a simulation environment for a radio spectrum with a PU, an SU and several helpers in Matlab it was possible to simulate various events to measure the network performance. By running several simulations, it was possible to conclude that spectrum sensing improves the throughput for the SU as well as lowers the collision probability with the PU. It was also noticeable that the spectrum sensing is extra beneficial when the PU activity is high. Moreover, it was also possible to conclude that cheating helpers may affect the overall performance of the network, in particular a large proportion of
cheaters of the total available helpers.

Even if it was proved that offloading spectrum sensing can be an alternative to increase the performance in a network it would be necessary to perform further analysis whether it would be beneficial to offload the spectrum from a cost-perspective as well as investigate in more cheating scenarios.

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