Abstract
This paper proposes a novel optimum combiner that raises the time-averaged signal-to-interference-plus-noise ratio (SINR) for maximal-ratio combining (MRC) reception over spatially correlated Nakagami-m fading channels. By exploiting the principal component analysis (PCA) with eigenvalue decomposition (EVD) of the covariance matrix analytically evaluated offline, a complete set of orthonormal basis functions can be obtained. A decorrelation process analyzes and then projects the received signal into the space spanned by the basis functions. In accordance with the theorem of irrelevance, a principal component selection combining (PCSC) method is proposed to remove components in a few dimensions in which SINRs are considered low to raise the resulting time-averaged SINR on the subsequent MRC reception. The proposed technique also avoids noise enhancement occurring with MRC reception in the scenario where noises on different branches are correlated. The SINR distribution, level-crossing rate (LCR) and average fade duration (AFD) are derived. Based on a novel scattering model interpretation, a simulator consisting of spatially correlated Nakagami-m fading channels is developed according to the analytically evaluated covariance matrix. Computer simulations show that the proposed optimum combiner not only decreases interference and noise from the irrelevant subspace to achieve higher time-averaged SINR and lower AFD but also significantly reduces the complexity required for subsequent signal processing.
Highlights
D IVERSITY techniques are exploited to reduce the occurrence rate and average length of deep fades that occur in uncoded symbols, and they are the preferred primary approach for overcoming channel fading effects [1]
By applying analytical results derived through the momentgenerating function (MGF) method as presented in [24], the technique proposed on this paper evaluates the covariance matrix of a random vector whose elements represent the complex-valued gains of correlated Nakagami-m fading channels from measurement results of the envelope correlation coefficients and powers
By considering complex-valued channel gains as stochastic processes, the proposed optimum combiner employs the following: a) an analytical evaluation of the covariance matrix of multiple Nakagami-m fading channels, b) the principal component analysis (PCA) of the covariance matrix by means of eigenvalue decomposition (EVD) applied above to search for a set of orthonormal basis functions, c) decorrelation using the unitary matrix obtained from the EVD to project the received signal into the space spanned by all orthonormal basis functions, d) the principal component selection combining (PCSC) method proposed to omit the irrelevant subspace, which primarily contains interference and noise, and e) combining reception of the selected branches to increase the time-averaged signal-to-interference-plus-noise ratio (SINR)
Summary
D IVERSITY techniques are exploited to reduce the occurrence rate and average length of deep fades that occur in uncoded symbols, and they are the preferred primary approach for overcoming channel fading effects [1]. By applying analytical results derived through the momentgenerating function (MGF) method as presented in [24], the technique proposed on this paper evaluates the covariance matrix of a random vector whose elements represent the complex-valued gains of correlated Nakagami-m fading channels from measurement results of the envelope correlation coefficients and powers. By considering complex-valued channel gains as stochastic processes, the proposed optimum combiner employs the following: a) an analytical evaluation of the covariance matrix of multiple Nakagami-m fading channels, b) the PCA (or KLT) of the covariance matrix by means of EVD applied above to search for a set of orthonormal basis functions, c) decorrelation using the unitary matrix obtained from the EVD to project the received signal into the space spanned by all orthonormal basis functions, d) the PCSC method proposed to omit the irrelevant subspace, which primarily contains interference and noise, and e) combining reception of the selected branches to increase the time-averaged SINR.
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