Most existing industrial control systems (ICSs), such as building energy management systems (EMSs), were installed when potential security threats were only physical. With advances in connectivity, ICSs are now, typically, connected to communications networks and, as a result, can be accessed remotely. This extends the attack surface to include the potential for sophisticated cyber attacks, which can adversely impact ICS operation, resulting in service interruption, equipment damage, safety concerns, and associated financial implications. In this work, a novel cyber-physical security framework for ICSs is proposed, which incorporates an analytics tool for attack detection and executes a reliable estimation-based attack-resilient control policy, whenever an attack is detected. The proposed framework is adaptable to already implemented ICS and the stability and optimal performance of the controlled system under attack has been proved. The performance of the proposed framework is evaluated using a reduced order model of a real EMS site and simulated attacks.

Acquisition of code division multiple access (CDMA) signals can be carried out using fixed or variable dwell times. The choice of acquisition strategy is a trade-off between performance and computational complexity, and a number of variable parameters (number of dwells, dwell lengths and thresholds) must be carefully designed. In this work, the performance of a variable dwell time coincidence detector is analysed in terms of its mean time to verify the acquisition of Global Positioning System (GPS) L1 C/A signals. A new expression for the variance of the coincidence detector dwell time is derived. A general framework for the optimisation of dwell parameters for the coincidence detector is outlined. Both immediate- and non-immediate reject cases are analysed and compared to the fixed dwell time single dwell strategy, which is, itself, a special case of the coincidence detector. Case-specific numerical optimisation results are illustrated across a range of signal-to-noise ratios and general rules-of-thumb for the best choice of parameters are highlighted.

Acquisition of signals in noise, in particular CDMA signals like the Global Positioning System (GPS) L1 C/A signal, can be carried out using fixed or variable dwell times. In this work, a sequential multiple dwell procedure for verifying acquisition is examined and compared to a fixed time single dwell strategy. The procedure under analysis is the sequential probability ratio test (SPRT) which has not been widely used for GPS applications, possibly due to its sensitivity to attenuation of the received signal relative to the design point. In this paper, it is shown that for the received signal to noise ratios (SNR) typically encountered in GPS, the SPRT can outperform the single dwell detector strategy in terms of mean acquisition time. In addition, it is shown that the single dwell (SD) detector's fixed dwell time approaches the worst case dwell time for the SPRT, as design point carrier to noise ratio decreases. Thus, for very weak signals, the SPRT can be a better choice of verification algorithm than the SD strategy, under certain constraints.