Efficient Sum-of-Sinusoids based Spatial Consistency for the 3GPP New-Radio Channel Model

Spatial consistency was proposed in the 3GPP TR 38.901 channel model to ensure that closely spaced mobile terminals have similar channels. Future extensions of this model might incorporate mobility at both ends of the link. This requires that all random variables in the model must be correlated in 3 (single-mobility) and up to 6 spatial dimensions (dual-mobility). Existing filtering methods cannot be used due to the large requirements of memory and computing time. The sum-of-sinusoids model promises to be an efficient solution. To use it in the 3GPP channel model, we extended the existing model to a higher number of spatial dimensions and propose a new method to calculate the sinusoid coefficients in order to control the shape of the autocorrelation function. The proposed method shows good results for 2, 3, and 6 dimensions and achieves a four times better approximation accuracy compared to the existing model. This provides a very efficient implementation of the 3GPP proposal and enables the simulation of many communication scenarios that were thought to be impossible to realize with geometry-based stochastic channel models

Quasi-deterministic channel modeling and experimental validation in cooperative and massive MIMO deployment topologies

Das enorme Wachstum des mobilen Datenaufkommens wird zu substantiellen Veränderungen in mobilen Netzwerken führen. Neue drahtlose Funksysteme müssen alle verfügbaren Freiheitsgrade des Übertragungskanals ausnutzen um die Kapazität zu maximieren. Dies beinhaltet die Nutzung größerer Bandbreiten, getrennter Übertragungskanäle, Antennenarrays, Polarisation und Kooperation zwischen Basisstationen. Dafür benötigt die Funkindustrie Kanalmodelle, welche das wirkliche Verhalten des Übertragungskanals in all diesen Fällen abbilden. Viele aktuelle Kanalmodelle unterstützen jedoch nur einen Teil der benötigten Funktionalität und wurden nicht ausreichend durch Messungen in relevanten Ausbreitungsszenarien validiert. Es ist somit unklar, ob die Kapazitätsvorhersagen, welche mit diesen Modellen gemacht werden, realistisch sind. In der vorliegenden Arbeit wird ein neuen Kanalmodell eingeführt, welches korrekte Ergebnisse für zwei wichtige Anwendungsfälle erzeugt: Massive MIMO und Joint-Transmission (JT) Coordinated Multi-Point (CoMP). Dafür wurde das häufig verwendete WINNER Kanalmodell um neue Funktionen erweitert. Dazu zählen 3-D Ausbreitungseffekte, sphärische Wellenausbreitung, räumliche Konsistenz, die zeitliche Entwicklung von Kanälen sowie ein neues Modell für die Polarisation. Das neue Kanalmodell wurde unter dem Akronym "QuaDRiGa" (Quasi Deterministic Radio Channel Generator, dt.: quasideterministischer Funkkanalgenerator) eingeführt. Um das Modell zu validieren wurden Messungen in Dresden und Berlin durchgeführt. Die Messdaten wurden zunächst verwendet um die Modellparameter abzuleiten. Danach wurden die Messkampagnen im Modell nachgestellt um die Reproduzierbarkeit der Ergebnisse nachzuweisen. Essentielle Leistungsindikatoren wie z.B. der Pfadverlust, die Laufzeitstreuung, die Winkelstreuung, der Geometriefaktor, die MIMO Kapazität und die Dirty-Paper-Coding Kapazität wurden für beide Datensätze berechnet. Diese wurden dann miteinander sowie mit Ergebnissen aus dem Rayleigh i.i.d. Modell und dem 3GPP-3D Kanalmodell verglichen. Für die Messungen in Dresden erzeugt das neue Modell nahezu identische Ergebnisse wenn die nachsimulierten Kanäle anstatt der Messdaten für die Bestimmung der Modellparameter verwendet werden. Solch ein direkter Vergleich war bisher nicht möglich, da die vorherigen Modelle keine ausreichend langen Kanalsequenzen erzeugen können. Die Kapazitätsvorhersagen des neuen Modells sind zu über 90% korrekt. Im Vergleich dazu konnte das 3GPP-3D Model nur etwa 80% Genauigkeit aufweisen. Diese Vorhersagen konnten auch für das Messszenario in Berlin gemacht werden, wo mehrere Basisstationen zeitgleich vermessen wurden. Dadurch konnten die gegenseitigen Störungen mit in die Bewertung eingeschlossen werden. Die Ergebnisse bestätigen die generelle Annahme, dass es möglich ist den Ausbreitungskanal sequenziell für einzelne Basisstationen zu vermessen und danach Kapazitätsvorhersagen für ganze Netzwerke mit der Hilfe von Modellen zu machen. Das neue Modell erzeugt Kanalkoeffizienten welche ähnliche Eigenschaften wie Messdaten haben. Somit können neue Algorithmen in Funksystemen schneller bewertet werden, da es nun möglich ist realistische Ergebnisse in einem frühen Entwicklungsstadium zu erhalten.The tremendous growth of mobile data traffic will lead to substantial architectural changes in wireless networks. New wireless systems need to exploit all available degrees of freedom in the wireless channel such as wider bandwidth, multi-carrier operation, large antenna arrays, polarization, and cooperation between base stations, in order to maximize the performance. The wireless industry needs channel models that reproduce the true behavior of the radio channel in all these use cases. However, many state-of-the-art models only support parts of the required functionality and have not been thoroughly validated against measurements in relevant propagations scenarios. It is therefore unclear if the performance predictions made by these models are realistic. This thesis introduces a new geometry-based stochastic channel model that creates accurate results for two important use cases: massive multiple-input multiple-output (MIMO) and joint transmission (JT) coordinated multi-point (CoMP). For this, the popular WINNER channel model was extended to incorporate 3-D propagation, spherical wave propagation, spatial consistency, temporal evolution of channels, and a new model for the polarization. This model was introduced under the acronym ``QuaDRiGa'' - quasi deterministic radio channel generator. To validate the model, measurements were done in downtown Dresden, Germany, and downtown Berlin, Germany. Those were used to derive the model parameters. Then, the measurements were resimulated with the new channel model and benchmarked against the Rayleigh i.i.d. model and the 3GPP-3D channel model. Essential performance indicators such as path gain, shadow fading, delay spread, angular spreads, geometry factor, single-link capacity, and the dirty-paper coding capacity were computed from both the measured and resimulated data. In Dresden, the resimulated channels produce almost identical results as the measured channels. When using the resimulated channels to derive the model parameters, the same results can be obtained as when using the measurement data. Such a direct comparison was not possible with the previous models because they cannot produce sufficiently long sequences of channel data. The performance predictions from the new model are more than 90% accurate whereas only 80% accuracy could be achieved with the 3GPP-3D model. In Berlin, accurate performance predictions could also be made in a multi-cellular environment where the mutual interference between the base stations could be studied. This confirms that it is generally sufficient to use single-link measurements to parameterize channel models that are then used to predict the achievable performance in wireless networks. The new model can generate channel traces with similar characteristics as measured data. This might speed up the evaluation of new algorithms because it is now possible to obtain realistic performance results already in an early stage of development

Lymphotoxin expression in human and murine renal allografts

The kidney is the most frequently transplanted solid organ. Recruitment of inflammatory cells, ranging from diffuse to nodular accumulations with defined microarchitecture, is a hallmark of acute and chronic renal allograft injury. Lymphotoxins (LTs) mediate the communication of lymphocytes and stromal cells and play a pivotal role in chronic inflammation and formation of lymphoid tissue. The aim of this study was to assess the expression of members of the LT system in acute rejection (AR) and chronic renal allograft injury such as transplant glomerulopathy (TG) and interstitial fibrosis/tubular atrophy (IFTA). We investigated differentially regulated components in transcriptomes of human renal allograft biopsies. By microarray analysis, we found the upregulation of LT beta, LIGHT, HVEM and TNF receptors 1 and 2 in AR and IFTA in human renal allograft biopsies. In addition, there was clear evidence for the activation of the NF kappa B pathway, most likely a consequence of LT beta receptor stimulation. In human renal allograft biopsies with transplant glomerulopathy (TG) two distinct transcriptional patterns of LT activation were revealed. By quantitative RT-PCR robust upregulation of LTa, LT beta and LIGHT was shown in biopsies with borderline lesions and AR. Immunohistochemistry revealed expression of LT beta in tubular epithelial cells and inflammatory infiltrates in transplant biopsies with AR and IFTA. Finally, activation of LT signaling was reproduced in a murine model of renal transplantation with AR. In summary, our results indicate a potential role of the LT system in acute renal allograft rejection and chronic transplant injury. Activation of the LT system in allograft rejection in rodents indicates a species independent mechanism. The functional role of the LT system in acute renal allograft rejection and chronic injury remains to be determined

An explicit ground reflection model for mm-wave channels

5G mobile communication systems are likely to use the enormous bandwidths available at mm-wave frequencies. However, there is an important propagation effect that can have a major impact on the performance - the ground reflection (GR). This effect is currently not sufficiently covered by existing 3GPP propagation models. The GR causes fading both on the small-scale level, e.g., multi-path fading, and on the large-scale level, e.g., path loss and shadow fading. However, the small-scale effects become more dominant at mm-wave frequencies. This paper presents a method to explicitly include the GR in geometry-based stochastic channel models. First, an improved small-scale fading model is proposed that covers the influence of the GR on the delay and angular spreads as well as on the polarization. Second, the influence of the electromagnetic properties of the ground is discussed. Third, the path loss and shadow fading models are adjusted to accommodate the large-scale effects of the GR. The updated model allows taking GR fading into account when designing new radio communication systems and evaluate the performance before the standardization, prototyping and product development phase

Radio resource management techniques for high throughput satellite communication systems

In this paper, interference-aware radio resource management (RRM) algorithms are presented for the forward and return links of geostationary orbit (GEO) high throughput satellite (HTS) communication system. For the feeder link, satellite-switched smart gateway diversity is combined with two scheduling methods to improve the feeder link availability in rain conditions. For the user link, interference-aware scheduling (IAS) for the forward link and scheduling based on multi-partite graph matching for the return link are shown to enable full frequency reuse (FR) multi-beam satellite systems. The performance assessment of scheduling algorithms is carried out in a system-level simulator with realistic channel models and system assumptions. The improvements of the system capacity and user rates are evaluated