1,721,033 research outputs found
A "Rayleigh-ness" test for DS/SS code acquisition
No full textTesting for statistical distribution has received increasing attention in signal processing for communications. Noncoherent receivers, based on correlation magnitude, are employed when the actual carrier phase of the received samples,is unknown. This paper presents a new test, based on high-order statistics, to decide whether a real positive white series is a realization of a Rayleigh-distributed random process. Such a "Rayleigh-ness" test is based on a testing variable that measures the "Ricianity" of the series under investigation. That is, it estimates the possible presence of the mean of the complex Gaussian model generating both Rayleigh and Rice distributions. The asymptotic testing statistics have been derived as explicit functions of the higher order moments of the noise-plus-interference distribution. The performance of the Rayleigh-ness test has been analyzed in comparison with a conventional power detector. The devised test has application to noncoherent initial synchronization of the chip offset (code acquisition) in a symbol-length spreading sequence of direct-sequence code-division multiple-access systems. In such a case, the noise-plus-interference variance under the out-of-sync condition is much larger than the effective variance in the in-sync case. The obtained results evidence the robustness of the Rayleigh-ness test, avoiding the severe performance, degradation in the presence of large Gaussian and non-Gaussian noise, as well as multiuser interference in a downlink scenario
LOS/NLOS detection by the normalized RAYLEIGH-NESS test
No full textPublication in the conference proceedings of EUSIPCO, Glasgow, Scotland, 200
Enhancing the performance of personal identity authentication systems by fusion of face verification experts
No full textWe investigate the behavior knowledge space method (see Xu, L. et al., IEEE Transactions SMC,2, no.3, p.418-35, 1992) and decision templates method (see Kuncheva, L. et al., Pattern Recognition, vol.34, p.299-314, 2001) of classifier fusion in the context of face verification. The study involves six experts which are not only correlated, but also their performance levels differ by as much as a factor of three. Through extensive experiments on the XM2VTS database using the Lausanne protocol, we found that the behavior knowledge space fusion strategy achieved consistently better results than the decision templates method. Most importantly, it exhibited quasi monotonic behavior as the number of experts combined increased. This is a very important conclusion, as it means that the performance of the multimodal system is not degraded by adding experts
Improving Pre-Post Rake Schemes for DS/CDMA Mobile Communications
No full textA technique known as Pre-Post-Rake has been recently proposed
in the field of mobile communications. It provides a capacity
increase in the downlink by means of alternative solution to the
standard Rake processing and to the Pre-Rake approach. In this
paper we focused our work on the Pre-Post-Rake and presented a
new Pre-Post-Rake scheme that acts as a multi-path channel
equalizer. Compared with conventional methods, it reduces the
effect of interferences and further improves the performance, in
both single user and multi-user environments. The penalizing of
this new method is just little extra computational complexity
which can be compensated by a reasonable capacity gain
A Game Theoretical Approach for Coded Cooperation in Cognitive Radio Networks
No full textIn this paper, the authors focus on a game theoretical approach for cooperation in cognitive radio (CR) networks. In particular, an integrated design framework which relies on the effective SNR methodology is proposed. The authors derive a distributed power allocation policy aimed at maximizing the reliability of a cooperative BIC OFDM link wherein pragmatic modulation and coding schemes are considered. More in detail, the cognitive devices adapt their power to enable efficient cooperation and coexistence between cognitive nodes and primary networks. First of all, the gain due to the cooperation protocol is analytically derived, resorting to a simple first order recursive equation that depends on the current channel conditions. Then, after an accurate formalization of the optimization problem, a distributed iterative solution based on a novel algorithm, named Successive Set Reduction, is proposed. In particular, the authors show that : i) the proposed power allocation policy takes into account the cooperative gain through a simple scalar value, named cooperative effective SNR; ii) it is effective in improving the packet error rate performance with respect to other conventional power allocation strategies, thus allowing a better coverage for the secondary network; iii) the convergence of the distributed algorithm has exponential speed and requires only local signaling between secondary users
Further Results on Link Performance Prediction for Coded Multi-Antenna OFDM Systems
No full textAn efficient and flexible air interface is the necessary condi- tion to achieve the high data rate required from the next gen- eration wireless systems. Coded multi-antenna and multi- carrier techniques combined together with link resources adaptation algorithms are a practical answer to this need. The practicability of this concept, however, requires that the transmitter can perform accurate and simple evaluation of the actual link performance. This paper contributes to this issue with a novel method specifically developed to predict the link performance of bit-interleaved coded MIMO-OFDM links, which offers improved accuracy with the same degree of complexity when compared with conventional techniques. Its effectiveness is confirmed through extensive simulation results obtained over typical wireless channel environments
Packet Transmissions in Cognitive Radio Networks: How to Cheaply Get Efficiency and Reliability
No full textThe ever growing demand for wireless multimedia applications and services occurred in the last years has spurred the research community to tackle several demanding technical challenges. Advanced next-generation wireless systems solicit the designer to solve a hard multi-facet severely constrained problem, that is to say, providing very high data rates under strict quality of service (QoS) levels, while at the same time facing the lack of wide available segments in the overcrowded electromagnetic spectrum
- …
