EVEREST IST - 2002 - 00185 : D23 : final report

Deliverable públic del projecte europeu EVERESTThis deliverable constitutes the final report of the project IST-2002-001858 EVEREST. After its successful completion, the project presents this document that firstly summarizes the context, goal and the approach objective of the project. Then it presents a concise summary of the major goals and results, as well as highlights the most valuable lessons derived form the project work. A list of deliverables and publications is included in the annex.Postprint (published version

Performance of adaptive bayesian equalizers in outdoor environments

Outdoor communications are affected by multipath propagation that imposes an upper limit on the system data rate and restricts possible applications. In order to overcome the degrading effect introduced by the channel, conventional equalizers implemented with digital filters have been traditionally used. A new approach based on neural networks is considered. In particular, the behavior of the adaptive Bayesian equalizer implemented by means of radial basis functions applied to the channel equalization of radio outdoor environments has been analyzed. The method used to train the equalizer coefficients is based on a channel response estimation. We compare the results obtained with three channel estimation methods: the least sum of square errors (LSSE) channel estimation algorithm, recursive least square (RLS) algorithm employed only to obtain one channel estimation and, finally, the RLS algorithm used to estimate the channel every decided symbol for the whole frame.Peer ReviewedPostprint (published version

Radio-communications systems in indoor environments: performances of the channel equalization

The performance of the diversity and equalization techniques in an indoor radio environment is analyzed. Four and 16 QAM have been considered. Based on experimental results, it is concluded that a system without protection has very limited performance. When the channel introduces a low level of distortion the diversity technique produces better performance than the equalizer technique, but if the channel introduces a high degree of intersymbol interference, then the equalizer techniques are slightly better than the diversity techniques. On the other hand, joint equalization and diversity techniques are an effective tool to combat the degrading effect introduced by the indoor channel. Improvements in system performance, with respect to a system without any protection, ranging from 10 to 100 have been obtainedPeer ReviewedPostprint (published version

The linc transmitter

A technique for producing linear amplification of a bandpass signal using both non-linear components and digital signal processing is the subject of this article. With this technique the bandpass signal is decomposed into two constant-amplitude phase modulated signals. These two phase modulated signals can be nonlinearily amplified and passively recombined to produce a linearly amplified signal.Peer ReviewedPostprint (published version

Analysis of diversity and equalization techniques applied to M-QAM digital mobile radio systems

Presents an investigation of diversity and/or equalization techniques applied to 4 and 16-QAM TDMA radio systems for rapid fading dispersive channels. In particular, typical urban (TU) environments have been considered. A least sum of squared errors (LSSE) channel estimator has been introduced in order to allow the analytic calculation of the equalizer coefficients. By means of simulation methods the authors have found that a degradation of 4 dB can be expected in relation to ideal estimation. Furthermore, the degrading effects of non-linear power amplifiers have been analyzed and a degradation of 2 dB has been found.Peer ReviewedPostprint (published version

Issues on packet transmissioin strategies in a TDD-TD/CDMA scenario

This paper presents a packet transmission scheme that deals with the problems of a TDD CDMA scenario with different levels of frame structure asymmetry in adjacent base stations by distributing the users in the slots depending on their Time Advance. A multiple access protocol and a scheduling algorithm are also proposed to provide a certain degree of Quality of Service.Peer ReviewedPostprint (published version

Performance of soft-output equalization and convolutional coding over frequency-selective fading radio channels

This paper presents an analysis of soft-output equalization and coding techniques applied to 4 and 16-QAM TDMA radio systems for frequency selective fading channels. In particular, typical urban and hilly terrain environments have been considered. The use of the soft information provided by the equalizer enhances the system performance considerably. Specifically, an improvement of more than 4 dB can be achieved in relation to hard decoding techniques. The necessity of introducing some interleaving in order to destroy the channel memory has also been stated. The actual investigated equalizers have been a soft-output decision-feedback equalizer (SODFE) and a soft-decision M-algorithm (SDMA) jointly with convolutional coding and both ideal and finite interleaving.Peer ReviewedPostprint (published version

Performance of blind equalization with higher order statistics in indoor radio environments

This paper analyzes the performance of blind equalization using the complex cepstrum of third-order moments applied to 4-QAM time division multiple access (TDMA) indoor radio communication systems. In particular, we have modeled a dispersive indoor channel with Rice statistics. We used the blind algorithms to estimate the channel-impulse response, and from this, we computed the equalizer coefficients using a classical minimum mean square error (MMSE) algorithm. In order to evaluate the system performance, we calculated the bit error rate (BER) of a decision feedback equalizer (DFE) that uses a tricepstrum algorithm to estimate the channel-impulse response. The results are compared with those obtained using a least sum of square errors (LSSE) algorithm as a channel estimator and considering the exact channel response. The results obtained show that this kind of blind equalizer performs better than the more classically trained equalizer when Rice channels with a strong direct path and signal-to-noise ratios (SNR’s) lower than 20 dB are taken into account. However, some problems relating to the length of time needed for convergence must be solved.Peer Reviewe

Rate adaptive resource allocation with fairness control for OFDMA networks

The use of opportunistic radio resource allocation techniques in order to efficiently manage the resources generates a low fairness among the users in a cellular system due to uneven Quality of Service (QoS) distribution. Some classic rate adaptive policies tried to tackle this problem for OFDMA systems by proposing solutions to maximize capacity, maximize fairness, or find a static trade-off between these two objectives. This work generalizes these classic policies and propose a dynamic fairness/rate adaptive technique based on dynamic sub-carrier assignment and equal power allocation that considers a new fairness constraint in the optimization problem. By means of extensive system-level simulations, it is demonstrated that the proposed technique is able to provide an instantaneous (short-term) fairness control, which provides to the network operator the flexibility to operate on any desired trade-off point.Peer ReviewedPostprint (published version

Análisis de prestaciones de algoritmos pseudo-mlse en sistemas TCM aplicados a comunicaciones móviles

This article describes the problematic of using TCM (frellis Coded Modulations) in a mobile indoor environment characterized by a fast fading Rayleigh channel. This modulation technique involves the use of MLSE (Maximum Likelihood Sequence Estimation) algorithms (Viterbi algorithm), with the problem of exponential increasing of the number of surviving paths along with the interferent samples of the channel. To avoid this problem severa! NMLSE (Near MLSE) algorithms have been proposed . In this paper we consider one of these consisting in an adaptive threshold that limits severely the number of survivors. Different studies of the behavior of this algorithm, alone or assisted with Frequency Hopping and/or interleaving techniques, will be shown.Peer ReviewedPostprint (published version