CN102143101A - Mirror-extended frequency domain windowing orthogonal frequency division multiple access channel estimation method - Google Patents
Mirror-extended frequency domain windowing orthogonal frequency division multiple access channel estimation method Download PDFInfo
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Abstract
The invention discloses a mirror-extended frequency domain windowing orthogonal frequency division multiple access channel estimation method, which is characterized by comprising the following steps of: 1, mirror extension, namely, performing mirror extension by L points on a received orthogonal frequency division multiple access frequency domain reference signal with the length of M points, wherein M is an orthogonal frequency division multiple access transmission bandwidth as well as the length of the reference signal in a frequency domain, and L is an extended length specifically determined by the transmission bandwidth; and 2, frequency domain windowing, namely, multiplying an obtained mirror-extended channel frequency domain response by using a window, wherein the window is an L-point ring shifts left window with the length of M+L points and adjustable parameters, the parameters are related to a signal to noise ratio, M is the orthogonal frequency division multiple access transmission bandwidth as well as the length of the reference signal in the frequency domain, and L is the extended length specifically determined by the transmission bandwidth. By the method, estimation performance can be improved, and the interference of code division multiplexing can be resisted under the condition of multiplexing the reference signals of a plurality of transmitters by different ring shifts.
Description
Technical Field
The invention relates to a channel estimation applied to an MIMO (Multiple Input and Multiple Output) -OFDMA (Orthogonal Frequency Division Multiple Access) system, belonging to the technical field of communication transmission.
Background
Information is distorted by a channel during transmission and noise is introduced, and especially in wireless communication, the wireless channel condition is very bad, and the channel is multipath and time-varying. Theoretically, the transmitted information can be recovered as long as it is accurately estimated how the channel acts on the transmission signal. In practical communication systems, pilot-assisted channel estimation is often used, i.e. a transmitter transmits a known signal (also called a reference signal), and a receiver extracts channel information from the received reference signal.
As one of the multicarrier systems, OFDMA (Orthogonal Frequency Division Multiple Access) is an evolution of OFDM (Orthogonal Frequency Division multiplexing) technology, and is a transmission technology in which transmission data is loaded on a part of subcarriers after a channel is formed into subcarriers by OFDM. Due to the good properties of the OFDMA system, the linear convolution of the transmission signal and the channel impulse response in the time domain can be fully equivalent to a multiplication of the two after transformation to the frequency domain. The receiver obtains the received reference signal in the frequency domain after OFDM demodulation, and then divides the received reference signal by the transmitted reference signal to obtain the channel frequency domain response.
The channel frequency domain response obtained above contains noise and interference, and a practical communication system needs to ensure reliable channel estimation under the condition of low signal-to-noise ratio. Considering that most of the energy of the channel impulse response is concentrated on the time domain samples within the delay spread, and the noise is distributed on all the time domain samples (the noise is generally regarded as white noise), the channel estimation of the OFDMA system usually adopts an algorithm for suppressing the noise based on the transform domain of DFT (discrete fourier transform), which can achieve good channel estimation performance and low complexity. The basic scheme is that IDFT (inverse discrete Fourier transform) is carried out on the frequency domain response of a channel containing noise, and after the frequency domain response is converted into a time domain, the noise is suppressed on the time domain through a certain method, such as a method of adding a window with a cutoff length being the maximum time delay expansion of the channel.
Since the transmission bandwidth of OFDMA is small relative to the system bandwidth, the receiving end can obtain only a small portion of the channel frequency domain response. After the channel frequency domain response is subjected to IDFT and is converted into the time domain, the energy of the channel impulse response can be leaked to all sampling points, so that the time domain windowing keeps most of the energy of the channel impulse response, the noise is removed, but the useful leakage energy of the channel impulse response is also removed, and the channel estimation error is Gibbs (Gibbs) in the frequency domain, namely the channel frequency domain response estimation error on the edge subcarrier is much larger than the error on the central subcarrier. This also causes a large estimation bias, which may be referred to as an error floor, in the DFT-based transform-domain noise suppression algorithm even under high snr conditions.
In addition, in the multi-antenna technology in modern communication systems, such as space division multiple access, multi-point cooperation, etc., the receiver needs to distinguish different transmitting ends by code division multiplexed reference signals. In practical systems, multiplexing is generally achieved by different cyclic shifts, since the energy of the channel impulse response is concentrated within the delay spread. However, in an actual system, power may be different when reference signals of different transmitting ends are received, so that energy leakage of a channel impulse response of a transmitting end with higher receiving power interferes with a transmitting end with lower receiving power, which is referred to as code division multiplexing interference in the present invention. Especially, in the case of a small OFDMA transmission bandwidth, the energy leakage of the channel impulse response is more serious, thereby causing serious code division multiplexing interference.
Disclosure of Invention
The technical problem is as follows:the invention aims to provide a frequency domain windowing orthogonal frequency division multiple access channel estimation method for image spreading, which can improve the estimation error performance and can resist code division multiplexing interference under the condition that reference signals of a plurality of sending ends are multiplexed by different cyclic shifts.
The technical scheme is as follows:in order to solve the above technical problem, the present invention provides a frequency domain windowed ofdma channel estimation method of image spreading, which includes the following steps:
step one, mirror image expansion: to a received length of
Orthogonal frequency division multiple access frequency domain reference signal processing of points
Mirror image expansion of points;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
for the extended length, the specific value depends on the size of the transmission bandwidth;
second, frequency domainWindowing: multiplying the obtained mirror image expanded channel frequency domain response by a window
Window
Is a length ofWindow with adjustable point parameters
Is/are as follows
Point left cyclic shift, wherein
Is related to the signal-to-noise ratio;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
for the extended length, the specific value depends on the size of the transmission bandwidth;
thirdly, the channel frequency domain response after the image expansion and the frequency domain windowing is implemented
Point inverse discrete Fourier transform is carried out to transform the point inverse discrete Fourier transform into a time domain;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
to extend the lengthThe specific value depends on the size of the transmission bandwidth;
fourthly, separating channel impulse response energy and noise of a plurality of sending ends by windowing the obtained time domain signals;
fifthly, zero-filling the channel impulse response energy of each transmitting end toPoint, respectively carry out
Point discrete Fourier transform to frequency domain;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,for the extended length, the specific value depends on the size of the transmission bandwidth;
sixthly, the channel frequency domain response of each sending end is preceded by
Dot divided by windowFront of
Point, obtaining channel estimation result;
is the bandwidth of the ofdma transmission and is also the length of the reference signal in the frequency domain.
Preferably, in the first step, the method of mirror image extension is as follows:
wherein,
for the received channel frequency domain response, the length is
，For mirror-extended frequency domain response, length is
，
Is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
the specific value for the extended length depends on the size of the transmission bandwidth.
Preferably, in the second step, the frequency domain windowing method comprises:
whereinTo mirror the extended frequency domain response,is the serial number of the sampling point in the frequency domain,
is defined as:
Preferably, in the third step, the specific implementation method is as follows: channel frequency domain response to image spreading and frequency domain windowing
Practice of
Point inverse discrete Fourier transform to time domain signal
；
Wherein,
is the serial number of the sampling point in the frequency domain,
the time domain sample point serial number;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
the specific value for the extended length depends on the size of the transmission bandwidth.
Preferably, in the fifth step, the specific implementation method comprises: channel impulse response to each transmitting end
Do respectively to
Discrete Fourier transform to obtain frequency domain channel responses of multiple transmitting ends
WhereiniTo distinguish different users;
is the serial number of the sampling point in the frequency domain,the time domain sample point serial number;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
the specific value for the extended length depends on the size of the transmission bandwidth.
Preferably, in the sixth step, the specific implementation method is as follows: for each user
Front of
Sample divided by window function
I.e. by
Is the serial number of the sampling point in the frequency domain,ito distinguish different users; obtaining channel frequency domain responses of multiple users
。
Has the advantages that:the invention carries out windowing and mirror image expansion on the frequency domain channel response before the channel estimation is converted into the time domain, wherein, the mirror image expansion method extends the position of discontinuous frequency response of the edge subcarrier between the virtual channel frequency domain responses, and can reduce the Gibbs (Gibbs) phenomenon of the estimation error, thereby improving the flat bottom effect of the error, and the windowing can fundamentally improve the energy leakage problem of multipath, and can further improve the estimation performance. At multiple transmitting ends
Under the scene that the reference signal passes through different cyclic shift multiplexing, windowing can effectively inhibit code division multiplexing interference and improve estimation performance.
Drawings
Fig. 1 is a flow chart of a frequency domain windowed channel estimation algorithm with mirror expansion.
Detailed Description
The channel estimation method of the invention comprises the following steps: suppose the system is an OFDMA (Orthogonal Frequency Division Multiple Access) system, having
The reference signals with different cyclic shifts of the transmitters are transmitted simultaneously on the same time-frequency domain resource block.
The receiver receives the OFDMA time domain signal, and obtains a Frequency domain reference signal as an input of the channel estimation module through steps of OFDM (Orthogonal Frequency Division multiplexing) demodulation, resource inverse mapping, and the like.
For convenience of description, the following variables are first defined: channel frequency domain response obtained by receiver
Is defined as:
wherein
Is a Frequency domain reference signal (including OFDM) obtained by OFDM (Orthogonal Frequency Division multiplexing) demodulation and inverse mappingPA sending end
The frequency domain reference signal of),Mis the bandwidth of the OFDMA transmission and is also the length of the reference signal in the frequency domain.
Is a reference signal on the local frequency domain.
Representing the frequency domain sample numbers.
In order to ensure the continuity of the frequency domain response expansion of the edge channel, the virtual frequency domain channel response is introduced, and the virtual frequency domain channel response is defined as mirror image expansion, namely, the tail of the original channel frequency domain response is added with the mirror images of the frequency domain responses at two sides of the original channel frequency domain response
WhereinLGenerally takes a value of 1 toKThe specific value depends on the transmission bandwidth size.
Defining the frequency domain channel response obtained after windowing:
wherein,
is defined as a window function with adjustable parameters
(e.g. usingKaiser(Catherin) windowLLeft circularly shifted version of the samples:
wherein
A fixed window may be used, or adjustments may be made based on the current signal-to-noise ratio, when the signal-to-noise ratio is large,
a window of larger curvature may be selected, and when the signal-to-noise ratio is small,
a window of smaller curvature may be selected.
To pair
To carry out
Point IDFT transform to obtain time domain signal
：
[5]
According to cyclic shift values of reference signals of different sending ends, time domain signals are subjected to cyclic shiftAnd adding rectangular windows at different positions to respectively intercept sampling points of the main energy of the channel impulse response of each user. It is assumed here thatMFor maximum delay spread length, if user a uses a reference signal with a cyclic shift value of 0, then the position of the window is at the beginning of the signalMOn each sample point. If user B employs a reference signal with a cyclic shift value of 1/2, then the window position is at the middle of the signal startMOn each sample point, and so on. Zero-filling the channel impulse response main energy sample point of each user toPointing to obtainPChannel impulse response of individual transmitting end。
Channel impulse response to each transmitting end
Do respectively to
Point DFT to get multiple sending ends
Frequency domain channel response of
：
Since frequency domain windowing was previously employed for the frequency domain response of multiple users, a frequency domain response for each user is required here
By dividing by a window function, respectively
To remove the windowing effect, and to truncate the tail length of the windowed frequency domain response for each userLMirror image extension of (1). The two steps of windowing and mirror expansion removal can be combined into one step, namely:
thus obtainingPChannel frequency domain response of individual users
As the output of the channel estimation module.
Based on the above discussion, we propose the following OFDMA channel estimation method.
In a first step, the received length isMOFDMA frequency domain reference signal of a pointLMirror image expansion of the dots.
Step two, multiplying the obtained expanded channel frequency domain response by a window with adjustable parameters
，
May be related to the signal-to-noise ratio.
Thirdly, the channel frequency domain response after frequency domain windowing and mirror image expansion is implemented
The point IDFT is transformed to the time domain.
And fourthly, separating channel impulse response energy and noise of a plurality of transmitting ends by windowing the obtained time domain signals.
Fifthly, zero-filling the channel impulse response main energy sample point of each transmitting end to
Point, respectively carry out
The point DFT is transformed into a frequency domain channel response.
Sixthly, dividing the first M points of the frequency domain channel response of each transmitting end by a window function
And obtaining a channel estimation result.
The invention provides a method for estimating a channel of a MIMO-OFDMA system.
Taking a base station channel estimation scheme that two users in an LTE system use a virtual MIMO mode, that is, space division multiple access, and uplink demodulation reference signals with a bandwidth of 24 subcarriers are multiplexed by different cyclic shifts as an example, an embodiment is given:
firstly, OFDM demodulation is carried out on the received OFDMA signal with the length of one symbol, and a frequency domain signal containing demodulation reference signals of two users is obtained through resource inverse mapping.
And secondly, performing mirror image expansion with the length of 6 points on the frequency domain signal obtained in the last step according to a formula [2 ].
Third step, multiplying the extended frequency domain signal point by 30 points in lengthKaiserA 6-point left circularly shifted version of the (kaiser) window.
And fourthly, performing 30-point IDFT on the 30-point frequency domain signal obtained by the last step of expansion to transform to a time domain.
And fifthly, windowing and zero filling are carried out on the 30-point time domain signals obtained in the last step according to the user cyclic shift position, and channel impulse responses of two users are obtained.
And sixthly, respectively carrying out 30-point DFT on the channel impulse responses of 30 sampling points of the two users to obtain the frequency domain responses of the two users.
Seventhly, dividing the first 24 samples of the frequency domain responses of the two users obtained in the sixth step by the length of 30 pointsKaiserThe central 24 points of the (Kaiser) window, 24 samples of two users are the estimated values of the channel frequency domain response obtained by the invention.
The invention provides a channel estimation algorithm suitable for an MIMO-OFDMA system, which can effectively improve the channel estimation performance and resist code division multiplexing interference.
In the first step, the received OFDMA frequency domain reference signal with the length of M points is subjected to L-point mirror image expansion.
Step two, multiplying the obtained expanded channel frequency domain response by a window with adjustable parameters
，
May be related to the signal-to-noise ratio.
Thirdly, the channel frequency domain response after frequency domain windowing and mirror image expansion is implemented
The point DFT is transformed to the time domain.
And fourthly, separating channel impulse response energy and noise of a plurality of transmitting ends by windowing the obtained time domain signals.
Fifthly, zero-filling the channel impulse response energy of each transmitting end to
Point, respectively carry outThe point IDFT is transformed to the frequency domain.
Sixthly, dividing the first M points of the channel frequency domain response of each transmitting end by a window
Front of
And obtaining a channel estimation result by using the point.
Claims (6)
1. A frequency domain windowing orthogonal frequency division multiple access channel estimation method of image spreading is characterized in that: the method comprises the following steps:
step one, mirror image expansion: to a received length of
Orthogonal frequency division multiple access frequency domain reference signal processing of points
Mirror image expansion of points;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
for the extended length, the specific value depends on the size of the transmission bandwidth;
second, frequency domain windowing: multiplying the obtained mirror image expanded channel frequency domain response by a window
WindowIs a length of
Window with adjustable point parameters
Is/are as follows
Point left cyclic shift, wherein
Is related to the signal-to-noise ratio;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
for extending the length, the specific value is takenDepending on the transmission bandwidth size;
thirdly, the channel frequency domain response after the image expansion and the frequency domain windowing is implemented
Point inverse discrete Fourier transform is carried out to transform the point inverse discrete Fourier transform into a time domain;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
for the extended length, the specific value depends on the size of the transmission bandwidth;
fourthly, separating channel impulse response energy and noise of a plurality of sending ends by windowing the obtained time domain signals;
fifthly, zero-filling the channel impulse response energy of each transmitting end to
Point, respectively carry out
Point discrete Fourier transform to frequency domain;
is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
for the extended length, the specific value depends on the size of the transmission bandwidth;
sixthly, the channel frequency domain response of each sending end is preceded by
DotDivided by window
Front ofPoint, obtaining channel estimation result;
is the bandwidth of the ofdma transmission and is also the length of the reference signal in the frequency domain.
2. The image-extended frequency-domain windowed ofdma channel estimation method of claim 1 wherein: in the first step, the method of mirror image expansion comprises the following steps:
wherein,
for the received channel frequency domain response, the length is，
For mirror-extended frequency domain response, length is
，Is the bandwidth of the ofdma transmission, and is also the length of the reference signal in the frequency domain,
the specific value for the extended length depends on the size of the transmission bandwidth.
3. The image-extended frequency-domain windowed ofdma channel estimation method of claim 1 wherein: in the second step, the frequency domain windowing method comprises the following steps:
wherein
To mirror the extended frequency domain response,is the serial number of the sampling point in the frequency domain,
is defined as:
，
a kaiser window.
4. The image-extended frequency-domain windowed ofdma channel estimation method of claim 1 wherein: in the third step, the specific implementation method is as follows: channel frequency domain response to image spreading and frequency domain windowing
Practice of
Point inverse discrete Fourier transform to time domain signal；
5. The image-extended frequency-domain windowed ofdma channel estimation method of claim 1 wherein: in the fifth step, the concrete implementation method comprises the following steps: channel impulse response to each transmitting end
Do respectively to
Discrete Fourier transform to obtain frequency domain channel responses of multiple transmitting ends
WhereiniTo distinguish different users;
6. The image-extended frequency-domain windowed ofdma channel estimation method of claim 1 wherein: in the sixth step, the specific implementation method comprises the following steps: for each user
Front of
Sample divided by window function
I.e. by
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| CN114745236A (en) * | 2022-04-07 | 2022-07-12 | 展讯通信（上海）有限公司 | Data preprocessing method and device for transform domain channel estimation and communication equipment |
| CN114844582A (en) * | 2022-04-07 | 2022-08-02 | 展讯通信（上海）有限公司 | Method and device for estimating signal-to-noise ratio of transform domain and communication equipment |
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Application publication date: 20110803 |