Man-made noise measurement in Sweden: Results, lessons learned and concept for future measurement

摘要

Man-made noise is often a factor that limits the range and data rate for communication in the HF, VHF and the lower UHF bands. Man-made noise is also a limiting factor for what can be achieved by a Signal Intelligence (SI) system or an eavesdropper. The ITU-R P.372, frequently used in link budget calculations, is based on extensive measurements carried out in the 70s. Most of the work was focused on the noise level, and not so much about noise characteristics. However, the noise characteristics are important, particularly for digital systems. In the late 90s to the first years after 2000, FOI performed a measurement campaign in different environment categories. The measurements included, noise levels, diurnal variations, spatial variations and noise characteristics. With a SI system or an eavesdropper in mind, the measurement system was design for low noise levels. In this paper, we will present experience from system design and lessons learned based on earlier measurement campaign of the noise environment. The results show no dramatic changes in noise levels compared to the ITU recommendations for corresponding environments. Measurements in Europe 2006/2007 show similar results in terms of noise levels. In rural environment, the diurnal variation was low, in contrast to the results for the residential environment, which show a clear difference between the day and night levels. Noise variations in space, especially in environment dominated by a few buildings, where evident. Also the deviation in noise characteristic was frequent compared to the commonly assumed Gaussian characteristics. This was palpable for frequencies below 100 MHz. A measuring system with high sensitivity and with directional antennas leads to a physically large system. This is a major limitation when choosing measurement sites. The system was far too unwieldy to be able to be smoothly use in many urban sites. In such environments, the noise levels are usually high and the high sensitivity is not necessary. The sensitivity of the measuring system can therefore be sacrificed for the benefit of flexibility. A source of problems was all the relays needed to switch between the antennas. The reliability of the system would probably have been increased by using a simpler antenna. After that we conducted our measurements, the use of electronic equipment, both in civilian and military applications, has increased significantly. Computer networks, which are potential sources of interference, are commonly used in most environments. Meanwhile, military units are expected to operate in dense urban and indoors environment without disruption or degradation of the communication and sensor systems. Therefore, there is a great need to obtain an over-all picture of the noise environment. In this paper, we present new design ideas of a noise measurement system. The technological development has opened up for the using many small and inexpensive measuring systems with high signal processing capability instead of a few expensive systems. This development paves the way for new opportunities when the noise environment will be investigated.