frequency hopping system's total bandwidth, by the convergence of several bands and do not form, is hopping anti-jamming of the important indicators. Hopping frequency hopping channel number (frequency hopping points) both width and frequency hopping, but also with the width of the hopping channel, channel width depends on the modulation method. In general, the hopping points better. Processing gain is frequency-hopping system bandwidth and channel bandwidth of the hopping ratio. If the hopping bandwidth W, the W is divided into N equally spaced channels, the frequency hopping system processing gain of GP = N, which is integrated frequency hopping anti-jamming ability of an indicator. Usually due to come into contact with the carrier frequency wireless communication systems are fixed communication systems, such as walkie-talkies, mobile phones and other vehicles are on the designated frequency to communicate, it is also known as fixed-frequency communications. This fixed-frequency communications system, the event of interference on the communication quality will decline,[url=http://www.uggsaleuks.co.uk/]UGG Sale[/url], even in severe disruption to communications. For example: radio programs, the general frequency of a transmitter to send a set of programs, different programs take different emission frequencies. Sometimes in order to allow the audience to listen to a good program, while the radio frequency transmitter to send the same with a few set of programs. Thus, if the frequency has been in a serious interference, listeners can also choose the clearest channel to listen to programs, which played an interference effect. But doing so requires a lot of the cost is the amount of spectrum resources in order to send a set of programs. If changing the number of carrier frequency to transmit a radio show, and also followed the radio listeners continue to tune in to receive these frequencies, so that even if a frequency has been disrupted, but also a good listen to this program. This becomes a frequency-hopping system. Also in the two sides of the confrontation of communication, the enemy attempts to find our communication frequency, so that the contents of intercepted information sent, or find the position where our communication equipment, so that guide fire destroyed. Fixed-frequency communication system is likely to expose and easy to be intercepted, this time, using frequency-hopping communication is more difficult to be intercepted hidden. Because the frequency-hopping communication is When the enemy lost in Therefore, the frequency-hopping communications with the anti-jamming and anti-intercept ability, and can be done to share the spectrum resources. So in the current modern electronic warfare frequency-hopping communications has shown great superiority. In addition, frequency-hopping communication also apply to civilian traffic in the anti-fading, anti-multipath, gateway anti-interference and spectrum efficiency. How Xiang hopping signal generated in the traditional fixed-frequency communication systems, the main transmitter oscillator frequency is fixed and set, so it's carrier frequency is fixed. In order to obtain the frequency hopping carrier frequency hopping signal, requiring the master oscillator frequency should be changed in accordance with control commands. This produces a device called frequency hopping hopping signal device. Typically, the device is frequency hopping and frequency hopping synthesizer generator, consisting of instruction. If the device as the master oscillator frequency hopping is not the traditional distinction between the transmitter. The information to be transmitted can be analog or digital signal format (marked in the figure for the letter code in), the corresponding modulation through the modulator, will be awarded for a fixed subcarrier frequency modulated wave signal, and then with the frequency synthesizer output mixing the primary carrier frequency signal, the output of the modulated wave signal to the RF carrier frequency passband, and following high-pass filter to the antenna after the feed out. This is the fixed-frequency signal transmission process. Frequency hopping system what frequency synthesizer output signal is affected by carrier frequency hopping command control. The role of the clock under the command generator continually hopping issue control instructions, constantly changing the frequency synthesizer output frequency of the carrier. Therefore, the mixer output frequency of the modulated carrier wave will continue to jump with the instructions, which by the high-pass filter and antenna hopping signal is sent. How to receive fixed-frequency signal frequency-hopping signal receiving device, generally used method of superheterodyne receiver, the receiver local oscillator frequency than the received signal carrier frequency outside a frequency difference, after mixing resulting from IF signal and a fixed combination of wave frequency generated by mixing ingredients. After filtering in the role of band-pass filter, filter combination wave frequency components, leaving the intermediate frequency signal into the demodulator. Demodulator output is to be sent to the receiving end of information. Frequency-hopping signal reception,[url=http://www.uggsaleuks.co.uk/]UGG Sale[/url], the process is similar with fixed frequency. In order to ensure access to the IF signal after the mixer, frequency synthesizer requires the output frequency of a frequency higher than the external signal. Because of external signal carrier frequency is hopping, then the requirements of the local frequency synthesizer output frequency with the external signal transition rules and transition, in order to get by mixing a fixed intermediate frequency signal. Hopping hopping device is a key component of the system, while the frequency-hopping synchronous frequency hopping system is the core technology. Synchronization of frequency hopping systems include the following: 1. Income side and frequency-hopping pattern generated by the same originator, that have the same frequency-hopping law. 2 received, the originator of hopping frequencies should be generated at the receiving end to ensure a fixed intermediate frequency signal that the carrier frequency hopping and locally generated revenue side difference of a frequency hopping frequencies. 3 the beginning and ending time frequency hopping synchronization in time, that is synchronized transition, or phase-coherent. 4 in the transmission of digital information, you should also do frame synchronization and bit synchronization. Further reading: 1
previous technology, while in fast frequency-hopping modulation accuracy is bound to bring down, receiver sensitivity degradation, as well as blocking stray increase performance and a series of negative effects. Huawei's base station is how to solve this issue? Here we start with the analysis of the RF phase-locked loop to illustrate. PLL lock time is mainly determined by the loop bandwidth,[url=http://www.uggsaleuks.co.uk/]UGG Sale[/url], the more wide-locking bandwidth, the shorter the time. The quality of the local oscillator signal from the reference clock (frequency phase), voltage-controlled oscillator, loop bandwidth and other factors, within the loop bandwidth depends on the local oscillator phase noise reference clock, outside the loop bandwidth depends on voltage-controlled oscillator. To the best loop bandwidth widen only two ways, first, reduce the voltage controlled oscillator performance, which is obviously undesirable; second reference is to improve performance. As the GSM system uses a 200kHz bandwidth, the phase frequency can not be too high, especially for the DCS1800 system N can not be too small, so the GSM system is difficult to improve loop bandwidth, which reduces the frequency lock time. In order to overcome these two difficulties, Huawei by adopting a unique dynamic loop bandwidth and ping-pong switching technology, can solve the signal quality and fast conversion between the contradictions. Dynamic loop bandwidth technology: work in the loop bandwidth is not fixed, but as the system needs change, but the system is inactive, the loop bandwidth to ensure optimum bandwidth back, so that the output signal best to ensure the system the best performance. Ping-pong switching technology: the circuit design of two identical oscillators, the two local oscillator through the switch to choose, when a local oscillator work, another fast local oscillator locked to the next desired frequency, in the through two slots in the middle switch to another local oscillator circuit. Thus, to avoid the emergence of slot of the first and last instantaneous system performance degradation. By using the unique dynamic loop bandwidth and ping-pong switching technology to achieve the 25MHz bandwidth of 900MHz, 1800MHz to 75MHz bandwidth at any frequency hopping, frequency hopping indicators are all over the GSM protocol requirements. Baseband frequency hopping technical difficulty is how to achieve high-speed exchange of information and data to meet the 217 jumps / s frequency hopping speed and 271kbits / s data transfer rate. Consider wireless interface slot as the basis for data exchange, the exchange method can be empty points, hours, packet switching. Huawei's base station in the design of advanced bus technologies to slot exchange as the basis for the baseband frequency hopping, the specific implementation method as follows: each transmitter (TRX) tuned at a fixed frequency, there is a fixed ID number. Transceiver downlink signal encoder will encode the formation of unexpected data format, the encoder algorithm based on frequency-hopping modulation of the burst should be the channel (ie TRX number), plus additional information about the formation of the power control specific data packet format, transceiver encoder at a fixed time (sub-slot) issued within the packet. Modulator for each sub-slot packet inspection TRX number, such as the ID number and the TRX is different, the child received the next time slot; if the same packet time slot will be receiving the book down, delay one o'clock gap and then launched into space interface enables the baseband frequency hopping. TRX baseband frequency hopping on the ID identifying real-time requirements are very high, at this point is to use Huawei's ASIC technology to solve, and can achieve high-speed, reliable TRX-ID recognition. Principle
frequency hopping (Frequency-Hopping Spread Spectrum; FHSS) in sync, and also in the case, accept the ends of a specific type of narrowband carrier to transmit signals, for a non-specific receptors, FHSS the beat signal generated by it is concerned, only be regarded as impulse noise. The launching of a FHSS signal to follow specifically designed to avoid noise or One-to-Many of the non-duplicate channels, and these frequency-hopping signals must comply with FCC requirements, the use of more than 75 frequency hopping signals, and frequency hopping to the next frequency of maximum time interval (Dwell Time) to 400ms.
to get direct sequence spread spectrum processing gain. Narrow-band frequency-hopping communications system is equivalent to the instantaneous, basically the same as conventional communication system, because no anti-multipath capability, while the emission efficiency is low, the same transmission power of the frequency hopping systems in the effective transmission distance is less than the DS system. The advantage of frequency hopping anti-jamming, interference will only interfere with the Department of the fixed-frequency crossover point. For voice information transmission, fixed-frequency interference when only a small part will not significantly affect the voice communication. Hopping frequency hopping system directly reflects the level of performance, the higher the frequency hopping anti-jamming performance better, military frequency hopping system can reach tens of thousands per second jump. GSM mobile communication system is in fact frequency-hopping system,[url=http://www.uggsaleuks.co.uk/]UGG Sale[/url], the provisions of 217 per second frequency hopping jump. Because of cost considerations, commercial frequency hopping systems are slower jump rate, generally 50 jump / sec. As the slow jumping frequency system for simple, low-speed wireless LAN products so often use this technique. A use to achieve carrier hopping spread spectrum technology, broadening the spectrum. Widely used in anti-jamming communication systems. The method is to a wideband frequency interval is divided into a number (called channels, or frequency slot), a pseudo-random sequence from the transmitter controls the dwell time at a given carrier frequency of the transmitted signal. When the receiver's local oscillator signal frequency and the receiver input signal frequency by the same law of synchronization transition, then, after a conversion later, will receive a fixed intermediate frequency signal that is to lift the original frequency hopping, a process known as solution jump or to jump. Classification from a technology point of view, GSM frequency hopping in the implementation is divided into base-band frequency hopping, frequency hopping two. Huawei's base station BTS supports two ways, the base station system design adequately take into account the hopping frequency diversity and interference in the diversity of roles that can support both baseband and RF frequency hopping hopping these two implementations and on-line access to the scale applications. From a practical point of view,[url=http://www.uggsaleuks.co.uk/]UGG Sale[/url], Huawei developed the frequency-hopping technology to improve the GSM system anti-jamming, anti-fading performance, greatly improved call quality, enhanced networking capabilities close multiplexing to increase the system capacity, with strong technical characteristics. RF frequency hopping to achieve the technical difficulties mainly in how to achieve the fast frequency and wideband fast frequency at the same time in how to ensure that the signal quality. Fast conversion and signal quality are mutually contradictory. In the GSM system in the space between each slot only two dozen microseconds, to achieve the RF frequency hopping, the system must be in the slot between the two within the protection of more than ten microseconds to quickly switch from one frequency to another frequency point. According to
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use classification principle characteristic hopping hopping frequency hopping processing gain bandwidth of the reasons for how produce Cheung received frequency hopping signal frequency-hopping signal how the definition: the so-called jump frequently, refers to pseudo-random code sequence for frequency shift keying, the carrier frequency hopping and spread spectrum continue a way. Hopping frequency hopping technology is currently used internationally as a more mature technology. Mainly used for military communications, it can effectively avoid the interference, play communication performance. Introduction to frequency hopping and direct sequence spread spectrum technology is completely different, is another sense of the spread spectrum. Hopping the carrier frequency by a pseudorandom code control, within its operating bandwidth, the frequency synthesizer according to pseudo-random code (PN code) of the random laws of changing frequency. In the receiver, the receiver's frequency synthesizer controlled by the pseudo-random code, and maintain the same variation of the transmitter. Is the carrier frequency hopping within a certain range of the sense of constantly hopping spread spectrum, rather than the information being transmitted spread spectrum, frequency hopping is not
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sender under the control of the clock, the pseudo-code pseudo-random sequence generator to control the frequency synthesizer to generate a frequency-hopping carrier series, called frequency-hopping pattern. Frequency-hopping communication system block diagram pictured above. Figure in the receiving end of the pre-modulation filter with a center frequency hopping pattern and the synchronization signal hopping narrowband filter (pass band allows the desired signal), aimed at increasing the selectivity of the receiver's time to reduce the strong interference of receiver may cause the obstruction. If the received frequency hopping sequence and the locally generated carrier frequency hopping sequence patterns consistent, then by mixing available after a fixed IF signal, and then demodulated to obtain the output. If the external frequency-hopping pattern is inconsistent with the local pattern is not a fixed intermediate frequency signal, after demodulation noise and not just some useful output. Therefore, time synchronization is critical hopping communication technologies. Hopping modulation signal according to the characteristics of choice. Should not be used in frequency hopping systems in demanding the phase modulation. Because the frequency-hopping communication system, the receiver's local carrier to do with the external signal to maintain phase coherence in the carrier is very difficult. Therefore, it is appropriate non-coherent detection methods. Hopping frequency synthesizer is an important part of communication system. Frequency synthesizer performance will be constrained hopping rate. Frequency synthesizer for frequency hopping rate requirement is fast, low spurious level and power consumption. Frequency synthesizer for frequency hopping, generally there are two stages: one is the transition period (transient time), one is the retention period (steady state time). Requirements to be a short transition period as far as possible, in order to achieve high conversion. Characteristic hopping bandwidth, frequency hopping
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