Alexandros Palaios

Measurements of spectrum use in London: Exploratory data analysis and study of temporal, spatial and frequency-domain dynamics

In this paper we present results from a week long measurement campaign on spectrum use in London (UK). The measurements were conducted in order to understand the characteristics and especially the variability in spectrum use over different types of areas in a major metropolitan area. Three spectrum analyzers were used in the measurement campaign, one used for long-term measurements at a single location in a given area, with the other two used to sample spectrum use around the stationary measurement point. This measurement approach yields much more detailed information about spectrum use than the typical single-location campaigns reported in the literature. We give a detailed description of the measurement campaign, including the equipment setup and rationale for the choice of areas in which the measurements were conducted. We also present results from the first exploratory data analysis of the obtained data, and study in detail the correlation structures and dynamics in spectrum use in temporal, spatial and frequency domains.

Measurements of Shadow Correlations in a Suburban Environment on the 485 MHz Band

Correlations in shadow fading play a key role in the performance of wireless networks. However, despite of this importance, relatively few comprehensive measurement studies have been made on shadow correlations, and the methodology followed in the existing studies is often poorly documented. In this paper we report results from an extensive measurement campaign on shadow correlation in the 485 MHz band in a suburban environment. In particular, we study carefully the influence of fast fading and different data processing choices on the results, as well as describe in detail the design and verification of the measurement set up. Our results show that shadow correlations decay exponentially as a function of distance also on this band, but that the details of the arising correlation model are highly dependent on the steps taken to process the measurement data. In particular, we show that unless fast fading is properly averaged over, highly incorrect conclusions would be drawn with respect to both marginal variance and the correlation distance of shadow fading.

A week in London: Spectrum usage in metropolitan London

We present results from an 8-day spectrum measurement campaign in the centre of the London metropolis. We analyze results from one of the densest central areas in our campaign from the perspective of spectrum measurements at a very exposed location at the roof of a high building. We present the main results of this measurement campaign in terms of spectrum utilization, powers received, and evolution of the activity among different days. The results presented in this paper here are very close to an upper bound of what one might expect to find in any given radio environment in terms of utilization and received power measurements. In addition to producing valuable measurement data on its own, special attention was given on acquiring comparable datasets with previous measurements campaigns we have conducted to allow direct comparisons with other European cities we have studied. In particular, we show a detailed comparison between the downtown London results against measurements carried out in other cities, quantifying the significantly higher levels of spectrum occupancy in London compared to other locations.

From Paris to London: Comparative analysis of licensed spectrum use in two European metropolises

We present results from a detailed comparative analysis of spectrum use based on extensive measurement campaigns in two major European metropolitan areas, namely in Paris and London. We focus on frequency bands assigned to cellular systems, and characterize in detail the similarities and differences between operators in terms of how their licensed spectrum is used. In particular, we present extensive cross-correlation analysis describing the complex interdependencies in spectrum use between the various bands together with their spatial correlation structures. We characterize both correlations in the use of the downlink bands of different operators, as well as between uplink and downlink bands. Our results show that there are in many instances strong correlations in especially the use of the downlink bands, but these are not present in all regions and for all technologies. In particular, the results indicate that much more refined models of spectrum use need to be developed compared to the state-of-the-art in order to realistically evaluate the potential of spectrum sharing and data offloading techniques.

Two days of European spectrum: Preliminary analysis of concurrent spectrum use in seven European sites in GSM and ISM bands

We report initial results from 48 hour spectrum occupancy measurement campaign that was done in time-correlated fashion in seven different European locations. We give a description of the measurement campaign and provide results from our preliminary analysis of overall duty cycle in the frequency range 110-3000 MHz. The paper particularly focuses on traffic and duty cycle patterns in GSM 900 and GSM 1800 bands. For the sake of completeness, we also discuss ISMband utilization in two of our measurement sites. We show that spectrum utilization is generally low, but that variance between frequency bands and locations is significant, which means that any statistical claims on occupancy statistics need to be done carefully before regulatory claims are made.

A measurement-based study on the use of spatial interpolation for propagation estimation

In this paper, we provide a first comprehensive comparison on the performance of two spatial estimation approaches used for propagation estimation. The first estimates the shadowing distribution with considerably low number of measurements and the second estimates the received power with no information of the transmitter location. We discuss in details the relative advantages of these techniques and study particularly their performance when using different number of measurement points. Our study is based on data from a very carefully conducted large-scale measurement campaign with a high spatial density. The robustness of our results is verified in different propagation environments and different frequencies. In particular, we show that for very small number of samples, prediction based on shadowing results in better performance. However, with small increase in the number of available measurements, this more complex approach becomes unnecessary and direct prediction of the received power yields very good results.

A Study on the Forest Radio Propagation Characteristics in European Mixed Forest Environment

We study the near ground propagation characteristics in a typical forest environment in the European region. The forest environment is important in the context of military communications, emergency networks and environmental monitoring systems. Our measurement setup focused in lower frequency bands, and in this paper we report our results for the 485 MHz measurement campaign. The lower frequencies offer better propagation characteristics, and the future digital dividends or TV white space rulings open an opportunity to use these frequencies in the forest environment. We propose an attenuation model and compare also our measurements against already suggested propagation models in the literature, which are typically used for this type of environments. We have also studied the shadowing characteristics of the propagation environment and report the preliminary results. The paper shows that the forest type has a significant effect to the propagation and thus European mixed-type of forests requires its own model.

Studying and mitigating the impact of GPS localization error on radio environment map construction

Localization errors can play an important role in measurements of radio propagation or spectrum utilization, especially in urban environment where GPS localization accuracy is highly varying. In this paper we present a low cost and simple method for mitigating the impact of localization errors, based on multiple GPS receivers. The presented results are based primarily on performance evaluation of multiple GPS receivers based method under realistic conditions. We show how to reduce the time needed to estimate the statistics of the spatial radio environment by combining the input of multiple GPS sensors. We also present a simple scenario for small cell size networks based on real measurements in three distinct environments, where the localization errors are the determining factor of the performance of such systems.

On the Study of Shadow Correlations of Two Radio Frequencies in an Urban Environment

We present the results of an extensive, high spatial density measurement campaign made for investigating the shadowing correlations on two different frequency bands, namely 485MHz and 2600MHz in an urban propagation environment. In particular, we report results using different analysis procedures and tools. Our results show that the signal detector has only a small impact on the extracted data, given that the fast fading is correctly averaged out. Moreover, we extract the main parameters of shadow correlations. Finally, we report a preliminary comparison between a suburban and an urban propagation environments by comparing the parameters of the fitted variograms.

Impact of the path loss model on the spatial structure of shadow fading

In this paper we describe the effects of the radio propagation model on the spatial characteristics of the radio environment. For this study we have conducted a dedicated propagation measurement campaign focusing on the three different frequency bands of 485 MHz, 1700 MHz and 2600 MHz in order to capture the impact of the used frequency on the radio propagation. The presented results are coming from a high number of samples of very high spatial resolution. We quantify how much the propagation modelling affects the calculation of spatial statistics of radio propagation and in particular shadow fading for the three different frequency bands. Our results show that while the used propagation model does play a role in both the marginal distribution and the spatial correlation characteristics derived, the impact of the precise propagation model chosen is small. This indicates that correlation structure of shadow fading can be accurately derived also using predefined propagation models not directly fitted to the data and radio environment at hand.