Gaoqi Dou

We propose a blind detection scheme for pilot-free short packets that eliminates the pilot structure, significantly enhancing information transmission efficiency. To thoroughly evaluate the proposed pilot-free short-packet transmission scheme, we analyze the packet capture, synchronization, and demodulation processes separately and jointly, highlighting that the synchronization process is a major limitation to pilot-free short-packet transmission performance. By incorporating a cyclic redundancy check (CRC) to optimize the pilot-free short-packet structure and leveraging CRC-based soft decision techniques to assist in synchronization and demodulation, the system’s joint blind detection performance is significantly improved. Both simulation and experimental results demonstrate that, given the same time and bandwidth resources, the proposed pilot-free short-packet blind detection scheme outperforms the widely used LoRa transmission scheme. At the cost of some spatial complexity, it achieves superior demodulation performance in AWGN, Rayleigh fading, Doppler frequency offset, and multipath channels. This scheme offers a promising alternative for large-scale machine-to-machine communication in Internet of Things (IoT) applications.

The suppression of evanescent waves (EWs) in the below cutoff frequency range of compact cavity packages (CPs) is rarely considered and reported due to their inherent attenuation characteristics. However, in the frequency band approaching the cutoff frequency, the coupling remains significant, potentially degrading the performance of components and circuits within densely packed cavity. This paper addresses the emerging EW interference problem in CPs by proposing, for the first time, an ungrounded anisotropic metasurface diaphragm (UAMD) capable of enhancing EW suppression below the CP’s cutoff frequency without inducing any parasitic transmission pole. First, by partially filling a single-layer UAMD in the cross-section of an CP, a transmission null (TN) can be generated in the target EW frequency band while keeping the inherent attenuation of EWs at other frequency bands basically unchanged. Then, by effectively combining two UAMDs as a second-order UAMD, a relative suppression bandwidth of 13.4% can be achieved. Finally, a mushroom structure is introduced to further expand the suppression bandwidth by properly controlling the coupling between the mushroom and UAMDs as a third-order UAMD. A prototype operating in the Sub-6G band was designed, fabricated, and measured, which has a thickness less than 0.1λ0 and a profile less than 0.15λ0, i.e., maintaining a clearance of more than 2 mm from the bottom of the cavity. The fabricated prototype demonstrates three well-defined TNs and achieves a −10 dB EW suppression bandwidth of 18.2% (5.08–6.10 GHz), indicating that our developed technique provides an effective solution to suppress EWs in the compact metallic CPs.

High mechanical quality factor (Q_m) for a magnetoelectric (ME) mechanical transmitter is normally desired to decrease the mechanical damping and thus to improve the coupling efficiency. However, a long time for the ring-up/down process is resulted due to the narrowband characteristics of a high-Q_m ME antenna, which causes severe intersymbol interference (ISI) and greatly limits the transmitting data rate with conventional modulation schemes, e.g., Amplitude Shift Keying (ASK). In this work, we propose a predistortion waveform design to suppress the ISI when transmitting a bitstream with high symbol rate for a narrowband ME antenna. Different from the arbitrary waveform design without any constraints, we limit the peak voltage of the predistortion waveform three times the level of the stable value after considering an economic power amplifier design. Accordingly, a modified binary amplitude shift keying (modified BASK) modulation scheme is established. Experimental and simulation results show that modified BASK achieves a 5-fold bandwidth improvement with only a 20% reduction in efficiency. Experimental results show that reliable communication rate based on the proposed waveform design can reach 1000 bps at a 15 m communication distance, while the counterpart for conventional BASK method is only 500 bps with 10 m distance. The proposed predistortion waveform and the established modulation method circumvent the mutual limitation between the information bandwidth and the physical bandwidth for a very-low frequency (VLF) mechanical antenna and are believed to speed up the communication application for ME antennas in VLF band.

The magnetoelectric (ME) antennas rely on the mechanical movement of magnetic dipoles, making it possible to break the constraints on physical dimensions decided by the wavelength of the electromagnetic wavelength. The ME antennas achieve super-low frequency (SLF) communications with a smaller size to provide a novel solution for long-range, underwater, and underground communications; navigation over the horizon; and geological exploring. As a result, further theoretical research and optimization of ME antennas have been an open challenge for decades. Here, we report on minitype arrays of acoustically actuated ME antenna and their more rigorous equivalent circuits. These arrays of ME antenna adjust amplitude-frequency response through the mechanical regulation method. The mechanical parameters of ME antennas in the arrays result in regulating amplitude-frequency response, such as working frequency, fractional bandwidth, and intensity of magnetic induction. Our work provides a more accurate theoretical model and diverse array form over state-of-the-art ME antenna arrays. The frequency, fractional bandwidth, and magnetic induction strength of the ME antenna arrays were achieved to be adjustable in the ranges of 84 to 181 Hz, 3.9% to 8.3%, and two to four times, respectively. In addition, we have calculated the attenuation characteristics of ME antennas and their minitype arrays in seawater. The results show that the ME antenna array described in this manuscript is able to enhance the radiation intensity and information-loading capability, which has a positive potential for application in SLF communication systems.

To solve the problem that radar performance is seriously affected by mainlobe deception jamming, a jamming suppression approach using singular value decomposition (SVD) and the fractional Fourier transform (FrFT) is proposed. First, Hankel matrix rearrangement and SVD are performed for the signals in each coherent processing interval. The energy of jamming and of the radar targets is aggregated from the slow-time dimension. Ensemble learning is then used for its cognitive properties. The corresponding relationship between jamming and the singular values is judged, and the interference is initially suppressed. Finally, the FrFT is applied for each pulse signal. The linear frequency modulation signal energy is aggregated from the fast-time dimension, and jamming is suppressed a second time. The results of simulations show that the proposed approach can be used to detect targets more effectively than existing methods in scenarios involving multiple strong mainlobe deception jammers.

Massive machine type communication (mMTC) is expected to support the connections of billion devices, where a sporadic short packet transmission is a key feature for mMTC applications. Conventional pilot-based coherent schemes suffer from a huge resource overhead as the pilot occupies a large portion in the short packet transmission. To avoid the overhead and latency caused by pilot symbols and mitigate the adverse effect of wireless fading, we develop a noncoherent single-input multiple-output (SIMO) framework with modulation on conjugate-reciprocal zeros (MOCZ) for short packet transmission. A novel lowcomplexity noncoherent Viterbi-like detector is proposed, which can exploit diversity of receive antennas by jointly testing the zeros of the received MOCZ symbol over independent channel realizations. Simulation results demonstrate that the proposed detector can outperform the pilot-based OFDM systems and get better performance than the direct zero-testing detector for short packet transmissions in frequency-selective fading environments.

To address the problem that array radar is seriously affected by complex mainlobe jamming, a method of mainlobe jamming suppression with space–time multichannel via blind source separation is proposed. First, 4 space–time sum–difference channels are constructed to enhance the discriminability of the source signals based on two-dimensional space–time information, and multiple channels are provided to suppress mainlobe jamming from multiple sources simultaneously. Then, the joint approximate diagonalization of eigenmatrices blind source separation (BSS) algorithm is used to separate the target echo signal from the mixed signal. On the basis of the pulse compression and signal phase statistics, the target distance information can be obtained. Finally, in accordance with the phase relationship between the subarray BSS results, sparse recovery is performed to obtain the target direction of arrival information. Simulation results show that the proposed method can effectively suppress interference and extract the target information in the presence of up to 3 near-mainlobe blanket jamming signals or self-defensive mainlobe deceptive jamming signals.

Since sky wave over-the-horizon radar is seriously affected by transient interference, a transient interference suppression method based on an improved Teager-Kaiser energy operator and fuzzy reasoning is proposed. Initially, due to the extraction of the information entropy of slow time samples, the resolution ability of the energy operator to short-term fluctuation characteristics is improved and used to more accurately locate transient interference. Then, four evaluation indexes are constructed to quantify the confidence of the data reconstruction results obtained via the autoregressive, subspace and smoothing methods. Finally, Dempster and Shafer evidence theory is introduced to conduct fuzzy reasoning on the various reconstruction results, and comprehensive results are obtained. The experimental results show that our proposed method has evident advantages in locating weak interference, preventing clutter broadening and maintaining high-speed target energy.

With the advent of the Internet of Things (IoT), short packet transmissions will dominate the future wireless communication. However, traditional coherent demodulation and channel estimation schemes require large pilot overhead, which may be highly inefficient for short packets in multipath fading scenarios. This paper proposes a novel pilot-free short packet structure based on the association of modulation on conjugate-reciprocal zeros (MOCZ) and tail-biting convolutional codes (TBCC), where a noncoherent demodulation and decoding scheme is designed without the channel state information (CSI) at the transceivers. We provide a construction method of constellation sets and demodulation rule for M-ary MOCZ. By deriving low complexity log-likelihood ratios (LLR) for M-ary MOCZ, we offer a reasonable balance between energy and bandwidth efficiency for joint coding and modulation scheme. Simulation results show that our proposed scheme can attain significant performance and throughput gains compared to the pilot-based coherent modulation scheme over multipath fading channels.

To solve the problem that a parameter search easily falls into a local optimum and the two-dimensional electron density profile construction error is large in the process of backscatter ionogram inversion, an improved method using neighborhood-aided and multistep fitting is proposed. The ionospheric parameter inversion results in the adjacent space are combined and reconstructed by using the neighborhood-aided correction method. The introduction of auxiliary information sources addresses the defects of the conventional genetic algorithm. The local region multistep fitting method is used to describe the local uniformity and global inhomogeneity of the two-dimensional electron density profile by dividing the fitting region. The experimental results show that the proposed method can improve the accuracy of backscatter ionogram inversion and provide reliable support for tracking radio ray trajectories.