Versatile Sensor Node (VSN)

The spectrum sensing system was implemented on a Versatile Sensor Node (VSN), which is a WSN platform with high processing capability, long-term autonomy and flexible radio. It supports a broad portfolio of sensors and actuators, while its modular approach allows adaptation to diverse application requirements. In this respect the platform consists of the core module – VSC and a set of special feature modules (radio module – VSR, expansion modules – VSE, power module – VSP) that are used as/if needed. The core module can be powered by batteries, solar panel or external power supply and together with radio module supports wireless sensor networks technologies such as ZigBee, 6LoWPAN and Wireless M-Bus. The core module is based on a high performance ARM Cortex-M3 microcontroller from ST, which offers a very good trade-off between processing power and energy consumption. It supports clock frequencies up to 72 MHz, has 512 kB of program memory and 64 kB of data memory. For storing large sets of data it also incorporates a mini SD card interface supporting the SD specification 2.0, which means that up to 32 GB of memory can be addressed. For attaching peripheral devices it offers analog-to-digital converter, a large number of general purpose input-output (GPIO) pins and interfaces like SPI, I2C and UART. For the purposes of CREW project dedicated VSE modules were developed, offering low-cost RSSI-based spectrum sensing in the ISM and TV frequency bands. The modules have integrated omnidirectional antennas, but will also allow the connection of additional antenna with desired gain and beam pattern. Different chips designed either for ISM band technologies (e.g. ZigBee, Bluetooth, Wi-Fi) or for the reception of digital TV signals will be evaluated. For sub-GHz ISM frequency bands these are CC1101 and AT86RF212, for 2.4 GHz ISM frequency band these are CC2500, CC2540 and MRF24WB0MB, while for VHF and UHF TV frequency bands these are ADMTV803 and TDA18218HN.

The existing outdoor wireless sensor network testbed based on VSN

Recently, JSI together with an industrial partner (Envigence Ltd.) and a public partner (Municipality of Miren-Kostanjevica) deployed an outdoor VSN (see above for the description of VSN) based testbed for environmental sensing and light control (see Figure 1). The first phase of deployment consisted of 5 VSN nodes, adding further 20 VSN nodes in the second phase. This deployment offered the opportunity to test the VSN hardware in outdoor operating conditions under temperatures around and below zero and at high precipitation levels (both snow and rain). The trials confirmed the robustness of VSN, therefore an extension of the testbed in size and functionality is agreed for Spring 2011. As part of the CREW project, the ISM spectrum sensing VSN nodes, so far tested in laboratory environment at JSI and in JSI campus, will be complemented with TV spectrum sensing capability and moved outdoor in the existing Miren testbed.

Universal Software Radio Peripheral (USRP)

The Universal Software Radio Peripheral (USRP) is a computer-hosted hardware platform enabling rapid design and implementation of flexible software define radio. It serves as a digital, high-bandwidth baseband and intermediate frequency section and extended with the radio frequency front-end daughterboards forms the physical layer of a wireless communication system. It has been designed to perform all the waveform-specific processing on the host CPU, while high-speed operations are done on the FPGA. The host computer can be connected through a high-speed USB or Gigabit Ethernet, while the front-end daughterboards with radio frequencies ranging from DC to 6 GHz are interfaced on high-speed and high precision analog-to-digital/digital-to-analog converters and allow simultaneous receive/transmit RF bandwidth of 50 MHz, thus covering a range of applications.

GRASS RaPlaT

GRASS-RaPlaT is an open-source radio planning tool developed at Jozef Stefan Institute, Department of Communication Systems. GRASS-PlaT is an add-on to the open source Geographical Information Systems (GIS) GRASS , which is one of the projects of the OSGeo foundation. It is one of the most important and widely used open source GIS tools. It is published under the GPL license and its usage is supported under various operating systems including Microsoft Windows, Linux and Mac OS X. GRASS operates over raster and vector data and includes methods for image processing and display. It comprises over 350 modules for processing, analysis and visualization of geographical data. The core modules and libraries are written in the C programming language, and a well documented API with a few hundred C functions is available to develop new modules. For large projects, processing may be automated by using a scripting language such as Phyton. MySQL, PostgreSQL and DBF database engines are currently supported by GRASS and can be used for storing the data table. In addition, other GIS software packages include modules to import GRASS maps. Recently, an open-source radio coverage simulation tool based on GRASS with user extendible set of radio propagation models has been developed, which is especially suitable for research work but at the same time also for professional communication network planning. The tool, "GRASS-RaPlaT," currently includes modules for a number of channel models, a module for sectorization according to given antenna patterns, a module for calculating and storing the complete radio network coverage data, and a number of supporting modules, e.g. for adapting input data and analyzing simulation results. It is especially designed for radio coverage calculation of GSM/UMTS systems, but can be applied also to other wireless systems in the frequency range 400 MHz - 2.4 GHz (e.g. TETRA, Wi-Fi). Its structure is modular and characterized by high level of flexibility and adaptability. Its accuracy has been tested with field measurements of GSM, UMTS and TETRA networks, as well the accuracy of results evaluated by comparing with those from a professional radio network planning tool. Within a project the GRASS-RaPlaT will mainly applied data analysis and visualization. In addition new modules will be designed and implemented for inverse channel modelling for determination of the interference region of the collaboratively detected hidden nodes.

Contribution to CREW

Within CREW, the VSN testbed environment will be integrated as a complementary testbed into the CREW open federated platform and benchmarking framework. The VSN testbed will be expanded with new/additional functionalities in accordance with the demands received from internal partners and/or external experimenters, and will be used for the implementation of internal and external usage scenarios. As depicted in Figure 2, the VSN testbed will consist of:

• Outdoor real-life testbed in a mixed rural/built-up environment for basic and advanced spectrum sensing in ISM and TV frequency bands.
• JSI campus indoor/outdoor installment composed of VSN modules operating in the ISM bands for testing semi-automated and automated protocol stack composition, and for pre-testing new HW/SW solutions before deployment in real-life testbed.

Basic spectrum sensing will be carried out by two sets of VSN-based spectrum sensors with omni-directional antennas, one operating in ISM frequency bands (VSN-ISM) and the other in TVWS frequency bands (VSN-TVWS). Sensors will support dynamic grouping in subsets with different number of sensing nodes per set, thus allowing for investigation of the trade-off between densely deployed low-cost spectrum sensing equipment providing basic capabilities and sparsely deployed advanced sensing equipment with high processing power. The latter will thus form the third subset of spectrum sensing nodes, based on USRP software radios (USRP-sense) deployed at selected fixed locations and will serve also as a reference of VSN-based testbed. Spectrum sensing measurements from all three types of sensing agents will be fed into the spectrum occupancy tables, which will be enhanced also by a GIS database and open-source GRASS-RaPlaT tools. The latter will be used for visualization of spectrum sensing measurements and for estimation of interference regions of identified hidden nodes by applying to the measurements antenna patterns and using inverse propagation channel modelling. A separate table will also host open data sets of raw spectral measurements obtained from the VSN testbed and will be used for post processing of measurement results and the development of sensing algorithms to be executed locally on individual sensing agent or on the modules supporting the operation of geo-location spectrum resource database. For the execution of various test cases VSN testbed will also provide USRP software radios integrated with VSN modules (USRP-VSN) to serve as interferers (in ISM usage scenarios) or secondary users (in TVWS usage scenarios). VSN modules will have two functionalities. They will provide CPC of the USRP VSN to the spectrum occupancy tables and by hosting a GPS module they will also provide internal geo-location and precise reference timing capability. With the VSN modules having high processing capabilities with respect to other WSN platforms, they will also be used to execute the algorithms of collaborative spectrum sensing in the USRP-VSN setup.