This article presents an iterative minimum mean square error-(MMSE-) based method for the joint estimation of signal-to-noise ratio (SNR) and frequency-selective channel in an orthogonal frequency division multiplexing (OFDM) context. We estimate the SNR thanks to the MMSE criterion and the channel frequency response by means of the linear MMSE (LMMSE). As each estimation requires the other one to be performed, the proposed algorithm is iterative. In this article, a realistic case is considered; i.e., the channel covariance matrix used in LMMSE is supposed to be totally unknown at the receiver and must be estimated. We will theoretically prove that the algorithm converges for a relevantly chosen initialization value. Furthermore simulations show that the algorithm quickly converges to a solution that is close to the one in which the covariance matrix is perfectly known. Compared to existing SNR estimation methods, the algorithm improves the trade-off between the number of required pilots and the SNR estimation quality.

International audienceLinear minimum mean square error (LMMSE) is by definition the optimal channel estimator in the sense of meansquare error criterion, but its practical application is limited by its high complexity. Furthermore, the LMMSE estimation methodrequires the knowledge of both the channel and the noise statistics, which are a priori unknown at the receiver. A wide range oftechniques are proposed in the literature in order to overcome these two drawbacks. In this study, the authors give an overviewof the LMMSE-based channel estimation in an orthogonal frequency division multiplexing (OFDM) context. A didactic reminderconcerning the basics of LMMSE estimation and its performance is provided, and a survey of techniques of the literature, whichenable the practical application of LMMSE and the reduction of its complexity, is presented in both single-input single-output andmultiple-input multiple-output contexts. Finally, some perspectives are provided, in particular the application of the LMMSEestimator to flexible waveforms beyond OFDM

The Internet of things (IoT) is transforming the whole of society. It represents the next evolution of the Internet and will significantly improve the ability to gather and analyze data, as well as the ability to control devices remotely. In this respect, the usage of connected devices is continuously growing with the expansion of the applications being offered to individuals and industries. To address IoT market needs, many low-power wide-area (LPWA) technologies have been developed, some operating on licensed frequencies (e.g., narrowband-IoT [NB-IoT] and Long-Term Evolution-M [LTE-M]), and others on unlicensed frequencies (e.g., LoRa, Sigfox, etc.). In this paper, we address the Release 13 of the NB-IoT 3rd generation partnership project (3GPP) standardized LPWA technology and provide a tutorial on its physical layer (PHY) design. Specifically, we focus on the characteristics and the scheduling of downlink and uplink physical channels at the NB-IoT base station side and the user equipment (UE) side. The goal is to help readers easily understand the NB-IoT system without having to read all the 3GPP specifications or the state-of-the-art papers that generally describe the system. To this end, each presented concept is followed by examples and concrete use-cases to further aid in the reader's comprehension. Finally, we briefly describe and highlight the new features added to the NB-IoT system in Releases 14 and 15.

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