Compressive Sensing Approaches for Sparse Distribution Estimation Under Local Privacy

TL;DR

This paper introduces compressive sensing techniques to efficiently estimate sparse or approximately sparse distributions under local differential privacy, reducing sample complexity compared to traditional methods especially in medium privacy regimes.

Contribution

It proposes novel privatization mechanisms based on compressive sensing that work for approximately sparse distributions and medium privacy, achieving optimal sample and communication complexity.

Findings

Reduces sample complexity for sparse distribution estimation under LDP.

Works effectively for approximately sparse distributions and medium privacy levels.

Achieves optimal sample and communication complexity.

Abstract

Recent years, local differential privacy (LDP) has been adopted by many web service providers like Google \cite{erlingsson2014rappor}, Apple \cite{apple2017privacy} and Microsoft \cite{bolin2017telemetry} to collect and analyse users' data privately. In this paper, we consider the problem of discrete distribution estimation under local differential privacy constraints. Distribution estimation is one of the most fundamental estimation problems, which is widely studied in both non-private and private settings. In the local model, private mechanisms with provably optimal sample complexity are known. However, they are optimal only in the worst-case sense; their sample complexity is proportional to the size of the entire universe, which could be huge in practice. In this paper, we consider sparse or approximately sparse (e.g.\ highly skewed) distribution, and show that the number of samples needed could be significantly reduced. This problem has been studied recently \cite{acharya2021estimating}, but they only consider strict sparse distributions and the high privacy regime. We propose new privatization mechanisms based on compressive sensing. Our methods work for approximately sparse distributions and medium privacy, and have optimal sample and communication complexity.