Reijo Ekman

Spectrum Occupancy Measurements: A Survey and Use of Interference Maps

In order to provide meaningful data about spectrum use, occupancy measurements describing the utilization rate of a specific frequency band should be conducted over a specific area instead of a single location. This paper presents a comprehensive methodology for the measurement and analysis of spectrum occupancy. This paper surveys spectrum measurement campaigns and associated interference maps, introducing the latter as a tool for spectrum analysis and management based on measurement data. An interference map characterizes the spectrum use by defining the level of interference over an area of interest in a certain frequency band. Building on findings from practical measurement studies, guidelines for spectrum occupancy measurements are given. While many scientific spectrum occupancy measurement papers tend to be too optimistic about the significance and generality of the results, we propose a cautionary perspective on drawing strong conclusions based on the often limited amount of data gathered. The different phases of the spectrum occupancy measurement and analysis process are described and a thorough discussion of interpolation methods is provided. Means to improve the measurement accuracy are discussed, especially regarding spatial domain considerations and the impact of the sampling interval on the results. A practical example of an improved measurement system design covering all the phases of the measurement process and used at the Turku, Finland; Blacksburg, VA, USA; and Chicago, IL, USA, spectrum observatories is given. Using the improved design, more realistic spectrum occupancy data can be obtained to lay the foundation for spectrum management decisions.

A series of trials in the UK as part of the Ofcom TV white spaces pilot

TV White Spaces technology is a means of allowing wireless devices to opportunistically use locally-available TV channels (TV White Spaces), enabled by a geolocation database. The geolocation database informs the device of which channels can be used at a given location, and in the UK/EU case, which transmission powers (EIRPs) can be used on each channel based on the technical characteristics of the device, given an assumed interference limit and protection margin at the edge of the primary service coverage area(s). The UK regulator, Ofcom, has initiated a large-scale Pilot of TV White Spaces technology and devices. The ICT-ACROPOLIS Network of Excellence, teaming up with the ICT-SOLDER project and others, is running an extensive series of trials under this effort. The purpose of these trials is to test a number of aspects of white space technology, including the white space device and geolocation database interactions, the validity of the channel availability/powers calculations by the database and associated interference effects on primary services., and the performances of the white spaces devices, among others. An additional key purpose is to undertake a number of research investigations such as into aggregation of TV White Space resources with conventional (licensed/unlicensed) resources, secondary coexistence issues and means to mitigate such issues, and primary coexistence issues under challenging deployment geometries, among others. This paper describes our trials, their intentions and characteristics, objectives, and some early observations.

Experimental Investigations on MIMO Radio Channel Characteristics on UHF Band

Pan-European project B21C (Broadcasting for the 21st Century) aims to develop technology for DVB-T2 (Digital Video Broadcasting, Terrestrial), which is a spectrum efficient broadcasting system for future. The evaluated technologies include MIMO, which has been widely studied in perspective of B3G (Beyond 3rd Generation) systems, but never for any UHF band systems. In addition, the latest decision of WRC (World Radiocommunication Conference) highlights that the B3G systems can be deployed in UHF bands. This paper introduces a measurement campaign performed in UHF frequency and presents the most important results with regard to channel modeling and MIMO.

Some Initial Results and Observations from a Series of Trials within the Ofcom TV White Spaces Pilot

TV White Spaces (TVWS) technology allows wireless devices to opportunistically use locally-available TV channels enabled by a geolocation database. The UK regulator Ofcom has initiated a pilot of TVWS technology in the UK. This paper concerns a large- scale series of trials under that pilot. The purposes are to test aspects of white space technology, including the white space device and geolocation database interactions, the validity of the channel availability/powers calculations by the database and associated interference effects on primary services, and the performances of the white space devices, among others. An additional key purpose is to perform research investigations such as on aggregation of TVWS resources with conventional resources and also aggregation solely within TVWS, secondary coexistence issues and means to mitigate such issues, and primary coexistence issues under challenging deployment geometries, among others. This paper provides an update on the trials, giving an overview of their objectives and characteristics, some aspects that have been covered, and some early results and observations.

Field measurements of WSD-DTT protection ratios over outdoor and indoor reference geometries

A currently prevalent view of the operation of white space cognitive radios is that they should use geolocation databases to determine their frequency band and maximum transmission power in any given location so that interference radiated to broadcast receivers is negligible. To estimate the level of such interference, physical reference geometries and path loss estimates have been proposed between co-located devices. In this paper we present results of a measurement campaign conducted over indoor and outdoor reference geometry scenarios in a digital terrestrial television test network. Applying a subjective error criterion, we provide practical estimates on the maximum relative transmit powers for white space devices in order to avoid visible interference in television reception. The study applies to various primary and secondary transmission and reception scenarios, and its results can be extended also to estimate protection ratios for signal configurations not considered in the reported measurements.

Electromagnetic irradiation exposure and its bioindication – An overview

Man made electromagnetic irradiation and fields cover now the globe due to the recent extensive propagation of mobile telephony. The increased load affects animals and also plants. Especially birds have been studied. Humans are also sensitive. They are good bioindicators as epidemiological methods are available. Humans can also report symptoms which cannot be directly measured with presently available technologies. The nonionizing irradiation can as the ionizing one break the DNA, damage proteins, even increase the blood brain barrier permeability, disturb the night rest, cause fatigue and hormonal disturbances. An increase of the tumours of human head has been described in correlation with the long-term mobile phone use and on that side more exposed. The regulations covering mobile telephony are already about two decades old and need re-evaluation. The multitude of irradiation and the interaction of the different wavelength exposures, i.e., frequency sensitivity is poorly known at present. We should not forget the comparative studies of different species especially those which rely in their lives on electromagnetic orientation physiology. Some countries have issued warnings on the exposures of children. The producers of mobile technology have recently warned the users not to keep those devices in active stage in skin contact.

Distributed Spectrum Sensing Using Low Cost Hardware

A distributed spectrum sensing network is prototyped using off the shelf hardware consisting of Raspberry Pi mini-computers and DVB-T receivers with software defined radio capabilities. Using the prototype network, coordinated, distributed wideband spectrum sensing is performed in a geographical area. The spectrum sensing data from the nodes is collected in a database. Well established low-complexity algorithms for distributed spectrum sensing are applied, and the results are compared against a professional spectrum sensing system. We show that with this simple low-cost setup, the decisions made on the availability of spectrum using the distributed sensing data correspond well with the decisions made on the reference data.

Field trial of the 3.5 GHz citizens broadband radio service governed by a spectrum access system (SAS)

In this paper, we describe a spectrum access system (SAS) based Citizens Broadband Radio Service (CBRS) field trial using a live LTE network in the 3.5 GHz band. The latest WInnForum specification guided the implementation of the relevant protocols for SAS operation. Here, we evaluate the performance of a CBRS field trial by using one of the most important performance indicators in a spectrum sharing scenario — the evacuation time. It indicates how rapidly the secondary user relinquishes the shared spectrum band to the primary user. Following the applied protocols, we measure and analyze the time scales for the evacuation and frequency change procedures in a field trial environment. Our work shows that the set time limits for the protection of primary users against interference are realistic when using commercially available mobile networks and equipment. Finally, utilizing knowledge of the latest base station models, we propose ways to reduce the evacuation and reconfiguration time by up to 70%.

Coexistence of DTT and Mobile Broadband: A Survey and Guidelines for Field Measurements

This article provides a survey and a general methodology for coexistence studies between digital terrestrial television (DTT) and mobile broadband (MBB) systems in the ultra high frequency (UHF) broadcasting band. The methodology includes characterization of relevant field measurement scenarios and gives a step-by-step guideline on how to obtain reliable field measurement results to be used in conjunction with link budget analyses, laboratory measurements, and simulations. A survey of potential European coexistence scenarios and regulatory status is given to determine feasible future use scenarios for the UHF television (TV) broadcasting band. The DTT reception system behavior and performance are also described as they greatly affect the amount of spectrum potentially available for MBB use and determine the relevant coexistence field measurement scenarios. Simulation methods used in determining broadcast protection criteria and in coexistence studies are briefly described to demonstrate how the information obtained from field measurements can be used to improve their accuracy. The presented field measurement guidelines can be applied to any DTT-MBB coexistence scenarios and to a wide range of spectrum sharing and cognitive radio system coexistence measurements.

Detecting the impact of human mega-events on spectrum usage

Dynamic spectrum access (DSA) has emerged as an enabling technology to allow more intensive sharing of the radio spectrum. A requirement for most proposed DSA techniques is prior knowledge of the primary users access pattern or the ability to predict primary user activities. Therefore, spectrum surveys are taking place on an even wider scale to provide data on spectrum usage and occupancy for developing new prediction models and for spectrum planning by regulators. This paper investigates the potential of mining spectrum data for correlation between human activities in a neighborhood and the resulting spectrum occupancy across different bands. We propose a systematic approach based on two clustering techniques: Gaussian mixture models (GMMs) and self-organizing map neural networks (SOMNNs). We mine spectrum measurements gathered by our network of spectrum observatories in Virginia and Illinois. The results confirm the existence of observable correlation and show that our proposed techniques detect correlation across various land mobile radio (LMR) and cellular bands under a wide range of scenarios with a high detection ratio. These results inspire us to develop more efficient prediction models for applications in opportunistic spectrum access (OSA) or self-organized networks.