Harsh Tataria

Performance and analysis of downlink multiuser MIMO systems with regularized zero-forcing precoding in Ricean fading channels

Analytical expressions to approximate the expected per-user signal-to-interference-plus-noise-ratio (SINR) and ergodic sum-rate of a multiuser multiple-input-multiple-output system are presented. Our analysis assumes uncorrelated Ricean fading channels with regularized zero-forcing precoding on the downlink. The derived expressions are averaged with respect to the previously unknown arbitrary eigenvalue densities of the complex non-central Wishart distributed channel correlation matrix. To aid the derivation of the expected SINR, we derive analytical expressions for the joint density of two arbitrary eigenvalues of the complex non-central Wishart matrix. Unlike previous studies, our model caters to the presence of a unique Rice factor for each user terminal, making it suitable for analysis of modern systems, such as small cells and millimeter-wave. Our findings suggest that while the presence of strong line-of-sight has an adverse effect on the expected SINR and ergodic sum-rates, increasing the variability of Rice factors enhances the peak rate performance of the system. Our analysis can be applied to arbitrary system dimensions and is seen to remain tight across the signal-to-noise-ratio range considered.

Zero-Forcing Precoding Performance in Multiuser MIMO Systems With Heterogeneous Ricean Fading

An accurate approximation is developed for the distribution of the instantaneous per-terminal signal-to-noise-ratio (SNR) of a downlink multiuser multiple-input multiple-output system with zero-forcing (ZF) precoding. Our analysis assumes a Ricean fading environment, where we show that the SNR at a given terminal is well approximated by the gamma distribution and we derive its parameters. The analysis relies on densities of an arbitrary eigenvalue and a pair of arbitrary eigenvalues of the uncorrelated complex non-standard, noncentral Wishart matrices. Unlike previous studies, we consider microwave and millimeter-wave channel parameters with a unique Rice factor for each terminal. We demonstrate that stronger line-of-sight adversely impacts the ZF SNR, while increasing the Rice factor variability results in higher peak ZF SNR. Our approximations are insensitive to changes in the system dimension and operating SNRs.

General analysis of multiuser MIMO systems with regularized zero-forcing precoding under spatially correlated Rayleigh fading channels

A general framework for the analysis of expected per-user signal-to-interference-plus-noise-ratio (SINR) of a multiuser multiple-input-multiple-output system is presented. Our analysis assumes spatially correlated Rayleigh fading channels with regularized zero-forcing precoding on the downlink. Unlike previous works, our analytical expressions are averaged over the eigenvalue densities of the complex Wishart distributed channel correlation matrix. To aid the derivation of the expected per-user SINR, we derive a closed-form expression for the joint density of two arbitrary eigenvalues of the complex Wishart matrix. In the high signal-to-noise-ratio (SNR) regime, with zero-forcing precoding, we derive analytical expressions to approximate the instantaneous per-user SNR and show that it is approximately gamma distributed. The generality of the approximations is validated with numerical results over a wide range of system dimensions, spatial correlation and SNR levels.

Uplink analysis of large MU-MIMO systems with space-constrained arrays in Ricean fading

Closed-form approximations to the expected perterminal signal-to-interference-plus-noise-ratio (SINR) and ergodic sum spectral efficiency of a large multiuser multiple-input multiple-output system are presented. Our analysis assumes correlated Ricean fading with maximum ratio combining on the uplink, where the base station (BS) is equipped with a uniform linear array (ULA) with physical size restrictions. Unlike previous studies, our model caters for the presence of unequal correlation matrices and unequal Rice factors for each terminal. As the number of BS antennas grows without bound, with a finite number of terminals, we derive the limiting expected perterminal SINR and ergodic sum spectral efficiency of the system. Our findings suggest that with restrictions on the size of the ULA, the expected SINR saturates with increasing operating signal-to-noise-ratio (SNR) and BS antennas. Whilst unequal correlation matrices result in higher performance, the presence of strong line-of-sight (LoS) has an opposite effect. Our analysis accommodates changes in system dimensions, SNR, LoS levels, spatial correlation levels and variations in fixed physical spacings of the BS array.

Impact of Line-of-Sight and Unequal Spatial Correlation on Uplink MU-MIMO Systems

Closed-form approximations of the expected per-terminal signal-to-interference-plus-noise-ratio (SINR) and ergodic sum spectral efficiency of a multiuser multiple-input multiple-output system are presented. Our analysis assumes spatially correlated Ricean fading channels with maximum-ratio combining on the uplink. Unlike previous studies, our model accounts for the presence of unequal correlation matrices, unequal Rice factors, as well as unequal link gains to each terminal. The derived approximations lend themselves to useful insights, special cases and show the combined impact of line-of-sight (LoS) and correlated components. Numerical results show that while unequal correlation matrices enhance the system performance, the presence of strong LoS has an opposite effect. The approximations are general and remain insensitive to changes in the system dimensions, signal-to-noise-ratios, LoS levels, and correlation levels.

On the General Analysis of Coordinated Regularized Zero-Forcing Precoding: An Application to Two-Tier Small-Cell Networks

General analysis of expected per-terminal signal-to-interference-plus-noise-ratio (SINR) and ergodic per-cell sum spectral efficiency for a multi-cellular system with coordinated regularized zero-forcing (RZF) precoding is presented. An application to two-tier small-cell networks is considered, assuming independent and identically distributed (i.i.d.) and semi-correlated Rayleigh fading channels, with spatial correlation at the base station. Our analysis caters for equal and unequal correlation matrices for each terminal. For the i.i.d. case and when each terminal is assigned an equal correlation matrix, our expressions are averaged over the eigenvalue densities of the channel correlation matrices, which follow an uncorrelated and correlated complex central Wishart distribution. With unequal correlation matrices, we exploit the high signal-to-noise-ratio (SNR) convergence of RZF precoding to zero-forcing (ZF) precoding and use a second-order Neumann series expansion to derive closed-form approximations to the expected RZF SINR and ergodic sum spectral efficiency, via the expected ZF SNR and ergodic sum spectral efficiency. Our numerical results show the adverse effects of intercellular interference, along with the improvements in the above-mentioned performance metrics with network-wide coordination over cell-wide and macro-only coordination strategies. The derived expressions are robust to changes in system dimensions, operating SNRs, and correlation levels.

Simultaneous channel estimation and joint time-frequency domain crosstalk cancellation in multichannel personal audio systems

In this paper, we present two important contributions. The first is demonstration of the use of subliminal levels of pseudo-random noise to enhance channel estimation, and the second is a joint time and frequency domain algorithm for multichannel inversion. An adaptive system is presented where the acoustic channel is accurately estimated and utilized. In this implementation, maximum length sequences in the form of pseudo-random noise are superimposed on the source signals to aid the estimation quality of the acoustic channels. Upon estimation, crosstalk cancellation filters are designed using a time and frequency domain technique which uses a window to achieve more efficient and effective cancellation of crosstalk. For a 3×2 crosstalk system, the presented results show the improvement in channel estimation quality when low levels of maximum length sequences are superimposed on the source signals. On average -25dB of crosstalk cancellation is achieved.

Impact of RF Processing and Switching Errors in Lens–Based Massive MIMO Systems (Invited Paper)

Lens-based massive multiple-input multiple-output (MIMO) systems have considerable potential to reduce signal processing cost at millimeter-wave frequencies. As a result, they are able to lower the effective channel dimension via beam selection, realized with a network of radio-frequency (RF) switches. However, lens arrays suffer from the inherent quantization of the beamspace, as well as errors due to imperfections in the lens construction itself. Unlike prior works, we model the above effects in the context of a Rotman lens-enabled massive MIMO system. Assuming line-of-sight propagation, we derive analytical approximations of the expected (average) signal-to-interference-plus-noise-ratio (SINR) of a terminal and ergodic sum spectral efficiency of the system. Our analysis caters for spillover losses in the Rotman lens and imperfections in the RF switching matrix, caused by impedance mismatches, as well as poor port isolation. The presented numerical results show large degradation in the expected SINR and ergodic spectral efficiency when considering the above imperfections, yielding more accurate performance assessment of lens-based massive MIMO systems.