CN1708142A - Method for realizing infomration channel estimation in orthogonal frequency division multiplexing system - Google Patents

Method for realizing infomration channel estimation in orthogonal frequency division multiplexing system Download PDF

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CN1708142A
CN1708142A CN 200410048682 CN200410048682A CN1708142A CN 1708142 A CN1708142 A CN 1708142A CN 200410048682 CN200410048682 CN 200410048682 CN 200410048682 A CN200410048682 A CN 200410048682A CN 1708142 A CN1708142 A CN 1708142A
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domain channel
ofdm symbol
time domain
channel information
place
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CN100359960C (en
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党淑君
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Huawei Technologies Co Ltd
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Huawei Technologies Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/022—Channel estimation of frequency response
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L25/00—Baseband systems
    • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
    • H04L25/0202—Channel estimation
    • H04L25/0224—Channel estimation using sounding signals
    • H04L25/0228—Channel estimation using sounding signals with direct estimation from sounding signals
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L27/00—Modulated-carrier systems
    • H04L27/26—Systems using multi-frequency codes
    • H04L27/2601—Multicarrier modulation systems
    • H04L27/2647—Arrangements specific to the receiver only

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Abstract

The method of realizing channel estimation in orthogonal multiplex FDM system includes the following steps: first receiving signal in the frequency domain the subcarrier receives based on received time domain in the receiving end; receiving signal based on the frequency domain the pilot subcarrier in the same OFDM sign receives to obtain the time domain channel information of the OFDM sign; and utilizing the time domain channel information in estimating frequency domain channel information in the subcarrier of the data sign. The scheme of the present invention can obtain better performance in the case of fast varying channel environment, raise the practical channel estimation performance in high delay channel and OFDM system, raise the adaptability of data communication system on channel environment and raise the data transmission efficiency of practical system.

Description

A kind of method that in orthogonal multi-path frequency-division duplicating system, realizes channel estimating
Technical field
The present invention relates to orthogonal multi-path frequency-division duplicating (OFDM) technology, relate to a kind of method that in ofdm system, realizes channel estimating or rather.
Background technology
The OFDM technology is as the frequency multiplexing technique with transmission of high-rate data service ability, and on the one hand, for traditional single-carrier technology, the OFDM technology can utilize simple equalization algorithm that higher spectrum efficiency is provided; On the other hand, in the system that adopts OFDM, do not need as traditional frequency division multiplex (FDM), between adjacent carrier wave, to distribute the protection bandwidth of broad, just can avoid the phase mutual interference between the subcarrier, thereby save bandwidth.
At present, the OFDM technology has been widely used in the existing communication system, and this technology has been embodied among the WLAN standard 802.11a, and among the fixed wireless access standard 802.16a.In addition, in the mobile radio telecommunications connecting system, the wireless access network of third generation partner program (3GPP), the physical layer of IEEE 802.20 are also considering to use the OFDM technology, have the mobile radio telecommunications connecting system of higher frequency efficient with structure.
Figure 1 shows that the networking diagram of a typical frequency cellular re-use system.Wherein, two radio network controllers (RNC), be that RNC1 links to each other with core net (CN) with RNC2, some base stations (BS) link to each other with these two RNC respectively, wherein, BS1, BS2 and BS3 link to each other with RNC1, and BS4, BS5 and BS6 link to each other with RNC2, two travelling carriages (MS), promptly MS1, MS2 and these base stations keep wireless connections.Fig. 2 is a typical sub-district omnidirectional antenna multiplex mode, abbreviates the cell reuse mode as, and Fig. 3 is typical sub-district 120 degree directional antenna multiplex modes, abbreviates the sector multiplex mode as.Adopted the data transmission system of OFDM technology to have the following advantages:
1) expansion has stronger fault-tolerance to multidiameter.As shown in Figure 4, comprise two parts on the OFDM symbol time domain: data division and Cyclic Prefix part, the Cyclic Prefix part is generated by the end circulation of data division, and the time that data division takies among the figure is T Data, the time that Cyclic Prefix partly takies is T CpThe fault-tolerance of OFDM technology shows: compare with the duration T s of an OFDM symbol, the duration of representative channel impulse response is very little, only takies very little part among the Ts, therefore can be by increasing less Cyclic Prefix, i.e. T CpTo overcome the interference between signals that causes by multipath fully.
2) frequency selective fading had stronger fault-tolerance.The OFDM technology can be recovered the entrained digital signal of deep fade subcarrier by redundancy schemes such as employing chnnel codings.
3) adopted simple equalization algorithm.Because the OFDM technology adopts frequency domain to transmit signal, and acting on of channel shows as simple multiplication on the frequency domain, thereby makes the data transmission system that adopts the OFDM technology when carrying out signal equalization, only needs a simple single tap equalizers to realize.
4) for the FDM technology, the OFDM technology has higher spectrum efficiency.
Though adopt the data transmission system of OFDM technology to have above-mentioned advantage, but above-mentioned advantage can be embodied fully in the practical application of system, the more important thing is to make system's operate as normal, must solve following key technology: Frequency Synchronization, sign synchronization, frame synchronization, channel estimating and equilibrium etc.The actual environment for use of these key technologies and system is closely related, and also the network configuration with system requires closely related.
The purpose of channel estimating is in the above-mentioned key technology: the recipient obtains the frequency domain channel information of the data of the side's of emission emission by channel estimating.After obtaining this frequency domain channel information, the recipient just can carry out processing such as equilibrium according to this frequency domain channel information, to obtain corresponding data.Therefore, channel estimation technique is the important prerequisite that the recipient correctly obtains data.
IEEE 802.11a agreement provides channel estimation technique.Specifically, 802.11a the frame structure in the system as shown in Figure 5, the beginning of every frame comprises a leading symbol (Preamble), is thereafter the OFDM data symbol of random length, this OFDM data symbol comprises user data and signaling, and the pilot frequency distribution scheme of 802.11a then as shown in Figure 6.In the physical layer selection scheme of 802.11a and 802.16a, be to utilize Preamble to carry out channel estimating.Specifically, because receiver is known each subcarrier institute data carried by data of the Preamble that transmitter is launched, therefore, the Preamble that utilization receives can obtain the channel condition that each subcarrier experienced of this Preamble, under channel circumstance changed slowly situation, the channel condition that each subcarrier experienced of Preamble can be thought the channel condition that experienced with the corresponding subcarrier of the corresponding OFDM data symbol of this Preamble.
That is to say that this scheme that 802.11 agreements are provided is the channel condition that the channel condition of OFDM data symbol is approximately corresponding Preamble.For this scheme, if the channel circumstance in the system changes very fast, then this approximate meeting brings bigger error, in addition, because the relative motion meeting between receiver and the transmitter causes the variation of channel circumstance, therefore say that this scheme changes faster and has certain limitation in the system being applied to channel circumstance.The channel variation of present mobile radio communication system is often very fast, obviously is not suitable for adopting such scheme in mobile radio communication system.
In addition, though having introduced pilot sub-carrier in the OFDM of 802.11a implementation follows the tracks of the variation of channel, to revise the channel condition that each subcarrier was experienced of Preamble, and with the channel value of revised channel condition as the subcarrier of corresponding OFDM data symbol, but this correction can not reflect the quick variation of channel fully, still can cause bigger performance loss.
For solving the deficiency of such scheme, industry has proposed the pilot frequency distribution pattern of time-frequency lattice point mode, and this allocation model as shown in Figure 7.Pilot tone OFDM symbol in this mode, promptly Preamble evenly distributes on time-frequency plane, therefore, utilizes the variation of pilot tone OFDM symbol tracking channel can solve the problem that channel circumstance changes to a certain extent.
At present, Siemens Company submits among one piece of motion Tdoc R1-030780 of 3GPP RAN1, has proposed a kind of concrete pilot frequency distribution pattern, Dui Ying channel estimation methods, and corresponding simulation result with it.This method specifically is to adopt the method for twice one dimension interpolation, at first carries out 3 times Lagrange's interpolation on time domain, carries out 7 times Lagrange's interpolation then on frequency domain, to obtain to transmit on the time-frequency plane channel condition of the subcarrier of data.Simulation result that Siemens provides shows: with respect to desirable channel estimating, the channel estimation scheme of Siemens has the performance loss of 0.5-0.7dB for PA3, PB3, VA30 channel, for the VB30 channel, at the BLER=0.13 place even the floor occurred.Thus, if channel is big delayedchannel, adopt the channel estimation methods of Siemens can show bigger performance loss.
Summary of the invention
In view of this, main purpose of the present invention is to provide a kind of method that realizes channel estimating in orthogonal multi-path frequency-division duplicating system, to reduce the performance loss of recipient when carrying out channel estimating.
For reaching above purpose, technical scheme of the present invention is achieved in that a kind of method that realizes channel estimating in orthogonal multi-path frequency-division duplicating system, and this method may further comprise the steps:
A. receiving terminal obtains the frequency domain received signal that pilot tone place subcarrier receives according to the time domain received signal that receives;
B. according to being positioned at the frequency domain received signal that receives on the pilot sub-carrier of same orthogonal multi-path frequency-division duplicating OFDM symbol, obtain the time domain channel information at this OFDM symbol place;
C. utilize the frequency domain channel information at the subcarrier place, time domain channel information data estimator symbol place that obtains.
Described step b may further comprise the steps:
B1. according to being positioned at the frequency domain received signal that receives on the pilot sub-carrier of same OFDM symbol, obtain the time domain channel reaction at this OFDM symbol place;
B2. from the time domain channel reaction that obtains, extract corresponding time domain channel information.
Described step b1 may further comprise the steps:
B11. according to described frequency domain received signal, and the frequency-region signal on the pilot sub-carrier in the corresponding OFDM symbol of transmitting terminal emission, the frequency domain channel reaction of obtaining corresponding pilot sub-carrier place on the corresponding OFDM symbol;
B12. obtain the time domain channel reaction of corresponding OFDM symbol place pilot sub-carrier according to described frequency domain channel reaction.
Described step b2 comprises: according to the time delay expansion that system supported, from the time domain channel reaction that step b1 obtains, determine the scope of blocking, obtain this and block scope corresponding time domain channel value in described time domain channel reaction, and replace the time domain channel value that quilt is clipped in the described time domain channel reaction with 0.
Described step b2 comprises: the time domain channel reaction at the OFDM symbol place by analyzing continuous time, determine in the time domain channel most powerful path of one or more, obtain the pairing time domain channel value of described most powerful path, and replace not selected time domain channel value in the described time domain channel reaction with 0.
Described step b2 comprises: the scope of blocking is determined in the time domain channel reaction at the OFDM symbol place by analyzing continuous time, obtain this and block scope corresponding time domain channel value in described time domain channel reaction, and replace not selected time domain channel value in the described time domain channel reaction with 0.
Described step c may further comprise the steps:
C11. estimate by the time domain channel information at the OFDM symbol place that comprises pilot sub-carrier is carried out interpolation, obtain adjacent and comprise the time domain channel information at the OFDM symbol place of data with the described OFDM symbol that comprises pilot sub-carrier;
C12. the time domain channel information at the OFDM symbol place that comprises data is carried out inverse fourier transform, obtain corresponding frequency domain channel information.
Among the described step c11, described receiving terminal carries out interpolation to time domain channel information adjacent and that comprise the OFDM symbol place of pilot sub-carrier and is estimated as: adopt 2 l-1 logarithm lagrange-interpolation carries out interpolation and estimates.
Described step c may further comprise the steps:
C21. obtain corresponding frequency domain channel information according to the time domain channel information that comprises the OFDM symbol place of pilot sub-carrier;
C22. according to the frequency domain channel information at the OFDM symbol place that comprises pilot sub-carrier of gained, estimate adjacent and comprise the frequency domain channel information at the OFDM symbol place of data with the described OFDM symbol that comprises pilot sub-carrier.
Among the described step c21, the described OFDM symbol that comprises pilot sub-carrier is the intensive OFDM symbol of pilot sub-carrier.
Described step c22 is: directly with the frequency domain channel information at the OFDM symbol place that comprises pilot sub-carrier of gained as adjacent with described OFDM symbol and comprise the frequency domain channel information at the OFDM symbol place of data.
Described step c22 is: the frequency domain channel information to the OFDM symbol place that comprises pilot sub-carrier of gained is revised, and with revised frequency domain channel information as adjacent with described OFDM symbol and comprise the frequency domain channel information at the OFDM symbol place of data.
Described step c22 is: the frequency domain channel information at the OFDM symbol place that comprises pilot sub-carrier is carried out interpolation estimate, obtain adjacent with described OFDM symbol and comprise the frequency domain channel information at the OFDM symbol place of data.
Described interpolation is estimated as: adopt 2 l-1 lagrange-interpolation or 1 Lagrange's interpolation algorithm carry out interpolation and estimate.
The present invention program obtains the frequency domain received signal that pilot tone place subcarrier receives by receiving terminal according to the time domain received signal that receives, again according to being positioned at the frequency domain received signal that receives on the pilot sub-carrier of same OFDM symbol, obtain the time domain channel information at corresponding pilot sub-carrier place on this OFDM symbol, again according to the frequency domain channel information at this subcarrier place, time domain channel information data estimator symbol place, make and comparatively fast and under the situation of high latency can obtain preferable performance afterwards in the channel circumstance variation.The present invention program has strengthened the applicability of data communication system to channel circumstance, has improved actual channel estimation performance in the ofdm system, thereby has improved the data transmission efficiency of real system.
Description of drawings
Fig. 1 is the networking diagram of typical frequency cellular re-use system;
Fig. 2 is a typical sub-district omnidirectional antenna multiplex mode schematic diagram;
Fig. 3 is typical sub-district 120 degree directional antenna multiplex mode schematic diagrames;
Fig. 4 is the OFDM schematic symbol diagram;
The frame structure schematic diagram that Fig. 5 provides for 802.11a;
Fig. 6 is the pilot frequency distribution scheme schematic diagram of 802.11a;
Fig. 7 is a pilot tone lattice point mode schematic diagram;
Fig. 8 is the schematic flow sheet of transmitting terminal emission OFDM symbol;
Fig. 9 receives the schematic flow sheet of OFDM symbol for receiver;
Figure 10 is the distribution relation schematic diagram between pilot tone OFDM symbol and the OFDM data symbol;
Figure 11 is the structural representation of pilot tone OFDM symbol;
Figure 12 is the structural representation of OFDM data symbol;
Figure 13 is the numbering segment schematic diagram of OFDM symbol among the present invention program;
Figure 14 carries out a kind of processing of channel estimating through schematic diagram for receiving terminal in the embodiment of the invention;
Figure 15 is the flow chart of first kind of processing mode among the present invention program;
Figure 16 is a kind of pilot frequency distribution pattern diagram of pilot tone lattice point;
Figure 17 is the process chart of first kind of processing mode of the present invention based on the pilot tone lattice point;
Figure 18 is the flow chart of second kind of processing mode among the present invention program;
Figure 19 is the distribution situation schematic diagram of irregular pilot tone OFDM symbol and OFDM data symbol;
Figure 20 is the flow chart of the third processing mode among the present invention program;
Figure 21 is 32 o'clock for blocking the footpath number, under Vehicle A channel, the 30kmph situation, and the channel estimating performance emulation schematic diagram that adopts the present invention program to obtain;
Figure 22 is 32 o'clock for blocking the footpath number, under Vehicle A channel, the 60kmph situation, and the channel estimating performance emulation schematic diagram that adopts the present invention program to obtain;
Figure 23 is 160 o'clock for blocking the footpath number, under Vehicle B channel, the 30kmph situation, and the channel estimating performance emulation schematic diagram that adopts the present invention program to obtain.
Embodiment
Among the present invention program, receiving terminal at first needs to receive the transmitting terminal OFDM symbols transmitted, again the ofdm signal of receiving is carried out channel estimating afterwards.
At first the process of transmitting terminal emission OFDM symbol is made brief description.Transmitting terminal is the multiplex mode on time-frequency plane according to frequency pilot sign and data symbol at first, carry out multiplexing to frequency pilot sign and data symbol, the frequency-region signal that generation is used to launch, afterwards, this frequency-region signal is further carried out processes such as inverse fourier transform, digital-to-analogue conversion, and the electromagnetic signal that will finally generate is launched.This processing procedure as shown in Figure 8.
For receiving terminal, behind the signal that receives the transmitting terminal emission, at first the electromagnetic signal that receives from channel is carried out data sampling; According to the synchronizing information of having obtained, on time domain, the sampled data that receives is carried out extraction, Fourier transform and the demultiplexing of OFDM symbol afterwards, form the frequency pilot sign and the data symbol that receive; Utilize frequency pilot sign and the transmitting terminal receive to carry out channel estimating afterwards at corresponding time-frequency position pilot transmitted symbol, obtain carrying data on the time-frequency plane the time frequency place frequency domain channel information.This processing procedure as shown in Figure 9.
Below in conjunction with drawings and the specific embodiments, the process that the OFDM symbol that comprises pilot sub-carrier that receiving terminal utilization among the present invention program is received carries out channel estimating is described in further detail.
Specifically, receiving terminal carries out channel estimating three kinds of processing modes, and first kind of processing mode is: receiving terminal at first obtains corresponding frequency domain received signal according to the time domain received signal of the pilot tone place subcarrier that receives; Afterwards, again according to being positioned at the frequency-region signal that receives on the pilot sub-carrier of same OFDM symbol, obtain the time domain channel reaction at this OFDM symbol place; And from the reaction of this time domain channel, obtain the delay such as the footpath, the channel informations such as attenuation in footpath; And then according to the time domain channel information at the OFDM symbol place that comprises pilot sub-carrier, and adopt specific interpolation algorithm, estimate the time domain channel information at the OFDM symbol place that comprises data; Afterwards, obtain the frequency domain channel information at this OFDM symbol place, also the frequency domain channel information at the subcarrier place of promptly corresponding carrying data according to the time domain channel information at the OFDM symbol place that comprises data.
Second kind of processing mode equally at first obtained the time domain channel information at the OFDM symbol place that comprises pilot sub-carrier according to the time domain received signal of the pilot tone place subcarrier that receives, different is, after the time domain channel information at the OFDM symbol place that obtains comprising pilot sub-carrier, obtain corresponding frequency domain channel information according to this information, obtain comprising the frequency domain channel information at the OFDM symbol place of data afterwards according to this frequency domain channel information.
The third processing mode is then similar with second kind of processing method, all be the frequency domain channel information that acquisition earlier comprises the OFDM symbol place of pilot sub-carrier, different with second kind of processing method is, when the frequency domain channel information at the OFDM symbol place that comprises pilot sub-carrier according to this is obtained the frequency domain channel information at the OFDM symbol place that comprises data, can be directly will comprise the frequency domain channel information at OFDM symbol place of pilot sub-carrier as adjacent with this OFDM symbol and comprise the frequency domain channel information at the OFDM symbol place of data.For the third processing mode, carry out the OFDM symbol that the comprises pilot sub-carrier OFDM symbol that preferably those pilot sub-carriers are intensive that channel estimating adopted.
Obviously, above-mentioned first kind with second kind of processing mode similar, different is: first kind of processing mode is after the time domain channel information of obtaining the OFDM symbol place that comprises pilot sub-carrier, at first estimate the time domain channel information at the OFDM symbol place that comprises data, and then obtain corresponding frequency domain channel information according to this time domain channel information; Second kind of processing method at first obtains corresponding frequency domain channel information after the time domain channel information of obtaining the OFDM symbol place that comprises pilot sub-carrier, and then estimates the frequency domain channel information at the OFDM symbol place that comprises data according to this frequency domain channel information.Therefore only first kind of processing mode is elaborated below with specific embodiment.
Present embodiment is with the pilot tone OFDM symbol on the time-domain of OFDM symbol employing rule and the pilot frequency distribution pattern that is distributed as of OFDM data symbol, and receiving terminal adopts first kind of processing method to carry out channel estimating based on this allocation model.
At first the distribution mode that OFDM symbol in the present embodiment is adopted describes.A specific embodiments of this pattern comprises n OFDM data symbol between two adjacent pilot frequencies OFDM symbols as shown in figure 10.Same as the prior art, the length of pilot tone OFDM symbol can be identical with the length of OFDM data symbol, also can be different, and pilot tone OFDM symbol and OFDM data symbol also are to be made of Cyclic Prefix part and data division, the Cyclic Prefix part is generated by the end circulation of data division, wherein, the Cyclic Prefix part is the number that this part takies sampled point with the length of data division.The structure of pilot tone OFDM symbol as shown in figure 11, the length of wherein Cyclic Prefix part is N P, cp, the length of data division is N P, dataThe structure of OFDM data symbol as shown in figure 12, the length of wherein Cyclic Prefix part is N D, cp, the length of data division is N D data
For ease of describing, OFDM symbol shown in Figure 10 is numbered according to coding rule as described below:
The numbering of pilot tone OFDM symbol: pilot tone OFDM symbol is numbered in turn according to the time sequencing of emission, and wherein, the numbering of first pilot transmitted OFDM symbol is less;
Naturally the numbering of the OFDM data symbol of the n between the adjacent pilot frequencies OFDM symbol: number in turn from 1 to n, wherein, the numbering of the OFDM data symbol of emission is less earlier;
The numbering of OFDM data symbol: adjacent with self and multiply each other prior to the numbering of self pilot transmitted OFDM symbol and the OFDM data symbol number between the adjacent pilot frequencies OFDM symbol, add the naturally numbering of this OFDM data symbol between adjacent pilot frequencies OFDM symbol then.
Adopt above-mentioned coding rule one section OFDM symbol the numbering segment as shown in figure 13, among the figure, k-1, k, k+1 and k+2 are the numbering of pilot tone OFDM symbol; N* (k-1)+1 ... n* (k-1)+n is the numbering of the OFDM data symbol between pilot tone OFDM symbol k-1 and the k; N*k+1 ... n*k+n is the numbering of the OFDM data symbol between pilot tone OFDM symbol k and the k+1; N* (k+1)+1 ... n* (k+1)+n is the numbering of the OFDM data symbol between pilot tone OFDM symbol k+1 and the k+2.
Based on above-mentioned numbering, suppose that i the frequency-region signal that subcarrier carried of k pilot tone OFDM symbol is D K, i, then k pilot tone OFDM symbol frequency-region signal sequence of being carried is (D K, 0, D K, 1..., D K, Np, data).
Based on above-mentioned pilot frequency distribution pattern, receiving terminal adopt above-mentioned first kind of processing mode carry out channel estimating through as shown in figure 14, its concrete processing procedure as shown in figure 15, corresponding following steps:
The time domain pilot OFDM symbol that step 1501, basis receive obtains the channel reaction of pilot tone OFDM symbol place time domain.
Because in the pilot frequency distribution pattern that present embodiment adopted, the OFDM symbol comprises pilot tone OFDM symbol and OFDM data symbol, wherein, pilot tone OFDM symbol only comprises pilot sub-carrier, OFDM data symbol then only comprises data, therefore, in above-mentioned first kind of processing mode, according to the time domain channel reaction that the frequency-region signal that receives on the pilot sub-carrier that is positioned at same OFDM symbol obtains this OFDM symbol place, be the time domain channel reaction that the frequency-region signal that receives according to pilot tone OFDM symbol obtains this pilot tone OFDM symbol place in the present embodiment.
If the time-domain signal sequence of k pilot tone OFDM symbol reception is (S K, 0', S K, 1' ..., S K, Np, data'), through Fourier transform, behind the process fast Fourier transform (FFT), the frequency domain received signal sequence that obtains is (D K, 0', D K, 1' ..., D K, Np, data'), the frequency-region signal sequence of being carried owing to k pilot tone OFDM symbol is (D K, c, D K, 1..., D K, Np, data), therefore the reaction of the frequency domain channel at k pilot tone OFDM symbol place is ( D k , 0 ′ D k , 0 , D k , 1 ′ D k , 1 , · · · , D k , N p , data ′ D k , N p , data ) , Brief note is (C K, 0 p, C K, 1 p..., C K, Np, data p).Should (C with the frequency domain inverse that obtains K, 0 p, C K, 1 p..., C K, Np, data p) carry out inverse fourier transform, such as carrying out invert fast fourier transformation (IFFT), the time domain channel that can obtain k pilot tone OFDM symbol place channel reacts, and notes by abridging to be (c K, 0 p, c K, 1 p..., c K, Np, data p).
Step 1502, the time domain channel information at pilot tone OFDM symbol place is extracted in reaction according to the time domain channel at pilot tone OFDM symbol place.This time domain channel information comprises the delay in footpath, the attenuation in footpath etc.
Behind the time domain channel response that obtains pilot tone OFDM symbol place,, also need these information are analyzed, to obtain effective channel information for reducing interchannel noise.
Channel information acquisition method has two kinds, and a kind of is the simple truncation method, can use under the situation of known wireless transmission environment channel delay span; Another kind is adaptive channel information extracting method.
For the simple truncation method, can expand according to the time delay that system supported and determine the scope of blocking, such as, suppose that the delay of channel mostly is N sampled point most, can be directly react (c to the time domain channel at the pilot tone OFDM symbol place that obtains in the step 1502 this moment K, 0 p, c K, 1 p..., c K, Np, data p) block, and the scope of blocking is slightly larger than the number of the maximum delay corresponding sampling points of channel, such as, the scope of blocking is N ', and N ' 〉=N.The time domain channel at k the pilot tone OFDM symbol place that obtain this moment is (c K, 0 p, c K, 1 p..., c K, N ' p, 0 ..., 0), wherein, 0 number is N P, data-N '.
Adaptive channel information extracting method is the time domain channel reaction (c by the pilot tone OFDM symbol that a period of time is received continuously specifically K, 0 p, c K, 1 p..., c K, Np, data p) analyze, and select wherein a part of most powerful path as effective diameter, selected effective diameter needs not to be continuous.Such as, in a period of time, can select (c K, i0 p, c K, i1 p..., c K, i, i p) as this section time efficient channel information.After having determined efficient channel information, replace not selected time domain channel value in the time domain channel reaction of pilot tone OFDM symbol with 0, like this, can obtain the time domain channel information of pilot tone OFDM symbol.
In addition, can also simplify above-mentioned adaptive channel information extracting method, such as, can incorporate in the method and block.Method after simplifying is called adaptive intercept method, and specifically, this method at first needs to determine to block length N ', when definite N ', can be at first the time domain channel at the pilot tone OFDM symbol place of continuous time be reacted (c K, 0 p, c K, 1 p..., c K, Np, data p) analyze, to determine the zone of its concentration of energy, and with this area relative length as N ', this N ' is the determined length of blocking, obtain pairing before all the time domain channel values of N ', replace in the time domain channel reaction at pilot tone OFDM symbol place not selectedly then with 0, also be all afterwards time domain channel values of N ', thereby determined time domain channel information.
Step 1503, utilize the time domain channel information at adjacent pilot frequencies OFDM symbol place, and utilize specific interpolation algorithm to estimate the time domain channel information at OFDM data symbol place.
At the time domain channel information (c that has obtained pilot tone OFDM symbol place K, 0 p, c K, 1 p..., c K, N ' p, 0 ..., 0) afterwards, can further estimate the time domain channel information (c of OFDM data symbol place channel according to this information S, 0 d, c S, 1 d..., c S, N ' d, 0 ..., 0), s is the numbering of OFDM data symbol in the formula.
Can utilize specifically, (..., c K-1, i p, c K, i p, c K+1, i p, c K+2, i p...) estimate c K*n+j, i dValue, in the formula j be in OFDM data symbol those OFDM data between adjacent two pilot tone OFDM symbols naturally the numbering.
Estimate c K*n+j, i dValue can adopt Lagrange's interpolation 2l-1 time, typical estimation formulas is:
c k * n + j , i d = Σ m = - l + 1 l c k + m , i p · ( 1 ( Π q = 1 l - m q ) · ( Π q = - l + 1 - m - 1 q ) ) · ( Π q = - l + 1 l ( j n + 1 - q ) ( j n + 1 - m ) )
Wherein, c K+m, i pThe time domain channel value of representing i the sample point in k+m pilot tone OFDM symbol place, c K*n+j, i dThe time domain channel value of representing i the sample point in k*n+j OFDM data symbol place, n represents the number of two OFDM data symbol between the adjacent pilot frequencies OFDM symbol.
When adopting a Lagrange's interpolation, promptly during linear interpolation, above-mentioned formula can be reduced to:
c k * n + j , i d = c k , i p + j n + 1 · ( c k + l , i p - c k , i p )
Wherein, c K, i pThe time domain channel value of representing i the sample point in k pilot tone OFDM symbol place, c K*n+j, i dThe time domain channel value of representing i the sample point in k*n+j OFDM data symbol place, n represents the number of two OFDM data symbol between the adjacent pilot frequencies OFDM symbol.
Can also adopt the logarithm Lagrange's interpolation 2l-1 time, typical estimation formulas is as follows:
ln ( c k * n + j , i d ) = Σ m = - l + 1 l ln ( c k + m , i p ) · ( 1 ( Π q = 1 l - m q ) · ( Π q = - l + 1 - m - 1 q ) ) · ( Π q = - l + 1 l ( j n + 1 - q ) ( j n + 1 - m ) )
Wherein, c K+m, i pThe time domain channel value of representing i the sample point in k+m pilot tone OFDM symbol place, c K*n+j, i dThe time domain channel value of representing i the sample point in k*n+j OFDM data symbol place, n represents the number of two OFDM data symbol between the adjacent pilot frequencies OFDM symbol.
Equally, when adopting a logarithm Lagrange's interpolation, promptly during the log-linear interpolation, top formula can be reduced to:
ln ( c k * n + j , i d ) = ln ( c k , i p ) + j n + 1 · ( ln ( c k + 1 , i p ) - ln ( c k , i p ) )
Wherein, c K, i pThe time domain channel value of representing i the sample point in k pilot tone OFDM symbol place, c K*n+j, i dThe time domain channel value of representing i the sample point in k*n+j OFDM data symbol place, n represents the number of two OFDM data symbol between the adjacent pilot frequencies OFDM symbol.
By above-mentioned any one formula, can estimate to obtain (c S, 0 d, c S, 1 d..., c S, N ' d) value, add N in its back D, data-N ' is individual 0, just can obtain (c S, 0 d, c S, 1 d..., c S, N ' d, 0 ..., 0).
The time domain channel information at the OFDM data symbol place that step 1504, utilization obtain obtains the frequency domain channel information at this OFDM data symbol place.
Specifically, exactly to the time domain channel reaction (c at s OFDM data symbol place of the time domain that obtains S, 0 d, c S, 1 d..., c S, N ' d, 0 ..., 0) and carry out IFFT, the frequency domain inverse that obtains s OFDM data symbol place channel should (C S, 0 d, C S, 1 d..., C S, Nd, data d).
Promptly realized under the situation of distribution as the pilot frequency distribution pattern of pilot tone OFDM symbol on the time-domain of rule and OFDM data symbol by above-mentioned steps, adopted first kind of processing mode to carry out channel estimating.
Certainly, this processing procedure also can be used for other pilot frequency distribution patterns, such as, being used for based on the channel estimating under the pilot frequency distribution pattern of pilot tone lattice point, its concrete processing procedure and said process are similar, therefore, only its processing procedure are made brief description below.Based on a kind of pilot frequency distribution pattern of pilot tone lattice point as shown in figure 16.Based on this pilot frequency distribution pattern, the idiographic flow of first kind of processing mode as shown in figure 17, corresponding following steps:
Step 1701, receiving terminal obtain the frequency domain received signal of pilot tone place subcarrier according to the time domain received signal that receives.
Step 1702, basis are positioned at the frequency domain received signal that receives on the pilot sub-carrier of same OFDM symbol, obtain the time domain channel reaction at corresponding OFDM symbol place.
Step 1703, from the reaction of this time domain channel, obtain time domain channel information.This time domain channel information can be the delay in footpath, the attenuation in footpath etc.
Step 1704, according to comprising the time domain channel information at the OFDM symbol place of pilot sub-carrier, and adopt specific interpolation algorithm, estimate adjacent and comprise the time domain channel information at the OFDM symbol place of data with this OFDM symbol.
The time domain channel information that step 1705, basis comprise the OFDM symbol place of data obtains corresponding frequency domain channel information of carrying the subcarrier place of data.
Above-mentioned first kind of processing mode done detailed explanation.Because second kind of processing mode and first kind of processing mode are similar substantially, therefore only the process that adopts second kind of processing mode to carry out channel estimating is made brief description.Still the distribution with pilot tone OFDM symbol on regular time-domain and OFDM data symbol is an example as the pilot frequency distribution pattern, the concrete processing procedure of its channel estimating as shown in figure 18, corresponding following steps:
The time domain pilot OFDM symbol that step 1801, basis receive obtains the channel reaction of pilot tone OFDM symbol place time domain.
This process is identical with step 1501 in the above-mentioned processing method.
Step 1802, extract the time domain channel information at pilot tone OFDM symbol place from the reaction of the time domain channel of pilot tone OFDM symbol channel.This time domain channel information comprises the delay in footpath, the attenuation in footpath etc.
This process step 1502 same and in the above-mentioned processing method is identical.
The time domain channel information at the pilot tone OFDM symbol place that step 1803, utilization obtain obtains the frequency domain channel information at corresponding pilot tone OFDM symbol place.
Step 1804, utilize the frequency domain channel information at adjacent pilot frequencies OFDM symbol place, and utilize the frequency domain channel information at interpolation method data estimator OFDM symbol place.
The interpolation method that adopts in step 1804 can be 2l-1 lagrange-interpolation.
Be example with the distribution of irregular pilot tone OFDM symbol and OFDM data symbol as the pilot frequency distribution pattern more below, above-mentioned the third processing mode is described.
The distribution of irregular pilot tone OFDM symbol and OFDM data symbol as shown in figure 19, the data number of the OFDM data symbol that comprises between per two adjacent OFDM symbol can be different, this pilot frequency distribution pattern relatively is applicable to channel variation situation slowly.At this pilot frequency distribution pattern, because OFDM symbol wherein comprises pilot tone OFDM symbol and OFDM data symbol, and pilot tone OFDM symbol only comprises pilot sub-carrier, OFDM data symbol then only comprises data, therefore receiving terminal adopts the third processing mode, specifically be that its processing procedure specifically may further comprise the steps as shown in figure 20 according to the frequency domain channel information of pilot tone OFDM sign estimation OFDM data symbol:
The time domain pilot OFDM symbol that step 2001, basis receive obtains the channel reaction of pilot tone OFDM symbol place time domain.
Step 2002, pilot tone OFDM symbol place time domain channel information is extracted in reaction according to the time domain channel at pilot tone OFDM symbol place.This time domain channel information comprises the delay in footpath, the attenuation in footpath etc.
Step 2003, utilize the time domain channel information at the pilot tone OFDM symbol place obtain, obtain the frequency domain channel information at this pilot tone OFDM symbol place.
Step 2004, directly the frequency domain channel information of the frequency domain channel information at the pilot tone OFDM symbol place of gained as the OFDM data symbol between this pilot tone OFDM symbol and the next pilot tone OFDM symbol.
Certainly, can also revise the frequency domain channel information at the pilot tone OFDM symbol place of gained, and with the frequency domain channel information of revised frequency domain channel information as the OFDM data symbol between this pilot tone OFDM symbol and the next pilot tone OFDM symbol.
The present invention program can change the preferable performance that obtains under situation and the high latency situation at channel circumstance.Specifically, by the present invention program, with respect to desirable channel estimating, block the footpath number be 32 o'clock, the channel estimation results under Vehicle A channel, the 30kmph situation as shown in figure 21, performance loss is less than 0.3dB; Channel estimation results under Vehicle A channel, the 60kmph situation as shown in figure 22, performance loss is less than 1.1dB.Blocking the footpath number is 160 o'clock, and under the situation of Vehicle B channel, 30kmph, as shown in figure 23, the channel estimating that adopts the present invention program to obtain estimates that with respect to ideal communication channel performance loss is also less than 0.7dB.
The above only is the present invention program's preferred embodiment, not in order to limit protection scope of the present invention.

Claims (14)

1, a kind of method that realizes channel estimating in orthogonal multi-path frequency-division duplicating system is characterized in that this method may further comprise the steps:
A. receiving terminal obtains the frequency domain received signal that pilot tone place subcarrier receives according to the time domain received signal that receives;
B. according to being positioned at the frequency domain received signal that receives on the pilot sub-carrier of same orthogonal multi-path frequency-division duplicating OFDM symbol, obtain the time domain channel information at this OFDM symbol place;
C. utilize the frequency domain channel information at the subcarrier place, time domain channel information data estimator symbol place that obtains.
2, method according to claim 1 is characterized in that, described step b may further comprise the steps:
B1. according to being positioned at the frequency domain received signal that receives on the pilot sub-carrier of same OFDM symbol, obtain the time domain channel reaction at this OFDM symbol place;
B2. from the time domain channel reaction that obtains, extract corresponding time domain channel information.
3, method according to claim 2 is characterized in that, described step b1 may further comprise the steps:
B11. according to described frequency domain received signal, and the frequency-region signal on the pilot sub-carrier in the corresponding OFDM symbol of transmitting terminal emission, the frequency domain channel reaction of obtaining corresponding pilot sub-carrier place on the corresponding OFDM symbol;
B12. obtain the time domain channel reaction of corresponding OFDM symbol place pilot sub-carrier according to described frequency domain channel reaction.
4, method according to claim 2, it is characterized in that, described step b2 comprises: according to the time delay expansion that system supported, from the time domain channel reaction that step b1 obtains, determine the scope of blocking, obtain this and block scope corresponding time domain channel value in described time domain channel reaction, and replace the time domain channel value that quilt is clipped in the described time domain channel reaction with 0.
5, method according to claim 2, it is characterized in that, described step b2 comprises: the time domain channel reaction at the OFDM symbol place by analyzing continuous time, determine in the time domain channel most powerful path of one or more, obtain the pairing time domain channel value of described most powerful path, and replace not selected time domain channel value in the described time domain channel reaction with 0.
6, method according to claim 2, it is characterized in that, described step b2 comprises: the scope of blocking is determined in the time domain channel reaction at the OFDM symbol place by analyzing continuous time, obtain this and block scope corresponding time domain channel value in described time domain channel reaction, and replace not selected time domain channel value in the described time domain channel reaction with 0.
7, method according to claim 1 is characterized in that, described step c may further comprise the steps:
C11. estimate by the time domain channel information at the OFDM symbol place that comprises pilot sub-carrier is carried out interpolation, obtain adjacent and comprise the time domain channel information at the OFDM symbol place of data with the described OFDM symbol that comprises pilot sub-carrier;
C12. the time domain channel information at the OFDM symbol place that comprises data is carried out inverse fourier transform, obtain corresponding frequency domain channel information.
8, method according to claim 7, it is characterized in that among the described step c11 that described receiving terminal carries out interpolation to time domain channel information adjacent and that comprise the OFDM symbol place of pilot sub-carrier and is estimated as: adopt 2l-1 logarithm lagrange-interpolation to carry out interpolation and estimate.
9, method according to claim 1 is characterized in that, described step c may further comprise the steps:
C21. obtain corresponding frequency domain channel information according to the time domain channel information that comprises the OFDM symbol place of pilot sub-carrier;
C22. according to the frequency domain channel information at the OFDM symbol place that comprises pilot sub-carrier of gained, estimate adjacent and comprise the frequency domain channel information at the OFDM symbol place of data with the described OFDM symbol that comprises pilot sub-carrier.
10, method according to claim 9 is characterized in that among the described step c21, and the described OFDM symbol that comprises pilot sub-carrier is the intensive OFDM symbol of pilot sub-carrier.
11, method according to claim 9, it is characterized in that described step c22 is: directly with the frequency domain channel information at the OFDM symbol place that comprises pilot sub-carrier of gained as adjacent with described OFDM symbol and comprise the frequency domain channel information at the OFDM symbol place of data.
12, method according to claim 9, it is characterized in that, described step c22 is: the frequency domain channel information to the OFDM symbol place that comprises pilot sub-carrier of gained is revised, and with revised frequency domain channel information as adjacent with described OFDM symbol and comprise the frequency domain channel information at the OFDM symbol place of data.
13, method according to claim 9, it is characterized in that, described step c22 is: the frequency domain channel information at the OFDM symbol place that comprises pilot sub-carrier is carried out interpolation estimate, obtain adjacent with described OFDM symbol and comprise the frequency domain channel information at the OFDM symbol place of data.
14, according to claim 7 or 13 described methods, it is characterized in that described interpolation is estimated as: adopt 2l-1 lagrange-interpolation or 1 Lagrange's interpolation algorithm to carry out interpolation and estimate.
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