Blind localisation of radio emitters using directional antennas
Creators: name: LI, Zhuyin
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 400607
subject: Signal processing
classificationCode: 400699
subject: Communications engineering not elsewhere classified

description: The proliferation of wireless communication has changed our lives in the past decades. The wireless devices have served more purposes in our society, such as daily communication, navigation, emergency rescue, national defence, to name a few. The strong reliance on wireless technologies has sped up the growth in the number of wireless devices and wireless services development. However, on the other hand, wireless communication has become a demanding technology with critical technical requirements such as bandwidth, data rate, network stability, and coverage.

Among all the wireless technologies, localisation, one of the fundamental enablers of wireless services and applications, also faces significant challenges. Global navigation satellite system estimates the user's position accurately in an outdoor environment under a clear sky. Still the results are not always satisfying in an indoor environment or with thick clouds. The positioning services embedded with the cellular networks have evolved together with the cellular technologies from the second-generation to the fifth-generation. However, there is a long way to go since the fifth-generation networks are designed to have new features such as higher frequency bands, ultra-dense networks, and ultra-low latency. Moreover, there are countless applications needed in the environment that no infrastructure networks are available, for example, the battlefield services and the first response after disasters.

In this thesis, we aim to propose novel localisation techniques using received signal strength and coarse direction of arrival measured by a set of sensing nodes equipped with directional antennas, yet requiring limited knowledge on the radio sources. We define the problem as "blind localisation" where the targets do not cooperate to perform the position estimation. Moreover, the utilisation of directional antennas benefits the transmission between the target and the sensing nodes in a certain direction. Thus, the localisation performance can be improved by the directionality information and better received signal strength brought by directional antennas. We present the problem formation, outline the system models, propose the localisation algorithms, and evaluate the algorithm performance. The proposed localisation algorithms can be perfectly applied to cognitive radio networks where the position of the primary user is crucial for dynamic spectrum sharing, but the primary users are not cooperative with the secondary users. However, the proposed algorithms are not limited to only cognitive radio scenarios. It is feasible for various technologies requiring position estimation on the non-collaborative radio emitters. 

We devote the first part of this thesis to a single primary user localisation problem. We estimate the primary user position by building a score map based on the measured data and compare the localisation error with conventional blind localisation approaches, centroid and weighted centroid localisation in terms of root mean square error. We further analyse the impact of the channel models on the algorithm and compare the root mean square error under an omnidirectional channel model and our proposed directional antenna channel model.

The second and third parts of this research are focused on an UAV-assisted multiple primary user localisation problem. We propose two novel localisation algorithms to address the problem. One is hierarchical clustering-based, and the other one is Gaussian mixture model-based. The two algorithms are further compared with a genie-aided single localisation algorithm.

In the fourth part of this thesis, we modelled the directional antenna channel since we adopt directional antennas for the localisation algorithm. It is evident that the multipath components arrive at the receiver in clusters, and the distribution of received signal strength and direction of arrival in clusters affects the localisation performance. We simulate a typical urban scenario using ray-tracing simulations, characterise the features of the channel model, and finally, verify the directional antenna channel model by ray-tracing and Monte-Carlo simulations.