Fangmin He

To address the limitations of traditional Signal-to-Interference-plus-Noise Ratio (SINR) estimation methods under non-cooperative malicious interference, such as their confinement to specific modulation signals and the narrow effective estimation range of Signal-to-Noise Ratio (SNR), this paper proposes an adaptive robust SINR estimation algorithm based on joint decoupling of eigenvalues and steering vectors. The algorithm first realizes the joint estimation of the number of sources and noise power under finite snapshots via Marchenko-Pastur (MP) law-based iteration, then completes the coarse estimation of desired signal power through steering vector-eigenvector matching and performs strategy switching according to the coarsely estimated Signal-to-Interference Ratio (SIR). In scenarios where the desired signal power is non-dominant, the robust Capon method with adaptive diagonal loading is adopted for fine estimation, and, finally, the interference power is decoupled using the matrix trace identity. The algorithm is independent of modulation characteristics, applicable to both constant-modulus and non-constant-modulus signals, and only requires prior information of the Direction of Arrival (DOA) of the desired signal. Simulation results demonstrate that under complex non-ideal conditions, including 30 dB Interference-to-Noise Ratio (INR), steering vector mismatch, and finite snapshots, the average Root Mean Square Error (RMSE) of the proposed algorithm across the entire SNR range is only 0.83 dB, which significantly outperforms mainstream blind estimation algorithms such as RMT-BSE, M2M4, and SSME. Its robustness and universality are more in line with the requirements of non-cooperative anti-jamming communications.

Simultaneous transmit-and-receive (STAR) antennas are important components of in-band full-duplex wireless front ends. However, transmit-to-receive leakage through the antenna limits the achievable antenna-domain isolation. This paper presents a dual-circularly polarized patch antenna incorporating a decoupling feeding network (DFN) to suppress the residual coupling between the transmit and receive ports. A stacked patch radiator with cross-aperture coupling generates right-hand and left-hand circularly polarized radiation from two separate ports. The DFN introduces an additional coupling path whose magnitude and electrical phase are adjusted to produce destructive interference near the target frequency. The fabricated prototype exhibits overlapping −10 dB impedance and 3 dB axial ratio bandwidths from 4.1 to 4.4 GHz, a minimum measured S₂₁ of −50 dB, isolation higher than 30 dB from 4.25 to 4.28 GHz, and a peak realized gain of 7 dBic. The measured high-isolation range has an absolute bandwidth of 30 MHz and a fractional bandwidth of approximately 0.70% around 4.265 GHz. Therefore, the proposed DFN provides narrowband antenna-domain isolation enhancement around the designed frequency without requiring additional patterned decoupling elements on the radiating aperture. The proposed antenna is primarily intended for fixed-frequency or narrow-channel STAR front ends rather than broadband high-isolation operation.

The increasing demand for more integrated communication systems results in complex radio-frequency environments. Due to the space limitation, communication receivers are extremely vulnerable to being blocked by high-power self-interference (SI) from the transmitter on the shared platform. The multipath amplitude and delay of the wireless channel are time-varying and frequency dispersion. As a result, the multitap self-interference cancellation (SIC) based on equal delay spacing is difficult to adapt to the dynamic changes of the SI channel over time and frequency, which leads to the degradation of SIC performance. The multitap SIC based on joint time-frequency domain channel measurement is proposed in the article. The multitap SIC model is established to analyze the demand for delay matching in the time-varying multipath channel. Under the joint constraints of the coherence time of the time-varying channel, the demand for interference cancellation ratio and delay resolution accuracy, the channel measurement method integrating time-domain correlation and frequency-domain sweep is designed to measure multipath delay. The prior information of the SI channel is provided to reconstruct the multitap SIC in real-time. Finally, the simulation and experiment results show that the proposed method in this article has high-precision delay measurement. The maximum error and standard deviation of the delay measurement are within 1ns and 0.5 ns. When the delay of the SI channel dynamically changes, compared with the equal delay spacing method, the SIC performance of the proposed method can be improved by more than 10 dB.

Adaptive interference cancellation is an effective means to fulfill the anti-interference requirements of communication systems. The radio frequency (RF) front-end gain plays a crucial role since it determines the communication sensitivity and anti-interference performance, especially in the presence of both high-power interference signals and weak communication signals. In this paper, the influences of the RF front-end gain on communication sensitivity as well as interference cancellation ratio (ICR) are thoroughly analyzed. Thereinafter, we derive the mathematical model of the RF front-end gain constrains taking communication sensitivity, ICR requirement and analog-to-digital converter quantization accuracy into consideration. Based on the upper and bottom boundaries gain analysis, we propose the gain design criterion for adaptive interference cancellation in communication systems. Extensive simulations demonstrate that: 1) the ICR performance improves with the increase of RF front-end gain when lower than the gain obtained from upper boundary analysis, and is saturated afterward; 2) the gain obtained from bottom boundary analysis can ensure the communication sensitivity. Experimental results verify that the gain design criterion ensures the communication sensitivity and satisfies the requirements of anti-interference performance under high-power interference signals.

With the extensive deployment of electronic information systems in modern RF integrated platforms, the issue of co-site, co-channel, or adjacent-channel interference has become increasingly severe. To address this problem effectively, the digitally controlled adaptive self-interference cancellation technology is considered as a viable solution. However, due to limitations in accuracy and the cost of high-speed analog-to-digital converters (ADCs), existing digitally controlled cancellation techniques face challenges when applied directly to the microwave band. In order to expand its working frequency range, mitigate the impact of ADC quantization noise, and accommodate diverse system configurations, three heterodyne self-interference cancellation structures are proposed and the working principle of the cancellation systems are derived in detail. Specially, the analytical expression between the cancellation performance and the system parameters is obtained, and the working boundary is also clarified. Simulation and experimental results demonstrate strong agreement with theoretical derivations, validating the effectiveness of the proposed structures.

Compared with traditional Low-Frequency transmitting antennas, rotating permanent magnet antennas are not limited by electrical size and have the potential to realize the miniaturization of Low-Frequency transmitting antennas. However, the existing modulation methods for rotating permanent magnet antennas have problems of low bit rate. This letter proposes a novel electro-mechanical PSK modulation for two-element rotating permanent magnet arrays. The theoretical model of the method is established based on Ampere's circuital law, Faraday's Law of Electromagnetic Induction, and the principle of magnetic field superposition. The PSK signal is synthesized by complementary amplitude modulation of the two elements with phase difference of 180°. Experimental results show that the bit rate of the proposed method can reach twice that of the chirp-rate shift keying with the highest symbol rate in current mechanical control.

Understanding fundamental limits of the antiinterference performance of direct sequence spread spectrum (DSSS) systems is essential for efficient state-of-the-art antiinterference implementation. Existing research contributions on anti-interference implementation mainly aims at blocking interference and DSSS with long period sequences (LPS-DSSS). However, broadband interference, due to high energy efficiency, is a more effective interference mode to DSSS systems. Conventional bit error rate (BER) models bring errors during the despreading process in DSSS with short period sequences (SPS-DSSS). Therefore, in this paper, we focus on the BER performance of SPS-DSSS systems. More particularly, we propose the maximum matching decision criteria (MMDC) based statistical BER model that is capable of accurately evaluating the BER performance for both LPS and SPS systems. Firstly, explicit mathematical model of the despreading of MSK signals in DSSS systems is established; Then, mathematical models of despreading under typical interference modes, i.e., multi-tone and pseudo-random noise (PN) code MSK interference, are derived. Finally, statistical BER model is proposed using the MMDC scheme to evaluate the BER performance. Extensive simulation and experimental results reveal that: 1) the proposed statistic BER model outperforms conventional BER model for SPS-DSSS systems, and is consistence with that for LPS-DSSS; 2) for MSK DSSS systems, PN code MSK interference outperforms multi-tone interference in the BER performance; 3) practical tests demonstrate that the same PN code length interference is capable of obtaining higher BER performance than different PN code lengths interference, due to the strong correlation between the interference signal and the desired signal in DSSS systems.

To improve the jamming cognitive level of radar in the complex and changeable electromagnetic environment, this paper proposes a YOLO-CJ (YOLO network for compound jamming detection) lightweight network for compound jamming signal detection. Firstly, the compound jamming image dataset is constructed by signal 0000-0000 © 2022 IEEE model and short-time Fourier transform (STFT). Secondly, based on the YOLOv7-tiny lightweight baseline model, the designed SimSPPFCSPC module, Triplet attention mechanism, and the C2f module are illustrated to improve the YOLOv7-tiny and establish the YOLO-CJ lightweight network, which aims to enhance the saliency and difference of the extracted features in the case of low SNR/JNR while effectively control the quantity of computation and parameters. Subsequently, combined with the compound jamming image dataset, the ablation experiment, algorithm comparison experiment, and robustness verification are carried out. The results demonstrate that the detection precision (mAP) and the inference time of a single image of the YOLO-CJ model can reach 98.69% and 12.73 ms, and the trade-off value of detection precision and speed can reach the highest 79.93%. Moreover, the mAP of the YOLO-CJ for compound jamming detection under SNR / JNR ≥ 0dB can reach more than 96%, which has good robustness and generalization ability under low SNR and JNR. Source code is released at https://github.com/zhuxuan-96/YOLO-CJ.