Spectrum sensing is a significant issue in cognitive radio networks which enables estimation of the frequency spectrum and hence provides frequency reuse. In the large‐scale cognitive radio networks, secondary users cannot share a common spectrum since the coverage area of primary users is limited. In this study, the authors suggest a diffusion adaptive learning algorithm based on correntropy cooperation policy, which first categorises received data of secondary users into several groups, and then learns a common spectrum inside each group. The mean‐square performance of proposed algorithm is analysed and supported by simulations. Experimental results show that, in a multitask cognitive network, the proposed algorithm can achieve a better mean‐square deviation learning performance both in transient and steady‐state regimes in comparison with other conventional algorithms.

ABSTRACT The deployment of multicarrier code division multiple access as the transmission scheme of the spectrum overlay based cognitive radio (CR) networks faces two challenging issues: (i) the need for spreading codes with arbitrary length and (ii) the interfering effect of the leaked power (due to spectral sidelobes) to the adjacent spectral band used by the primary system. To meet these challenges, we propose two novel complex spreading code sets. For this purpose, a cost function is defined as the ratio of the power leaked to the adjacent primary band to the power transmitted to the band allowed for CR operation. The cost function is shown to be convertible to a trace ratio problem. The two complex spreading code sets are determined by deploying two different standard solutions. The first is the conventional but approximate solution based on generalized eigenvalue decomposition (GEVD) method, and the other is an iterative algorithm that converges to the optimal solution and hence outperforms the GEVD based solution. Simulation results show that by a slight decrease in number of users, the code set yielded by iterative algorithm suppresses the leaked power to almost zero. The applicability of the proposed code sets in different scenarios is discussed. Copyright © 2012 John Wiley & Sons, Ltd.

Unique word (UW)-OFDM is a newly proposed multicarrier technique that has shown to outperform cyclic prefix (CP)-OFDM in fading channels. Until now, the spectrum of UW-OFDM is not thoroughly investigated. In this paper, we derive an analytical expression for the spectrum taking into account the DFT based implementation of the system. Simulations show that the proposed analytical results are very accurate. Compared to CP-OFDM, we show that UW-OFDM has much lower out-of-band (OOB) radiation, which makes it suitable for systems with strict spectral masks, as e.g. cognitive radios. Further, in this paper, we evaluate the effect of the redundant carrier placement on the spectrum.

Multiuser interference (MUI) and co-space interference (CSI) are two challenging issues in design of multicarrier code-division multiple-access (MC-CDMA) systems when multiple antennas are used at both the transmitter and receiver sides (MIMO transmission). On the other hand, in cognitive radio (CR) system, the secondary users that use MC-MCDA technique must deactivate the subcarriers used by the primary users. This leads to loss of orthogonality of the conventional spreading codes such as Hadamard Walsh codes. In this paper, we have modified two recently proposed linear receivers to be deployed in MIMO MC-CDMA based CR downlink transmission where some of the subcarriers are turned off. To solve the resultant non-orthogonality problem, the complex carrier interferometry (CI) codes are utilized that exist for any length. The first method, called total interference cancellation (CI-TIC), is able to completely eliminate the CSI and the MUI. The other method is called CI symbol-chip level minimum mean square error (CI-SC-MMSE) that shows superior bit error performance with respect to CI-TIC. For different scenarios, simulation results show that the proposed CI based receivers are able to effectively mitigate the MUI and the CSI in comparison with the case where Hadamard Walsh codes are utilized.

A new method is proposed in this paper to design the time-domain equalizer for orthogonal frequency division multiplexing systems based on maximizing signal-to-interference-plus-noise ratio (SINR) at the output of the equalizer. The method called Maximum SINR Time-domain Equalization (MSINR-TEQ) is derived based on a new formulation of SINR. Computer simulation and analytical results show the performance of the MSINR-TEQ method and its superiority in comparison with the performance of the much-used method of channel impulse response shortening.

A novel time domain equalizer (TEQ) design approach is proposed in this paper, based on maximizing the signal-to interference plus noise ratio (SINR). To increase the bandwidth efficiency of OFDM systems, the TEQ is used to mitigate the intersymbol interference (ISI) created by a channel with longer impulse response duration than that of the cyclic prefix (CP). The true ISI, ICI and noise parts of the signal at the output of the equalizer are formulated, based on the overall impulse response (OIR) (convolution of channel impulse response and equalizer impulse response). The SINR maximizing time-domain equalization (SMTE) method estimates the tap coefficients of the equalizer by maximizing the SINR of the signal at the output of the equalizer. Computer simulation and analytical results show that the performance of the SMTE method is superior to the performance of the much-used method of channel impulse response shortening (IRS).