CN103873397B - A kind of new joint time domain and frequency domain OFDM receive channel estimation methods - Google Patents
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Abstract
The present invention relates to a kind of new joint time domain and frequency domain OFDM to receive channel estimation methods, the described method comprises the following steps, 1）Transmitting terminal frame structure design, the frame structure design step is provided for the targeting sequencing of channel estimation in transmitting terminal and pilot tone is inserted, and 2）Receiving terminal carry out time domain channel estimation balancing, the time domain channel estimation balancing step using targeting sequencing progress channel estimation balancing, 3）Carry out channel estimation in frequency domain equilibrium and correct residual frequency departure, the channel estimation in frequency domain equalization step utilizes pilot frequency information to carry out channel estimation balancing.Transmission information content is the method increase, can preferably suppress the influence of noise, improves the performance of system；When using a pilot for frequency domain estimation balancing, the division channel equalization with multiplicative channel balanced realization, economized on resources when hardware is realized, reduce and calculate the time；Channel estimation balancing can be correctly completed under under relatively low signal to noise ratio snr and a variety of channels, there is stronger application adaptability.
Description
Technical Field
The invention relates to a channel estimation method, in particular to a novel method for estimating a joint time domain and frequency domain orthogonal frequency division multiplexing receiving channel, belonging to the technical field of wireless communication.
Background
Orthogonal Frequency Division Multiplexing, abbreviated as OFDM in english, is actually one of MCM Multi-carrier modulation, and the main principle is to divide a channel into a plurality of Orthogonal sub-channels, convert a high-speed data signal into parallel low-speed sub-streams, and modulate the parallel low-speed sub-streams onto each sub-channel for transmission. The orthogonal signals can be separated by using correlation techniques at the receiving end, which can reduce the mutual interference ICI between the sub-channels. The signal bandwidth on each subchannel is less than the associated bandwidth of the channel, so that on each subchannel it can be seen as flat fading, so that intersymbol interference can be eliminated, and since the bandwidth of each subchannel is only a fraction of the original channel bandwidth, channel equalization becomes relatively easy. Because the OFDM technology has a high frequency band utilization ratio and a good frequency selective fading resistance, it has been widely applied to broadband wireless communication systems, broadcast audio and video fields, and civil communication systems, and the main applications include: asymmetric Digital Subscriber Loop (ADSL), ETSI standard Digital Audio Broadcasting (DAB), Digital Video Broadcasting (DVB), High Definition Television (HDTV), Wireless Local Area Network (WLAN), etc., but the wireless channel of broadband mobile communication exhibits time-frequency dual selective fading characteristics, and the long symbol time of OFDM makes it more sensitive to time-selective fading of the channel. With the improvement of carrier frequency of a wireless communication system and the enhancement of terminal mobility, the time variation of a channel is aggravated, and the influence of ICI is far greater than noise power, so that the accurate time variation characteristic of the channel obtained at a receiving end is the key for ensuring the reliable communication of the OFDM system.
For the OFDM system, according to different transmitted training information, the method can be divided into two types, that is, channel estimation by using a training sequence and channel estimation by using pilot frequency auxiliary modulation, wherein a known training sequence is placed at the head or middle of each frame of a transmitted data sequence by using the training sequence, the transmission is performed periodically, and channel characteristics obtained by estimating the training sequence are equalized in channel response of a data sequence at a receiving end. The method is insensitive to frequency selective fading, and is mainly used in a slow fading channel environment, pilot symbols are periodically inserted in a transmitted data sequence by using a pilot frequency estimation mode, and the channel response of non-pilot frequency subcarriers at a receiving end is obtained only by performing two-dimensional interpolation on the channel characteristics of the pilot frequency subcarriers. This approach is sensitive to frequency selective fading, and too many pilot points reduce the amount of information transmitted in order to accurately estimate the fast fading channel. Therefore, a new technical solution is urgently needed to solve the technical problems.
Disclosure of Invention
Aiming at the technical problems in the prior art, the invention provides an OFDM receiver channel estimation and equalization method suitable for a broadband wireless channel, which can utilize a leading PN training sequence and fewer pilot frequency points to carry out LS channel estimation, and respectively complete channel estimation and equalization in a time domain and a frequency domain, thereby making up the characteristics that the number of pilot frequencies is too small, complete channel information cannot be effectively obtained, better inhibiting the influence of noise and improving the performance of a system. The channel estimation equalization can be completed correctly under lower signal-to-noise ratio SNR and Gaussian channels, itur3GVAx and hiperlan 2D', and the method has stronger application adaptability.
In order to achieve the above object, the technical solution of the present invention is as follows, a new method for estimating a joint time domain and frequency domain orthogonal frequency division multiplexing receiving channel, the method includes steps of 1) designing a frame structure at a transmitting end, the frame structure designing step setting a preamble sequence and pilot insertion for channel estimation at the transmitting end, 2) performing time domain channel estimation equalization at a receiving end, the time domain channel estimation equalization step performing channel estimation equalization using the preamble sequence, 3) performing frequency domain channel estimation equalization and correcting residual frequency offset, and the frequency domain channel estimation equalization step performing channel estimation equalization using pilot information.
As an improvement of the present invention, the specific method in step 1 is as follows, 11) the sending end puts a preamble sequence at the head every frame, the preamble sequence is an L-point sequence composed of (L-1) point PN sequence and a bit 0 is added later, and can be expressed as m = [ P ], [ P ]1P2… PL-1PL]TInstead of the preceding L-point cyclic prefix in the cyclic prefix OFDM (CP-OFDM) data frame, the preamble sequence is followed by the modulated N-point data symbols, where the pilot information is uniformly inserted into the data symbols.
As an improvement of the present invention, the specific method in step 2 is as follows, 21) at the receiving end, the channel estimation value obtained by using the preamble sequence of each frame based on the LS estimation principle is expressed as，Estimating states for time domain channels, where M isTwo-dimensional transmission block matrix, r is observation window received signalA two-dimensional sequence matrix; 22) converting the time domain channel estimation value into the frequency domain for compensationRear patchPoint 0, getPreparing to perform DFT operation, i.e. discrete Fourier transform operation, and obtaining the frequency domain channel estimation value after DFTAfter frequency domain channel equalization of the preamble training sequence, the frequency domain data is output as，Data symbols are received for the frequency domain.
As a modification of the present invention, the specific method in step 3 is as follows, 31) using the received frequency domain output data obtained in step 22)Extracting pre-inserted pilot dataEstimation using LS channel estimationCalculating the inverse of the channel impulse response at the pilot，Is the pilot information that is known to the transmitting end,pilot frequency information extracted for a receiving end; 32) using interpolation filtering in frequency domain, i.e. estimating the inverse of the impulse response of the frequency domain channel at the position of the data sub-carrier in the data symbol by interpolation algorithm in the frequency domain direction(ii) a 33) For the frequency domain data obtained in the step 22)Performing frequency domain equalization, and implementing division channel equalization by using multiplicative channel equalization to the original transmission sequence can be expressed as:。
as an improvement of the present invention, the transmission block matrix M in the step 21) is represented asThe received signal is represented as r。
As an improvement of the present invention, in the step 32), interpolation is performed in the frequency domain direction, and a lagrangian interpolation algorithm is adopted, where the lagrangian interpolation formula is:
wherein,is the input signal of the interpolator, is the corresponding sampling instantIs determined by the sampling value of (a),is the output of the interpolator, corresponding to the sampling instantRespectively corresponding to the continuously inputted M known signal sampling valuesTime, calculating an arbitrary timeThe signal value of (a); m is the number of sampling points participating in one-time interpolation calculation, generally called Lagrange interpolation order, and for the channel estimation of OFDM, the pilot symbols are assumed to be distributed at equal intervals and the interval distance isThen the above lagrange interpolation formula can be expressed as:
wherein,，is made byA set of all pilot subcarriers over one OFDM symbol;is the inverse of the channel response value at the pilot location;means taken not more thanIs an integer of (1).
As an improvement of the present invention, in the lagrangian interpolation algorithm, for different lagrangian interpolation algorithms corresponding to different "M", the lagrangian interpolation algorithm has first-order linear interpolation or second-order Parabolic interpolation (Parabolic) or third-order Cubic interpolation. Theoretically, the accuracy of interpolation estimation can be improved by increasing the order of the polynomial of the interpolation algorithm, but the algorithm complexity is increased.
Compared with the prior art, the invention has the following advantages:
obtaining a time domain channel estimation value by using a preamble training sequence; estimating a frequency domain channel estimation value of a pilot frequency position by utilizing comb-shaped pilot frequency in a data symbol, obtaining a channel estimation value of the whole data subcarrier by adopting an interpolation algorithm according to the channel estimation value of the pilot frequency position, finishing channel estimation in a time domain and a frequency domain respectively, and pre-determining a preamble sequence when a time domain LS channel estimation is carried out by adopting the preamble sequenceCalculating and storing, thus reducing resource utilization and calculation time during implementation and reducing the calculation complexity of the time domain LS estimation algorithm; meanwhile, the characteristics that the number of pilot frequencies is too small and complete channel information cannot be effectively obtained are compensated, the quantity of transmitted information is increased, the influence of noise can be well inhibited, and the performance of the system is improved; when the pilot frequency is used for carrying out frequency domain estimation equalization, the multiplication channel equalization is used for realizing division channel equalization, resources are saved when hardware is realized, and calculation is reducedA (c) is added; the channel estimation equalization can be completed correctly under the conditions of low signal-to-noise ratio SNR and various channels, and the method has stronger application adaptability.
Drawings
FIG. 1 is a frame structure diagram;
FIG. 2 is a pilot insertion pattern;
fig. 3 is a flow chart of channel estimation.
Detailed Description
For a better understanding and appreciation of the invention, the invention will be further illustrated and described below in connection with the accompanying drawings and detailed description.
Example 1:
a new method for estimating the channel of OFDM receiving in combined time domain and frequency domain includes such steps as designing the frame structure of transmitter, equalizing the channel estimation in time domain by the aid of preamble training sequence and equalizing the channel estimation in frequency domain by the aid of comb pilot frequency, and correcting the residual frequency offset.
1) Design of frame structure:
each transmission frame structure is as in figure 1,the point data symbol is obtained by carrying out channel coding, subcarrier mapping, modulation and channel interleaving on the originating data, and is periodically inserted before each data symbol is sent according to the 802.11p standardPoint leader sequence m = [ 1111-1-1-11-1-111-11-10 =]For time domain channel estimation, transmitting data symbols at 64 pointsInserting pilot frequency information on 4 th-point subcarriers of-21 th, 7 th and 21 th, wherein the pilot frequency information is used for frequency domain channel estimation and residual frequency offset correction; the-31, -5 point subcarriers are direct current and guard subcarriers.
2) And (3) carrying out time domain channel estimation equalization by using a preamble training sequence:
obtaining a time domain channel estimation value by utilizing the autocorrelation characteristic of a PN sequence and adopting a time domain channel estimation method based on an LS estimator principle;
at the receiving end, each frame of received OFDM symbols includes a preamble sequenceAnd a data sequenceThe received sequence is represented as. Based on the principle of LS algorithm, M is formed by leading sequence M = [ P = [)1P2… PL-1PL]TA transmission matrix block composed of cyclic shifts, denoted asH is channel impulse response, w is white gaussian noise, and in order to reduce resource utilization and calculation time, the channel impulse response and the white gaussian noise can be calculated in advanceAnd the calculation and storage can reduce the calculation complexity of the time domain LS estimation algorithm. The received signal of the observation window is represented as. The time domain channel estimate may be expressed as。
Converting channel time domain values to frequencyDomain equalization is performed to balance the domainThe later is supplemented with 0 to obtainTo facilitate DFT operation, the channel estimation after obtaining frequency domain after DFT isThe frequency domain output data after the frequency domain equalization of the preamble training sequence is。
3) Frequency domain channel estimation equalization and residual frequency offset correction using comb pilots, frequency domain output data obtained from aboveTo extract pre-inserted pilot dataEstimating the inverse of the channel impulse response at the pilot frequency by an LS channel estimation methodThus, in the following frequency domain equalization we can replace the division used by the equalization by multiplication.
Interpolation in the frequency domain direction adopts a Lagrange interpolation algorithm, Lagrange interpolation (Lagrange) is the most common interpolation algorithm, and the Lagrange interpolation formula is as follows:
wherein,is the input signal of the interpolator, is the corresponding sampling instantIs determined by the sampling value of (a),is the output of the interpolator, corresponding to the sampling instantSuch that the values of the M known signal samples (respectively corresponding to the M known signal samples) are successively inputTime of day), an arbitrary time of day can be calculatedThe signal value of (a); m is the number of samples that participate in one interpolation calculation, commonly referred to as the lagrangian interpolation order.
The pilot symbols are assumed to be equally spaced and spaced apart by a distance ofThen the above lagrangian interpolation formula for OFDM channel estimation can be expressed as:
wherein,，is made byAll pilot subcarriers on one OFDM symbolA set of compositions.Is the inverse of the channel response value at the pilot location.Means taken not more thanIs an integer of (1). For different M, different lagrangian interpolation algorithms. Commonly used lagrange interpolation algorithms are first order linear interpolation, second order Parabolic interpolation (Parabolic), and third order Cubic interpolation. Theoretically, the accuracy of interpolation estimation can be improved by increasing the order of the polynomial of the interpolation algorithm, but the algorithm complexity is increased.
The system adopts a first-order linear interpolation estimation formula,: the above equation can be converted into:
wherein if the pilot spacing is 13, the first-order interpolation coefficient is obtained as:
whereinIs the inverse of the channel estimate being sought,the inverse of the previous pilot channel response value,the inverse of the latter pilot channel response value. Obtaining frequency domain channel response reciprocal of all data sub-carrier position by interpolation method，
For the output frequency domain dataOriginal transmission sequence output by frequency domain equalization estimatorCan be expressed as:
the above formula realizes division channel equalization by multiplication channel equalization, and can save system resources and running time when a hardware chip such as a DSP writes codes for realization.
Example 2: as a preferred scheme of the present invention, the channel estimation equalization may be implemented by using a hardware chip, such as a Field Programmable Gate Array (FPGA) or a digital signal processing chip (DSP).
Example 3: as still another preferable aspect of the present invention, the channel estimation equalization may be implemented by computer-based software.
The invention can also combine the technical schemes described in the embodiments 2 and 3 with the embodiments to form a new technical scheme.
It should be noted that the above-mentioned embodiments illustrate only the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and that equivalents and substitutions made on the above-mentioned embodiments are included in the scope of the present invention, which is defined by the claims.
Claims (4)
1. A new method for estimating a combined time domain and frequency domain orthogonal frequency division multiplexing receiving channel comprises the following steps of 1) designing a frame structure of a sending end, wherein a preamble sequence and pilot frequency insertion for channel estimation are set at the sending end in the frame structure designing step, 2) carrying out time domain channel estimation equalization at the receiving end, carrying out channel estimation equalization by using the preamble sequence in the time domain channel estimation equalization step, and 3) carrying out frequency domain channel estimation equalization and correcting residual frequency offset, wherein the channel estimation equalization is carried out by using pilot frequency information in the frequency domain channel estimation equalization step;
the steps areThe specific method in step 1 is as follows, 11) the transmitting end puts a preamble sequence in the header every frame, the preamble sequence is an L-point sequence composed of (L-1) point PN sequence and a bit 0 is added later, and can be expressed as m ═ P1P2… PL-1PL]TReplacing the previous L-point cyclic prefix in the cyclic prefix OFDM data frame, and after the leader sequence, modulating N-point data symbols, wherein pilot frequency information is uniformly inserted into the data symbols; the specific method in the step 2 is as follows, 21) at the receiving end, the channel estimation value obtained by using the preamble sequence of each frame based on the LS estimation principle is expressed as Estimating a state for a time domain channel, wherein M is a (2L-1) L two-dimensional sending block matrix, and r is an observation window received signal (2L-1) 1 two-dimensional sequence matrix; 22) converting the time domain channel estimation value into the frequency domain for compensationAdding N-L point 0 to obtainPreparing to perform DFT operation, namely discrete Fourier transform operation, and obtaining a frequency domain channel estimation value after DFTThe frequency domain data output after the channel equalization of the preamble training sequence frequency domain is S' ═ RM/H，RMReceiving data symbols for a frequency domain;
the specific method in step 3 is as follows, 31) using the received frequency domain output data S' obtained in step 22) to extract the pilot data Y inserted in advancep(n) estimating the reciprocal of the channel impulse response at the pilot frequency by the LS channel estimation methodXpFor pilot information known to the transmitting end, YpPilot frequency information extracted for a receiving end; 32) using interpolation filtering in frequency domain, i.e. using interpolation algorithm to estimate inverse of impulse response of frequency domain channel at data sub-carrier position in data symbol in frequency domain direction33) Performing frequency domain equalization on the frequency domain data S' obtained in step 22), and implementing division channel equalization by using multiplicative channel equalization to obtain an original transmission sequence can be represented as:
2. the method as claimed in claim 1, wherein the transmission block matrix M in step 21) is expressed asThe received signal is represented as r
3. The method as claimed in claim 2, wherein the step 32) interpolates in the frequency domain direction by using lagrangian interpolation algorithm, and the lagrangian interpolation formula is:
<mrow> <mi>y</mi> <mo>=</mo> <munderover> <mo>&Sigma;</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>0</mn> </mrow> <mrow> <mi>M</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <mi>y</mi> <mrow> <mo>(</mo> <msub> <mi>x</mi> <mi>k</mi> </msub> <mo>)</mo> </mrow> <munderover> <munder> <mi>&Pi;</mi> <mrow> <mi>i</mi> <mo>=</mo> <mn>0</mn> </mrow> </munder> <mrow> <mi>i</mi> <mo>=</mo> <mi>k</mi> </mrow> <mrow> <mi>M</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <mrow> <mo>(</mo> <mfrac> <mrow> <mi>x</mi> <mo>-</mo> <msub> <mi>x</mi> <mi>i</mi> </msub> </mrow> <mrow> <msub> <mi>x</mi> <mi>k</mi> </msub> <mo>-</mo> <msub> <mi>x</mi> <mi>i</mi> </msub> </mrow> </mfrac> <mo>)</mo> </mrow> </mrow>
wherein, y (x)k) Is the input signal of the interpolator, is the corresponding sampling instant xkY is the output of the interpolator, corresponds to the signal value at the sampling instant x, and corresponds to x, respectively, from the continuously input M known signal sample valueskK is 0, 1, …, and M-1, calculating the signal value at any time x; m is the number of sampling points participating in one-time interpolation calculation, generally referred to as lagrangian interpolation order, and for the channel estimation of OFDM, assuming that pilot symbols are distributed at equal intervals and the interval distance is d, the lagrangian interpolation formula can be expressed as:
wherein lj-1＜x＜lj，lj-lj-1＝d，ljC is a set consisting of all pilot subcarriers on the nth OFDM symbol;is a pilotThe inverse of the channel response value at the location;meaning taking an integer no greater than X.
4. The method as claimed in claim 3, wherein the lagrangian interpolation algorithm comprises a first-order linear interpolation or a second-order Parabolic interpolation, parebolic interpolation or a third-order Cubic interpolation, and the lagrangian interpolation algorithm corresponds to different lagrangian interpolation algorithms for different "M".
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| CN105577585A (en) * | 2015-12-25 | 2016-05-11 | 广东顺德中山大学卡内基梅隆大学国际联合研究院 | High accuracy MIMO-OFDM (Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing) system channel estimation method |
| CN105743629B (en) | 2016-03-03 | 2019-07-19 | 华为技术有限公司 | Signaling method and device |
| CN107347041B (en) * | 2016-05-05 | 2020-03-20 | 华为技术有限公司 | Sequence-based channel estimation method and device |
| WO2017190556A1 (en) * | 2016-05-05 | 2017-11-09 | 华为技术有限公司 | Sequence-based channel estimation method and device |
| CN107682287A (en) * | 2017-09-14 | 2018-02-09 | 上海无线通信研究中心 | Detection method/system, computer-readable recording medium and the equipment of signal of communication |
| CN108718289B (en) * | 2018-06-13 | 2021-03-30 | 电子科技大学 | Frequency offset estimation and channel estimation method based on ZC sequence |
| CN113315611A (en) * | 2020-02-27 | 2021-08-27 | 北京新岸线移动多媒体技术有限公司 | Wireless communication method for realizing high reliability |
| CN111817990B (en) * | 2020-06-22 | 2022-08-09 | 重庆邮电大学 | Channel estimation improvement algorithm based on minimum mean square error in OFDM system |
| CN114006795B (en) * | 2021-11-01 | 2023-05-09 | 北京中科晶上科技股份有限公司 | Method and device for determining linear interpolation of 5G channel estimation data |
| CN114338326B (en) * | 2021-12-31 | 2024-03-22 | 北方联创通信有限公司 | Wireless communication processing method and device |
| CN117424784B (en) * | 2023-12-19 | 2024-02-23 | 成都国恒空间技术工程股份有限公司 | OFDM system channel estimation method based on leading and pilot frequency |
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Denomination of invention: Novel estimation method for orthogonal frequency-division multiplexing receiving channel combining time domain and frequency domain Effective date of registration: 20200313 Granted publication date: 20180109 Pledgee: Nanjing Bank Co., Ltd. Nanjing Financial City Branch Pledgor: JIANGSU ZHENGHETONG INFORMATION TECHNOLOGY Co.,Ltd. Registration number: Y2020980000677 |
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Date of cancellation: 20210316 Granted publication date: 20180109 Pledgee: Nanjing Bank Co.,Ltd. Nanjing Financial City Branch Pledgor: JIANGSU ZHENGHETONG INFORMATION TECHNOLOGY Co.,Ltd. Registration number: Y2020980000677 |
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