CN103001917A - Carrier synchronization method of underground coal mine orthogonal frequency division multiplexing (OFDM) communication system - Google Patents
Carrier synchronization method of underground coal mine orthogonal frequency division multiplexing (OFDM) communication system Download PDFInfo
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Abstract
The invention discloses a carrier synchronization method of an underground coal mine orthogonal frequency division multiplexing (OFDM) communication system. The OFDM communication system comprises an OFDM sending and receiving system, and the carrier synchronization method includes two parts of baseband processing and radio frequency processing and specifically includes baseband processing of the OFDM system and compensation after estimation of signal frequency deviation so that accuracy of processes of follow-up fast Fourier transform, channel estimation and the like is guaranteed. According to the carrier synchronization method, OFDM synchronization methods in the complicated environments of coal mine tunnels are improved, and implementability of the synchronization method of the coal mine OFDM system is further verified on the field programmable gate array (FPGA) hardware platform.
Description
Technical field
The present invention relates to ofdm communication system carrier synchronization method under a kind of coal mine, belong to areas of information technology, be specially adapted to the wireless communication field.
Background technology
Coal industry is the important foundation industry that concerns economic life line of the country, is the important disposable energy that supports China's GDP growth.Inner Mongolia Autonomous Region coal reserves is extremely abundant, and it has been established that contains the coal area and reach more than 10 ten thousand square kilometres, 2,400 hundred million tons of proved reserves of accumulative total, 12,000 hundred million tons of prospective reserves, and the position is the first in the nation.Coal and rare earth are Inner Mongolia Autonomous Region Two Mainstays resources.Reach 6.37 hundred million tons to Inner Mongolia Autonomous Region coal production in 2009, surpass 6.15 hundred million tons of Shanxi, occupy the whole nation first.Inner Mongol coal production will reach 7.82 hundred million tons in 2010.
Because the communication environment of complexity so that electromagnetic wave can not be propagated well, exists a large amount of reflections, refraction and scattering path under the coal mine, causes serious multipath transmisstion.Mine laneway is a non-freely restricted clearance, electromagnetic wave not only can be absorbed by the wall that is comprised of coal seam, rock, soil etc. in communication process, the more important thing is when electromagnetic wave runs into wall and barrier in communication process and can reflect and reflection by frequent occurrence, thereby generation multipath fading, this heavy damage phase place and the amplitude characteristic of signal, receiving system is produced greatly impact.Secondly, the electromechanical equipment in the tunnel starts frequently, power is high also destroys serious to the propagation characteristic of signal.Tunnel and working face roof and floor have fluctuating, and understand the various cambers of formation according to the variation of moving towards of coal seam and rock stratum in the horizontal direction, thereby but produced non-sighting distance propagation, greatly reduce the transmission range of wireless signal on tunnel and the working face.
Be limited by its specific environment requirement, so that correlative study work is very difficult, the development of Wireless Communication Technology in Coal Mine will far fall behind the radio communications such as GSM, CDMA, the OFDM on land, and the land mobile communication technology still can not be directly applied for mine laneway from aspects such as operation principle, transmitting power, interference protection measure, networking mode, construction costs.
Multipath fading under the above-mentioned coal mine and the problem of non-visual transmission have strengthened the realization difficulty of mine wireless communication, and Underground Wireless Communication System has been proposed great challenge.
At present the research of the key theory such as the propagation properties of mine laneway, system modelling, anti-multipath fading and technology still is in the stage of further developing, also do not form so far complete, reliable theoretical foundation and system, lack theoretic support.
OFDM (Orthogonal Frequency Division Multiplexing, OFDM) technology is a kind of efficient parallel Multicarrier Transmission Technology, it with the Data Modulation of high speed serialization in a plurality of parallel orthogonal sub-channels, thereby the symbol width of every sub-channels is expanded greater than channel delay, again by adding Cyclic Prefix, reduced intersymbol interference (Inter Symbol Interference, ISI) on the impact of system, can effectively resist multipath effect, be a kind of wireless communication technology that relatively is fit to the colliery subsurface environment.
Although ofdm system has plurality of advantages, also there is very large problem in it: responsive for carrier frequency shift.Frequency shift (FS) for receiving under the coal mine in the signal needs receiver to guarantee synchronously each intercarrier orthogonality.The precise synchronization theory is not only to channel estimating and mine receiving system, and significant to the wireless communication system under the whole mine.
Summary of the invention
The technical issues that need to address of the present invention just are to overcome the defective of prior art, ofdm communication system carrier synchronization method under a kind of coal mine is provided, it improves for the OFDM method for synchronous under the coal mine roadway complex environment, and has further verified the realizability of mine ofdm system method for synchronous at the FPGA hardware platform.
For addressing the above problem, the present invention adopts following technical scheme:
The invention provides ofdm communication system carrier synchronization method under the coal mine, ofdm communication system comprises that OFDM transmits and receives system, can be divided into Base-Band Processing and radio frequency two parts; Described carrier synchronization method is to the Base-Band Processing process in the ofdm system, and the frequency deviation of signal is estimated post-compensation, guarantees the accuracy of the processes such as follow-up FFT, channel estimating.
At first information source binary system input data are carried out scrambler, the effect of scrambler is for fear of 1 or 0 of long string occurring, helping receiver regularly to recover.The input data enter encoder through behind the scrambler, and it is carried out convolutional encoding, can resist the random error that wireless channel causes like this.Data behind the coding enter interleaver, finish interleaving process, and signal domain is carried out one-level and interweaved, and interweave and data field need to carry out two-stage, can avoid like this impact of burst error in the transmission course.Data after interweaving are carried out the 16QAM mapping, Data Modulation can be become the two paths of signals of homophase (I) quadrature (Q), thereby form complex signal.Insert 4 pilot tones in the complex signal relevant position, the complex signal of inserting pilot frequency information is carried out IFFT, data message being modulated on 52 subcarriers, the OFDM symbol begins to take shape.Data after the IFFT modulation are carried out parallel serial conversion the most at last, multiple signals are synthesized one road signal, and this road signal is done operations such as adding Cyclic Prefix and windowing process, and so far, the OFDM baseband signal forms, and the OFDM Base-Band Processing finishes.Baseband signal process digital to analog converter with forming converts analog signal to, and it is carried out quadrature modulation, convert real signal to, signal is carried out intermediate frequency Modulation become intermediate-freuqncy signal, be modulated at last radiofrequency signal by antenna transmission, above process is the radio frequency processing process.The whole process of Here it is ofdm signal formation and emission.
The receiving course of ofdm system receiver is the process opposite with emission.Ofdm signal becomes analog intermediate frequency signal through tuner, and analog signal becomes digital intermediate frequency signal through amplifying and analog to digital converter.Become baseband complex signal after digital intermediate frequency signal process digital demodulation and the quadrature demodulation, transmitting has so just returned to baseband form.The signal that obtains is carried out synchronously, the pure noise section in the filtered signal, the frequency deviation that channel and equipment are caused is estimated and is compensated, and finally finds comparatively exactly the position of FFT window, prepares for being about to carry out FFT.Signal will go the processes such as training symbol and Cyclic Prefix through after synchronous, removes the slave part in the OFDM grouped data, obtains signal domain and data field signal.Through behind the serial to parallel conversion, they become multiple signals, can pass through the FFT conversion.Because the amplitude error the when impact of wireless channel can cause OFDM demodulation subcarrier affects the correctness that follow-up 16QAM separates mapping, so the signal after the conversion need to be carried out channel estimation and equalization, phase place and the amplitude of signal is proofreaied and correct.Data after the channel equalization are separated mapping through 16QAM, deinterleaving, and decoding, the processes such as descrambling the most at last original source binary data recover comparatively exactly.The present invention mainly pays close attention to the Base-Band Processing process in the ofdm system, proposes a kind of carrier synchronization method.
Multipath in the downhole wireless channel disturbs comparatively serious, the receive-transmit system local oscillator Incomplete matching that in addition mutually forms between the staff, the carrier frequency that receives signal is offset, thereby destroys the orthogonality between the OFDM subcarrier, cause inter-carrier interference.Carrier synchronization is in time estimated post-compensation to the frequency deviation of signal, guarantees follow-up FFT(Fast Fourier Transformation), the accuracy of the process such as channel estimating.
If baseband transmit signals is
, the complex baseband signal that then receives is:
In the formula,
For sending carrier frequency;
Be the sampling period.If the time-delay between two continuous replicators is
Individual sampling length, the OFDM symbol lengths is
, the delay-correlated of cycle repeating signal and be then:
Can calculate thus exemplary frequency deviation values is:
，
Because getting the angle computing is arctangent cp cp operation, so its angle span exists
Between, then the estimable maximum frequency deviation of the method is:
If improve frequency offset estimation accuracy, by increasing sampling
Method can make the maximum frequency deviation estimation range
Reduce, and increase sampling and also can increase the length of training symbol simultaneously, thereby power system capacity is reduced.The present invention improves classical time domain approach in the situation that does not increase training symbol length, and frequency offset estimation accuracy is highly improved.
The frequency deviation estimated value is averaging computing improves to a certain extent estimated accuracy, improve one's methods and adopted a plurality of training symbols, a plurality of frequency offset estimation result of trying to achieve are folded take advantage of addition to be averaging computing, behind the first two Short Training symbol related operation, sampled value in the Short Training symbol is carried out translation and is multiplied each other, the stack of constantly multiplying each other thus as unit, utilize less training symbol resource, carried out repeatedly being averaging operation.If chosen
Individual training symbol has then carried out
Inferior frequency deviation is estimated computing, and common be averaging computing can only carry out (
) inferiorly be averaging computing.Utilize identical training symbol resource, that improves one's methods is averaging number of times far away more than the common method that is averaging.The concrete formula of improving one's methods is as follows:
In the formula
Be the Short Training symbol numbers of method use,
Be the sample value number of each Short Training symbol,
Be the sampling period.
Value larger, the Short Training symbol that participates in computing is more, it is more to be averaging number of times, estimates more accurate.
The OFDM method for synchronous that the present invention is directed under the coal mine roadway complex environment improves, and has further verified the realizability of mine ofdm system method for synchronous at the FPGA hardware platform.
The present invention improves classical time domain approach in the situation that does not increase training symbol length, and frequency offset estimation accuracy is highly improved.
Safety of coal mines is the significant problem of colliery industry always.Because the wireless channel environment under the coal mine is complicated, multipath disturbs comparatively serious, so general terrestrial wireless communication system can't directly apply to underground communica tion.The maximum characteristics of OFDM technology are exactly that the anti-multipath interference performance is strong, for the particular surroundings under the coal mine, ofdm communication system can be applied to underground radio communication.Ofdm system is tentatively filtered the reception signal under the coal mine synchronously and is made an uproar, and keeps the OFDM data-signal, and then the carrier frequency shift that multipath fading causes is carried out bias estimation and compensation to data-signal.
The electromagnetic interference and the multipath that the present invention is directed under the coal mine disturb, and have carried out the test to improving one's methods in the simulation laboratory, mine.The simulation dark 9.42m in tunnel, wide 5.833m, high 2.514m, 26 ℃ of selected dry-bulb temperatures, relative temperature is 70%, and wind speed 0.5m/s, receive-transmit system are comprised of two Spartan-3E development boards respectively, and according to actual conditions the receiving system detection threshold being set is 0.7.The result shows that improved reception synchro system frequency departure maintains about 10k～50k substantially, compares with former method, and its error is much smaller, and has higher practical significance.
Description of drawings
Fig. 1 is the ofdm system structured flowchart.
Fig. 2 is that carrier synchronization is improved one's methods and former method comparison diagram.
Fig. 3 is the carrier synchronization block diagram.
Fig. 4 is data top control module design drawing.
Fig. 5 is delay-correlated modular design figure.
Fig. 6 is estimation of deviation modular design figure.
Fig. 7 is carrier wave frequency deviation compensating module global design figure.
Fig. 8 is the former datagram without frequency offset interference.
Fig. 9 is the datagram through frequency offset interference.
Embodiment
OFDM transmits and receives system can be divided into Base-Band Processing and radio frequency two parts, and its structured flowchart as shown in Figure 1.
In order to verify the validity of improving one's methods, the transmission data that we produce with MATLAB add the frequency deviation of 10 ~ 100kHz, and the channel of the different signal to noise ratios of process, it is carried out frequency deviation estimate, investigate two kinds of method estimated value mean square errors and the ratio in carrier spacing.It is larger to consider that divider takies hardware resource, and too much training symbol can increase system burden, reduces power system capacity, has chosen 6 training symbols and has carried out frequency deviation and estimate, gets simultaneously
The simulation result of improving one's methods as shown in Figure 2.
Find out obviously that from the result of above emulation with respect to classical way, the error of improving one's methods is less, precision improvement is obvious.Although the operand of improving one's methods increases to some extent, consider, in the particular surroundings of mine danger, the significantly lifting of relative accuracy, the increase of operand can be born, and multiply-add operation realizes that easily therefore improving one's methods is a kind of comparatively reasonable and feasible method.
In addition, be the further realizability of verification method, we have also carried out the hardware realization to carrier synchronization method, have used the Spartan-3E FPGA development board of XILINX company as hardware environment, with the Verilog hardware description language as the realization means.The Spartan-3E development board comprises 500,000, and the clock frequency of 50MHz can be provided, and the 128 Mbit Flash that walks abreast is arranged, 16 Mbit SPI Flash, and the memory resource [30] that 64 MByte DDR SDRAM etc. are abundant is enough to finish frame synchronization designs.Realize the ISE software of software application XILINX company, finish the processes such as comprehensive, functional simulation to design code, pinout, realization download.After download is finished, can utilize online logic analyzer (chipscope) that development board pin signal is caught sampling, observe thereby plate is carried signal, understand the ruuning situation of design in actual hardware.
Receive data is produced by the IEEE 802.11a OFDM transmitting system of MATLAB emulation,
Realize adopting modular programming idea, concrete step as shown in Figure 3.
The design of data top control module (Data_control) as shown in Figure 4, it mainly utilizes counter controls to enable to realize.Receive data at first is stored in the buffer memory, and top control module can be exported a control signal and control counting at this moment.Counting controlled condition mainly is set to two: when
The time, counter can transmit control signal and control buffer memory output Short Training symbol.On frame synchronization entirely accurate ground foundation, should be
But because the result of frame synchronization has certain error, judge that rule of thumb its error is 2, will give up the first two data in the historical facts or anecdotes border.When
The time, buffer memory can partly be exported the signal domain data field of short training sequence and back.When
Counting is when other situations, and buffer memory can not exported any data, and can regard loss of data this moment as.
The design of delay-correlated module (Delay_correlate) as shown in Figure 5, receive data is through being divided into DateA and DateB two paths of data through the data shunt module, two paths of data enters respectively the delay-correlated module and deposits among the buffer memory A and B that sets in advance.Wherein buffer memory A and B are divided into real part and imaginary part two parts, are 4 road real parts and imaginary data through the data behind the buffer memory, and next step carries out the phase multiplication to it.According to the algorithm of complex multiplication, computing needs 4 multipliers to finish as can be known.After finishing, the delay-correlated computing enters relevant cumulative part.Relevant adding up mainly finished by shifter-adder, it is 16 that displacement progression is set, every all can have new data to move into relevant accumulator through a clock, having simultaneously one, to differ be that the legacy data of 16 samplings shifts out, accumulator does not stop the data of all shift registers are carried out accumulating operation, so just can finish relevant accumulating operation.
The design of estimation of deviation module (Deviation_estimate) as shown in Figure 6, at first according to the output data bulk of delay-correlated module, the count range that counter counter is set is 64.So as counter〉63 the time, no longer export the buffer control useful signal, thereby guarantee the correctness of following computing.Arctangent cp cp operation hardware during frequency deviation is estimated is realized comparatively difficulty, and in FPGA, we can utilize IP kernel to realize.The design adopts the CORDIC IP kernel to realize arctangent cp cp operation, CORDIC endorses to be configured to the several functions pattern, here it is configured to Arc Tan pattern, and the processing mode of its data entry mode and result of calculation is configured, the binary data of real part and imaginary part as input, can be obtained binary radian data at output port.The cumulative operation of radian data can enable to finish by counter controls, and it is 64 that counting is set, and it is cumulative to finish 64 radians.Cumulative result moves to right 6, namely finally altogether move to right 10, has finished in the formula process divided by 1024.The use of divider has been removed in shifting function from, and it is larger that divider takies resource, and the cycle of operation is long, can consume too much clock.In cumulative process, it should be noted that and to carry out sufficient cover operation, when decision module is finally exported, need to analyze the data component before exporting.The delay-correlated module is connected with the estimation of deviation module, so just consisted of Nonlinear Transformation in Frequency Offset Estimation module (CFO_estimate).
The design of carrier wave frequency deviation compensating module (CFO_compensating) as shown in Figure 7.Before carrying out specific design, need to simplify the compensation formula of improving one's methods.The compensation calculating formula is shown below:
Can find out that from following formula the calculating of compensating factor has related to exponent arithmetic, and exponent arithmetic realizes it being very difficult in hardware, so process still needs to use IP kernel.For this reason, continue following formula is carried out abbreviation, can obtain following formula:
By Euler's formula, following formula Exponential form has been changed into the sine and cosine form, so just can realize by the CORDIC IP kernel computational process of compensating factor.
Carrier wave frequency deviation compensation can be divided into for two steps to be carried out, and at first carries out the carrier wave compensating factor and calculates, and then compensate and multiply each other.Because compensation process is for long training symbol and follow-up data thereof, so in the formula
, increasing severely but compensate like this amount of calculation that can make compensating factor, thereby make the register figure place of operation result larger, the result is difficult for processing.So need with
Counting mode change, namely
, like this each
Variation can realize by accumulator.If long training symbol and further part data thereof are compensated, the result of compensation can differ with actual value 160 phase place, for fear of the appearance of phase difference, compensates from the Short Training sign-on, so just phase deviation can not occur.In this module, the CORDIC caryogamy is set to Sin and Cos pattern, two output pin is respectively X_OUT and Y_OUT, respectively corresponding sin and cos operation result.Data behind the accumulating operation can not directly be sent in the CORDIC nuclear, because CORDIC nuclear requires the phase angular region of input to be
So, need to carry out conversion to trying to achieve radian value, can add and subtract it
Finish, make it in allowed band.Radian number after the conversion is input in the IP kernel, final pin X_OUT output sine function, pin Y_OUT output cosine function value has so just been finished the calculating of compensating factor.
Compensation is multiplied each other, and module (Compensate_multiplier) is mainly finished receive data and carrier wave compensates the process that result of calculation multiplies each other, and utilizes 4 multipliers and register can finish this process.It should be noted that the result that compensation is multiplied each other is 17 bit data, and the final output format of module is data after 8 binary compensation, need to carry out the intercepting of data bit to the compensation multiplied result, the compensation multiplied result is 3 bit sign positions, 2 integer-bit, 12 decimal places, so final result intercepts 6 ~ 12 as decimal place and integer-bit, the 16th is sign bit.
So far, the BAM of carrier synchronization is finished.In practice, because the time of each module arithmetic is different, if the operation time sequence entanglement can appear in therefore direct connection, cause the mistake of Output rusults.For guarantee computing accurately and sequential correct, added respectively two time delay modules of Clk_delay and Compensate_delay, respectively the sequential coupling is done in the computing in the each several part.Mainly used in the time-delay and enabled time-delay and data delay, enabling time-delay can finish by counting control, and data delay then is to finish by multi-stage shift register.
Good effect:
Result on the emulation rank of method is comparatively desirable for carrier synchronization, but its accuracy in actual hardware also needs further checking, so we use above-mentioned hardware system that method has been carried out hardware experiments and checking.Owing to repeatedly used the CORDIC IP kernel when writing the carrier synchronization code, the computing of CORDIC nuclear itself just has certain approximation, and floating number transfers the afterwards loss of precision of binary number in addition, all can affect the result of carrier synchronization.The Nonlinear Transformation in Frequency Offset Estimation precision problem that these reasons cause and compensation precision problem all are difficult to avoid, and we can only start with from the configuration mode of IP kernel and the reasonability of code, and then improve frequency offset estimation accuracy, and carrier synchronization is carried out comparatively exactly.
The checking of synchronized result mainly is divided into the checking of frequency offset estimation result and the checking of final compensation result.The proof scheme of frequency offset estimation result: the data that produce with the MATLAB transmitter artificially add certain frequency deviation as the carrier synchronization receive data, with frequency offset estimation result and the artificial frequency deviation contrast that adds of hardware as transmitting data.Convenient contrast in order to verify enlarges 10 times to real part and the imaginary part of input data respectively, and the result who like this frequency deviation is estimated can not impact.Result for the frequency deviation estimation, the present invention mainly adopts the intermediate object program of CFO_estimate module, phase_data is the radian result of Nonlinear Transformation in Frequency Offset Estimation, owing to design method is simplified, so only have the intermediate object program of the calculating of frequency deviation estimation among the result.Phase_datad is corresponding to the part in the formula (1), and is as follows:
64 Short Training symbols are adopted in design, so the result of phase_data is 64.The phase_data Output rusults is 16,1 bit sign position wherein, two integer-bit, 13 decimal places.These binary frequency deviations are estimated that intermediate object programs are converted to metric floating number, and to ask its mean value, result be 1.505.According to carrier synchronization frequency deviation meter formula, can carry out computing to it, the frequency deviation estimated value that finally obtains receive data process hardware handles is 300.010KHz.The Nonlinear Transformation in Frequency Offset Estimation that this shows actual hardware is comparatively accurate, and the unreasonable mistake of artificial code can be got rid of, and the result is comparatively desirable.
The below verifies the final compensation result of carrier synchronization.Major programme is: on the basis of above checking, utilize MATLAB to produce one group of former data of OFDM that do not add frequency shift (FS), the compensation result that hardware is carried out and the former data of OFDM and compare through the MATLAB data of frequency offset interference are made analysis.Utilize the former data of part OFDM of MATLAB generation as shown in Figure 8, utilize the data of passing through the 300KHz frequency offset interference of MATLAB generation as shown in Figure 9.
To be converted to through the offset data behind the hardware decimal system floating number, available data are 0.2188+0.2188i,-1.3125+0.04683i,-0.1718-0.7816i, 1.4063-0.1563i, 0.9063-0.0156i, 1.4219-0.1406i,-0.1406-0.7656i etc. are because the back data are more, so no longer enumerate.By with former data without overdeviation, through the MATLAB Data Comparison of frequency offset interference, can find out that obviously carrier synchronization can finish the compensation correction of carrier wave frequency deviation, the result is comparatively accurate.
By above two-part checking work, can get rid of the existence of mistake in the design, it is comparatively reasonable for the processing of data to prove in the design.Because the error that the precision of system conversion and IP kernel inside causes makes the data through hardware compensating can not be equal to former data fully, but this part error is acceptable.
Safety of coal mines is the significant problem of colliery industry always.Because the wireless channel environment under the coal mine is complicated, multipath disturbs comparatively serious, so general terrestrial wireless communication system can't directly apply to underground communica tion.The maximum characteristics of OFDM technology are exactly that the anti-multipath interference performance is strong, for the particular surroundings under the coal mine, ofdm communication system can be applied to underground radio communication.Ofdm system is tentatively filtered the reception signal under the coal mine synchronously and is made an uproar, and keeps the OFDM data-signal, and then the carrier frequency shift that multipath fading causes is carried out bias estimation and compensation to data-signal.The electromagnetic interference and the multipath that the present invention is directed under the coal mine disturb, and have carried out the test to improving one's methods in the simulation laboratory, mine.The simulation dark 9.42m in tunnel, wide 5.833m, high 2.514m, 26 ℃ of selected dry-bulb temperatures, relative temperature is 70%, and wind speed 0.5m/s, receive-transmit system are comprised of two Spartan-3E development boards respectively, and according to actual conditions the receiving system detection threshold being set is 0.7.The result shows that improved reception synchro system frequency departure maintains about 10k～50k substantially, although the still existence error to a certain degree of improving one's methods is compared with former method, its error is much smaller, and has higher practical significance.
It should be noted that at last: obviously, above-described embodiment only is for example of the present invention clearly is described, and is not the restriction to execution mode.For those of ordinary skill in the field, can also make other changes in different forms on the basis of the above description.Here need not also can't give all execution modes exhaustive.And the apparent variation of being amplified out thus or change still are among protection scope of the present invention.
Claims (3)
1. ofdm communication system carrier synchronization method under the coal mine, ofdm communication system comprises that OFDM transmits and receives system, can be divided into Base-Band Processing and radio frequency two parts; It is characterized in that: described carrier synchronization method is estimated post-compensation for to the Base-Band Processing process in the ofdm system to the frequency deviation of signal, guarantees the accuracy of the processes such as follow-up FFT, channel estimating.
2. ofdm communication system carrier synchronization method under the coal mine as claimed in claim 1 is characterized in that:
The OFDM emission process is:
At first information source binary system input data are carried out scrambler, the input data enter encoder through behind the scrambler, it is carried out convolutional encoding, data behind the coding enter interleaver, finish interleaving process, and signal domain is carried out one-level and interweaved, data field carries out two-stage and interweaves, data after interweaving are carried out 16QAM mapping, Data Modulation is become the two paths of signals of homophase (I) quadrature (Q), form complex signal;
Insert 4 pilot tones in complex signal, the complex signal of inserting pilot frequency information is carried out IFFT, data message being modulated on 52 subcarriers, the OFDM symbol begins to take shape;
Data after the IFFT modulation are carried out parallel serial conversion the most at last, with synthetic one road signal of multiple signals, and this road signal done add Cyclic Prefix and windowing process, and the OFDM baseband signal forms, and the OFDM Base-Band Processing finishes;
Baseband signal process digital to analog converter with forming converts analog signal to, and it is carried out quadrature modulation, convert real signal to, signal is carried out intermediate frequency Modulation become intermediate-freuqncy signal, be modulated at last radiofrequency signal by antenna transmission, above process is the radio frequency processing process;
The OFDM receiving course is:
The receiving course of ofdm system receiver is the process opposite with emission, and ofdm signal becomes analog intermediate frequency signal through tuner, and analog signal becomes digital intermediate frequency signal through amplifying and analog to digital converter;
Become baseband complex signal after digital intermediate frequency signal process digital demodulation and the quadrature demodulation, transmitting has so just returned to baseband form;
The signal that obtains is carried out synchronously, the pure noise section in the filtered signal, the frequency deviation that channel and equipment are caused is estimated and is compensated, and finds the position of FFT window, prepares for being about to carry out FFT;
Signal removes training symbol and Cyclic Prefix through after synchronous, removes the slave part in the OFDM grouped data, obtains signal domain and data field signal;
Through behind the serial to parallel conversion, they become multiple signals, through the FFT conversion; Signal after the conversion is carried out channel estimation and equalization, phase place and the amplitude of signal are proofreaied and correct;
Data after the channel equalization are separated mapping through 16QAM, deinterleaving, and decoding, descrambling the most at last original source binary data recovers comparatively exactly.
3. ofdm communication system carrier synchronization method under the coal mine as claimed in claim 2 is characterized in that:
If baseband transmit signals is
, the complex baseband signal that then receives is:
If the time-delay between two continuous replicators is
Individual sampling length, the OFDM symbol lengths is
, the delay-correlated of cycle repeating signal and be then:
，
Can calculate thus exemplary frequency deviation values is:
Its angle span is
, the estimable maximum frequency deviation of the method is:
，
By increasing sampling
Method make the maximum frequency deviation estimation range
Reduce, increase simultaneously the length of training symbol, thereby power system capacity is reduced, improve frequency offset estimation accuracy;
Again the frequency deviation estimated value is averaging computing, concrete formula is as follows:
In the formula
Be the Short Training symbol numbers of method use,
Be the sample value number of each Short Training symbol,
Be the sampling period;
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| CN107171993A (en) * | 2017-05-22 | 2017-09-15 | 东南大学 | Up united carrier synchronization hardware implementation method based on extensive MIMO |
| CN108768908A (en) * | 2018-06-07 | 2018-11-06 | 重庆大学 | A kind of expansible lightweight OFDM system design method based on FPGA |
| CN112929315A (en) * | 2021-01-20 | 2021-06-08 | 西安电子科技大学 | Mine wireless communication method based on multi-antenna single carrier modulation |
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| CN112929315A (en) * | 2021-01-20 | 2021-06-08 | 西安电子科技大学 | Mine wireless communication method based on multi-antenna single carrier modulation |
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