Abstract
Spectrum sharing cognitive radio aims to improve the spectrum efficiency via sharing the spectrum band licensed to the primary user (PU) with the secondary user (SU) concurrently provided that the interference caused by the SU to the PU is limited. The channel state information (CSI) between the secondary transmitter (STx) and the primary receiver (PRx) is used by the STx to calculate the appropriate transmit power to limit the interference. We assume that this CSI is not only having channel estimation errors but also outdated due to feedback delay, which is different from existing studies. We derive closed-form expressions for the ergodic capacities of the SU with this imperfect CSI under the average interference power (AIP) constraint and the peak interference power (PIP) constraint. Illustrative results are presented to show the effects of the imperfect CSI. It is shown that the ergodic capacity of the SU is robust to the channel estimation errors and feedback delay under high feedback delay. It is also shown that decreasing the distance between STx and secondary receiver (SRx) or increasing the distance between STx and PRx can mitigate the impact of the imperfect CSI and significantly increase the ergodic capacity of the SU.
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Notes
For Jakes’ [17] model, the channel recorrelates after it becomes uncorrelated and the highest \(|\rho |\) is equal to 0.4. However, in Sects. 3 and 4, we show that the ergodic capacity of the SU depends on \(\rho ^{2}\), and in Sect. 5, we show that for \(0\le \rho \le 0.4\), the ergodic capacity of the SU changes negligibly. Therefore, similar to most of existing studies [18], we assume once \(\rho \) is equal to zero, \(\rho \) remains zero at all higher \(\tau \) and \(0\le \rho \le 1\).
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This work was supported by the 973 Program (2009CB320400), Sino-Finland ICT Collaborations Program (2010DFB10410) and European COST Action IC0902 Project.
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Xu, D., Feng, Z. & Zhang, P. On the Impacts of Channel Estimation Errors and Feedback Delay on the Ergodic Capacity for Spectrum Sharing Cognitive Radio. Wireless Pers Commun 72, 1875–1887 (2013). https://doi.org/10.1007/s11277-013-1100-5
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DOI: https://doi.org/10.1007/s11277-013-1100-5