Abstract
The presence of intrinsic inter-carrier interference (ICI) and inter-symbol interference (ISI) at the output of the matched filter receiver in filter bank multi-carrier with offset quadrature amplitude modulation (FBMC-OQAM) systems complicates the task of channel estimation (CE). The conventional approach is to use a pilot symbol preamble structure, such as in the interference approximation/cancellation methods (IAM/ICM), together with a simple virtual symbol (VS) based CE scheme. However, this virtual symbol approach ignores the residual interference from the data portion of the FMBC burst as well as the correlation of the noise across the sub-carriers; both of these factors ultimately limit the performance. In this paper, we propose a generalized least squares (GLS) based CE scheme which, when applied to the IAM/ICM pilot structures, takes into account both the correlated noise and data interference effects. Closed-form expressions are derived for the channel estimation mean-squared error (CE-MSE) of the proposed GLS method and for the conventional VS method, and it is shown that the proposed method leads to a significant reduction of the CE-MSE by up to 6 dB when compared with the VS based method. This is demonstrated to result in improved bit error rate (BER) performance, especially when higher-order modulation is employed, making it an attractive channel estimation method for many modern deployment scenarios. The proposed GLS-based channel estimation scheme is parameterized allowing a flexible trade-off between channel frequency selectivity, estimation complexity and CE-MSE gain. Finally, symmetry properties of the intrinsic interference coefficients for a general FBMC-OQAM system are also proved, which facilitate the computation of the noise and interference autocorrelation matrices required by the proposed algorithm.
Highlights
The use of cyclic-prefixed orthogonal frequency division multiplexing (CP-OFDM) enables low-complexity equalization of wideband channels [1] and has resulted in widespread adoption in many modern communication protocols, e.g. 4G, Wi-Fi, DVB [2]
We propose a parameterizable channel estimation (CE) scheme, called GLS-u, based on generalized least squares (GLS) estimation [20], [21], which generates each channel estimate based on a number of consecutive matched filter outputs while taking fully into account the correlated nature of the noise and interference components present in these matched filter outputs
SIMULATION RESULTS AND DISCUSSION a simulation study is conducted in MATLAB to compare the performance of different preamble-based channel estimation techniques in terms of channel estimation mean-squared error (CE-MSE) and bit error rate (BER), for a low (ITU Indoor A) and a medium (ITU Vehicular A) frequency selective channel model [24], under various mobility conditions
Summary
The use of cyclic-prefixed orthogonal frequency division multiplexing (CP-OFDM) enables low-complexity equalization of wideband channels [1] and has resulted in widespread adoption in many modern communication protocols, e.g. 4G, Wi-Fi, DVB [2]. FBMC achieves its spectral efficiency improvement by the use of smooth pulse shaping filters (typically based on a prototype filter) on each sub-carrier, resulting in reduced OOBE In this new parallel filter bank arrangement we no longer have a set of orthogonal sub-carriers; rather, they interfere with each other both in frequency and in time. The most widely established preamble-based CE techniques for FBMC-OQAM follow a virtual symbol (VS) approach often applied to the pilot structures in either the interference approximation method (IAM) [14] or the interference cancellation method (ICM) [15] These schemes suffer from a severe CE meansquared error (CE-MSE) floor at high SNR (>20 dB) which limits the performance.
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