In this method, different signals can be transmitted by s ignals randomly hop among a set of predefined arrangement of frequencies. Even if interference is occurring it only affects the signal for a very short interval. A narrow frequency band is required for a single carrier frequency whereas a much wider bandwidth is required for frequencyhopping of signals while transmitting the data. At a given time, just a minor part of bandwidth is used for transmission. As a result the whole bandwidth remains the same . FHSS does not provide any extra protection against wideband noise, however this method significantly reduces the losses that occur due to narrowband interference sources.
solving dense multipath interference (a consequence of the extremely high delay resolution of the signals), low con- sumption, high resistance to the interference from other communication systems, low probability of interception, high spatial resolution or the possibility of coexistence with other radio systems in the same frequency bands. After the FCC ruling in February 2003, the development of UWB tech- nology has been accelerated by the entry of new enterprises and research centers that are providing new approaches to solve some of the main problems of UWB systems.
The last decade has witnessed a paradigm shift from low- bitrate narrowband wireless systems to broadband wireless sys- tems. This trend continued with the recent emergence of the family of Ultra-WideBand (UWB) systems  - , also re- ferred to as impulse radio or time domain radio systems, which have received considerable attention both in the USA and in Eu- rope. The first UWB propagation results were reported in . It was shown in  -  that UWB signals do not suffer from severe fading, since they benefit from the presence of a huge number multipath components. Therefore the performance of UWB systems is robust against the hostile channel-induced im- pairments of conventional narrower bandwidth systems.
Abstract— A patch antenna is a type of radio antenna with a low profile, which can be mounted on a flat surface. It consists of a flat rectangular sheet or "patch" of metal, mounted over a larger sheet of metal called a ground plane. This thesis presents the idea of recent developments and advancements in the field of wireless technology to realize high-speed communications which are performed in wideband technology. In this graduate qualification, work the wideband patch antenna is designed to analyze the results. The most commonly designed microstrip antenna is a rectangular patch. The rectangular patch antenna is a one-half wavelength long strip of rectangular microstrip transmission line that is shown in this work. The simulation is done using CST STUDIO SUITE simulation software.
The variation of ac conductivity with respect to that of frequency for all composites is shown in Fig 3. It can be seen that at higher frequencies the conductivity has highest values when compared to that of lowest frequencies. The conductivity tends to increase with increase in frequency which indicates increased hoppingfrequency of the charge carriers. Further the increase in conductivity can also be attributed to the formation of interfacial p-n hetero-junction barrier between PANI and Co 3 O 4 . The
The clock distribution network consumes nearly 70% of the total power consumed by the IC since this is the only signal which has the highest switching activity. Normally for a multi clock domain network we develop a multiple PLL to cater the need, this project aim for developing a low power single clock multiband network which will supply for the multi clock domain network. This project is highly useful and recommended for communication applications like Bluetooth, Zigbee. WLAN frequency synthesizers are proposed based on pulse-swallow topology and the designed is modeled using Verilog simulated using Modelsim and implemented in Xilinx.
Polycrystalline BFN-ST40 nanoceramic has been successfully synthesized by Ball milling induced solid sate reaction technique. The present sample shows the good crystalline and homogenous nature. At low temperature, ac conductivity of BFN-ST40 sample increases sharply with increase in frequency. This implies the presence of dispersion in conductivity with respect to frequency. Conductivity of the present sample increases with increase in frequency at higher temperature. Universal dielectric response (UDR) law can be a possible cause in this case of ac conductivity variation with frequency. Variation in Activation energies with the increase in frequency exhibits that at lower frequency the long range hopping involves to overcome the high barrier width while the lower activation energy at high frequency involves the short range or localized hopping.
Diﬀerent kinds of dual-band directional antennas are proposed in [7–10]. The antenna proposed in  consists of a pair of printed dipoles for the lower frequency band and two pairs of dipoles for the higher frequency band. Luk and Wong proposed ME dipole antennas in  ﬁrstly, and then ME dipole antennas attract much attention from several research institutions and scholars. Diﬀerent types of ME dipole antennas were proposed in [6–15]. As discussed in [6–15], ME antennas have outstanding radiation and impedance bandwidth performance. A dual-band directional antenna is presented in , and the antenna consists of an irregular shorted patch and three planar dipoles. A V-slot is loaded on the planar dipole acting as a capacitive loading in the lower frequency band (0 . 780 ∼ 1 . 1 GHz), enhancing the band impedance matching. Two additional smaller planar dipoles are placed and connected to the irregular short patch for achieving another wideband performance in the higher frequency band (1 . 58 ∼ 2 . 62 GHz). A dual-wideband double-layer ME dipole antenna with a modiﬁed horned reﬂector was proposed in . A double-layer folded electric dipole structure with a certain inclination is utilized to provide wideband nature by changing the current distribution. A feeding structure with a U-shaped and tapered line is designed to reduce the size and enhance the impedance matching performance. The
PSD of MAT within the shared frequency stop-bands behaves unsteadily and irregularly; besides, the suppres- sion bandwidth is much more narrow than the required bandwidth. SCAN can achieve at least − 15 dB, but at most − 20 dB, whereas the spectrums of the generated sequence by CAN, CYC, and FRE show no suppression abilities on the stop-bands, because these three algorithms optimize the SIR of the radar system by designing the receive fil- ters adaptively. For CYC and FRE, the PSD levels within the stop-bands are even higher than those out of the stop- bands. It is fair to say that GFT behaves better than the other five algorithms, and it almost achieves the required level: the PSD comes to at least −24 dB, at most −27 dB for each channel in average.
In this research paper, a digitally tuned quadrature oscillator has been designed and simulated which provides the facility of tuning the frequency of oscillations digitally having good linearity with digital control word. Now a days, digitally tuned devices are very useful because hybrid systems (i.e., a combination of analog & digital systems) are preferred due to the advances in IC technology to obtain the advantages of both the analog and digital world. This type of digitally tuned quadrature oscillator will be very attractive from the point of view of interfacing. Here, the wide range of the frequency of oscillations for oscillator circuit can be achieved which is controlled by a digital control word (n-bit long). The main aim of designing the oscillator circuit is for synthesising the frequencyhoppingsignals used in indirect method of frequencyhopping spread spectrum. In order to perform the software implementation of this oscillator, PSPICE simulation tool on Windows platform has been used with conforming results in support of the theory. The density and speed of N-MOSFETs are very high that’s why these transistors have been used for switching purpose.
The growing demand of short-range wireless connectivity for indoor application has lead to the development of various standards to meet the requirements of different segments of the market. The frequencyhopping spread spectrum (FHSS) technique has become a subject of interest, as it has been applied in many applications. The theories of phase-locked loops (PLL) and FHSS have been analyzed in details in the literatures -. The FHSS approach has been adopted by several commercial wireless communication standards, such as wireless LAN, Bluetooth etc . The FHSS offers advantages, like resistance to jamming, resistance to interference and multipath fading. The transceiver in a FHSS based system switches carrier frequency rapidly and a PLL based system is required to generate the hopping carrier frequency. The settling time is an important design requirement for such PLL based frequency-hopping operation. This settling time is determined by the loop characteristics and is inversely proportional to the loop band width (BW) .
This paper proposes a technique called uncoordinated frequencyhopping to counteract the jamming attack without using any shared keys. With the use of node cooperation this proposal achieves communication efficiency and stronger jamming resistance. In this network the nodes are acting as relay nodes i.e., it will broadcast the message to all nodes. This paper proposes collaborative broadcast protocol which analyses the successful packet reception rate and node cooperation. In these schemes the broadcast message is subdivided into multiple short packets and each packet is transmitted over a selected channel which is known to the sender. Such channel switching over a large frequency range effectively eliminates jamming attack. Further enhance the same in uncoordinated direct sequence spread spectrum, in which each transmitter sends the message with the help of spreading sequence randomly selects from a set. The receiver can retrieve the message only by choosing the same synchronised message chose by the transmitters. So the jamming effect eliminated with the use of UDSSS and collaborative protocol.
Frequency-hopping communication has good anti-interference, low probability of interception and strong networking capability. It has been greatly developed in the military field. Radio frequency-hopping technology has been widely used in military communications and has greatly improved anti-interception and anti-interference capabilities of military equipmen  . However, in modern warfare, not only voice information is required to be transmitted, but also a large amount of data and video information are required to be transmitted at a high speed. Since short-wavelength channels have characteristics such as multi-path effect and band limitation, conventional short-wave frequencyhopping systems employ MFSK and other modulation methods for high-speed data. Transmission can no longer meet the demand. Gaussian minimum frequency shift keying (GMSK) method has the advantages of good spectrum utilization efficiency, good anti-jamming performance, and non-coherent demodulation, so it has been widely used in mobile communications  . Under the fixed channel bandwidth, using GMSK modulation can give higher data transmission rate than using FSK or MFSK modulation  . Therefore, this paper will explore the anti-jamming performance of GMSK in short-wave frequencyhopping.
In the fast frequencyhopping (FFH) system, due to a symbol in a plurality of frequencyhoppingfrequency to send, hopping with the function of frequency diversity, the receiving end can through proper diversity combining techniques enhance the system's anti-jamming ability. But in the partial band jamming, the performance of the fast frequencyhopping system will decrease. The partial band jamming can be effectively suppressed if the full use of the frequency diversity in the fast frequencyhopping system can be effectively suppressed by the receiver diversity combining technique. Therefore, it is a key to improve the anti-jamming ability of the fast frequencyhopping system.
Due to the increase use of widebandsignals in the ﬁelds of wireless communication system and radar, the problem of direction of arrival (DOA) estimation of wideband sig- nals has been of considerable interest to the array signal processing in recent years. Many methods have been pro- posed to estimate the DOAs of widebandsignals, among which the maximum-likelihood (ML) methods and sub- space methods are most studied. The ML estimators show excellent performance but it needs multidimensional non- linear global search . The subspace methods, although not optimal, are computationally more attractive than ML methods. The subspace methods can be classiﬁed into two major categories: incoherent signal-subspace method (ISSM)  and coherent signal-subspace method (CSSM) [3-6]. These methods decompose the incident widebandsignals into narrowband components by pass- ing them through a bank of narrowband ﬁlters, and then obtain the DOA estimation incoherently or coherently. The ISSM incoherently constructs the ﬁnal result by tak- ing an average of diﬀerent frequency bins. Although it
Abstract: A frequency reconfigurable micro strip antenna using a feed line for frequency agile applications is demonstrated in this paper. This antenna consists of two rectangular strips separated by rectangular slots Four RF switches (PIN Diodes) are placed in the rectangular ring slot to bridge the gap and to switch the frequency between WLAN bands resonating at 5.2 GHz and 5.8 GHz. PIN diodes are used to switch the frequency among WLAN bands. When compared to traditional micro strip antenna, the proposed antenna provides a size reduction of 8% at 5.2 GHz, and 60% at 5.8 GHz. The simulated return loss, and radiation patterns are presented and compared with the experimental data. This antenna can be used for modern wireless networks to improve spectrum efficiency.
This paper introduces a new direction-of-arrival (DOA) estimation method for wideband signal sources. The new method estimates the DOA of wideband signal sources based on squared test of orthogonality of projected subspaces (Squared TOPS) which is an improved method of TOPS. TOPS and Squared TOPS use the signal and noise subspaces of multiple frequency components of wideband signal sources. Although coherent wideband method, such as coherent signal subspace method (CSSM), performs high DOA estimation accuracy, it requires the initial estimate of signal source directions. On the other hand, TOPS and Squared TOPS can provide good performance of DOA estimation without the initial value of signal sources; however, some false peaks appear in spatial spectrum based on these methods. The proposed method, called weighted Squared TOPS (WS-TOPS), uses the modified squared matrix and selective weighted averaging process to improve DOA estimation performance. The performance of WS-TOPS is compared with those of TOPS, Squared TOPS, incoherent MUSIC, and test of orthogonality of frequency spaces (TOFS) through computer simulations. The simulation results show that WS-TOPS can suppress all false peaks in spatial spectrum and improve DOA estimation accuracy and also keep the same resolution performance as Squared TOPS.
analyzed regardless of the effect of the speed of locomotion. The average values reported in Table 1 represent the mean of data measured over the whole speed range of locomotion obtained in each animal. In Table 2, step frequency and natural frequency of the bouncing system were measured by averaging N runs obtained over the whole speed range in all subjects; hysteresis was measured on n subjects during one run at a speed approaching their average speed; similarity to an elastic bounce was measured on all runs of the subjects studied by Legramandi et al. (2013) and Cavagna et al. (2008) over a speed range less than 11 km h −1 where the freely chosen step frequency equals the resonant frequency of the system (on-/off-ground symmetrical rebound) (Schepens et al., 1998) and the deviation from similarity to a symmetrical bounce (landing – take-off asymmetry) is largest (Cavagna, 2009).
In this PTM modulation scheme, the interval between adjacent constant duration pulses is determined by the amplitude of the modulating signal. This is an anisochronous technique where the duration of each sampling episode is determined by the modulating signal. Therefore, it does not have a fixed clock interval. The pulse interval modulation (PIM) waveform can be generated when a comparator and ramp generator are connected as a feedback loop to reset as equivalence between the ramp and the DC shifted signal is detected, see Fig 2.12. The addition of the DC voltage to the modulating signal is necessary to ensure the existence of a sufficient headroom for the ramp to sample the most negative input swings under all conditions. In the case of uniformly sampled PIM a sample and hold is inserted at the input stage, while in the case of naturally sampled PIM it is omitted. In the case when the modulating signal is absent, the PIM modulator output is a series of uniformly spaced narrow pulses at a constant free-running frequency. The modulation index M (0 < M\ < 1) can be defined in this context as the peak-to-peak modulating signal swing divided by twice the DC level. Operation at very high levels of modulation index should be avoided since the negative swing of the shifted modulating signal tends to zero hence results in a rapid increase in the instantaneous pulse interval [48, 49].
In JT-60U, the confinement properties and onset con- ditions of the internal transport barrier (ITB) in weak pos- itive magnetic shear, and weak and strong reversed mag- netic shear plasmas have been studied [1, 2]. Although the turbulence suppression by E × B shear is believed to play an important role in ITB formation , the relation- ship among ITB performance, E × B shear, and the char- acteristics of plasma turbulence is not fully understood. Thus, microwave reflectometer systems using O-mode and X-mode propagation have been developed [4, 5]. In a pre- vious study using a three-channel fixed-frequency reflec- tometer system, no drastic change in the frequency spec- trum was observed during the ITB formation phase, and broadband density fluctuations still existed in the ITB re- gion even after a box-type ITB formed . On the other hand, a considerable reduction in the correlation length of the reflectometer signal was observed after the ITB forma- tion without a clear change in the fluctuation amplitude . To evaluate the E r profile, charge exchange recombi-