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Agilent Techniques and Trends in Signal Monitoring, Frequency Management and Geolocation of Wireless Emitters Application Note Monitoring RF signals in a wireless evolved into cooperative networks environment is often required by of low-cost sensors that collectively a variety of wireless equipment monitor the wireless spectrum over a operators, facility and test managers large geographic area. This applica- and government agencies. Signal tion note reviews various issues, monitoring applications can range techniques and associated equipment from compliance of carrier-specific required for signal monitoring and fre- transmissions to the discovery quency management of RF spectrum and location of unknown or illegal in the VHF/UHF frequency range. The transmitters. Traditional methods for goals and automation requirements signal monitoring rely on high perfor- for various monitoring applications mance spectrum analyzers and digi- will be discussed and the concepts tizers often operating as a standalone of implementing a distributed sensor system. With the current widespread network for determining the geoloca- availability of broadband connectiv- tion of a wireless "emitter" will be ity, signal monitoring systems have introduced. Introduction Monitoring the frequency spectrum in a wireless environment for known and unknown RF signals is required by a variety of equipment operators and govern- ment agencies. Applications can range from carrier-specific measurements to wide bandwidth spectrum searching and data logging. In all cases, the spectrum or signal monitoring equipment requires several basic characteristics such as a broad range of frequency coverage, high-speed channel scanning, high frequency resolution and dynamic range, data storage and some level of system automation for determining a course of action when a signal of interest is detected. In some applications, spectrum monitoring is required to ensure compliance with local regulatory requirements while other applications require discovery of unknown transmitters or "emitters". The discovery process may involve uncovering the type of signal including duration of transmission, number of occurrences, carrier frequency, bandwidth, and modulation type and emitter geolocation. Figure 1 shows a typical monitoring system that may contain fixed, stationary and mobile receivers placed throughout a geographic area. Several receivers may be networked together to improve the performance and localiza- tion accuracy of the overall system. Figure 1. Signal monitoring and surveillance system 2 Frequency Management