Pilot-aided Channel Research Articles

Real-Time LR-DDO-OFDM Transmission System Using EML With 1024-Point FFT

In this letter, we experimentally demonstrate a complete Field Programmable Gate Array (FPGA)-based real-time point-to-point long-reach (LR) direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) transmission system using a cost-effective electroabsorption modulated laser with 1024-point fast Fourier transform (FFT). To the best of our knowledge, it is the so-far reported largest FFT size used in real-time DDO-OFDM system. Based on the system, in an asynchronous way, an adaptively 16-quadratic-amplitude modulation/quadrature phase shift keying/binary phase shift keying modulated real-time optical OFDM LR transmission has been experimentally demonstrated without sampling frequency offset compensation, which is achieved by utilizing the effective symbol timing synchronization and the pilot-aided and linear-interpolated channel estimation scheme. Moreover, the bit-error rate of below than 1e-3 can be successfully achieved after 150-km standard single mode fiber transmission.

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

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

Multiuser channel estimation and prediction in two dimensions for MIMO–OFDM uplinks

This paper addresses the pilot-aided multiuser channel estimation for the uplink of multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The channel estimate is performed in two dimensions, i.e., time and frequency (2D), by exploiting their correlation. With the properly designed separable pilot symbols, a multiuser signal separation can be achieved and a multiuser channel estimator can be designed as well. To reduce the high computational complexity for a truly 2D estimator, two cascaded one dimensional (1D) estimators are used instead, which corresponds to two estimation stages with two different filters. At the 1st stage, the Wiener filter is implemented in the frequency direction, which separates the received multiuser signals and outputs the tentative estimate corresponding to an individual user. Whereas, at the 2nd stage, the Kalman filter is adopted in the time direction to estimate and predict the desired channel state information.

Algorithm for exploiting channel time selectivity in pilot-aided MIMO systems

The problem of channel estimation and symbol detection in fast fading channels using multiple antennas is dealt with. This is one of the many challenges faced by extending spatial multiplexing to mobile terminals. A commonly used method of resolving this problem is pilot‐aided channel interpolation. An iterative algorithm that substantially improves the performance of pilot-aided MIMO channel interpolation systems is proposed. The algorithm involves alternating projection of parameters onto different sub-spaces so as to exploit the time selectivity of the channel to improve the quality of symbol detection. Simulations have shown that the algorithm, when applied to any interpolation scheme, improves the bit error performance of the system significantly.

PILOT-AIDED MULTIUSER CHANNEL ESTIMATION AND TRACKING IN MIMO-OFDM SYSTEMS

This paper addresses the pilot-aided multiuser least square (LS) channel estimation for the uplink of multiple-input multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems. The systems under consideration allow all users use all available subcarriers independently and thus involve multiuser interference in the frequency domain. Direct application of the known pilot-aided single-user channel estimation methods to these systems is prohibited, requiring much more new investigations. The decentralized and centralized channel estimation algorithms are developed according to different multiuser scenarios. Optimal multiuser pilots are proposed, especially for centralized estimation methods with respect to the mean square error (MSE) of LS channel estimate. In addition, channel tracking algorithms are represented in terms of individual user's channels.