Jung-Min Jerry Park

Security vulnerabilities in IEEE 802.22

Cognitive Radio (CR) is seen as one of the enabling technologies for realizing a new spectrum access paradigm, viz. Opportunistic Spectrum Sharing (OSS). IEEE 802.22 is the worlds first wireless standard based on CR technology. It defines the air interface for a wireless regional area network (WRAN) that uses fallow segments of the licensed (incumbent) TV broadcast bands. CR technology enables unlicensed (secondary) users in WRANs to utilize licensed spectrum bands on a non-interference basis to incumbent users. The coexistence between incumbent users and secondary users is referred to as incumbent coexistence. On the other hand, the coexistence between secondary users in different WRAN cells is referred to as self-coexistence. The 802.22 draft standard prescribes several mechanisms for addressing incumbent- and self-coexistence issues. In this paper, we describe how adversaries can exploit or undermine such mechanisms to degrade the performance of 802.22 WRANs and increase the likelihood of those networks interfering with incumbent networks. The standard includes a security sublayer to provide subscribers with privacy, authentication, and confidentiality. Our investigation, however, revealed that the security sublayer falls short of addressing all of the key security threats. We also discuss countermeasures that may be able to address those threats.

A taxonomy of coexistence mechanisms for heterogeneous cognitive radio networks operating in TV white spaces

With the development of dynamic spectrum access technologies, such as cognitive radio, the secondary use of underutilized TV broadcast spectrum has come a step closer to reality. Recently, a number of wireless standards that incorporate CR technology have been finalized or are being developed to standardize systems that will coexist in the same TV white spaces. In these wireless standards, the widely studied problem of primary-secondary network coexistence has been addressed by the use of incumbent geolocation databases augmented with spectrum sensing techniques. However, the challenging problem of secondary-secondary coexistence¿in particular, heterogeneous secondary coexistence- has garnered much less attention in the standards and related literature. The coexistence of heterogeneous secondary networks poses challenging problems due to a number of factors, including the disparity of PHY/MAC strategies of the coexisting systems. In this article, we discuss the mechanisms that have been proposed for heterogeneous coexistence, and propose a taxonomy of those mechanisms targeting TVWSs. Through this taxonomy, our aim is to offer a clear picture of the heterogeneous coexistence issues and related technical challenges, and shed light on the possible solution space.

An Overview of Dynamic Spectrum Sharing: Ongoing Initiatives, Challenges, and a Roadmap for Future Research

We are in the midst of a major paradigm shift in how we manage radio spectrum. This paradigm shift is necessitated by the growth of wireless services of all types and the demand pressure imposed on limited spectrum resources under legacy management regimes. The shift is feasible because of advances in radio and networking technologies that make it possible to share spectrum dynamically in all possible dimensions-i.e., across frequencies, time, location, users, uses, and networks. Realizing the full potential of this shift to Dynamic Spectrum Sharing will require the co-evolution of wireless technologies, markets, and regulatory policies; a process which is occurring on a global scale. This paper provides a current overview of major technological and regulatory reforms that are leading the way toward a global paradigm shift to more flexible, dynamic, market-based ways to manage and share radio spectrum resources. We focus on current efforts to implement database-driven approaches for managing the shared co-existence of users with heterogeneous access and interference protection rights, and discuss open research challenges.

A Coexistence-Aware Spectrum Sharing Protocol for 802.22 WRANs

IEEE 802.22 is the first wireless standard based on cognitive radio (CR) technology. It defines the air interface for a wireless regional area network (WRAN) that uses fallow segments of the TV broadcast bands. CR technology enables unlicensed users in WRANs to utilize licensed (incumbent) spectrum bands on a non-interference basis to incumbent users. The coexistence between incumbent users and unlicensed users is referred to as incumbent coexistence. On the other hand, the coexistence between unlicensed users in different WRAN cells is referred to as self-coexistence. 802.22 defines several inter-base station (BS) dynamic resource sharing mechanisms to enable overlapping cells to share spectrum. However, those mechanisms do not adequately address some of the key issues concerning incumbent and self coexistence. In this paper, we propose an inter-BS CoexistenceAware Spectrum Sharing (CASS) protocol for overlapping 802.22 cells that takes into account coexistence requirements. We show that the proposed protocol outperforms 802.22’s self-coexistence solutions using simulation results. To the best of our knowledge, the work presented here is the first systematic study of the selfcoexistence problem in the context of 802.22 WRANs.

BRESAP: A Policy Reasoner for Processing Spectrum Access Policies Represented by Binary Decision Diagrams

Declarative spectrum management through policy-based dynamic spectrum access has garnered significant attention recently. Policy-based spectrum access decouples spectrum access policies from the radio platform. In policy-based spectrum access, a reasoning engine called the policy reasoner plays a critical role. The policy reasoner assists in policy enforcement and carries out a number of tasks related to policy analysis and processing. One of the most important tasks performed by the policy reasoner is evaluating transmission requests in the context of the currently active set of policies. This paper describes the design and implementation of a novel policy reasoner. The proposed policy reasoner uses multi-terminal binary decision diagrams (MTBDDs) to represent, interpret, and process policies. It uses a set of efficient graph-theoretic algorithms to translate policies into MTBDDs, merge policies into a single meta-policy, and compute opportunity constraints. In this paper, we demonstrate that policies can be processed efficiently by reframing the policy reasoning problem as a graph-based Boolean function manipulation problem. The proposed policy reasoner has the capability to respond to either under-specified or invalid transmission requests (sent by the system strategy reasoner) by returning a set of opportunity constraints that prescribes how the transmission parameters should be modified in order to make them conform to the policies. We propose three different algorithms for computing the opportunity constraints. The first algorithm computes opportunity constraints for under-specified transmission requests and its complexity is proportional to the number of variables in the meta-policy BDD. The second and third algorithms compute opportunity constraints for invalid transmission requests and their complexities are proportional to the number of variables and the size of the meta-policy BDD, respectively.

Robustness against Byzantine Failures in Distributed Spectrum Sensing

Distributed Spectrum Sensing (DSS) enables a Cognitive Radio (CR) network to reliably detect licensed users and avoid causing interference to licensed communications. The data fusion technique is a key component of DSS. We discuss the Byzantine Failure problem in the context of data fusion, which may be caused by either malfunctioning sensing terminals or Spectrum Sensing Data Falsification (SSDF) attacks. In either case, incorrect spectrum sensing data is reported to a data collector which can lead to the distortion of data fusion outputs. We investigate various data fusion techniques, focusing on their robustness against Byzantine Failures. In contrast to existing data fusion techniques that use a fixed number of samples, we propose a new technique that uses a variable number of samples. The proposed technique, which we call Weighted Sequential Probability Ratio Test (WSPRT), introduces a reputation-based mechanism to the Sequential Probability Ratio Test (SPRT). We evaluate WSPRT by comparing it with a variety of data fusion techniques under various conditions. We also discuss practical issues that need to be considered when applying the fusion techniques to CR networks. Our simulation results indicate that WSPRT is the most robust against Byzantine Failures among the data fusion techniques that were considered.

PHY-layer authentication by introducing controlled inter symbol interference

Spectrum security and enforcement is one of the major challenges that need to be addressed before spectrum-agile and opportunistic spectrum access technologies can be deployed. Rogue transmitters are a major threat to opportunistic spectrum access. One approach for deterring rogue transmissions is to enable receivers to authenticate or uniquely identify secondary transmitters. Although cryptographic mechanisms at the higher layers have been widely used to authenticate transmitters, the ability to authenticate transmitters at the physical (PHY) layer has a number of key advantages over higher-layer approaches. In existing schemes, the authentication signal is added to the message signal in such a way that the authentication signal appears as noise to the message signal and vice versa. Hence, existing schemes are constrained by a fundamental tradeoff between the message signals signal-to-noise ratio (SNR) and the authentication signals SNR. In this paper, we propose a novel PHY-layer authentication scheme called Precoded Duobinary Signaling for Authentication (P-DSA). P-DSA introduces some controlled amount of inter-symbol interference (ISI) into the data stream. The addition of the controlled ISI introduces redundancy in the message signal which can be utilized to embed the authentication signal. In this way, P-DSA relaxes the constraint on the aforementioned tradeoff. Our results show that P-DSA achieves superior detection performance compared to the prior art without sacrificing message throughput or increasing power.

Coexistence Decision Making for Spectrum Sharing Among Heterogeneous Wireless Systems

This paper focuses on the problem of spectrum sharing between secondary networks that access spectrum opportunistically in TV spectrum. Compared to the coexistence problem in the ISM (Industrial, Scientific and Medical) bands, the coexistence situation in TV whitespace (TVWS) is potentially more complex and challenging due to the signal propagation characteristics in TVWS and the disparity of PHY/MAC strategies employed by the systems coexisting in it. In this paper, we propose a novel decision making algorithm for a system of coexistence mechanisms, such as an IEEE 802.19.1-compliant system, that enables coexistence of dissimilar TVWS networks and devices. Our algorithm outperforms existing coexistence decision making algorithms in terms of fairness, and percentage of demand serviced.

Channel Aggregation in Cognitive Radio Networks with Practical Considerations

In cognitive radio (CR) networks, spectrum resource that can be shared by secondary users (SUs) is always restricted by primary users (PUs). Although channel aggregation (CA) enables each SU to access multiple channels at a time, whether it is beneficial is subject to the PU activity and radio capability. In this paper, we study the feasibility and efficiency of CA in consideration of various such practical constraints and costs. First, we propose a novel channel usage model to analyze the impact of both PU and SU behaviors on the availability of white spaces. This model is very general and can capture a wide range of user behaviors. Next, we model the costs in time for performing CA. User demands in both frequency and time domains are considered to evaluate the costs for making negotiation and renewing transmission. Further, an optimal CA strategy is defined to minimize the cumulative delay for transmitting a certain amount of data. Numerical and simulation results based on real data of PU activity show that user demands on both bandwidth and duration should be carefully chosen to achieve the optimal delay performance in practice.

A credit-token-based spectrum etiquette framework for coexistence of heterogeneous cognitive radio networks

The coexistence of cognitive radio (CR) networks in the same swath of spectrum has become an increasingly important problem, which is especially challenging when coexisting networks are heterogeneous (i.e., use different air interface standards), such as the case in TV white spaces. In this paper, we propose a credit-token-based spectrum etiquette framework that enables spectrum sharing among distributed heterogeneous CR networks with equal priority. Specifically, we propose a game-auction coexistence framework. Each network acts as either an offerer or a requester, and coexists with other networks via a non-cooperative game and a truthful multi-winner auction. The framework addresses the trade-offs among social welfare and offerers revenue in the auction and requesters utility in the game. We prove that the framework guarantees system stability. Our simulation results show that the proposed coexistence framework always converges to a near-optimal distributed solution and improves coexistence fairness and spectrum utilization.