Abstract
In this article, challenges regarding the provision of channel state information (CSI) in non-contiguous orthogonal frequency division multiplexing (NC-OFDM) cognitive radio (CR) systems are addressed. We propose a novel scheme that utilizes cross entropy (CE) optimization together with an analytical pilot power distribution technique to design pilot symbols that minimizes the channel estimate mean squared error (MSE) of frequency-selective channels. The optimal selection of pilot subcarriers is a combinatorial problem that requires heavy computations. To reduce the computational complexity, the CE optimization is utilized to determine the position of pilot subcarriers. Then, for a given pilot placement obtained by the CE algorithm, a closed form expression to obtain optimal pilot power distribution is employed. Simulation results indicate that, the proposed pilot symbol design provides better channel estimate MSE as well as the bit error rate (BER) performance when compared with the conventional equal powered pilot design.
Highlights
The immense growth of wireless access technologies calls for more and more spectrum resources following the conventional spectrum framework, where most of the spectrum bands are exclusively allocated to specific licensed services
We propose a novel method that utilizes cross entropy (CE) optimization together with the analytical pilot power optimization to design pilot symbols for non-contiguous orthogonal frequency division multiplexing (NC-OFDM) to lower the mean squared error (MSE) of the least square (LS) channel estimate of the frequency-selective channel
4.1 Computational complexity analysis we evaluate the computational complexity of our proposed scheme over the exhaustive search (ES) and the conventional reference design in [7,8]
Summary
The immense growth of wireless access technologies calls for more and more spectrum resources following the conventional spectrum framework, where most of the spectrum bands are exclusively allocated to specific licensed services. Measurements have shown that, a lot of licensed bands are underutilized [1,2,3], which results into spectrum wastage and promotes artificial spectrum scarcity. This has fostered the spectrum regulatory bodies such as Federal Communications Commission (FCC) to open the licensed bands to unlicensed users through the use of cognitive radio (CR) technology [4,5]. To exploit limited spectrum efficiently, CR technology allows unlicensed users to access licensed spectrum bands. CR improves spectral efficiency by sensing the spectrum, detects the presence of the primary users (PUs) and exploits the unused spectrum without disturbing the PUs [3].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
