Abstract

     Integrating cognitive radio (CR) with traditional wireless networks is helping solve the problem of spectrum scarcity in an efficient manner. The opportunistic and dynamic spectrum access features of CR provide the functionality to its unlicensed users to utilize the underutilized spectrum at the time of need because CR nodes can sense vacant bands of spectrum and can also access them to carry out communication. Various capabilities of CR nodes depend upon efficient and continuous reporting of data with each other and centralized base stations, which in turn can cause leakage in privacy. Experimental studies have shown that the privacy of CR users can be compromised easily during the cognition cycle, because they are knowingly or unknowingly sharing various personally identifiable information (PII), such as location, device ID, signal status, etc. In order to preserve this privacy leakage, various privacy preserving strategies have been developed by researchers, and according to us differential privacy is the most significant among them. In this article, we provide a thorough survey on how differential privacy can play an active role in preserving privacy of cognitive radio networks (CRN). Firstly, we provide a thorough comparison of our work with other similar studies to show its novelty and contribution, and afterwards, we provide a thorough analysis from the perspective of various CR scenarios which can cause privacy leakage. After that, we carry out an in-depth assessment from the perspective of integration of differential privacy at different levels of CRN. Then, we discuss various parameters which should be considered while integrating differential privacy in CRN alongside providing a comprehensive discussion about all integrations of differential privacy carried out till date. Finally, we provide discussion about prospective applications, challenges, and future research directions. The discussion about integration of differential privacy in different CR scenarios indicates that differential privacy is one of the most viable mechanisms to preserve privacy of CRN in modern day scenarios. From the discussion in the article, it is evident that the proposed integration of differential privacy can pave the way for futuristic CRN in which CR users will be able to share information during the cognition cycle without the risk of losing their private information.

Introduction

     The exponential surge in the usage of hand-held Internet of Things (IoT) devices caused a huge rise in wireless trafc. Statista report revealed that the number of hand-held mobile devices is projected to reach up to 17.72 billion by the end of the year 2024 [1]. This surge is causing an irregular usage of spectrum, which is further responsible to cause the issue of ‘artifcial spectrum scarcity’ [۲]. Similarly, the worldwide analysis and measurement of spectrum utilization revealed that only 5-10 % of wireless spectrum is being used by licensed/authorized users [3]. All these factors lead researchers to investigate mechanisms which provide spectrum efciency, and cognitive radio (CR) is one of them. Cognitive radio is a widely accepted model for efcient spectrum utilization [4]. CR was frst coined by J. Mitola in 1999. CR is an ambiance-aware intelligent wireless system which can dynamically adapt changes depending upon its surrounding RF environment [5]. CR works over the principle of allowing CR users (also known as Secondary Users (SUs)), to access spectrum of licensed users (also known as Primary Users (PUs)), during idle time. This functionality of CR allows SUs to exploit underutilized bands of spectrum without causing any harmful inference to the communication of PUs [6]. Thus, SUs can dynamically access available spaces in the spectrum band in order to manage it efciently [7, 8].

Conclusion

     Spectrum is a non-renewable resource. It is therefore important to use this precious resource in an efcient manner. In order to carry out efcient utilization of spectrum, scientists developed the notion of CR, which works over the principle of spectrum access at vacant times. CR nodes have the ability to sense the loopholes in the spectrum and then use these loopholes to carry out communication. In this way, CR nodes can play a vital role in overcoming spectrum scarcity. Nevertheless, CRN has a large number of benefts, they are not immune to all threats and one of the most critical ones is the privacy leakage, which causes serious consequences if not handled properly. Certain research works have highlighted the use of various privacy preservation approaches to protect privacy of CRN, and diferential privacy is one of them. Diferential privacy can play an important role in the design and development of modern, private, and more secure CRN of the future. In this paper, we carried out a comprehensive survey targeting the integration of diferential privacy in CRN from various aspects. Firstly, we highlight the importance of privacy preservation in CRN, by discussing the functioning of diferential privacy. We then provide an in-depth discussion about the sources of privacy leakage in CRN. Next we provide insights into how diferential privacy can play a critical role in protecting this leakage. We then present an analysis of certain parameters that should be taken into account while developing diferential privacy-based CRN protocols. Then, an in-depth analysis of technical works integrating diferential privacy in various scenarios of CRN. Finally, we provide analysis about prospective future directions alongside highlighting certain challenges that researchers may face.