Frequency Hopping System Research Articles

Chinese remainder theorem‐based construction of optimal no‐hit‐zone frequency sequence set with wide gap

In frequency-hopping (FH) communication systems, frequency-hopping sequences (FHSs) determine systems' performance. For the quasi-synchronous FH communication systems, no-hit-zone (NHZ) frequency sequences are good at preventing multi-path interferences. If the two neighbouring frequency components of an FHS have enough gap, the FH communication system's anti-interference ability will be significantly improved. Here, a Chinese remainder theorem-based construction of optimal NHZ-FHS sets with wide gap is proposed.

Construction and Characterization of Optical Orthogonal Codes (n,w,1) for Fast Frequency Hopping-Optical Code Division Multiple Access

This paper investigates a new combinatorial construction approach based on cyclic difference packings for the construction of an optical orthogonal code that is suitable as a time spreading sequence for fast frequency hopping optical code division multiple access (OCDM) systems. The proposed construction provides a solution to the electrical decoding delay problem when compared to its optical counterpart, as well as other optimization issues. The criteria for optimizing the performance of such an OCDMA system are provided, namely: the flexibility and simplicity in constructing the optimal code for any length and weight, a reduction in the encoding/decoding complexity that complies with changes in the fast frequency hopping system, and the provision of system transfer transparency, a decoding rule that exploits the embedded asymmetric error correcting capability of the code. Our neighbor difference approach refers to the partition of different solutions into sub-classes, given in the correlation matrix form. It takes into account both direct and recursive combinatorial code construction methods, and the resulting characteristics are evaluated accordingly. A performance analysis based on the OCDMA channel is given, and a comparison with other difference family solutions is performed.

An Innovative FPGA Implementations of the Secure Frequency Hopping Communication System Based on the Improved ZUC Algorithm

Frequency Hopping (FH) is a significant anti-interception and anti-interference, so some wireless communication systems extensively use it. Then it can offer better security performance of the system via combining cryptographic algorithms with FH. This paper presents a detailed theoretical design and hardware implementation of an evolutionary ZUC stream cipher algorithm on FPGA. Using some encryption algorithms can improve the security of the FH system by increasing its complexity, including SNOW3g, ZUC algorithm, Chaos system, and other cipher methods. ZUC (named for Zu Chongzhi, a famous mathematician in ancient China) is bitstream encryption that builds the core of the 3GPP integrity algorithm 128-EIA3 and the 3GPP confidentiality algorithm 128-EEA3, providing authentic security services in 4G, even in 5G (IMT-2020) to some extent. The article presented an evolutionary three-layers structure of the ZUC FH system, which innovatively applied the permutation polynomial algorithm and an evolutionary DES cipher algorithm. The introduction of that new DES and the permutation polynomial can efficiently increase the security performance of the ZUC system but also avoid some shortcomings of the UHF (Ultra High Frequency) communication. The experiment of this research designed software by coding VHDL language and implemented hardware using a XILINX Virtex-5 FPGA. The finished experiment gave, analyzed, and compared all results according to the performance of the proposed system and hardware resources. The tests for evaluating the randomness and security denote that the constructed sequences have better performance, including the randomness, linear complexity, and hamming correlations, and pass the NIST test finally. The experimental results show that this improved ZUC cipher stream algorithm proposed in the article can provide a high throughput of 2.08 Gbps under a 65MHz clock frequency. The authors will focus their future work on applying the evolutionary S-box and the algorithm with better security performance.

Joint Radar and Communications for Frequency-Hopped MIMO Systems

Contention in the frequency spectrum has seen the emergence of Dual-Function Radar Communications (DFRC) systems, enabling frequency-hopped (FH) multiple-input-multiple-output (MIMO) waveforms to carry communication symbols. While a variety of novel signaling strategies have been developed to facilitate the communication function, their implementation in slow-time results in the achievable data rate being limited by the radar pulse repetition interval. We develop a generalized framework for performing information embedding in DFRC systems by exploiting the fast-time structure of the transmitted radar waveform. By defining a unified formulation, we show that a variety of existing signaling strategies can be accommodated, including FH index modulation, FH permutation, quadrature amplitude modulation (QAM), M-arry PSK (MPSK) modulation and/or frequency carrier index modulation. In addition, we use this framework to propose hybrid modulation strategies constructed using combinations of the aforementioned schemes to produce significant improvements in the achievable data rate over the individual signaling schemes. Simulation results demonstrate that the hybrid schemes can deliver significantly higher bit rates with only small increases in the required <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$E_b/N_0$</tex-math></inline-formula> . They also show that, in terms of the impact on the radar operation, the frequency hopping code selection has the highest range sidelobes whereas the PSK schemes suffer from significant spectral leakage. Finally, we also give a discussion of the issues and open problems that remain unaddressed.

Sets of Wide-Gap Frequency-Hopping Sequence With Optimal Maximum Hamming Correlation

In application, frequency-hopping (FH) communication system often suffers various interferences, such as single frequency narrow-band interference, partial band blocking interference and tracking interference, and so on. For all that, by using optimal Wide-Gap (WG) FH sequences, FH communication system can significantly improve the anti-interference performances. In this paper, the relations betweenWG FH sequence theoretic bounds published in the journal IEEE Access (Peihua Li et al., 2019) are first made clear, and then five types of generalized methods are presented to design new classes of WG FH sequence sets. It is shown that all designed WG FH sequence sets are optimal according to the bound derived by Peihua Li et al. And by selecting appropriate original sequence sets, many of the optimal WG FH sequence sets can be obtained by our methods. Most importantly, these WG FH sequence sets have new parameters that are not covered in the literature.

High-Security Sequence Design for Differential Frequency Hopping Systems

Differential frequency hopping (DFH) technique is widely used in wireless communications by exploiting its capabilities of mitigating tracking interference and confidentiality. However, electronic attacks in wireless systems become more and more rigorous, which imposes a lot of challenges on the DFH sequences designed based on the linear congruence theory, fuzzy and chaotic theory, etc. In this article, we investigate the sequence design in DFH systems by exploiting the equivalence principle between the G-function algorithm and the encryption algorithm, in order to achieve high security. In more details, first, the novel G-function is proposed with the aid of the Government Standard algorithm and the Rivest–Shamir–Adleman algorithm. Then, two sequence design algorithms are proposed, namely, the G-function-assisted sequence generation algorithm, which takes the full advantages of the symmetric and asymmetric encryption algorithms, and the high-order G-function-aided sequence generation algorithm, which is capable of enhancing the correlation of the elements in a DFH sequence. Moreover, the security and ergodicity performance of the proposed algorithms are analyzed. Our studies and results show that the DFH sequences generated by the proposed algorithms significantly outperform the sequences generated by the reversible hash algorithm and affine transformation in terms of the uniformity, randomness, complexity, and the security.

Anti-follower jamming performance analysis of dual sequence frequency hopping in Gaussian white noise channel

With the increasingly severe wireless communication confrontation, the traditional conventional frequency hopping (CFH) system has poor performance in anti-follower jamming, so a new dual frequency hopping mode is proposed from the perspective of frequency hopping principle. Firstly, the communication model and anti-jamming principle of the dual sequence frequency hopping (DSFH) system are introduced. Secondly, the typical follower jamming model and its parameters in communication are summarized, and the anti-follower jamming performance of different parameters of the system under follower jamming is analyzed. Finally, the CFH and DSFH system are compared. Bit error rate performance under different parameter conditions. The results show that under the AWGN channel, the anti-follower jamming performance of the DSFH system is better than that of CFH, and the value of the bit error rate is lower than that of CFH.

Anti-Interference Design Based on Prime Interleaving for a Combined FH and DS Spreading Spectrum System

A combined prime interleaving design is proposed for a spreading spectrum system with frequency hopping (FH), direct sequence (DS), and coherent detection. Obtaining a lower bit error rate (BER) is the object of classical anti-jamming communication systems. By employing combined prime interleaving, we get lower BER results compared with conventional block interleaving under the same signal-to-noise ratio (SNR) level by merit of superior storage and interleaving effects. Prime interleaving requires only one row to interleave while both block and random interleaving require the whole interleaving matrix, which results in lower latency time. Simulations reveal that the proposed combined interleaving design has comparative performance with random interleaving, and has advantages in transmission reliability and system delay. Moreover, the prime interleaving outputs slightly worse BER compared with random interleaving over the same SNR. Compared with random interleaving, the proposed combined interleaving has 0.25 dB worse SNR over the same average BER.

Miniaturization of Frequency-Reconfigurable Antenna Using Periodic Slow-Wave Structure

A challenge for frequency-reconfigurable antennas is how to realize miniaturized structures while preserving satisfying radiation performance in whole operation bandwidth. To address this problem, we apply planar periodic slow-wave structure (PSWS) with controlled dispersion features for miniaturization of antenna. Due to the subwavelength property and large propagation constant, this design holds a much more compact size than conventional microstrip structures. The proposed antenna consists of a double-layered dielectric substrate with the tunable patch on the top and a bias network combining with the feeding part on the bottom. The operating frequency is electronically controlled by the varactors shortened to the ground on nonradiating edges. It ranges from 4.87 to 5.52 GHz when the bias voltage varies from 9 to 16 V. Both simulated and measured results show that the proposed antenna maintains acceptable gains and similar radiation patterns while shrinking the size effectively. The proposed miniaturized and frequency-reconfigurable antenna holds potential applications in the ultracompact frequency hopping communication systems.

A joint STFT-HOC detection method for FH data link signals

The anti-interference, anti-interception, anti-spoofing ability and complex electromagnetic environment of the data link signal of the frequency hopping system pose formidable challenges to the reconnaissance of the frequency hopping signal. Therefore, this paper proposes a joint STFT-HOC detection method for FH data link signals. This method combines time-frequency analysis and high-order cumulant to realize effective detection of frequency hopping data link signals. Theoretical analysis and simulation experiments show that the proposed method can successfully detect the data link signal of the frequency hopping system when the signal-to-noise ratio is greater than −2 dB.

Artificial Noise Shielded Frequency-Hopping Systems: Transceiver Design and Performance Analysis

To further protect frequency-hopping (FH) systems against severe wiretapping, an architecture of artificial noise (AN) shielded FH systems (ANS-FH) is proposed, wherein an AN cancellation architecture is utilized at the authorized receiver, and the secrecy performance is analyzed in the presence of an eavesdropper. First, an inter-frequency interference (IFI) model is employed to depict the residual AN after AN cancellation. Then, the tolerable range of frequency deviation is given, and the signal to AN plus noise ratio (SANR) is provided to measure the AN cancellation performance. Finally, the secrecy performance is analyzed using secrecy capacity under the assumption that frequency deviation is uniformly distributed within frequency synchronization accuracy. Theoretical and simulation results confirm that frequency deviation in practical FH systems will degrade both AN cancellation and system secrecy performance, and shorter hop length or proper power allocation for secret data and AN can mitigate the negative impact of frequency deviation, which in turn guides the practical transceiver design.

Jamming Detection in Broadband Frequency Hopping Systems Based on Multi-Segment Signals Spectrum Clustering

Accurate jamming detection in the broadband frequency hopping (FH) systems plays a vital role in improving the anti-jamming performance of the communication systems. The traditional jamming detection algorithms are prone to misjudge FH communication signals as jamming signals, leading to inaccurate jamming detection. Therefore, this paper proposes a jamming detection algorithm for broadband FH systems based on multi-segment signals spectrum clustering (MSSC). According to the difference in the time-frequency characteristics between FH signals and jamming signals, the proposed algorithm accurately detects the jamming by clustering the spectral components of signals in multiple periods. In addition, a jamming detector suitable for broadband FH systems is designed and the theoretical solution to the threshold factor of signal detection based on the Welch spectrum is also given in this paper. The simulation results show that the MSSC-based jamming detection algorithm proposed in this paper can reduce the jamming false detection probability and significantly improve the estimation accuracy of jamming parameters, effectively overcoming the defects of the traditional FFT-based energy detection and the multi-hop accumulation algorithms whose detection accuracy is sensitive to FH signals.

Signal Sorting Algorithm of Hybrid Frequency Hopping Network Station Based on Neural Network

In a non-cooperative frequency hopping communication system, the frequency hopping network station sorting of the received hybrid signals plays an important role and becomes an active research area in recent years. In order to solve the problem that the currently widely used clustering algorithm can not achieve satisfactory accuracy. In this paper, we propose a signal sorting method for hybrid frequency hopping network stations by applying the neural network to classify the frequency hopping description words of signals. Additionally, the conjugate gradient algorithm is utilized in the neural network training process to improve the convergence speed. Simulation results demonstrate that when compared with the clustering algorithm, the proposed algorithm converges with fewer iterations and delivers better sorting accuracy, especially in a low signal to noise ratio environment.

A New Frequency Hopping Signal Detection of Civil UAV Based on Improved K-Means Clustering Algorithm

The rapid development of civil UAV promotes the social and economic development, and the frequent “flying illegally” events has brought great challenges to aviation safety and government supervision. The frequency hopping communication system used in UAV data transmission and control link has the advantages of anti-jamming and anti-interception, and its complex electromagnetic environment, which also brings great difficulties to UAV detection. In this paper, the detection of civil UAV is realized by frequency hopping signal monitoring. Firstly, by analyzing the signal characteristics of UAVs, an adaptive noise threshold calculation method is proposed for find the signals from spectrum data. Then, the improved clustering analysis algorithm is proposed based on constructed the waveform shape characteristics and peak characteristics of UAV frequency hopping signal. Finally, according to the designed experimental process, the experimental environment is set up, and the UAV monitoring, discovery and parameter estimation are realized by using the improved clustering analysis algorithm, and compared with K-means, K-means++, DBSCAN, Multi-hop and Auto-correlation methods. The results show that the method has certain robustness and has a good application prospect.

Signal Sorting Algorithm of Hybrid Frequency Hopping Network Station Based on Neural Network

In non-cooperative frequency hopping communication system, the frequency hopping network station sorting of the received hybrid signals plays an important role and becomes an active research area in recent years. In order to solve the problem that the currently widely used clustering algorithm cannot achieve satisfactory accuracy. In this paper, we propose a signal sorting method for hybrid frequency hopping network stations by applying the neural network to classify the frequency hopping description words of signals. Additionally, the conjugate gradient algorithm is utilized in the neural network training process to improve the convergence speed. Once the neural network training is finished, only one frequency hopping description word of the input signal is required to obtain its own network station label in real time. Simulation results demonstrate that when compared with the clustering algorithm, the proposed algorithm converges with less iterations and delivers better sorting accuracy, especially in a low signal to noise ratio environment.

Binary-Sequence Frequency Hopping Communication Method Based on Pseudo-Random Linear Frequency Modulation

To improve the signal detection performance of binary-sequence frequency hopping communication when the complementary channel is jammed, a binary-sequence frequency hopping communication system based on pseudo-random liner frequency modulation (LFM) is proposed. The transmitting end uses the chirp signal to carry out the in-band spread spectrum of the binary-sequence frequency hopping signal, and then sends it out through the radio frequency front end. At the receiving end, the received signal is dehopped and processed by fractional Fourier transform. The source information is obtained by sampling decision. Firstly, a binary-sequence frequency hopping system model based on pseudo-random LFM is constructed. Secondly, the bit error rate expression of anti-partial band jamming and follower jamming under the Rice channel is derived. The results show that this method has at least 5 dB performance gain than binary sequence frequency hopping for different parameter settings under partial band jamming and follower jamming, and the anti-jamming performance is significantly better than the conventional frequency hopping communication.

A Rapid Serial Timing Acquisition Algorithm for Hybrid DS/FFH Packet Radio Communication

In this article, we propose a simple, reliable, and rapid serial timing acquisition algorithm for hybrid direct-sequence and fast frequency-hopping packet radio communication systems. The proposed algorithm is designed in both the frequency domain of frequency hopping and the pseudonoise code domain of direct sequence. We provide the performance analysis for our proposed algorithm and confirm its exactness by simulation. Compared with the conventional serial search algorithm, the proposed algorithm shows much faster acquisition time while obtaining similar performance.

Two-Dimensional Jamming Recognition Algorithm Based on the Sevcik Fractal Dimension and Energy Concentration Property for UAV Frequency Hopping Systems

Unmanned aircraft vehicle frequency hopping (UAV-FH) systems face multiple types of jamming, and one anti-jamming method cannot cope with all types of jamming. Therefore, the jamming signals of the environment where the UAV-FH system is located must be identified and classified; moreover, anti-jamming measures must be selected in accordance with different jamming types. First, the algorithm extracts the Sevcik fractal dimension from the frequency domain (SFDF) and the degree of energy concentration from the fractional Fourier domain of various types of jamming. Then, these parameters are combined into a two-dimensional feature vector and used as a feature parameter for classification and recognition. Lastly, a binary tree-based support vector machine (BT-SVM) multi-classifier is used to classify the jamming signal. Simulation results show that the feature parameters extracted by the proposed method have good separation and strong stability. Compared with the existing box-dimensional recognition algorithm, the new algorithm not only can quickly and accurately identify the type of jamming signal but also has more advantages when the jamming-to-noise ratio (JNR) is low.

Bit Error Rate Analysis for FH/MFSK System with Follower Jamming

At present, methods of bit error rate (BER) analysis for frequency-hopping (FH) system can only solve the problem of barrage jamming, but these are no comprehensive means to follower jamming (FJ). This paper proposes a method of BER analysis with FJ based on frequency hopping M-ary frequency-shift keying (FH/MFSK) system. Through the analysis of the mechanism of FH/MFSK system, assuming the wireless channel is an AWGN channel, the BER formulas for different jamming types are derived, respectively, from the point of one-dimensional probability density function of the output signal of the envelope detector, while judgment principle of envelope detecting method is used. Results show that the BER of multiple FH/MFSK system with FJ is relatively lower. In the worst case of FJ, the BER of FH/4FSK system and FH/8FSK system is reduced by 2 dB and 3 dB, respectively, compared with that of FH/2FSK system. The method of BER analysis proposed provides an effective means to research the BER with FJ in depth.

Implementation of Mixing Sequence Optimized Modulated Wideband Converter for Ultra-Wideband Frequency Hopping Signals Detection

Frequency hopping (FH) communications are widely used in Satcom systems. The latest FH systems have exceeded 3 GHz with hop rates up to 100 000 hops/s. Traditional spectrum sensing systems hardly monitor such signals. Modulated wideband converter (MWC) is an emerging compressive sampling structure applied to sample multiband signals. This article analyses the effects of the nonlinearity of analog devices and proposes an optimization method based on a greedy algorithm for mixing sequences to make reconstruction performance uniform across sub-bands. To correct the errors caused by the nonideality of analog front end circuits between the theoretical sensing matrix and the practical one, we also develop a calibrating method that obtains all the sensing matrix coefficients through a single measurement. In conventional MWC, out-band noise will be blended during reconstruction. Instead of matrix factorization, we reserve signal characters and designed sliding filters to improve narrowband signals reconstruction sensitivities. We produced a four-branch MWC principle prototype for FH signal detection. The sensing bandwidth is 3 GHz, and the sampling rate is 400 MHz, whereas the reconstruction sensitivity is as low as 13-dB in-band signal-to-noise.