A dual-layer multibeam conformal slot array antenna operating at a center frequency of 10 GHz is proposed in this paper. The antenna consists of a microstrip Rotman lens and a substrate-integrated waveguide (SIW) array of 10×10 radiating slots, which is axially mounted onto a cylindrical surface with a radius of 90 mm, i.e., 3λ ₀ . The Rotman lens feeds the slot array through the coupling slots in the broad sides of the SIWs. An improved design process is introduced for realizing a conformal Rotman lens for cylindrically conformal arrays. There are unique requirements for the phase distribution and phase compensation in cylindrically conformal applications. The Rotman lens and slot antenna are built and optimized in fullwave simulation software. To validate the proposed concepts, a conformal antenna prototype is implemented and measured. The experimental results demonstrate a scanning range of ±46°, with a -3 dB crossover level between adjacent radiation beams in the E-plane and a -20 dB sidelobe level in the H-plane. The measured and simulated radiation patterns of all the scanned beams are in good agreement. This type of multibeam conformal slot array has been theoretically and experimentally studied, and it demonstrated the potential for applications in aircraft, missiles, and high-speed vehicles.

Great attention has been paid to wireless communication security in recent years. Directional modulation (DM) is one of the promising secure wireless communication techniques. Multi-beam DM has the capability of sending multiple data streams to cooperative users in different desired directions while distorting signal constellations in all other directions. Dynamic multi-beam DM has been proven to be more secure in real communication scenarios. However, previous synthesis approaches for dynamic multi-beam DM are relatively complex and demand a lot of computations. Therefore, an artificial-noise-aided zeroforcing synthesis approach is proposed. The calculation process of the baseband-weighted vector is simplified using the zeroforcing method, which is closely related to the concept of pseudoinverse. The dynamic property of multi-beam DM is achieved by randomly changing the artificial noise vector. Compared with previous classical dynamic multi-beam DM synthesis approaches, the proposed approach is more efficient and easier to implement in practical systems with tolerable performance loss.

The artificial noise (AN) aided multi-beam directional modulation (DM) technology is capable of wireless physical layer secure (PLS) transmissions for multiple desired receivers in free space. The application of AN, however, makes it less powerefficient for such a DM system. To address this problem, the weighted fractional Fourier transform (WFRFT) technology is employed in this paper to achieve power-efficient multi-beam DM transmissions. Specifically, a power-efficient multi-beam WFRFTDM scheme with cooperative receivers and a power-efficient multi-beam WFRFT-DM scheme with independent receivers are proposed based on frequency diverse array (FDA), respectively. The bit error rate (BER), secrecy rate, and robustness of the proposed multi-beam WFRFT-DM schemes are analyzed. Simulations demonstrate that 1) the proposed multi-beam WFRFT-DM schemes are more power-efficient than the conventional multibeam AN-DM scheme; 2) the transmission security can also be guaranteed even if the eavesdroppers are located close to or the same as the desired receivers; and 3) the proposed multi-beam WFRFT-DM schemes are capable of independent transmissions for different desired receivers with different modulations.

The frequency diverse array (FDA)-based directional modulation (DM) technology plays an important role in the physical-layer security (PLS) transmission of 5G and beyond communications. In order to meet the tremendous increase in mobile data traffic, a new memory-efficient design for the FDA-DM-based PLS transmission is urgently demanded. In this article, an analytical symmetrical multi-carrier FDA model is proposed in three dimensions, namely, range, azimuth angle, and elevation angle, differing from the conventional analytical approach with only range and azimuth angle considered. Then, a single-point (SP) artificial noise (AN) aided FDA-DM scheme is proposed, which reduces the memory consumption significantly compared with the conventional zero-forcing (ZF) and singular value decomposition (SVD) approaches. Moreover, the PLS performance of the proposed FDA-DM scheme is analyzed in fluctuating two-ray (FTR) fading channels for the first time, including the average secrecy capacity (ASC) and the secrecy outage probability (SOP). More importantly, the closed-form expressions for the lower bound on ASC and the upper bound on SOP are derived, respectively. The effectiveness of the analytical expressions is verified by numerical simulations. This work opens a way to lower the memory requirements for DM-based PLS transmission of 5G and beyond communications.

Recently, orthogonal frequency division multiplexing with index modulation (OFDM-IM) has been known by its potential diversity gain. In this letter, genetic algorithm aided OFDM with all index modulation (GA-OFDM-AIM) scheme is proposed, where the legitimate subblock realizations in look-up table are regarded as the chromosomes of genetic algorithm. Note that the average bit error probability (ABEP) based on pairwise error probability (PEP) gives an tight upper bound of the BER under medium and high SNR and thus the proposed scheme utilizes ABEP as the population fitness. Through the crossover, mutation and selection processes, the subblock realizations with low BER are obtained. Simulation results show that GA-OFDMAIM can significantly enhance BER performance compared to other OFDM-IM schemes.

We present algorithms to suppress the asynchronous co-channel interference (CCI) in MIMO OFDM systems, which is becoming the dominant limiting factor in the performance of the emerging high-density WLANs. The key challenge is that the cyclic prefix of the interference signal does not line up with that of the intended signal due to asynchronous transmission in WLAN. Therefore, the orthogonality among the different tones of the interference signal is destroyed and conventional frequency domain minimum mean square error (MMSE) cancelation techniques that measure the interference channel response for each tone can not work effectively. To suppress the asynchronous interference, we design an efficient estimator to measure the interference spatial covariance matrix using Cholesky decomposition and low-pass smoothing. Both a MMSE and a maximum a posteriori (MAP) receiver are derived based on the estimated interference statistics. Simulation results demonstrate the effectiveness of our solution.