CN101557366B - Channel estimation method based on orthogonal frequency division multiplexing system - Google Patents
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Abstract
The invention relates to a channel estimation method based on an orthogonal frequency division multiplexing system, which comprises the following steps: according to received frequency domain scattered pilot signals, dynamically estimating Doppler maximum frequency value R in a time slot; according to the Doppler maximum frequency value R, dynamically acquiring the type of a channel where a systemis positioned; and according to the channel type, dynamically selecting coefficients interpolated in a pilot time axis in channel estimation. The method can judge channel change in real time, and sel ect reasonable interpolation coefficients so as to effectively reduce system performance loss brought by Doppler spread.
Description
Technical field
The present invention relates to the communications field, relate in particular to a kind of channel estimation methods based on ofdm system.
Background technology
OFDM (Orthogonal Frequency Division Multiplexing; Hereinafter to be referred as OFDM) technology is the regulation technology that carries out a large amount of digital data transfer through radio wave; OFDM is divided into multiple small-sized subsignal to wireless signal, in the different frequency of receiver, carries out synchronous transmission then.OFDM technology receives concern more and more widely owing to the frequency selective fading with effective opposing channel and impulsive noise, higher advantages such as the availability of frequency spectrum.Yet, very easily receive because Doppler expands interference (Inter cell interference is hereinafter to be referred as ICI) between the interfered cell that time varying channel brought that causes based on the communication system of OFDM technology, and then cause system performance degradation.China Mobile multimedia broadcasting (China Mobile Multimedia Broadcast; Hereinafter to be referred as CMMB) the channel frame structure just is being based on the structure of OFDM, is example with CMMB, and the core transmission technology of CMMB system is that satellite adds upper ground surface benefit spot net (Stimi); Because this system carrier frequency higher (2.6GHz); The intercarrier distance is merely 2.44kHz, and is designed to the mobile DTV of watching, so this system very is vulnerable to the influence of Doppler frequency deviation; The characteristics that are directly proportional with object of which movement speed and carrier frequency according to Doppler's maximum frequency deviation; Even can know 100 kilometers/hour translational speeds, Doppler frequency deviation just will reach 240Hz, and Doppler frequency deviation will cause the systematic function rapid deterioration.Conventional channel is estimated to be employed in the method for inserting in the frequency domain pilot tone and is accomplished channel estimating, and wherein frequency axis adopts complicated higher order polynomial interpolation algorithm, and time shaft then adopts the method for simple polynomial interpolation.Research is illustrated in Doppler frequency deviation bigger the time when (normalization Doppler frequency deviation＞0.1), and systematic function will be inserted in time shaft and worsens along with pilot tone, otherwise insert in the axle hour service time at Doppler frequency deviation, and systematic function will improve.Therefore how choice of dynamical time shaft interpolation coefficient becomes key.A kind of time shaft interpolation coefficient is only chosen in present a lot of researchs, and can not dynamically choose rational interpolation coefficient according to channel variation, therefore when channel is in the fast time variant fading channel, will bring very big performance loss to system.
Summary of the invention
The purpose of this invention is to provide a kind of channel estimation methods based on ofdm system, can the real-time judge channel variation, choose rational interpolation coefficient, thereby effectively reduce because the performance loss that Doppler's expansion brings.
For realizing above-mentioned purpose, the invention provides a kind of channel estimation methods based on ofdm system, comprising:
According to the frequency domain discrete guide-frequency signal that receives, in a time slots, dynamically estimate Doppler's maximum frequency values R;
Become the division of decline speed during according to system's channel of living in, channel is divided into N kind channel type in advance, Doppler's maximum frequency range of every type of correspondence;
Doppler's maximum frequency values R that estimates when finishing according to each time slot and the pairing Doppler's maximum frequency range of N kind channel type of delimiting in advance dynamically draw system's channel type of living in;
Become the relation of decline speed during according to slotting in the pilot time axis and channel,, store N kind channel type time corresponding axle interpolation coefficient separately according to the N kind channel type of delimiting in advance;
According to the channel type of judging, choose the pairing time shaft interpolation coefficient of this channel type.
When being specially channel, said channel type becomes the speed of decline.
The said Doppler's maximum frequency values R that estimates when finishing and the pairing Doppler's maximum frequency range of N kind channel type of delimitation in advance according to each time slot; Dynamically drawing system's channel type of living in is specially: in a time slot, reappraise Doppler's maximum frequency values R; And, dynamically draw system's channel type of living in according to the Doppler's peak frequency estimated value R after upgrading and the pairing Doppler's maximum frequency range of N kind channel type of delimitation in advance.
At the channel type that said basis is judged, also comprise after choosing the pairing time shaft interpolation coefficient of this channel type: output time axle channel estimation results, carry out simple single order balancing operational then.
The frequency domain discrete guide-frequency signal that said basis receives dynamically estimates Doppler's maximum frequency values R and comprises in a time slots:
According to the system frame structure characteristics, the channel response value of the scattered pilot position of the consistent consecutive frame symbol in pilot tone insertion position is carried out the computing of conjugation multiply accumulating;
Accumulation result is asked arithmetic mean T in a frame, obtain the angle values Z of arithmetic mean T then;
All angle values Z to obtaining in the time slot carry out the computing of absolute value arithmetic average, draw phase angle mean value M, and the normalized value according to phase angle mean value M draws its corresponding Doppler's maximum frequency values R then.
The channel response value of said scattered pilot position to the consistent consecutive frame symbol in pilot tone insertion position is carried out the computing of conjugation multiply accumulating and is:
Respectively the channel response value of the scattered pilot position of the consistent consecutive frame symbol in pilot tone insertion position is carried out the computing of conjugation multiply accumulating; Then the computing of conjugation multiply accumulating is: the channel response value at the frame symbol scattered pilot place that the channel response value at scattered pilot place is consistent with previous pilot tone insertion position in the present frame is carried out complex conjugate phase multiplication, and the result is carried out accumulating operation in a frame.
Said all angle values Z that obtain in the time slot are carried out the computing of absolute value arithmetic average, draw phase angle mean value M, draw its corresponding Doppler's maximum frequency values R according to the normalized value of phase angle mean value M then and comprise:
According to the system frame structure characteristics, the angle values Z that in a time slot, all frame correspondences is tried to achieve carries out the computing of absolute value arithmetic average, draws phase angle mean value M;
Normalized value according to phase angle mean value M draws its corresponding Doppler's maximum frequency values R.
The consecutive frame symbol of said position consistency is for being all odd-numbered frame or even frame.
Channel estimation methods based on ofdm system provided by the invention dynamically draws system's channel type of living in then through estimating Doppler maximum frequency values R dynamically; And dynamically choose in the channel estimating coefficient of inserting in the pilot time axis according to channel type; Thereby real-time judge channel variation; Choose rational interpolation coefficient, effectively reduce because the performance loss that Doppler's expansion brings.
Description of drawings
Fig. 1 is the first embodiment flow chart that the present invention is based on the channel estimation methods of ofdm system;
Fig. 2 is the second embodiment flow chart that the present invention is based on the channel estimation methods of ofdm system;
Fig. 3 is the 3rd embodiment flow chart that the present invention is based on the channel estimation methods of ofdm system;
Fig. 4 is the hardware block diagram that the present invention is based on the channel estimation methods of ofdm system;
Fig. 5 is the sketch map that between normalization phase angle that a slot time arithmetic internal is on average tried to achieve and Doppler's maximum frequency values, concerns according to the first embodiment of the invention rule;
Fig. 6 compares sketch map according to first embodiment of the invention rule choice of dynamical channel estimating time shaft interpolation coefficient with the error rate of fixing one group of interpolation coefficient.
Embodiment
Through accompanying drawing and embodiment, technical scheme of the present invention is done further detailed description below.
Fig. 1 is the first embodiment flow chart that the present invention is based on the channel estimation methods of ofdm system, and as shown in Figure 1, the method for present embodiment comprises:
Step 1:, in a time slots, dynamically estimate Doppler's maximum frequency values R according to the frequency domain discrete guide-frequency signal that receives;
Step 2: according to said Doppler's maximum frequency values R, dynamically draw system's channel type of living in, promptly become the speed of decline during channel;
Step 3:, dynamically choose the coefficient of inserting in the pilot time axis in the channel estimating according to said channel type.
The embodiment of the invention proposes the method based on the choice of dynamical channel estimating time shaft interpolation coefficient of OFDM structure, through dynamically choosing rational channel estimating time shaft interpolation coefficient, effectively reduces the deterioration of Doppler frequency deviation for systematic function.
Fig. 2 is the second embodiment flow chart that the present invention is based on the channel estimation methods of ofdm system; As shown in Figure 2; On the basis of the foregoing description; Step 2 is specially: in a time slot, reappraise Doppler's maximum frequency values R, and according to the Doppler's peak frequency estimated value R after upgrading, dynamically draw system's channel type of living in.
The method of present embodiment also comprises after step 3:
Step 4: output time axle channel estimation results, carry out simple single order balancing operational then.
Particularly, insert in the channel estimating time shaft, adopt the channel response of present frame and contiguous two same sub-carrier positions of frame to compute weighted.Become when slow under the fading channel when system is in, the weight of three frames (being interpolation coefficient) is close to and equates; When system received Doppler frequency deviation to influence increasing, the weight of present frame (being interpolation coefficient) increased, and the weight (being interpolation coefficient) of contiguous two frames reduces.Therefore system's time shaft interpolation coefficient that can dynamically provide according to step 1-step 3 carries out the computing of time shaft channel estimating.The time shaft channel estimating needs the bigger memory of expense in hardware; Memory need be stored the channel response value of three frames; In the CMMB system frame structure; The valid data of each frame are 3076, so memory needs 3076 * 3 * WIDTH * 2 (in system design, I, Q channel response value are designed to each WIDTH position bit wide).
Simple single order balancing operational; For
Y is the frequency domain signal that receives; H is the channel response estimated value that obtains through interpolation algorithm, and X is the estimated value of signal.But in hardware designs, the hardware spending of division is very big, so the realization of division need be accomplished with multiplication: X * (H
Estimation* conj (H
Estimation))=Y * conj (H
Estimation), wherein conj () representes conjugate operation, wherein (H
Estimation* conj (H
Estimation)) be expressed as mould square, therefore establish α=(H
Estimation* conj (H
Estimation)), α is the scaling factor, directly influences the scaling of judgement yardstick in the subsequent module soft-decision part.
The embodiment of the invention proposes the method based on the choice of dynamical channel estimating time shaft interpolation coefficient of OFDM structure, through dynamically choosing rational channel estimating time shaft interpolation coefficient, effectively reduces the deterioration of Doppler frequency deviation for systematic function.
Fig. 3 is the 3rd embodiment flow chart that the present invention is based on the channel estimation methods of ofdm system, and is as shown in Figure 3, and on the basis of the foregoing description, particularly, above-mentioned steps 1 comprises:
11,, the channel response value of the scattered pilot position of the consistent consecutive frame symbol in pilot tone insertion position is carried out the computing of conjugation multiply accumulating according to the system frame structure characteristics;
With the CMMB system is example, and to the frame structure of CMMB system, this step is specially: according to CMMB system frame structure characteristics, be that the channel response value of the scattered pilot position of odd number or even frame is carried out the computing of conjugation multiply accumulating to the consecutive frame value of symbol.
12, accumulation result is asked arithmetic mean T in a frame, obtain the angle values Z of arithmetic mean T then;
13, all angle values Z that obtain in the time slot are carried out the computing of absolute value arithmetic average, draw phase angle mean value M, the normalized value according to phase angle mean value M draws its corresponding Doppler's maximum frequency values R then.
In above-mentioned steps 11; The channel response value of the scattered pilot position of the consistent consecutive frame symbol in pilot tone insertion position is carried out the conjugation multiply accumulating is: respectively the channel response value of the scattered pilot position of the consistent consecutive frame symbol in pilot tone insertion position is carried out the computing of conjugation multiply accumulating; Then the computing of conjugation multiply accumulating is: the channel response value at the frame symbol scattered pilot place that the channel response value at scattered pilot place is consistent with previous pilot tone insertion position in the present frame is carried out complex conjugate phase multiplication, and the result is carried out accumulating operation in a frame.
With the CMMB system is example; Because present position in odd-numbered frame and even frame, scattered pilot position is different in the CMMB system, so needs are that the channel response value of the scattered pilot position of odd number or even frame is carried out the computing of conjugation multiply accumulating to the consecutive frame symbol respectively.Then in above-mentioned steps 11; The computing of conjugation multiply accumulating is: the channel response value at scattered pilot place is carried out complex conjugate multiplication mutually with the previous channel response value that is all odd-numbered frame or even frame scattered pilot place in the present frame, and the result is carried out accumulating operation in a frame.
Formula does
Wherein P is the set of all scattered pilots in the frame, wherein H
L, n, H
L-2, nRepresent the n subcarrier frequencies response of l frame and l-2 frame.
Fig. 4 is the hardware block diagram that the present invention is based on the channel estimation methods of ofdm system; As shown in Figure 4; The hardware designs of step 11 comprises that the storage frame value of symbol is the memory of odd and even number frame scattered pilot, and according to CMMB Frame Protocol characteristics, the scattered pilot inserted mode is suc as formula shown in (1).ifmod(n，2)＝＝0
ifmod(n，2)＝＝1
Wherein n representes the frame value of symbol, and m is the position registration of scattered pilot subcarrier in frame, can know that from formula (1) distance between continuous two scattered pilots is 8,8 timeticks of promptly in The Hardware Design, being separated by between two adjacent discrete pilot tones.And from memory, read H
L-2, n, and completing steps 1
Complex multiplication operation, at last with H
L, nThe time of write memory is merely 6 timeticks, so only needs two 384 * WIDTH * 2 (I, Q channel response value are designed to each WIDTH position bit wide in the hardware designs) memories in the hardware designs.
In above-mentioned steps 12, T=S/384, the quantity of the scattered pilot that wherein comprises in 384 the frames for CMMB system-frame agreement regulation.Z=angle (T) wherein asks the hardware designs of phase angle part can use the cordic algorithm to realize, concrete realization is adopted 18 level production line methods to accomplish and asked phase angle.
In above-mentioned steps 13; All angle values Z to obtaining in the time slot carry out the computing of absolute value arithmetic average; Draw phase angle mean value M; Can draw its corresponding Doppler's maximum frequency values R according to the normalized value of M then comprises: according to the system frame structure characteristics, the angle values Z that in a time slot, all frame correspondences is tried to achieve carries out the computing of absolute value arithmetic average, draws phase angle mean value M; Normalized value according to phase angle mean value M draws its corresponding Doppler's maximum frequency values R.
According to CMMB system frame structure characteristics; Time slot of CMMB comprises 53 frames; The angle values Z that in a time slot, all frame correspondences is tried to achieve carries out the computing of absolute value arithmetic average; Draw phase angle mean value M;
wherein N is the quantity of the frame that comprises of a time slot, is 53 in the CMMB system; Normalized value according to phase angle mean value M can draw its corresponding Doppler's maximum frequency values R.
In the present invention, the method that dynamically estimates Doppler's maximum frequency values R is not limited to the said method of above step 1.
Above-mentioned steps 2 comprises:
Become the division of decline speed during 21, according to system's channel of living in, channel is divided into N kind channel type in advance, every type corresponding to Doppler's maximum frequency range;
Doppler's maximum frequency values R that estimates when 22, finishing according to each time slot and the pairing Doppler's maximum frequency range of N kind channel type of delimiting in advance dynamically draw system's channel type of living in, promptly become the speed of decline during channel.
In hardware designs, after completing steps 1 and the step 2, all the variable reset alls in the step 1 are 0 in a time slot, waits for new time slot arrival after, repeating step 1 and step 2 are dynamically judged system's channel type of living in.
Above-mentioned steps 3 comprises:
Become the relation of decline speed during 31, according to slotting in the pilot time axis and channel,, store N kind channel type time corresponding axle interpolation coefficient separately according to the N kind channel type of delimiting in advance;
32, according to the channel type of judging, choose the pairing time shaft interpolation coefficient of this channel type.
Fig. 5 is the sketch map that between normalization phase angle that a slot time arithmetic internal is on average tried to achieve and Doppler's maximum frequency values, concerns according to first embodiment of the invention (satellite mobile channel environment) rule; As shown in Figure 5, wherein different colours is represented the different signal to noise ratios of white Gaussian noise; Fig. 6 is according to the error rate of the regular choice of dynamical channel estimating time shaft of first embodiment of the invention (satellite mobile channel environment) interpolation coefficient and fixing one group of interpolation coefficient (interpolation coefficient is assumed to and becomes the fading channel interpolation coefficient when slow) sketch map relatively; As shown in Figure 6; Wherein solid line is represented the method for the used choice of dynamical channel estimating of the present invention time shaft interpolation coefficient; Dotted line is represented system only with one group of fixing method of interpolation coefficient (interpolation coefficient is assumed to and becomes the fading channel interpolation coefficient when slow), and wherein different colours represent white Gaussian noise difference signal to noise ratios.
The embodiment of the invention proposes the method based on the choice of dynamical channel estimating time shaft interpolation coefficient of OFDM structure, through dynamically choosing rational channel estimating time shaft interpolation coefficient, effectively reduces the deterioration of Doppler frequency deviation for systematic function.
What should explain at last is: above embodiment is only in order to technical scheme of the present invention to be described but not limit it; Although the present invention has been carried out detailed explanation with reference to preferred embodiment; Those of ordinary skill in the art is to be understood that: it still can make amendment or be equal to replacement technical scheme of the present invention, also can not make amended technical scheme break away from the spirit and the scope of technical scheme of the present invention and these are revised or be equal to replacement.
Claims (8)
1. the channel estimation methods based on ofdm system is characterized in that, comprising:
According to the frequency domain discrete guide-frequency signal that receives, in a time slots, dynamically estimate Doppler's maximum frequency values R;
Become the division of decline speed during according to system's channel of living in, channel is divided into N kind channel type in advance, Doppler's maximum frequency range of every type of correspondence;
Doppler's maximum frequency values R that estimates when finishing according to each time slot and the pairing Doppler's maximum frequency range of N kind channel type of delimiting in advance dynamically draw system's channel type of living in;
Become the relation of decline speed during according to slotting in the pilot time axis and channel,, store N kind channel type time corresponding axle interpolation coefficient separately according to the N kind channel type of delimiting in advance;
According to the channel type of judging, choose the pairing time shaft interpolation coefficient of this channel type.
2. method according to claim 1 is characterized in that:
When being specially channel, said channel type becomes the speed of decline.
3. method according to claim 2; It is characterized in that; The said Doppler's maximum frequency values R that estimates when finishing according to each time slot and the pairing Doppler's maximum frequency range of N kind channel type of delimitation in advance dynamically draw system's channel type of living in and are specially:
In a time slot, reappraise Doppler's maximum frequency values R, and, dynamically draw system's channel type of living in according to the Doppler's peak frequency estimated value R after upgrading and the pairing Doppler's maximum frequency range of N kind channel type of delimitation in advance.
4. method according to claim 2 is characterized in that, at the channel type that said basis is judged, also comprises after choosing the pairing time shaft interpolation coefficient of this channel type: output time axle channel estimation results, carry out simple single order balancing operational then.
5. according to the described method of arbitrary claim among the claim 1-4, it is characterized in that the frequency domain discrete guide-frequency signal that said basis receives dynamically estimates Doppler's maximum frequency values R and comprises in a time slots:
According to the system frame structure characteristics, the channel response value of the scattered pilot position of the consistent consecutive frame symbol in pilot tone insertion position is carried out the computing of conjugation multiply accumulating;
Accumulation result is asked arithmetic mean T in a frame, obtain the angle values Z of arithmetic mean T then;
All angle values Z to obtaining in the time slot carry out the computing of absolute value arithmetic average, draw phase angle mean value M, and the normalized value according to phase angle mean value M draws its corresponding Doppler's maximum frequency values R then.
6. method according to claim 5 is characterized in that, the channel response value of said scattered pilot position to the consistent consecutive frame symbol in pilot tone insertion position is carried out the computing of conjugation multiply accumulating and is:
Respectively the channel response value of the scattered pilot position of the consistent consecutive frame symbol in pilot tone insertion position is carried out the computing of conjugation multiply accumulating; Then the computing of conjugation multiply accumulating is: the channel response value at the frame symbol scattered pilot place that the channel response value at scattered pilot place is consistent with previous pilot tone insertion position in the present frame is carried out complex conjugate phase multiplication, and the result is carried out accumulating operation in a frame.
7. method according to claim 5; It is characterized in that; Said all angle values Z that obtain in the time slot are carried out the computing of absolute value arithmetic average, draw phase angle mean value M, draw its corresponding Doppler's maximum frequency values R according to the normalized value of phase angle mean value M then and comprise:
According to the system frame structure characteristics, the angle values Z that in a time slot, all frame correspondences is tried to achieve carries out the computing of absolute value arithmetic average, draws phase angle mean value M;
Normalized value according to phase angle mean value M draws its corresponding Doppler's maximum frequency values R.
8. method according to claim 6 is characterized in that, the consecutive frame symbol of said position consistency is for being all odd-numbered frame or even frame.
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| CN1883170A (en) * | 2003-11-13 | 2006-12-20 | 艾利森电话股份有限公司 | Channel estimation by adaptive interpolation |
| WO2007036866A2 (en) * | 2005-09-27 | 2007-04-05 | Nxp B.V. | A method, a program and a module to estimate a doppler maximum frequency and an oscillator frequency offset, receiver including the module |
| CN101257471A (en) * | 2008-03-31 | 2008-09-03 | 浙江大学 | Mobile multimedia digital broadcast OFDM system channel estimation method |
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| CN1883170A (en) * | 2003-11-13 | 2006-12-20 | 艾利森电话股份有限公司 | Channel estimation by adaptive interpolation |
| WO2007036866A2 (en) * | 2005-09-27 | 2007-04-05 | Nxp B.V. | A method, a program and a module to estimate a doppler maximum frequency and an oscillator frequency offset, receiver including the module |
| CN101257471A (en) * | 2008-03-31 | 2008-09-03 | 浙江大学 | Mobile multimedia digital broadcast OFDM system channel estimation method |
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