When Does Relay Transmission Give a More Secure Connection in Wireless Ad Hoc Networks?

Relay transmission can enhance coverage and throughput, while it can be vulnerable to eavesdropping attacks due to the additional transmission of the source message at the relay. Thus, whether or not one should use relay transmission for secure communication is an interesting and important problem. In this paper, we consider the transmission of a confidential message from a source to a destination in a decentralized wireless network in the presence of randomly distributed eavesdroppers. The source-destination pair can be potentially assisted by randomly distributed relays. For an arbitrary relay, we derive exact expressions of secure connection probability for both colluding and non-colluding eavesdroppers. We further obtain lower bound expressions on the secure connection probability, which are accurate when the eavesdropper density is small. By utilizing these lower bound expressions, we propose a relay selection strategy to improve the secure connection probability. By analytically comparing the secure connection probability for direct transmission and relay transmission, we address the important problem of whether or not to relay and discuss the condition for relay transmission in terms of the relay density and source-destination distance. These analytical results are accurate in the small eavesdropper density regime.Comment: Accepted for publication in IEEE Transactions On Information Forensics and Securit

Thermal Performance and Moisture Accumulation of Mechanical Pipe Insulation Systems Operating at Below Ambient Temperature in Wet Conditions with Moisture Ingress

When pipes are used for chilled water, glycol brines, refrigerants, and other chilled fluids, energy must be spent to compensate for heat gains through the wall of the pipes. Higher fluid temperature at the point of use decreases the efficiency of the end-use heat exchangers and increases the parasitic energy consumption. Mechanical pipe insulation systems are often used to limit the heat gains and save energy in commercial buildings. Pipe insulation systems play an important role for the health of the occupied space. When a chilled pipe is uninsulated or inadequately insulated, condensation might occur and water will drip onto other building surfaces possibly causing mold growth. The critical issue with cold pipes is that the temperature difference between the pipe and its surrounding ambient air drives water vapor inside the insulation system and condensation commonly occurs when the water vapor comes in contact the chilled pipe surface. This paper experimentally studies this issue for pipe insulation systems operating at below ambient temperature. The moisture content and the associated thermal conductivity of several pipe insulation systems were measured under various wet condensing conditions with moisture ingress. Accelerated type tests in laboratory highlighted the propensity of moisture accumulation in the insulation systems with cylindrical configuration and with split longitudinal joints. The moisture accumulation rate was measured and the apparent thermal conductivity increased significantly in a 60 days period when water vapor entered a pipe insulation syste