SP: Development of an Interference Temperature Monitor

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

Intellectual Merit: Radio Frequency Interference (RFI) monitoring is an important tool in the assignment of frequency bands and in the reduction of harmful interference between users. In the past, a major source of man-made interference was from automobile ignition. Now a major source of man-made interference is from electronic devices, digital answering machines, computers etc. Communication devices like cellular phones, and wireless computer networks are relative new comers and are making efficient use of the spectrum using Code Division Multiple Access (CDMA) with power control to maximize capacity with the minimum transmitter power. These devices generate a spread spectrum which cannot be easily distinguished from Gaussian noise without knowledge of the code to de-spread the signal. Another source of noise-like signals comes from the new digital television transmitters. In order to avoid harmful interference and minimize the elevation of the noise level in the environment, it is important to monitor the level of this noise. The natural environmental noise for frequencies between 500 MHz and 20 GHz consists mainly of about 300 K from the ground, 3K from the cosmic background, and about 5 to 30 K from the atmosphere. In the radio astronomy bands and other itreceive onlyle bands, it is important to prevent any increase in the noise temperature while measurement of the noise temperature in other bands can be useful information needed to optimize the efficient use of the spectrum for various applications including radio astronomy and wireless communications. MIT Haystack Observatory proposes to develop a monitor to measure the interference levels in the frequency range 30 to 1500 MHz, calibrated to provide the output metric in units of degrees Kelvin, and with sufficient sensitivity to be able to quantify, to a level of a few degrees Kelvin, the unwanted noise in the protected receive-only bands like those for radio astronomy, remote sensing, and deep space bands. This supports the joint initiative between the NSF and the FCC. In phase 1, the proposers plan to study receiver and calibration designs needed to provide the sensitivity and accuracy without significant internal inter-modulation, spurious responses and spurious signals. In this phase they will also set specifications for the design based upon preliminary measurements, using currently available equipment, of the RFI environment at the MIT Haystack Observatory, in Westford, MA. In phase 2 we propose to prototype the interference temperature monitor and test the design at Haystack. In phase 3 we propose to conduct tests of the system at a few locations in the Massachusetts and Southern New Hampshire area. In the future, depending on the results, such a monitoring system could be replicated elsewhere to gather a data set to characterize the RFI environment at other locations. Broader Impact: Through this project, the proposers aim to enhance the awareness of the properties of radio wave technology and its various applications such as radio astronomy and wireless communications, as well as the radio frequency interference environment. Thus, a simple RFI monitoring system will be developed for use in pre-college educational settings to acquaint students and teachers with the measurement techniques of radio wave signals and the environment around their schools and towns. Such data could be inter-compared using the Internet, and Haystack Observatory will develop web-based educational materials to introduce the study of radio waves and their various applications. In particular, the proposers will arrange for the deployment of simple radio receivers and antennas, available commercially, to local area schools around the Observatory to engage students in RFI measurements. A collaboration with students and teachers in Australia, as part of the Australian SEARFE project will be promoted to enhance international networking on this topic. A project with local area teachers as part of NSF's program 'Research Experiences for Teachers (RET)' at Haystack Observatory is starting in summer 2003 to initiate this activity.