KR20230105510A - Apparatus for receiving in ofdm system and method for reducing phase noise thereof - Google Patents

Abstract

A phase noise mitigation method of a receiving device in an OFDM system is provided. The phase noise mitigation method includes estimating a channel using a first reference signal and estimating a phase of the first reference signal; estimating the phases of a plurality of corresponding subcarriers, using the phases of the first reference signal and the phases of the plurality of second reference signals, for a plurality of common phase errors (CPEs) calculated within the OPDM symbol; Calculating a variance value, and correcting a Log-Likelihood Ratio (LLR) value calculated using the estimated channel for received data using the calculated variance value.

Description

Receiving device of OFDM system and phase noise mitigation method thereof

The present disclosure relates to a receiving apparatus of an orthogonal frequency-division multiplexing (OFDM) system and a method for mitigating phase noise thereof, and more particularly, performance deterioration due to phase noise by estimating common phase error (CPE) generated due to phase noise It relates to a receiving apparatus of an OFDM system capable of reducing , and a phase noise mitigation method thereof.

User demand for large-capacity data transmission through wireless transmission will continue to increase in the future. However, large-capacity data transmission through wireless transmission has limitations due to the depletion of available frequency resources in the existing frequency band. It is a trend.

The frequency of the ultra-high frequency band has the advantage of being able to create a beam with excellent directivity as well as miniaturization and light weight of the antenna and transceiver because the wavelength is very short. As a means to solve this problem, a method capable of improving performance deterioration due to phase noise is required.

In an OFDM (Orthogonal Frequency-Division Multiplexing) based radio system, the components that cause performance degradation due to phase noise are the CPE (common phase error) component in which all subcarriers present in one OFDM symbol experience the same phase noise and the orthogonal characteristics of each subcarrier It can be classified as an ICI (Inter Carrier Interference) component that destroys , and since the ICI component has statistical characteristics such as white noise, the process of correcting the phase noise can be seen as a process of estimating the CPE component and compensating for it.

In the OFDM-based wireless system environment as described above, there is a characteristic that phase noise varies according to OFDM symbol time. In particular, as one OFDM symbol time becomes longer, phase noise is more likely to generate more ICI components, which can have a more serious effect on performance degradation. Therefore, even if the same number of phase noise estimation reference signals are used to compensate for the CPE in one OFDM symbol, the performance degradation characteristics according to one OFDM symbol period can be variously displayed by ICI. You need a means.

The problem to be solved by the present disclosure is to provide a receiving apparatus of an OFDM system capable of improving performance degradation due to phase noise in an OFDM-based wireless system and a phase noise mitigation method thereof.

According to an embodiment, a phase noise mitigation method of a receiving device of an OFDM system is provided. The phase noise mitigation method includes estimating a channel using a first reference signal, estimating a phase of the first reference signal, and determining the phases of a plurality of subcarriers respectively corresponding to the plurality of second reference signals within one OPDM symbol. estimating, calculating variance values for a plurality of common phase errors (CPE) calculated within the OPDM symbol using the phase of the first reference signal and the phase of the plurality of second reference signals, and receiving and correcting a Log-Likelihood Ratio (LLR) value calculated using the estimated channel for data using the calculated variance value.

According to the embodiment, performance is finally improved by estimating CPE caused by phase noise in an OFDM-based wireless communication system, estimating CPE variance estimated based on OFDM symbols, and correcting the soft LLR value through the estimated variance value. There are possible effects.

1 is a diagram illustrating a CPE and a channel estimation unit for improving performance degradation due to phase noise in a receiving apparatus of an OFDM system according to an embodiment.
FIG. 2 is a flowchart illustrating a CPE and channel estimation method of the CPE and channel estimation unit shown in FIG. 1 .
3 is a diagram showing CPE dispersion values of each OFDM symbol.
4 is a diagram illustrating a receiving apparatus of an OFDM system according to an embodiment.
5 is a flowchart illustrating a phase noise mitigation method of the OFDM system shown in FIG. 4;
6 is a diagram showing LLR distribution curves according to CPE dispersion values for each OFDM symbol.
7 is a diagram illustrating a receiving device of an OFDM system according to another embodiment.

Hereinafter, with reference to the accompanying drawings, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. And in order to clearly explain the present invention in the drawings, parts irrelevant to the description are omitted, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification and claims, when a certain component is said to "include", it means that it may further include other components without excluding other components unless otherwise stated.

Now, a receiver of an OFDM system according to an embodiment and a phase noise mitigation method thereof will be described in detail with reference to the drawings.

1 is a diagram showing a CPE and a channel estimation unit for improving performance degradation due to phase noise in a receiver of an OFDM system according to an embodiment, and FIG. 2 is a diagram illustrating a CPE and a channel estimation method of the CPE and channel estimation unit shown in FIG. It is the flow chart shown.

Referring to FIG. 1, the CPE and channel estimator 100 includes a channel estimator 110, a carrier phase estimator 120, a CPE estimator 130, a CPE average calculator 140, and a channel compensator 150. ) and a CPE variance calculation unit 160.

Referring to FIGS. 1 and 2 , the channel estimator 110 estimates a channel state through a channel estimation reference signal and estimates a phase of the estimated channel (S110).

The carrier phase estimator 120 estimates the phase of a subcarrier corresponding to each phase noise estimation reference signal within one OFDM symbol through a plurality of phase noise estimation reference signals (S120).

The CPE estimator 130 independently estimates a plurality of CPEs within one OFDM symbol as shown in Equation 1 using the phase difference between the phase of the channel estimation reference signal and each phase noise estimation reference signal (S130).

는 추정된 CPE 값을 나타내고,

는 채널 추정 기준 신호를 통해 추정된 위상을 나타내며,

는 위상 잡음 추정 기준 신호를 통해 추정된 위상을 나타낸다. here,

denotes the estimated CPE value,

Represents the phase estimated through the channel estimation reference signal,

denotes the phase estimated through the phase noise estimation reference signal.

At this time, each phase noise component is composed of a CPE component and an ICI component. The CPE component represents a characteristic generated by the same phase noise for all OFDM symbols, and the ICI component represents a characteristic generated due to overlapping signals of each subcarrier component, which can be assumed to follow a Gaussian distribution characteristic like white noise.

One OFDM symbol is composed of N subcarriers, and some of the N subcarriers are used for CPE estimation. That is, a plurality of CPEs are independently estimated by each subcarrier corresponding to a plurality of assigned phase noise estimation reference signals within one OFDM symbol. Therefore, a plurality of CPEs following the white noise Gaussian distribution characteristics by ICI are configured in one OFDM symbol, and an average value of the plurality of CPEs can be finally estimated as a commonly applied CPE within one OFDM symbol.

The CPE average calculation unit 140 averages each CPE estimated by each phase noise estimation reference signal to calculate an average value of the CPEs within the OFDM symbol (S140).

The channel compensator 150 compensates for the estimated channel using an average value of CPEs within the OFDM symbol (S150).

However, since the estimated CPE component within each OFDM symbol can be assumed to have a Gaussian distribution characteristic according to the ICI component, and the phase noise has a characteristic that varies randomly with time, in the present disclosure, to use the above characteristic To do this, we measure the variance of the phase noise distribution of each subcarrier corresponding to a plurality of phase noise estimation reference signals within each OFDM symbol, and use the measured variance later to correct the LLR (Log-Likelihood Ratio) value. .

Accordingly, the CPE variance calculation unit 160 calculates a variance value of the CPE estimated by each phase noise estimation reference signal within the OPDM symbol (S160).

The channels compensated by the channel compensator 150 and the CPE variance calculation unit 160 and the calculated CPE variance values of the corresponding OFDM symbol are output (S170).

3 is a diagram showing CPE dispersion values of each OFDM symbol.

As shown in FIG. 3, since the CPE dispersion value changes with time, each OFDM symbol has independent values (CPE dispersion value_0, CPE dispersion value_1, CPE dispersion value_2, ...) can be assumed Such an assumption can be seen that phase noise having a characteristic that varies with time is generated in an OFDM-based system. In particular, as the OFDM symbol period becomes longer, there may be more ICI components affecting the entire OFDM symbol due to phase noise. Therefore, since the reliability of the ICI component on the CPE component varies for each OFDM symbol, the variance value of the CPEs corresponding to each OFDM symbol is used to correct the LLR value when determining the final LLR value.

FIG. 4 is a diagram illustrating a receiver of an OFDM system according to an embodiment, and FIG. 5 is a flowchart illustrating a phase noise mitigation method of the OFDM system shown in FIG. 4 .

Referring to FIG. 4 , the receiver of the OFDM system includes a CPE and channel estimator 310 , an equalizer 320 and an LLR corrector 330 .

The CPE and channel estimator 310 corresponds to the CPE and channel estimator 100 shown in FIG. 1 .

The compensated channel by the CPE and channel estimator 310 and CPE variance values for each OFDM symbol are output.

4 and 5, the equalizer 320 equalizes the received data using the CPE and the compensated channel output from the channel estimation unit 310 (S410), and generates an LLR for the equalized signal. A value is extracted (S420).

When the LLR value extracted by the equalizer 320 is output in units of OFDM symbols, the LLR correction unit 330 corrects the LLR value using the CPE variance value of each OFDM symbol, and outputs the final LLR value. (S430). Information bits are decoded according to the final LLR value. Here, the CPE variance value is independently input for each OFDM symbol, and the LLR value is corrected for each OFDM symbol. At this time, there may be various rules for correcting the LLR value using the CPE variance value.

Referring to FIG. 6, an applicable example of a method of correcting an LLR value using a CPE variance value will be described.

6 is a diagram showing LLR distribution curves according to CPE dispersion values for each OFDM symbol.

Referring to FIG. 6, the LLR value has a soft value, and the LLR distribution value may be different for each OFDM symbol according to the CPE dispersion value. Therefore, it can be generally assumed that the LLR distribution follows the Gaussian characteristic, and that the ICI effect caused by phase noise can vary depending on the degree of spread of the LLR distribution curve, that is, the CPE dispersion value of the OFDM symbol. At this time, the smaller the CPE dispersion value of the OFDM symbol, the narrower the spread of the LLR distribution curve, and the larger the CPE dispersion value, the wider the spread of the LLR distribution curve. In the above situation, when the CPE dispersion value is small, that is, when the LLR distribution curve narrows, the reliability of the soft LLR value increases, and when the CPE dispersion value is large, that is, when the LLR distribution curve widens, the reliability of the soft LLR value increases. can be seen falling. Accordingly, the LLR corrector 330 may use a weight value that is inversely proportional to the CPE variance value when finally correcting the soft LLR value.

In other ways, the soft LLR value may be corrected using the CPE variance value.

7 is a diagram illustrating a receiving apparatus of an OFDM system according to another embodiment.

Referring to FIG. 7 , the receiver 700 of the OFDM system may represent a computing device in which the phase noise mitigation method of the OFDM receiver described above is implemented.

The receiver 700 of the OFDM system may include at least one of a processor 710, a memory 720, an input interface device 730, an output interface device 740, and a storage device 750. Each component may be connected by a common bus 760 to communicate with each other. In addition, each of the components may be connected through individual interfaces or individual buses centering on the processor 710 instead of the common bus 760 .

The processor 710 may be implemented in various types such as an Application Processor (AP), a Central Processing Unit (CPU), a Graphic Processing Unit (GPU), and the like, and executes commands stored in the memory 720 or the storage device 750. It may be any semiconductor device that The processor 710 may execute a program command stored in at least one of the memory 720 and the storage device 750 . The processor 710 stores program commands for implementing at least some functions of the CPE and channel estimation unit 310, equalizer 320, and LLR correction unit 330 described in FIG. 4 in the memory 720, The operation described with reference to FIGS. 1 to 6 may be controlled to be performed.

The memory 720 and the storage device 750 may include various types of volatile or non-volatile storage media. For example, the memory 720 may include read-only memory (ROM) 721 and random access memory (RAM) 722 . The memory 720 may be located inside or outside the processor 710, and the memory 720 may be connected to the processor 710 through various known means.

Input interface device 730 is configured to provide data to processor 710 .

Output interface device 740 is configured to output data from processor 710 .

At least some of the phase noise mitigation methods of the OFDM receiver according to embodiments may be implemented as a program or software running on a computing device, and the program or software may be stored in a computer-readable medium.

In addition, at least some of the phase noise mitigation methods of the OFDM receiving device according to the embodiment may be implemented in hardware that can be electrically connected to the computing device.

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the following claims are also included in the scope of the present invention. that fall within the scope of the right.

Claims (1)

In the phase noise mitigation method of the receiving device of the OFDM system,
Estimating a channel using a first reference signal and estimating a phase of the first reference signal;
estimating phases of a plurality of subcarriers respectively corresponding to a plurality of second reference signals within one OPDM symbol;
Calculating variance values for a plurality of common phase errors (CPEs) calculated within the OPDM symbol using the phase of the first reference signal and the phase of the plurality of second reference signals; and
Correcting a Log-Likelihood Ratio (LLR) value calculated using the estimated channel for received data using the calculated variance value
Phase noise mitigation method comprising a.

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