Carlos J. Escudero

A blind signal separation method for multiuser communications

A new approach based on the constant modulus (CM) criterion is proposed to separate instantaneous linear mixtures of signals using a linear memoryless multiple input multiple output (MIMO) system. Even though a nonconvex cost function is minimized, analyses show that minima correspond to parameter settings where perfect separation is achieved.

A Toeplitz displacement method for blind multipath estimation for long code DS/CDMA signals

The problem of blind channel identification for direct-sequence/code-division multiple-access (DS/CDMA) multiuser systems is explored. For wideband DS/CDMA signals, multipath distortion is well modeled by a finite-impulse response filter. In this work, a blind channel identification technique based on second-order statistics is investigated. The method exploits knowledge of the spreading code of the user of interest via matched filtering, as well as properties of spreading codes. The current scheme focuses on a method appropriate for randomized long sequence DS/CDMA. This access scheme poses special challenges as the spreading codes are time varying. An analytical approximation of the mean-squared error is derived using perturbation techniques. The performance of the algorithm is studied via simulation and through the mean-squared error approximation, which is observed to be tight.

Real-time personal protective equipment monitoring system

The use of personal protective equipment (PPEs) in the construction industry is necessary to guarantee the safety of the workers. However, this equipment is not usually worn properly. Nowadays, the only control performed over the use of PPEs consists of a visual inspection. This paper introduces a novel cyber-physical system (CPS) to check in real time how the PPEs are worn by the workers. In order to perform such a control, an architecture composed of a wireless local area network and a body area network is considered. A system prototype was developed by using Zigbee and RFID technologies that support the deployment of both kinds of networks. The worker carries a microcontroller-based device that detects the presence of the PPEs and sends a report to a central unit where alerts and historical data are generated. This paper is basically aimed at introducing the monitoring system, describing its hardware and software components, and analyzing the coverage and consumption of the workers device.

Analysis of a subspace channel estimation technique for multicarrier CDMA systems

In this paper we investigate a blind channel estimation method for multicarrier CDMA systems that uses a subspace decomposition technique. This technique exploits the orthogonality property between the noise subspace and the received user codes to obtain a channel identification algorithm. In order to analyze the performance of this algorithm, we derived a theoretical expression of the estimation MSE using a perturbation approach. This expression is compared with the numerical results of some computer simulations to illustrate the validity of the analysis.

Bluetooth Sensor Network Positioning System with Dynamic Calibration

Positioning systems based on sensor networks is one of the most promising fields in mobile computing. This paper considers the Bluetooth standard to locate devices using the RSSI (Received Signal Strength Indicator). The major problem of working with this parameter is its fluctuation that happens very fast due to changes in the environment. These changes can be caused by humidity or temperature, presence and movement of people, opening and closing of doors, multipath effect, etc... This paper introduces an innovative approach that uses the RSSI information between several fixed wireless beacons to improve the reliability of a Bluetooth positioning system. This information is used to calibrate the sensor responses. The results of several experiments illustrate how the real time calibration improves the precision and the stabilization of the position estimations. Moreover, we show the improvement obtained when increasing the number of beacons.

Bayesian filtering for a bluetooth positioning system

Positioning systems are one of the multiple applications of the wireless sensor networks. These networks are very adequate in environments where other positioning technologies, as satellite systems, do not work. Bluetooth is a promising technology, since it is present in any kind of portable devices. By using the received signal strength indicator (RSSI) it is possible to make an estimation of the distance between a transmitter and a receiver. By using this information, it is possible to develop an algorithm that estimates positions, even with the bluetooth constraints when the RSSI is obtained. Our experimental results show that our algorithm, based on a particle filter, can achieve a good performance.

Performance analysis of a CMA-based adaptive multiuser detector

We present a performance analysis of a linear multiuser detector whose parameters are selected according to a statistical criterion for blind source separation previously proposed by the authors. Our approach exploits the properties of the well-known constant modulus (CM) criterion and has been shown to be free of undesirable minima in the absence of noise. We provide a closed-form expression of the mean square error (MSE) achieved at the minima when noise is present and show that it is reached the same value as with the conventional minimum MSE (MMSE) detector. This way, we demonstrate that our blind adaptive source separation algorithm is able to implement the MMSE detector without the need of training sequences.

Design and Practical Evaluation of a Family of Lightweight Protocols for Heterogeneous Sensing through BLE Beacons in IoT Telemetry Applications

The Internet of Things (IoT) involves a wide variety of heterogeneous technologies and resource-constrained devices that interact with each other. Due to such constraints, IoT devices usually require lightweight protocols that optimize the use of resources and energy consumption. Among the different commercial IoT devices, Bluetooth and Bluetooth Low Energy (BLE)-based beacons, which broadcast periodically certain data packets to notify their presence, have experienced a remarkable growth, specially due to their application in indoor positioning systems. This article proposes a family of protocols named Lightweight Protocol for Sensors (LP4S) that provides fast responses and enables plug-and-play mechanisms that allow IoT telemetry systems to discover new nodes and to describe and auto-register the sensors and actuators connected to a beacon. Thus, three protocols are defined depending on the beacon hardware characteristics: LP4S-6 (for resource-constraint beacons), LP4S-X (for more powerful beacons) and LP4S-J (for beacons able to run complex firmware). In order to demonstrate the capabilities of the designed protocols, the most restrictive (LP4S-6) is tested after implementing it for a telemetry application in a beacon based on Eddystone (Google’s open beacon format). Thus, the beacon specification is extended in order to increase its ability to manage unlimited sensors in a telemetry system without interfering in its normal operation with Eddystone frames. The performed experiments show the feasibility of the proposed solution and its superiority, in terms of latency and energy consumption, with respect to approaches based on Generic Attribute Profile (GATT) when multiple users connect to a mote or in scenarios where latency is not a restriction, but where low-energy consumption is essential.

Architecture for Multi-Technology Real-Time Location Systems

The rising popularity of location-based services has prompted considerable research in the field of indoor location systems. Since there is no single technology to support these systems, it is necessary to consider the fusion of the information coming from heterogeneous sensors. This paper presents a software architecture designed for a hybrid location system where we can merge information from multiple sensor technologies. The architecture was designed to be used by different kinds of actors independently and with mutual transparency: hardware administrators, algorithm developers and user applications. The paper presents the architecture design, work-flow, case study examples and some results to show how different technologies can be exploited to obtain a good estimation of a target position.

Performance evaluation of multiple-antenna IEEE 802.11p transceivers using an FPGA-based MIMO vehicular channel emulator

The IEEE 802.11p standard has been optimized for low-delay small-bandwidth wireless communications to provide vehicular safety services. However, IEEE 802.11p transceivers can considerably improve their robustness by incorporating MIMO transmission methods. Moreover, multiple antennas can also be used to increase the data transfer rate of IEEE 802.11p transceivers, a requirement necessary to implement, for instance, non-critical safety applications. In this article we describe the design and development of a multiple-antenna IEEE 802.11p performance evaluation system made of two IEEE 802.11p software-based transceivers and two different, flexible low-cost FPGA-based multi-antenna channel emulators. Our channel emulators are able to recreate seven vehicular communication environments including highways, urban canyons and suburban areas. Using our performance evaluation system, we obtained performance curves showing that IEEE 802.11p can dramatically improve its performance by using multiple transmit and receive antennas. In addition, our channel emulators accelerated the performance evaluation task between 6 and 209 times compared to that of conventional software-based simulation approaches.