Mao-Zhong Song

Bio: Mao-Zhong Song is an academic researcher from Nanjing University. The author has contributed to research in topics: Computer science & Delta modulation. The author has an hindex of 1, co-authored 1 publications receiving 105 citations.

Dual-Beam Directional Modulation Technique for Physical-Layer Secure Communication

Abstract: A dual-beam directional modulation (DM) technique is proposed for physical-layer secure communication. The main idea is that the in-phase and quadrature (IQ) baseband signals are used to excite two different antennas unlike a traditional transmitter, which is used to excite the same antenna. In this way, the constellation points of the transmit signal maintain their positions as traditional digital modulation signal at the desired direction, but scramble in the phase at the undesired directions because of the transmit signal both modulated at the baseband and the antenna level. Simulation results show that this dual-beam DM technique offers a security transmission method for wireless communication.

Position‐sensitivity security transmission with orbital angular momentum directional modulation based on frequency diverse array

Abstract: The position‐sensitivity security communication scheme with orbital angular momentum (OAM) directional modulation (DM) beam pattern generated by the uniform circular frequency diverse array (FDA) is proposed. The transmitter employs FDA antennas to generate dual‐mode range‐dependent OAM beam and the direction information of OAM beam is modulated into the signal. The designed signal with random frequency offset excites the element of the uniform circular FDA to generate orthogonal OAM signals in the desired position. In the undesired position, the intensity pattern and the phase front of the radio beam vary randomly with the digital sequence transmission, which can make eavesdropping difficult. Since the modulation waveform has position‐dependent, the signal can be purposely distorted in undesired positions to provide transmission security for the legitimate user. The composite dual‐mode OAM signal makes it more difficult for eavesdroppers to demodulate correct messages. The receiver with a single antenna employs the phase compensation and helical phase factor to restore the correct digital signal in the desired position. Numerical results show that the space position‐sensitivity OAM‐DM technology based on FDA offers a security transmission scheme.

Inter-satellite Pseudorange Difference Indoor Positioning Using Simulator Pseudolites

Abstract: The positioning system combining pseudolite technology and the navigation signal simulator is proposed to solve the problem that the indoor satellite navigation signal is lost. We adopted the simulator to generate the virtual orbit pseudolite and broadcast satellite signals through four indoor antennas. The simulator pseudolite is designed with Inclined Geosynchronous Orbit (IGSO) satellite to reduce the folding error caused by the fact that the simulator pseudolite, indoor antenna and receiver are not in a straight line. Furthermore, the observation equation is constructed using the position of the indoor transmitting antenna and the arrival receiver pseudo-range difference as the reference, which time difference of arrival (TDOA) localization algorithm is employed to further eliminate the fold line error. Experiments show that the position results of about 93.6% cases are better than 1m.

UWB channel modeling and simulation with continuous frequency response

Abstract: Ultra-wideband (UWB) technology is a prospective technology for high-rate transmission and accurate localization in the future communication systems. State-of-art channel modeling approaches usually divide the UWB channel into several sub-band channels and model them independently. By considering frequency-dependent channel parameters, a novel analytical UWB channel model with continuous frequency response is proposed. The composite effect of all frequency components within the UWB channel on the channel impulse response (CIR) of delay domain is derived based on the continuous channel transfer function (CTF) of frequency domain. On this basis, a closed-form simulation model for UWB channels and geometry-based parameter calculation method are developed, which can guarantee the continuity of channel characteristics on the frequency domain and greatly reduce the simulation complexity. Finally, the proposed method is applied to generate UWB channel with 2 GHz bandwidth at sub-6GHz and millimeter wave (mmWave) bands, respectively. The channel measurements are also carried out to validate the proposed method. The simulated CIR and power gain are shown to be in good agreement with the measurement data. Moreover, the comparison results of power gain and Doppler power spectral density (DPSD) show that the proposed UWB channel model achieves a good balance between the simulation accuracy and efficiency.

Vortex Wave Directional Modulation With Time-Dependent Phase Offset FDA

Abstract: A direction-range-time dependent vortex wave directional modulation (DM) scheme based on the frequency diverse array (FDA) is proposed for secure transmission. We design the random frequency offset for the array element in a circular arc FDA, which generates the quasi-helical phase front and the irregular phase front at the specific range. In order that the time-variance phase front can maintain the helical phase characteristics at the desired range, according to the designed frequency offset function, we design a DM excitation signal with the specific time-variance phase offset for each array element. The direction-range-time dependent phase pattern is modulated into the vortex signal constellation for the desired transmission. Theoretical analyses and numerical simulations validate the effectiveness of our proposed approach with no artificial noise.

A Survey on Multiple-Antenna Techniques for Physical Layer Security

Abstract: As a complement to high-layer encryption techniques, physical layer security has been widely recognized as a promising way to enhance wireless security by exploiting the characteristics of wireless channels, including fading, noise, and interference. In order to enhance the received signal power at legitimate receivers and impair the received signal quality at eavesdroppers simultaneously, multiple-antenna techniques have been proposed for physical layer security to improve secrecy performance via exploiting spatial degrees of freedom. This paper provides a comprehensive survey on various multiple-antenna techniques in physical layer security, with an emphasis on transmit beamforming designs for multiple-antenna nodes. Specifically, we provide a detailed investigation on multiple-antenna techniques for guaranteeing secure communications in point-to-point systems, dual-hop relaying systems, multiuser systems, and heterogeneous networks. Finally, future research directions and challenges are identified.

Antenna Subset Modulation for Secure Millimeter-Wave Wireless Communication

Abstract: The small carrier wavelength at millimeter-wave (mm-Wave) frequencies enables featuring a large number of co-located antennas. This paper exploits the potential of large antenna arrays to develop a low-complexity directional modulation technique, Antenna Subset Modulation (ASM), for point-to-point secure wireless communication. The main idea in ASM is to modulate the radiation pattern at the symbol rate by driving only a subset of antennas in the array. This results in a directional radiation pattern that projects a sharply defined constellation in the desired direction and expanded further randomized constellation in other directions. Two techniques for implementing ASM are proposed. The first technique selects an antenna subset randomly for every symbol. While randomly switching antenna subsets does not affect the symbol modulation for a desired receiver along the main direction, it effectively randomizes the amplitude and phase of the received symbol for an eavesdropper along a sidelobe. Using a simplified statistical model, an expression for the average uncoded symbol error rate (SER) is derived as a function of the observation angle. To overcome the problem of large sidelobes in random antenna subset switching, the second technique uses an optimized antenna subset selection procedure based on simulated annealing to achieve superior performance compared with random selection. Numerical comparisons of the SER performance and secrecy capacity of the proposed techniques against those of conventional array transmission are presented to highlight the potential of ASM.

A Vector Approach for the Analysis and Synthesis of Directional Modulation Transmitters

Abstract: In order to formalize and extend on previous ad-hoc analysis and synthesis methods a theoretical treatment using vector representations of directional modulation (DM) systems is introduced and used to achieve DM transmitter characteristics. An orthogonal vector approach is proposed which allows the artificial orthogonal noise concept derived from information theory to be brought to bear on DM analysis and synthesis. The orthogonal vector method is validated and discussed via bit error rate (BER) simulations.

Directional Modulation Based on 4-D Antenna Arrays

Abstract: Four-dimensional (4-D) antenna arrays are formed by introducing a fourth dimension, time, into traditional antenna arrays. In this paper, a time-modulated 4-D array with constant instantaneous directivity is proposed for directional modulation. The main idea is that the 4-D array transmits correct signal without time modulation in the desired direction, while transmitting time-modulated signals in other directions. As longs as the time modulation frequency is less than the bandwidth of the transmitted signal, the time-modulated signals cannot be demodulated correctly due to the aliasing effect, implying that time-modulated signals go distorted. Thus, the 4-D array can be used to transmit direction-dependent signals in secure wireless communications. The proposed idea is verified by experiments based on AM signal transmission through the 4-D array. Moreover, BPSK signal transmission through the 4-D array is studied and the bit error rate (BER) performance is investigated. Simulation results show that the BERs of time-modulated BPSK (TM-BPSK) signals transmitted through the sidelobes of the 4-D array are much higher than those of BPSK signals and almost keep unchanged even under higher SNR. Finally, two enhanced methods are presented to improve the feasibility of directional modulation by using random time sequences and random time modulation frequency.

Robust Synthesis Method for Secure Directional Modulation With Imperfect Direction Angle

Abstract: Directional modulation (DM) is a secure transmission technology that is able to retain the original constellation of transmitted signals along the desired direction, while distort the constellation in the undesired directions at the same time. In this letter, we develop novel and robust DM synthesis methods for enhancing the transmission performance. Specifically, we first propose a low-complexity dynamic DM synthesis method. In this method, we derive a closed-form expression for the null space of conjugate transpose of the steering vector in the desired direction. Based on the expression derived, we construct a projection matrix in order to form artificial noises to those undesired directions. Then, we focus our attention on more practical scenarios, where there is uncertainty in the estimated direction angle. This uncertainty will cause estimation errors and seriously jeopardize the receiving performance in the desired direction. To mitigate the uncertainty effect, we further propose a robust DM synthesis method based on conditional minimum mean square error. The proposed method aims to minimize the distortion of the constellation points along the desired direction. Simulation results show that our proposed robust DM method is capable of substantially improving the bit error rate performance compared with the state-of-the-art methods.