The purpose of this paper is to provide a comprehensive presentation and interpretation of the Ensemble Kalman Filter (EnKF) and its numerical implementation. The EnKF has a large user group, and numerous publications have discussed applications and theoretical aspects of it. This paper reviews the important results from these studies and also presents new ideas and alternative interpretations which further explain the success of the EnKF. In addition to providing the theoretical framework needed for using the EnKF, there is also a focus on the algorithmic formulation and optimal numerical implementation. A program listing is given for some of the key subroutines. The paper also touches upon specific issues such as the use of nonlinear measurements, in situ profiles of temperature and salinity, and data which are available with high frequency in time. An ensemble based optimal interpolation (EnOI) scheme is presented as a cost-effective approach which may serve as an alternative to the EnKF in some applications. A fairly extensive discussion is devoted to the use of time correlated model errors and the estimation of model bias.

The Ensemble Kalman Filter: Theoretical formulation and practical implementation

Technology has become ubiquitous, it is all around us and is becoming part of us. Togetherwith the rise of the Internet of Things (IoT) paradigm and enabling technologies (e.g., Augmented Reality (AR), Cyber-Physical Systems, Artificial Intelligence (AI), blockchain or edge computing), smart wearables and IoT-based garments can potentially have a lot of influence by harmonizing functionality and the delight created by fashion. Thus, smart clothes look for a balance among fashion, engineering, interaction, user experience, cybersecurity, design and science to reinvent technologies that can anticipate needs and desires. Nowadays, the rapid convergence of textile and electronics is enabling the seamless and massive integration of sensors into textiles and the development of conductive yarn. The potential of smart fabrics, which can communicate with smartphones to process biometric information such as heart rate, temperature, breathing, stress, movement, acceleration, or even hormone levels, promises a new era for retail. This article reviews the main requirements for developing smart IoT-enabled garments and shows smart clothing potential impact on business models in the medium-term. Specifically, a global IoT architecture is proposed, the main types and components of smart IoT wearables and garments are presented, their main requirements are analyzed and some of the most recent smart clothing applications are studied. In this way, this article reviews the past and present of smart garments in order to provide guidelines for the future developers of a network where garments will be connected like other IoT objects: the Internet of Smart Clothing.

https://www.mdpi.com/2079-9292/7/12/405/pdf

Towards The Internet of Smart Clothing: A Review on IoT Wearables and Garments for Creating Intelligent Connected E-Textiles

: In previous publications, the authors introduced a new class of polyphase pulse-compression codes and techniques for use in digitally coded radars. Such codes and compressors can be employed to obtain much larger time-bandwidth products (pulse compression ratios) than are feasible with analog dispersive delay lines. It is the purpose of this report to extend this class to include two new codes, one of which is tolerant of precompression bandwidth limitation. These new phase codes are conceptually derived from a linear frequency modulation waveform (LFMW) and are more doppler tolerant than other phase codes derived from a step approximation to a LFMW. This report will also describe an efficient technique for implementing these new phase codes in a digital pulse-expander-compressor and will present performance data. It should be noted that these phase codes are designed to be used both on transmission and reception to insure that the receive filter matches the transmitted waveform independent of time differences between the leading edge of the echo and a sampling pulse, i.e., independent of target range. The two new phase codes will be called the P3 and P4 codes to distinguish them from the P1 and P2 codes. The P3 code is not precompression bandwidth limitation tolerant, but is much more doppler tolerant than the Frank or P1 and P2 codes. The P4 code is a rearranged P3 code with the same doppler tolerance and with better precompression bandwidth limitation tolerance.

Linear Frequency Modulation Derived Polyphase Pulse-Compression Codes and an Efficient Digital Implementation.

An accurate and reliable Indoor Positioning System (IPS) applicable to most indoor scenarios has been sought for many years. The number of technologies, techniques, and approaches in general used in IPS proposals is remarkable. Such diversity, coupled with the lack of strict and verifiable evaluations, leads to difficulties for appreciating the true value of most proposals. This paper provides a meta-review that performed a comprehensive compilation of 62 survey papers in the area of indoor positioning. The paper provides the reader with an introduction to IPS and the different technologies, techniques, and some methods commonly employed. The introduction is supported by consensus found in the selected surveys and referenced using them. Thus, the meta-review allows the reader to inspect the IPS current state at a glance and serve as a guide for the reader to easily find further details on each technology used in IPS. The analyses of the meta-review contributed with insights on the abundance and academic significance of published IPS proposals using the criterion of the number of citations. Moreover, 75 works are identified as relevant works in the research topic from a selection of about 4000 works cited in the analyzed surveys.

https://www.mdpi.com/1424-8220/19/20/4507/pdf

A Meta-Review of Indoor Positioning Systems.

It is well known that if each coefficient value of a digital filter is a sum of signed power-of-two (SPT) terms, the filter can be implemented without using multipliers. In the past decade, several methods have been developed for the design of filters whose coefficient values are sums of SPT terms. Most of these methods are for the design of filters where all the coefficient values have the same number of SPT terms. It has also been demonstrated recently that significant advantage can be achieved if the coefficient values are allocated with different number of SPT terms while keeping the total number of SPT terms for the filter fixed. In this paper, we present a new method for allocating the number of SPT terms to each coefficient value. In our method, the number of SPT terms allocated to a coefficient is determined by the statistical quantization step-size of that coefficient and the sensitivity of the frequency response of the filter to that coefficient. After the assignment of the SPT terms, an integer-programming algorithm is used to optimize the coefficient values. Our technique yields excellent results but does not guarantee optimum assignment of SPT terms. Nevertheless, for any particular assignment of SPT terms, the result obtained is optimum with respect to that assignment.

Signed Power-of-Two Term Allocation Scheme for the Design of Digital Filters

Acoustic local positioning systems (ALPSs) are an interesting alternative for indoor positioning due to certain advantages over other approaches, including their relatively high accuracy, low cost, and room-level signal propagation. Centimeter-level or fine-grained indoor positioning can be an asset for robot navigation, guiding a person to, for instance, a particular piece in a museum or to a specific product in a shop, targeted advertising, or augmented reality. In airborne system applications, acoustic positioning can be based on using opportunistic signals or sounds produced by the person or object to be located (e.g., noise from appliances or the speech from a speaker) or from encoded emission beacons (or anchors) specifically designed for this purpose. This work presents a review of the different challenges that designers of systems based on encoded emission beacons must address in order to achieve suitable performance. At low-level processing, the waveform design (coding and modulation) and the processing of the received signal are key factors to address such drawbacks as multipath propagation, multiple-access interference, near–far effect, or Doppler shifting. With regards to high-level system design, the issues to be addressed are related to the distribution of beacons, ease of deployment, and calibration and positioning algorithms, including the possible fusion of information obtained from maps and onboard sensors. Apart from theoretical discussions, this work also includes the description of an ALPS that was implemented, installed in a large area and tested for mobile robot navigation. In addition to practical interest for real applications, airborne ALPSs can also be used as an excellent platform to test complex algorithms (taking advantage of the low sampling frequency required), which can be subsequently adapted for other positioning systems, such as underwater acoustic systems or ultrawideband radio-frequency (UWB RF) systems.

Acoustic Local Positioning With Encoded Emission Beacons

Spreading sequences in active sensing

This paper presents the design of a novel receiver for a broadband ultrasonic Local Positioning System (LPS). As in other devices based on matched filtering of the transmitted encoded signals, this receiver features high robustness to noise and multiple access capability. Unlike previous solutions, the proposed receiver is capable of detecting beacons emissions despite being installed in a fast moving device, and it also provides estimation of its velocity. The system has been implemented in an FPGA-based architecture. An experimental analysis of performance has been carried out. Firstly using a set of test signals synthetically generated to simulate different positions and velocities of the receiver. Secondly, a set of real signals obtained with a prototype have been used. The simulated results show the capability of the system to detect the encoded signals emitted by the LPS infrastructure when the device is moving at velocities of up to 3 m/s under low SNR conditions. The real results confirm the improved system capability, but also make evident the negative influence that phenomena such as the transducers response and multipath propagation can have on system performance.

Doppler-tolerant receiver for an ultrasonic LPS based on Kasami sequences

In this paper it is proposed a new method for generating multilevel Complementary Sets of Sequences (CSS) based on the existence of Hadamard matrices of odd order. Then it is generated a family of M2 Multilevel Loosely Synchronized (MLS) codes from a multilevel CSS. These codes have inherent advantages that make interesting their use in UWB-based local positioning systems.

Multilevel Complementary Sets of Sequences and their application in UWB

This paper presents the different levels of signal processing applied to an extensive Ultrasonic Local Positioning System (ULPS) intended for mobile robot (MR) indoor navigation. The working area is covered using several single LPSs, each of them composed of a set of closely arranged ultrasonic beacons. Low-level signal processing deals with the simultaneous encoded emission of the beacons that compose each single LPS and the detection carried out in each ultrasonic receiver on board the MR, with the aim of determining Differences of Times of Flights (DoTFs) to be applied to a positioning algorithm. High-level signal processing takes into account the positions obtained with each single ULPS to reference them to a global coordinate system and to perform navigation tasks in which the typical cumulative errors of MR odometer are corrected. The whole system has been developed and tested within the LORIS project.

M. Carmen Perez

Papers

Acoustic Local Positioning With Encoded Emission Beacons

Spreading sequences in active sensing

Doppler-tolerant receiver for an ultrasonic LPS based on Kasami sequences

Multilevel Complementary Sets of Sequences and their application in UWB

Ultrasonic local positioning system for mobile robot navigation: From low to high level processing