An Overlay Cognitive Radio Model Exploiting the Polarization Diversity and Relay Cooperation
TL;DR: A dual-polarized antenna is incorporated at the secondary transmitter, one of which acts as a relay to the primary user’s signal and cancels out the interference via space–time coding.
Abstract: Interference mitigation is one of the significant challenges in overlay cognitive radio (CR). This paper proposes a scheme to avoid the interference in an overlay CR scenario by exploiting the polarization diversity and relay cooperation. In this scheme, a dual-polarized antenna is incorporated at the secondary transmitter, one of which acts as a relay to the primary user’s signal and cancels out the interference via space–time coding. Analytical results about the error performance and the outage probability for the scheme have been calculated. The performance degradation in the absence of perfect CSI has also been shown.
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TL;DR: Estimates for the uncoded average symbol error rate of spatial multiplexing and transmit diversity are derived and channel conditions where the use of polarization diversity yields performance improvements are identified.
Abstract: Multiple-input multiple-output (MIMO) antenna systems employ spatial multiplexing to increase spectral efficiency or transmit diversity to improve link reliability. The performance of these signaling strategies is highly dependent on MIMO channel characteristics, which, in turn, depend on antenna height and spacing and richness of scattering. In practice, large antenna spacings are often required to achieve significant multiplexing or diversity gain. The use of dual-polarized antennas (polarization diversity) is a promising cost- and space-effective alternative, where two spatially separated uni-polarized antennas are replaced by a single antenna structure employing orthogonal polarizations. This paper investigates the performance of spatial multiplexing and transmit diversity (Alamouti (see IEEE J. Select. Areas Commun., vol.16, p.1451-58, Oct. 1998) scheme) in MIMO wireless systems employing dual-polarized antennas. In particular, we derive estimates for the uncoded average symbol error rate of spatial multiplexing and transmit diversity and identify channel conditions where the use of polarization diversity yields performance improvements. We show that while improvements in terms of symbol error rate of up to an order of magnitude are possible in the case of spatial multiplexing, the presence of polarization diversity generally incurs a performance loss for transmit diversity techniques. Finally, we provide simulation results to demonstrate that our estimates closely match the actual symbol error rates.
302 citations
TL;DR: A new and simple analytical framework is presented to model dual-polarized Rayleigh and Ricean fading channels for arbitrary array sizes and investigates the multiplexing advantage of dual- polarized transmissions through the evaluation of the ergodic mutual information.
Abstract: In this paper, we address the potential benefits of dual-polarized arrays in multi-antenna wireless systems. After an extensive literature overview of experimental data, we present a new and simple analytical framework to model dual-polarized Rayleigh and Ricean fading channels for arbitrary array sizes. The model relies on a limited number of physical parameters, such as the channel spatial correlations, the channel co-polar and the cross-polar ratios and the antenna cross-polar discrimination. Then, we investigate the multiplexing advantage of dual-polarized transmissions through the evaluation of the ergodic mutual information, for both TITO and MIMO systems. Finally, the performance of two space-time coding schemes (Alamouti OSTBC and uncoded spatial multiplexing) is evaluated via a detailed analysis of the pairwise error probability.
224 citations
TL;DR: In this paper, the authors presented outdoor propagation measurements together with derivative analysis, modeling, and simulation of the 2/spl times/2 fixed wireless MIMO channel with dual-polarized antennas.
Abstract: This paper presents outdoor propagation measurements together with derivative analysis, modeling, and simulation of the 2/spl times/2 fixed wireless multiple-input multiple-output (MIMO) channel Experimental data were collected in the suburban residential areas of San Jose, CA, at 248 GHz by using dual-polarized antennas Measurement results include the estimation of path loss, Rician K-factor, cross-polarization discrimination (CPD), correlation coefficients, and the MIMO channel capacity An elaborate K-factor model that assumes variation over location, time, and frequency is developed Distance-dependent CPD models of the variable and constant signal components are proposed A generalized 2/spl times/2 MIMO channel model is then derived based on the correlation among the path loss, the copolarized K-factor, and the CPD's distribution of the constant and scattered signal components Finally, the MIMO channel response is simulated using the newly developed model, and results are found to be well in agreement with measurements
162 citations
11 May 2008
TL;DR: The main conclusion is that DP antennas might not always yield the best MIMO performance, but instead offer compact antenna solutions for mobile devices and robust performance that is more insensitive to the aforementioned imperfections.
Abstract: In this work the modeling and capacity of a dual polarized (DP) MIMO channel is addressed. The modeling includes channel parameters such as receive and transmit correlation, channel cross-polarization discrimination (XPD), and antenna parameters such as polarization state, polarization parallelity and coupling. The capacity of the DP MIMO channel is evaluated and compared to the capacity of a single polarized (SP) MIMO system. The SP MIMO system with spatially separated antenna sensors has the advantage that it also offers array gain and will therefore during idealized conditions outperform the DP MIMO system. However, in this work it is found that this advantage often is reduced and sometimes even lost when channel and antenna imperfections such as, e.g., correlation, channel XPD, and polarization mismatch are introduced. The main conclusion is that DP antennas might not always yield the best MIMO performance, but instead offer compact antenna solutions for mobile devices and robust performance that is more insensitive to the aforementioned imperfections.
115 citations
TL;DR: This paper considers a cooperative scenario with multiple relays and amplify-and-forward protocol over frequency flat fading channels and presents lower and upper bounds on the effective SNR and closed-form expressions for the bounds on average symbol error rate (ASER), outage probability and average capacity per bandwidth of the received signal in the presence of channel estimation errors.
Abstract: In this paper, we investigate the performance of selection cooperation in the presence of imperfect channel estimation. In particular, we consider a cooperative scenario with multiple relays and amplify-and-forward protocol over frequency flat fading channels. In the selection scheme, only the "best" relay which maximizes the effective signal-to-noise ratio (SNR) at the receiver end is selected. We present lower and upper bounds on the effective SNR and further we provide closed-form expressions for the bounds on average symbol error rate (ASER), outage probability and average capacity per bandwidth of the received signal in the presence of channel estimation errors. A simulation study is presented to corroborate the analytical results and to demonstrate the performance of relay selection with imperfect channel estimation.
67 citations