Enhancing the Utility of Privacy-Preserving Techniques in Location-based Services (LBS) Applications

The Hong Kong University of Science and Technology
Department of Computer Science and Engineering


PhD Thesis Defence


Title: "Enhancing the Utility of Privacy-Preserving Techniques in 
Location-based Services (LBS) Applications"

By

Mr. Maocheng LI


Abstract:

The widespread use of GPS-enabled devices has led to the proliferation of 
spatial data (e.g., locations, trajectories), enabling applications like 
ride-hailing and contact tracing. However, sharing such data raises 
significant privacy concerns, as sensitive information — such as personal 
habits or health conditions — can be inferred from spatial patterns. While 
Differential Privacy (DP) provides rigorous theoretical guarantees for 
privacy preservation, its noise-injection mechanisms often degrade data 
utility, limiting the accuracy of location-based services (LBS). Thus, there 
is an urgent need for privacy-preserving techniques that maintain data 
utility.

This thesis addresses this challenge by developing novel frameworks that 
integrate DP with security-based methods (e.g., Secure Multiparty Computation 
(SMC) and Homomorphic Encryption (HE)) across three critical applications: 
(1) spatial crowdsourcing, where we propose k-Switch, which achieves 37% 
improvement in task assignment success rates compared to the baseline; (2) 
contact tracing, where we introduce ContactGuard, which accelerates SMC 
operations using Geo-I-perturbed trajectories, maintaining 98% recall in 
identifying close contacts; and (3) spatial federation, where we develop 
FedGroup, which reduces the aggregate Laplace noise by 72% compared to other 
standard DP baselines.

We demonstrate that our frameworks achieve provable privacy guarantees 
(satisfying epsilon-differential privacy or its variants) while significantly 
improving the utility and efficiency over state-of-the-art methods, verified 
by extensive experiments. The thesis concludes with open challenges and 
future directions.


Date:                   Tuesday, 12 August 2025

Time:                   2:00pm - 4:00pm

Venue:                  Room 3494
                        Lifts 25/26

Chairman:               Prof. Wai Ho MOW (ECE)

Committee Members:      Prof. Lei CHEN (Supervisor)
                        Prof. Ke YI
                        Prof. Xiaofang ZHOU
                        Prof. Can YANG (MATH)
                        Prof. Jianliang XU (HKBU)