ACO-Based Multi-User Detection in Cooperative CDMA Networks

In this paper, the cooperative diversity is investigated in the uplink of a Code Division Multiple Access (CDMA) network in which users cooperate by relaying each other’s messages toward the Base Station (BS). It is assumed that the spreading waveforms are not orthogonal and hence, Multiple Access Interference (MAI) exists at the relay nodes as well as the BS. MAI degrades the signal quality at both relays and BS and decreases the cooperative diversity gain. To alleviate this problem, an Ant Colony Optimization (ACO) based Multi-User Detector (MUD) has been proposed to efficiently combine the received signals from the direct and relay paths and sub-optimally extract transmitted bits at the BS. The computational complexity of proposed algorithm is significantly lower than that of the Maximum Likelihood (ML) detector. More explicitly, for a cooperative network supporting 15 users, the computational complexity of the proposed ACO algorithm is a factor of 103 lower than that of the optimum Bayesian detector. Simulation results show that the performance of the proposed ACO-based detector can closely approach the maximum diversity in terms of BER and efficiently cancel the MAI at the BS

LiS: Lightweight Signature Schemes for continuous message authentication in cyber-physical systems

Agency for Science, Technology and Research (A*STAR) RIE 202

GNSS Signal Authenticity Verification in the Presence of Structural Interference

GNSS dependant timing and positioning systems have become widespread in various civilian applications such as communication networks, smart power distribution grids and vehicular and airplane navigation systems. However, GNSS signals are quite vulnerable to different types of interference since they are very weak once received on the earth surface. Among various intentional interference signals, structural interferences (e.g. spoofing and meaconing) are much more dangerous since they are designed to mislead their target receiver(s) that are not aware of the attack and this can lead to disastrous consequences in scores of applications. Spoofing and meaconing signals’ features are very similar to those of authentic GNSS signals; therefore, it is very difficult for a GNSS receiver to discriminate their presence. This dissertation analyses the effects of spoofing signals on different processing levels of civilian GPS L1 C/A receivers and accordingly proposes some possible countermeasure techniques. It is shown that the presence of spoofing interference increases the power content of structural signals within the GNSS frequency bands and this feature can reveal the presence of spoofing interference before the despreading process of the receiver. Spoofing and meaconing interference can affect the acquisition process of a GNSS receiver. It is shown that monitoring the absolute received power of received GNSS signals is highly effective to reduce receiver vulnerability to spoofing attack during the acquisition process. Spoofing signals can also compromise the tracking process of GNSS receivers by generating synchronized higher power PRN signals. The effects of different spoofing attacks on a tracking receiver are analysed and two possible countermeasure techniques have been proposed to detect the interaction between spoofing and authentic signals. Furthermore, the effect of spoofing signals has been analysed on the position level observables of a GNSS receiver and it is shown that these observations can practically reveal the presence of a spoofed position/timing solution for a moving receiver. The performances of the proposed authenticity verification techniques are validated using several real data collection and processing scenarios. Finally, a possible structure for a spoofing aware GPS receiver is proposed that checks the authenticity of received GNSS signals at different processing layers without imposing extensive hardware or software modifications to conventional GNSS receivers