Capacity of The Discrete-Time Non-Coherent Memoryless Gaussian Channels at Low SNR

We address the capacity of a discrete-time memoryless Gaussian channel, where the channel state information (CSI) is neither available at the transmitter nor at the receiver. The optimal capacity-achieving input distribution at low signal-to-noise ratio (SNR) is precisely characterized, and the exact capacity of a non-coherent channel is derived. The derived relations allow to better understanding the capacity of non-coherent channels at low SNR. Then, we compute the non-coherence penalty and give a more precise characterization of the sub-linear term in SNR. Finally, in order to get more insight on how the optimal input varies with SNR, upper and lower bounds on the non-zero mass point location of the capacity-achieving input are given.Comment: 5 pages and 4 figures. To appear in Proceeding of International Symposium on Information Theory (ISIT 2008

Impact of Spatial Correlation on the Finite-SNR Diversity-Multiplexing Tradeoff

The impact of spatial correlation on the performance limits of multielement antenna (MEA) channels is analyzed in terms of the diversity-multiplexing tradeoff (DMT) at finite signal-to-noise ratio (SNR) values. A lower bound on the outage probability is first derived. Using this bound accurate finite-SNR estimate of the DMT is then derived. This estimate allows to gain insight on the impact of spatial correlation on the DMT at finite SNR. As expected, the DMT is severely degraded as the spatial correlation increases. Moreover, using asymptotic analysis, we show that our framework encompasses well-known results concerning the asymptotic behavior of the DMT.Comment: Accepted for publication to IEEE Transaction on Wireless Communication on June 4th 200

Opportunistic Adaptive Relaying in Cognitive Radio Networks

Combining cognitive radio technology with user cooperation could be advantageous to both primary and secondary transmissions. In this paper, we propose a first relaying scheme for cognitive radio networks (called "Adaptive relaying scheme 1"), where one relay node can assist the primary or the secondary transmission with the objective of improving the outage probability of the secondary transmission with respect to a primary outage probability threshold. Upper bound expressions of the secondary outage probability using the proposed scheme are derived over Rayleigh fading channels. Numerical and simulation results show that the secondary outage probability using the proposed scheme is lower than that of other relaying schemes. Then, we extend the proposed scheme to the case where the relay node has the ability to decode both the primary and secondary signals and also can assist simultaneously both transmissions. Simulations show the performance improvement that can be obtained due to this extension in terms of secondary outage probability.Comment: 5 pages, 4 figures. Accepted for publication in Proc. IEEE International Communications Conference (ICC), Ottawa (ON), Canada, June 201

Sequential decoding of high rate convolutional codes

A modified version of the stack algorithm of sequential decoding is presented for the decoding of high rate convolutional codes. It is based on the use of a rejection threshold to discard some of the unlikely branch extensions at each node extension of the algorithm . Using computer simulation with the best known codes of rates 2/3 and 3/4, we show that large savings in the stack memory of the decoder may be achieved at hardly any degradation of either the error performance or the computational effort.Une variante de l'algorithme à pile du décodage séquentiel des codes convolutionnels de taux élevés est présentée . La procédure consiste essentiellement à établir et à utiliser un seuil de rejet pour éliminer certaines branches inutiles à chaque cycle d'extension d'un nceud . Des résultats de simulation à l'ordinateur avec des codes de taux R=2/3 et 3/4 montrent que des économies substantielles d'espace mémoire du décodeur peuvent être réalisées sans porter atteinte à la performance d'erreur ou à l'effort de calcul du décodeur

La coexistence interprofessionnelle au sein d’un hôpital psychiatrique

Voulant organiser une journée d’étude sur les relations de travail interprofessionnelles au centre de psychiatrie communautaire du centre hospitalier Douglas, nous avons, au préalable, distribué à 81 professionnels (infirmières, psychiatres, psychologues et travailleurs sociaux) des unités internes et/ou des cliniques externes, un questionnaire dont nous analysons ici les résultats, avant de dresser un bilan de la journée elle-même. L’auteur présente les difficultés de coordination du personnel, et les différences de satisfaction au travail et de croyances dans l’efficacité de l’institution.The results of a survey on interprofessional collaboration in a psychiatrie hospital indicated difficulties in staff coordination as well as differences between professions in job satisfaction and belief in the institution's effectiveness. Reasons for these differences and suggestions for improvement of the present system are cited

Computational variability and overflows of stack sequential decoders

This paper presents the Zigangirov-Jelinek (Stack) algorithm of sequential decoding and sonie of its variants . The objective of all the variants is to reduce the computational variability of the decoding effort . Using computer simulation we show that this variability can be substantially reduced at a cost of a larger average decoding effort, but with no de gradation of the error performance . The required decoder stack sizes and their impact on the waiting line at the input buffer is examined. It is shown that by properly choosing the decoder speed factor, stack size and length of the data blocks, the length of the waiting line cannot exceed two data blocks . Finally by containing the overflows in the stack and by using a retransmission procedure on the overflowed blocks, the input buffer overflows can be controlled and the error probability reduced. These advantages are obtained at a cost of a small decrease of the system throughput and a slight increase of the decoder complexity .Etude du codage convolutionnel et décodage séquentiel par l'algorithme à pile de Zigangisov, Jelinek et de certaines de ses variantes. On montre que ces variantes permettent une variabilité qui peut être diminuée au prix d'un accroissement de l'effort de calcul moyen et sans dégradation de la performance d'erreur. Le remplissage de la pile du décodeur est examiné ainsi que son impact sur la taille de la file d'attente dans le tampon d'entrée du décodeu

Une analyse des comportements de travailleurs masculins et féminins selon deux formes d'absence au travail

Les auteurs utilisent des données provenant d'entrevues afin de décrire les activités hors-travail d'un échantillon d'employés d'hôpital lors de journées passées à l'extérieur du travail.Even if the last fifty years of research is a testimony to its' importance to organizations, a satisfactory understanding of employee absence remains to be achieved. In reviewing the literature, this article shows that research on absence may be critiqued on two major grounds: a) A clear lack of mutual relationship between the empirical findings, the explanatory theories and the applied interventions, b) An over reliance on the absence record of employees as the dependent variable. It is further diagnosed that this problem may be directly attributed to the limitations in the basic paradygm used to study absence in organizations. Indeed, there has been practically no attempt to describe absence from the point of view of the absent person.This article attempts to contribute to the descriptive issue by presenting a complete re-analysis of a previously reported data set detailing how a sample of hospital workers spent their absence time.The data was gathered from 75 semi-skilled men and women employees who were interviewed immediately upon their return from a one day absence, which was either previously scheduled (day-off) or unplanned (absence). This data structuring presents the opportunity for investigating sex differences in absence time behaviors under two different types of absences. The raw interview information was subjected to content analyses by independent raters providing numerical structures which were then analysed quantitatively.The principal dependent variable was structured, using Robinson's (1977) classification scheme, around an «obligatory-leisure» continuum. Using this information structuring process and appropriate data transformation procedures it was possible to derive a single score for each respondent. This score expresses the total activity patterns during absence time in terms of the obligatory-leisure measure. The data was analysed using analyses of variance which were followed by hierarchical regressions. The initial analysis showed that women tend to engage in more obligatory activities during absences than their maie counterparts who maintained a greater equilibrium between leisure and obligatory activities (this accounting for 16% of the variance). There was a modest (p < .10) tendency for people to weight their activities towards leisure rather than obligatory activities during casual absence days. The hierarchical regressions showed that, in general, respondent sex was the single best predictor of absence time activities. This was particularly true for married (or cohabitating) women whose activities were clearly more obligatory. The marital status variable was a much better predictor of absence time activity structures than whether or not the respondent was responsable for dependents. For single people rather than gender it was age which best predicted how absence time was spent. However that equation showed low levels of prediction. The data was interpreted to indicate support for the generalized idea by which absences are generally taken for «purposive» reasons as opposed to respond to a desire for increased leisure time. This basic conclusion allows for an analysis of existing absence control programs in organizations. Other work has shown that absence control programs are indeed less powerful than might have once been thought. This data suggests a preliminary explanation: If absence is purposive the typical control of absence strategies (placing pressure on individuals, either by punishing absence or rewarding presence) will indeed yield sub optimal results. Consequently this report recommends the institution of absence control strategies which allow the employee greater flexibility in the distribution of time to meet work and non-work obligations.The paper presents an appraisal of this unusual procedure for the study of absence. It highlights the potential contributions as well as the inferential limits it forces upon both the practice and the theories of absence behavior. Suggestions for improvements in the research design close the paper

Recent Advances in Polymeric Materials Used as Electron Mediators and Immobilizing Matrices in Developing Enzyme Electrodes

Different classes of polymeric materials such as nanomaterials, sol-gel materials, conducting polymers, functional polymers and biomaterials have been used in the design of sensors and biosensors. Various methods have been used, for example from direct adsorption, covalent bonding, crossing-linking with glutaraldehyde on composites to mixing the enzymes or use of functionalized beads for the design of sensors and biosensors using these polymeric materials in recent years. It is widely acknowledged that analytical sensing at electrodes modified with polymeric materials results in low detection limits, high sensitivities, lower applied potential, good stability, efficient electron transfer and easier immobilization of enzymes on electrodes such that sensing and biosensing of environmental pollutants is made easier. However, there are a number of challenges to be addressed in order to fulfill the applications of polymeric based polymers such as cost and shortening the long laboratory synthetic pathways involved in sensor preparation. Furthermore, the toxicological effects on flora and fauna of some of these polymeric materials have not been well studied. Given these disadvantages, efforts are now geared towards introducing low cost biomaterials that can serve as alternatives for the development of novel electrochemical sensors and biosensors. This review highlights recent contributions in the development of the electrochemical sensors and biosensors based on different polymeric material. The synergistic action of some of these polymeric materials and nanocomposites imposed when combined on electrode during sensing is discussed