Jawad Mirza

Limited feedback multiuser MISO systems with differential codebooks in correlated channels

In this paper, we present a differential codebook design by modifying the Grassmannian codebook for a single-cell multiuser (MU) multiple-input single-output (MISO) system operating under spatially and temporally correlated channels. The differential codebook design involves scaling and rotation methods that help a codebook to track the slow varying channel. We propose an adaptive scaling technique that improves the performance of the system in correlated channels without any additional feedback information. Monte Carlo simulations show that the proposed differential codebook reduces quantization errors and improves sum-rate performance as compared to other differential codebooks designed for spatially and temporally correlated MISO channels.

Hybrid Precoding via Successive Refinement for Millimeter Wave MIMO Communication Systems

We propose a hybrid precoding design for spatial multiplexing in millimeter wave massive multiple-input multiple-output systems. The proposed design relies on the popular orthogonal matching pursuit (OMP) algorithm. The OMP algorithm uses necessary columns of the right/left (for receiver/transmitter) unitary matrix of the channel (obtained via a singular value decomposition) to obtain the initial baseband (digital) precoder using principles of basis pursuit. The resulting baseband precoder is then used to refine the RF (analog) precoder. This iterative refinement improves the quality of hybrid preocders. Quantization of the RF and baseband precoding matrices is also discussed for limited feedback systems, where the high-dimensional RF precoder is quantized using codebooks generated using the

A Differential Codebook with Adaptive Scaling for Limited Feedback MU MISO Systems

K-

Coordinated Regularized Zero-Forcing Precoding for Multicell MISO Systems With Limited Feedback

means clustering algorithm. On the other hand, the low-dimensional baseband precoder is quantized using well-known Grassmannian codebooks. Simulation results show that the proposed scheme performs close to the fully digital precoding scheme.

Double-Cap Differential Codebook Structure for MU MISO Systems in Correlated Channels

In this letter, we propose an adaptive scaling technique for a differential codebook (DCB) in multiuser (MU) multiple-input single-output (MISO) systems operating under spatially and temporally correlated channels. The proposed adaptive scaling technique depends on the mean channel variation due to spatial/temporal correlation in the channel and the mean quantization error associated with the previous feedback, hence avoiding the need to periodically reset the codebook. The performance of the proposed DCB is evaluated for both zero-forcing beamforming (ZFBF) and signal-to-leakage-and-noise ratio beamforming (SLNR BF) schemes. Simulation results show the effectiveness of the proposed adaptive scaling and also the superiority of the SLNR BF scheme over the ZFBF scheme.

Capacity loss for multilayer codebook precoding in MIMO systems

We investigate coordinated regularized zero-forcing (RZF) precoding for limited feedback multicell multiuser (MU) multiple-input–single-output (MISO) systems. We begin by deriving an approximation to the expected signal-to-interference-plus-noise (SINR) ratio for the proposed scheme with perfect channel direction information (CDI) at the base station (BS). We also derive an expected SINR approximation for limited feedback systems with random vector quantization (RVQ)-based codebook CDI at the BS. Using the expected interference result for the RVQ-based limited feedback CDI, we propose an adaptive feedback bit allocation strategy to minimize the expected interference by partitioning the total number of bits between the serving and out-of-cell interfering channels. Numerical results show that the proposed adaptive feedback bit allocation method offers a spectral efficiency gain over the existing coordinated zero-forcing (ZF) scheme.

Maximum Doppler shift frequency estimation using Autocorrelation Function for MIMO OFDM systems

We propose a double-cap differential codebook (DCB) design for multiuser (MU) multiple-input-single-output systems. The MU transmission uses signal-to-leakage-and-noise ratio precoding. The double-cap DCB is designed for temporally/ spatially correlated channels and is based on a combined spherical and polar cap structure. We consider an inner spherical cap and an outer polar cap structure with different radii. The design allows us to systematically alter the radii of the caps over the feedback time depending on the previously selected codeword. The proposed double-cap DCB does not require knowledge of temporal or spatial channel correlation at the base-station, thus removing the overhead of additional feedback from the user. Simulation results show the effectiveness of the proposed double-cap DCB over a single polar cap DCB in terms of sum capacity gain and quantization errors.

Measurements of 3D channel impulse response for outdoor-to-indoor scenario: Capacity predictions for different antenna arrays

In limited feedback multiple-input multiple-output (MIMO) systems, it is important that the codebooks used provide a good approximation to the channel. Any mismatch between the codebook entries and the actual channel creates a non zero chordal distance (or subspace angle) between the codebook element and the corresponding columns of the right singular matrix of the channel. As a result, the system exhibits a capacity loss. We evaluate and quantify the amount of this capacity loss with long term evolution (LTE) and Grassmannian codebooks in the case of Layer 1 (L1) and Layer 2 (L2) transmission using linear receivers in three different channel models. We evaluate the distribution of the minimum distance for LTE and Grassmannian codebooks via simulations. We also derive capacity loss approximations for zero forcing (ZF), minimum mean-squared error (MMSE) and singular value decomposition (SVD) receivers. We find that the capacity loss approximations for L1 transmission are accurate for all receivers and lead to an extremely simple relationship between capacity loss and minimum distance.

Characterisation of ictal and interictal states of epilepsy: A system dynamic approach of principal dynamic modes analysis

In this paper, a method for estimating the maximum Doppler shift frequency is presented for Multiple Input Multiple Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) systems. This method uses the Autocorrelation Function (ACF) for estimating frequency shift that induces ICI between adjacent OFDM subcarriers. The simulation results investigate the BER performance of OFDM system that achieves transmit and receive diversity by using Alamouti/MRC, as well as the BER performance of MIMO linear detectors Zero Forcing (ZF) and Minimum Mean Square Error (MMSE) under the effect of a Doppler spread channel.

Limited-Feedback Massive MISO Systems With Trellis-Coded Quantization for Correlated Channels

We present the results of a 3 dimensional (3D) multiple-input multiple-output (MIMO) channel impulse response (CIR) measurement conducted in China and New Zealand (NZ) for an outdoor-to-indoor (O2I) urban macro environment. Key channel parameters are computed from the measured data using the space-alternating generalized expectation-maximization (SAGE) algorithm, and are used to re-construct the 16 × 16 3D MIMO CIR according to the guidelines given in the 3GPP 3D MIMO channel model. The CIR is then used to evaluate the channel capacity for four different antenna configurations. These different topologies, along with different antenna spacings, allow us to study the characteristics of the MIMO channel with different spatial correlation structures.