Frequency Hopping System Research Articles

Interceptor complexity analysis for mixed BPSK–QPSK modulated frequency hopping spread spectrum systems

In this paper, we propose a method of mixing modulation schemes to make it very difficult to intercept information from frequency hopping signals and assess analytically the difficulty of information interception using the interceptor computational complexity as a metric. In particular, we consider, to illustrate the effectiveness of mixing modulation schemes for secure communications, a method of randomly mixing BPSK and QPSK modulations in frequency hopping systems and compare it with conventional frequency hopping systems using BPSK only or QPSK only modulation scheme by deriving simple to evaluate upper and lower bounds on the interceptor complexity.

Analysis and Design of Systematic Rateless Codes in FH/BFSK System with Interference

The asymptotic analysis of systematic rateless codes in frequency hopping (FH) systems with interference is first provided using discretized density evolution (DDE) and compared with the traditional fixed-rate scheme. A simplified analysis with Gaussian assumption of initial message is proposed in the worst case of interference, which has much lower complexity and provides a very close result to DDE. Based on this simplified analysis, the linear programming is employed to design rateless codes and the simulation results on partial-band interference channels show that the optimized codes have more powerful antijamming performance than the codes originally designed for conventional systems.

Ultrafast and Wideband Microwave Photonic Frequency-Hopping Systems: A Review

The increasing demands to enhance information security in data transmission, providing countermeasures against jamming in military applications, as well as boosting data capacity in mobile and satellite communication, have led to a critical need for high-speed frequency-hopping systems. Conventional electronics-based frequency-hopping systems suffer from low data rate, low hopping speed, and narrow hopping-frequency bandwidth. Unfortunately, those are important aspects to facilitate frequency-hopping in emerging microwave systems. The recent advancement of microwave photonics—the use of light to process microwave signals—provides promising solutions to tackle the challenges faced by electronic frequency-hopping systems. In this paper, the challenges of achieving real-time frequency-hopping systems are examined. The operation principles and results of various microwave photonics-enabled frequency-hopping systems are comprehensively discussed, which have wide hopping-frequency bandwidth and frequency-hopping speed from nanoseconds to tens of picoseconds. Lastly, a bio-inspired jamming-avoidance system that could potentially be used for adaptive frequency-hopping is also introduced.

A Multi-Domain Anti-Jamming Strategy Using Stackelberg Game in Wireless Relay Networks

In this paper, we study the influence of a smart jammer on the design of a three-node frequency hopping communication system using an amplify-and-forward relay. The jammer is smart that it senses the frequency and transmit powers used by the legitimate transmitters including the source node and the relay, and optimally adjusts the sensing time and the jamming power allocation to maximize the performance damage of the relay system. We jointly consider the time domain and the power domain to design a multi-domain anti-jamming strategy. To model the interaction between the legitimate transmitters and the jammer, we use Stackelberg game and let the legitimate transmitters act as the leader while the jammer act as the follower. Based on backward induction, a genetic algorithm based on exponential distribution algorithm is proposed to obtain the optimal frequency-hopping speed and the optimal transmit powers of the legitimate transmitters. Simulation results show that the proposed multi-domain strategy outperforms single-domain schemes and the multi-domain random scheme. Moreover, the optimal placement of the relay is also discussed through simulations.

Optimum Combining for Coherent FFH/DS Spread Spectrum Receivers in the Presence of Multi-Tone Jammer

Fast Frequency Hopping/Direct Sequence (FFH/DS) hybrid spread spectrum is an effective technique of the communication network for the robot swarms operating in complex electromagnetic environment. It combines the advantages of both Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS), and also uses the diversity-combining in time and frequency domain to effectively reject unwanted jamming. Multi-Tone Interference (MTI) is one of the most deleterious jamming waveforms for frequency hopping systems, and consequently a severe threat for FFH/DS systems. In this article, we explore the effect of MTI on coherent FFH/DS, and we have shown that, if spectral sensing mechanism for MTI frequency and power monitoring is available, the MTI in FFH/DS reception is a set of complex sinusoid components with deterministic amplitudes and random phases, instead of the conventionally assumed Gaussian random variables. In light of this new finding, a novel combining method is proposed. It utilizes the spectral sensing information to adaptively compute the combining weights, following Maximum Signal to Interference plus Noise (MSINR) law. Its combining performance is analyzed and compared with other existing methods, and verified by simulations. It is shown that the proposed adaptive MSINR combining has satisfactory performance under both medium and strong MTI scenarios.

A Fast Settling Fractional-$N$ DPLL With Loop-Order Switching

The enhancement in the settling response of frequency synthesizers would open up prospects for new applications such as spread spectra and frequency hopping systems. Toward deriving a methodology for a fast settling response, we present a switched-loop digital phase locked loop (DPLL) incorporating an integral-derivative controller-based subsystem. The dominant features accelerating the settling response with low jitters in this DPLL are: 1) hybrid phase detection with a state machine using differential and double integration filtering effect and 2) a time-interleaved direct digital synthesizer (DDS)-based digital-to-time converter (DTC) with stable-edge sampling. A 5-GHz fractional- $N$ DPLL (FNDPLL) has been implemented in CMOS 65-nm-LL technology with the proposed technique of loop-order switching. The measured results of the implemented FNDPLL highlight that the system is capable of fastest reported frequency settling to ±25-ppm error within 1.5 ${\mu }\text{s}$ , using a reference clock frequency of 100 MHz. With one-time calibration, the downsampled output of DDS array-based phase interpolator achieves an integral nonlinearity (INL) of 0.25 ps, as a fractional divider in the loop.

Preliminary Application of Scale Transformation Stochastic Resonance in Dual-Sequence Frequency Hopping System

Aiming at the detection failure of strong noise interference in the dual channel of the dual-sequence frequency hopping (DSFH), the scale transformation stochastic resonance (STSR) is applied for the first time, and the output signal to noise ratio (SNR) is raised effectively, at the same time, the symbol reception is completed for DSFH at low input SNR. Firstly, the radio frequency (RF) and intermediate frequency (IF) signals are analyzed based on the super-heterodyne reception of DSFH; secondly, the equations of probability density function (PDF), output power spectrum and SNR of the STSR output are derived for the IF signal; finally, the algorithm of the optimal matching STSR is proposed with the optimal matching parameters. The simulation results show that the algorithm can effectively solve the detection failure, as the global output SNR of DSFH is strongly improved that the output SNR can reach −17.72 dB when the input SNR is −20 dB after the processing of the optimal matching STSR.

A Novel Optical Frequency-Hopping System Based on DFB Laser Integrated With an EA Modulator

A novel optical frequency-hopping system based on distributed feedback laser integrated with an electroabsorption modulator is proposed and demonstrated. In the proposed system, a user's data are split into segments and modulated onto multiple optical frequency shift keying carries, therefore, a single wavelength of optical carrier only carries partial user's data. By this way, the security of optical communication system is improved. In this paper, we demonstrate an error free transmission through 32-km single mode fiber and 8-km dispersion compensation fiber with 2.5 Gb/s hopping rate and 10 Gb/s data rate. Meanwhile, we also compare and analyze the performance of the proposed system with different hopping rate and data rate.

Decimated m-sequences families with optimal partial Hamming correlation

In quasi-synchronous frequency-hopping multiple-access systems where relative delays are restricted within a certain zone, low hit zone frequency-hopping sequences (LHZ FHSs) with favorable partial Hamming correlation properties are desirable. In this paper, we present a new class of LHZ FHS sets with optimal partial Hamming correlation based on t-decimation of m-sequence.

New Extension Constructions of Optimal Frequency-Hopping Sequence Sets

In this paper, a general framework of constructing the optimal frequency-hopping sequence (FHS) sets is presented based on the designated direct product. Under this framework, we obtain infinitely many new optimal FHS sets by combining some one-coincide (OC) sequence sets that are newly constructed in this paper with some known optimal FHS sets. Our constructions are also based on extension method. However, our constructions give new and flexible parameters due to the free choice of OC sequence set. As a result, our constructions allow a great flexibility of choosing parameters of FHS sets for a given frequency-hopping spread spectrum system.

Anti-follower jamming wide gap multi-pattern frequency hopping communication method

This paper deals with the follower jamming (FJ) resistance for the frequency hopping (FH) communication system over additive white Gaussian noise (AWGN) channel. Conventional FH systems are susceptible to be jammed by FJ, and multi-pattern frequency hopping (MPFH) has good resistance to FJ. To further improve the FJ rejection capability of MPFH, we propose a wide gap multi-pattern frequency hopping (WGMPFH) scheme. WGMPFH uses channels to represent messages, and the data channel and complementary channel are hopping on orthogonal frequency slots according to wide gap FH patterns. The transmitted signal lures FJ to aim at the data channel and the complementary channel is away from FJ by adopting wide gap frequency patterns. FJ does not affect the complementary channel but increases the signal energy in the data channel, thus the effect of FJ is reduced. Its bit error rate (BER) is derived under FJ and the effects of three FJ parameters (tracking success probability, jamming duration ratio and jamming bandwidth ratio) on the BER performance of WGMPFH are investigated versus the conventional FH/BFSK and MPFH system. Numerical and simulation results show that when under the worst-case FJ, the proposed WGMPFH outperforms the MPFH by about 1–3 dB and outperforms the conventional FH/BFSK by more than 4 dB. The proposed WGMPFH shows superior jamming rejection performance under FJ especially in severe signal-to-jamming ratio (SJR).

Anti - follower jamming analysis of multi - sequence frequency hopping in AWGN channel

The modulated signals sent by conventional frequency-hopping systems are easily affected by follower jamming. Multi-sequence frequency-hopping is a frequency hopping communication system that uses channels to represent messages. It has good anti-follower jamming performance.Compared with differential frequency hopping, which uses user data to determine the transmission frequency, increasing frequency hopping sequence as a constraint can better suppress out-of-band jamming. In order to further study the effect of multi-sequence frequency hopping under follower jamming, a new multi-sequence frequency hopping transmission model under AWGN channel is established, the principle of multi-sequence frequency hopping anti-jamming was analyzed, and the performance of multi-sequence frequency hopping under follower jamming with different parameters is studied. The oretical analysis and simulation results show that multi-sequence frequency hopping can gain about 2.47-2.7dB when the SNR is 13.35dB and the BER requirement is 10^(-4), compared with the conventional frequency hopping.

A Rapid Capture Method of Frequency Hopping Communication System in Airborne Data-Link

In frequency hopping communication systems, synchronization of frequency hopping sequences is a prerequisite for ensuring normal communication. In this paper, a rapid frequency hopping synchronization capture method is designed based on MSK modulation. A method of solving the constant false alarm threshold is given, and a set of high performance synchronization codes are selected. We assessed the effectiveness of the proposed process by simulation based on MATLAB and Vivado, and it can complete rapid synchronous capture in the frequency hopping communication system.

New Bounds on Wide-Gap Frequency-Hopping Sequences

In a frequency-hopping (FH) system, to avoid that the received signal would be prone to be interfered, the equipped FH sequence of each user should have wide FH gap, i.e., the adjacent two frequencies should have some gap. In this letter, we extend the Lempel–Greenberger bound and Peng-Fan bounds for wide-gap frequency-hopping sequences (WGFHSs). The proposed bounds are tight in the sense that they can be achieved by the parameters of some WGFHSs.

Design and Performance Analysis of an Index Time-Frequency Modulation Scheme for Optical Communications

In this article, we propose an index modulation system suitable for optical communications, based on jointly driving the time and frequency of the signal: an index-time frequency hopping (I-TFH) system. We analyze its performance from the point of view of its efficiency in power and spectrum, and its behavior in terms of error probability for the non-turbulent free-space optical (FSO) channel. We compare I-TFH with already proposed index modulated systems of the same nature, but where the amplitude or the number of transmitters are driven instead of the signal frequency. We derive and compare approximations for the average symbol and bit error probabilities of all these systems. The simulation results show that said approximations are tight enough for a wide range of signal-to-noise ratios and system parameters. Moreover, I-TFH shows to be better performing in BER and/or power efficiency than the comparative alternatives, and may offer interesting properties in a variety of contexts.

An Experimental Study of Sub-1 GHz Frequency-Hopping-Based 6LoWPAN Mesh Networking for Smart-Grid Applications

This paper presents an experimental study of a multihop Internet Protocol Version 6 over Low-Power Wireless Personal Area Networks (6LoWPAN)-based mesh system that uses un-slotted channel hopping (USCH) medium access control (MAC). Designers of wireless smart-grid networks are using (or looking to use) the Sub-1 GHz spectrum, given its longer radio range compared to the traditional 2.4 GHz spectrum used in Wi-Fi® or Bluetooth® low energy. The frequency-hopping (FH) technique is attractive in this area, as it provides improved robustness and longer range owing to the higher transmission power that regulatory requirements allow. Although Sub-1 GHz allows for a longer range, smart-grid networks deployed over a large geographic area still require multiple hops to provide the required coverage. Many proprietary and standards-based solutions have been proposed to implement such a networking protocol. Notable specifications in this area include the Field Area Networks (FAN) specification from the Wi-SUN (smart utility networks) Alliance and the JupiterMesh specification from the Zigbee Alliance. Little is known about the performance of FH systems over a multihop network, however. This paper presents an implementation of an FH-based multihop networking protocol based on the Texas Instruments (TI) SimpleLink™ TI 15.4-stack, with an experimental study of such a system over multiple hops compared to a non-frequency-hopping (non-FH) system. Results show that the proposed FH-based 6LoWPAN mesh system significantly improves network coverage, network capacity, and communication robustness to interference while demonstrating coexistence capabilities.

Design of Multistate Diplexers on Uniform- and Stepped-Impedance Stub-Loaded Resonators

This paper presents the proposal and design of multistate diplexer on uniform- and stepped stub-loaded resonators, that is, a three-state diplexer (TSD) and a four-state diplexer (FSD). The two proposed diplexers have an attractive application in a frequency-hopping system with miniaturization in their overall size. Next, three and four sets of second-order bandpass filters are applied to form the three and four filtering channels, respectively. These filtering channels are then used to comprise these multiple-state diplexers. In this way, compact size and high-frequency selectivity have been well achieved. For the purpose of demonstration, the prototypes of TSD and FSD are fabricated and measured. The measured results are found in good agreement with the simulated results.

Research on Frequency Hopping Synchronization Strategies based on TOPSIS Method

The synchronization of hopping frequency is a key step in frequency hopping communication systems. During system synchronization, the contradiction emerges between synchronization duration and credibility in the capture confirmation process after frequency acquisition, which make it difficult for the system to establish synchronization quickly and steadily. Thus, a solution is presented based on the classic Technique for Order Preference by Similarity to an Ideal Solution (TOPSIS) to solve this problem. Firstly, a mathematic model for recognition process is built by Markov chains. Secondly, TOPSIS is employed to make analysis and suggestions to the recognition strategies. Results show that the presented mothed can shorten the synchronization time, ensure the reliability of the synchronization systems, and achieve an optimal effect in frequency hopping capture confirmation process.

An optical frequency-hopping scheme based on phase modulator-embedded optical loop mirror

An optical frequency-hopping scheme using phase modulator-embedded optical loop mirror (PME-OLM) is proposed, analyzed and demonstrated to achieve long distance secure communications. In the proposed system, the data from every user are separated into small data segments in time domain and carried by different wavelength carriers instead of being fixed on one carrier all the time. The segments from different users occupy different wavelengths at different time according to the hopping pattern, which can be regarded as encryption key. Therefore, any particular user data are interference to data from other users. The feasibility and performance of the frequency-hopping scheme has been investigated through simulation by VPI transmission Maker. A 4-frequency-hopping system demonstration was designed to support a 20 Gb/s non-return-to-zero (NRZ) data error-free transmission through 8-km dispersion compensated fiber (DCF) and 32-km single mode fiber (SMF). And an analysis based on a theoretical model was established to evaluate the security performance of the frequency-hopping communication system.

A new family of optimal FHS sets with composite lengths

In frequency-hopping spread spectrum systems, frequency-hopping sequences (FHSs) are widely used to alleviate the interferences caused by the hits of frequencies. In this paper, based on the Zeng–Cai–Tang–Yang cyclotomy and the Chinese Remainder Theorem, a family of FHS sets with composite lengths is constructed and the Hamming correlations of the new FHS sets are derived by some basic properties of cyclotomic numbers. The results show that the proposed FHS sets are optimal with respect to the Peng–Fan bound. Furthermore, it generalizes some earlier cyclotomic constructions of optimal FHS sets and produces optimal FHS sets with new parameters which are not covered in the literature.