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In this paper, we present the sum-rate analysis of multiuser multiple-input multiple-output (MIMO) downlink systems with incremental beamforming (IB). We develop the analytical expressions of the ergodic sum-rate for the dual-transmit-antenna scenario. Based on the analytical results, we compare the performance of the proposed IB scheme with popular random beamforming techniques, such as random unitary...
We describe a channel sounding system designed for small outdoor cell (~400 meter radius) wireless channel characterization. We report on a program of path loss measurements using a 2×2 MIMO configuration and data reduction in the frequency range of 5.7-5.75 GHz. The results are based on over 10,000 independent complex frequency responses collected in residential neighborhoods in northern New Jersey...
A joint channel impulse response (CIR) and noise-variance estimation scheme is proposed for multi-user Multiple-Input-Multiple-Output (MIMO) Orthogonal Frequency-Division Multiplexing/Space Division Multiple Access (OFDM/SDMA) systems, which is based on the Expectation Maximization (EM) algorithm. Multiple users communicating over time-invariant and/or time-variant channels are considered in this...
In this paper, the variational expectation-maximization (VEM) algorithm is used to provide channel estimates in a space-time decoder. The proposed estimator works for many types of space-time codes (STC), including full-rate full-diversity (FRFD) codes, Bell Laboratories layered space-time architecture (BLAST) and orthogonal STC's. The principle idea is to treat the channel coefficients as the unknown...
In this paper we propose a scheme with a dedicated relay node for an OFDM-based system. We consider an antenna array at the base station and a single antenna at both the user terminal and the relay node. The relay-assisted protocol considered is equalize-and-forward. The proposed scheme requires the computation of parameters which depend on unknown variables at the destination and we show that under...
This paper studies the problem of pilot-aided joint carrier frequency offset (CFO) and channel estimation using a Bayesian approach in multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) transmissions over time- and frequency-selective (doubly selective) channels. Unlike the joint CFO and channel impulse response (CIR) estimation over block-fading channels, the...
The Wiener Interpolation Filter is commonly used to reconstruct a stochastic process from noisy samples. We focus on the case of a multi-dimensional stochastic process and the practical example of application of the filter for estimation of mobile radio propagation channels at a wireless receiver. We show that computational complexity of the implementation can be considerably reduced by exploiting...
In the LTE-Advanced downlink, to satisfy high-level performance requirements, advanced multi-antenna transmission techniques such as higher-order single-user (SU)-MIMO, multi-user (MU)-MIMO, and coordinated multi-point transmission/reception (CoMP) are key. At the 3GPP RAN WG1 meeting, the demodulation reference signal (DM-RS) was defined to support channel estimation and data demodulation for up...
Obtaining reliable channel state information (CSI) in future wireless standards is critical for the operation of downlink closed-loop techniques such as SU-MIMO, MU-MIMO, and coordinated multipoint (CoMP). However, this CSI is difficult to obtain especially when considering the potentially strong interference from neighboring sectors/base stations on the downlink reference symbols (RSs, aka pilot...
The sensitivity of MIMO error performance to imperfect receiver channel state information is examined. Measurements made at three different UHF frequencies are used to show the effect of parameters such as training and frame lengths on error performance. The results show that the amount of training directly influences the supportable symbol rate and that the level of degradation in performance due...
In this paper, we study the influence of training-based channel estimation on the information-theoretic capacity of closed-loop MIMO systems with imperfect channel state information (CSI) feedback. First, a lower bound on capacity is formulated as a function of various parameters such as received signal-to-noise ratio, number of training symbols, feedback delay time, and the feedback noise variance...
An estimation technique for Time-Invariant (TI) channels that utilizes an Extrapolation Matrix (EM) and specially designed pilot sequences is presented. We address the topic of pilot aided multi-user channel estimation for a proposed wireless system that uses OFDM in a synchronous SDMA environment, which can also be regarded as a Multiple-Input Multiple-Output (MIMO) environment. Unlike most multi-user...
In this paper, we study the channel estimation problem for time division multiplex amplify-and-forward (AF) relay channels. Both the source and the destination and also the in-between relay node comprise multiple antennas, and there are spatial fading correlations in each hop. We first derive a linear minimum mean square error (LMMSE) channel estimator from a simple scenario where there are no correlations...
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