This paper presents a wide stopband filtering antenna element and its application in multi-input multi-output (MIMO) system. Microstrip terminated coupled lines (TCLs) and a rectangle patch are utilized to generate the filtering function. By varying the length of the parallel coupled lines and opencircuited stubs, multiple transmission zeros can be introduced in the spurious band. Appropriate positioning the location of these transmission zeros enables a wide harmonic suppression. To demonstrate the proposed method, a wide stopband filtering antenna is designed and further applied in a four-element MIMO array. The measured and simulated results agree well. The proposed MIMO antenna obtains an attenuation of 12.6 dB up to 6.6 times the center frequency.

Cooperative braking control is a very important operation in vehicle platoon control for developing intelligent transportation systems, which can effectively increase road capacity, decrease safety hazard, and avoid serial rear-end collisions. This paper focuses on cooperative braking control of autonomous vehicles, the objectives of which are to ensure intervehicles keep within the safe spacing range and rapidly, smoothly, and accurately stop at the desired target stopping positions with zero velocity. To achieve these goals, a three-vehicle platoon framework is presented and the corresponding dynamic model is established based on only information about front-end and rear-end sensors of vehicles, so communication is not needed. The explicit solutions on the three-vehicle platoon are derived by rigorous convergent analysis and detailed proof, such that intrinsic characteristic of the interconnected vehicles is revealed. The resulting convergent conditions and convergent rate are obtained under three cases including: 1) considering internal virtual forces; 2) considering external braking forces; and 3) considering both the internal virtual forces and external braking forces simultaneously. Moreover, an example is further provided to verify that the derived convergence conditions are effective and sufficient under the different controller parameter selection. These results can provide a solution for a wide class of interconnected systems and a guide for controller design to select control parameters in real engineering applications. Simulation results demonstrate the validity of the proposed control approaches.

In this paper, we enhance physical layer security for downlink heterogeneous networks by using friendly jammers and full-duplex users. The jammers are selected to transmit jamming signal if their interfering power on the scheduled users is below a threshold, meanwhile the scheduled users confound the eavesdroppers using artificial noise by full-duplexing. Using the tools of stochastic geometry, we derive the expressions of connection probability and secrecy probability. In particular, the locations of active jammers are modeled by a modified Poisson hole process. Determining the jammer selection threshold is further investigated for connection probability maximization subject to the security constraints. A greedy algorithm is proposed to efficiently solve this problem. The accuracy of the theoretical analysis and the efficiency of the proposed algorithm are evaluated by numerical simulations.

In light of recent advances in deep learning and Synthetic Aperture Radar (SAR) technology, there has been a growing adoption of ship detection models that are based on deep learning methodologies. However, the efficiency of SAR ship detection models is significantly impacted by complex backgrounds, noise, and multi-scale ships (the number of pixels occupied by ships in SAR images varies significantly). To address the aforementioned issues, this research proposes a Pyramid Pooling Attention Network (PPA-Net) for SAR multi-scale ship detection. Firstly, a Pyramid Pooled Attention Module (PPAM) is designed to alleviate the influence of background noise on ship detection while its parallel component favors the processing of multiple ship sizes. Different from the previous attention module, the PPAM module can better suppress the background noise in SAR images because it considers the saliency of ships in SAR images. Secondly, an Adaptive Feature Balancing Module (AFBM) is developed, which can automatically balance the conflict between ship semantic information and location information. Finally, the detection capabilities of the ship detection model for multi-scale ships are further improved by introducing the Atrous Spatial Pyramid Pooling (ASPP) module. This innovative module enhances the detection model’s ability to detect ships of varying scales by extracting features from multiple scales using atrous convolutions and spatial pyramid pooling. PPA-Net achieved detection accuracies of 95.19% and 89.27% on the High-Resolution SAR Images Dataset (HRSID) and the SAR Ship Detection Dataset (SSDD), respectively. The experimental results demonstrate that PPA-Net outperforms other ship detection models.

In dynamic scenarios such as walking, wireless body area networks (WBANs) have unique dynamic features, for instance, the sensor nodes placed on the limbs have approximately periodic link qualities. To realize energy-efficient and reliable communication in dynamic WBANs, this paper focuses on designing a scheduling strategy, that exploits the dynamic channel periodicity. In walking scenarios, we first construct a WBAN testbed, then conduct experiments to show the channel periodicity between the sensor nodes deployed at different positions and quantify the correlation between the received signal strength indication (RSSI) and the acceleration signals. Next, we propose a gait cycle detection algorithm to detect the periodic motion and calculate the acceleration periodicity and phase. Then, we propose a channel periodicity based scheduling (CPBS) strategy that exploits the periodic fluctuations of link qualities, to improve energy efficiency and reliability. With the CPBS strategy, the transmission time is allocated according to the motion state and the rate requirement of each sensor node, which can avoid channel collision. Finally, we evaluate the performance of the CPBS strategy in both periodic and realistic (approximately 23% of the time for aperiodic movements) scenarios. The results show that, compared to stochastic scheduling (SS) strategy, the proposed CPBS strategy can save 17.61% and 13.56% energy consumption in periodic and realistic scenarios, respectively. In addition, the packet loss rate (PLR) can be made as low as zero in both scenarios. Therefore, the proposed CPBS strategy can achieve energy-efficient and reliable communication in dynamic WBANs.

Direction-of-arrival (DOA) estimation with a co-prime linear array, composed of two uniform linear arrays with inter-element spacing larger than half-wavelength of incoming signals, has been investigated a lot thanks to its high resolution performance. For better computational efficiency, one class of methods treats the co-prime linear array as two sparse uniform linear subarrays. From each of them, high-precision but ambiguous DOA estimation is obtained, and the ambiguities are eliminated according to the co-prime property. However, the existing methods of this kind suffer from the insufficient reliability and high complexity. In this paper, the potential problems associated to the DOA estimation with two co-prime subarrays are discussed, and a reliable and efficient DOA estimation method is proposed. For each subarray, the true DOAs are treated as their equivalent angles, and the pair matching of them is accomplished by exploring the cross-correlations between the equivalent signals associated with the equivalent angles. Compared with other existing methods, the proposed method is able to achieve a better estimation performance in all situations, in terms of accuracy and complexity.