• Mohammad Robat Mili

Student thesis: Phd


This thesis describes how to design and analyze ad hoc cognitive radio networks. In a cognitive radio scenario which consists of primary users and secondary users, secondary users are allowed to opportunistically access the existing spectrum without adverse effect on primary users. A cognitive radio network is allowed to detect its communication environment, replace the parameters of its communication scheme to raise the quality of service for secondary users and decrease the interference to primary users. Alternatively, the other approach to implementing a cognitive radio network is to allow simultaneous transmission of primary users and secondary users, which is also termed as spectrum sharing. In this technique, a secondary transmitter can transmit while its maximum interference to the primary receiver is smaller than the predefined threshold. However, a secondary user must control its transmit power to get a reasonable transmission rate. In spectrum sharing approach, we maximize the ergodic capacity and minimize bit error rate under different constraints at the primary users. The effect of reducing channel side information at the secondary transmitter is discussed for both optimization problems. We will then extend the simple model to ad hoc cognitive radio network where higher number of links in primary and secondary networks exists. The interference from primary and other secondary transmitters were separately discussed. In a similar system model, we also analyze outage probability of secondary users under AWGN and Rayleigh fading channels, while applying Poisson distribution to accurately account for the spatial distribution of secondary users in a 2-dimensional plane. The explicit expressions are derived based on different parameters such as signal-to-interference-plus-noise ratio threshold, path loss exponent, signal-to-noise-ratio in the absence of interference and density of secondary interferes. The obtained results can be used to design and implementation of new protocols in ad hoc networks such that the highest data rate can be transmitted from a source node to a destination node with the lowest bit error rate. The next part of this thesis is concerned with minimization of power transmission in co-channel femtocell networks in order to reduce the interference inflicted on the macrocell users while satisfying a target constraint on either the capacity or the BER. This minimization is applied in two different system models. We also prove that minimizing the transmit power can be utilized to further enhance energy efficiency in femtocell networks.
Date of Award31 Dec 2012
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorKhairi Hamdi (Supervisor)

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