KR102113875B1 - Method for correcting channel status information based on symbol energy change rate - Google Patents

Abstract

According to an embodiment of the present invention, a method of calibrating channel state information based on a symbol energy change rate, in which an orthogonal frequency division multiplexing (OFDM) receiving device corrects channel state information based on an energy change rate of a received signal, may comprise the steps of: calculating a symbol energy change rate on a time axis; setting a scale weight based on an amount of change in a scale value generated during a fast Fourier transform operation of the received signal; correcting channel state information estimated from a pilot symbol based on the calculated symbol energy change rate and the scale weight; and correcting an error of the received signal based on the corrected channel state information.

Description

How to correct channel status information based on symbol energy change rate {METHOD FOR CORRECTING CHANNEL STATUS INFORMATION BASED ON SYMBOL ENERGY CHANGE RATE}

The present invention relates to a method for correcting channel state information based on a symbol energy change rate, and more specifically, to improve reliability of FEC (Forward Error Correction) by correcting channel state information based on an energy change rate for each symbol section of a received signal. It relates to a method for correcting channel state information based on a possible rate of symbol energy change.

Orthogonal frequency division multiplexing (OFDM) is a modulation method of a communication signal, and is a modulation method that modulates and transmits a high-speed transmission signal by hundreds of orthogonal narrow-band subcarriers.

The OFDM scheme is a very flexible scheme capable of adapting to channel state information. Optimal radio resource allocation is possible for each time interval, and different modulation schemes can be applied to each OFDM subcarrier. It has a feature that it is possible to allocate optimal resources.

On the other hand, in mobile communication, since the state of a channel transmitting a subcarrier changes rapidly, channel status information (CSI) for a communication channel is essential, and to compensate for packet errors and losses in data communication through the channel. As a technology, Forward Error Correction (FEC) and Automatic Repeat Request (ARQ) are applied.

Among them, the forward error correction method refers to a method in which a data error is detected by a receiving side and is encoded and transmitted by a transmitting device so that the detected error can be corrected by the receiving side.

To this end, the receiver determines the state of the corresponding communication channel by using channel status information (CSI) estimated from the pilot symbols in the process of forward error correction. PSAM (Pilot Symbol Assisted Modulation) uses pilot symbols. As a modulation method, by inserting and transmitting symbols of known sizes and phases in addition to data symbols (digital symbols), the receiving side can estimate the channel state from the pilot symbols included in the received signal, thereby distorting the channel. The size and phase of data symbols can be compensated.

However, in the related art, there is a problem in that the channel state cannot be accurately estimated because the channel state information is estimated from the pilot symbol transmitted from the transmitting side, and as a result, there is a limit that reliability of forward error correction itself is deteriorated.

On the other hand, the above-mentioned background technology is the technical information acquired by the inventor for the derivation of the present invention or acquired in the derivation process of the present invention, and is not necessarily a known technology disclosed to the general public before filing the present invention. .

Korean Patent Publication No. 10-2014-0116769 Korean Patent Publication No. 10-2019-0088841

One aspect of the present invention provides a method for correcting channel state information based on a rate of symbol energy change that can improve reliability of an error correction process of a received signal by correcting channel state information estimated from pilot symbols based on characteristics of a received signal. .

The technical problems of the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

A method of calibrating channel state information based on a symbol energy change rate that an OFDM receiver according to an embodiment of the present invention corrects channel state information based on an energy change rate of a received signal includes: calculating a symbol energy change rate on a time axis; Setting a scale weight based on an amount of change in a scale value generated during a fast Fourier transform operation of the received signal; Correcting channel state information estimated from a pilot symbol based on the calculated rate of symbol energy change and the scale weight; And correcting an error of the received signal based on the corrected channel state information.

The calculating of the symbol energy change rate is characterized by extracting a maximum energy value and a minimum energy value for each symbol section on a time axis, and calculating a difference value between the extracted maximum energy value and the minimum energy value as the symbol energy change rate. and,

The setting of the scale weight is characterized by extracting a scale value generated during a fast Fourier transform operation of a received signal, comparing the extracted scale value with a preset target scale value, and setting the difference value as the scale weight And

To correct the channel state information, the channel state information estimated from the pilot symbol reflects the weight according to the symbol energy change rate, and then calculates the scale weight to the channel state information in which the weight according to the symbol energy change rate is changed to the channel. The amplitude value of the state information may be calculated, and the amplitude value of the channel state information may be increased or decreased so as to have the calculated amplitude value.

According to one aspect of the present invention, the channel state information estimated from the pilot symbol can be corrected based on the energy change rate and scale weight for each symbol of the received signal, thereby improving the reliability of the error correction process of the received signal.

1 is a block diagram showing a schematic configuration of an OFDM receiving apparatus according to an embodiment of the present invention.
FIG. 2 is a flowchart illustrating a schematic flow of a channel state information correction method based on a symbol energy change rate performed by the OFDM receiver of FIG. 1.
3 to 5 are diagrams illustrating specific examples in which channel state information is corrected by a channel state information correction method based on a symbol energy change rate according to the present invention.

For a detailed description of the present invention, which will be described later, reference is made to the accompanying drawings that illustrate, by way of example, specific embodiments in which the invention may be practiced. These examples are described in detail enough to enable those skilled in the art to practice the present invention. It should be understood that the various embodiments of the present invention are different, but need not be mutually exclusive. For example, the specific shapes, structures, and properties described herein can be implemented in other embodiments without departing from the spirit and scope of the invention in connection with one embodiment. In addition, it should be understood that the location or placement of individual components within each disclosed embodiment can be changed without departing from the spirit and scope of the invention. Therefore, the following detailed description is not intended to be taken in a limiting sense, and the scope of the present invention, if appropriately described, is limited only by the appended claims, along with all ranges equivalent to those claimed. In the drawings, similar reference numerals refer to the same or similar functions throughout several aspects.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the drawings.

1 is a block diagram showing a schematic configuration of an OFDM receiving device 1 according to an embodiment of the present invention.

The OFDM receiving apparatus 1 according to an embodiment of the present invention includes a filter unit 100, an AGC unit 200, an FFT unit 300, a CSI correction unit 400, and an FEC unit 500, Specifically, the filter unit 100, the AGC unit 200, the FFT unit 300, the CSI correction unit 400, and the FEC unit 500 may be characterized as being implemented in a circuit form for digital signal processing. .

The filter unit 100 removes noise and the like included in the received signal, and may be in the form of a band pass filter (BPF), a low pass filter (LPF), or the like.

The AGC unit 200 converges the amplitude of the received signal to the signal level required for the fast Fourier transform operation in the FFT unit 300, which will be described later. That is, the AGC unit 200 maintains the output level at a relatively constant value even when the input level fluctuates by increasing the gain in the attenuated signal so that the amplitude of the received signal does not fluctuate excessively and decreasing the gain when the signal strength is too large. It may be in the form of an automatic gain control circuit (AGC).

The FFT unit 300 converts a received signal that has passed through the AGC unit 200 into a frequency domain by using a Fast Fourier Transform (FFT) algorithm. Since the FFT unit 300 is a technology widely used in the field of digital communication technology, a detailed description will be omitted.

The CSI correction unit 400 estimates channel state information used for error signal correction in the FEC unit 500, which will be described later, from a pilot symbol.

At this time, the CSI correction unit 400 according to the present invention corrects the channel status information (CSI) estimated from the pilot symbol based on the energy change rate of the received signal, and then corrects the corrected channel status information (CSI). By transmitting to the FEC unit 500, it is possible to improve reliability of an error correction process performed by the FEC unit 500. Details related to this will be described later.

The FEC unit 500 may detect an error of the received signal and correct the detected error by a predetermined error detection method based on channel state information received from the CSI correction unit 400. That is, the FEC unit 500 may compensate for the size and phase of data symbols distorted by the channel based on channel state information estimated from pilot symbols included in the received signal.

As described above, the OFDM receiving apparatus 1 according to an embodiment of the present invention corrects a signal distorted by a channel through a forward error correction technique based on channel state information on a received signal generated in an OFDM mobile communication process. The reception performance can be improved.

At this time, the FEC unit 500 according to the present invention corrects the error signal more effectively by compensating the distorted signal based on the channel status information corrected by the CSI correction unit 400 rather than the channel status information estimated from the pilot symbol. can do.

Since the first channel state information estimated from the pilot symbol is transmitted from the transmitting side, there is a limitation that it cannot reflect information on the correct channel state. To overcome this problem, the CSI correction unit 400 according to the present invention corrects an error performed by the FEC unit 500 by correcting the initial channel state information based on the energy change rate and scale weight of the received signal. Can improve the reliability. In this regard, it will be described with reference to FIG. 2.

FIG. 2 is a flowchart illustrating a schematic flow of a method for correcting channel state information performed by the CSI correction unit 400 of FIG. 1.

As illustrated, a method for correcting channel state information based on a symbol energy change rate according to an embodiment of the present invention, which is performed by the CSI correction unit 400, comprises: calculating a symbol energy change rate on a time axis (S10); Setting a scale weight based on the amount of change in the scale value generated during the fast Fourier transform operation of the signal (S20), correcting the channel state information estimated from the pilot symbol based on the calculated symbol energy change rate and the scale weight Step S30 may be included.

First, the CSI correction unit 400 may calculate a symbol energy change rate on the time axis (S10).

As is known, the received signal may consist of symbol data representing meaningful information. At this time, the CSI correction unit 400 may extract the highest energy value and the lowest energy value in each symbol time interval. The CSI correction unit 400 may calculate the amount of change between the extracted maximum energy value and the minimum energy value, that is, a difference value between the maximum energy value and the minimum energy value, and set it as a symbol energy change rate.

Next, the CSI correction unit 400 may collect the scale values generated in the process of the fast Fourier transform operation of the communication signal through the FFT unit 300 and calculate the rate of change of the scale values for each collected symbol (S20). ).

For example, if the preset target scale value is 5 and the scale value of the received signal generated in the Fourier transform process through the FFT unit 300 is 3, the CSI correction unit 400 scales the received signal at the target scale value 5 2 minus the value 3 can be calculated as a scale change rate and set as a scale weight. As another example, when the target scale value is 5 and the scale value of the Fourier transformed received signal is 6, the scale weight may be set to -1.

Thereafter, the CSI corrector 400 may correct the channel state information estimated from the pilot symbol based on the calculated symbol energy change rate and the scale weight (S30).

In general, the channel state information estimated from the pilot symbol can be calculated by the following equation.

[Equation 1]

In Equation 1 above, C (t, i) is the channel state information (CSI) of the i-th subcarrier of the OFDM symbol at time t, and P (t, i) is the power of the i-th subcarrier of the OFDM symbol at time t. And α and β are weighting factors for determining the convergence speed and characteristics of the extractor (CSI correction unit 400 in this embodiment) that estimates channel state information, and satisfies α + β = 1. The α and β values can be adjusted by the user's selection, and the degree of change of the CSI changes according to the selected values. 3 is a diagram illustrating an example of channel state information (C (t, i)) estimated from a pilot symbol.

The CSI correction unit 400 extracts the estimated channel state information (C (t, i)) from the pilot symbol, and then extracts the symbol energy change rate calculated in the above-described process into the extracted channel state information (C (t, i)). And calculating the scale weight to correct initial channel state information (C (t, i)). This is expressed by the following equation.

[Equation 2]

Here, C _n (t, i) is the corrected channel state information, C (t, i) is the initial channel state information calculated from the pilot symbols calculated by Equation 1, w ₁ is the weight according to the symbol energy change rate, w ₂ means scale weight.

FIG. 4 is a diagram illustrating an example of channel status information corrected by the CSI correction unit 400. Referring to FIG. 3 together, it can be seen that the channel status information is attenuated by the CSI correction unit 400. .

In addition, as illustrated in FIG. 5, the CSI correction unit 400 may attenuate (degrade) the amplitude of the channel state information as the magnitude of the absolute value of the scale weight increases.

That is, the CSI correcting unit 400 analyzes the received signal received through the first established communication channel, and when it is determined that the energy change rate or scale value of the received signal changes rapidly, attenuates the amplitude of the channel state information to decrease the current communication channel. It can be emphasized that the condition is not good.

Thereafter, the FEC unit 500 may correct the error of the received signal based on the corrected channel state information (S40).

Accordingly, the OFDM receiver 1 to which the channel state information correction method based on the symbol energy change rate according to the present invention is applied receives the channel state information estimated from the pilot symbols based on the energy change rate and the scale weight for each symbol of the received signal. This has the effect of improving the reliability of the error correction process of the signal.

In some other embodiments, the OFDM receiving device 1 according to the present invention may correct the channel state information in a state in which the influence of the scale is excluded from the mobile channel by changing the position of the configuration that sequentially processes the received signal.

That is, in the embodiment of the present invention shown in FIG. 1, the input signal is processed in the order of the filter unit 100-AGC unit 200- FFT unit 300-CSI correction unit 400-FEC unit 500. On the other hand, in some other embodiments of the present invention, the received signal may be processed in the order of the filter unit 100-FFT unit 300-AGC unit 200-CSI correction unit 400-FEC unit 500. .

That is, in the OFDM receiving apparatus 1 according to another embodiment of the present invention, a fast Fourier transform operation process may be first performed by the FFT unit 300 before the input level is adjusted by the AGC unit 200. In this case, the FFT unit 300 may express the received signal more precisely by processing the received signal using a floating-point FFT method.

Although described above with reference to embodiments, those skilled in the art understand that various modifications and changes can be made to the present invention without departing from the spirit and scope of the present invention as set forth in the claims below. Will be able to.

Note-This patent was filed with the support of "2019 ICT Innovative Enterprise Technology Development Support Project-Driver-oriented Next Generation Vehicle DRM Infotainment Solution Development".

1: OFDM receiver
100: filter unit
200: AGC Division
300: FFT unit
400: CSI correction unit
500: FEC section

Claims (2)

In the method for calibrating channel state information based on a symbol energy change rate, an OFDM receiving device corrects channel state information based on an energy change rate of a received signal,
Calculating a symbol energy change rate on the time axis;
Setting a scale weight based on an amount of change in a scale value generated during a fast Fourier transform operation of the received signal;
Correcting channel state information estimated from a pilot symbol based on the calculated rate of symbol energy change and the scale weight; And
And correcting an error of the received signal based on the corrected channel state information.
According to claim 1,
The calculating of the symbol energy change rate is characterized by extracting a maximum energy value and a minimum energy value for each symbol section on a time axis, and calculating a difference value between the extracted maximum energy value and the minimum energy value as the symbol energy change rate. and,
The setting of the scale weight is characterized by extracting a scale value generated during a fast Fourier transform operation of a received signal, comparing the extracted scale value with a preset target scale value, and setting the difference value as the scale weight And
Correcting the channel state information reflects the weight according to the symbol energy change rate in the channel state information estimated from the pilot symbol, and then calculates the scale weight on the channel state information in which the weight according to the symbol energy change rate is changed to the channel. A channel state information correction method based on a symbol energy change rate, characterized in that the amplitude value of the state information is calculated and the amplitude value of the channel state information is increased or decreased to have the calculated amplitude value.

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