CN103117966A - Channel estimation method based on dynamic pilot frequency adjustment - Google Patents

Abstract

The invention discloses a channel estimation method based on dynamic pilot frequency adjustment. The channel estimation method at least comprises the following steps of acquiring data frames which are currently input; subjecting the data frames to pilot frequency pattern analysis; performing channel estimation according to the result of pilot frequency pattern analysis to obtain mean square error (MSE) values; subjecting the MSE values of the data frames to MSE statistic analysis; judging whether the data frames need to be subjected to pilot frequency pattern adjustment; and using a pilot frequency pattern adjustment algorithm to confirm pilot frequency pattern adjustment strategies when the pilot frequency patterns need to be adjusted, and calling the pilot frequency patterns in a pilot frequency pattern base for adjustment. Compared with traditional fixation pilot frequency pattern channel estimation methods, the channel estimation method has higher estimation accuracy so that the whole transmission performances of communication systems in satellite moving multi-path channel environments are effectively improved.

Description

A kind of channel estimation methods of adjusting based on dynamic pilot tone

Technical field

The invention belongs to the mobile communication technology field, a kind ofly dynamically adjust by pilot frequency design being carried out density the method that realizes channel estimating thereby relate to.

Background technology

Technology of New Generation Mobile Communications take the OFDM system as representative makes rapid progress.The OFDM system is a kind of communication system of multicarrier, it has higher than the availability of frequency spectrum of General System and very strong interference free performance, these advantages make it be able to extensive use in the terrestrial wireless mobile communication, and also are subject to paying close attention to more and more widely in satellite mobile communication system.yet, the channel disturbance factors such as abominable satellite transmission environment such as the multipath fading in wireless channel, multipath delay, Doppler frequency deviation have but seriously affected the performance of system, amplitude to received signal and phase place have caused interference in various degree, this impact mainly is reflected in it and symbol constellation is deflected (multipath delay) and distort (multipath fading), thereby impact receives phase place and the amplitude of signal, causes certain error code, in real system, in the mobile reception platform is in, the high-speed mobile situation is when (comprising relatively moving and the local motion of ground moving receiver on-board etc. of the satellite that causes due to factors such as orbital drifts and ground target), except above-mentioned multidiameter fading channel disturbing factor, also to consider Doppler shift impact to received signal, Doppler frequency deviation mainly is reflected in to the interference of data symbol the phase place generation dynamic rotary that it can make symbol constellation, and rotary speed can be accelerated along with the increase of phase error, thereby cause a large amount of error codes, thereby increased the bit error rate of system.The all negative effects that bring in order to eliminate to greatest extent channel disturbance at receiving terminal, must effectively be estimated the channel response of data symbol, thereby improve systematic function, the problem of channel estimating that Here it is.

At present, the method that solves channel estimation problems is generally to insert the dynamic change that channel response was followed the tracks of and estimated to various pilot frequency informations in Frame, and this pilot frequency information is main mainly with the fixing pilot configuration of certain pattern configuration greatly.Generally, the satellite mobile communication broadcast channel is a kind of transmission channel with time/frequency selectivity fading characteristic, the disturbing factors such as the multipath fading of channel, multipath delay and Doppler frequency deviation are all constantly occuring to change, particularly have under the mobile multidiameter fading channel environment of deep fading and fast-fading, this variation is more violent.At this moment, any channel estimation methods based on fixing pilot frequency design all can not be effectively and is followed the tracks of in real time and data estimator symbol channel response complicated and changeable, channel estimation methods according to a certain special pilot pattern Model Design also can only adapt to certain single channel circumstance usually, existing channel method of estimation ubiquity can't in time be followed the tracks of the channel response problem of dynamic fluctuation on a large scale, this makes precision of channel estimation descend, and error rate of system rises.

Summary of the invention

Technology of the present invention is dealt with problems and is: for the deficiencies in the prior art, a kind of channel estimation methods of adjusting based on dynamic pilot tone has been proposed, adopt this method to obtain to compare traditional fixedly higher estimated accuracy of pilot frequency design channel estimation methods, move overall transfer performance in the multipath channel environment thereby effectively promoted communication system at satellite.

Technical solution of the present invention:

A kind of channel estimation methods of adjusting based on dynamic pilot tone comprises the following steps at least:

Obtain the Frame of current injection;

Described Frame is carried out pilot frequency design resolves;

Carry out channel estimating according to described pilot frequency design analysis result, and obtain the MSE value;

MSE value to described Frame is carried out the MSE statistical analysis; Described MSE value is carried out statistical analysis for historical statistical data minimum value MIN (MSE), the mathematic expectaion E (MSE) of MSE and the variances sigma (MSE) of MSE of the historical statistical data maximum MAX (MSE), the MSE that obtain MSE, and over MAX (MSE) number of times MaxC1, lower than MIN (MSE) number of times MinC2 and σ (MSE) rising number of times VarRMSC3;

Judge whether described Frame needs to adjust pilot frequency design;

When needs are adjusted described pilot frequency design, utilize the pilot frequency design adjustment algorithm to determine that pilot frequency design adjusts strategy, and the pilot frequency design that calls in the pilot frequency design storehouse is adjusted; Described pilot frequency design adjustment algorithm comprises the following steps:

The statistical value that carries out the statistical analysis acquisition according to described MSE value makes the following judgment:

If the MSE value of current data frame surpasses MAX (MSE) or less than MIN (MSE), carries out the first branch: judge whether MaxC1 surpasses the threshold value of MaxC1; Otherwise, carry out the second branch: judge whether VarRMSC3 surpasses the threshold value of VarRMSC3;

In described the first branch, if MaxC1 surpasses the threshold value of MaxC1, transfer close pilot tone spacing; Otherwise, judge whether MinC2 surpasses the threshold value of MinC2; In described the second branch, if VarRMSC3 surpasses the threshold value of VarRMSC3, transfer close pilot tone spacing; Otherwise, do not adjust pilot tone;

In described the first branch, if MinC2 surpasses the threshold value of MinC2, transfer and dredge pattern frequently; Otherwise, do not adjust pilot tone.

The present invention's advantage compared with prior art:

The present invention is varistructure with pilot frequency pattern design, by more accurately tracking and the estimation of dynamic adjustment realization to channel response, designed a kind of dynamic adjustment algorithm of pilot frequency design, set up the dynamic pilot frequency design storehouse of containing multiple density pattern, expanded the channel estimation methods based on the pilot tone system.

The present invention adopts dynamic pilot frequency design to adjust mechanism, obtained than the more excellent precision of channel estimation of pilot frequency design method of traditional static/fixedly, in identical signal to noise ratio (under the condition of SNR=10～20dB), the emulated data statistical research shows, the inventive method is on average promoting approximately 1～2 order of magnitude than conventional method aspect precision of channel estimation (MSE), have the performance boost of about 8～9dB.

The present invention adopts dynamic pilot frequency design to adjust mechanism, make dynamic pilot frequency system can save approximately 20% system subcarrier frequency resource than traditional static pilot frequency system maximum, the sub-carrier frequencies resource of having saved can be for data subcarrier, thereby has significantly promoted the utilance of system frequency resource.The inventive method has also been optimized the system subcarrier frequency resource when improving precision of channel estimation MSE performance.

Description of drawings

Fig. 1 is the inventive method flow chart;

Fig. 2 is pilot frequency design dynamic adjustment algorithm flow chart of the present invention;

Fig. 3 is a kind of dynamic pilot frequency design structure of transferring close pilot tone density of the present invention;

Fig. 4 is that the dynamic pilot frequency design structure of density frequently dredged in a kind of accent of the present invention;

Fig. 5 is that COST-207 channel model lower channel is estimated the MSE performance comparison;

Fig. 6 is that SFN-4 channel model lower channel is estimated the MSE performance comparison;

Fig. 7 is dynamic pilot tone density (interval) change curve under the COST-207 channel model;

Fig. 8 is dynamic pilot tone density (interval) change curve under the SFN-4 channel model;

Embodiment

As shown in Figure 1, a kind of channel estimation methods main modular based on dynamic pilot tone adjustment of the present invention comprises: MSE statistical analysis module, pilot frequency design adjustment algorithm module, pilot frequency design library module.

As shown in Figure 1, MSE (mean square error) statistical analysis module is responsible for current and MSE data message in the past are analyzed and processed, thereby make the judgement that whether needs to adjust pilot frequency design, and how the order next frame adjusts the density of pilot frequency design.

In the processing data information process of MSE statistical analysis module, consider the historical statistics information of MSE, this mainly comprises following four parameters:

A) the historical statistical data maximum of MSE, i.e. MAX (MSE);

B) the historical statistical data minimum value of MSE, namely; MIN (MSE);

C) mathematic expectaion of MSE, i.e. average E (MSE) is calculated as follows:

$E\left(\mathrm{MSE}\right)=\frac{1}{M}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{\mathrm{MSE}}_m$

D) variance of MSE, namely the MSE of MSE, be also meansquaredeviationσ (MSE), is calculated as follows:

$\mathrm{\σ}\left(\mathrm{MSE}\right)=E\left({\mathrm{MSE}}^2\right)-{\left(E\left(\mathrm{MSE}\right)\right)}^2$

$=\frac{1}{M}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{\left({\mathrm{MSE}}_m\right)}^2-{\left(\frac{1}{M}\underset{m=1}{\overset{M}{\mathrm{\Σ}}}{\mathrm{MSE}}_m\right)}^2$

In formula, M represents the length of observed quantity sample space.

Except above-mentioned four statistical parameters, also to consider following three factors of influence when making the judgement of whether adjusting pilot frequency design:

A) surpass MAX (MSE) number of times, be denoted as MaxC1;

B) lower than MIN (MSE) number of times, be denoted as MinC2;

C) σ (MSE) rising number of times, be denoted as VarRMSC3.

The design of these three parameters is to be frequent some constraintss of adding of adjusting of the pilot frequency design density of avoiding causing because of the channel circumstance acute variation in practical engineering application in order to consider.

As shown in Figure 2, the present invention is in the pilot frequency design adjustment algorithm, and definition MaxC1TH, MinC2TH and VarRMSC3TH represent respectively the threshold value of MaxC1, MinC2 and VarRMSC3.At the MSE that has calculated a Frame, MAX (MSE), MIN (MSE), E (MSE) and σ (MSE) afterwards, these parameters are carried out comprehensive assessment.If the MSE (MSE of present frame _m) surpassed the fluctuation margin of historical data, carry out so the right branch judgement, relatively surpass the number of times MaxC1 in the upper bound, if greater than MaxC1TH, so the pilot frequency design of next frame is transferred closely, namely selected new pilot frequency design to substitute from the pilot frequency design storehouse and have pilot frequency design now.Definition L represents the pilot frequency design density, and the larger expression pattern of L numerical value pilot interval is more sparse, otherwise expression pattern pilot interval is more intensive.

As shown in Figure 3, store the pilot frequency design that contains in a large number multiple density configuration in pilot frequency design of the present invention storehouse, provided a kind of dynamic pilot frequency design of close pilot frequency design density of transferring here and adjusted structure, in this structure, current data frame L=8, next frame L=4.

If less than MaxC1TH, further compare the number of times MinC2 lower than lower bound, if greater than MinC2TH, so the pilot frequency design of next frame is transferred and dredged, Fig. 4 has provided a kind of accent and has dredged the dynamic pilot frequency design adjustment structure of pattern density frequently, current data frame L=8, next frame L=16.

If less than MinC2TH, so the pilot frequency design density of next frame will do not adjusted, namely the pilot frequency design of next frame is still consistent with present frame.

If the MSE of present frame does not surpass the fluctuation margin of historical data, carry out so the left branch judgement, further compare σ (MSE) rising number of times VarRMSC, if less than VarRMSC3TH, to the pilot frequency design density of next frame not adjusted so, otherwise, transfer the pilot frequency design of next frame close.

In practical engineering application, pilot frequency design number in the pilot frequency design storehouse is always limited, therefore, and if there is the situation of all pilot frequency designs in limit pilot tone storehouse after repeatedly adjusting, to stop so carrying out above-mentioned dynamic adjustment algorithm, continue operation according to current pattern.Suppose that channel circumstance worsens always, MSE raises always, should constantly transfer close pilot interval according to above-mentioned rule so, until be adjusted into pilot interval the closeest, if still can not contain the deterioration of MSE this moment, keep by this interval, until channel circumstance makes moderate progress (MSE reduction), vice versa, and this is a kind of mechanism that prevents the algorithm deadlock.

Further with dynamic pilot-based channel estimation method of the present invention and traditional static/fixedly the pilot frequency design channel estimation methods carries out the contrast of precision of channel estimation.

Simulate two kinds of satellite Mobile Multimedia Broadcasting reception environments, be respectively these two kinds representative mobile multipath channels of COST207 typical urban environment channel and SFN-4 broadcast single frequency network channel and carry out emulation testing, wherein, COST207/TU-6 moves the multipath fading reception environment in main simcity, consider the characteristics of city pile shadow fading, it is 6 that multipath quantity is set, maximum multipath time-delay distance 1～2 kilometer range, and the maximum relative moving speed of receiving terminal is 120km/h; SFN-4 broadcast single frequency network channel is mainly simulated the more mobile multipath fading reception environment of broad regions, the characteristics of the mobile reception environment such as consideration such as highway, high-speed mobile object (high-speed train), it is 4 that multipath quantity is set, maximum multipath time-delay distance 10 kilometer range, the maximum relative moving speed of receiving terminal is 300km/h.

As shown in Fig. 5,6, under the COST207/TU-6 channel circumstance, adopt the system of traditional static pilot-based channel estimation method when SNR is 20dB, MSE all is in 10 ^-2Magnitude, and the system that adopts dynamic pilot frequency design channel estimation methods can be reduced to below 0.001 at MSE under similar circumstances improves approximately 1～2 order of magnitude than the estimated accuracy of conventional method; Accordingly, under the SFN-4 channel circumstance, new method makes that MSE is minimum can be down to 10 ^-2～10 ^-3Between, compare with the estimated accuracy of traditional static pilot tone system, also there is the approximately performance boost of 8～9dB, obvious this improvement is very considerable.Even in the situation that SNR lower (SNR=0～10dB), although be subject to having a strong impact on of noise, yet the analysis showed that precision of channel estimation at this moment compares the gain that conventional method still has about 4～5dB.

As shown in Fig. 7,8, no matter be under the COST207/TU-6 channel circumstance or under the SFN-4 channel circumstance, the average (L that the fluctuation of pilot frequency design density changes _ave) all large than specified standard pilot tone density representative value L=8 in traditional static pilot-based channel estimation method, its average can expand respectively 9.6 and 8.2 to, this means that dynamic pilot frequency system can save approximately 20% system subcarrier frequency resource than traditional static pilot frequency system maximum, the sub-carrier frequencies resource of having saved can be for data subcarrier transmission solid data, thereby has significantly promoted the utilance of system frequency resource.

New method of the present invention has also realized the optimization of system subcarrier frequency resource when improving precision of channel estimation MSE performance.

The unspecified part of the present invention belongs to general knowledge as well known to those skilled in the art.

Claims (1)

1. a channel estimation methods of adjusting based on dynamic pilot tone, is characterized in that, comprises the following steps at least:

Obtain the Frame of current injection;

Described Frame is carried out pilot frequency design resolves;

Carry out channel estimating according to described pilot frequency design analysis result, and obtain the MSE value;

MSE value to described Frame is carried out the MSE statistical analysis; Described MSE value is carried out statistical analysis for historical statistical data minimum value MIN (MSE), the mathematic expectaion E (MSE) of MSE and the variances sigma (MSE) of MSE of the historical statistical data maximum MAX (MSE), the MSE that obtain MSE, and over MAX (MSE) number of times MaxC1, lower than MIN (MSE) number of times MinC2 and σ (MSE) rising number of times VarRMSC3;

Judge whether described Frame needs to adjust pilot frequency design;

When needs are adjusted described pilot frequency design, utilize the pilot frequency design adjustment algorithm to determine that pilot frequency design adjusts strategy, and the pilot frequency design that calls in the pilot frequency design storehouse is adjusted; Described pilot frequency design adjustment algorithm comprises the following steps:

The statistical value that carries out the statistical analysis acquisition according to described MSE value makes the following judgment:

If the MSE value of current data frame surpasses MAX (MSE) or less than MIN (MSE), carries out the first branch: judge whether MaxC1 surpasses the threshold value of MaxC1; Otherwise, carry out the second branch: judge whether VarRMSC3 surpasses the threshold value of VarRMSC3;

In described the first branch, if MaxC1 surpasses the threshold value of MaxC1, transfer close pilot tone spacing; Otherwise, judge whether MinC2 surpasses the threshold value of MinC2; In described the second branch, if VarRMSC3 surpasses the threshold value of VarRMSC3, transfer close pilot tone spacing; Otherwise, do not adjust pilot tone;

In described the first branch, if MinC2 surpasses the threshold value of MinC2, transfer and dredge pattern frequently; Otherwise, do not adjust pilot tone.

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