CN109120559B - Self-adaptive ICI inter-carrier interference elimination method and device - Google Patents
Self-adaptive ICI inter-carrier interference elimination method and device Download PDFInfo
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- CN109120559B CN109120559B CN201710480625.6A CN201710480625A CN109120559B CN 109120559 B CN109120559 B CN 109120559B CN 201710480625 A CN201710480625 A CN 201710480625A CN 109120559 B CN109120559 B CN 109120559B
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- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
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- H04L25/03821—Inter-carrier interference cancellation [ICI]
Abstract
The invention provides a self-adaptive ICI inter-carrier interference elimination method and a device, which are characterized by comprising the following steps: estimating an ICI inter-carrier interference value, and performing corresponding ICI elimination on the received data based on the estimated ICI inter-carrier interference value; comparing the first level signal-to-noise ratio result calculated before ICI elimination with the second level signal-to-noise ratio result calculated after ICI elimination, and selecting the processing result corresponding to the larger one to output.
Description
Technical Field
The present invention relates to multimedia transmission and mobile communication technologies, and in particular, to an Inter-Carrier Interference (ICI) cancellation device in an Orthogonal Frequency Division Multiplexing (OFDM) system.
Background
OFDM, a physical layer air interface technology with a high spectrum utilization rate, has been widely applied to multimedia transmission, mobile communication standards and systems such as DVB-T2, ATSC3.0, LTE, and the like.
In an OFDM system, the channel is divided into several orthogonal sub-channels (i.e., sub-carriers) so that a high-speed data signal can be converted into parallel low-speed sub-streams that are modulated onto each sub-carrier for transmission. Because the sub-carrier bandwidth is narrow, each sub-data stream is equivalent to flat fading propagation, and because each sub-carrier has orthogonality, each sub-data stream does not interfere with each other.
However, factors such as time-varying property of a wireless channel, frequency offset during signal transmission, and frequency error between a transmitter and a receiver crystal oscillator of a system may destroy orthogonality between subcarriers of the OFDM system, thereby generating ICI and affecting performance of the OFDM system. Therefore, since the birth of the OFDM system, research on techniques for eliminating ICI has never been stopped.
Most of the currently used ICI cancellation techniques add an independent ICI cancellation module after the original channel estimation and equalization module. As shown in fig. 1, the module estimates the additive ICI of each sub-carrier by using the frequency domain channel response H output by channel estimation and the constellation diagram X output by the equalizer through a certain method, and then performs subtraction on the frequency domain data of the original sub-carrier to achieve ICI cancellation of the frequency domain received data. And then, the frequency domain data after ICI elimination passes through the channel estimation and equalization module again to obtain an equalization result after ICI elimination, so that the influence of ICI is reduced, and the equalization demodulation performance is improved.
In these methods, the effectiveness of ICI cancellation depends entirely on the accuracy of the ICI estimation by the system, which is directly related to the accuracy of the results of the channel estimation modules. When the channel condition is better, the accuracy of channel estimation is ensured, and the ICI elimination module can provide positive gain; when the channel condition is not good, the accuracy of the channel estimation may be poor, and the ICI cancellation module may provide negative gain to the system.
Disclosure of Invention
The invention provides an ICI elimination method and a device of a self-adaptive structure, which can self-adaptively select a better one of two equalization results to be transmitted to a subsequent module before or after ICI elimination according to the ICI elimination effect, thereby avoiding performance reduction caused by inaccurate ICI estimation.
The invention provides a self-adaptive ICI inter-carrier interference elimination method, which is characterized by comprising the following steps: estimating an ICI inter-carrier interference value, and performing corresponding ICI elimination on the received data based on the estimated ICI inter-carrier interference value; and comparing the first-stage signal-to-noise ratio result obtained by calculation before ICI elimination with the second-stage signal-to-noise ratio result obtained by calculation after ICI elimination, and selecting the processing result corresponding to the larger one of the first-stage signal-to-noise ratio result and the second-stage signal-to-noise ratio result for output.
Further optionally, in the adaptive ICI inter-carrier interference cancellation method provided by the present invention, the first stage processing is performed on the received data to obtain a first stage processing result; calculating to obtain a first-stage signal-to-noise ratio result by using the first-stage processing result; estimating an ICI inter-carrier interference value by using the first-stage processing result, and correspondingly eliminating received data based on the ICI inter-carrier interference value to obtain first-stage eliminated data; performing second-stage processing by using the data after the first-stage elimination to obtain a second-stage processing result; calculating to obtain a second-stage signal-to-noise ratio result by using the second-stage processing result; and comparing the first-stage signal-to-noise ratio result with the second-stage signal-to-noise ratio result, and selecting the processing result corresponding to the larger one of the first-stage signal-to-noise ratio result and the second-stage signal-to-noise ratio result for outputting.
Further optionally, in the adaptive ICI intercarrier interference cancellation method provided in the present invention, the received data is frequency domain input data, and the first stage processing includes: the first-stage channel estimation obtains a first-stage frequency domain channel result, and then the first-stage equalization obtains a first-stage processing result; the second stage of processing comprises: the first-stage frequency domain channel result or the second-stage frequency domain channel result after ICI elimination can be directly used as the input of the second-stage equalization to obtain the second-stage processing result.
Further optionally, in the adaptive ICI intercarrier interference cancellation method provided in the present invention, the first stage of equalization includes: performing equalization processing by using the frequency domain channel result, the noise power estimation value and the frequency domain input data; the second stage of equalization comprises: and performing equalization processing by using the primary frequency domain channel result or the secondary frequency domain channel result, the noise power estimation value and the frequency domain input data after ICI elimination.
Further optionally, in the adaptive ICI intercarrier interference cancellation method provided by the present invention, the equalization process includes a zero-breaking by ZF method and a minimum mean square error by MMSE method.
Further optionally, in the adaptive ICI intercarrier interference cancellation method provided by the present invention, the ICI intercarrier interference value of each subcarrier is estimated by using the first-stage processing result, the first-stage frequency domain channel result, and the first-stage processing result.
Further optionally, in the adaptive ICI inter-carrier interference cancellation method provided by the present invention, the first stage snr result and the second stage snr result are obtained by using the corresponding processing result and the standard constellation diagram, respectively.
Further optionally, in the adaptive ICI intercarrier interference cancellation method provided in the present invention, the signal-to-noise ratio result calculation method includes: and extracting the processing result and the pilot frequency part in the standard constellation diagram, and performing power normalization processing between the processing result and the pilot frequency part in the standard constellation diagram to calculate the signal-to-noise ratio result.
In addition, the present invention also provides an adaptive ICI inter-carrier interference cancellation apparatus, which is characterized by comprising: ICI elimination module: estimating an ICI inter-carrier interference value, and performing corresponding ICI elimination on the received data based on the estimated ICI inter-carrier interference value; a comparison selector: and comparing the first-stage signal-to-noise ratio result obtained by calculation before ICI elimination with the second-stage signal-to-noise ratio result obtained by calculation after ICI elimination, and selecting the processing result corresponding to the larger one of the first-stage signal-to-noise ratio result and the second-stage signal-to-noise ratio result for output.
Further optionally, in the adaptive ICI intercarrier interference cancellation apparatus provided in the present invention, the apparatus further includes: the first-stage processing module is used for carrying out first-stage processing on the received data to obtain a first-stage processing result; the first-stage signal-to-noise ratio estimation module is used for calculating a first-stage signal-to-noise ratio result by utilizing the processing result of the first stage; the ICI elimination module estimates an ICI inter-carrier interference value by using the first-stage processing result, and correspondingly eliminates the received data based on the ICI inter-carrier interference value to obtain first-stage eliminated data; the second-stage processing module is used for carrying out second-stage processing on the data after the first-stage elimination to obtain a second-stage processing result; the second-stage signal-to-noise ratio estimation module is used for calculating a second-stage signal-to-noise ratio result by utilizing the second-stage processing result; and the comparison selector is used for comparing the first-stage signal-to-noise ratio result with the second-stage signal-to-noise ratio result and selecting the processing result corresponding to the larger one of the first-stage signal-to-noise ratio result and the second-stage signal-to-noise ratio result for outputting.
Effect of the invention
The invention utilizes the constellation diagram obtained by twice equalization before and after ICI elimination to calculate the SNR, and selects the equalization result corresponding to high SNR by comparing the SNR of twice, thereby avoiding the performance reduction caused by inaccurate ICI estimation to the system.
Drawings
Fig. 1 is a structure of a conventional ICI cancellation apparatus;
FIG. 2 is a schematic structural diagram of an adaptive ICI cancellation apparatus according to an embodiment of the present invention; and
fig. 3 is a schematic processing flow diagram of an adaptive ICI cancellation apparatus according to an embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
For convenience of illustration, the ICI specific estimation method and the SNR specific estimation method in the present invention are described by using a currently common scheme, but the scope of the present invention is not limited to the description herein.
The adaptive ICI inter-carrier interference cancellation method and apparatus provided by the present invention are described with reference to fig. 2 and 3 in the specification.
In this embodiment, the adaptive ICI intercarrier interference cancellation method includes the following steps:
step 1: the first-stage channel estimation module obtains a first frequency domain channel result, namely a first-stage frequency domain channel result H1;
step 2: the first stage equalization module utilizes the frequency domain channel result H1 of the first time and the noise power estimated value sigma2And frequency domain input data R, and obtaining a result X1 after the first-stage equalization by methods such as ZF (Zero Force: Zero breaking), MMSE (Minimum Mean square Error) and the like;
and step 3: and the first-stage SNR estimation module calculates a first-stage signal-to-noise ratio result SNR1 corresponding to the first-stage equalization result by using the result X1 after the first-stage equalization and the standard constellation diagram. The estimation method is exemplified by: extracting the result X1 after the first stage of equalization and the pilot part in the standard constellation diagram, which are respectively marked as X1PilotAnd DPilotThen, then
And because the sending constellation diagram is always subjected to over-power normalization, the method has the advantages of low cost and high efficiency
And 4, step 4: and the ICI elimination module estimates the ICI value of each subcarrier by using the first-stage channel estimation and the first-stage equalization results H1 and X1 and subtracts the ICI value on the frequency domain data R.
The specific ICI estimation method for performing subtraction on the frequency domain data R based on the ICI value can be performed by using the scheme described in the published paper "ICI subtraction for Pilot-aid OFDM Mobile Systems, Yasamin Mostofi, Donald c.cox", that is: obtaining the change situation H1 of H1 by using the channel estimation results of the current OFDM symbol and the last OFDM symbolslope＝H1-H1pre. Then, filtering the subcarrier to obtain an ICI estimated value of the subcarrier i:
wherein the filter coefficient
N and G respectively represent the length of the OFDM symbol and the length of the cyclic prefix, L represents the filtering length and is set artificially, and X1 is a hard judgment result corresponding to X1.
And (3) ICI elimination is carried out on the frequency domain data: r' (i) ═ R (i) -ici (i), data after first-order cancellation are obtained.
And 5: and performing second-stage channel estimation by using the first-stage eliminated data R' to obtain a result H2.
Step 6: and performing second-stage equalization processing by using the first-stage eliminated data R', H2 to obtain a second-stage processing result X2.
And 7: and performing second-stage SNR estimation by using the second-stage processing result X2 and the standard constellation diagram to obtain a second-stage SNR result SNR 2. The estimation method needs to be consistent with the first-stage SNR estimation module: extracting the pilot parts in the X1 and standard constellation diagrams, which are respectively marked as X2PilotAnd DPilotThen, then
And will not be described in detail.
And 8: comparing SNR1 with SNR2, and if SNR1 > SNR2, outputting X1 to a subsequent module; if the SNR1 is less than or equal to the SNR2, the X2 is output to the subsequent module, that is, the larger one of the processing results is selected to be output, and the SNR1 and the SNR2 are equal in size, and then one of the processing results of the first stage or the processing result of the second stage is selected to be output.
It should be noted that the first-stage equalization and the second-stage equalization are necessary, and two stages are required for channel estimation in fig. 2 in principle, but in practical implementation, different from the embodiment corresponding to fig. 2, only the first-stage channel estimation may be used, (in this case, the second-stage equalization directly uses the h obtained by the first-stage channel estimation).
In this embodiment, fig. 2 further provides an adaptive ICI intercarrier interference cancellation apparatus, including:
the device comprises a first-stage processing module, a first-stage signal-to-noise ratio estimation module, an ICI elimination module, a first-stage processing module, a second-stage signal-to-noise ratio estimation module and a comparison selector.
The first-stage processing module comprises a first-stage channel estimation submodule and a first-stage equalization processing submodule, and the second-stage processing module comprises a second-stage channel estimation submodule and a second-stage equalization processing submodule.
The first-stage processing module is used for carrying out first-stage processing on the received data to obtain a first-stage processing result; the first-stage signal-to-noise ratio estimation module is used for calculating a first-stage signal-to-noise ratio result by utilizing the processing result of the first stage; the ICI elimination module estimates an ICI inter-carrier interference value by using the first-stage processing result, and correspondingly eliminates the received data based on the ICI inter-carrier interference value to obtain first-stage eliminated data; the second-stage processing module is used for carrying out second-stage processing on the data after the first-stage elimination to obtain a second-stage processing result; the second-stage signal-to-noise ratio estimation module is used for calculating a second-stage signal-to-noise ratio result by utilizing the second-stage processing result; and the comparison selector is used for comparing the first-stage signal-to-noise ratio result with the second-stage signal-to-noise ratio result and selecting the processing result corresponding to the larger one of the first-stage signal-to-noise ratio result and the second-stage signal-to-noise ratio result for outputting.
And obtaining a second-stage processing result by using a second-stage frequency domain channel result after ICI elimination and first-stage eliminated data as input of second-stage equalization.
In addition, in addition to the embodiment in fig. 2, the second processing module may also choose not to provide the second-stage channel estimation sub-module, and choose to directly utilize the first-stage frequency domain channel result to perform the second-stage equalization.
As shown in fig. 2, compared to fig. 1 in the prior art, two SNR estimators are added to estimate SNR of the equalization result before and after ICI cancellation, and since SNR can directly reflect the quality of the equalization result, a subsequent comparator can be used to select an equalization result with a high SNR to achieve adaptive ICI.
Claims (7)
1. An adaptive ICI inter-carrier interference cancellation method, comprising:
carrying out first-stage channel estimation and first-stage equalization on received data to obtain a first-stage processing result, and then calculating to obtain a first-stage signal-to-noise ratio result;
estimating an ICI inter-carrier interference value by using the processing result of the first stage, and performing corresponding ICI elimination on the received data based on the estimated ICI inter-carrier interference value;
performing second-stage channel estimation and second-stage equalization on the data after ICI elimination, and then calculating to obtain a second-stage signal-to-noise ratio result;
and comparing the first-stage signal-to-noise ratio result obtained by calculation before ICI elimination with the second-stage signal-to-noise ratio result obtained by calculation after ICI elimination, and selecting the processing result corresponding to the larger one of the first-stage signal-to-noise ratio result and the second-stage signal-to-noise ratio result for output.
2. The adaptive ICI inter-carrier interference cancellation method of claim 1,
wherein the received data is frequency domain input data,
the first stage of processing comprises: the first-stage channel estimation obtains a first-stage frequency domain channel result, and then the first-stage equalization obtains a first-stage processing result;
the second stage of processing comprises: the first-stage frequency domain channel result or the second-stage frequency domain channel result after ICI elimination can be directly used as the input of the second-stage equalization to obtain the second-stage processing result.
3. The adaptive ICI inter-carrier interference cancellation method of claim 2,
wherein the first stage of equalization comprises: performing equalization processing by using the frequency domain channel result, the noise power estimation value and the frequency domain input data;
the second stage of equalization comprises: and performing equalization processing by using the primary frequency domain channel result or the secondary frequency domain channel result, the noise power estimation value and the frequency domain input data after ICI elimination.
4. The adaptive ICI inter-carrier interference cancellation method of claim 1,
and respectively and correspondingly obtaining a first-stage signal-to-noise ratio result and a second-stage signal-to-noise ratio result by utilizing the corresponding processing result and the standard constellation diagram.
5. The adaptive ICI inter-carrier interference cancellation method of claim 4,
the signal-to-noise ratio result calculating method comprises the following steps: and extracting the processing result and the pilot frequency part in the standard constellation diagram, and performing power normalization processing between the processing result and the pilot frequency part in the standard constellation diagram to calculate the signal-to-noise ratio result.
6. The adaptive ICI inter-carrier interference cancellation method of claim 1,
and if the first-stage signal-to-noise ratio result and the second-stage signal-to-noise ratio result are equal, selecting any one of the first-stage signal-to-noise ratio results or the processing result corresponding to the second-stage signal-to-noise ratio result for outputting.
7. An adaptive ICI inter-carrier interference cancellation apparatus, comprising:
the first-stage processing module is used for carrying out first-stage channel estimation and first-stage equalization on the received data to obtain a first-stage processing result;
the first-stage signal-to-noise ratio estimation module is used for calculating a first-stage signal-to-noise ratio result by utilizing a first-stage processing result;
ICI elimination module: estimating an ICI inter-carrier interference value, and performing corresponding ICI elimination on the received data based on the estimated ICI inter-carrier interference value;
the second-stage processing module is used for carrying out second-stage channel estimation and second-stage equalization on the data subjected to ICI elimination to obtain a second-stage processing result;
the second-stage signal-to-noise ratio estimation module is used for calculating a first-stage signal-to-noise ratio result by utilizing a second-stage processing result;
a comparison selector: and comparing the first-stage signal-to-noise ratio result obtained by calculation before ICI elimination with the second-stage signal-to-noise ratio result obtained by calculation after ICI elimination, and selecting the processing result corresponding to the larger one of the first-stage signal-to-noise ratio result and the second-stage signal-to-noise ratio result for output.
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| US7706428B2 (en) * | 2005-04-21 | 2010-04-27 | Telefonaktiebolaget L M Ericsson (Publ) | Low complexity inter-carrier interference cancellation |
| CN1984109A (en) * | 2006-04-24 | 2007-06-20 | 华为技术有限公司 | Channel estimater and channel estimating method in telecommunication system |
| US8363536B2 (en) * | 2006-08-28 | 2013-01-29 | Qualcomm Incorporated | OFDM channel estimation |
| CN101778069B (en) * | 2010-01-18 | 2013-04-10 | 北京交通大学 | OFDM signal channel estimation combination ICI self elimination method |
| CN102710577A (en) * | 2012-06-15 | 2012-10-03 | 上海大学 | High-speed movement-based intercarrier interference (ICI) eliminating and decoding method for space frequency block coding (SFBC) coordinated orthogonal frequency division multiplexing (OFDM) system |
| US20150249554A1 (en) * | 2013-06-21 | 2015-09-03 | Dhadesugoor Vaman | Adaptive demodulation method and apparatus using an artificial neural network to improve data recovery in high speed channels |
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