A Joint MMSE Channel and Noise Variance Estimation for OFDM/OQAM Modulation

Abstract

International audienceThis paper deals with the minimum mean square error-(MMSE-) based multipath channel and noise variance estimation in the case of a pilot-aided orthogonal frequency division multiplexing/offset quadrature amplitude modulation (OFDM/OQAM) system. The theoretical expression of the LMMSE channel estimation is formulated, and a simpler closed-form is derived. The MSE analysis shows that LMMSE inevitably reaches an error floor due to the interference inherent to OFDM/OQAM modulation. Furthermore, an algorithm for the joint MMSE estimation of both the channel and the noise variance (J-MCNE) is proposed, and features a reduced complexity thanks to the low-rank approximation method. The noise level estimation represents a challenge as it is concealed in the intrinsic interferences generated by the OFDM/OQAM. Simulations reveal the capability of the proposed J-MCNE method to estimate the noise variance, and show that the achieved bit error rate (BER) is close to that of the perfect estimation

OFDM/OQAM Blind Equalization Using CNA Approach

“…where the weight 1 corresponds to the position (m, n), and where a, b, and c values depend on M and K. Note that, due to (5), the noise component w m,n cannot be white. However, the assumption of "whiteness" of the noise in OFDM/OQAM has proven to be accurate, such as in [20].…”

“…It must be emphasized that the results presented for the estimator using IAM are only indicative. In fact, a fair comparison would induce to test different channel estimation methods (IAM-R [6], MMSE [20]), pilot energy, or equalizers [8]. A more exhaustive comparison with pilot-aided methods is out of the scope of this paper, but numerous estimation and equalization techniques can be found [6], [8], [20].…”

Low-complexity approximations for LMMSE channel estimation in OFDM/OQAM

“…In the case where H m,n = 1, the challenge is to estimate and remove the frequency selective channel. In order to achieve this, it has been proposed in [6] to use in OFDM/OQAM the LMMSE channel estimation method, which has been originally presented for OFDM systems in [7].…”

“…In order to adapt the LMMSE estimator to OFDM/OQAM scheme, the channel frequency response is assumed to be constant at the frequency and time positions surrounding the position (m, n) [6]. This leads to the approximation H p,q ≈ H m,n , where p ∈ {m−1, m, m+1} and q ∈ {n−1, n, n+1}.…”

“…Overviews on different preamble-based channel estimation methods in OFDM/OQAM have been deeply presented in [3]- [5]. More recently, an adaptation of the linear minimum mean square error (LMMSE) technique using OFDM/OQAM modulation scheme has been proposed in [6]. It has been observed in [6] that, as in OFDM systems, the complexity of the LMMSE estimator is one of its main drawback.…”