Frequency hopping spread spectrum fhss is a method of transmitting radio signals by hopping or shifting carrier signals across numerous channels with pseudorandom sequence which is already known to the sender and receiver. Frequency hopping also can effectively reduce the influence of fast fading. Fhss utilizes frequency hopping while dsss utilizes pseudo noise to modify the phase of the signal. Receiver hops between frequencies in sync with transmitter. What is the difference between fasttwitch and slowtwitch muscles. The main difference between conventional and cognitive multibeam systems is that in the latter multiple beams within a cluster share available spectrum in the time domain instead of the frequency.
A comparison of frequency hopping and direct sequence spread spectrum. Pdf slow frequency hopping solutions for gsm networks of. Fhss offers many advantages including high resistance to narrowband interference, low probability of intercept and capability to share spectrum with. Difference between slow frequency hopping and fast. Depending upon relation between hopping rate and symbol rate there are two types viz. Link 22 was also designed to complement and interoperate easily with link 16. In fast frequency hopping, multiple hops are required to transmit one symbol. Therefore, the delay difference between any two paths from the reference. The difference between slow frequency hopping and fast frequency hopping is that the frequency of latter changes faster than frequency modulation. Nov 21, 2016 frequency hopping spread spectrum fhss is a method of transmitting radio signals by hopping or shifting carrier signals across numerous channels with pseudorandom sequence which is already known to the sender and receiver. Bluetooth adaptive frequency hopping and scheduling n. Bluetooth adaptive frequency hopping and scheduling. During any one hop, however, an fh signal appears to be a narrowband signal. It avoids that a stationary terminal that happens to be located in a fade looses its link to the base station.
System model and method of analysis frequency hopping improves the system performance by providing immunity to fast fading rayleigh fading 4 and cochannel interference. A frequency hopping radio is capable of hopping its operating frequency over a given bandwidth many times a second with hf radio, this bandwidth is limited due to changes in propagation. Frequency hopping is the only effective counter measure to both forms of electronic attack. Frequency hopping spread spectrum fhss and direct sequence spread spectrum dsss. Reliable adaptive modulation and interference mitigation. Performance of fast frequency hopping ofdm under doppler spread. In fast frequency hopping ffh, the carrier frequency is allowed to change more than once during a bit duration, but this is not implemented in gsm at first, the frequency hopping was used in military applications in order to improve the secrecy and to make the system more robust against jamming. The difference between fast and slow frequency hopping is based on the chip duration, and the signal rate of the encoded signal to be sent.
However, in order to achieve a significant gain from frequency hopping, it has been shown that at least 3. Difference between fhss and dsss difference between. Therefore, you would need to report the range of noise fluctuations e. What is the difference between slow frequency hopping.
Sound level meter time weightings fast, slow or impulse. Draw a similar block diagram for a slow frequency hopping sfh demodulator, and. Each of these methods encodes the data into a series of signals at l different power levels. A narrowband radio being interfered with will experience a pop or burst of noise when the hopper hits its channel. Publishers pdf, also known as version of record includes final page. On the other hand, afh is rather slow in responding to changes in the environment and the packet loss is more signi. One or more symbols are transmitted over the same carrier frequency. Fast frequency hopping a recorded conversation is to be transmitted by pn spread spectrum. Study of fast frequency hopping spread spectrum and jamming systems er. The difference between slow frequency hopping and fast frequency hopping is that the frequency of latter changes faster than frequency modulation asked in.
Reliable adaptive modulation and interference mitigation for. Difference between slow frequency hopping and fast frequency. The use of fasthopping frequency synthesis is a critical component of frequencyhopped spread spectrum fhss systems. View notes difference between slow frequency hopping and fast frequency hoping from computer 101 at computer systems institute, chicago. The simulation sequences for fast and slow frequency hopping is the same in number and frequencies of spreading carriers and both used bpsk traditional. Slow frequency hopping is a popular technique for wireless lans. One symbol is transmitted over multiple carriers in different hops. For example, slow twitch muscles in the lower leg aid in standing, while fast twitch muscles in the eyelid enable blinking. In the fast ring any new build is available through windows update as soon as it is released by ms engineers.
Bluetooth began with a hopping rate of 10 hz but now uses 1600 hops per second. For slow frequency hoppers, the path propagation times are too fast to allow the receiver to reject the interference. A theoretical study of the performance improvement in. In slow frequency hopping, multiple symbols are transmitted in one frequency hop. Study of fast frequency hopping spread spectrum and.
From the beginning it was designed to be resistant to noise, interference, jamming, and unauthorized detection. Pdf performance of fast frequency hopping ofdm under. In slow frequency hopping, time duration between two hops th or tc as shown data bit duration tb. Fast is generally the chosen time weighting for noise measurements. Slow frequency hopping spreadspectrum how is slow frequency hopping spreadspectrum abbreviated.
Frequency hopping spread spectrum linkedin slideshare. Fast twitch and slow twitch muscles are types of muscle fiber used to perform different kinds of physical activity. This is called slow frequency hopping sfh, because more than one bit is transmitted using the same frequency. Please go through the following link, its quite straightforw. Slow frequency hopping is a quality and capacity enhancement feature for the gsm system. The individual signal is a much, much wider bandwidth signal as compared to sfhss. Data communication and networking question bank crazyengineers. The derivation of probability density function pdf of carrier to interference ratio ci is presented in the appendix. Slow fhss has tc ts fast fhss has tc 1 ece interview questions and answers tutorial for fresher beginners wireless communication interview questions pdf. Pdf passive optical fast frequencyhop cdma communications. Frequency diversity frequency hopping systems provide frequency diversity since many frequencies are used in the. The study in 15 continues the study of 14, and its main difference from 14 is the introduction of softoutput computation. What are the applications and advantages of the frequency. When the carrier frequency changes every few bits of data stream, it is a system with slow frequency.
With slow hopping, the interference reductions are slight. Slow frequency hopping is used to reduce the effects of radio signal fading and to minimize the effects of interference from radio channels that are operating on the same frequency. In slow frequency hopping type, more than one symbols are transmitted during the time between two frequency hops. Adaptive frequency hopping is a system which is used to revamp. As fhss systems rely on varying rf carrier frequency, it leads to bursty nature of errors due to frequency selective fading mainly. Th and if the system is a slow hopping or a fast hopping system. John burns, performance comparison of frequency hopping and direct. Frequency hopping spread spectrum fhss is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. Study of fast frequency hopping spread spectrum and jamming. Fhss is a spread spectrum technology sst and offers greater protection from interference as compared to narrowband technologies. The changes are controlled by a code known to both transmitter and receiver. The impulse time weighting is about four times faster than fast, with a short rising time constant but a slow falling one.
Hf frequency hopping radio knm media llp knm media llp. Chevrollier national institute of standards and technology gaithersburg, maryland 20899 email. The difference between slow frequency hopping and fast frequency hopping is that the frequency of latter changes faster than frequency modulation asked in electrical engineering what is fast. Fhss frequency hopping spread spectrum i discrete changes of carrier frequency sequence of frequency changes determined via pseudo random number sequence two versions fast hopping. Radio signal fading is often limited to a specific frequency range. Thus, to be effective, the hopping rate must be kept higher than the inverse of any interfering path delay time. Radio frequencies that are separated by more than 1 mhz may do not fade simultaneously iii. Frequency hopping verus direct sequence spread spectrum.
Slow and fast frequency hopping in gsm frequency hopping can be briefly defined as a sequential change of carrier frequency on the radio link between the mobile and the base station. It is little used in most countries these days and so can usually be ignored. Frequency hopping is achieved by dividing the large bandwidth into smaller channels that would fit the data. The fast time weighting is usually used for measuring all the sound in your environment, which may vary widely over time. Transceiver architectures and submw fast frequencyhopping. The phase difference for the nth path between two frequencies f i and f j is n. Dec 27, 2016 top 30 wireless communication 1 ece interview questions and answers tutorial for fresher beginners wireless communication interview questions pdf wireless communication interview questions. Advantages, disadvantages and applications of fhss. In gsm, one carrier frequency is divided into eight time slots. A comparison of frequency hopping and direct sequence.
Simulation and comparison between slow and fast fhbpsk. By transmitting the message energy over a bandwidth much wider than the minimum required, spread spectrum modulation techniques present two major advantages. There may be a number of builds released to the fast ring that are then tested by the fast ring and the next build may contain corrections from the previous builds. A frequency hopped signal can be encoded using many different approaches such as fsk, psk, and mfsk. Using fast frequency hopping technique to improve reliability of. Slow frequency hopping spreadspectrum listed as sfhss. The differences were probably in the reinforcements.
Hybrid fhdss system, 36 hopping frequencies spread across the entire 2. Solved what is the difference between fast hopping and. Fhss system, 30 hopping frequencies always located in one side of the 2. Advantages, disadvantages and applications of direct advantages and applications of spread spectrum. In gsm telephony, slow frequency hopping can be used, at the discretion of the network control software. Frequencyhopping spread spectrum fhss is a method of transmitting radio signals by rapidly changing the carrier frequency among many distinct frequencies occupying a large spectral band. Mar 26, 2014 types of fhss there are two types of frequency hopping. Frequency hopping spread spectrum fhss is a method of transmitting radio signals by shifting carriers across numerous channels with pseudorandom sequence which is already known to the sender and receiver. Slow frequency hopping vs fast frequency hopping gsm. Link 22 was developed to replace and overcome the known deficiencies of link 11. Major differences in fasst and sfhss page 2 rc groups. Fhss and dsss, which stand for frequency hopping spread spectrum and direct sequence spread spectrum, are two spread spectrum techniques.
This is fast enough to thwart an eavesdropper who would need to first lock onto the signal before they could intercept or jam it, but slow enough to include thousands of. There are no difference between our fasst and sfhss in the communication distance. What is the difference between fasttwitch and slowtwitch. Frequency hopping is an alternative technique for wireless. Direct sequence spread spectrum techniques spread spectrum technology was first introduced about 50 years ago by the military as a way of sending secure communications. Fhss is used to avoid interference, to prevent eavesdropping, and to enable codedivision multiple access cdma communications.
The main difference is in how they spread the data into the wider bandwidth. Frequency hopping spread spectrum is defined in the 2. A cognitive beam hopping satellite can enhance the spectrum use assuming that the secondary gateway is aware of the primarys beam hopping pattern. Difference between dsss and fhss figure3 depicts dsss spectrum and fhss spectrum. Pdf this paper proposes an allfiber fast optical frequencyhop code division multiple access ffhcdma for highbandwidth. This program is called nato improved link eleven, which is. It was designed with automated and simple management to ensure that it is easier to manage than both link 11 and link 16. Top 30 wireless communication 1 ece interview questions and.
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