SAGE Algorithm Based MAP Channel Estimation for Multi-Cell Massive MIMO Systems

This paper represents an efficient space-alteraing generalized expectation-maximization (SAGE) algmorithm based maximum a posteriori (MAP) channel estimation method for multi-cell massive multiple input multiple output (MIMO) sytems. MAP channel estimation method requires conjugate transpose of a tau x K pilot matrix where tau is the number of pilot symbols per user and K is the number of single antenna users. Conjugate transpose of the large-size matrix increases computational complexity. The proposed method estimates the channel iteratively and converges to the same mean square error (MSE) performance of the MAP estimator with the increasing number of iterations. Consequently, the proposed method with low-rank approximation avoids conjugate transpose of the large-size matrix and hence reduces the computational complexity significantly

EM Algorithm Based MAP Channel Estimation for Multi-Cell Massive MIMO Systems

This paper represents an efficient expectation-maximization (EM) algorithm based maximum a posteriori (MAP) channel estimation method for multi-cell massive multiple input multiple output (MIMO) systems. MAP channel estimation method requires conjugate transpose of a T x K pilot matrix where T is the number of pilot symbols per user and K is the number of single antenna users. Conjugate transpose of large-size matrix increases computational complexity. The proposed method estimates the channel iteratively and converges to the same mean square error (MSE) performance of the MAP estimator with the increasing number of iterations. Consequently, the proposed method with low-rank approximation avoids conjugate transpose of large-size matrix and hence reduces the computational complexity significantly

Doppler compensation for D-STBC coded time-varying underwater acoustic channels

In this paper we investigate the performance of distributed space-time block coding (D-STBC) orthogonal frequency division multiplexing (OFDM) over underwater acoustic (UWA) channels. In particular, we consider a relaying system consisting of one source, two relays, and one destination. The relays operate in amplify-and-forward (AF) mode. The underlying channels are assumed to be time-varying frequency selective channels, where the only source of time variation is the relative motion between transceivers. Alamouti D-STBC scheme is used in the second hop, and a two stage receiver is adopted at the destination: in the first stage, multiple resampling (MR) preprocessing of the received signals is performed to minimize the effect of intercarrier interference (ICI), and in the second stage ICI equalization is performed in the frequency domain to further reduce the effect of the residual ICI. To further boost the performance, successive interference cancellation (SIC) is used, where the estimates of the signals at the output of the ICI equalizer are used as tentative decisions. Compared to the single resampling (SR) front end preprocessing, simulation results show the superiority of MR front-end receiver. Also, SIC further boosts the performance, but still, there is a significant gap with respect to the ICI-free limit, when the receiver has perfect knowledge of ICI coefficients and eliminates them completely.Scopu

Two-way Relay Underwater Acoustic Communication Channels with Distributed Space-Time Block Coding

In this paper we study the performance of two-way relaying (TWR) over underwater acoustic (UWA) channels in conjunction with distributed space-time block coding (D-STBC). In particular, we consider the communication between two sources via relay nodes. The underlying channels are characterized as doubly selective channels. Orthogonal frequency division multiplexing (OFDM) is used to combat frequency selectivity of the channels, while front-end multiple resampling (MR) combined with frequency-domain equalization is used to combat intercarrier interference (ICI) resulting from time selectivity of the channel caused by the relative motion between the transceivers. Simulation results show the superiority of MR over its single resampling (SR) counterpart. Also, under total power constraint, AF-D-STBC (when only one source is activated at a time) outperforms AF-TWR-D-STBC, however, at the expense of less bandwidth efficiency. Also, AF-TWR-D-STBC outperforms AF-TWR (when one relay is activated) even though the former contributes more interference. Finally, to further boost the performance, successive interference cancellation (SIC) is used to extract the spatial diversity offered by the relays

An Adaptive Channel Interpolator Based on Kalman Filter for LTE Uplink in High Doppler Spread Environments

<p/> <p>Long-Term Evolution (LTE) systems will employ single carrier frequency division multiple access (SC-FDMA) for the uplink. Similar to the Orthogonal frequency-division multiple access (OFDMA) technology, SC-FDMA is sensitive to frequency offsets leading to intercarrier interference (ICI). In this paper, we propose a Kalman filter-based approach in order to mitigate ICI under high Doppler spread scenarios by tracking the variation of channel taps jointly in time domain for LTE uplink systems. Upon acquiring the estimates of channel taps from the Kalman tracker, we employ an interpolation algorithm based on polynomial fitting whose order is changed adaptively. The proposed method is evaluated under four different scenarios with different settings in order to reflect the impact of various critical parameters on the performance such as propagation environment, speed, and size of resource block (RB) assignments. Results are given along with discussions.</p