Leonard E. Lightfoot

On PHY-layer security of cognitive radio: Collaborative sensing under malicious attacks

In cognitive radio networks, physical layer spectrum sensing plays a key role in helping cognitive radios adapt to changes in spectrum availability. However, it raises significant security issues at the physical layer as well. In this paper, we investigate collaborative sensing of cognitive radio networks under malicious attacks, and analyze the system performance in a generalized framework. The system design goal is to improve efficiency of spectrum access on a non-interfering basis, which is formulated as a constrained parameter optimization problem. A numerical algorithm is provided to resolve the problem. The system performances are evaluated under various conditions, and discussions are provided to help better understand the effectiveness of the attacks and their countermeasures.

Secure collision-free frequency hopping for OFDMA-based wireless networks

This paper considers highly efficient antijamming system design using secure dynamic spectrum access control. First, we propose a collision-free frequency hopping (CFFH) system based on the OFDMA framework and an innovative secure subcarrier assignment scheme. The CFFH system is designed to ensure that each user hops to a new set of subcarriers in a pseudorandom manner at the beginning of each hopping period, and different users always transmit on nonoverlapping sets of subcarriers. The CFFH scheme can effectively mitigate the jamming interference, including both random jamming and follower jamming. Moreover, it has the same high spectral efficiency as that of the OFDM system and can relax the complex frequency synchronization problem suffered by conventional FH. Second, we enhance the antijamming property of CFFH by incorporating the space-time coding (STC) scheme. The enhanced system is referred to as STC-CFFH. Our analysis indicates that the combination of space-time coding and CFFH is particularly powerful in eliminating channel interference and hostile jamming interference, especially random jamming. Simulation examples are provided to illustrate the performance of the proposed schemes. The proposed scheme provides a promising solution for secure and efficient spectrum sharing among different users and services in cognitive networks.

Distributed Detection in Mobile Access Wireless Sensor Networks under Byzantine Attacks

This paper explores reliable data fusion in mobile access wireless sensor networks under Byzantine attacks. We consider the q-out-of-m rule, which is popular in distributed detection and can achieve a good tradeoff between the miss detection probability and the false alarm rate. However, a major limitation with it is that the optimal scheme parameters can only be obtained through exhaustive search, making it infeasible for large networks. In this paper, first, by exploiting the linear relationship between the scheme parameters and the network size, we propose simple but effective sub-optimal linear approaches. Second, for better flexibility and scalability, we derive a near-optimal closed-form solution based on the central limit theorem. Third, subjecting to a miss detection constraint, we prove that the false alarm rate of q-out-of-m diminishes exponentially as the network size increases, even if the percentage of malicious nodes remains fixed. Finally, we propose an effective malicious node detection scheme for adaptive data fusion under time-varying attacks; the proposed scheme is analyzed using the entropy-based trust model, and shown to be optimal from the information theory point of view. Simulation examples are provided to illustrate the performance of proposed approaches under both static and dynamic attacks.

Reliable data fusion in wireless sensor networks under Byzantine attacks

In this paper, Byzantine attacks in wireless sensor networks with mobile access (SENMA) points is considered, where a portion of the active sensors are compromised to send false information. One effective method to combat with Byzantine attacks is the q-out-of-m scheme, where the sensing decision is based on q sensing reports out of m polled nodes. In this paper, first, by exploiting the approximately linear relationship between the scheme parameters and the network size, we propose a simplified q-out-of-m scheme which can greatly reduce the computational complexity, and at the same time keeping good performance. We show that for a fixed percentage of malicious sensors, the detection accuracy of the simplified q-out-of-m scheme increases almost exponentially as the network size increases. Second, we propose a simple but effective method to detect the malicious sensors before decision making. The performance of the proposed approach is evaluated under both static and dynamic attacking strategies. It is observed that with the pre-detection procedure, the performance of the q-out-of-m scheme can be improved significantly under various attacking strategies. Simulation results are provided to illustrate the effectiveness of the proposed approaches.

Architecture design of mobile access coordinated wireless sensor networks

This paper considers architecture design of mobile access coordinated wireless sensor networks (MC-WSN) for reliable and efficient information exchange. In sensor networks with mobile access points (SENMA), the mobile access points collect information directly from individual sensors as they traverse the network, such that no routing is needed in data transmission. While being energy efficient, a major limitation with SENMA is the large delay in data collection, making it undesirable for timesensitive applications. In the proposed MC-WSN architecture, the sensor network is coordinated by powerful mobile access points (MA), such that the number of hops from each sensor to the MA is minimized and limited to a prespecified number through active network deployment and network topology design. Unlike in SENMA, where the data collection delay depends on the physical speed of the MA, in MC-WSN, the delay depends on the number of hops and the electromagnetic wave speed, and is independent of the physical speed of the MA. This innovative architecture is energy efficient, resilient, fast reacting and can actively prolong the lifetime of sensor networks. Our simulations show that the proposed MC-WSN can achieve higher energy-efficiency and orders of magnitude lower delay over SENMA, especially for large-scale networks.

Performance of QO-STBC-OFDM in partial-band noise jamming

Quasi-orthogonal space-time block codes with orthogonal frequency division multiplexing (QO-STBC-OFDM) can exploit multipath diversity and achieve spectrally efficient communications. However, future wireless communication systems must be robust against both unintentional and intentional interference. As a result, there is a need for proper analytical tools to assess the performance of QO-STBC-OFDM in the presence of partial-band noise jamming. First, analytical expressions for the exact pairwise error probability (PEP) of the QO-STBC-OFDM system is derived using the moment generating function (MGF). Second, the PEP is calculated under various situations, and the closed-form expressions and union bound for the bit error probability (BEP) are derived. Finally, simulations are performed and compared with the theoretical results.

Space-time coded collision-free frequency hopping in hostile jamming

This paper considers spectrally efficient and robust wireless system design under malicious jamming as well as unintentional interference. Due to limited spectrum and lack of a protected physical boundary, wireless systems are facing much more serious challenges in capacity and security than wired networks. When transmitted through the airlink, wireless signals are vulnerable to hostile jamming and interception. Frequency hopping (FH) system, which is robust under hostile jamming, was originally developed for secure communications in military applications. However, the efficiency of the conventional FH scheme is very low due to inappropriate use of the total available bandwidth and transmission collisions. To improve the system capacity, we develop a space-time coded collision-free frequency hopping (STC-CFFH) system based on the OFDM framework. Performance analysis of the proposed scheme is presented under frequency selective fading and partial band jamming through both theoretical analysis and simulation examples. Our analysis indicates that the STC-CFFH scheme improves the spectral efficiency and inherent anti-jamming features of conventional FH systems. Potentially, the proposed spectrally efficient anti-jamming scheme can be applied directly to military communications under hostile environments.

Jamming mitigation using space-time coded collision-free frequency hopping

Frequency hopping (FH) system, which is robust under jamming interference, was originally developed for secure military communication applications. However, the efficiency of the conventional FH scheme is very low due to inappropriate use of the total available bandwidth and transmission collisions. To improve the system capacity, we develop a space-time coded collision-free frequency hopping (STC-CFFH) system based on the OFDM framework. The capacity and performance analysis of the proposed scheme is presented under frequency selective fading and partial-band jamming through both theoretical analysis and simulation examples. Our analysis indicates that the STC-CFFH scheme improves the spectral efficiency and inherent anti-jamming features of conventional FH systems.

Jamming-resilient subcarrier assignment for OFDMA based space-time coded systems

This paper considers highly efficient jammingresilient wireless system design. First, we introduce a collisionfree frequency hopping (CFFH) system based on the OFDMA framework and an innovative secure subcarrier assignment scheme. The secure subcarrier assignment algorithm is designed to ensure that: (i) Each user hops to a new set of subcarriers in a pseudo-random manner at the beginning of each hopping period; (ii) Different users always transmit on non-overlapping sets of subcarriers, such that malicious users cannot predict or repeat the hopping pattern of the authorized users, and hence cannot launch follower jamming attacks. Second, we enhance the anti-jamming property of CFFH by incorporating the space-time coding (STC) scheme. The enhanced system is referred to as STC-CFFH. Our analysis indicates that STC-CFFH is particularly powerful in eliminating channel distortion and hostile jamming interference, including both random jamming and follower jamming attacks. Simulation examples are provided to illustrate the performance of the proposed schemes.

Reliable Communications over Multihop Networks under Routing Attacks

This paper considers reliable multihop transmission under routing attacks, where a malicious relay can modify or drop a packet as it is being forwarded to the destination. We propose a transmission scheme that detects malicious nodes launching routing attacks through incorporating diversity over multi-layer relays, where each relay can establish a direct connection with relays at preceding and succeeding hop levels. We prove that the proposed approach can efficiently detect malicious nodes, provided that there is at least one honest relay at each hop level. We highlight the trade-off between network efficiency and security, and show the impact of the diversity level and the number of hops on the network performance through theoretical analysis and simulation examples. Our results provide insights on general network architecture development and topology design.