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Performance analysis of selection schemes in relay assisted underlay cognitive radio networks

Contact: <Unknown username: salka35>


Cognitive radio (CR) has emerged as a promising alternative to increasing the spectrum utilization efficiency. In underlay CR, a secondary user (SU) can transmit concurrently with a primary user–who are the licensed owners of the spectrum–provided that it does not cause excessive interference at the primary receiver. These interference constraints can significantly reduce the data rates at which an SU transmits and limit its coverage. This motivates the use of cooperative relaying in an underlay CR system.

Relay assisted underlay CR networks employ large number of relays to in- crease the reliability and data rates of an underlay CR system. However, in order to harness spatial diversity due to multiple relays, a tight synchronization needs to be maintained across all the relays. Moreover, if there are N relays, you need N orthogonal channels (time/frequency slots) to forward data to the destination, which brings the spectral efficiency down by a factor of N. Relay selection eliminates the need for coordination/synchronization among the relay nodes without compromising on the diversity benefts that multiple relays can provide. Howvever, depending on the nature of the interference constraint, the relay selection policies will change.

Problem statement

The main goal of the project is to investigate relay selection policies for different kinds of interference constraints such that the symbol error probability (SEP) of the CR network is minimized or the end to end signal-to-noise ratio is maximized and the corresponding interference constraint at the primary user is met with equality. The impact of imperfect channel state information on the SEP of the CR network and the interference at the primary can also be investigated.


The student needs a strong background in mathematics (e.g. calculus and probability theory), wireless communications, and good skills in Matlab programming.


[1] A. Goldsmith, S. Jafar, I. Maric, and S. Srinivasa, Breaking spectrum gridlock with cognitive radios: An information theoretic perspective , Proc. IEEE, vol. 97, no. 5, pp. 894-914, May 2009.
[2] Minghua Xia and Aissa, S., Underlay cooperative af relaying in cellular networks: performance and challenges , IEEE Commun. Mag., vol. 51, no. 12, pp. 170-176, Dec. 2013.
[2] A. Ribeiro, X. Cai, and G. B. Giannakis, Symbol error probabilities for general cooperative links , IEEE Trans. Wireless Commun., vol. 4, no. 3, pp. 1264-1273, May 2005.

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Last updated: 2015 02 23   13:16