Abstract A LoRa self‐jamming scheme that enables secure and covert communications by adding jamming symbols when transmitting is proposed. The scheme has been validated in simulations. The work is continued by evaluating the scheme on real‐world software defined radio (SDR) equipment. Experiments immediately showed that a demodulation is impossible as the received signal is highly distorted. This comes from the fact that adding symbols at transmission actually generates high peak‐to‐average power ratio (PAPR) preventing proper waveform generation by the equipment's hardware. This paper presents a PAPR correction scheme that modifies the waveform. The properties of this modified waveform are analysed and the performances are assessed in simulations with realistic time and frequency synchronization assumption. For the ideal 0 dB PAPR corrected output, the SER performances are close to that of a legacy LoRa communication, while preserving the physical layer security capabilities of the self‐jamming scheme. It is finally shown that our PAPR correction scheme effectively recovers the self‐jamming properties on SDR devices.

This article presents a semianalytical approximation of symbol error rate (SER) for the well known long-range (LoRa) Internet of Things (IoT) modulation scheme in the following two scenarios: 1) in multipath frequency selective fading channel with additive white Gaussian noise (AWGN) and 2) in the presence of a second interfering LoRa user in the flat-fading AWGN channel. Performances for both coherent and noncoherent cases are derived by considering the common discrete Fourier transform (DFT)-based detector on the received LoRa waveform. By considering these two scenarios, the detector exhibits parasitic peaks that severely degrade the performance of the LoRa receiver. We propose in that sense a theoretical expression for this result, from which a unified framework based on peak detection probabilities allows us to derive SER, which is validated by Monte Carlo simulations. Fast computation of the derived closed-form SER allows to carry out deep performance analysis for these two scenarios.

This article presents a novel long-range (LoRa) receiver operating in the frequency selective multipath channel (MPC). The dechirped received LoRa waveforms under MPC allows us to derive a simple and efficient LoRa receiver scheme by using a matched filter (MF) approach that aims to maximize the signal-to-noise ratio (SNR) at the symbol index frequency of the discrete Fourier transform (DFT) output. We show that the MF receiver can be seen as a RAKE structure where interference peaks related to multipath, exhibited at DFT output, are recombined in a constructive way. Detection performance is driven by channel energy and the benefit of this novel MF/RAKE receiver over original coherent and noncoherent receiver appears only for MPC that exhibits significant paths energy. These two MF and RAKE receivers have however different implementation complexities that are studied in detail. We provide in that sense recommendations on which receiver variant to use for real operations, depending on complexity constraints. Finally, the proposed MF/RAKE receiver outperforms previous results on time-delay estimation LoRa (TDEL) receiver over MPC, especially at low SNR and higher LoRa spreading factor (SF) parameter, at the cost of higher but reasonable complexity.

The concatenation of the multiple-input multiple-output (MIMO) linear precoder with an outer forward error correction (FEC) code at the transmitter is investigated in this paper. At the receiver side, the turbo detection is taken into account. It iteratively exchanges the extrinsic information between a soft-demapper and a FEC soft-decoder. We firstly propose a new precoder named FI1designed from an extrinsic information transfer (EXIT) chart analysis. The proposed precoder aims to optimize the iterative receiver convergence by maximizing the ending point I1of the soft-demapper EXIT function. For the sake of low-complexity, FI1is designed for two data streams MIMO transmission with 4-QAM only. Secondly, to cope with the higher data streams transmission, a global b = 2K data streams system is split into K two data streams subsystems. FI1is then applied at each subsystem. Finally, we propose a new algorithm to optimize the inter-subsystems power allocation by maximizing the I1of the global system.

Precoder optimization with full channel state information for finite alphabet signals over multiple-input multiple-output random channels is investigated in this paper. The precoder is represented by a product of power allocation matrix and constellation-forming matrix. There was an optimal algorithm introduced in the literature to globally maximize the channel mutual information by iteratively optimizing these two matrices. However, the computational complexity of the optimal algorithm is painfully high, especially when it is used with the high-order modulation and the high-data stream number. In this paper, we propose a novel sub-optimal low-complexity precoding algorithm and compare it with the optimal one. The new algorithm proceeds in two steps. First, the constellation-forming matrix is fixed in order to maximize the minimum Euclidean distance between the received symbols, which ensures high channel mutual information. Then, given the constellation-forming matrix, an iterative algorithm searches for the power allocation matrix that maximizes the channel mutual information. Since optimizing only one matrix instead of two, the new algorithm not only achieves a lower computational complexity but also avoids the use of initial values, which must be carefully selected for each channel and signal-to-noise ratio for fast convergence. Another advantage of the new algorithm is that the resulting precoder has a fixed form of received constellation thanks to the fixed constellation-forming matrix. This allows us to optimize the symbol mapping on the received constellation. Simulation results show that the proposed low-complexity precoder achieves error-rate performance that is close to performance of the optimal one when the conventional mapping is used. In addition, the new precoder used with optimized mapping at received constellation shows significant error-rate performance improvement.

In this paper, we focus on a multiple-input multiple-output (MIMO) linear precoder based on the minimum Euclidean distance criterion, the max- dmin precoder. We propose an optimization of this precoder for the case of an association with a non-binary low density parity check code (NB- LDPC). After recalling the well-known max-dmin precoder, we set forth an optimization of the mutual information of initial message, i.e. I(0), through the extrinsic information transfer (EXIT) analysis of the system. We present a new adaptive precoder whose forms are determined in function of an adaptive threshold angle, optimized in terms of the mutual information I(0), and depending on the signal-to-noise ratio at the reception (SNR_R). The performance of the new precoder is brought out through a theoretical study along with a series of numerical simulations.

In this paper, we investigate the concatenation of the multiple input multiple output (MIMO) max-dminlinear precoder with an outer forward error correction (FEC) code at the transmitter. At the receiver side, the turbo equalization is taken into account, which iteratively exchanges the extrinsic information between a minimum mean square error interference canceller (MMSE IC) and a FEC decoder. The analysis done by extrinsic information transfer (EXIT) chart shows that a higher mutual information (MI) at the convergence state of the turbo equalization is observed thanks to the linear precoder. In addition, we exploit this property to propose a new precoder named max-dmin-mod. Numerical simulations are in accordance with the theoretical analysis, which exhibits a significant improvement of the error-rate of the turbo equalization as well as a significant gain of max-dmin-mod compared to original max-dminprecoder.

The performance of the maximum-SNR design for multiple-input multiple-output (MIMO) systems is analyzed. An average symbol error probability (SEP), expressed in closed form, is derived assuming both i.i.d. Rayleigh fading MIMO channel and coherently detected M-ary PSK/QAM. This form highlights a modulation gain, which permits comparison of SEP performances between different modulations schemes. The maximum diversity advantage can be retrieved by using a Taylor series expansion around infinity from the exact SEP. The performance of the max-SNR MIMO systems is compared by changing the transmit and receive diversity, modulations and constellation size.

Previous papers have shown that multipath wireless channels are capable of enormous capacities, provided that the multipath scattering is sufficiently rich and is properly exploited. A layered space-time architecture, known as BLAST, has been proposed. A basic hypothesis made by the BLAST algorithm is that the symbol period is large compared to the maximum echo delay (hence, the data rate cannot be too high). In this paper, we use an approach that combines BLAST and OFDM. Its interest is to suppress the data rate constraint. First, the symbols are packed into matrices; then matrix manipulations prior to BLAST transmission provide a transmission system which is theoretically equivalent to many independent BLAST channels. Results obtained with the UHF COST 207 channel corresponding to GSM transmission in an urban area are provided and discussed.

This paper presents the determination of bathymetric maps from the analysis of multispectral SPOT images. To this end, we have developed a multispectral segmentation method based on a hierarchical Markovian modeling including the unsupervised estimation of the model parameters. In each segmented region, an adaptive bathymetric inversion model is then applied in order to recover the water depth (mainly in coastal areas). Bathymetric estimation has been validated on real data, for which control points are available and correspond to bathymetric measures supplied by previous hydrographic campaigns.

The paper deals with the analytical evaluation of the asymptotic detection and false-alarm probabilities of multicycle and single-cycle detectors operating in additive white Gaussian noise with unknown and nonrandom spectral level, which are based on the cyclostationarity properties of the signal to be intercepted. The receiver operating characteristics are derived by using the asymptotic complex normality and the covariance expression of the sample average estimator of the cyclic covariance in an observed discrete-time series. A numerical example for interception of a binary phase-shift keying signal is considered.

The purpose of this paper is to evaluate theoretically in terms of receiver operating characteristics (ROC) the performance of a statistical test (based on the second order statistic) for the presence of cyclostationarity in a noisy observation. In order to obtain false alarm and detection probabilities, we consider the following specific situation: we choose a cycle frequency contained in a binary-phase-shift-keyed (BPSK) signal of interest (SOI) (BPSK signal is considered for its increasing attention in digital communications) and we test the presence of cyclostationarity of the SOI in a noisy observation. Two examples are considered, the SOI is buried either in a stationary Gaussian noise or in an another BPSK signal.

This paper deals with detection of weak cyclostationary signals embedded in colored Gaussian noise. We consider the normalized correlation function of the noise to be known and the noise power to be unknown. We propose a temporal structure of the single cycle detector which includes a prewhitening filter. We compare the performance of this detector to the classical radiometer and the modified radiometer. The performance is quantified in terms of receiver operating characteristics for two different noise power spectral densities. We compute the theoretical deflection, this measure gives a means to choose the best cyclic frequency used in the single cycle detector. We conclude that cyclic methods outperform radiometric methods when the noise and the signal power spectral densities strongly overlap and for a unknown noise power.