Frequency Domain Channel Estimation Methods Research Articles

Frequency-Domain Channel Estimation for Polarization-Division-Multiplexed CO-OFDM/OQAM Systems

Intrinsic imaginary interference (IMI) induced by a multiple-path fading channel is an important impairment for orthogonal frequency division multiplexing/offset-quadrature amplitude modulation (OFDM/OQAM) systems. Therefore, the accurate channel estimation is highly desired for such a system. Recently both the simulation studies and the experimental demonstrations for coherent optical OFDM/OQAM (CO-OFDM/OQAM) have been reported. However, there are no theoretical discussions on the IMI effect and the channel estimation method for polarization-division-multiplexed (PDM) CO-OFDM/OQAM systems so far. In this paper, we systematically analyze the frequency-domain optical fiber channel transmission model for PDM CO-OFDM/OQAM systems with the IMI effect induced by chromatic dispersion (CD) and polarization mode dispersion (PMD). The full loaded (FL) and the half loaded (HL) frequency-domain channel estimation methods are discussed to mitigate the IMI effect. The computational complexities and robustness against CD and PMD are also compared for both of the FL and the HL methods. The theoretical analysis is validated by numerical Monte Carlo simulations of PDM CO-OFDM/OQAM systems.

Training sequence based frequency-domain channel estimation for indoor diffuse wireless optical communications

Channel estimation is a key technology for wireless optical communication (WOC) systems. Based on the training sequence (TS), this article develops three frequency domain (FD) channel estimation approaches for diffuse wireless optical channels. Considering the propagation property of light and the characteristics of optical modulation, this article establishes a link model for the indoor WOC systems. Using the established link model, three FD channel estimation methods, such as the LS method, the minimum mean square error (MMSE) method and the ORL-MMSE method are proposed. The computational complexity analysis gives time complexities of the three channel estimation methods in FD. This article also evaluates the performance of the proposed three methods by computer simulation, measuring in terms of MSE and BER, respectively. Further more, based on the Cramer–Rao Bound theorem, optimal TSs are found and tabulated for different channel responses and TS lengths. By using the optimal TSs, channel estimation errors measured by BER performance are also investigated.

An Accurate and Efficient Two-Stage Channel Estimation Method Utilizing Training Sequences with Closed Form Expressions

A novel two-stage frequency domain channel estimation method especially suitable for the estimation of long channels such as ultra wide band channels is proposed. The proposed method can efficiently use the sequences with closed form analytical expressions such as the Legendre sequences. (The suggested method does not require a computationally intense search for good training sequences which is infeasible for long training sequences.) The method is shown to present a minor improvement in the total estimation error variance when compared with the conventional single stage frequency domain channel estimation. In addition, the proposed method has a very efficient time domain implementation requiring at most 2N multiplications, where N is the training sequence length, in comparison to O(N log N) multiplications required for the conventional method.

Improved Frequency Domain Channel Estimation and Equalization for MIMO Wireless Communications

This paper introduces an improved frequency domain channel estimation method based on interpolation vectors for single carrier frequency domain equalization (SC-FDE) with the multiple-input multiple-output (MIMO) scheme. The proposed algorithm is derived by employing the least squares (LS) criterion, and a specified application for the wide sense stationary uncorrelated scattering (WSSUS) Rayleigh fading channel is presented. The channel frequency domain responses estimated at two adjacent pilot blocks are used to track the time-variant channel information, which can effectively improve the accuracy of channel estimation without significantly increasing complexity. Maximum mean square error (MMSE) frequency domain equalization based on the estimated channel is employed in the receiver to recover transmitted signals. This paper also investigates a training sequence design method for multiple transmit antennas and a noise variance estimation method. Numerical simulation results show that the proposed methods can perform very well for fading channels with long multipath delay and high Doppler spread.

A Two-Dimensional Multipath Channel Estimator for CDMA Systems With Timing-Offset Errors

This letter proposes a two-dimensional pilot-aided channel estimator for multicarrier and single carrier cyclic prefix assisted code division multiple access systems in the presence of timing-offset errors. Using optimal training sequences with special cyclic correlation properties can minimize the timing offset errors. Optimal and binary sub-optimal training sequences are designed in this context. Both theoretic analysis and simulation studies demonstrate significant performance improvement for the proposed method over conventional frequency domain channel estimation methods.