JP2016181917A - Ofdm received signal processing method and ofdm receiving device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for improving performance of a receiving device when cochannel interference is present or signal distortion occurs at a specific frequency position, and to provide and an OFDM (Orthogonal Frequency Division Multiplexing) receiving device using the method.SOLUTION: An OFDM received signal processing method is provided that comprises: a Fourier transformation step of performing fast Fourier transform of an OFDM symbol to transform the OFDM symbol to a frequency domain complex symbol; a channel compensation step of estimating channel condition information on the basis of the frequency domain complex symbol, and generating a data symbol whose channel distortion is compensated using a channel estimation value; a de-mapping step of quantizing the data symbol into data bits; and a decoding step of reconstructing transmitted data bits by decoding the data bits. The method further comprises, between the Fourier transformation step and the decoding step, a step of adjusting a weighting value for a signal value, corresponding to a location of an interference signal on the basis of location information of the interference signal.SELECTED DRAWING: Figure 1

Description

The present embodiment relates to an OFDM (Orthogonal Frequency Division Multiplexing) received signal processing method and an OFDM receiver using the same, and more specifically, there is co-channel interference (co-channel interference) or at a specific frequency position. The present invention relates to a method for improving the performance of an OFDM receiver when signal distortion occurs and an OFDM receiver using the same.

The contents described in this part merely provide background information for this embodiment, and do not constitute the prior art.

In a general OFDM system, an error correction code is used to increase the reliability of data to be transmitted / received. In the transmitter, the signal to be transmitted is transmitted after adding a different form of structural margin (redundancy) according to the channel code scheme, and in the receiver, the information of the corresponding margin is transmitted. Used to detect and correct errors contained in the signal. The input of the channel decoding unit used in the receiving apparatus is made by combining the received signal and the estimated channel information, but each value receives '0' or '1' as the corresponding signal. Means the possibility. For example, the closer the input of the channel decoding unit is to “0”, the less the value of the corresponding received signal is, and the larger the absolute value of the input is, the more the corresponding received signal becomes “ This means that it knows more precisely whether it is 0 'or' 1 '.

In the OFDM system, the larger the channel state information of a specific subcarrier, the smaller the intensity of noise added to the signal of the corresponding subcarrier. Therefore, it is considered that the reception accuracy of the corresponding subcarrier is high. And such information is expressed as a value and enters the channel decoding unit.

However, if there is a co-channel interference signal, the stability of the various synchronization blocks may be greatly reduced, and not only is the channel state information estimated very inaccurate but also damaged at the corresponding frequency position. The input of the channel decoding unit is entered in a state where the signal value has a considerably large value, and the performance of the channel decoding unit can be considerably reduced.

In the prior art, the co-channel interference signal is generally detected in advance, and the co-channel interference signal is removed in advance using a notch filter (notch filter) that sharply reduces the signal value of the affected subcarrier position, The operation stability of the receiving apparatus is ensured, the estimation accuracy of the channel state information is increased, and the input of the channel decoding unit is prevented from becoming abnormally large.

However, even if the method using the notch filter as described above is followed, the co-channel interference signal is not always removed cleanly. For example, if the interfering signal is in the form of single tone noise but is located between two subcarriers, or if the size of the interfering signal is much larger than the desired signal, a notch filter The interference signal may remain even after passing through the signal, and if the removal bandwidth of the notch filter is increased so that the interference signal does not remain, each signal value around the interference signal position is also removed. Therefore, the adverse effect that the performance deteriorates may occur.

The present embodiment provides a method for improving the performance of a receiving apparatus when co-channel interference exists in the OFDM receiving apparatus or distortion occurs in a signal at a specific frequency position, and an OFDM receiving apparatus using the same. Is the main purpose.

In this embodiment, the reception information of the subcarrier corresponding to the position where the co-channel interference is detected is set to a value less than 1 at any position after the output of the Fourier transformer and before entering the channel decoding unit. We propose a method for improving the stability of each block operating in the latter stage of the Fourier transformer and the performance of the channel decoder by multiplying. The above method can be used for performance improvement in the case where signal distortion occurs at a specific position, similarly to the analog high-frequency pass filter used in the tuner.

According to one aspect of the present embodiment, a fast Fourier transform (FFT) is performed on the OFDM symbol to convert an ODFM signal into a frequency domain complex symbol, and the frequency domain complex symbol is converted into a complex symbol in the frequency domain. A channel compensation process for estimating channel state information and generating a data symbol in which channel distortion is compensated using the channel estimation value, and a demapping process for quantizing the data symbol into data bits (quantization) And a decoding step of decoding the data bits to restore the transmission data bits, and the interference between the Fourier transform step and the decoding step based on position information of an interference signal. The process of adjusting the weight of the signal value corresponding to the signal position. It provides a method for processing OFDM received signal in the OFDM receiver characterized in that it is carried out in the.

The step of adjusting the weight value includes adding a weight value N (where 0 ≦ N <1) to a signal value corresponding to a position (coordinate, phase, frequency) where an interference signal is detected for the complex symbol. It can be configured to be granted.

Further, the step of reducing the weight value is configured to give a weight value N (where 0 ≦ N <1) to the signal value corresponding to the position where the interference signal is detected, with respect to the data bit. can do.

The interference signal may be a co-channel interference signal included in the OFDM reception signal or a signal that distorts a signal value (at a specific frequency and at a specific frequency) at a specific frequency position.

In addition, a method of processing an OFDM reception signal includes detecting a position (phase, frequency component) of an interference signal from the OFDM symbol, and notch filtering (Notch) for the OFDM symbol to remove the interference signal. And a step of performing filtering.

According to another aspect of the present embodiment, fast Fourier transform is performed on the OFDM symbol, and a Fourier transform step of transforming the OFDM symbol into a complex symbol in the frequency domain, and channel state information based on the complex symbol in the frequency domain are obtained. Estimating and generating a channel estimate, adjusting a weight of the channel estimate corresponding to the position of the interference signal based on the position information of the interference signal, and a channel estimate with the weight adjusted A channel compensation step for generating data symbols compensated for channel distortion using, a demapping step for quantizing the data symbols into data bits, and a decoding for decoding the data bits and restoring transmission data bits And a method for processing an OFDM received signal of an OFDM receiving apparatus.

The step of adjusting the weight value of the channel estimation value may be configured to give a weight value N (where 0 ≦ N <1) to the channel estimation value corresponding to the position where the interference signal is detected. .

According to another aspect of the present embodiment, a Fourier transform unit that converts an OFDM symbol into a frequency-domain complex symbol, and a channel estimation unit that generates a channel estimation value that estimates channel state information based on the frequency-domain complex symbol. A channel compensation unit that generates a data symbol in which channel distortion is compensated using the channel estimation value, demapping that quantizes the data symbol into data bits, and decodes the data bits to convert transmission data bits. A channel decoding unit to be restored, and any one of the Fourier transform unit, the channel compensation unit, and the demapping unit includes a function of adjusting a weight value of a signal value corresponding to a position of an interference signal An OFDM receiver characterized by being configured as follows is provided.

According to another aspect of the present embodiment, a Fourier transform unit that converts an OFDM symbol into a complex symbol in a frequency domain, a channel state information is estimated based on the complex symbol, a channel estimation value is generated, and the generated channel A channel estimator configured to adjust a weight value of an estimated value corresponding to a position of an interference signal among estimated values, and a data symbol in which channel distortion is compensated using the channel estimated value whose weight value is adjusted. There is provided an OFDM receiver including a channel compensation unit to be generated, a demapping unit that quantizes the data symbols into data bits, and a decoding unit that decodes the data bits to restore transmission data bits.

According to another aspect of the present embodiment, a step of generating an OFDM symbol in a frequency domain based on an RF (Radio Frequency) signal (a high frequency signal), and at least channel distortion compensation and derating for the OFDM symbol in the frequency domain. An interference signal in any one of the steps of performing a calculation in the frequency domain, including a step of performing mapping to generate data bits and a step of decoding the data bits to restore transmission data bits A signal processing method for an OFDM receiving apparatus is provided, wherein a weight value greater than or equal to 0 and less than 1 is assigned to a frequency component corresponding to a frequency position of.

According to another aspect of the present embodiment, a step of generating a frequency-domain OFDM symbol based on an RF signal, and a data bit is generated by performing at least channel distortion compensation and demapping on the frequency-domain OFDM symbol. And decoding the data bits to recover the transmitted data bits, wherein the channel distortion compensation is a weight greater than or equal to 0 and less than 1 to a value corresponding to a frequency position of the interference signal Provided is a signal processing method of an OFDM receiver characterized by using a channel estimation value to which a value is assigned.

As described above, according to the present embodiment, the residual (redundant) interference component included in the notch-filtered received signal for removing the co-channel interference is a function block in the subsequent stage of the Fourier channel converter. And / or preventing it from being input to the channel decoding unit, thereby improving the performance of the receiving apparatus.

Further, according to the interference signal removal method according to the present embodiment, the residual interference component included in the notch-filtered received signal can be effectively removed, so that a notch filter having a narrower bandwidth than the existing one can be used. , The loss of the original signal generated by notch filtering, that is, the undistorted signal component, can be minimized.

In addition, even when signal distortion occurs at a specific frequency, the performance of the channel decoding unit is improved by processing so that an incorrect signal value at the corresponding position (coordinate, phase, frequency) is not input to the channel decoding unit. Can be improved.

It is the figure which illustrated the structure of the general OFDM receiver. It is the figure which illustrated in the frequency domain the signal processed with each functional block of an OFDM receiver when there exists a co-channel interference signal of a single tone form. 3 is a flowchart illustrating a method of processing a co-channel interference signal with an OFDM reception signal according to an embodiment of the present invention. 6 is a flowchart illustrating a method of processing a co-channel interference signal with an OFDM received signal according to another embodiment of the present invention.

Hereinafter, some embodiments of the present invention will be described in detail through exemplary drawings. It should be noted that the same reference numerals are given to the same components as much as possible even if they are displayed on different drawings. is there. In the description of the present invention, if it is determined that a specific description of a related known configuration or function can obscure the gist of the present invention, a detailed description thereof will be omitted.

Throughout the specification, when a part “includes” or “comprises” a component, this does not exclude other components, unless specifically stated to the contrary, It can be further included. In addition, terms such as '... part' and 'module' described in the specification mean a unit for processing at least one function or operation, and this is a combination of hardware, software, or hardware and software. It can be implemented.

FIG. 1 is a diagram illustrating the structure of a general OFDM receiver.

Referring to FIG. 1, a general OFDM receiver includes an interference detection unit 110 that detects co-channel interference signals, a notch filter 120 that performs filtering on OFDM symbols in order to remove the detected interference signals, Performs Fast Fourier Transform (FFT) on the notch-filtered OFDM signal, and estimates channel state information for each subcarrier using an FFT unit 130 that generates a complex symbol in the frequency domain and a pilot signal. A channel estimator 140, a channel compensator 150 for performing channel compensation on complex symbols in the frequency domain based on the estimated channel state information, and generating data symbols with compensated channel distortion, and channel compensated Signal and channel status Demapping using information, that is, a demapper 160 that quantizes data symbols into data bits, and a channel decoding unit 170 that decodes the demapped signal (ie, data bits) to restore transmission data bits. .

Unlike the example of FIG. 1, the OFDM receiving apparatus may change the order of some functional blocks depending on the application field, or may include other functional blocks not shown between the functional blocks. it can. For example, before the FFT unit, an RF unit that receives an RF (Radio Frequency) signal and converts it into an OFDM symbol, an S / P conversion unit that converts the OFDM symbol of the RF unit into a parallel form, and an S / P conversion A protection interval removing unit that removes a protection interval between OFDM symbols from the unit. Further, a subcarrier demapping unit that separates frequency-domain complex symbols into data symbols and pilot symbols can be further included after the FFT, and the channel estimation unit estimates channel distortion using the pilot symbols. Can be configured to.

FIG. 2 is a diagram illustrating, in the frequency domain, a signal processed by each functional block of the OFDM receiver when there is a single-tone co-channel interference signal.

FIG. 2A shows the shape of the received signal before passing through the notch filter 120. In the OFDM receiver, the interference signal is detected, and the received signal is passed through the notch filter 120 in order to remove the interference component at the detected position (frequency). When the size of the interference signal is large, even if notch filtering is performed, the interference signal component is slightly reduced as shown in FIG. 2B, but may still be larger than other signals. In this case, the remaining interference signal component affects the subsequent synchronization block, so that the stability of the receiving apparatus can be lowered. In particular, when the remaining interference signal component is larger than other signals, erroneous information is input to the channel decoding unit in a state having a large weighted value, thereby reducing the performance of the channel decoding unit. By setting the removal bandwidth of the notch filter 120 wide in order to prevent such performance degradation, the interference signal can be made sufficiently small as shown in FIG. However, due to the wide rejection bandwidth, each reception signal in the vicinity is cut by the notch filter 120, resulting in a decrease in performance of the receiving device.

In this embodiment, when co-channel interference is detected, in order to prevent information in the vicinity of the subcarrier that has been distorted by the interference from entering the synchronization block and channel decoding unit 170, the corresponding position (phase , Frequency) channel-compensated data weighting and a method for reducing the estimated channel state information value weighting are proposed.

According to an embodiment of the present invention, at any one position between the FFT unit 130 and the channel decoding unit 170 of FIG. 1, the received signal near the position where the co-channel interference is detected is greater than or equal to zero. The weight is reduced by multiplying by a value less than 1. For example, the weight value is decreased at the output of the FFT unit 130 of FIG. 1 so that interference and distortion components do not affect the synchronization block using the output of the FFT unit 130 and the functional block 140 that estimates channel state information. It is also possible to cut off, and it is also possible to reduce the weight of the output value by the log likelihood ratio output from the output of the demapper (demapping unit, quantization unit) 160 immediately before entering the input of the channel decoding unit 170. Since it can be easily realized in any case, the load value can be changed at an appropriate position according to the situation.

According to another embodiment of the present invention, the channel state information generated by the channel estimation unit 140 of FIG. 1 (ie, the channel estimation value) is multiplied by a value greater than or equal to 0 and less than 1. Decrease. By performing channel compensation and demapping based on the channel estimation value with the weight value adjusted, it is possible to prevent the information value from entering the channel decoding unit in a distorted state.

According to each proposed method, it is possible to ensure the stability of the receiving apparatus by blocking that the value corresponding to the interference signal is input to the function block at the subsequent stage of the FFT unit 130, and damaged by the interference signal. By preventing each input signal from entering channel decoding section 170 with a large value, the performance of channel decoding section 170 can be improved as compared to the case where only notch filtering is simply applied.

Each method described above has been described by exemplifying a case where there is co-channel interference, but the application range of the present embodiment is not limited to this. For example, in the case of generating a signal distortion at a specific frequency position, such as an analog high-frequency pass filter used in a tuner, the estimated channel state information at the corresponding position becomes inaccurate. The performance of the receiving apparatus can be improved by applying the method and setting the information value of the position to be prevented from entering the channel decoding unit in a distorted state.

FIG. 3 is a flowchart illustrating a method of processing a co-channel interference signal with an OFDM reception signal according to an embodiment of the present invention.

In the embodiment illustrated in FIG. 3, processing (that is, weight value application) is performed on the co-channel interference signal before channel compensation is performed on complex symbols in the frequency domain. First, co-channel interference signal information (for example, the size and frequency of the interference signal) is detected from the received signal or the OFDM symbol (S310). Next, notch filtering is performed on the OFDM symbol based on the detected interference signal information (S320). Next, a fast Fourier transform is performed on the filtered signal to convert the OFDM symbol in the time domain into a complex symbol in the frequency domain (S330). Next, for the complex symbol based on the detected interference signal information, the signal value near the position (coordinate, frequency component) where the co-channel interference is detected is set to a value greater than or equal to 0 and less than 1. The weight value is decreased by multiplying (S340). Next, the complex symbol to which the weight value is given is separated into data symbols and pilot symbols, channel state information, that is, channel distortion is estimated using the pilot symbols, and channel distortion of the data symbols is estimated using the channel estimation values. Is compensated (S350). Next, a decoding process is performed in which the channel-compensated data symbols are demapped and quantized into data bits, and the data bits are decoded to restore the transmission data bits (S360 to S370).

As described above, the processing for the co-channel interference signal proposed in the present embodiment can also be applied to the complex symbol before channel compensation is performed as illustrated in FIG. It can also be performed immediately before the data symbol is quantized into data bits in the complex symbol or demapping process after the channel compensation is performed.

FIG. 4 is a flowchart illustrating a method of processing a co-channel interference signal with an OFDM received signal according to another embodiment of the present invention.

In the embodiment illustrated in FIG. 4, by applying a weight to a channel estimation value used to perform channel compensation on complex symbols in the frequency domain, distortion due to co-channel interference is performed simultaneously with channel compensation. To compensate. First, co-channel interference signal information (for example, the size and frequency of the interference signal) is detected from the received signal or the OFDM symbol (S410). Next, notch filtering is performed on the OFDM symbol based on the detected interference signal information (S420). Next, fast Fourier transform is performed on the filtered signal to convert the OFDM symbol in the time domain into a complex symbol in the frequency domain (S430). Next, the complex symbols are separated into data symbols and pilot symbols, and channel state information is estimated using the pilot symbols to generate a channel estimation value. By multiplying the generated channel estimate by a value greater than or equal to 0 and less than 1 to the channel estimate corresponding to the position where co-channel interference is detected based on the detected interference signal information Decrease the weight value. The channel estimation value to which the weight is added is used to compensate for channel distortion of the data symbol, so that distortion due to co-channel interference is simultaneously compensated simultaneously with channel compensation (S440). Next, a decoding process is performed in which the compensated data symbols are demapped and quantized into data bits, and the data bits are decoded to restore the transmission data bits (S450 to S460).

3 and 4 describe that the respective steps (S310 to S370, S410 to S460) are sequentially performed, this is just an example of the technical idea of the embodiment of the present invention. Not too much. In other words, a person having ordinary knowledge in the technical field to which the embodiment of the present invention belongs has the order described in FIGS. 3 and 4 without departing from the essential characteristics of the embodiment of the present invention. FIG. 3 is not limited to a chronological order because various modifications and changes can be made by changing and executing one or more processes in parallel.

On the other hand, each step of the flowcharts shown in FIGS. 3 and 4 can be embodied as computer-readable code on a computer-readable recording medium. Computer-readable recording media include all types of recording devices that store data to be read by a computer system. That is, computer-readable recording media include mafnetic storage media (for example, ROM (Read Only Memory), floppy (registered trademark) disk, hard disk, etc.), optical interpretation media (for example, CD-ROM, DVD, etc.) and carrier wave ( For example, storage media such as transmission over the Internet. The computer-readable recording medium is distributed in a computer system connected via a network, and can store and execute computer-readable code in a distributed manner.

The above description is merely illustrative of the technical idea of the present embodiment. Any person having ordinary knowledge in the technical field to which the present embodiment belongs will depart from the essential characteristics of the present embodiment. Various modifications and variations are possible without departing from the scope. Therefore, the present embodiment is not intended to limit the technical idea of the present embodiment, but is for explanation, and the scope of the technical idea of the present embodiment is not limited by such an embodiment. . The protection scope of the present embodiment should be construed by the following claims, and all technical ideas within the equivalent scope should be construed as being included in the scope of rights of the present embodiment.

100: interference detection unit, 120: notch filter, 130: FFT unit, 140: channel estimation unit, 150: channel compensation unit, 160: demapper, 170: channel decoding unit

Claims (12)

An OFDM (Orthogonal Frequency Division Multiplexing) receiving apparatus that processes an OFDM received signal,
A Fourier transform step of performing a fast Fourier transform (FFT) on the OFDM symbol to convert the OFDM symbol to a complex symbol in the frequency domain;
A channel compensation step of estimating channel state information based on the complex symbol in the frequency domain and generating a data symbol in which channel distortion is compensated using the channel estimation value;
A demapping step of quantizing the data symbols into data bits;
Decoding the data bits to restore the transmitted data bits,
The OFDM reception further comprising a step of adjusting a weight value of a signal value corresponding to the position of the interference signal based on position information of the interference signal between the Fourier transforming step and the decoding step. How to process the signal.     The step of adjusting the weight value includes assigning a weight value N (where 0 ≦ N <1) to the signal value corresponding to the position where the interference signal is detected for the complex symbol. The OFDM received signal processing method according to claim 1.     The step of decreasing the weight value includes assigning a weight value N (where 0 ≦ N <1) to a signal value corresponding to a position where an interference signal is detected, with respect to the data bit. The OFDM received signal processing method according to claim 1.     The method of claim 1, wherein the interference signal is a co-channel interference signal included in the OFDM reception signal.     2. The method of processing an OFDM reception signal according to claim 1, wherein the interference signal is a signal that distorts a signal value at a specific frequency position. Detecting a position of an interference signal from the OFDM symbol;
The method of claim 1, further comprising performing notch filtering on the OFDM symbol to remove the interference signal. A method for processing an OFDM reception signal in an OFDM receiver,
A Fourier transform process for performing a fast Fourier transform on the OFDM symbol and transforming the OFDM symbol into a complex symbol in the frequency domain;
Estimating channel state information based on the frequency domain complex symbols to generate a channel estimate;
Adjusting a weight value of a channel estimation value corresponding to the position of the interference signal based on the position information of the interference signal;
A channel compensation step of generating data symbols compensated for channel distortion using a weighted channel estimate, and
A demapping step of quantizing the data symbols into data bits;
A method for processing an OFDM received signal, comprising: a decoding step of decoding the data bits to restore transmission data bits.     The step of adjusting a weight value of the channel estimation value includes assigning a weight value N (where 0 ≦ N <1) to a channel estimation value corresponding to a position where an interference signal is detected. 8. A method for processing an OFDM reception signal according to 7. A Fourier transform unit for transforming OFDM symbols into complex symbols in the frequency domain;
A channel estimation unit for generating a channel estimation value for estimating channel state information based on the complex symbol in the frequency domain;
A channel compensation unit that generates data symbols in which channel distortion is compensated using the channel estimation value;
A demapper for quantizing the data symbols into data bits;
A channel decoding unit for decoding the data bits and restoring transmission data bits;
One of the Fourier transform unit, the channel compensation unit, and the demapper is configured to include a function of adjusting a weight value of a signal value corresponding to a position of an interference signal. apparatus. A Fourier transform unit for transforming OFDM symbols into complex symbols in the frequency domain;
Channel estimation configured to estimate channel state information based on the complex symbol to generate a channel estimation value, and to adjust a weight value of the estimation value corresponding to the position of the interference signal among the generated channel estimation values And
A channel compensator for generating a data symbol in which channel distortion is compensated using a channel estimation value with an adjusted weight;
A demapper for quantizing the data symbols into data bits;
An OFDM receiving apparatus comprising: a decoding unit that decodes the data bits to restore transmission data bits. An OFDM receiver signal processing method comprising:
Generating a frequency domain OFDM symbol based on an RF (Radio Frequency) signal;
Performing at least channel distortion compensation and demapping on the frequency domain OFDM symbols to generate data bits;
Decoding the data bits to recover the transmitted data bits;
In any one of the steps, the frequency component corresponding to the frequency position of the interference signal is given a weight value greater than or equal to 0 and less than 1 in any one of the steps. A signal processing method for an OFDM receiver. An OFDM receiver signal processing method comprising:
Generating a frequency-domain OFDM symbol based on the RF signal;
Performing at least channel distortion compensation and demapping on the frequency domain OFDM symbols to generate data bits;
Decoding the data bits to restore transmitted data bits; and
The channel distortion compensation uses a channel estimation value in which a weight value greater than or equal to 0 and less than 1 is assigned to a value corresponding to a frequency position of an interference signal, and a signal processing method for an OFDM receiver .

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