Characterisation and Modeling of RF environment

University essay from Uppsala universitet/Signaler och system

Abstract: Devices that transmit and receive electromagnetic signals are today central to the way people communicate and acquire information from the surroundings. WiDAR, Wideband Digital Array Receiver, is the name of a new system of digital antenna array receivers, which has recently been developed at Saab in Järfälla and is the focus of this thesis. Digital antenna arrays have the benefit over conventional antennas of having their lobes steered electrically, allowing for beamforming, both in reception and transmission. The goal of the thesis has been to characterise certain signal technologies operating in the spectrum of WiDAR, and during the process learn about the limitations of digital antenna array receivers and the system. After studying the system and telecommunication technologies present in the wideband, several measurements were conducted using WiDAR in the field to gather raw data for processing in Matlab. With WiDAR having numerous channels, as well as high sampling rate, large amounts of data was received, leading to difficulties in the processing thereafter. Concluding that three types of signal technologies are certain to be found in WiDAR's spectrum, UMTS/3G, LTE/4G, and DVB-T, their respective narrowbands were studied further through the production of spectrograms of the signal data. Within each band, probability distributions were fit to the histograms of the data. Each of the signal technologies were then characterised by their respective fit to the probability distributions. This resulted in a way of identifying unknown signals from new measurement data from WiDAR. While this method could prove useful as a first step in characterisation, weaknesses such as its lack of depth in the narrowbands are discussed. For further work and the future of the system, it is suggested to e.g. explore the concepts of the multipath problem, or TDM/TDMA in the data. Ultimately, the characterisation of the found signal technologies was moderately successful, however with a sizeable list of limitations and area of improvements.

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