Conference Paper

# Adaptive rate transmission for spectrum sharing system with quantized channel state information

Electr. & Comput. Eng., Texas A&M Univ. at Qatar, Doha, Qatar

DOI: 10.1109/CISS.2011.5766156 Conference: Information Sciences and Systems (CISS), 2011 45th Annual Conference on Source: IEEE Xplore

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**ABSTRACT:**Traditionally, the frequency spectrum is licensed to users by government agencies in a rigid manner where the licensee has the exclusive right to access the allocated band. Therefore, licensees are protected from any interference all the time. From a practical standpoint, however, an unlicensed (secondary) user may share a frequency band with its licensed (primary) owner as long as the interference it incurs is not deemed harmful by the licensee. In a fading environment, a secondary user may take advantage of this fact by opportunistically transmitting with high power when its signal, as received by the licensed receiver, is deeply faded. In this paper we investigate the capacity gains offered by this dynamic spectrum sharing approach when channels vary due to fading. In particular, we quantify the relation between the secondary channel capacity and the interference inflicted on the primary user. We further evaluate and compare the capacity under different fading distributions. Interestingly, our results indicate a significant gain in spectrum access in fading environments compared to the deterministic caseIEEE Transactions on Wireless Communications 03/2007; · 2.42 Impact Factor - [Show abstract] [Hide abstract]

**ABSTRACT:**In this paper, we analyze the capacity gains of opportunistic spectrum-sharing channels in fading environments with imperfect channel information. In particular, we consider that a secondary user may access the spectrum allocated to a primary user as long as the interference power, inflicted at the primar's receiver as an effect of the transmission of the secondary user, remains below predefined power limits, average or peak, and investigate the capacity gains offered by this spectrum-sharing approach when only partial channel information of the link between the secondaryiquests transmitter and primary's receiver is available to the secondary user. Considering average received-power constraint, we derive the ergodic and outage capacities along with their optimum power allocation policies for Rayleigh flat-fading channels, and provide closedform expressions for these capacity metrics. We further assume that the interference power inflicted on the primaryiquests receiver should remain below a peak threshold. Introducing the concept of interference-outage, we derive lower bounds on the ergodic and outage capacities of the channel. In addition, we obtain closedform expressions for the expenditure-power required at the secondary transmitter to achieve the above-mentioned capacity metrics. Numerical simulations are conducted to corroborate our theoretical results.IEEE Transactions on Communications 12/2009; · 1.75 Impact Factor -
##### Article: Capacity Limits and Performance Analysis of Cognitive Radio With Imperfect Channel Knowledge

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**ABSTRACT:**Cognitive radio (CR) design aims to increase spectrum utilization by allowing the secondary users (SUs) to coexist with the primary users (PUs), as long as the interference caused by the SUs to each PU is properly regulated. At the SU, channel-state information (CSI) between its transmitter and the PU receiver is used to calculate the maximum allowable SU transmit power to limit the interference. We assume that this CSI is imperfect, which is an important scenario for CR systems. In addition to a peak received interference power constraint, an upper limit to the SU transmit power constraint is also considered. We derive a closed-form expression for the mean SU capacity under this scenario. Due to imperfect CSI, the SU cannot always satisfy the peak received interference power constraint at the PU and has to back off its transmit power. The resulting capacity loss for the SU is quantified using the cumulative-distribution function of the interference at the PU. Additionally, we investigate the impact of CSI quantization. To investigate the SU error performance, a closed-form average bit-error-rate (BER) expression was also derived. Our results are confirmed through comparison with simulations.IEEE Transactions on Vehicular Technology 06/2010; · 2.06 Impact Factor

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