Frequency Hopping Technique Research Articles

Research of Frequency-Hopping Communication for Arbitrary Array Based on Adaptive Beam-Forming

Aiming at the problem of poor performance of suppressing the wide band jamming and fast following jamming in Frequency-Hopping (FH) communication system, a communication scheme by combination of the complementally transformed minimum variance with FH technique for arbitrary array (CTMV-FH) is proposed, based on the purpose to maximize the output Signal to Interference and Noise Ratio (SINR). Basic theory of CTMV is introduced. The algorithm is used to suppress the wide band jamming and fast following jamming. Simulation results show that the scheme can suppress the wide band jamming and fast following jamming effectively in FH communication system.

Differential Frequency Hopping Systems Using Soft Decision Viterbi Decoding Algorithm

Differential frequency-hopping (DFH) technique has been widely studied and applied in the military communications due to its many desirable features, such as reliable high data rate transmission characteristics, anti-jamming abilities and information security. In order to improve the information security of the conventional DFH systems, a novel DFH system with the G-function controlled by the well-known maximal length sequences, is proposed in this paper. In addition, both BCH code and soft decision Viterbi algorithm are also used in the proposed scheme to further improve the system performance. Our results show that the proposed scheme not only provides the higher information security but also improves the system performance indeed, compared to the conventional schemes.

A Fast Fixed-Frequency Adaptive-On-Time Boost Converter With Light Load Efficiency Enhancement and Predictable Noise Spectrum

An integrated fixed-frequency adaptive-on-time (AOT) DC-DC converter with fast transient response and enhanced high light-load efficiency is presented. At both Continuous-Conduction-Mode (CCM) and Discontinuous-Conduction-Mode (DCM) operation, the on-time is adaptively controlled by a frequency locked loop so that the switching frequency tracks the reference frequency with less than ±0.5% error in the whole operating range. At CCM operation, the reference frequency is fixed at 1 MHz. At light load with DCM operation, the reference frequency hops between 1 MHz and 1 MHz/N where N = 2 i and i = 1 to 5 according to the loads without load current sensor. Frequency hopping is introduced to boost the efficiency as well as reduce the EMI noise problem. A glitch-free on-time control circuit is introduced to increase the track accuracy and speed of the frequency locked loop. A mode decision circuit with digital hysteretic window is used to ensure a smooth transition between CCM and DCM operation. An on-time generator with proper logics is used to suppress frequency bouncing during frequency hopping. A prototype with 1.8 V-3.2 V input voltage, 3.0 V-4.2 V output voltage and 0 mA-800 mA load current range has been fabricated in a 0.35 μm 2P4M CMOS process. Load transient measurements verify that 8 μs-20 μs recovery time is achieved for load current increase. Measurement results also show a maximum efficiency of 94.8% is achieved at total output power of 3.269 W, and the light load efficiency is enhanced by the proposed frequency hopping technique with a predictable noise spectrum.

Swarm Based Defense Technique for Denial-of-Sleep Attacks in Wireless Sensor Networks

In Wireless Sensor Networks (WSN), the denial of sleep attack consumes more amount of energy which leads to depletion of battery power. This consumption of power makes the nodes more susceptible to the vulnerabilities and hence denial of service through denial of sleep. If a large percentage of network nodes, or a few critical nodes, are attacked in this way, the network lifetime can be reduced severely. In order to overcome the denial of sleep attack in this paper, we propose to develop a swarm based defense technique for denial of sleep attack. Initially an anomaly detection model is developed which determines the affected traffic between the nodes and based on this, the frequency hopping technique is initiated. Ant agents of Swarm intelligence are applied in each channel to collect the communication frequency and the frequency hopping time. Based upon the frequency hopping time the faulty channel is identified and the when the administer node gets this information it deletes the faulty channel. From our simulation results, we prove that this technique proves to be efficient in detecting the faulty channel and consumes less energy since the information about the all the attackers can be known using ants.

Self and static interference mitigation scheme for coexisting wireless networks

High density of coexisting networks in the Industrial, Scientific and Medical (ISM) band leads to static and self interferences among different communication entities. The inevitability of these interferences demands for interference avoidance schemes to ensure reliability of network operations. This paper proposes a novel Diversified Adaptive Frequency Rolling (DAFR) technique for frequency hopping in Bluetooth piconets. DAFR employs intelligent hopping procedures in order to mitigate self interferences, weeds out the static interferer efficiently and ensures sufficient frequency diversity. We compare the performance of our proposed technique with the widely used existing frequency hopping techniques, namely, Adaptive Frequency Hopping (AFH) and Adaptive Frequency Rolling (AFR). Simulation studies validate the significant improvement in goodput and hopping diversity of our scheme compared to other schemes and demonstrate its potential benefit in real world deployment.

System design for broadband digital radio broadcasting

In this article, we present an in-band onchannel (IBOC) broadcasting system suitable for digital audio and data broadcasting in FM and AM channels. The new design synergistically integrates frequency hopping, LDPC coding, hierarchical modulation, and band aggregation techniques to increase the data rate, improve spectrum efficiency, and at the same time provide the spectrum flexibility necessary in highquality audio and multimedia services. A prototype has been developed on a personal computer-based software defined radio platform. Numerical results and initial laboratory tests demonstrate the significant performance advantages of the new system design.

Formal Verification of Device Discovery Mechanism using UPPAAL

communication among the mobile devices is the growing area of research. Ad hoc networks are created among them for exchanging information over the small distances. The distance among the devices uniquely determines the topology of these ad hoc networks. Bluetooth is a low-cost and low-power wireless technology used to form short-range wireless ad hoc networks. It is based on frequency hopping technique. In order to guarantee the accurate functioning and to verify the connectivity of the devices, there are numerous tools and techniques exits. Formal verification is one of the technique used to validate and verify the correctness of any protocol. Using the verification tool UPPAAL a Bluetooth ad hoc system is modeled to formally verify the device discovery mechanism. In the tool, an ad hoc network consisting of Bluetooth transmitter and receiver is designed using frequency hopping technique. The transmitter and receiver verified the properties in the tool. These properties are for checking the connectivity of transmitter and receiver and reception of data among them. The connectivity of transmitter and receiver is confirmed by verifying the receivers reply to the transmitter and data connectivity is verified by checking the energy level of receiver. From the simulation, it is found that the high energy level of receiver depicts the acceptance of data and the zero energy level depicts the non-acceptance of data. These results were verified using the verifier component of the tool and proved to be satisfied.

MAC Design of Uncoordinated FH-Based Collaborative Broadcast

Uncoordinated Frequency Hopping (UFH) techniques are promising to address jamming attacks in wireless networks without requiring pre-shared secret keys, and its communication efficiency in the broadcast scenario can be significantly improved through node cooperation. In this letter, we take a first step to investigate efficient Media Access Control (MAC) strategies for the UFH-based collaborative broadcast, and derive closed-form expressions of the channel access probabilities for time-slotted systems to minimize the broadcast delay and to significantly reduce the energy cost. Numerical and simulation results are provided to verify our analysis and reveal some insights.

Jamming-Resistant Collaborative Broadcast Using Uncoordinated Frequency Hopping

We propose a jamming-resistant collaborative broadcast scheme for wireless networks, which utilizes the Un coordinated Frequency Hopping (UFH) technique to counteract jamming without preshared keys, and exploits node cooperation to achieve higher communication efficiency and stronger jamming resistance. In this scheme, nodes that already obtain the broadcast message serve as relays to help forward it to other nodes. Relying on the sheer number of relay nodes, our scheme provides a new angle for jamming countermeasure, which not only significantly enhances the performance of jamming-resistant broadcast, but can readily be combined with other existing or emerging antijamming approaches in various applications. We present the collaborative broadcast protocol, and analyze its successful packet reception rate and the corresponding cooperation gain for both synchronous and asynchronous relays for a snapshot scenario. We also investigate the full broadcast process based on a Markov chain model and derive a closed-form expression of the average broadcast delay. Simulation results in both single-hop and multihop networks indicate that our scheme is a promising antijamming technique in wireless networks.

Towards Optimal Adaptive UFH-Based Anti-Jamming Wireless Communication

Anti-jamming communication without pre-shared secrets has gained increasing research interest recently and is commonly tackled by utilizing the technique of uncoordinated frequency hopping (UFH). Existing researches, however, are almost all based on ad hoc designs of frequency hopping strategies, mainly due to lack of theoretical foundations for scheme performance evaluation. To fill this gap, in this paper we introduce the online optimization theory into our solution and, for the first time, make the thorough quantitative performance characterization possible for UFH-based anti-jamming communications. Specifically, we formulate the UFH-based anti-jamming communication as a non-stochastic multi-armed bandit (MAB) problem and propose an online learning-based UFH algorithm achieving asymptotic optimum. To reduce the time and space complexity, we further develop an enhanced algorithm exploiting the internal structure of strategy selection process. We analytically prove the optimality of the proposed algorithms under various message coding scenarios. An extensive simulation study is conducted to validate our theoretical analysis and show that the learning-based UFH algorithms are resilient against both oblivious and adaptive jamming attacks.

Parallel and Gaussian frequency hopping for dynamic coexistence in the unlicensed band

AbstractWith the surge of short‐range wireless applications, more networks are being deployed in the unlicensed radio band. The challenge that emerges is to accommodate these networks without breaching current rules and regulations on frequency usage. This paper studies the coexistence of several independent and dynamic wireless networks using the frequency hopping technique. We propose a novel hopping scheme that minimizes mutual interference and allows more networks to collocate effectively, but does not violate restrictions imposed by the Federal Communications Commission (FCC) regarding frequency constraint (related to the minimum number of frequencies in a hopping set) and time constraint (related to the maximum duration of using a particular frequency). The coexisting networks follow the Gaussian distribution in choosing transmission frequencies from parallel hopping spaces without the overhead of extra message exchange among networks. Simulation results on key metrics such as channel collision rate, goodput, and fairness in channel usage are presented to establish the viability of the proposed scheme in comparison with other contemporary approaches. Copyright © 2011 John Wiley & Sons, Ltd.

MODEL ORDER REDUCTION FOR PEEC MODELING BASED ON MOMENT MATCHING

Accurate and efiective system-level modeling has become necessary to address electromagnetic compatibility (EMC) issues in modern circuit and system design. Model order reduction (MOR) techniques provide a feasibility to approximate complex circuit models with compact reduced-order models. In this paper, an efiective MOR technique entitled multi-point moment matching (MMM) is implemented for the partial element equivalent circuit (PEEC) modeling. Moment information at multiple frequency points is used in this method in order to accurately estimate a given system over an entire frequency range of interest, and for each frequency an enhanced asymptotic waveform evaluation (AWE) is applied to obtain a reduced-order model by constructing a pole-residue representation of the original transfer function. The improvements of conventional AWE in aspects of both moment computation and moment matching can avoid ill-conditioned moment matrices and unstable dominant poles. The complex frequency hopping (CFH) technique is employed to select the multiple expansion points by using a newly developed upward- search algorithm. Numerical simulations of coupled microstrip lines in both frequency and time domain indicate the efiectiveness of the proposed method.

Design, calibration and application of wireless sensors for structural global and local monitoring of civil infrastructures

Structural Health Monitoring (SHM) gradually becomes a technique for ensuring the health and safety of civil infrastructures and is also an important approach for the research of the damage accumulation and disaster evolving characteristics of civil infrastructures. It is attracting prodigious research interests and the active development interests of scientists and engineers because a great number of civil infrastructures are planned and built every year in mainland China. In a SHM system the sheer number of accompanying wires, fiber optic cables, and other physical transmission medium is usually prohibitive, particularly for such structures as offshore platforms and long-span structures. Fortunately, with recent advances in technologies in sensing, wireless communication, and micro electro mechanical systems (MEMS), wireless sensor technique has been developing rapidly and is being used gradually in the SHM of civil engineering structures. In this paper, some recent advances in the research, development, and implementation of wireless sensors for the SHM of civil infrastructures in mainland China, especially in Dalian University of Technology (DUT) and Harbin Institute of Technology (HIT), are introduced. Firstly, a kind of wireless digital acceleration sensors for structural global monitoring is designed and validated in an offshore structure model. Secondly, wireless inclination sensor systems based on Frequency-hopping techniques are developed and applied successfully to swing monitoring of large-scale hook structures. Thirdly, wireless acquisition systems integrating with different sensing materials, such as Polyvinylidene Fluoride(PVDF), strain gauge, piezoresistive stress/strain sensors fabricated by using the nickel powder-filled cement-based composite, are proposed for structural local monitoring, and validating the characteristics of the above materials. Finally, solutions to the key problem of finite energy for wireless sensors networks are discussed, with future works also being introduced, for example, the wireless sensor networks powered by corrosion signal for corrosion monitoring and rapid diagnosis for large structures.

Experimental Microwave Validation of Level Set Reconstruction Algorithm

The capability of the level set method is illustrated for shape and location reconstruction using real measurement data in the range of 3-8 GHz. An experimental setup is utilized to measure the S-parameters using two Vivaldi antennas revolving around metallic pipes of different cross-sections. A two-dimensional reconstruction of the pipe's cross section is retrieved using the level set algorithm combined with the method of moments and the frequency hopping technique. The results show good agreement between the reconstructed cross section and the true configuration. This indicates to the strength of the level set method and its ability to cope with the noise in real measurements.

Capacity of FH wireless multi-hop networks

In this article, the capacity of wireless multi-hop networks with the frequency hopping (FH) technique is derived. Different from the previous work based on non- spread spectrum (SS) system, this study is based on frequency hopping spread spectrum (FHSS) and the retransmission mechanism. The analysis results show that the normalized transport capacity decreases as 1 / M λ , when the total available frequency band is divided into M sub-bands for frequency hopping and the nodes are randomly distributed in space according to a Poisson point process with intensity λ. In this work, the best transmission range per hop to get the maximum capacity is also derived. Besides, the results summarize how the capacity of FH wireless multihop networks is affected by the outage probability, target signal to interference plus noise ratio (SINR) and other system parameters.

An Adjoint-Field Technique for Shape Reconstruction of 3-D Penetrable Object Immersed in Lossy Medium

An inversion algorithm is presented that is based on hybridization of the adjoint scheme for calculating gradient directions with the method of moments. The goal is to reconstruct the shapes of 3D objects immersed in a lossy medium. The irregular shape of the reference object is modeled by a representation with spherical harmonics functions, whereas during the reconstruction, individual surface nodes are updated. In the adjoint scheme, gradient directions for the least squares data misfit cost functional are calculated by solving the forward problem twice in each iteration, regardless of the number of spherical harmonics parameters used in the reference model or the number of surface nodes used for the discretization of the shapes. The numerical results show that implementing the well known frequency hopping technique helps the algorithm avoid dropping in local minima.

Internally coded multicarrier frequency-hopping CDMA communication system and its performance analysis

A new internally coded scheme that combines frequency hopping (FH) and multicarrier (MC) code division multiple access (CDMA) techniques using a super-orthogonal encoder is proposed. In this method, the total bandwidth is partitioned into Ns1 disjoint bands and each band is also segmented into Ns2 subbands. On the basis of a super-orthogonal encoder output and a pseudorandom sequence, one of the Ns1 bands is selected. The data bit is then transmitted in the band in the form of the multicarrier FH (MC-FH) CDMA scheme, that is, Ns2 carriers are transmitted in the Ns2 subbands of the selected band. At the receiver, both hard and soft detectors are used. The performance of the proposed method in the additive white Gaussian noise (AWGN) and fading channels is evaluated. The results indicate that the proposed method outperforms the previously presented uncoded and coded MC-FH-CDMA systems, where the data are transmitted over the whole bandwidth, keeping the same bandwidth (spectral efficiency). Further, in the new method, the carriers hop in part of the total bandwidth, and hence coherent detection is more feasible.

Multigrid Optimization Method Applied to Electromagnetic Inverse Scattering Problem

An iterative reconstruction algorithm of accelerating the estimation of the complex relative permittivity of a cylindrical dielectric object based on the multigrid optimization method (MGOM) is presented. A cost functional is defined by the norm of a difference between the scattered electric fields measured and calculated for an estimated contrast function, which is expressed as a function of the complex relative permittivity of the object. Then the electromagnetic inverse scattering problem can be treated as an optimization problem where the contrast function is determined by minimizing the cost functional. We apply the conjugate gradient method (CGM) and the frequency-hopping technique (FHT) to the minimization of the cost functional, and also employ the multigrid method (MGM) with a V-cycle to accelerate the rate of convergence for getting the reconstructed profile. The reconstruction scheme is called the multigrid optimization method. Computer simulations are performed for lossy and inhomogeneous dielectric circular cylinders by using single-frequency or multifrequency scattering data. The numerical results demonstrate that the rate of convergence of the proposed metod is much faster than that of the conventional CGM for both noise-free and noisy cases.

Secure transmission over an existing public WDM lightwave network

We develop a spread-spectrum-based approach to security-enhanced transmission over an existing public wavelength-division-multiplexing (WDM) lightwave network. Secure transmission for a dedicated user is achieved by overlaying a covert channel onto a multichannel WDM network. The covert channel is spectrally encoded using the technique of frequency hopping and then temporally spread by a dispersive element, with the resulting average power below the noise floor in the fiber. The presence of the WDM channels provides an ad hoc security expansion and increases the difficulty for an eavesdropper to intercept and decode the secure signal

FHSS optical wireless transceiver for short range low‐speed indoor sensor interconnection

AbstractExperimental and simulation results from the operation of a prototype of wireless indoor optical transceiver based on frequency hopping techniques are presented. We choose spread spectrum techniques, as it allows multiple simultaneous accesses and also increases the robustness of the system against multipath‐induced distortion. It also reduces the effect of narrowband interference, as could be low‐frequency optical noise from fluorescence or incandescence lamps. FHSS techniques also allow coexistence with IrDA or remote control emitting devices without causing of suffering interferences. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 2193–2197, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21889