Pilot-aided Joint Research Articles

Joint Estimation of Carrier Frequency Offset and Channel Impulse Response for Linear Periodic Channels

In many communications scenarios, the channel exhibits periodic characteristics, e.g., power line communications and interference-limited communications. Additionally, certain approximations for mobile radio channels over finite time intervals may result in periodic channel models. In this paper, we study pilot-aided joint estimation of the channel impulse response (CIR) and of the carrier frequency offset (CFO) for linear periodic channels, in which both the CIR and the noise statistics vary periodically in time. We first consider the joint maximum likelihood estimator (JMLE) for the CIR and the CFO, and discuss the practical drawbacks associated with this estimator. When the coefficients of the delay-Doppler spread function of the CIR are approximately sparse, we propose two estimation schemes with higher spectral efficiency and lower computational complexity compared with the JMLE, which are obtained by exploiting both the periodicity and the sparsity of the channel, without requiring a priori knowledge of the sparsity pattern. Finally, we study the design of pilot sequences aimed at improving the estimation performance in sparse periodic channels. Simulation studies corresponding to practical scenarios of the proposed estimators demonstrate that substantial benefits can be obtained by properly accounting for the sparsity and periodicity in the design of estimation schemes.

DVB-S2 Channel Estimation and Decoding in The Presence of Phase Noise for Non-Linear Channels

In a multipath fading channel of DVB-S2, smallscalevariations occur due to unwanted noise signal, which isdirectly related to the impulse response of a radio channel. Thevarying channel has to be estimated before decoding the signal atthe receiver for proper signal recovery. However, In the presenceof a time varying and correlated phase noise, proper estimation ofthe Channel Impulse Response (CIR) becomes difficult. Toovercome this problem, a pilot-aided joint channel estimation anddecoding method is proposed to obtain the initial estimate of thechannel. This technique is reliable and important for satellitecommunication as the Ku-band capacity is almost over crowdedand more satellite resources are needed. The results show thatIterative Channel Estimation technique results in a lower BER andimproved signal quality for DVB-S2, which fine-tunes the systemfor an efficient use of power and bandwidth of satellite resources.

Pilot-Aided Joint Estimation of Doubly Selective Channel and Carrier Frequency Offsets in OFDMA Uplink With High-Mobility Users

In this paper, we propose a novel pilot-aided joint channel and carrier frequency offset (CFO) estimation method for orthogonal frequency-division multiple access (OFDMA) uplink systems with users operating in time- and frequency-selective (doubly selective) fading environments. We use Bernstein basis polynomials (BBPs) to capture rapid time variations of the channel, which avoids the identifiability issue in estimating large number of actual channel coefficients. We make use of space-alternating generalized expectation–maximization maximum a posteriori probability (SAGE-MAP) algorithm for the joint estimation of CFOs and channel coefficients. The convergence properties of the proposed method is assessed and proved analytically. The exact Bayesian Cramer–Rao bound (BCRB) for the MAP estimation problem is also derived and is shown to be comparable to the mean squared error (MSE) of the proposed technique.

Pilot-aided Joint Channel Estimation for OFDM Based Cooperative Multi-cell Networks

Multi-cell joint channel estimation (JCE) is the basis for application of multi-cell cooperative processing. For weakness of the existing algorithms that power delay profile (PDP) knowledge of all multiple cells need be known or pilot sequence sets of all cells must be identical, in this paper, a pilot-aided time domain JCE algorithm is presented. And then, by using Generalized Akaike Information Criterion (GAIC) to estimate PDPs of all cells for reducing the signal space of channel estimation, the paper further optimizes this JCE algorithm. Simulation results show that the proposed algorithms have good mean square error (MSE) and corresponding space frequency block coded (SFBC) cooperative multi-cell transmission system has the good bit error rate (BER) performance too.

Pilot-aided Joint Channel Estimation for OFDM Based Cooperative Multi-cell Networks

Pilot-aided Joint Channel Estimation for OFDM Based Cooperative Multi-cell Networks

Pilot-Aided Joint CFO and Doubly-Selective Channel Estimation for OFDM Transmissions

This paper studies the problem of pilot-aided joint carrier frequency offset (CFO) and channel estimation using Fisher and Bayesian approaches in orthogonal frequency division multiplexing (OFDM) transmissions over time- and frequency-selective (doubly selective) channels. In particular, the recursive-least-squares (RLS) and maximum-likelihood (ML) techniques are used to facilitate the Fisher estimation implementations. For the Bayesian estimation, the maximum-a-posteriori (MAP) principle is employed in formulating the joint estimation problem. With known channel statistics, the MAP-based estimation is expected to provide better performance than the RLS- and ML-based ones. To avoid a possible identifiability issue in the joint estimation problem, various basis expansion models (BEMs) are deployed as fitting parametric models for capturing the time-variation of the channels. Numerical results and related Bayesian Cramér Rao bounds (BCRB) demonstrate that the deployment of BEMs is able to alleviate performance degradation in the considered estimation techniques using the conventional block-fading assumption over time-varying channels. Among the considered schemes, the MAP-based estimation using the discrete prolate spheroidal (DPS) or Karhuen Loève (KL) basis functions would be the best choice that can provide mean-squared-error (MSE) performance comparable to BCRB in low signal-to-noise ratio (SNR) conditions (e.g., coded OFDM transmissions).

RLS-Based Joint Estimation and Tracking of Channel Response, Sampling, and Carrier Frequency Offsets for OFDM

This paper proposes a pilot-aided joint channel estimation and synchronization scheme for burst-mode orthogonal frequency division multiplexing (OFDM) systems. Based on the received signal samples containing pilot tones in the frequency domain, a cost function that includes the carrier frequency offset (CFO), sampling clock frequency offset (SFO) and channel impulse response (CIR) coefficients is formulated and used to develop an accompanying recursive least-squares (RLS) estimation and tracking algorithm. By estimating the channel <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CIR</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">coefficients</i> instead of the channel frequency response in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">frequency</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">domain</i> , the proposed scheme eliminates the need for an IFFT block while reducing the number of parameters to be estimated, leading to lower complexity without sacrificing performance and convergence speed. Furthermore, a simple maximum-likelihood (ML) scheme based on the use of two long training symbols (in the preamble) is developed for the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">coarse</i> estimation of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">initial</i> CFO and SFO to suppress dominant ICI effects introduced by CFO and SFO and to enhance the performance and convergence of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">fine</i> RLS estimation and tracking. Simulation results demonstrate that, over large ranges of CFO and SFO values, the proposed pilot-aided joint channel estimation and synchronization scheme provides a receiver performance that is remarkably close to the ideal case of perfect channel estimation and synchronization in both AWGN and Rayleigh multipath fading channels.

Joint channel and phase noise estimation in OFDM using KL expansion

In mobile orthogonal frequency division multiplexing (OFDM) systems, time-varying channels result in severe intercarrier interference (ICI). At the same time, random phase noise introduced by the oscillator also causes two effects: the common phase error (CPE), and the ICI. The upper two factors together greatly degrade the OFDM system performance. However, the existing ICI reduction method is only aimed at a single interference source, i.e., either time-varying channels or phase noise. So, it cannot solve the actual case. In this paper, we analyze the ICI generated by the two factors together and propose a pilot-aided joint time-varying channel and phase noise estimation algorithm based on Karhunen-Lòeve basis expansion model (KL-BEM). The model is optimal in the minimum mean square error (MMSE) sense. So, it can make ICI reduction more effective. Simulation results confirm our theoretical results and illustrate that the proposed algorithm is capable of jointly estimating time-varying channels and phase noise.

Pilot embedding for joint channel estimation and data detection in MIMO communication systems

A novel pilot-aided joint channel estimation and data detection method for MIMO communication systems is proposed. Unlike, conventional methods where pilots are time-multiplexed with data symbols, a pilot-embedding method where low-level pilots are transmitted concurrently with the data is used to obtain an initial estimate of the channel such that a turbo decoding process can be started. The soft information obtained from the turbo decoder is subsequently used to improve channel estimates.