CN103973628A - Doppler frequency shift resisting technology integrating OFDM technology with double differential technology - Google Patents
Doppler frequency shift resisting technology integrating OFDM technology with double differential technology Download PDFInfo
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- CN103973628A CN103973628A CN201410215807.7A CN201410215807A CN103973628A CN 103973628 A CN103973628 A CN 103973628A CN 201410215807 A CN201410215807 A CN 201410215807A CN 103973628 A CN103973628 A CN 103973628A
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Abstract
The invention relates to the technical field of high-rate data wireless communication transmission under high-speed moving environment, in particular to a Doppler frequency shift resisting technology integrating an OFDM technology with a double differential technology. The Doppler frequency shift resisting technology is characterized in that the transmission rate of communication data is increased by the adoption of the OFDM technology, the influence on the performance of a wireless communication system from Doppler frequency shift under the high-speed moving environment is avoided through the double differential technology, and compared with a traditional OFDM system, the double differential technology is integrated and can effectively prevent the influence from the large-range and rapid-time-varying Doppler frequency shift. The OFDM technology is integrated with the double differential technology, when the signal to noise ratio reaches the certain condition, the high-rate data wireless communication is achieved under the high-speed moving environment, the influence on the performance of the wireless communication system from the Doppler frequency shift can be resisted effectively, high-rate data transmission communication of the wireless communication system is achieved under the high-speed moving environment, and the performance of the wireless communication system is improved.
Description
Technical field
The present invention relates to high-rate wireless communication transfer of data communication technical field under high-speed mobile environment, specifically a kind of technology that adopts orthogonal multiple carrier frequency division multiplexing to incorporate two differential pair anti-Doppler effects.
Background technology
Orthogonal multiple carrier frequency division multiplexing (claiming again OFDM) technology is as the key technology of radio communication high speed data transfer, it is very responsive to frequency departure, especially under high-speed mobile environment, Doppler effect and Doppler spread can be very obvious, cause disturbing between signal amplitude decay, spectrum offset and subcarrier, the performance of system is reduced greatly.Therefore, when safeguards system realizes radio communication high speed data transfer under high-speed mobile environment, how effectively resisting the Doppler frequency shift that high-speed motion causes, is the important topic of needing research badly.
The basic thought of OFDM technology is by data flow string at a high speed and is converted to the parallel low rate data streams in N road, carries out parallel transmission after removing respectively to modulate N way carrier wave.The speed of subcarrier data stream becomes original 1/N, and symbol period is expanded as original N doubly, and the time delay expansion that wireless transmission multipath effect causes diminishes, and can effectively resist the impact of wireless transmission multipath effect; Wideband frequency Selective Fading Channel is divided into N the accurate flat fading channel in arrowband, the impact that can effectively resist wireless channel frequency selective fading; Intercarrier is mutually orthogonal, spectral aliasing, and each sub-channels can adopt multi-system modulation simultaneously, and therefore ofdm system has the higher availability of frequency spectrum, is suitable for transmitting high speed data.
But OFDM technology is very responsive to frequency offset error, because the frequency spectrum of subchannel covers mutually, the orthogonality of intercarrier is proposed to strict requirement.In transmitting procedure, occur having frequency departure between signal spectrum skew or transmitter and receiver local oscillator, all can make the orthogonality between ofdm system subcarrier be destroyed, cause inter-carrier interference (ICI).While is due to the time variation of wireless channel, and platform is in high-speed motion state, in signals transmission, can exist larger Doppler frequency shift, cause signal amplitude decay, spectrum offset, destroy the orthogonality of intercarrier simultaneously, therefore adopt OFDM technology to improve when message transmission rate, must research how to overcome the impact of Doppler frequency shift.
In order to solve ofdm system to Doppler frequency shift sensitive issue, the general method adopting is to carry out radio channel estimation or prediction at receiving terminal, first estimates the frequency offseting value in wireless channel, and then carries out frequency compensation through respective algorithms.But while utilizing said method opposing Doppler frequency shift to communicate, generally wish can make estimation to Doppler frequency shift within the utmost point short time, and use corresponding algorithm to carry out in time frequency compensation at receiving terminal, to ensure the real-time of communication.But above-mentioned algorithm all needs repeatedly iterative computation to obtain more accurate Doppler frequency shift value conventionally, and iterations is more, and estimated Doppler frequency shift value more approaches actual value, thereby frequency compensation result is more accurate, but corresponding computing time also can be longer.The algorithm of visible existing estimation and compensation frequency displacement still can not reach extraordinary real-time effect, so that the real time high-speed rate transmission of data can be affected under high-speed mobile environment.
Based on above analysis, selecting or designing a kind of modulation-demodulation technique that can effectively resist Doppler frequency shift is to solve under high-speed mobile environment the effective ways of Doppler effect in high data rate communication process.Adopt two differential modulation and demodulation technology can effectively resist Doppler frequency shift, this technology has stronger stability for the Doppler frequency shift becoming fast time on a large scale, the frequency displacement and the phase shift that cause because of relative motion are all cancelled at solution timing, thereby eliminate the impact of Doppler frequency shift for ofdm system, realize the high speed data transfers communication under high-speed mobile environment.
Summary of the invention
The object of the invention is on the basis of orthogonal multiple carrier frequency division multiplexing, propose one and can effectively resist Doppler effect, incorporate two difference anti-Doppler frequency displacement technology to realize the orthogonal multiple carrier frequency division multiplexing of efficient communication under high-speed mobile environment.
The present invention can reach by following measures:
Orthogonal multiple carrier frequency division multiplexing incorporates two difference anti-Doppler frequency displacement technology, it is characterized in that ofdm signal to adopt two differential modulation technology, and the Doppler frequency shift causing due to relative motion is cancelled in signal demodulating process.Under signal to noise ratio reaches certain condition, the present invention can reduce the sensitiveness of orthogonal multiple carrier frequency division multiplexing to Doppler frequency shift effectively, thereby can realize the two-forty real time communication under high-speed mobile environment.
Orthogonal multiple carrier frequency division multiplexing of the present invention incorporates two difference anti-Doppler frequency displacement technology, be specially: two differential modulation technology have adopted the method for second differnce, by the signal frequency that combines to eliminate to cause because of relative motion after three continuous channel samplings and the variation of phase place.Orthogonal frequency division multiplexing is used as efficient multi-carrier broadband digital modulation technique, can on the basis of high rate data transmission data, effectively resist arrowband and disturb and frequency selective fading, but it is responsive especially to frequency shift (FS).In orthogonal frequency division multiplexi, incorporate two differential modulation, both retained the original advantage of OFDM, made up again the defect of orthogonal multiple carrier frequency division multiplexing to frequency shift (FS) sensitivity.
The present invention compared with prior art, does not need to arrange corresponding frequency estimation algorithm and frequency compensation algorithm at receiving terminal, thereby has ensured the real-time work of system.
embodiment:
Below in conjunction with accompanying drawing, the present invention is further illustrated.
Main contributions of the present invention is to improve the defect of orthogonal multiple carrier frequency multiplexing technique to Doppler frequency shift sensitivity by incorporating two differential techniques.Incorporate two difference anti-Doppler effect technology and not only effectively resist the Doppler frequency shift producing in high-speed motion environment, and ensured the systematic function of complete real-time working.
As shown in Figure 1, the frequency division multiplexing of orthogonal multiple carrier described in the present invention incorporates two difference anti-Doppler frequency displacement technology and can realize by following steps:
Step 1: the binary radix band signal to input carries out randomization.
Step 2: to the binary system base band digital signal after randomization, carry out the mapping of base-band digital modulation constellation.
Step 3: serial/parallel conversion is multichannel by data parallel.
Step 4: data are carried out to IFFT conversion, then carry out parallel/serial conversion.
Step 5: add Cyclic Prefix, protection coefficient interval time can be got the derivative parameter such as 1/4,1/8,1/16.
Step 6: signal is carried out to two differential modulation.
Step 7: the signal modulating is delivered in channel and transmitted, and signal is subject to the impact of Doppler frequency shift and noise.
Step 8: receiving terminal receives signal.
Step 9: signal is carried out to two differential ference spirals.
Step 10: serial/parallel conversion, multiple signals are carried out to FFT conversion.
Step 11: parallel/serial conversion, signal is carried out to the inverse mapping of base-band digital modulation, go to recover original transmitted signal after randomization.
the principle of two differential techniques:
The modulation block diagram of two difference is as shown in Figure 2:
z n for initialize signal,
v n for modulating rear signal, can be able to lower relational expression by schematic diagram:
:
, order
,
can obtain:
If two encoded difference signals that receiving terminal receives are
,
ωfor carrier frequency,
The demodulation block diagram of two difference is as shown in Figure 3:
When
n>=0 o'clock, consideration had Gauss's single-input single-output channel of frequency shift (FS).If the signal receiving is:
Wherein:
efor the signal energy receiving;
ω d the Doppler frequency shift causing for transmitting terminal and receiving terminal relative motion;
e n for the noise in channel, it is white Gaussian noise;
Wherein:
for
the noise of middle entirety is white Gaussian noise.Known by above formula,
with the time
tirrelevant, with Doppler frequency shift
ω d relevant;
z n phase place
out demodulated, eliminate the impact of Doppler frequency shift, after two differential ference spirals, the Doppler frequency shift of being introduced by channel is balanced out completely as seen, and correctly recovers the phase place of primary signal.
the realization of two differential techniques:
By analyzing, can adopt block-scheme method and phase method to realize the modulation and demodulation of two differential techniques.
one, block-scheme method
In modulation, demodulating process, while adopting block diagram coding and decoding, relate to a large amount of phase multiplications, if certain symbol amplitude is too small, after two difference processing, may there is unblind, affect the accuracy of coding and decoding result.Because two differential techniques mainly utilize the relation between phase place, therefore for avoiding the appearance of invalid signals, before modulation, demodulation, symbol is carried out to amplitude normalization processing, modulate accordingly, symbol amplitude is still 1 after demodulation process, there will not be unblind, for ensureing the authenticity of signal, need to recover signal amplitude afterwards.Two differential technique modulation, the demodulation revised realize block diagram respectively shown in accompanying drawing 4,5.
For avoiding the appearance of invalid signals, signal is modulated, first signal carried out to amplitude normalization processing before demodulation, for ensureing signal amplitude correspondence, when carrying out modulation /demodulation processing, amplitude is carried out to time delay, finally, for ensureing the authenticity of signal, amplitude is recovered.
two, phase method
Modulation block diagram by two differential techniques can find, the phase relation of modulation signal and initialize signal is shown below:
Wherein:
for modulating signal phase,
for initialize signal phase place.
Demodulation block diagram by two differential techniques can be found, can obtain the relation between phase place by the relation between signal.
Due to
, can obtain the two phase relation and be shown below:
Wherein,
for signal
x n phase place,
for signal
x n phase place.
Due to
, phase relation is shown below:
Can obtain the relation between restituted signal and input signal, be shown below.
Adopt phase method can realize the modulation and demodulation of DDPSK, concrete methods of realizing: process separately for signal amplitude and phase place, determine the phase place of modulation signal when modulation by relation, and amplitude is recovered; Separate timing and determine the phase place of restituted signal by relation, and amplitude is recovered.
Claims (2)
1. orthogonal multiple carrier frequency division multiplexing incorporates two difference anti-Doppler frequency displacement technology, it is characterized in that utilizing two differential modulation and demodulation technology to solve the sensitiveness of ofdm system for frequency shift (FS), greatly improve the communication performance of ofdm system under high-speed mobile environment, OFDM incorporates two difference anti-Doppler frequency displacement technology, not only ensure the good orthogonality of OFDM intercarrier, and by adopting multilevel code, in conjunction with the operating factor of highband of ofdm system, can realize the RFDC of two-forty under high-speed mobile environment.
2. orthogonal multiple carrier frequency division multiplexing according to claim 1 incorporates two difference anti-Doppler frequency displacement technology, it is characterized in that the technology proposing according to us can realize in the following manner:
Mode 1: the hardware description language based on FPGA platform is realized;
Mode 2: the software program based on microprocessor platform is realized;
Mode 3: realize based on building special large scale digital logical circuit;
Orthogonal multiple carrier frequency division multiplexing incorporates two difference anti-Doppler frequency displacement technology has realized the application of two differential techniques by means of above-mentioned three kinds of mode platforms, utilize two differential technique thought, the Doppler frequency shift that antagonism high-speed motion produces, finally realizes the high data rate communication under high-speed mobile environment effectively.
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| CN112787610A (en) * | 2020-12-22 | 2021-05-11 | 湖南艾科诺维科技有限公司 | Parallel implementation device and method for constantly establishing time digital AGC loop |
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Application publication date: 20140806 |