We address the problem of data detection for the multiple-input multiple-output (MIMO) channel employing one-bit quantizers at the receiver, taking into account different settings of channel state information (CSI) at the receiver (CSIR). In the first part and under perfect CSI conditions, we propose a two-step low-complexity data detection algorithm that reduces the maximum likelihood (ML) search space. The key idea is based on constructing a list of constellation points exploiting the Hessian matrix of the log-likelihood function. We convert the original detection problem under binary observations into the classical integer least-squares optimization enabling direct use of efficient sphere-decoding algorithms. This method is then extended to the multi-bit case along with an assessment of the computational complexity. In the second part, we focus on a real channel model and assume only the availability of statistical CSIR. We formulate the optimal detection metric under a pilot training scheme and present the main challenges in its evaluation, then employ the Laplace method to retrieve an approximation in closed form. We demonstrate through numerical experiments near-optimality of our proposed solutions in terms of vector error rates with respect to oracle lower bounds on their corresponding ML metric. Finally, we also investigate the performance in practical spatially correlated massive MIMO channels.

We address in this article the uplink transmission in a multiple-input multiple-output channel employing 1-bit analog-to-digital converters at the base station, assuming no a priori channel state information. In particular, we investigate under the original "probit" statistical model, the problems of channel estimation and data detection by first formulating them as binary classification procedures based on the cross-entropy loss. Under perfect CSI, the proposed data detection scheme relaxes the exhaustive search requirement to a convex problem with a box boundary constraint that can be solved using gradient descent methods. Achievable mismatched rates of proposed metrics are evaluated with the generalized mutual information and symbol error rates are presented. Simulation results show that the proposed channel estimation scheme under the probit model does not exhibit any instability with imperfect CSI in comparison with the Bussgang linear minimum mean square error estimator.

Weighted K nearest neighbor (WKNN) algorithm provides good result for indoor localization by searching for matching fingerprints in the dataset. However, due to the nature of this method, computation load increases as the size of dataset. In this paper, we propose a hierarchical localization method to reduce the computation load during the online phase. A two-level structure first localizes the user to a smaller subset and then position estimation is obtained by WKNN with feature extraction. On a public accessed WiFi fingerprinting dataset, the proposed method achieves a 98% reduction without sacrificing localization performance.

With the large deployment of WiFi networks, in-door localization using WiFi fingerprinting with received signal strength has been widely studied. One of the common localization methods is weighted K-nearest neighbor method (WKNN), which localizes the user to the weighted center of the K best matching points. The performance of this method is affected by the choice of parameter K. Once tuned, this parameter is usually applied to all test samples. In this paper, we study how far localization performance can be improved if this parameter is adapted for different test points. We show with two public access datasets that adapting parameter K for different test points can potentially improve localization performance by over 45% compared to the baseline of only choosing the closest neighbor. Additionally, we analyze the dataset to obtain some stochastic thresholds for dataset filtering and K selection.

Wifi fingerprinting using received signal strength has been widely studied for indoor localization. Classic similarity-based methods like weighted K-nearest neighbor (WKNN) localize targets by searching for the best matching fingerprint in the dataset. Performance of these methods suffers from RSS variance and they are slow under a large size of fingerprint dataset. In this paper, we propose a WKNN localization strategy using k-means clustering radio mapping that balances localization precision and computational complexity.

In this contribution we study the challenging issue of WiMedia solution which the ability to support high data rate applications but is limited to three piconets simultaneously communicating in the same area. For this reason we analyze the suitability of Channel Division Multiple Access (ChDMA) approach for Multiband Orthogonal Frequency Division Multiplexing (MBOFDM) Ultra Wide Band (UWB) (MB-UWB) system over IEEE 802.15.3a (UWB) channel model. ChDMA approach exploits the characteristics of MB-UWB system to separate the piconets. Each piconet employs its own Channel Frequency Response (CFR) as a signature code which introduces diversity. We have presented analytical analysis in terms of spectral efficiency (bits/s/Hz) assuming that the receiver knows the channel. Numerical analysis is run over IEEE 802.15.3a high data rate channel justified the importance of ChDMA solution to improve the spectral efficiency of MB-UWB system. Then, performance evaluation is investigated when minimum mean square error (MMSE) and matched filter (MF) receiver is applied. Simulations results show the importance of MMSE receiver to improve the performance of MB-UWB ChDMA system.

Interference between radio systems may occur if they share the same environment and use close frequencies at the same time. To ensure their successful coexistence, the Electromagnetic Compatibility (EMC) established rules and regulations within standardisation bodies and aims to protect these systems from harmful interference. Nowadays, with the proliferation of wireless communications and digital technologies, in addition to electronics evolution inside radio terminals, some additional parameters and new techniques are needed to represent more accurately the interference environment and guarantee radio systems coexistence. In this work, we provide an overview of the main standards related to EMC approaches and measurement techniques currently in use, and we show the benefits of considering time-domain parameters in the EMC analysis.

In this paper, we consider the Radio-Frequency Compatibility (RFC) of a candidate system for the future aeronautical communication infrastructure. This infrastructure is being developed within the International Civil Aviation Organization since 2004, to accommodate the air traffic load and improve the aerial security. The system presented in this paper is one of the two preselected proposals for the L-band Digital Aeronautical Communication System (L-DACS), which will be responsible for the continental communications. This proposed candidate is named L-DACS2 and is foreseen to use part of the L-band spectrum (960 to 1164 MHz) allocated to the Aeronautical Mobile Service reserved for communications relating to safety and regularity of flight. Despite its potentially large spectrum, the L-band is a challenging environment for aeronautical communications because of the channel propagation characteristics and the dense spectral occupation by a large number of aeronautical systems. On the other hand, the RFC characterizes the electromagnetic compatibility between two radio systems and determines if they can coexist in the same electromagnetic environment. For this reason, the RFC is one of the main issues for L-DACS deployment and if it is not satisfied, the flight safety could be endangered. Hence, we propose to study in this paper the impact of the L-DACS on the Distance Measuring Equipment (DME), which is a very important equipment that has been using this band for decades. According to recent studies performed in the frequency domain , that is assuming continuous transmissions and no time domain variations, the achieved RFC level seems insufficient. The main objective of this work is to analyze the RFC between L-DACS2 and DME taking into account the time domain aspects of both systems. The idea is to verify and quantify the impact of the radio- frequency signals generated by a L-DACS2 interferer on the performance of a DME victim receiver. The study is performed for the co-site case (i.e. when both equipments are onboard of the same airplane), which is the most critical interference scenario due to the proximity of both systems. The results are obtained through computer simulations as well as laboratory measurements. They present the DME performance degradation for some values of the Signal to Interference Ratio, assuming a constant DME signal level and different L-DACS2 interference powers.

General and commercial aviation authorities have been using amplitude modulation communication systems for more than 70 years. Due to the great increase of air traffic during the last years, the VHF band tends towards saturation, whereas the aeronautical community faces new requirements: data rate, spectral efficiency and network capacity (maximum number of aircrafts simultaneously connected). Recently, the development of a new digital aeronautical communication system, named L-DACS, was proposed. This system will operate in the L band part allocated to aeronautics. There were many proposals but only two candidates have been pre-selected by the ITU and ICAO for this future communication system: L-DACS1 and L-DACS2. The deployment of this new system is expected to start after 2020. Among other issues, one important aspect is the impact of L-DACS on legacy systems. Actually, there are many onboard systems operating in L band, and any disfunction can put in danger the flight safety. This paper studies the maximum interference level generated by the two L-DACS candidates on a generic onboard receiver. Taking into account the antenna radiation pattern and the specific transmission mask of both candidates, the study determines the worst interference level and the corresponding spatial positions of the aircrafts around the receiver. The results show that the interference level can be determined by considering the several nearest aircrafts to the victim.

In this paper, a unified framework for Ultra-Wideband channel (UWB channel) modeling based on the maximum entropy approach is provided. For a given set of constraints, a consistent model which takes into account the information at hand is obtained. Two cases are considered: channel power knowledge and knowledge of the covariance matrix. The channel power delay spectrum is also derived and the impact of the channel bandwidth is assessed through information theoretic considerations. The information variation slope with respect to the bandwidth is also studied, based on wideband measurements performed at Institut Eurecom1.

Ultra-wideband (UWB) has been recently presented as a promising radio technology due to the large bandwidth available. This feature enables point to point high data rates at short range as well as high temporal resolution with long channel impulse responses (CIR). Due to the their large bandwidth, UWB systems enables high temporal resolution with long CIR. In this paper, we evaluate an original multiple access scheme called channel division multiple access (ChDMA), where we use the CIR as a user signature. The signature code is given by the channel and the users are separated by their position: this signature is uniquely determined by the user's position, which changes from one position to another. This signature location- dependent property provides decentralized flexible multiple access as the codes are naturally generated by the radio channel. The framework is analyzed and validated by capacity assessments using UWB measurements performed at Eurecom and compared with classical CDMA schemes with random spreading codes. The analysis is focused on the impact of the user's asynchronism and the period of symbol on system performance. Two structures are considered at the receiver: single-user matched filter and MMSE receiver with Gaussian and BPSK signaling schemes.