Increased demand for higher spectrum efficiency, especially in the space-limited chip, base station, and vehicle environments, has spawned the development of full-duplex communications, which enable the transmitting and receiving to occur simultaneously at the same frequency. The key challenge in this full-duplex communication paradigm is to reduce the self-interference as much as possible, ideally, down to the noise floor. This paper provides a comprehensive review of the self-interference cancellation (SIC) techniques for co-located communication systems from a circuits and fields perspective. The self-interference occurs when the transmitting antenna and the receiving antenna are co-located, which significantly degrade the system performance of the receiver, in terms of the receiver desensitization, signal masking, or even damage of hardwares. By introducing the SIC techniques, the self-interference can be suppressed and the weak desired signal from the remote transmitter can be recovered. This, therefore, enables the full-duplex communications to come into the picture. The SIC techniques are classified into two main categories: the traditional circuit-domain SICs and the novel field-domain SICs, according to the method of how to rebuild and subtract the self-interference signal. In this review paper, the field-domain SIC method is systematically summarized for the first time, including the theoretical analysis and the application remarks. Some typical SIC approaches are presented and the future works are outlooked.

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.

Aimed at radio-frequency (RF) interference suppression, this article presents an RF interference adaptive cancellation system (RFIACS) with the down-conversion correlator and proposes the time domain model of the RFIACS with integrated delay mismatch about mixers, RF circuit, and intermediate frequency (IF) circuit. Then, the influence of the integrated delay mismatch and loop gain on the system stability, convergence time, and interference cancellation ratio is analyzed based on the time model. Studies show that the RF and IF delay mismatch each must be matched on their respective frequency bands and the proper arrangement of circuits and loop gain can effectively improve the cancellation performance of the system. Results of simulations and experiments with different parameters show that the theoretical model is valid and accurate. The research result is of much value to the circuit design and delay-matching debugging of the RFIACS.

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.

Cross-eye jamming is a technique to counter monopulse radar. The impact of the amplitude-phase error on the jamming performance is one of the key problems for cross-eye jamming. The tolerance of amplitude-phase error for cross-eye jamming has been analyzed by deterministic analysis. However, the amplitude-phase errors of a practical jammer are commonly stochastic variables due to the variation of working conditions. In this paper, the probabilistic analysis of the amplitude-phase error tolerance for cross-eye jamming is studied. By demonstrating that the contours of cross-eye gain can be approximate to a set of ellipses, the probability distributions of cross-eye gain and angle factor are derived, based on the assumption that the amplitude-phase errors of cross-eye jammer are Gaussian distributed. The paper presents the instructions to determine the required standard deviation of the amplitude-phase error to produce a specific confidence level of cross-eye jamming performance metric.

Coupling analysis of shielded and unshielded star quad cables excited by an intentional electromagnetic pulse (IEMP) is investigated using the transmission line theory-based perturbation technique. A detailed modal analysis is presented to obtain the modal per-unit-length parameters of the modal signals in such shielded/unshielded star quad cables. Due to their geometrical balanced structures, with opposite wires used for +leg and −leg to transfer the differential-mode (DM) signal, the external coupling is dramatically suppressed. Moreover, stochastic analyses based on the Monte Carlo simulation are also performed to study the sensitivity of the induced common-mode (CM) and DM currents, due to the deformation effects of the twisting structure of the cable. It is found that the induced CM and DM currents are slightly affected by the twisting deformation of the cable because the interference cancelations do not mainly depend on the twisting loops of the cable. In particular, time domain analysis is performed to study the field-to-wire coupling of the star quad cables exposed to an IEMP, where the worst-case waveform signals in the presence of an IEMP attack are captured and analyzed.