Fanggang Wang

Specific Emitter Identification via Hilbert–Huang Transform in Single-Hop and Relaying Scenarios

In this paper, we investigate the specific emitter identification (SEI) problem, which distinguishes different emitters using features generated by the nonlinearity of the power amplifiers of emitters. SEI is performed by measuring the features representing the individual specifications of emitters and making a decision based on their differences. In this paper, the SEI problem is considered in both single-hop and relaying scenarios, and three algorithms based on the Hilbert spectrum are proposed. The first employs the entropy and the first- and second-order moments as identification features, which describe the uniformity of the Hilbert spectrum. The second uses the correlation coefficient as an identification feature, by evaluating the similarity between different Hilbert spectra. The third exploits Fishers discriminant ratio to obtain the identification features by selecting the Hilbert spectrum elements with strong class separability. When compared with the existing literature, we further consider the identification problem in a relaying scenario, in which the fingerprint of different emitters is contaminated by the relays fingerprints. Moreover, we explore the identification performance under various channel conditions, such as additive white Gaussian noise, non-Gaussian noise, and fading. Extensive simulation experiments are performed to evaluate the identification performance of the proposed algorithms, and results show their effectiveness in both single-hop and relaying scenarios, as well as under different channel conditions.

Wireless MIMO switching with zero-forcing relaying

A wireless relay with multiple antennas is called a multiple-input-multiple-output (MIMO) switch if it forms a one-to-one mapping from the inputs (uplinks) to the outputs (downlinks). This paper studies the case with N source stations and N destination stations (which may be the same set), so that the mapping is any permutation of the N inputs. Moreover, the switching is achieved by “precode-and-forward”, i.e., the relay precodes the received vector signal by a zero-forcing matrix and transmits it, so that each destination station receives only its desired signal with enhanced noise but no interference. Assuming full channel state information is available at the switch, the design of the zero-forcing precoder for maximizing some performance metric based on the received signal-to-noise ratios is investigated. The problem with two stations is completely solved in closed form in certain cases. In other cases, heuristic algorithms are proposed to optimize the precoder. These algorithms are shown to be near-optimal.

Bidirectional Cellular Relay Network with Distributed Relaying

In this paper, we consider a bidirectional cellular relay network with distributed relays where a single base station exchanges information with multiple independent users through multiple single-antenna relays. We design the transceivers at the base station, the relays, and the users. The related optimization problems are generally non-convex and difficult to solve. In this paper, we propose a unified framework to design the transceiver algorithms based on two criteria, i.e. weighted sum MSE minimization and sum rate maximization. Specifically, we show that the sum rate maximization problem can be converted into an iterative weighted sum MSE minimization problem. Low-complexity iterative algorithms are developed for both weighted sum MSE minimization and sum rate maximization optimization problems. However, the convergence points of the proposed iterative algorithms are sensitive to the initial conditions, especially in the high signal-to-noise ratio (SNR) regime. For this reason, we further derive the high-SNR asymptotically optimal solutions and use them as the initials for the proposed iterative algorithms. Simulation results show that the proposed scheme can approximately double the system throughput, compared to the conventional four-stage transmission schemes.

Fold-based Kolmogorov–Smirnov Modulation Classifier

Modulation classification is crucial in applications such as electronic warfare and interference cancellation. In this letter, a novel feature-based Kolmogorov-Smirnov classifier is proposed for the identification of the modulation formats. The received signal is first preprocessed with a folding operation that helps identify the modulation formats based on their different axes of symmetry. Simulation results show that the performance of the proposed classifier is close to that of the optimal likelihood-based classifier, while its robustness to noise uncertainty is improved and its computational complexity is reduced compared to that of the optimal likelihood-based classifier.

Secure communication via jamming in massive MIMO Rician channels

Jamming eavesdroppers with artificial noise can protect the communication between legitimate users. In this paper, we investigate the jamming design for a massive multiple-input multiple-output (MIMO) transmitter in a Rician fading channel. A generic analytical result on the secrecy outage probability (SOP) is derived to determine a location range of eavesdroppers, where the SOP is reduced by uniformly jamming the eavesdroppers. Then, the optimization of power allocation between messages and artificial noise is investigated for different scenarios. To further decrease the SOP, we propose a directional jamming scheme that can generate jamming signal towards the suspicious area where eavesdroppers can be located. At last, the numerical results validate our conclusion.

Novel Hilbert Spectrum-Based Specific Emitter Identification for Single-Hop and Relaying Scenarios

A novel approach for specific emitter identification using Hilbert spectrum is proposed for both single-hop and relaying scenarios. In particular, two features, i.e., the energy entropy and color moments, are extracted from the Hilbert spectrum of the signal of interest as identification features. The spectrum is obtained through the Hilbert-Huang transform, which is a powerful tool for the analysis of non-linear and nonstationary signals by decomposing them into a set of intrinsic mode functions. The identification task is solved by applying the support vector machine. We further extend the identification problem to a relaying scenario, in which the fingerprint of different emitters may be contaminated by the relays fingerprints. To the best of our knowledge, this case has not been investigated so far in the literature. At last, simulation results validate that the proposed approach can effectively cope with the specific emitter identification problems in both single-hop and relaying scenarios.

Transceiver Design for Multi-Pair Two-Way Relay Networks with Analogue Network Coding

In this letter, we consider multi-pair two-way relay networks where multiple user pairs simultaneously exchange information via a common multi-antenna relay station. We develop a relaying protocol based on analogue network coding to avoid inter-pair interference in such networks. The user pair selection and power allocation for active user pairs are developed and integrated in the design to enhance the system sum rate. Numerical results show that our proposed design can significantly increase the sum rate compared with the existing scheme.

Wireless MIMO switching with MMSE relaying

A wireless relay which forms a one-to-one mapping from the inputs (uplinks) to the outputs (downlinks) is called a multiple-input-multiple-output (MIMO) switch. The MIMO switch carries out precode-and-forward, where all users send their signals in the uplink and then the MIMO switch precodes the received vector signal for broadcasting in the downlink. Ideally, each user employs a receive filter to recover its desired signal from one other user with no or little interference from other users. We propose a joint design of the precoder and the receive filters to achieve the minimum-mean-square-error (MMSE), assuming full channel state information is available at the relay. Our results indicate that the proposed MMSE relaying scheme outperforms the existing ZF/MMSE schemes.

Local and cooperative spectrum sensing via Kuiper's test

A novel Kuipers test-based spectrum sensing approach in cognitive radio is proposed in this paper. The Kuiper-based detector is a computationally efficient spectrum sensing algorithm, which exploits the maximum positive and negative deviations between the empirical cumulative distribution function (cdf) of received samples and that of noise signals as the test statistic, and is insensitive to the model mismatch. The Kuiper-based detector is further considered in the cooperative detection, where an improved fusion rule is adopted. Simulation results validate that compared with the existing detectors, the Kuiper-based detector provides superior detection performance and robustness with low computational complexity.

Transceiver Design for Multi-User Cellular Two-Way Relay Networks

In this paper, we consider a general cellular two-way relay network, where a common multi-antenna relay station (RS) helps multiple base stations (BSs) to exchange messages with their served users simultaneously. This network model includes the thoroughly studied two-way relay (TWR) networks, multi-pair TWR networks and multi-user TWR cellular networks as special cases. We first develop a transceiver design for such a network under interference free constraints. The power allocation at the RS, BSs and users is then investigated to maximize the system sum rate. The performance of the proposed algorithm is evaluated through numerical examples. The results show that the proposed design outperforms the existing ones for those special TWR networks, and the sum rate is improved significantly through the proposed power allocation method compared to equal power allocation.