Channel division multiple access: The access solution for UWB networks

International audience—In this paper we study a promising multiple access scheme entitled Channel Division Multiple Access (ChDMA). ChDMA was developed to cope with the particularities of low duty cycle Impulsive Radio Ultra Wideband systems (IR-UWB). The idea is based upon the fact that Channel Impulse Responses (CIR) could be exploited as users signatures. Based on the knowledge of the CIRs at the receiver, transmitted signals can be detected and estimated in a very similar approach as performed by DS-CDMA systems. We present in this contribution initial analysis of the spectral efficiency performance of ChDMA systems. As a matter of fact, ChDMA overcomes the multiple access paradigm of impulsive-radio signaling and provides an efficient and low complex technique to exploit the diversity of UWB communications. For the study, we consider three different receiver structures: optimal receiver, matched filter (MF) and linear minimum mean square error receiver (l-MMSE). As a result, it is shown that under certain conditions ChDMA can even outperform CDMA in terms of Shannon's capacity, providing a real option for future communication systems

Spectral Efficiency of Spectrum Pooling Systems

In this contribution, we investigate the idea of using cognitive radio to reuse locally unused spectrum to increase the total system capacity. We consider a multiband/wideband system in which the primary and cognitive users wish to communicate to different receivers, subject to mutual interference and assume that each user knows only his channel and the unused spectrum through adequate sensing. The basic idea under the proposed scheme is based on the notion of spectrum pooling. The idea is quite simple: a cognitive radio will listen to the channel and, if sensed idle, will transmit during the voids. It turns out that, although its simplicity, the proposed scheme showed very interesting features with respect to the spectral efficiency and the maximum number of possible pairwise cognitive communications. We impose the constraint that users successively transmit over available bands through selfish water filling. For the first time, our study has quantified the asymptotic (with respect to the band) achievable gain of using spectrum pooling in terms of spectral efficiency compared to classical radio systems. We then derive the total spectral efficiency as well as the maximum number of possible pairwise communications of such a spectrum pooling system

Primary Outage-Based Resource Allocation Strategies

Cognition & cognitive psycholog

Chapter Primary Outage-Based Resource Allocation Strategies

Cognition & cognitive psycholog

ETSI RRS - The Standardization Path to Next Generation Cognitive Radio Systems

This paper details the current work status of the ETSI Reconfigurable Radio Systems (RRS) Technical Committee (TC) and gives an outlook on the future evolution. While previous publications have presented an overview of ETSI RRS' main working axes related to i) Cognitive Radio System Aspects, ii) Radio Equipment Architecture (including a Cognitive Pilot Channel (CPC) proposal and a Functional Architecture (FA) for Management and Control of Reconfigurable Radio Systems), iii) Cognitive Management and Control and iv) Public Safety, this document focuses on latest progress related to UHF White Spaces work and the definition of an SDR Handset Architecture. In particular, it is outlined how Cognitive Radio principles can help to adapt existing and/or evolving Radio Standards, such as 3GPP Long Term Evolution, to a possible operation in UHF White Space bands

Einfluss extrazellulärer Proteinkonzentration auf die Reaktivität afferenter Arteriolen der Niere

Die Niere nimmt eine zentrale Stellung bei Regulation des Osmo- und Volumenhaushaltes des Organismus ein. Dehnungsrezeptoren im Niederdrucksystem als auch zentral und peripher gelegene Osmorezeptoren sind an der Regulation durch Beeinflussung der Vasopressinausschüttung beteiligt. Vasopressin fördert den Einbau von Wasserkanälen im Sammelrohr, damit die Wasserresorption, und hemmt die Diurese. Aber auch Änderungen der Filtrationsrate können für die Flüssigkeitsausscheidung eine Rolle spielen. Die Filtrationsrate wird durch den effektiven Filtrationsdruck und unter physiologischen Umständen damit durch den Widerstand afferenter und efferenter Arteriolen bestimmt. Es wurde in Tierexperimenten gezeigt, dass die interstitielle Proteinkonzentration in der Niere vom Hydratationszustand des Körpers abhängt. In der folgenden Arbeit wird die Hypothese aufgestellt, dass die interstitielle Proteinkonzentration den Tonus und die Reaktivität afferenter Arteriolen moduliert und damit via Änderung der glomerulären Filtrationsrate zur Volumenregulation beitragen könnte. Zur Testung der Hypothese wurden Experimente an Mäuse- (C57Bl6) und Rattengefäßen (Sprague Dawley) durchgeführt. Der Proteingehalt (Albumin) der Badlösung wurde variiert (proteinfrei, 0,1% oder 4% Albumin). Afferente Arteriolen der Maus wurden isoliert, perfundiert, videomikroskopisch dargestellt und Änderungen des Gefäßdurchmessers auf Angiotensin II bewertet. Mannitol wurde als Kontrolle für osmolare Effekte von Protein eingesetzt. Fluoreszenzuntersuchungen mit DAF-FM ermöglichten die Bewertung der Stickstoffmonoxidverfügbarkeit in den Arteriolen. Die Antwort großer Nierenarterien der Maus und Ratte auf Vasokonstriktoren wurde im Drahtmyographen, isometrisch, bei verschiedenen Proteinkonzentrationen im Bad gemessen, um die Spezifität einer möglichen Proteinwirkung beurteilen zu können. Die Expression endothelialer, induzierbarer und neuronaler Stickstoffmonoxidsynthase wurde auf mRNA-Ebene in den Gefäßen bestimmt. Wir sahen eine größere Reaktivität afferenter Arteriolen bei 4% Albumin in der Badlösung im Vergleich mit 0,1%. Dieser Effekt konnte durch Mannitol in der Badlösung, welches einen gleichen osmotischen Druck wie bei 4% Albumin entwickelte, simuliert werden. Die Bioverfügbarkeit von Stickstoffmonoxid war bei 4% Albumin im Bad deutlich vermindert. In großen Nierenarterien der Maus waren keine signifikanten Differenzen in den Antworten auf Angiotensin II und Azetylcholin im Vergleich von 0,1% und 4% Albumin zu sehen. Noradrenalinantworten unterschieden sich in großen Nierenarterien der Ratte ebenfalls im Vergleich von 4% Proteinanteil und proteinfreier Lösung nicht. Die induzierbare Stickstoffmonoxidsynthase-mRNA war deutlich geringer bei 4% Albuminkonzentration exprimiert. Die Studie zeigt, dass eine erhöhte Proteinkonzentration die Gefäßreaktivität afferenter Arteriolen, aber nicht die von großen Nierengefäßen verstärkt. Die erhöhte Osmolalität und eine verminderte Verfügbarkeit von Stickstoffmonoxid vermitteln die Wirkung einer erhöhten Proteinkonzentration. Die Befunde unterstützen die Hypothese eines intrarenalen Mechanismus der Volumenregulation.The kidney is an important part in the control of volume and osmolality in the body. Stretch receptors in the low-pressure system as well as central and peripheral osmoceptors contribute to the control by modulating the vasopressin release in the hypothalamus/pituitary gland. In addition, changes in the glomerular filtration rate may influence the diuresis. The effective filtration pressure is regulated via changes of the resistance of afferent and efferent arterioles. Studies showed that the extracellular protein concentration in the kidney increases with dehydration of the body. We hypothesize that the interstitial protein concentration influences the tone and reactivity of afferent arterioles in the kidney and this may contribute to volume control. To test the hypothesis, renal vessels of mice (C57Bl6) and rats (Sprague Dawley) were included. The protein concentration (albumin) of the bath solution was varied (protein free, 0.1% or 4% albumin). Mouse afferent arterioles were isolated and perfused. Angiotensin II was applied and the diameter was obtained by using video microscopy. To test for the effect of increased osmolality due to increased protein concentration, mannitol was applied. The fluorescent dye DAF-FM served for estimation of the nitric oxide bioavailability. The function of big renal arteries in presence of different protein concentrations in the bath solution was investigated by using wire myography. The mRNA expression of endothelial, inducible, and neuronal nitric oxide synthase in renal vessels was measured by using the qPCR. We found an increased reactivity of afferent arterioles to angiotensin II in presence of 4% protein in the bath. This effect could be mimicked by using mannitol instead of protein. The nitric oxide bioavailability was decreased at 4% protein compared to 0.1%. In the big renal arteries, angiotensin II and acetylcholine responses were similar comparing 4% and 0.1% protein concentrations. The response to norepinephrine was similar when using 4% albumin or protein free solution in big renal arteries of rats. Die inducible nitric oxide synthase was less expressed in big arteries exposed to 4% albumin compared to 0.1%. Nitric oxide synthases expression did not differ in arterioles. The study shows that increased protein concentration in the extracellular fluid leads to enhanced angiotensin II reactivity of afferent arterioles, but not big renal arteries. The protein effect may be due to the elevation in the osmolality of the solution and to reduced nitric oxide bioavailability. The finding supports the hypothesis of an intrarenal mechanism of volume control