Smart mapping applications- Google Maps, Apple Maps, Waze- have become ubiquitous in the modern smart city. While the use of these apps undoubtedly eases a number of daily frustrations, their rapid acceptance and integration into every facet of transportation, public safety, and disaster response raises security concerns. Among these concerns is the possibility of an easily-implemented client-side attack; the traffic state shown on a smart map indicates the number of users- not cars- and this disconnect between the ground truth and virtual environment could be exploited by an adversary simply operating a disingenuous number of client devices. In this paper we examine the vulnerabilities exposed by such an adversary and propose a model which combines machine learning traffic prediction and real-time statistical analysis to screen for anomalous traffic attacks. Extensive simulations suggest that our model greatly increases the resources (number of client devices) required to noticeably influence traffic patterns. We show that our model correctly identifies 54.17 % of attacks immediately and reduces the duration of initially undetected attacks by 60.4 % compared to a typical polling system under ideal circumstances, where an adversary has access to an average of 76.0 % more client devices.

The Graph isomorphism problem involves determining whether two graphs are isomorphic and the computational complexity required for this determination. In general, the problem is not known to be solvable in polynomial time, nor to be NP-complete. In this paper, by analyzing the algebraic properties of the adjacency matrices of the undirected graph, we first established the connection between graph isomorphism and matrix row and column interchanging operations. Then, we prove that for undirected graphs, the complexity in determining whether two graphs are isomorphic is at most O(n3).

Growing evidence has unveiled the dynamic nature of human brain networks. However, the dynamic and hierarchical organization that supports information transmission in brain networks remains unexplored across the adult lifespan. In this study, we developed an analytical framework to investigate the spatiotemporal reorganization of dynamic brain networks during adult development and aging. Specifically, using resting-state fMRI data from the Cam-CAN lifespan dataset, we examined the age effects on the topological stability of egocentric structures and the average length of temporal paths. As the egocentric structure reflects the relationships between a node’s neighbors, we further explored whether the stability of egocentric structures mediates age effects on information diffusion. The results showed that the topological stability of egocentric structures has an impact on information processing in the spatiotemporal domain. In particular, the age-related changes observed in some functional systems followed different progressive patterns from that of other systems, which might be explained by some compensation mechanisms. Taken together, the present work may provide an additional perspective for understanding the underlying neuro-mechanisms of healthy aging.

Brain anatomical age is an effective feature to assess the status of the brain, such as atypical development and aging. Although some deep learning models have been developed for estimating infant brain age, the performance of these models was unsatisfactory because few of them considered the developmental characteristics of brain anatomy during the perinatal period-the most rapid and complex developmental stage across the lifespan. The present study proposed an attention-based hemispheric relation inference network (HRINet) that takes advantage of the nature of brain structural lateralization during early development. This model captures the inter-hemispheric relationship using a graph attention mechanism and transmits lateralization information as features to describe the interactive development between bilateral hemispheres. The HRINet was used to estimate the brain age of 531 preterm and full-term neonates from the Developing Human Connectome Project (dHCP) database based on two metrics (mean curvature and sulcal depth) characterizing the folding morphology of the cortex. Our results showed that the HRINet outperformed other benchmark models in fitting the perinatal brain age, with mean absolute error of 0.53 and determination coefficient of 0.89. We also verified the generalizability of the HRINet on an extra independent dataset collected from the Gansu Provincial Maternity and Child-care Hospital. Furthermore, by applying the best-performing model to an independent dataset consisting of 47 scans of preterm infants at term-equivalent age, we showed that the predicted age was significantly lower than the chronological age, suggesting a delayed development of premature brains. Our results demonstrate the effectiveness and generalizability of the HRINet in estimating infant brain age, providing promising clinical applications for assessing neonatal brain maturity.

Neurophysiological measurements suggest that human information processing is evinced by neuronal activity. However, the quantitative relationship between the activity of a brain region and its information processing capacity remains unclear. In this paper, we introduce an information conservation law for regional brain activation, and establish a mathematical model to quantify the relationship between the information processing capacity, input storage capacity, the arrival rate of exogenous information, and the neuronal activity of a brain region—referred to as the brain information processing capacity (IPC) model. We apply the IPC model to event related fMRI data from a flanker test, designed to determine age-related differences in brain activation. Our analysis demonstrates the predictive validity of the model in terms of providing accurate account of fMRI responses, and shows that for a given cognitive task, higher information processing capacity leads to lower neuronal activity level and faster response. Relying solely on the information conservation law, the IPC model provides a framework for modeling distributed neuronal processing—and can be applied to different data types and scales: i.e., single neurons, brain regions, and networks.

As more and more data is produced, finding a secure and efficient data access structure has become a major research issue. The centralized systems used by medical institutions for the management and transfer of Electronic Medical Records (EMRs) can be vulnerable to security and privacy threats, often lack interoperability, and give patients limited or no access to their own EMRs. In this paper, we first propose a privilege-based data access structure and incorporates it into an attribute-based encryption mechanism to handle the management and sharing of big data sets. Our proposed privilege-based data access structure makes managing healthcare records using mobile healthcare devices efficient and feasible for large numbers of users. We then propose a novel distributed multilevel EMR (d-EMR) management scheme, which uses blockchain to address security concerns and enables selective sharing of medical records among staff members that belong to different levels of a hierarchical institution. We deploy smart contracts on Ethereum blockchain and utilize a distributed storage system to alleviate the dependence on the record-generating institutions to manage and share patient records. To preserve privacy of patient records, our smart contract is designed to allow patients to verify attributes prior to granting access rights. We provide extensive security, privacy, and evaluation analyses to show that our proposed scheme is both efficient and practical.

As a popular modulation technique in wireless communications, orthogonal frequency-division multiplexing (OFDM) has two major disadvantages—one is its high peak-to-average power ratio (PAPR), which causes nonlinear distortion, lower power efficiency, and performance losses; the other is its fragility under hostile jamming attacks, where the authorized user asciitext’s signal is deliberately interfered by the adversary, leading to communication failures. In this article, first, we reintroduce the IFFT-relocated OFDM (IR-OFDM), which is essentially a single-carrier system with frequency-domain equalization. By relocating the inverse fast Fourier transform (IFFT) block in OFDM from the transmitter to receiver, IR-OFDM can completely liberate OFDM from the barriers of high PAPR while achieving the same spectral efficiency. Second, to combat hostile jamming, especially disguised jamming, where the jamming is highly correlated with the authorized signal, we propose a securely precoded IR-OFDM (SP-IR-OFDM). By integrating the advanced encryption standard (AES) into IR-OFDM transceiver design, we obtain a random (or dynamic) constellation. The shared secure randomness introduced by AES breaks the symmetry between the authorized signal and the jamming interference and, hence, ensures reliable performance of the system under disguised jamming. The efficiency and robustness of IR-OFDM and SP-IR-OFDM are demonstrated through simulation examples. It is shown that IR-OFDM can deliver comparable or better performances than OFDM under multipath propagation, and SP-IR-OFDM can achieve strong resistance under disguised jamming while enjoying low PAPR and relatively high spectral efficiency. Our result indicates that, potentially, SP-IR-OFDM can serve as a promising modulation candidate for next-generation secure and energy-efficient high-speed communications, especially for the resource-constrained Internet of Things (IoT) networks.

Large volumes of data are being generated daily from IoT networks, healthcare, and many other applications, which makes secure, reliable, and cost-effective data storage a critical infrastructure of the computing system. Existing data storage largely depends on centralized clouds, which is not only costly but also vulnerable to single points of failure and other types of security attacks. Moreover, cloud providers will have full access to user data and revision history beyond user control. To provide data security, data encryption has to be used, which requires extensive computing power and cumbersome key management. Distributed storage system (DSS) is being widely viewed as a natural solution to future online data storage due to improved access time and lower storage cost. However, the existing DSS also has the limitations of low storage efficiency and weak data security. In this article, we investigate multi-layer code-based distributed data storage systems that can achieve inherit content confidentiality and optimal storage efficiency. Our comprehensive performance analysis shows that the optimal code can improve the feasible region in reliable data storage by 50% under various adversarial attack scenarios.

Current systems used by medical institutions for the management and transfer of Electronic Medical Records (EMRs) can be vulnerable to security and privacy threats. In addition, these systems are centralized, often lack interoperability, and give patients limited or no access to their own EMRs. In this article, we propose a novel distributed data sharing scheme that applies the security benefits of blockchain to address these concerns. We deploy smart contracts on Ethereum blockchain and utilize a distributed storage system to alleviate the dependence on the record-generating institutions to manage and share patient records. To preserve privacy of patient records, we implement our smart contracts as a method to allow patients to verify attributes prior to granting access rights. Our proposed scheme also facilitates selective sharing of medical records among staff members that belong to different levels of a hierarchical institution. We provide extensive security, privacy, and evaluation analyses to show that our proposed scheme is both efficient and practical.

Fertility refers to the ability of animals to maintain reproductive function and give birth to offspring, which is an important indicator to measure the productivity of animals. Fertility is affected by many factors, among which environmental factors may also play key roles. During the past years, substantial research studies have been conducted to detect the factors related to fecundity, including genetic factors and environmental factors. However, the identified genes associated with fertility from countless previous studies are randomly dispersed in the literature, whereas some other novel fertility-related genes are needed to detect from omics-based datasets. Here, we constructed a fertility index factor database FifBase based on manually curated published literature and RNA-Seq datasets. During the construction of the literature group, we obtained 3301 articles related to fecundity for 13 species from PubMed, involving 2823 genes, which are related to 75 fecundity indicators or 47 environmental factors. Eventually, 1558 genes associated with fertility were filtered in 10 species, of which 1088 and 470 were from RNA-Seq datasets and text mining data, respectively, involving 2910 fertility-gene pairs and 58 fertility-environmental factors. All these data were cataloged into FifBase (http://www.nwsuaflmz.com/FifBase/), where the fertility-related factor information, including gene annotation and environmental factors, can be browsed, retrieved and downloaded with the user-friendly interface.

Electronic voting (e-voting) presents a convenient and cost-effective alternative to current paper ballot-based voting. It provides many benefits such as increased voter turnout and accuracy in the decision-making process. While presenting many improvements, e-voting still faces serious security challenges that hinder its adoption, especially when designed to be run over mobile devices. In this article, we propose a novel remote e-voting model for large-scale elections by proposing the participation of two conflicting parties to ensure election integrity and accountability. Our scheme can be implemented in IoT devices such as smartphones, which we believe can significantly increase voter turnout of the election process. Our proposed work is secure and preserves voter privacy through secure multiparty computations performed by parties of differing allegiances. It also leverages a blockchain running smart contracts as a publicly accessible and tamper-resistant bulletin board to permanently store votes and prevent double voting. In our security and privacy analysis, we show that our proposed scheme is secure against potential security threats and provides voter anonymity. We show orthogonality between universal verifiability and coercion resistance in our proposed scheme, allowing an election to favor one over the other. Our performance analysis and smartphone simulation results show that the proposed scheme is practical for large-scale elections.

Blockchain is a technology that was proposed to enable the decentralized digital currency, Bitcoin. Since its inception, blockchain has been widely used in many other areas, including tracing sensor data and mitigating its duplication in IoT applications, the healthcare industry, and e-voting. In this article, we provide a comprehensive review and analysis of the major security and privacy issues of Bitcoin and blockchain, the major challenges, and opportunities in utilizing the technology. First, we present a comprehensive background of Bitcoin and the preliminary on security. Second, the major security threats and countermeasures of Bitcoin are investigated. We analyze the risk of double-spending attacks, evaluate the probability of success in performing the attacks, and derive the profitability for the attacker to perform such attacks. Third, we analyze the underlying Bitcoin peer-to-peer network security risks and Bitcoin storage security. We compare three types of Bitcoin wallets in terms of security, types of services, and their tradeoffs. Finally, we discuss the security and privacy features of alternative cryptocurrencies and present an overview of emerging technologies today. Our results can help Bitcoin users to determine a tradeoff between the risk of double-spending attempts and the transaction time delay or confidence before accepting transactions. These results can also assist miners to develop suitable strategies to get involved in the mining process and maximize their profits.

In this paper, we propose a securely precoded OFDM (SP-OFDM) system for efficient and reliable transmission under disguised jamming, where the jammer intentionally misleads the receiver by mimicking the characteristics of the authorized signal and causes complete communication failure. More specifically, we bring off a dynamic constellation by introducing secure randomness shared between the legitimate transmitter and receiver, and hence, break the symmetricity between the authorized signal and the disguised jamming. We analyze the channel capacities of both the traditional OFDM and SP-OFDM under hostile jamming using the arbitrarily varying channel (AVC) model. It is shown that the deterministic coding capacity of the traditional OFDM is zero under the worst disguised jamming. On the other hand, due to the secure randomness shared between the authorized transmitter and receiver, SP-OFDM can achieve a positive capacity under disguised jamming since the AVC channel corresponding to SP-OFDM is not symmetrizable. A remarkable feature of the proposed SP-OFDM scheme is that while achieving strong jamming resistance, it has roughly the same high spectral efficiency as the traditional OFDM system. The robustness of the proposed SP-OFDM scheme under disguised jamming is demonstrated through both theoretic and numerical analyses.

Securely precoded OFDM (SP-OFDM) is a newly proposed secure and efficient anti-jamming scheme designed to enhance the physical layer security of OFDM based 4G and 5G systems under hostile environments. In this paper, by exploiting tools in constrained functional optimization, we explore the worst jamming distribution that minimizes the channel capacity of SP-OFDM under practical assumptions, where the transmitted symbols are uniformly distributed over a finite alphabet, and the jamming interference is subject to an average power constraint, but may or may not have a peak power constraint. First, we prove the existence and uniqueness of the worst jamming distribution. Second, by analyzing the Kuhn-Tucker conditions for the worst jamming, we prove that the worst jamming distribution is discrete in amplitude with a finite number of mass points, either with or without peak power constraints. Numerical results are provided on the worst jamming distribution and the minimum channel capacity under disguised jamming. It is shown that the minimum channel capacity of SP-OFDM is guaranteed to be positive under the worst disguised jamming, while the minimum capacity of the traditional OFDM under disguised jamming is zero. Both our theoretical and numerical results demonstrate the robustness of SP-OFDM and also reveal its performance lower bound under disguised jamming.

Regenerating code is a class of distributed storage codes that can optimally trade the bandwidth with the amount of data stored per node to repair a failed node. There are two extreme points in the optimal regenerating trade-off curve, which correspond to minimum-storage regenerating (MSR) and minimum-bandwidth regenerating (MBR). Recently, Reed-Solomon (RS) code based regenerating codes (RS-RC) were constructed under the product-matrix framework. It can also achieve the maximum distance separable (MDS) property in code regeneration and reconstruction. However, in case that the network is hostile and the storage nodes could be compromised or packets be modified, the storage capacity and the bandwidth required to regenerate or reconstruct the original file can be significantly affected. In this paper, we propose Hermitian code based regenerating codes (H-RC) by developing constructions under the product-matrix framework for minimum storage regenerating (H-MSR) and the minimum bandwidth regenerating (H-MBR). We also propose data regeneration and reconstruction algorithms for both H-MSR and H-MBR codes under both error-free and hostile networks. We demonstrate that the proposed algorithms can also successfully determine the erroneous decodings in hostile networks. Theoretical evaluation shows that our proposed H-RC can detect and correct more errors in hostile networks well beyond the RS-RC with the same code rate. Our analysis shows that the proposed H-RC have lower computational complexity than the RS-RC for both code regeneration and code reconstruction.

This paper considers malicious link detection in multi-hop wireless sensor networks (WSNs). Existing work on malicious link detection generally requires that the detection process being performed at the intermediate nodes, leading to considerable overhead in system design, as well as unstable detection accuracy due to limited resources and the uncertainty in the loyalty of the intermediate nodes themselves. In this paper, we propose an efficient and robust malicious link detection scheme by exploiting the statistics of packet delivery rates only at the base station. More specifically, first, we present a secure packet transmission protocol to ensure that except the base station, any intermediate nodes on the route cannot access the contents and routing paths of the packets. Second, we design a malicious link detection algorithm that can effectively detect the irregular dropout at every hop (or link) along the routing path. We prove that the proposed algorithm has guaranteed false alarm rate and low miss detection rate. Simulation results are provided to validate the proposed approaches.

In the era of big data and artificial intelligence, almost every aspect of research is driven by collecting data. However, privacy concerns substantially limit the usability of such data. This prevents a vast amount of possible advances in all branches of science. While privacy rules are inevitable, data owners will always seek data publishing models and techniques that can maximize data utility within the frame of the imposed privacy rules. In this paper we propose a negotiation-based data publishing model to jointly address the utility requirements of the Data User (DU) and the privacy and possibly the monetary requirements of the Data Owner (DO). We also re-define the data utility based on the DU's rather than the DO's perspective. Based on the proposed model, we present two data publishing scenarios that satisfy a given privacy constraint while achieving the DU's required data utility. The variation in a DO's flat or variable monetary rate objective motivates the data publishing scenarios. Our protocol fills the gap between the existing theoretical work and the ultimate goal of practicality.

In this paper, we address the problem of finding the worst jamming distribution in terms of channel capacity for the securely precoded OFDM (SP-OFDM) system, so as to evaluate the performance of SP-OFDM under destructive hostile jamming. We consider a practical communication scenario, where the transmitting symbols are uniformly distributed over a discrete and finite alphabet, and the jamming interference is subject to both average and peak power constraints. Using tools in functional analysis and complex analysis, first, we show the existence and uniqueness of the worst jamming distribution; then we further prove that the worst jamming distribution is discrete in amplitude with a finite number of mass points. Numerical examples are provided under different scenarios to demonstrate our theoretical results.

In this paper, we investigate whether we can distinguish that a subject is making a correct or incorrect behavioral response by analyzing the fMRI data of localized brain regions, obtained from a feature-based attention experiment. For each subject, we first construct the feature vectors for each region of interest (including V1, MT or IPS1) from the fMRI signals. Second, we project the feature vectors onto a lower dimensional subspace using Linear Discriminant Analysis (LDA), where the difference between two classes (correct vs. incorrect response) is maximized. Finally, we apply the Bayesian classifier to the projected data, and find that the classification accuracies corresponding to V1, MT and IPS1 are 87.2%, 90.8% and 81.7%, respectively, when all the trials are considered. Our analysis indicates that: when people make correct or incorrect responses, significant difference exists in the fMRI signals, especially in V1 and MT regions, and the difference can be effectively captured by the LDA-Bayesian classifier. We also prove that: when the original data are normally distributed, LDA, which aims to maximize the difference between different classes, is equivalent to the optimal Maximum Likelihood (ML) based classification method.

Patients rely on their public health records shared among medical institutions to receive the appropriate treatment they require. They must completely trust that these institutions will secure their records, protect their privacy, and efficiently share them when requested by other institutions. Unfortunately, medical institutions cannot fully be trusted for several reasons. First, patient records are stored on the servers of the medical institutions which could result in security issues and also a single point of failure. Second, centralized storage may also result in privacy concerns if records are incorrectly shared or leaked. Third, institutions may purposely delay sharing patient records for competitive reasons. To address these issues, we propose an attribute-based distributed data sharing scheme for patients to control how their records are shared. The distributed file sharing can effectively prevent the single point of failure and ensure data availability upon its request. Moreover, patients are also given the capability of selectively sharing their records for privacy protection. Our analysis shows that while ensuring attribute-based sharing of medical records, the proposed scheme can also work with the peer-to-peer distributed network storage such as InterPlanetary File System (IPFS) to improve efficient data retrieval.

A lot of research has been focused on secure outsourcing of biometric identification in the context of cloud computing. In such schemes, both the encrypted biometric database and the identification process are outsourced to the cloud. The ultimate goal is to protect the security and privacy of the biometric database and the query templates. Security analysis shows that previous schemes suffer from the enrolment attack and unnecessarily expose more information than needed. In this paper, we propose a new secure outsourcing scheme aims at enhancing the security from these two aspects. First, besides all the attacks discussed in previous schemes, our proposed scheme is also secure against the enrolment attack. Second, we model the identification process as a fixed radius similarity query problem instead of the kNN search problem. Such a modelling is able to reduce the exposed information thus enhancing the privacy of the biometric database. Our comprehensive security and complexity analysis show that our scheme is able to enhance the security and privacy of the biometric database and query templates while maintaining the same computational savings from outsourcing.

In the upcoming 5G era, many new types of networks will greatly expand the connectivity of the world such as vehicular ad hoc networks (VANETs), Internet of Things (IoT), and device‐to‐device communications (D2D). Network coding is a promising technology that can significantly improve the throughput and robustness of these emerging 5G multihop networks. However, network coding is generally very fragile to malicious attacks such as message content corruption and node compromise attacks. To take advantage of network coding in performance gain while refraining malicious network attacks is an interesting and challenging research issue. In this paper, we propose a new error‐detection and error‐correction (EDEC) scheme that can jointly detect and remove the malicious attacks based on the underlying error‐control scheme for general multihop networks that can model the 5G multihop networks. The proposed scheme can increase the throughput for network with pollution attacks compared to existing error‐detection based schemes. Then we propose a low‐density parity check (LDPC) decoding based EDEC (LEDEC) scheme. Our theoretical analysis demonstrates that the LEDEC scheme can further increase the throughput for heavily polluted network environments. We also provide extensive performance evaluation and simulation results to validate the proposed schemes. This research ensures the expected performance gain for the application of network coding in the 5G network under malicious pollution attacks.

Regenerating code is a class of distributed storage codes that can optimally trade the bandwidth required to repair a failed node with the amount of data stored per node. There are two optimal points in the regeneration tradeoff curve: the minimum storage regeneration code and the minimum bandwidth regeneration code. However, in hostile networks where the storage nodes may be compromised, the storage capacity of the network can be significantly affected. In this paper, we propose two optimal regenerating code constructions through rate-matching to combat this kind of adversarial attacks in hostile networks. We first develop a two-layer rate-matched regenerating code construction. By matching the parameters of the full rate code and the partial rate code, we can optimize the overall storage efficiency while maintaining the corrupted node detection probability. Through comprehensive analysis, we show that the two-layer rate-matched regenerating code can achieve 70% higher storage efficiency than the universally resilient regenerating code. We then propose an optimal m-layer regenerating code construction. While the principle remains the same as the two-layer code, it is designed to optimize the total number of detectable corrupted nodes of m layers from which the errors can be corrected under the constraint of any given code efficiency. Compared with the universally resilient regenerating code with the same rate, our m-layer code can detect 50% more corrupted nodes.

This paper considers robust CDMA receiver design and jamming evaluation under disguised jamming, where the jammer generates a fake signal using the same spreading code, constellation and pulse shaping filter as that of the authorized signal. First, we analyze the performance of conventional CDMA systems under disguised jamming, and show that due to the symmetricity between the authorized signal and the jamming interference, the receiver cannot really distinguish the authorized signal from jamming, leading to complete communication failure. Second, by exploiting the small time difference between the authorized signal and the jamming interference, the conventional CDMA receiver can be redesigned to achieve robust performance under disguised jamming. More specifically, we propose to estimate the authorized signal, the phase and power level or range of the jamming interference by minimizing the MSE between the received signal and the jammed signal, which is the sum of the authorized signal and the disguised jamming. The effectiveness of the proposed approach is demonstrated through simulation examples. It is shown that with the proposed receiver design, the BER performance of CDMA can be improved significantly under disguised jamming, and an analytical evaluation about jamming can also be obtained.

This paper introduces the mobile access coordinated wireless sensor network (MC-WSN)-a novel energy efficient scheme for time-sensitive applications. In conventional sensor networks with mobile access points (SENMA), the mobile access points (MAs) traverse the network to collect information directly from individual sensors. While simplifying the routing process, a major limitation with SENMA is that data transmission is limited by the physical speed of the MAs and their trajectory length, resulting in low throughput and large delay. In an effort to resolve this problem, we introduce the MC-WSN architecture, for which a major feature is that: through active network deployment and topology design, the number of hops from any sensor to the MA can be limited to a pre-specified number. In this paper, we investigate the optimal topology design that minimizes the average number of hops from sensor to MA, and provide the throughput analysis under both single-path and multipath routing cases. Moreover, putting MC-WSN in the bigger picture of network design and development, we provide a unified framework for wireless network modeling and characterization. Under this general framework, it can be seen that MC-WSN reflects the integration of structure-ensured reliability/efficiency and ad-hoc enabled flexibility.

Abstract Communication anonymity is becoming an increasingly important, or even indispensable, security requirement for many applications. The existing research in anonymous communications can largely be divided into two categories: mix‐based systems and secure multiparty computation‐based systems, originating from mixnet and DC‐net, respectively. However, they either cannot provide provable anonymity or suffer from transmission collision problem. In this paper, we first propose a novel unconditionally secure source anonymous message authentication code that can be applied to any messages without relying on any trusted third parties. While ensuring message sender anonymity, secure source anonymous message authentication code can also provide message content authenticity. We then propose a novel communication protocol that can hide the senders and the recipients from each other and thus can be used for secure file sharing. The security analysis demonstrates that the proposed protocol is secure against various attacks. Our analysis also shows that it is efficient and practical. Copyright © 2012 John Wiley & Sons, Ltd.

This paper considers optimal multiband transmission under hostile jamming, where both the authorized user and the jammer are power-limited and operate against each other. The strategic decision making of the authorized user and the jammer is modeled as a two-party zero-sum game, where the payoff function is the capacity that can be achieved by the authorized user in the presence of the jammer. First, we investigate the game under AWGN channels. It is found that: either for the authorized user to maximize its capacity, or for the jammer to minimize the capacity of the authorized user, the best strategy for both of them is to distribute the transmission power or jamming power uniformly over all the available spectrum. The minimax capacity can be calculated based on the channel bandwidth and the signal-to-jamming and noise ratio, and it matches with the Shannon channel capacity formula. Second, we consider frequency selective fading channels. We characterize the dynamic relationship between the optimal signal power allocation and the optimal jamming power allocation in the minimax game, and then propose an iterative water pouring algorithm to find the optimal power allocation schemes for both the authorized user and the jammer.

This paper considers robust code division multiple access (CDMA) system design and capacity analysis under disguised jamming, where the jammer generates a fake signal using the same spreading code, constellation, and pulse shaping filter as that of the authorized signal. Unlike Gaussian jamming, which is destructive only when jamming is dominant, disguised jamming can be devastating even if the jamming power is comparable to the signal power. In this paper, first, we analyze the performance of the conventional CDMA under disguised jamming, and show that due to the symmetricity between the authorized signal and the jamming interference, the receiver cannot really distinguish the authorized signal from jamming, leading to complete communication failure. Second, we propose to combat disguised jamming using secure scrambling. Instead of using conventional scrambling codes, we apply advanced encryption standard to generate the security-enhanced scrambling codes. Theoretical analysis based on the arbitrarily varying channel model shows that the capacity of conventional CDMA without secure scrambling under disguised jamming is actually zero; however, secure scrambling can break the symmetricity between the authorized signal and the jamming interference, and hence ensures positive channel capacity under disguised jamming. Numerical examples are provided to demonstrate the effectiveness of secure scrambling in combating disguised jamming.

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.

Regenerating code is a class of code very suitable for distributed storage systems, which can maintain optimal bandwidth and storage space. Two types of important regenerating code have been constructed: the minimum storage regeneration (MSR) code and the minimum bandwidth regeneration (MBR) code. However, in hostile networks where adversaries can compromise storage nodes, the storage capacity of the network can be significantly affected. In this paper, we propose a rate-matched MSR code that can combat against this kind of adversaries in hostile networks. We optimize the code parameters for given system requirements. Our comprehensive analysis shows that our code can detect and correct malicious nodes with higher storage efficiency compared to the normal error correction MSR code.

Hostile jamming can cause significant performance degradation in wireless communications, but it also provides an unexplored source of additional signal power. In this letter, we propose an energy-harvesting receiver for two-way orthogonal frequency division multiplexing (OFDM) systems under hostile jamming. More specifically, in the downlink, the receiver is designed to simultaneously process information and harvest energy from the received desired signal as well as the jamming interference through a power splitter. The harvested energy can then be used as an additional source of power to enhance the uplink transmission. We investigate the optimal power allocation and power splitting ratio to maximize the sum-rate of the uplink and downlink transmissions. To reduce the complexity, a suboptimal energy harvesting scheme with closed-form solution is proposed. We also obtain a lower bound on the sum-rate of the proposed scheme under strong full-band jamming.

This paper considers malicious user detection and energy harvesting in orthogonal frequency division multiplexing-based cognitive radio networks under primary user emulation attack (PUEA). The digital TV (DTV) model adopted is the second generation terrestrial digital television standard (DVB-T2). In this paper, first, we propose an efficient advanced encryption standard (AES)-based DTV scheme, where the existing reference sequence used to generate the P2 pilot symbols in the DVB-T2 frames is encrypted using the AES algorithm to facilitate accurate primary user and malicious user detection. With the proposed scheme, we can detect PUEA accurately over all subcarriers or subbands where the P2 symbols present. Second, we come up with an effective communication scheme for the secondary users (SUs) under PUEA by exploiting the energy harvesting techniques. Optimal power splitting is considered for sum-rate maximization. As the optimal solution relies on multidimensional exhaustive search, we propose an effective suboptimal solution with much lower computational complexity. It is observed that the sum-rate of the SU network can be improved significantly with the energy harvesting technique. Third, we evaluate the worst case PUEA interference in terms of minimizing the sum-rate for the SUs. We show that for practical systems, as channel state information among the SUs is not available to the malicious user, the worst jamming for the SUs is when the malicious user performs equal power allocation over all the white space subcarriers. Simulation results are provided to illustrate the proposed approaches.

Lifetime optimization and security are two conflicting design issues for multi-hop wireless sensor networks (WSNs) with non-replenishable energy resources. In this paper, we first propose a novel secure and efficient Cost-Aware SEcure Routing (CASER) protocol to address these two conflicting issues through two adjustable parameters: energy balance control (EBC) and probabilistic-based random walking. We then discover that the energy consumption is severely disproportional to the uniform energy deployment for the given network topology, which greatly reduces the lifetime of the sensor networks. To solve this problem, we propose an efficient non-uniform energy deployment strategy to optimize the lifetime and message delivery ratio under the same energy resource and security requirement. We also provide a quantitative security analysis on the proposed routing protocol. Our theoretical analysis and OPNET simulation results demonstrate that the proposed CASER protocol can provide an excellent tradeoff between routing efficiency and energy balance, and can significantly extend the lifetime of the sensor networks in all scenarios. For the non-uniform energy deployment, our analysis shows that we can increase the lifetime and the total number of messages that can be delivered by more than four times under the same assumption. We also demonstrate that the proposed CASER protocol can achieve a high message delivery ratio while preventing routing traceback attacks.

In this paper, we analyze the throughput of a novel mobile access coordinated wireless sensor network architecture (MC-WSN) under single path and multipath routing. The obtained throughput expressions highlight the trade-off between achieving high throughput performance and improving the network security strength. The results reveal the importance of: (i) minimizing the number of hops in maximizing the throughput, and (ii) adopting routing diversity in combating malicious attacks and network failure conditions. We control the number of hops in data transmission through optimal topology design and active network deployment achieved by the mobile access point (MA). To combat routing attacks, we propose a secure routing path selection approach, and show the impact of the proposed approach on improving the throughput performance under malicious attacks.

Distributed storage plays a crucial role in the current cloud computing framework. After the theoretical bound for distributed storage was derived by the pioneer work of the regenerating code, Reed-Solomon code based regenerating codes, including the minimum storage regeneration (MSR) code and the minimum bandwidth regeneration (MBR) code, were developed. However, in the hostile network with passive eavesdroppers and active attackers, the data confidentiality and storage capacity of the network can be significantly affected. In this paper, we propose a secure MSR code that can combat against the passive eavesdroppers and active attackers in the network. We also provide theoretical analyses showing that our code can provide better security with less computational cost and bandwidth overhead.

This paper considers jamming-resistant OFDM system design under full-band disguised jamming, where the jamming symbols are taken from the same constellation as the information symbols over each subcarrier. First, we analyze the impact of disguised jamming on OFDM systems. It is shown that due to the symmetricity between the authorized signal and jamming, the BER of OFDM systems without symbol-level precoding or only with repeated symbol-level coding is lower bounded by a modulation specific constant, which cannot be improved by increasing SNR. Second, we develop an optimal precoding scheme which minimizes the BER of OFDM systems under full-band disguised jamming. It is shown that the most efficient way to combat full-band disguised jamming in OFDM systems is to concentrate the total available power and distribute it uniformly over a particular number of subcarriers instead of the entire spectrum. The underlying argument is that for a particular subcarrier, when the signal-to-jamming ratio is large enough, then the receiver can distinguish the authorized signal from disguised jamming under the presence of noise. Both theoretical analysis and numerical results demonstrate that the BER performance of OFDM systems under full-band disguised jamming can be improved significantly with the proposed precoding scheme.

Distributed storage plays a crucial role in the current cloud computing framework. After the theoretical bound for distributed storage was derived by the pioneer work of the regenerating code, Reed-Solomon code based regenerating codes were developed. The RS code based minimum storage regeneration code (RS-MSR) and the RS code based minimum bandwidth regeneration code (RS-MBR) can achieve the theoretical bounds on the MSR point and the MBR point respectively in code regeneration. They can also maintain the MDS property in code reconstruction. However, in the hostile network where the storage nodes can be compromised and the packets can be tampered with, the storage capacity of the network can be significantly affected. In this paper, we propose a Hermitian code based regenerating (H-MSR) code. We first prove that this code can achieve the theoretical MSR bound. We then propose data regeneration and reconstruction algorithms for the H-MSR code in both error-free network and hostile network. Theoretical evaluation shows that our proposed schemes can detect the erroneous decodings and correct more errors in the hostile network than the RS-MSR code with the same code rate. Our analysis also demonstrates that the proposed H-MSR code has a lower complexity than the RS-MSR code in both code regeneration and code reconstruction.

This paper develops two spectrally efficient orthogonal frequency division multiplexing (OFDM)-based multicarrier transmission schemes: a scheme with message-driven idle subcarriers (MC-MDIS) and another with message-driven strengthened subcarriers (MC-MDSS). The basic idea in MC-MDIS is to carry part of the information, which is named carrier bits, through an idle subcarrier selection while regularly transmitting the ordinary bits on all the other subcarriers. When the number of subcarriers is much larger than the adopted constellation size, higher spectral and power efficiency can be achieved compared with OFDM. The reason is that each idle subcarrier carries more bits than a regular symbol, with no power consumption. Moreover, the existence of idle subcarriers can also decrease possible intercarrier interference between their neighboring subcarriers. In MC-MDSS, the idle subcarriers are replaced by strengthened subcarriers, which, unlike idle subcarriers, can carry both carrier bits and ordinary bits. Therefore, MC-MDSS achieves even higher spectral efficiency than MC-MDIS. Both theoretical analysis and numerical results are provided to demonstrate the performance of the proposed schemes.

This paper considers primary user emulation attacks in cognitive radio networks operating in the white spaces of the digital TV (DTV) band. We propose a reliable AES-assisted DTV scheme, in which an AES-encrypted reference signal is generated at the TV transmitter and used as the sync bits of the DTV data frames. By allowing a shared secret between the transmitter and the receiver, the reference signal can be regenerated at the receiver and used to achieve accurate identification of the authorized primary users. In addition, when combined with the analysis on the autocorrelation of the received signal, the presence of the malicious user can be detected accurately whether or not the primary user is present. We analyze the effectiveness of the proposed approach through both theoretical analysis and simulation examples. It is shown that with the AES-assisted DTV scheme, the primary user, as well as malicious user, can be detected with high accuracy under primary user emulation attacks. It should be emphasized that the proposed scheme requires no changes in hardware or system structure except for a plug-in AES chip. Potentially, it can be applied directly to today's DTV system under primary user emulation attacks for more efficient spectrum sharing.

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.

This paper considers primary user emulation attacks (PUEA) in cognitive radio networks operating in the white spaces of the digital TV (DTV) band. We propose a reliable AES-encrypted DTV scheme, in which an AES-encrypted reference signal is generated at the TV transmitter and used as the sync bytes of each DTV data frame. By allowing a shared secret between the transmitter and the receiver, the reference signal can be regenerated at the receiver and be used to achieve accurate identification of authorized primary users. We analyze the effectiveness of the proposed approach through both theoretical derivation and simulation examples. It is shown that with the AES-encrypted DTV scheme, the primary user can be detected with high accuracy and low false alarm rate under primary user emulation attacks. It should be emphasized that the proposed scheme requires no changes in hardware or system structure except of a plug-in AES chip. Potentially, it can be applied to today's DTV system directly to mitigate primary user emulation attacks, and achieve efficient spectrum sharing.

Linear network coding provides a new communication diagram to significantly increase the network capacity by allowing the relay nodes to encode the incoming messages. However, this communication diagram is fragile to communication errors and node compromising attacks. How to combat errors while maintaining the network efficiency is a challenging research problem. In this paper, we characterize a linear network coding through a series of cascaded linear error-control codes. This representation enables us to determine the independent source of errors in the cascaded network level. It could lead to a successful decoding of the original message and locating of the malicious network nodes. We provide comprehensive theoretical analysis on network coding in both unicast and multicast scenarios. Our research provides a new approach to understand network coding schemes and also a novel methodology to develop network coding schemes that can combat node compromising attacks and locate the malicious nodes.

This paper develops a highly efficient multi-carrier transmission scheme by using message-driven idle subcarrier identification. The basic idea is to carry part of the information, named carrier bits, through idle subcarrier selection while transmitting ordinary bits regularly on all the other subcarriers. When the number of subcarriers is much larger than the adopted constellation size (e.g., in most OFDM systems), a high spectral efficiency as well as power efficiency can be achieved. This is because that the number of carrier bits transmitted through each idle subcarrier is larger than the number of ordinary bits carried by a regular symbol, and all the carrier bits are transmitted with no power consumption through idle subcarrier selection. When applied to the OFDM framework, the proposed scheme can achieve an even higher spectral efficiency than OFDM, while keeping a higher power efficiency.We further enhance its security and error-tolerance using secure subcarrier assignment, secure symbol mapping and bit vector rearrangement. Both theoretical analysis and numerical results are provided to demonstrate the performance of the proposed scheme.

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.

This is part II of a two-part paper that explores efficient anti-jamming system design based on message-driven frequency hopping (MDFH). In Part I, we point out that under disguised jamming, where the jammer mimics the authorized signal, MDFH experiences considerable performance losses like other wireless systems. To overcome this limitation, we propose an anti-jamming MDFH scheme (AJ-MDFH), which enhances the jamming resistance of MDFH by enabling shared randomness between the transmitter and the receiver using an AES generated ID sequence transmitted along the information stream. In part II, using the arbitrarily varying channel (AVC) model, we analyze the capacity of MDFH and AJ-MDFH under disguised jamming. We show that under the worst case disguised jamming, as long as the secure ID sequence is unavailable to the jammer (which is ensured by AES), the AVC corresponding to AJ-MDFH is nonsymmetrizable. This implies that the deterministic capacity of AJ-MDFH with respect to the average probability of error is positive. On the other hand, due to lack of shared randomness, the AVC corresponding to MDFH is symmetric, resulting in zero deterministic capacity. We further calculate the capacity of AJ-MDFH and show that it converges as the ID constellation size goes to infinity.

This is Part I of a two-part paper that considers anti-jamming system design in wireless networks based on message-driven frequency hopping (MDFH), a highly efficient spread spectrum technique. In this paper, we first analyze the performance of MDFH under hostile jamming. It is observed that while MDFH is robust under strong jamming, it experiences considerable performance losses under disguised jamming from sources that mimic the true signal. To overcome this limitation, we propose an anti-jamming MDFH (AJ-MDFH) system. The main idea is to transmit a secure ID sequence along with the information stream. The ID sequence is generated through a cryptographic algorithm using the shared secret between the transmitter and the receiver, it is then exploited by the receiver for effective signal extraction. It is shown that AJ-MDFH can effectively reduce the performance degradation caused by disguised jamming, and is also robust under strong jamming. In addition, we extend AJ-MDFH to the multi-carrier case, which can increase the system efficiency and jamming resistance significantly through jamming randomization and frequency diversity, and can readily be used as a collision-free multiple access system. Part II of the paper focuses on the capacity analysis of MDFH and AJ-MDFH under disguised jamming.

Along with the advent of reconfigurable radios, hostile jamming is no longer limited to military applications, but has become a serious threat for civilian wireless communications, where OFDM has been identified as one of the most efficient transmission technologies. In this paper, we consider reliable transmission of OFDM systems under multi-tone jamming. We propose to enhance the jamming resistance of OFDM through symbol level precoding. Our approach is to find the optimal precoder and decoder that can minimize the MSE between the transmitted and the estimated symbols, subject to a given transmit power constraint. Closed-form solutions are derived, and further demonstrated through simulation examples. It is observed that adding controlled redundancy at symbol level is an effective way to mitigate hostile jamming in OFDM systems.

While linear network coding can improve the throughput significantly in network environment with little additional computational overhead, it is fragile to communication errors and node compromising attacks. To combat the errors in network coding, both error-detection and error-correction based schemes have been proposed. In this paper, we provide a novel methodology to characterize linear network coding through error-control coding. Our main idea is to represent each linear network coding with an error-control coding. We provide comprehensive theoretical analysis on the relationships between linear network coding and error-control coding in both unicast and multicast scenarios. We find that these two codes are essentially identical in algebraic aspects. Our research provides a new approach to understand network coding schemes and also a novel methodology to develop network coding schemes that can combat communication errors and also node compromising attacks.

SEAR is a novel secure and energy aware routing protocol proposed to address the energy balance and routing security through a balanced energy consumption and probabilistic random walking. Recently, a quantitative security measurement scheme for source-location privacy based on source-location disclosure index (SDI) and source-location space index (SSI) has been proposed. In this paper, we first derive a numerical formula to quantitatively estimate the routing efficiency through the number of routing hops for a given routing security level. We then consider the reverse problem: For a given routing cost factor, how to determine the maximum security level for a message to be transmitted. Our simulation results demonstrate that the theoretical results provide a very tight estimation of the actual routing hops for various security parameters. Finally, we prove that the SEAR scheme can provide provable security under the quantitative security measurement criteria.

This paper considers cooperative sensing in cognitive networks under Spectrum Sensing Data Falsification attack (SSDF) in which malicious users can intentionally send false sensing information. One effective method to deal with the SSDF attack is the q-out-of-m scheme, where the sensing decision is based on q sensing reports out of m polled nodes. The major limitation with the q-out-of-m scheme is its high computational complexity due to exhaustive search. In this paper, we prove that for a fixed percentage of malicious users, the detection accuracy increases almost exponentially as the network size increases. Motivated by this observation, as well as the linear relationship between the scheme parameters and the network size, we propose a simple but accurate approach that significantly reduces the complexity of the q-out-of-m scheme. The proposed approach can easily be applied to the large scale networks, which can be much more reliable under malicious attacks.

This paper considers spectrally efficient anti-jamming system design based on code-controlled frequency hopping. Unlike conventional frequency hopping systems where hopping patterns are determined by preselected pseudo-random sequences, in the proposed scheme, part of source information is passed through a block encoder, and used to determine the selected frequency bands for signal transmission. By exploiting the redundancy provided by the block coding, the receiver can retrieve the hopping pattern without a priori knowledge. Through an integrated decoding-and-encoding process, the receiver can also perform partial jamming detection. It is observed that due to the combination of dynamic frequency hopping and coding diversities, the proposed system can effectively mitigate random jamming interference while maintaining high spectral efficiency.

This paper considers channel and power allocation for cognitive radio (CR) networks. We assume that the total available spectrum is divided into several bands, each consisting of a group of channels. A centralized base station, enabled by spectrum sensing, is assumed to have the knowledge of all vacant channels, which will be assigned to various CRs according to their requests. The objective of resource allocation is to maximize the sum data rate of all CRs. Since the activities of primary users may cause heavy traffic in some bands while leaving other bands idle, load balancing is first performed to equalize the traffic. A multi-level subset sum algorithm as well as a simpler greedy algorithm is proposed to achieve excellent load balancing performance. After that, an algorithm incorporated with constant-power water filling is proposed to maximize the sum data rate. Simulation results are presented to illustrate the effectiveness of the proposed algorithms.

This paper considers spectrally efficient anti-jamming system design based on coded three-dimensional (3D) frequency hopping. Unlike conventional frequency hopping systems where the hopping pattern is determined by a preselected pseudo-random sequence, in the proposed scheme, part of the information is passed through a block encoder, and used to determine the selected frequency bands for signal transmission. The receiver is designed to retrieve the hopping pattern without a priori knowledge. The proposed system can effectively mitigate random jamming interference while maintaining high spectral efficiency. Simulation results are provided to illustrate the system's jamming mitigation performance.

This paper considers spectrally efficient anti-jamming system design based on message-driven frequency hopping (MDFH). As a highly efficient frequency hopping scheme, MDFH is particularly robust under strong jamming. However, disguised jamming from sources of similar power strength can cause performance losses. To overcome this drawback, in this paper, we propose an anti-jamming MDFH (AJ-MDFH) system. The main idea is to transmit an ID sequence along with the information stream. The ID sequence is generated through a cryptographic algorithm using the shared secret between the transmitter and the receiver. It is then exploited by the receiver for effective signal detection and extraction. It is shown that AJ-MDFH can effectively reduce the performance degradation caused by disguised jamming. Moreover, AJ-MDFH can be extended to a multi-carrier scheme for higher spectral efficiency and/or more robust jamming resistance. Simulation examples are provided to demonstrate the performance of the proposed approaches.

This paper considers spectrally efficient antijamming system design based on message-driven frequency hopping (MDFH). As a highly efficient frequency hopping scheme, MDFH is particularly robust under strong jamming. However, disguised jamming from sources of similar power strength can cause performance losses. To overcome this drawback, in this paper, first, we propose an anti-jamming MDFH (AJ-MDFH) system. The main idea is to transmit an ID sequence along with the information stream. The ID sequence is generated through a cryptographic algorithm using the shared secret between the transmitter and the receiver. It is then exploited by the receiver for effective signal detection and extraction. It is shown that AJ-MDFH is robust under strong jamming, and can effectively reduce the performance degradation caused by disguised jamming. Second, we extend AJ-MDFH to a multicarrier scheme, named MC-AJ-MDFH, which can increase the system efficiency and jamming resistance significantly through jamming randomization and enriched frequency diversity. Moreover, by assigning different carriers to different users, MC-AJ-MDFH can readily be used as a collision-free multiple access system. Simulation examples are provided to demonstrate the performance of the proposed approaches.

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.

Wireless sensor networks (WSN) have the potential to be widely used in many areas for unattended event monitoring. Mainly due to lack of a protected physical boundary, wireless communications are vulnerable to unauthorized interception and detection. Privacy is becoming one of the major issues that jeopardize the successful deployment of wireless sensor networks. While confidentiality of the message can be ensured through content encryption, it is much more difficult to adequately address the source-location privacy. For WSN, source-location privacy service is further complicated by the fact that the sensor nodes consist of low-cost and low-power radio devices, computationally intensive cryptographic algorithms (such as public-key cryptosystems) and large scale broadcasting-based protocols are not suitable for WSN. In this paper, we propose a scheme to provide both content confidentiality and source-location privacy through routing to a randomly selected intermediate node (RRIN). While being able to provide source-location privacy for WSN, our simulation results also demonstrate that the proposed scheme is very efficient and can be used for practical applications.

This paper considers spectrally efficient anti-jamming system design based on message-driven frequency hopping (MDFH). We first analyze the performance of the MDFH system under different jamming scenarios. It is observed that MDFH is particularly robust under strong jamming. However, it experiences a performance bottleneck under disguised jamming, for which the jamming power is close to the signal power. To overcome this drawback, we propose an anti-jamming MDFH (AJ-MDFH) system. The main idea is to transmit an ID sequence along with the information stream. The ID sequence is generated through a cryptographic algorithm using the shared secret between the transmitter and the receiver. It is then exploited by the receiver for effective signal detection and extraction. It was shown that AJ-MDFH is robust under strong jamming, and can effectively reduce the performance degradation caused by disguised jamming. Simulation examples are provided to demonstrate the performance of the proposed approaches.

Communication privacy is becoming an essential security requirement for mission critical communications and communication infrastructure protection. This is especially true for mobile ad hoc networks (MANETs) due to mobility of the communication nodes and the nature of wireless communications. Existing research in privacy-preserving communications can largely be divided into two categories: cryptosystem-based techniques and broadcasting-based techniques. The cryptosystem-based techniques include mix-based systems and secure multiparty computation-based systems, originating from mixnet and DC-net respectively. All mix-based approaches require a trusted third party to provide the mix and are not quite feasible in MANET. However, DC-net based approaches suffer from transmission collision problem that cannot be easily resolved practically. Broadcasting based schemes provide communication privacy by mixing the real messages with dummy packets so that it is infeasible for the adversaries to identify the real packets and track the message source. However, the transmission of dummy messages not only increases the energy consumption significantly, but also increases the network collisions and decreases the packet delivery ratio. In this paper, we first propose a novel unconditionally secure source anonymous message authentication scheme (SAMAS) that enables messages to be released without relying on any trusted third parties. While providing source privacy, the proposed scheme can also provide message content authenticity. We then propose a novel communication protocol for MANET that can ensure communication privacy of both communication parties and their end-to-end routing. The proposed protocol can be used for critical infrastructure protection and secure file sharing. The security analysis demonstrates that the proposed protocol is secure against various attacks. The theoretical analysis and simulation show that the proposed scheme is efficient and can ensure high message delivery ratio.

This paper considers spectrally efficient frequency hopping (FH) system design. Relying on time-frequency diversity over large spectrum, FH systems are robust against hostile jamming interference. However, the spectral efficiency of existing FH systems is very low due to inappropriate use of the total available bandwidth. To improve the system capacity, in this paper, we propose an innovative message-driven frequency hopping (MDFH) scheme. Unlike in traditional FH where the hopping pattern of each user is determined by a pre-selected pseudo-random (PN) sequence, inMDFH, part of the message stream will be acting as the PN sequence, and transmitted through hopping frequency control. As a result, system efficiency is increased significantly since additional information transmission is achieved at no extra cost on either bandwidth or power. We further enhance MDFH by allowing simultaneous transmissions over multiple frequency bands. The enhanced MDFH scheme, named E-MDFH, can achieve high spectral efficiency, and can readily be extended to an FH-based collision-free multiple access scheme. Quantitative performance analysis on the proposed schemes demonstrates that: transmission through hopping frequency control essentially introduces another dimension to the signal space, and the corresponding coding gain can increase the system efficiency by multiple times.

Originally developed for secure communications in military applications, frequency hopping systems possess anti-jamming and anti-interception features by exploiting time- frequency diversity over large spectrum. However, the spectral efficiency of existing FH systems is very low due to inappropriate use of the total available bandwidth. To improve the system capacity, in this paper, we propose an innovative message-driven frequency hopping (MDFH) scheme. Unlike in traditional FH systems where the hopping pattern of each user is determined by a pre-assigned pseudo-random (PN) sequence, in MDFH, part of the message stream will be acting as the PN sequence for hopping frequency selection. Essentially, transmission of information through hopping frequency control introduces another dimension to the signal space, and the corresponding coding gain increases system efficiency by multiple times. The MDFH scheme can be further enhanced by allowing simultaneous transmissions over multiple frequency bands. Including both MDFH and OFDM as special cases, the enhanced MDFH scheme, named E-MDFH, can achieve high spectral efficiency while providing excellent design flexibility. E-MDFH can readily be extended to a FH-based collision-free multiple access scheme.

Communication anonymity is becoming an increasingly important, or even indispensable security requirement for many applications. The existing research in anonymous communications can largely be divided into two categories: mix- based systems and secure multi-party computation-based systems, originating from mixnet and DC-net respectively. However, they either cannot provide provable anonymity, or suffer from transmission collision problem. In this paper, we first propose a novel unconditionally secure source anonymous message authentication code (SA-MAC) that can be applied to any messages without relying on any trusted third parties. While ensuring message sender anonymity, SM-MAC can also provide message content authenticity. We then propose a novel communication protocol that can hide the senders and the receivers from each other, and thus can be used for secure file sharing. The security analysis demonstrates that the proposed protocol is secure against various attacks. Our analysis also shows it is efficient and practical.

Frequency hopping systems have been widely used in military communications to prevent hostile jamming, interception and detection. In traditional frequency hopping (FH) systems, the transmitter hops in a pseudo-random manner among available frequencies according to a pre-specified algorithm, and the receiver operates accordingly in exact synchronization with the transmitter's hopping pattern. In multiple access systems, a collision may happen when more than one users transmit in the same frequency band simultaneously. Two major limitations with the conventional frequency hopping systems are: strict requirement on frequency acquisition/synchronization, and very low spectral efficiency due to inefficient utilization of the available bandwidth. In this paper, we introduce a new concept - collision-free frequency hopping (CFFH). Based on the OFDM framework and the secure subcarrier assignment algorithm, the proposed CFFH system can achieve high information capacity through collision-free multiple access, and can successfully resolve the strict synchronization limitation. At the same time, as each user still transmits through a pseudo-random frequency hopping scheme, CFFH can maintain the inherent anti-jamming, anti-interception security features of the conventional FH system.

Frequency hopping systems have been widely used in military communications to prevent hostile jamming, interception and detection. In traditional frequency hopping (FH) systems, hopping frequency selection at the transmitter end is controlled by a pseudo-random code sequence, and the receiver operates accordingly in exact synchronization with the transmitters hopping pattern. In an effort to meet the ever increasing requirement on information capacity and reduce the burden of synchronization, in this paper, an innovative message-driven frequency hopping (MDFH) system is proposed. By embedding part of information into the process of hopping frequency selection, the spectral efficiency of the FH system can be significantly improved. Quantitative analysis on the proposed scheme is presented to demonstrate its superior performance and enhanced security features.

This letter considers average input-output distortion minimization through joint optimization of source index assignment and modulation design. First, we derive the general optimization criterion and discuss simultaneous minimization of bit-error rate (BER) and distortion. Second, we propose a novel source-aware information transmission approach by exploiting the nonuniformity in Gray-coded constellations. The proposed approach makes it possible for simultaneous BER and distortion minimization and outperforms the existing schemes with big margin when channel coding is involved. Third, optimal source-aware constellation design for minimum distortion is proposed by incorporating the source information into constellation design. The power efficiency of the proposed source-aware nonuniform transmission scheme makes it attractive for any digital systems with analog inputs, particularly for systems with tight power constraints such as wireless sensor networks and space communications

In this paper, a novel medium access control (MAC) protocol, name hybrid ALOHA, is proposed to improve the system performance by allowing collision-free channel estimation and simultaneous multiuser data transmission. The idea behind it is to design an MAC protocol that is in favor of the physical (PHY) layer information transmission, and the improved PHY layer, in turn, can improve the MAC performance. Using the general multipacket reception (MPR) model as an interface between the MAC layer and the PHY layer, the hybrid ALOHA protocol is analyzed in terms of throughput, stability, as well as delay behavior. Significant performance improvement is observed in comparison with the traditional ALOHA either with the MPR model or with the collision model.

This paper aims to relax the restrictive conditions on blind MIMO channel identification by exploiting structured transmitter design. First, a simple structured transmit delay scheme is proposed, in which each antenna transmits an independent zero-padded data stream. Secondly, a second-order statistics based blind channel estimation algorithm is developed. Simulation results demonstrate that the proposed approach is robust in MIMO environment, even if when there are common zeros among the sub-channels.

In this paper, a channel estimation and multiuser detection method is presented for uplink MC-CDMA systems in time-varying environment. Based on the fact that the channel coefficients of two successive symbols are highly correlated, joint channel tracking and signal detection are carried out iteratively. A major contribution of the proposed approach is that it enables robust error propagation control, and is capable of detecting and tracking abrupt channel changes effectively. Simulation examples demonstrate the robustness of the proposed algorithms.

In this paper, a joint channel estimation and multiuser detection method is presented for uplink MC-CDMA systems in time-varying environment. Unlike the conventional channel tracking schemes which generally need to insert pilot bits in every OFDM symbol, in the proposed approach, only one pilot symbol is required at the beginning of each data frame. Based on the fact that the channel coefficients of two successive symbols are highly correlated, subsequent channel tracking and signal detection are carried out iteratively. A major contribution of the proposed approach is that it enables robust error propagation control, and is capable of detecting and tracking abrupt channel changes effectively. Simulation examples demonstrate the robustness of the proposed algorithms.

In this paper, space-time transmit diversity is exploited to relax the restrictive blind channel identifiability constraints for multiple-input multiple-output (MIMO) systems. First, a simple structured transmit delay diversity scheme is proposed. Unlike existing transmit diversity schemes, in which different antennas transmit delayed, zero-padded, or time reversed versions of the same signal, in the proposed scheme, each antenna transmits an independent data stream and therefore promises higher data rate. Secondly, a second-order statistics based blind channel estimation algorithm is developed for MIMO systems with the structured transmit diversity. The proposed approach involves no pre-equalization, has no limitations on channel zero locations and does not require the MIMO channel matrix to be irreducible. Simulation results demonstrate the robustness and effectiveness of the proposed scheme.

As shown in Daemen, J. et al, (1999) and Zhang, M. et al, (2000), the physical layer built-in information privacy of the conventional CDMA system, provided by pseudo-random scrambling, is far from adequate and can be improved by applying cryptographic techniques in the scrambling process. Motivated by the fact that after scrambling, chips spread from one symbol still cluster together and could be fragile to strong burst errors and fading effects, in this paper, a chip-level secure interleaving procedure is proposed to improve the system performance while enhancing the security measure. More specifically, the AES algorithm is combined with block interleaving. It should be noted that interleaving is in fact a special case of scrambling. Security analysis is provided to demonstrate the effectiveness of the proposed secure interleaving scheme under exhaustive search attack. Simulation examples are presented to illustrate the robustness of chip-level interleaving over channels with severe fading or strong burst errors.

Wireless communications often exploit guard intervals between data blocks to reduce inter-block-interference in frequency selective channels. Here we propose a dual-branch transmission scheme that utilizes guard intervals for blind channel estimation and equalization. Unlike existing diversity schemes, in which different antennas transmit delayed, zero-padded, or time reversed versions of the same signal, we use two antennas to transmit independent data streams. It is shown that for systems with two transmit antennas and one receive antenna, blind channel estimation can be carried out based only on the second order statistics of the symbol rate sampled channel output. The proposed approach involves no pre-equalization and has no requirement on channel coprimeness. It is also shown that in combination with the T-BLAST structure and turbo coding, significant improvement can be achieved in the overall system performance.

In this letter, blind detection of multirate code-division multiple-access (CDMA) signals is revisited by exploiting a fast converging blind deconvolution approach-the super-exponential algorithm. Here, only the desired user's spreading code is assumed to be known, while its transmission delay may be unknown. Compared with existing higher order statistics-based blind multiuser detectors in a paper by Ma and Tugnait, when the system actually converges to the desired user (generally needs SNR>10 dB for both existing methods and the proposed approach), the proposed approach can achieve much better performance with significantly faster convergence speed.

Pseudo-random sequences with good correlation properties and large linear complexity are widely used in code-division multiple-access (CDMA) communication systems and cryptology for reliable and secure information transmission. In this paper sequences with long period, large complexity, balance statistics and low correlation properties are constructed from addition of m-sequences with pairwise-prime periods (AMPP). Using m-sequences as building blocks, the proposed method proved to be an efficient and flexible approach to construct long period pseudo-random sequences with desirable properties from short period sequences. Applying the proposed method to two Gold sequences, a signal set ((2/sup n/ - 1) (2/sup m/ - 1), (2/sup n/ + 1)(2/sup m/ + 1), (2/sup (n+1)/2/ + 1)(2/sup (m+1)/2/ + 1)) is constructed.

This paper considers blind channel identification and signal separation in long-code CDMA systems. First, by modeling the received signals and MUIs as cyclostationary processes with modulation introduced cyclostationarity, long-code CDMA system is characterized using a time-invariant system model. Secondly, based on the time-invariant model, multistep linear prediction method is used to reduce the intersymbol interference introduced by multipath propagation, and channel estimation can then be performed using the non-constant modulus precoding technique and the matrix pencil approach. After channel estimation, equalization is carried out using cyclic Wiener filter. Simulation examples arc provided to illustrate the proposed approaches.

In this letter, code-constrained super-exponential algorithms (CSEA) are presented for blind detection of asynchronous short-code direct-sequence code-division multiple-access signals over multipath channels. Constrained SEA leads to the extraction of the desired user whereas unconstrained SEA leads to the extraction of any one of the actives users. The results are further improved by following the constrained SEA by unconstrained SEA. Convergence of the constrained SEA is proved and simulation examples are provided to illustrate the proposed approaches.

For long code DS-CDMA systems, where the spreading codes are aperiodic and extending over a large number of data symbols, chip-rate sampled signals and MUI (multiuser interferences) are generally modeled as time-varying vector processes. This complicates the application of traditional blind multiuser detectors, since consistent estimation of the needed signal statistics can not be obtained by time-averaging over received data record. In this paper, we propose an equivalent time-invariant system model for long code CDMA, in which the received signals and MUI are modeled as cyclostationary processes with modulation introduced cyclostationarity. Based on knowledge of the desired user's code sequences, channel estimation is carried out using a frequency domain subspace method.

We revisit the recently presented code-constrained super-exponential algorithm (SEA) (Li-Tugnait, 2001) for blind detection. of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals over multipath channels. Convergence of the algorithm is proved by showing that the constrained SEA is a special case of “undermodeled” SEA which is equivalent to a gradient search algorithm. Given appropriate initialization, constrained SEA can lead to the extraction of the desired user, whereas unconstrained SEA leads to the extraction of any one of the actives users.

A code-constrained inverse filter criterion (CC-IFC) based approach was presented Tugnait and Li (see Proc. IEEE 2000 ICASSP, p.V-246-64, Istanbul, Turkey, June 2000) for blind-detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. The equalizer was determined by maximizing the magnitude of the normalized fourth cumulant of inverse filtered (equalized) data with respect to the equalizer coefficients subject to the fact that the equalizer lies in a subspace associated with the desired user's code sequence. In this paper we analyze the identifiability properties of the approach of Tugnait and Li. Global maxima and some of the local maxima of the cost function are investigated. These aspects were not discussed by Tugnait and Li. More extensive simulation comparisons with existing approaches are also provided.

Code-constrained super-exponential algorithms (SEA) are presented for blind detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals over multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. By exploiting the fact that the equalizer always lies in a subspace associated with the desired user's code sequence, a projection operator is imposed at every iteration so that the algorithm can extract the desired user. The results are further improved by following the constrained SEA by unconstrained SEA. An illustrative simulation example is provided.

A multistep linear prediction approach is presented for blind channel estimation, multiuser interference (MUI) suppression, and detection of asynchronous short-code direct sequence code division multiple access signals in multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. We exploit the previously proposed multistep linear prediction approach for blind multiple-input multiple-output channel estimation in conjunction with the structure imposed by the desired user's spreading code sequence. With the knowledge of the desired user's code sequence, only the second-order statistics of the data are needed under certain sufficient conditions on the underlying multiuser MIMO transfer function. Based on the desired user's channel estimate, a linear minimum mean square error filter is designed for simultaneous equalization and MUI suppression. Three illustrative simulation examples are presented.

A code-aided constant modulus algorithm (CMA) based approach is presented for blind detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in intersymbol interference (ISI)/multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. A linear equalizer is designed by minimizing the Godard/CMA cost function of the equalizer output with respect to the equalizer coefficients subject to the fact that the equalizer lies in a subspace associated with the desired user's code sequence. Constrained CMA leads to the extraction of the desired user's signal whereas unconstrained minimization leads to the extraction of any one of the active users. The results are further improved by using unconstrained CMA initialized by the results of the code-aided CMA. Identifiability properties of the approach are analyzed. Illustrative simulation examples are provided.

A multistep linear prediction approach is presented for blind channel estimation and detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. We exploit the previously proposed multistep linear prediction (MSLP) approach for blind multiple-input multiple-output (MIMO) channel estimation in conjunction with the structure imposed by the desired user's spreading code sequence. With the knowledge of the desired user's code sequence, only the second-order statistics of the data are needed under certain sufficient conditions on the underlying multiuser MIMO transfer function. An illustrative simulation example is provided.

A code-constrained inverse filter criteria based approach is presented for blind detection of asynchronous short-code DS-CDMA (direct sequence code division multiple access) signals in multipath channels. Only the spreading code of the desired user is assumed to be known; its transmission delay may be unknown. We focus on maximization of the normalized fourth cumulant of inverse filtered (equalized) data w.r.t. the equalizer coefficients subject to the equalizer lying in a subspace associated with the desired user's code sequence. Constrained maximization leads to extraction of the desired user's signal whereas unconstrained maximization leads to the extraction of any one of the existing users. An illustrative simulation example is provided.