Daniel I. Iglesia

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.

Channel estimation techniques for linear precoded systems: Supervised, unsupervised, and hybrid approaches

Linear precoding is an attractive technique to combat interference in multiple-input multiple-output systems because it reduces cost and power consumption at the receiver. Frequency division duplex systems with linear precoding acquire the channel state information at the receiver side by using supervised algorithms. Such methods make use of pilot symbols periodically provided by the transmitter. Next, this channel state information is sent to the transmitter side through a low-cost feedback channel. Thus, the available channel information allows the transmitter to adapt signals to the channel conditions. Given that pilot symbols do not convey user data, they penalize throughput, spectral efficiency, and transmission energy consumption of the system. In this work, we propose to mitigate the aforementioned limitations by combining both supervised and unsupervised algorithms to acquire the channel state information needed by the transmitter. The key idea consists in introducing a simple criterion to determine whether the channel has suffered a significant variation which requires the transmission of pilot symbols. Otherwise, when small fluctuations happen, an unsupervised method is used to track these channel variations instead. This criterion will be evaluated by considering two types of strategies for the design of the linear precoders: Zero-Forcing and Wiener criteria.

Multiple Antennas Bluetooth System for RSSI Stabilization

In this paper we introduce a Bluetooth system which achieves an important improvement in the RSSI stability thanks to the use of multiple antennas. The main advantage of our system is that it reduces the effects produced by fading in the received signal power, that is obtained by the RSSI (received signal strength indicator). In most positioning systems the RSSI stability is very important, because it is the main reference for obtaining the desired positions. Using spatial diversity our system tries to stabilize this RSSI measurement. We present a study of this important improvement in which we compare different combination/selection techniques which use the RSSIs obtained from the received signals. We have carried out an empirical evaluation of this multiple antenna Bluetooth system, and we have verified how these spatial diversity techniques reduce the mean square error of the measured RSSI with respect to a theoretical propagation model.

A novel hybrid approach to improve performance of frequency division duplex systems with linear precoding

Linear precoding is an attractive technique to combat interference in multiple-input multiple-output systems because it reduces costs and power consumption in the receiver equipment Most of the frequency division duplex systems with linear precoding acquire the channel state information at the receiver by using supervised algorithms Such algorithms make use of pilot symbols periodically sent by the transmitter In a later step, the channel state information is sent to the transmitter side through a limited feedback channel. In order to reduce the overhead inherent to the periodical transmission of training data, we propose to acquire the channel state information by combining supervised and unsupervised algorithms, leading to a hybrid and more efficient approach Simulation results show that the performance achieved with the proposed scheme is clearly better than that with standard algorithms.

Blind subspace methods for code and channel estimation in multicarrier CDMA

In multicarrier code-division multiple access systems the linear distortion introduced by the channel causes a perturbation in the received user codes that produces multiple access interference. This paper introduces two new techniques to combat this distortion that are based on subspace decomposition. The first one consists of obtaining an approximation of the received desired user code to improve the output signal to interference noise ratio in blind linear receivers. This approximation is obtained by means of the projection of the known transmitted desired user code onto the signal subspace. The second one is a blind channel estimation method that uses the orthogonality property between the received user codes and the noise subspace. We demonstrate that the performance of channel estimation methods based on this property are severely limited by the number of simultaneous users. Nevertheless, it is shown how this limitation is overcome if user codes spanning several transmitted symbols (long codes) are used.

An external short message entity for gambling services

This paper introduces a new platform designed for mobile gambling services. The special characteristics of these services lead us to developed a multiservice platform that easily brought mobility to applications and services not designed for that.This system was designed to work over SMS, allowing automation of the tedious work of programming reliable SMS-based interfaces. The new system automatically generates user front-ends for a wide variety of services based on forms. As we will see in the paper, the interfaces are defined by means of the novel W3C XForms standard.The resulting platform was designed to be highly efficient, reliable and fault tolerant. Choosing Erlang/OTP as the development environment was a key factor to acquire these goals.As part of the project an open source Erlang SMPP implementation was developed, key features of this library, named OSERL, are also described in this paper.

A SUBSPACE METHOD FOR BLIND CHANNEL IDENTIFICATION IN MULTI-CARRIER CDMA SYSTEMS

Blind channel estimation in Multi-Carrier CDMA systems using sub space decomposition techniques is considered. We demonstrate that the performance of these techniques is severely limited by the number of users and show that this limitation is considerabily reduced if we use signature codes that span several transmitted symbols (log codes). Finally, we propose a channel identification algorithm specifically devel oped for MC-CDMA systems using long codes.

Using fractional cyclic moments of CPFSK signals in blind adaptive beamforming

This paper explains how fractional cyclic moments of CPFSK signals can be used in adaptive beamforming. It is shown that CPFSK signals have non-zero fractional cyclic moments because they generate spectral lines when they are raised to the inverse of its modulation index, which is generally a fractional number. To exploit this property, an optimization criterion is proposed to compute the antenna coefficients that maximize the output SINR. The resulting technique is blind because it does not need to know the transmitted symbols: only the carrier frequency, the symbol rate and the modulation index is required.