CN107248967B - Channel estimation method and device applied to OFDM system - Google Patents
Channel estimation method and device applied to OFDM system Download PDFInfo
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- CN107248967B CN107248967B CN201610579107.5A CN201610579107A CN107248967B CN 107248967 B CN107248967 B CN 107248967B CN 201610579107 A CN201610579107 A CN 201610579107A CN 107248967 B CN107248967 B CN 107248967B
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- 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
- H04L27/2655—Synchronisation arrangements
- H04L27/2689—Link with other circuits, i.e. special connections between synchronisation arrangements and other circuits for achieving synchronisation
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- H—ELECTRICITY
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- 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
- H04L25/06—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
- H04L25/061—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection providing hard decisions only; arrangements for tracking or suppressing unwanted low frequency components, e.g. removal of dc offset
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Abstract
The invention discloses a channel estimation method and a device applied to an OFDM system, which belong to the technical field of wireless communication, each frame of data transmitted by the OFDM system comprises M training sequences and N OFDM symbols, each OFDM symbol comprises P data subcarriers and Q pilot subcarriers, the channel estimation method is based on the frequency response of the training sequences at the pilot subcarriers and the data subcarriers respectively to obtain the weight of a first OFDM symbol, then the difference value of the frequency response at the data subcarriers and the pilot subcarriers is used as the weight, the change rule among the subcarriers is saved, iterative computation is sequentially carried out to obtain the frequency response of each OFDM symbol at the data subcarriers, the technical problem that the current interpolation algorithm is used for carrying out OFDM system channel estimation, and the time selective fading caused by the Doppler frequency shift is difficult to resist is solved.
Description
Technical Field
The present invention relates to the field of wireless communications technologies, and in particular, to a channel estimation method and apparatus applied to an OFDM system.
Background
With the progress of the age, mobile communication, especially the rapid development of cell, makes users thoroughly get rid of the constraint of terminal equipment, and realizes complete personal mobility, reliable transmission means and connection modes. In the 21 st century, mobile communications will gradually evolve into an indispensable tool for social development and progress.
Currently, the development history of mobile communication technology is as follows: 1) The first generation mobile communication system (1G) standard was made in the 80 s of the 20 th century, which is a system limited to voice communication only. Because 1G is realized based on an analog circuit, the stability of the system is limited, the communication quality cannot be completely ensured, and the system mainly adopts a frequency division multiplexing technology, has low broadband utilization rate and is not suitable for the current situation of scarce frequency spectrum. 2) The second generation mobile communication system (2G) originates from the 90 th generation of the 20 th century, and the 2G standard starts to adopt digital technology, so that the stability and reliability of the system are greatly improved. 3) The third generation mobile communication system (3G) has been developed in recent years, and the 3G technology has been raised to a new level with respect to the first two generation technologies, but the 3G technology cannot provide the application of broadband multimedia services. Thus, in a new generation communication system (4G), high-rate, high-quality and diversified data services are one of the important research points.
In the past wireless communication systems, single carrier transmission is often used, and this transmission mode may cause intersymbol interference (ISI, inter Symbol Interference) due to excessive channel bandwidth at high rates. The orthogonal frequency division multiplexing (OFDM, orthogonal Frequency Division Multiplexing) technology divides a carrier into a plurality of subcarriers, so that data packets are transmitted on each subcarrier, and thus, the bandwidth of each subcarrier is very small, which is smaller than the coherence bandwidth, so that ISI can be reduced. In addition, the OFDM technology selects proper carrier intervals so that all subcarriers are orthogonal, adjacent carriers are overlapped in a frequency domain, and the frequency band utilization rate is improved. OFDM technology is thus a key technology for 4G communication, wireless local area networks (WLAN, wireless Local Area Newworks), wireless personal area networks (WPAN, wireless Personal Area Network), and broadcasting, with its technical advantages of high transmission rate, high spectrum utilization, and effective against frequency selective fading signals. Among them, 4G communications include long term evolution project (LTE, long Term Evolution) of the 4G standard and worldwide interoperability for microwave access (WiMAX, worldwide Interoperability for Microwave Access) (i.e. 802.16 wireless metropolitan area network); WLAN includes the 802.11a/g/n protocol of the institute of electrical and electronics engineers (IEEE, institute of Electrical an Electronics Engineers) standard; the broadcast includes digital audio broadcast (DAB, digital Audio Broadcasting) and digital video broadcast (DVB, digital Video Broadcasting).
When the frequency domain response of the channel is known, the OFDM receiver can completely eliminate the influence of the multipath channel by frequency domain equalization without considering the influence of additive noise. However, in most OFDM receivers, the information of the channel is unknown. In the coherent detection of an OFDM system, the channel needs to be estimated; specifically, the channel estimation has three main steps: estimation, interpolation and equalization. Wherein, the estimation is to use pilot frequency, remove the pilot frequency information of the sending end with the pilot frequency information of the receiving end, in order to get the frequency response of the channel; "interpolation" is the recovery of the frequency response (also an estimate) of all subcarriers with an interpolation algorithm using the frequency response at the pilot; the "equalization" is to divide the received signal at the receiving end by the recovered frequency response to obtain an estimated value of the signal at the transmitting end. The accuracy of the channel estimation will directly affect the performance of the overall OFDM system.
In the prior art, channel estimation is performed on an OFDM system by the following two schemes:
scheme one: and (3) adopting a linear interpolation algorithm to estimate response estimated values of the front and rear two pilot frequency points of the OFDM channel to obtain the frequency response of the channel. However, this approach interpolates the channel response at the data carrier between two pilots using only the channel estimates for two adjacent pilot locations. The basis is that the transfer function of each data sub-channel between adjacent pilot channels is assumed to be linearly changed according to a certain slope, and in a mobile communication system with a higher moving speed at the receiving end, time selective fading caused by Doppler frequency shift (the Doppler frequency shift in the system is within 180 Hz) exists, and the linear interpolation precision is not high.
Scheme II: and a Gaussian interpolation algorithm (namely a quadratic interpolation algorithm) is adopted, and the responses of the data sub-channel, the front pilot channel and the rear pilot channel are utilized for estimation. However, the method is very complex and is not robust against time selective fading.
That is, in the prior art, there are: the interpolation algorithm is used for carrying out OFDM system channel estimation, and the technical problems that time selective fading caused by Doppler frequency shift is difficult to resist in frequency response recovery, the channel estimation accuracy is not high, and the system error rate is not optimized are solved.
Disclosure of Invention
Aiming at the technical problems that in the prior art, an interpolation algorithm is utilized to perform OFDM system channel estimation, time selective fading caused by Doppler frequency shift is difficult to resist in frequency response recovery, the channel estimation accuracy is not high, and the system error rate is not optimized enough, the invention provides a channel estimation method and a device applied to an OFDM system, which can effectively resist certain Doppler frequency shift, thereby improving the accuracy of channel estimation and reducing the error rate.
In one aspect, the present invention provides a channel estimation method applied to an OFDM system, where each frame of data used for transmission in the OFDM system includes M training sequences and N OFDM symbols, M is a positive integer, and N is an integer greater than or equal to 2, where each OFDM symbol in the N OFDM symbols includes P data subcarriers and Q pilot subcarriers, and the channel estimation method includes the following steps:
S1, obtaining a first frequency response and an ith second frequency response through a minimum variance criterion algorithm, wherein i is an integer in a range of 1-N in sequence, the first frequency response is the frequency response of the M training sequences, and the ith second frequency response is the frequency response of the ith OFDM symbol in the N OFDM symbols at Q pilot subcarriers included by the ith OFDM symbol;
s2, acquiring a third frequency response and a fourth frequency response based on the first frequency response, and acquiring a first weight based on the third frequency response and the fourth frequency response; wherein the third frequency response is the frequency response of the first frequency response at the positions corresponding to P data subcarriers, and the fourth frequency response is the frequency response of the first frequency response at the positions corresponding to Q pilot subcarriers;
s3, enabling i to sequentially take integers in the intervals 1-N-1, obtaining an ith fifth frequency response based on the ith weight and the ith second frequency response when i takes a value, updating the ith weight based on the ith fifth frequency response to obtain an (i+1) th weight until i takes a value of N-1, and obtaining an (N) th weight; wherein the ith fifth frequency response is a frequency response of the ith OFDM symbol at P data subcarriers included therein;
S4, obtaining an Nth fifth frequency response based on the Nth weight and the Nth second frequency response;
s5, dividing the received signal by the Nth fifth frequency response to obtain an Nth estimated frequency response of the transmitted signal.
Optionally, the first weight is specifically a difference between the third frequency response and the fourth frequency response.
Optionally, the ith second frequency response includes: an ith pilot amplitude frequency response and an ith pilot phase frequency response; the i pilot frequency amplitude frequency response is the amplitude frequency response of the i OFDM symbol at the Q pilot frequency subcarriers included by the i OFDM symbol, and the i pilot frequency phase frequency response is the phase frequency response of the i OFDM symbol at the Q pilot frequency subcarriers included by the i OFDM symbol; the step S3 specifically includes:
sequentially taking an integer from the interval 1 to N-1 by i, and obtaining an ith data amplitude frequency response based on an ith weight and the ith pilot frequency amplitude frequency response when the i takes a certain value; meanwhile, based on the ith weight and the ith pilot frequency phase frequency response, obtaining an ith data phase frequency response; wherein the i-th data amplitude frequency response is an amplitude frequency response of the i-th OFDM symbol at P data subcarriers included by the i-th OFDM symbol, and the i-th data phase frequency response is a phase frequency response of the i-th OFDM symbol at P data subcarriers included by the i-th OFDM symbol;
Obtaining the ith fifth frequency response based on the ith data amplitude frequency response, the ith data phase frequency response, and formula (I); wherein, formula (I) is expressed as:e is the base of natural logarithm, j is the imaginary unit;
updating the ith weight based on the ith fifth frequency response to obtain an (i+1) th weight until the value of i is N-1, and obtaining the (N) th weight.
Optionally, in the step S3: sequentially taking an integer from i to N-1, and obtaining an ith fifth frequency response based on an ith weight and the ith second frequency response when the i takes a certain value, wherein the fifth frequency response specifically comprises:
and taking an integer from i to 1-N-1 in sequence, and summing the ith weight and the ith second frequency response when the i takes a certain value to obtain the ith fifth frequency response.
Optionally, in the step S3, updating the ith weight based on the ith fifth frequency response to obtain an ith+1 weight, specifically includes:
obtaining an ith estimated frequency response of the transmitted signal corresponding to the ith fifth frequency response by dividing the received signal by the ith fifth frequency response;
performing hard decision on the ith estimated frequency response to obtain an ith hard decision frequency response;
Obtaining an i-th modified frequency response by dividing the received signal by the i-th hard decision frequency response;
and updating the ith weight by differencing the ith corrected frequency response and the ith second frequency response to obtain an (i+1) th weight.
On the other hand, the present invention also provides a channel estimation device applied to an OFDM system, where each frame of data used for transmission in the OFDM system includes M training sequences and N OFDM symbols, M is a positive integer, and N is an integer greater than or equal to 2, where each OFDM symbol in the N OFDM symbols includes P data subcarriers and Q pilot subcarriers, and the channel estimation device includes:
a training sequence and pilot frequency response obtaining unit, configured to obtain a first frequency response and an ith second frequency response through a minimum variance criterion algorithm, where i is an integer in sequence from 1 to N, the first frequency response is a frequency response of the M training sequences, and the ith second frequency response is a frequency response of an ith OFDM symbol in the N OFDM symbols at Q pilot subcarriers included in the ith OFDM symbol;
a first weight acquisition unit configured to acquire a third frequency response and a fourth frequency response based on the first frequency response, and acquire a first weight based on the third frequency response and the fourth frequency response; wherein the third frequency response is the frequency response of the first frequency response at the positions corresponding to P data subcarriers, and the fourth frequency response is the frequency response of the first frequency response at the positions corresponding to Q pilot subcarriers;
The weight updating unit is used for enabling i to sequentially take integers from the interval 1 to N-1, obtaining an ith fifth frequency response based on the ith weight and the ith second frequency response when i takes a certain value, updating the ith weight based on the ith fifth frequency response to obtain an (i+1) th weight until the i takes a value of N-1, and obtaining an (N) th weight; wherein the ith fifth frequency response is a frequency response of the ith OFDM symbol at P data subcarriers included therein;
a frequency response obtaining unit at the subcarrier of the OFDM symbol data, configured to obtain an nth fifth frequency response based on the nth weight and the nth second frequency response;
a final estimated frequency response obtaining unit for obtaining an nth estimated frequency response of the transmission signal by dividing the reception signal by the nth fifth frequency response.
Optionally, the first weight is specifically a difference between the third frequency response and the fourth frequency response.
Optionally, the ith second frequency response includes: an ith pilot amplitude frequency response and an ith pilot phase frequency response; the i pilot frequency amplitude frequency response is the amplitude frequency response of the i OFDM symbol at the Q pilot frequency subcarriers included by the i OFDM symbol, and the i pilot frequency phase frequency response is the phase frequency response of the i OFDM symbol at the Q pilot frequency subcarriers included by the i OFDM symbol; the weight updating unit specifically includes:
The amplitude phase frequency acquisition module is used for enabling i to sequentially take integers from interval 1 to N-1, and acquiring an ith data amplitude frequency response based on an ith weight and the ith pilot frequency amplitude frequency response when i takes a certain value; meanwhile, based on the ith weight and the ith pilot frequency phase frequency response, obtaining an ith data phase frequency response; wherein the i-th data amplitude frequency response is an amplitude frequency response of the i-th OFDM symbol at P data subcarriers included by the i-th OFDM symbol, and the i-th data phase frequency response is a phase frequency response of the i-th OFDM symbol at P data subcarriers included by the i-th OFDM symbol;
a frequency response obtaining module at the digital subcarrier, configured to obtain the ith fifth frequency response based on the ith data amplitude frequency response, the ith data phase frequency response, and formula (I); wherein, formula (I) is expressed as:e is the base of natural logarithm, j is the imaginary unit;
and the weight updating module is used for updating the ith weight based on the ith fifth frequency response so as to obtain the (i+1) th weight until the value of i is N-1, and obtaining the (N) th weight.
Optionally, the weight updating unit is configured to make i sequentially take integers from interval 1 to N-1, and obtain the ith fifth frequency response based on the ith weight and the ith second frequency response when i takes a certain value, specifically configured to:
And taking an integer from i to 1-N-1 in sequence, and summing the ith weight and the ith second frequency response when the i takes a certain value to obtain the ith fifth frequency response.
Optionally, the weight updating unit is configured to update the ith weight based on the ith fifth frequency response to obtain an ith+1 weight, and specifically includes:
obtaining an ith estimated frequency response of the transmitted signal corresponding to the ith fifth frequency response by dividing the received signal by the ith fifth frequency response;
performing hard decision on the ith estimated frequency response to obtain an ith hard decision frequency response;
obtaining an i-th modified frequency response by dividing the received signal by the i-th hard decision frequency response;
and updating the ith weight by differencing the ith corrected frequency response and the ith second frequency response to obtain an (i+1) th weight.
One or more technical schemes provided by the invention have at least the following technical effects or advantages:
since in the present invention the frequency response of the OFDM symbols at the data sub-carriers in the frame data to be transmitted is estimated by using the frequency response of the known training sequences and pilots inherent in the OFDM system communication protocol, and thus an estimate of the original signal is obtained. The method effectively solves the technical problems that in the prior art, an interpolation algorithm is utilized to carry out OFDM system channel estimation, time selective fading caused by Doppler frequency shift is difficult to resist in frequency response recovery, the channel estimation accuracy is not high, and the system error rate is not optimized enough, and realizes channel estimation and equalization under the condition of severe environment (Doppler frequency shift is less than 180 Hz) so as to reduce the error rate of the system.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are required in the embodiments or the description of the prior art will be briefly described, it being obvious that the drawings in the following description are only embodiments of the present invention, and that other drawings may be obtained according to the provided drawings without inventive effort for a person skilled in the art.
Fig. 1 is a schematic diagram of a matrix sequence of frame data transmitted based on an OFDM system according to an embodiment of the present invention;
fig. 2 is a flowchart of a channel estimation method applied to an OFDM system according to an embodiment of the present invention;
fig. 3 is a block diagram of a channel estimation device applied to an OFDM system according to an embodiment of the present invention;
fig. 4 is a block diagram of another channel estimation apparatus applied to an OFDM system according to an embodiment of the present invention.
Detailed Description
The embodiment of the invention solves the technical problems that the time selective fading caused by Doppler frequency shift is difficult to resist in frequency response recovery, the channel estimation precision is not high, and the system error rate is not optimized by providing the channel estimation method applied to the OFDM system, which exists in the prior art, and carrying out the channel estimation of the OFDM system by utilizing an interpolation algorithm. By adopting the scheme, certain Doppler frequency shift can be effectively resisted, so that the accuracy of channel estimation is improved, and the error rate is reduced.
The technical scheme of the embodiment of the invention aims to solve the technical problems, and the overall thought is as follows:
the embodiment of the invention provides a channel estimation method applied to an OFDM system, wherein each frame of data used for transmission of the OFDM system comprises M training sequences and N OFDM symbols, M is a positive integer, N is an integer greater than or equal to 2, each OFDM symbol in the N OFDM symbols comprises P data subcarriers and Q pilot subcarriers, and the channel estimation method comprises the following steps: s1, obtaining a first frequency response and an ith second frequency response through a minimum variance criterion algorithm, wherein i is an integer in a range of 1-N in sequence, the first frequency response is the frequency response of the M training sequences, and the ith second frequency response is the frequency response of the ith OFDM symbol in the N OFDM symbols at Q pilot subcarriers included by the ith OFDM symbol; s2, acquiring a third frequency response and a fourth frequency response based on the first frequency response, and acquiring a first weight based on the third frequency response and the fourth frequency response; wherein the third frequency response is the frequency response of the first frequency response at the positions corresponding to P data subcarriers, and the fourth frequency response is the frequency response of the first frequency response at the positions corresponding to Q pilot subcarriers; s3, enabling i to sequentially take integers in the intervals 1-N-1, obtaining an ith fifth frequency response based on the ith weight and the ith second frequency response when i takes a value, updating the ith weight based on the ith fifth frequency response to obtain an (i+1) th weight until i takes a value of N-1, and obtaining an (N) th weight; wherein the ith fifth frequency response is a frequency response of the ith OFDM symbol at P data subcarriers included therein; s4, obtaining an Nth fifth frequency response based on the Nth weight and the Nth second frequency response; s5, dividing the received signal by the Nth fifth frequency response to obtain an Nth estimated frequency response of the transmitted signal.
It can be seen that in the scheme of the present application, the frequency response of the OFDM symbol at the data sub-carrier in the frame data to be transmitted is estimated by using the frequency response of the known training sequence and pilot frequency inherent in the OFDM system communication protocol, and thus the estimated value of the original signal is obtained. The method effectively solves the technical problems that in the prior art, an interpolation algorithm is utilized to carry out OFDM system channel estimation, time selective fading caused by Doppler frequency shift is difficult to resist in frequency response recovery, the channel estimation accuracy is not high, and the system error rate is not optimized enough, and realizes channel estimation and equalization under the condition of severe environment (Doppler frequency shift is less than 180 Hz) so as to reduce the error rate of the system.
In order to better understand the above technical solutions, the following detailed description will be made with reference to the accompanying drawings and specific embodiments, and it should be understood that specific features in the embodiments and examples of the present application are detailed descriptions of the technical solutions of the present application, and not limit the technical solutions of the present application, and the technical features in the embodiments and examples of the present application may be combined with each other without conflict.
Example 1
Referring to fig. 1 and 2, an embodiment of the present invention provides a channel estimation method applied to an OFDM system including M training sequences (a 1 ～A M ) And N OFDM symbols (B 1 ～B N ) M is a positive integer, N is an integer of 2 or more, wherein the N OFDM symbols (B 1 ～B N ) Each OFDM symbol of (C) includes P data subcarriers (C 1 ～C P ) And Q pilot subcarriers (D 1 ～D Q ) The channel estimation method comprises the following steps:
s1, obtaining a first frequency response (H) through a Least Square (LS) algorithm LTS ) And an ith second frequency response (H pilot_i ) Wherein i is an integer in the interval 1 to N in turn, and the first frequency response (H LTS ) For the frequency response of the M training sequences, the ith second frequency response (H pilot_i ) Q pilots included in itself for the ith OFDM symbol of the N OFDM symbolsFrequency response at the subcarrier;
specifically, according to different transmission protocols of the OFDM system, the specific number and arrangement of the P data subcarriers and the Q pilot subcarriers of each OFDM symbol transmitted by the OFDM system are different. For example, using a known training sequence and pilot inherent in 802.11a/g to obtain a frequency response and deriving an estimate of the original signal from the frequency response; there are 2 training sequences in a frame specified in 802.11a/g, and there are 64 subcarriers in each OFDM symbol, of which 64 subcarriers, 48 subcarriers are information subcarriers (called data subcarriers) that only carry transmission information, 4 subcarriers are known pilot subcarriers, and the other 12 subcarriers are zero subcarriers. Fig. 1 is only an arrangement of P data subcarriers and Q pilot subcarriers for a certain transmission protocol, and for convenience of understanding, Q pilot subcarriers are arranged under P data subcarriers in a concentrated manner.
In the transmission protocol of an OFDM system, an inherent, known training sequence and pilot subcarrier are typically included, and the frequency response of both the training sequence and pilot subcarrier can be calculated. In the present embodiment, the first frequency response (H is calculated using the LTS algorithm LTS ) (corresponding to training sequence) and ith second frequency response (H pilot_i ) (corresponding pilot subcarriers). Since each OFDM symbol includes Q pilot subcarriers (D 1 ～D Q ) Therefore, for N OFDM symbols, i is sequentially integer-wise taken over intervals 1 to N, and the second frequency response (H) corresponding to each of the N OFDM symbols can be obtained pilot_i )。
S2, based on the first frequency response (H LTS ) Acquiring a third frequency response (H LTS_data ) And a fourth frequency response (H LTS_pilot ) And based on the third frequency response (H LTS_data ) And said fourth frequency response (H LTS_pilot ) Obtain a first weight (w 1 ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the third frequency response (H LTS_data ) For the first frequency response (H LTS ) Frequency response at corresponding P data subcarriers, the fourth frequency response (H LTS_pilot ) For the firstFrequency response (H) LTS ) Frequency response at corresponding Q pilot subcarriers;
specifically, referring to fig. 1, the first frequency response (H LTS ) M longitudinal sequences (A 1 ～A M ) Third frequency response (H LTS_data ) For the first frequency response (H LTS ) Corresponding to P data subcarriers (i.e., transverse sequence C' 1 ～C' P ) Frequency response at (H), fourth frequency response (H LTS_pilot ) For the first frequency response (H LTS ) Corresponding to Q pilot subcarriers (i.e., transverse sequence D' 1 ～D' Q ) Frequency response at (a).
S3, making i take integers in the intervals 1-N-1 in turn, and when i takes a certain value, based on the ith weight (w i ) And said ith second frequency response (H pilot_i ) Obtain the ith fifth frequency response (H data_i ) And based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Until the value of i is N-1, the N weight (w N ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith fifth frequency response (H data_i ) Frequency response at P data subcarriers included per se for the i-th OFDM symbol;
s4, based on the N weight (w N ) And an nth second frequency response (H pilot_N ) Obtain the nth fifth frequency response (H data_N )；
S5, dividing the received signal (Y) by the Nth fifth frequency response (H data_N ) Obtaining an nth estimated frequency response (X est_N )。
In a specific implementation, the LS algorithm in step S1 may be simply expressed as the following formula (II):
in the above formula (II), H LS Corresponding to the first frequency response (H LTS ) Or the ith second frequency response (H pilot_i )，Y LS Is a training sequence signal or a pilot signal received by a receiving end, X LS Is a training sequence signal or a pilot signal sent by a sending end.
In step S2, the first weight (w 1 ) In particular the third frequency response (H LTS_data ) And said fourth frequency response (H LTS_pilot ) Is a difference in (c). I.e. can be represented by the following formula (III):
w 1 ＝H LTS_data -H LTS_pilot (III)
in formula (III), the weight w 1 In fact, the change rule of the training sequence in the frequency domain is preserved. Since the change rule of the adjacent OFDM symbol in the frequency domain is small, the change rule of the previous OFDM symbol in the frequency domain can be used for replacing the change of the current OFDM symbol in the frequency domain. The frequency response (H) at the pilot sub-carriers and at the data sub-carriers by the training sequence can be determined LTS_pilot 、H LTS_data ) The first weight w 1 As the N OFDM symbols (B 1 ～B N ) Weights of the 1 st OFDM symbol.
Further, since the transmission Signal (Signal) of the OFDM system is a complex Signal, it can be expressed as a form of negative exponent of amplitude and phase, as shown in the following formula (IV):
Signal＝Ae jP (IV)
in the formula (IV), a represents amplitude, P represents phase, e is a base of natural logarithm, and j is an imaginary unit. In step S3, the i-th weight (w i ) For calculating and obtaining the frequency response of the ith OFDM symbol at the P data subcarriers included in the ith OFDM symbol, when the transmission signal of the channel is a complex signal, the ith weight (w i ) Can be divided into amplitude weights and phase weights.
Correspondingly, the ith second frequency response (H pilot_i ) Comprising: the ith pilot amplitude frequency response (A pilot_i ) And the ith pilot phase frequency response (P pilot_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith pilot amplitude frequency response (A pilot_i ) Amplitude-frequency response at Q pilot subcarriers included by itself for an ith OFDM symbol, said ith pilotPhase frequency response (P pilot_i ) Phase frequency response at Q pilot subcarriers included per se for the i-th OFDM symbol; the step S3 specifically includes:
let i take an integer over the interval 1 to N-1 in turn, and when i takes a certain value, based on the i-th weight (w i ) And the ith pilot amplitude frequency response (a pilot_i ) Obtain the ith data amplitude frequency response (A data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Meanwhile, based on the i-th weight (w i ) And the ith pilot phase frequency response (P pilot_i ) Obtain the ith data phase frequency response (P data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith data amplitude frequency response (A data_i ) For the amplitude frequency response of the ith OFDM symbol at the P data subcarriers comprised by itself, the ith data phase frequency response (P data_i ) A phase frequency response at P data subcarriers included for the i-th OFDM symbol itself;
Based on the ith data amplitude frequency response (a data_i ) The ith data phase frequency response (P data_i ) And equation (I) to obtain the ith fifth frequency response (H data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein, formula (I) is expressed as:e is the base of natural logarithm, j is the imaginary unit;
based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Until the value of i is N-1, the N weight (w N )。
Further, in the implementation process, in step S3: let i take an integer over the interval 1 to N-1 in turn, and when i takes a certain value, based on the i-th weight (w i ) And said ith second frequency response (H pilot_i ) Obtaining the ith fifth frequency response (H data_i ) The method specifically comprises the following steps:
let i take an integer in the interval 1-N-1 in turn, and when i takes a certain value, pass through the ith weight (w i ) And the ith second frequency response (H pilot_i ) Summing to obtain said ith fifth frequency response (H data_i ). Specifically, it can be represented by the following formula (V):
H data_i ＝w i +H pilot_i (V)
in addition, in the step S3, a frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) The method specifically comprises the following steps:
by dividing the received signal (Y) by the ith fifth frequency response (H data_i ) Obtain a frequency response (H data_i ) The ith estimated frequency response (X est_i )；
For the ith estimated frequency response (X est_i ) Hard decision is made to obtain the ith hard decision frequency response (X HD_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein "hard decision" is the frequency response (X est_i ) Demodulation is performed first, and then modulation is performed, specifically as shown in the following formula (VI):
X HD_i ＝mod(demod(X est_i )) (VI)
further, the received signal (Y) is divided by the i-th hard decision frequency response (X HD_i ) Obtaining the ith corrected frequency response
By the ith modified frequency responseAnd the ith second frequency response (H pilot_i ) Difference is obtained for the ith weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Specifically, the formula (VII) is as follows:
in short, the central idea of step S3 is: (1) With the ith weight (w i ) Find the frequency response (H data_i ) The method comprises the steps of carrying out a first treatment on the surface of the (2) Using frequency response (H data_i ) Estimating a frequency response (X est_i ) The method comprises the steps of carrying out a first treatment on the surface of the (3) Based on the frequency response (X est_i ) Obtaining a corrected frequency response(4) With corrected frequency response->Updating the ith weight (w i ) And acquires the (i+1) th weight (w i+1 ). Wherein i is an integer in the interval 1 to N-1 in turn. Until i takes on the value of N-1, the N weight (w N )。
Further, step S5 is performed to obtain an nth estimated frequency response (X est_N ) I.e. the final estimated frequency response of the channel.
In summary, the scheme of the application firstly obtains the weight of the first OFDM symbol based on the frequency response of the training sequence at the pilot frequency subcarrier and the data subcarrier respectively, then adopts the difference value between the frequency response at the data subcarrier and the frequency response at the pilot frequency subcarrier as the weight, saves the change rule among the subcarriers, and sequentially carries out iterative computation to obtain the frequency response of each OFDM symbol at the data subcarrier, thereby solving the technical problems that the prior art carries out OFDM system channel estimation by utilizing an interpolation algorithm, the time selective fading caused by Doppler frequency shift is difficult to resist when the frequency response is recovered, the channel estimation precision is not high, and the system error rate is not optimized enough.
Example two
Based on the same inventive concept, please refer to fig. 3, the embodiment of the present application further provides a channel estimation device applied to an OFDM system, where each frame of data used for transmission in the OFDM system includes M training sequences and N OFDM symbols, M is a positive integer, N is an integer greater than or equal to 2, and each OFDM symbol in the N OFDM symbols includes P data subcarriers and Q pilot subcarriers, and the channel estimation device includes:
A training sequence and pilot frequency response acquisition unit 31 for obtaining a first frequency response (H by a minimum variance criterion algorithm LTS ) And an ith second frequency response (H pilot_i ) Wherein i is an integer in the interval 1 to N in turn, and the first frequency response (H LTS ) For the frequency response of the M training sequences, the ith second frequency response (H pilot_i ) The frequency response of the ith OFDM symbol in the N OFDM symbols at Q pilot frequency subcarriers included by the ith OFDM symbol is given;
a first weight acquisition unit 32 for acquiring a first frequency response (H LTS ) Acquiring a third frequency response (H LTS_data ) And a fourth frequency response (H LTS_pilot ) And based on the third frequency response (H LTS_data ) And said fourth frequency response (H LTS_pilot ) Obtain a first weight (w 1 ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the third frequency response (H LTS_data ) For the first frequency response (H LTS ) Frequency response at corresponding P data subcarriers, the fourth frequency response (H LTS_pilot ) For the first frequency response (H LTS ) Frequency response at corresponding Q pilot subcarriers;
weight updating means 33 for taking i as an integer over the intervals 1 to N-1 in order, and when i takes a certain value, based on the i-th weight (w i ) And said ith second frequency response (H pilot_i ) Obtain the ith fifth frequency response (H data_i ) And based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Until the value of i is N-1, the N weight (w N ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith fifth frequency response (H data_i ) Frequency response at P data subcarriers included per se for the ith OFDM symbol；
A frequency response acquisition unit 34 at the OFDM symbol data sub-carrier for acquiring a frequency response based on the Nth weight (w N ) And an nth second frequency response (H pilot_N ) Obtain the nth fifth frequency response (H data_N )；
A final estimated frequency response acquisition unit 35 for dividing the received signal (Y) by the nth fifth frequency response (H data_N ) Obtaining an nth estimated frequency response (X est_N )。
In a specific implementation, the first weight (w 1 ) In particular the third frequency response (H LTS_data ) And said fourth frequency response (H LTS_pilot ) Is a difference in (c).
In an implementation, the ith second frequency response (H pilot_i ) Comprising: the ith pilot amplitude frequency response (A pilot_i ) And the ith pilot phase frequency response (P pilot_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith pilot amplitude frequency response (A pilot_i ) Amplitude-frequency response at Q pilot subcarriers included per se for an ith OFDM symbol, the ith pilot phase-frequency response (P pilot_i ) Phase frequency response at Q pilot subcarriers included per se for the i-th OFDM symbol; the weight updating unit 33 specifically includes:
an amplitude phase frequency acquisition module 331 for making i sequentially take integers over the intervals 1 to N-1, and based on an i-th weight (w when i takes a certain value i ) And the ith pilot amplitude frequency response (A pilot_i ) Obtain the ith data amplitude frequency response (A data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Meanwhile, based on the i-th weight (w i ) And the ith pilot phase frequency response (P pilot_i ) Obtain the ith data phase frequency response (P data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith data amplitude frequency response (A data_i ) For the amplitude frequency response of the ith OFDM symbol at the P data subcarriers comprised by itself, the ith data phase frequency response (P data_i ) A phase frequency response at P data subcarriers included for the i-th OFDM symbol itself;
a digital subcarrier frequency response acquisition module 332 for acquiring a frequency response (a based on the ith data amplitude frequency response (a data_i ) The ith data phase frequency response (P data_i ) And equation (I) to obtain the ith fifth frequency response (H data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein, formula (I) is expressed as:e is the base of natural logarithm, j is the imaginary unit;
A weight update module 333 for updating the frequency response based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Until the value of i is N-1, the N weight (w N )。
In a specific implementation, the weight updating unit 33 is configured to make i take an integer over the intervals 1 to N-1 in order, and when i takes a value, based on the i-th weight (w i ) And said ith second frequency response (H pilot_i ) Obtaining the ith fifth frequency response (H data_i ) The method is specifically used for:
let i take an integer in the interval 1-N-1 in turn, and when i takes a certain value, pass through the ith weight (w i ) And the ith second frequency response (H pilot_i ) Summing to obtain said ith fifth frequency response (H data_i )。
In a specific implementation, the weight updating unit 33 is configured to update the weight based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) The method specifically comprises the following steps of:
by dividing the received signal (Y) by the ith fifth frequency response (H data_i ) Obtain a frequency response (H data_i ) The ith estimated frequency response (X est_i )；
For the ith estimated frequency response (X est_i ) Hard decision is made to obtain the ith hard decision frequency response (X HD_i )；
By dividing the received signal (Y) by said i-th hard decision frequency response (X HD_i ) Obtaining the ith corrected frequency response
By the ith modified frequency responseAnd the ith second frequency response (H pilot_i ) Difference is obtained for the ith weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 )。
According to the above description, the channel estimation device applied to the OFDM system is used to implement the channel estimation method, so the channel estimation device is consistent with one or more embodiments of the channel estimation method, and will not be described in detail herein.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. It is therefore intended that the following claims be interpreted as including the preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (10)
1. A channel estimation method applied to an OFDM system, where each frame of data used for transmission in the OFDM system includes M training sequences and N OFDM symbols, M is a positive integer, and N is an integer greater than or equal to 2, where each OFDM symbol in the N OFDM symbols includes P data subcarriers and Q pilot subcarriers, and the channel estimation method includes the steps of:
s1, through a minimum variance criterion algorithmObtain a first frequency response (H LTS ) And an ith second frequency response (H pilot_i ) Wherein i is an integer in the interval 1 to N in turn, and the first frequency response (H LTS ) For the frequency response of the M training sequences, the ith second frequency response (H pilot_i ) The frequency response of the ith OFDM symbol in the N OFDM symbols at Q pilot frequency subcarriers included by the ith OFDM symbol is given;
s2, based on the first frequency response (H LTS ) Acquiring a third frequency response (H LTS_data ) And a fourth frequency response (H LTS_pilot ) And based on the third frequency response (H LTS_data ) And said fourth frequency response (H LTS_pilot ) Obtain a first weight (w 1 ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the third frequency response (H LTS_data ) For the first frequency response (H LTS ) Frequency response at corresponding P data subcarriers, the fourth frequency response (H LTS_pilot ) For the first frequency response (H LTS ) Frequency response at corresponding Q pilot subcarriers;
s3, making i take integers in the intervals 1-N-1 in turn, and when i takes a certain value, based on the ith weight (w i ) And said ith second frequency response (H pilot_i ) Obtain the ith fifth frequency response (H data_i ) And based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Until the value of i is N-1, the N weight (w N ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith fifth frequency response (H data_i ) Frequency response at P data subcarriers included per se for the i-th OFDM symbol;
s4, based on the N weight (w N ) And an nth second frequency response (H pilot_N ) Obtain the nth fifth frequency response (H data_N )；
S5, dividing the received signal (Y) by the Nth fifth frequency response (H data_N ) Obtaining an nth estimated frequency response (X est_N )。
2. Channel estimation method applied to OFDM system according to claim 1, characterized in that the first weights (w 1 ) In particular the third frequency response (H LTS_data ) And said fourth frequency response (H LTS_pilot ) Is a difference in (c).
3. Channel estimation method applied to OFDM system according to claim 1, characterized in that the ith second frequency response (H pilot_i ) Comprising: the ith pilot amplitude frequency response (A pilot_i ) And the ith pilot phase frequency response (P pilot_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith pilot amplitude frequency response (A pilot_i ) Amplitude-frequency response at Q pilot subcarriers included per se for an ith OFDM symbol, the ith pilot phase-frequency response (P pilot_i ) Phase frequency response at Q pilot subcarriers included per se for the i-th OFDM symbol; the step S3 specifically includes:
let i take an integer over the interval 1 to N-1 in turn, and when i takes a certain value, based on the i-th weight (w i ) And the ith pilot amplitude frequency response (A pilot_i ) Obtain the ith data amplitude frequency response (A data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Meanwhile, based on the i-th weight (w i ) And the ith pilot phase frequency response (P pilot_i ) Obtain the ith data phase frequency response (P data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith data amplitude frequency response (A data_i ) For the amplitude frequency response of the ith OFDM symbol at the P data subcarriers comprised by itself, the ith data phase frequency response (P data_i ) A phase frequency response at P data subcarriers included for the i-th OFDM symbol itself;
based on the ith data amplitude frequency response (a data_i ) The ith data phase frequency response (P data_i ) And equation (I) to obtain the ith fifth frequency response (H data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein, formula (I) is expressed as:e is the base of natural logarithm, j is the imaginary unit;
based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Until the value of i is N-1, the N weight (w N )。
4. The channel estimation method applied to the OFDM system according to claim 1, wherein in the step S3: let i take an integer over the interval 1 to N-1 in turn, and when i takes a certain value, based on the i-th weight (w i ) And said ith second frequency response (H pilot_i ) Obtaining the ith fifth frequency response (H data_i ) The method specifically comprises the following steps:
let i take an integer in the interval 1-N-1 in turn, and when i takes a certain value, pass through the ith weight (w i ) And the ith second frequency response (H pilot_i ) Summing to obtain said ith fifth frequency response (H data_i )。
5. The channel estimation method applied to the OFDM system according to claim 1, wherein in the step S3, the channel estimation method is performed based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) The method specifically comprises the following steps:
by dividing the received signal (Y) by the ith fifth frequency response (H data_i ) Obtain a frequency response (H data_i ) The ith estimated frequency response (X est_i )；
For the ith estimated frequency response (X est_i ) Hard decision is made to obtain the ith hard decision frequency response (X HD_i )；
By dividing the received signal (Y) by said i-th hard decision frequency response (X HD_i ) Obtaining the ith corrected frequency response
By the ith modified frequency responseAnd the ith second frequency response (H pilot_i ) Difference is obtained for the ith weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 )。
6. A channel estimation device applied to an OFDM system, each frame of data used for transmission of the OFDM system includes M training sequences and N OFDM symbols, M is a positive integer, N is an integer greater than or equal to 2, wherein each OFDM symbol in the N OFDM symbols includes P data subcarriers and Q pilot subcarriers, the channel estimation device comprising:
a training sequence and pilot frequency response acquisition unit for obtaining a first frequency response (H LTS ) And an ith second frequency response (H pilot_i ) Wherein i is an integer in the interval 1 to N in turn, and the first frequency response (H LTS ) For the frequency response of the M training sequences, the ith second frequency response (H pilot_i ) The frequency response of the ith OFDM symbol in the N OFDM symbols at Q pilot frequency subcarriers included by the ith OFDM symbol is given;
a first weight acquisition unit for acquiring a first weight based on the first frequency response (H LTS ) Acquiring a third frequency response (H LTS_data ) And a fourth frequency response (H LTS_pilot ) And based on the third frequency response (H LTS_data ) And said fourth frequency response (H LTS_pilot ) Obtain a first weight (w 1 ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the third frequency response (H LTS_data ) For the first frequency response (H LTS ) Frequency response at corresponding P data subcarriers, the fourth frequency response (H LTS_pilot ) For the first frequency response (H LTS ) Frequency response at corresponding Q pilot subcarriers;
a weight updating unit for making i take integers in the intervals 1-N-1 in turn, and when i takes a certain valueBased on the i-th weight (w i ) And said ith second frequency response (H pilot_i ) Obtain the ith fifth frequency response (H data_i ) And based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Until the value of i is N-1, the N weight (w N ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith fifth frequency response (H data_i ) Frequency response at P data subcarriers included per se for the i-th OFDM symbol;
A frequency response acquisition unit at the OFDM symbol data sub-carrier for acquiring a frequency response based on the Nth weight (w N ) And an nth second frequency response (H pilot_N ) Obtain the nth fifth frequency response (H data_N )；
A final estimated frequency response acquisition unit for dividing the received signal (Y) by the nth fifth frequency response (H data_N ) Obtaining an nth estimated frequency response (X est_N )。
7. Channel estimation device applied to OFDM system according to claim 6, characterized in that the first weight (w 1 ) In particular the third frequency response (H LTS_data ) And said fourth frequency response (H LTS_pilot ) Is a difference in (c).
8. Channel estimation device applied to OFDM system according to claim 6, characterized in that the ith second frequency response (H pilot_i ) Comprising: the ith pilot amplitude frequency response (A pilot_i ) And the ith pilot phase frequency response (P pilot_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith pilot amplitude frequency response (A pilot_i ) Amplitude-frequency response at Q pilot subcarriers included per se for an ith OFDM symbol, the ith pilot phase-frequency response (P pilot_i ) Phase frequency response at Q pilot subcarriers included per se for the i-th OFDM symbol; the weight updating unit specifically includes:
amplitude phase frequency acquisition module for When i is sequentially given an integer in the interval 1 to N-1 and i takes a certain value, the i weight (w i ) And the ith pilot amplitude frequency response (A pilot_i ) Obtain the ith data amplitude frequency response (A data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Meanwhile, based on the i-th weight (w i ) And the ith pilot phase frequency response (P pilot_i ) Obtain the ith data phase frequency response (P data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein the ith data amplitude frequency response (A data_i ) For the amplitude frequency response of the ith OFDM symbol at the P data subcarriers comprised by itself, the ith data phase frequency response (P data_i ) A phase frequency response at P data subcarriers included for the i-th OFDM symbol itself;
a frequency response acquisition module at the digital subcarrier for acquiring a frequency response (a data_i ) The ith data phase frequency response (P data_i ) And equation (I) to obtain the ith fifth frequency response (H data_i ) The method comprises the steps of carrying out a first treatment on the surface of the Wherein, formula (I) is expressed as:e is the base of natural logarithm, j is the imaginary unit;
a weight updating module for updating the weight based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) Until the value of i is N-1, the N weight (w N )。
9. The channel estimation device applied to OFDM system as recited in claim 6, wherein said weight update unit is configured to make i sequentially take an integer over intervals 1-N-1, and when i takes a value, based on an i-th weight (w i ) And said ith second frequency response (H pilot_i ) Obtaining the ith fifth frequency response (H data_i ) The method is specifically used for:
let i take an integer in the interval 1-N-1 in turn, and when i takes a certain value, pass through the ith weight (w i ) And the ith of theSecond frequency response (H pilot_i ) Summing to obtain said ith fifth frequency response (H data_i )。
10. The channel estimation device applied to an OFDM system according to claim 6, wherein the weight updating unit is configured to update the weight based on the ith fifth frequency response (H data_i ) For the i-th weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 ) The method specifically comprises the following steps of:
by dividing the received signal (Y) by the ith fifth frequency response (H data_i ) Obtain a frequency response (H data_i ) The ith estimated frequency response (X est_i )；
For the ith estimated frequency response (X est_i ) Hard decision is made to obtain the ith hard decision frequency response (X HD_i )；
By dividing the received signal (Y) by said i-th hard decision frequency response (X HD_i ) Obtaining the ith corrected frequency response
By the ith modified frequency responseAnd the ith second frequency response (H pilot_i ) Difference is obtained for the ith weight (w i ) Update is performed to obtain the (i+1) th weight (w i+1 )。
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