It is shown that the performance of high-resolution techniques usually implemented for DOA estimation are seriously impacted by any size-constraint applied on the DF, particularly in multi-path propagation conditions.Subsequently, a review of interactive parameter mapping sonification is proposed. Based on these tools, a case study is proposed regarding the performance that might be expected from a lightweight DF design tailored to portable operation. The thesis' ambition is to exploit the natural mechanisms of human hearing to improve the global performance of the search process rather than to develop new Direction-Of-Arrival (DOA) estimation techniques.Classical DOA estimation techniques are introduced along with a range of tools to assess their efficiency. The conception is focused on an audio interface, using sound to progressively guide rescuers towards their target. This research investigates the design of a radio Direction Finder (DF) for rescue operation using victims' cellphone as localization beacons. In a study we conducted over a two year period in several US metropolitan areas, we found that a significant fraction of the "encrypted" P25 tactical radio traffic sent by federal law enforcement surveillance operatives is actually sent in the clear, in spite of their users' belief that they are encrypted, and often reveals such sensitive data as the names of informants in criminal investigations. We also found that even the passive attacks represent a serious practical threat. We introduce new selective subframe jamming attacks against P25, in which an active attacker with very modest resources can prevent specific kinds of traffic (such as encrypted messages) from being received, while emitting only a small fraction of the aggregate power of the legitimate transmitter. We found a number of protocol, implementation, and user interface weaknesses that routinely leak information to a passive eavesdropper or that permit highly efficient and difficult to detect active attacks. This paper analyzes the security of P25 systems against both passive and active adversaries. The protocols include security options in which voice and data traffic can be cryptographically protected from eavesdropping. APCO Project 25 ("P25") is a suite of wireless communications protocols used in the US and elsewhere for public safety two-way (voice) radio systems.
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