KR102030921B1 - Channel Estimation Method based on Updated-Weight Matrix for OFDM Systems and System using same - Google Patents

Abstract

The present invention relates to a method for estimating a channel based on an update weight matrix in an OFDM system and a system using the same, wherein an i th in a packet is determined using a reliability test using correlation of a plurality of adjacent data symbols in a time domain. Calculating an i-th channel estimate and an update matrix, which are channel estimates of the OFDM data symbols, and when the sum of the values passed through the reliability test among the vectors of the update matrix is less than a reference value, the i-th channel estimate is calculated. Determining the new channel estimate value, and adding the weighted sum using the i-th channel estimate value and the weighted sum included in the update matrix when the sum of the values passed the reliability test among the vectors of the update matrix is equal to or greater than a reference value. determining the i-channel estimate as the new channel estimate The channel estimation method of the time and frequency domain characterized in that it comprises a.

Description

Channel Estimation Method based on Updated-Weight Matrix for OFDM Systems and System using same}

The present invention relates to a channel estimation method based on an update weight matrix in an orthogonal frequency division multiplexing (OFDM) system and a system using the same. The present invention relates to a time and frequency domain channel estimation method using an update matrix and an estimation system using the same that can improve transmission performance when transmitting a signal.

IEEE 802.11 is a technology used in computer wireless networks for wireless local area networks, commonly referred to as Wi-Fi, and is the 11th working group of the IEEE's LAN / MAN Standards Committee (IEEE 802). Means the standard technology developed by.

The terms 802.11 and Wi-Fi are sometimes used interchangeably, but the Wi-Fi Alliance defines the term "Wi-Fi" as another set of standards.

IEEE 802.11p is an approved revision of the IEEE 802.11 standard that adds wireless access in vehicular environments (WAVE).

Recently, with the development of vehicles and information communication, research on next-generation intelligent traffic systems is actively conducted, and the importance of V2X (Vehicle to Everything), which can improve driver stability by forming a network between vehicles, is emerging.

V2X refers to the technology by which cars communicate with various elements on the road for autonomous driving. It is composed of V2V (vehicle to vehicle) communication to inform traffic conditions and vehicle-to-vehicle traffic, vehicle to infrastructure (V2I) communication to traffic infrastructure such as traffic lights, and vehicle to pedestrian (V2P) communication to support pedestrian information.

In the highway environment of 100Km / h or more, the data transmitted between vehicles must be reliable, and IEEE 802.11p, which defines the physical layer and the media access control layer of WAVE communication, has been standardized to support such traffic safety services.

Currently, channel estimation techniques for estimating time-varying channel changes without changing the IEEE 802.11p standard have been studied. For example, LS (Least Square), Space-Time Averaging (STA), Constructed Data Pilots (CDP), and TRFI (Time domain Reliable test Frequency domain Interpolation) techniques have been published in an academic paper.

6 to 16 are problems of the related art, and show a different performance according to channel environment, modulation index, and SNR. For example, when STA and CDP (TRFI) are compared, STA is superior in low SNR, but CDP (TRFI) is superior in high SNR.

Korea Patent Registration No. 10-1637838 (Registration date 2016.07.01.)

In order to solve the above problems, an object of the present invention is to show the excellent performance of the channel estimation technique in the time and frequency domain in all the SNR region through a small increase in complexity.

In order to achieve the above object, the present invention provides a channel estimation value of the i th (where i is a natural number of 1 or more) OFDM data symbols in a packet using a reliability test using correlation of a plurality of adjacent data symbols in the time domain. Calculating an i-th channel estimate and an update matrix; determining the i-th channel estimate as a new channel estimate when the sum of values passed through a reliability test among the vectors of the update matrix is less than a reference value; and Determining the weighted sum of the i-th channel estimate as a new channel estimate using the i-th channel estimate and the weighted sum included in the update matrix, when the sum of the values that pass the reliability test is greater than the reference value. Channel estimation method of the time and frequency domain, characterized in that it comprises The.

The calculating of the i-th channel estimate and the update matrix may include calculating a channel estimate by using a combination of pilots on a frequency axis with similar characteristics of channels of adjacent symbols in a time and frequency domain.

The method of determining whether the sum of the values passed through the reliability test among the vectors of the update matrix is equal to or greater than a reference value is obtained by using the following equation,

이상

이하에 해당하는 자연수, k는 부반송파의 차수 및

는 업데이트 매트릭스 값을 의미하고, 상기 수학식이 기준값 이상인지 여부를 판단하는 것을 특징으로 하는 시간 및 주파수 영역의 채널 추정 방법이다.Where m is

More than

K is the order of subcarriers and

Denotes an update matrix value and determines whether the equation is equal to or greater than a reference value.

The weighted sum is equal to the following equation,

는 종래의 CDP 기법에 따른 i번째(여기서, i는 1 이상의 자연수) 채널 추정값,

는 업데이트 매트릭스 값, 및 k는 부반송파의 차수를 의미하며, 상기 업데이트 매트릭스의 벡터들 중 신뢰도 테스트를 통과한 값의 합이 기준값 이상인 경우 (즉,

을 만족할 경우), 상기 산출된 가중치 합으로 새로운 채널 추정값으로 결정하는 것을 특징으로 한다.here

Is the i-th channel where i is a natural number of 1 or more according to the conventional CDP technique,

Is an update matrix value, and k is an order of subcarriers, and when the sum of the values that pass the reliability test among the vectors of the update matrix is greater than or equal to the reference value (that is,

If satisfactory), the new channel estimate is determined based on the calculated weighted sum.

According to the present invention, an i-th channel estimate and an update matrix, which are channel estimates of the i th (where i is a natural number of 1 or more) OFDM data symbols in a packet, using a reliability test using correlation of a plurality of adjacent data symbols in the time domain. A calculating unit for determining a value, a determining unit for determining whether a sum of values passed through a reliability test among the vectors of the update matrix is equal to or greater than a reference value, and a determining unit for determining a new channel estimate value according to a determination result of the determining unit. It is characterized in that the channel estimation system in the time and frequency domain.

The calculator may be configured to calculate a channel estimate using similar characteristics of channels of a plurality of adjacent symbols in a time and frequency domain, and pilots on a frequency.

The determination unit uses the following equation,

이상

이하에 해당하는 자연수, k는 부반송파의 차수 및

는 업데이트 매트릭스 값을 의미하고, 상기 수학식이 기준값 이상인지 여부를 판단하는 것을 특징으로 하는 시간 및 주파수 영역의 채널 추정 시스템이다.Where m is

More than

K is the order of subcarriers and

Denotes an update matrix value and determines whether the equation is equal to or larger than a reference value.

In addition, the weighted sum in the decision unit is equal to the following equation,

는 종래의 CDP 기법에 따른 i번째(여기서, i는 1 이상의 자연수) 채널 추정값,

는 업데이트 매트릭스 값 및 k는 부반송파의 차수를 의미하며, 상기 업데이트 매트릭스의 벡터들 중 신뢰도 테스트를 통과한 값의 합이 기준값 이상인 경우 (즉,

을 만족할 경우), 상기 산출된 가중치 합으로 새로운 채널 추정 값으로 결정하는 시스템이다. here

Is the i-th channel where i is a natural number of 1 or more according to the conventional CDP technique,

Is the update matrix value and k is the order of the subcarriers, and if the sum of the values that passed the reliability test among the vectors of the update matrix is greater than or equal to the reference value (that is,

Is satisfied), a new channel estimate value is determined based on the calculated weight sum.

 According to the present invention as described above, it is possible to improve the channel estimation performance that can improve the performance of the WAVE device without changing the frame structure in the IEEE 802.11p standard by proposing a time and frequency domain channel estimation method.

As a channel estimation technique applicable to an OFDM-based system, it is useful when the number of pilot symbols for channel estimation is small, such as IEEE 802.11p.

In addition, it can be applied to TRFI, which is an existing technique, and the performance improvement can be obtained.

In addition, it can be applied to the channel estimation method using the decoding information, and the performance improvement can be obtained.

1 is a flowchart illustrating a method of estimating a channel in a time and frequency domain based on an update weight matrix in an OFDM system according to the present invention.
2 is a block diagram of a system using a method for estimating a time and frequency domain based on an update weight matrix in an OFDM system according to the present invention.
3 is an overall configuration diagram of a channel estimator in time and frequency domain according to the present invention.
4 is an overall configuration diagram of a channel estimator in time and frequency domain according to the present invention.
5 is an IEEE 802.11p WAVE packet structure.
6 is a packet structure in the IEEE 802.11p WAVE frequency, time domain.
7 is a structure of an IEEE 802.11p WAVE communication transceiver.
8 through 16 are performance comparison graphs of a new channel estimation technique in a Cohda channel.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It will be described in detail focusing on the parts necessary to understand the operation and action according to the present invention. In describing the embodiments of the present invention, descriptions of technical contents that are well known in the technical field to which the present invention belongs and are not directly related to the present invention will be omitted. This is to more clearly communicate without obscure the subject matter of the present invention by omitting unnecessary description.

In addition, in describing the components of the present invention, different reference numerals may be given to components having the same name according to the drawings, and the same reference numerals may be given to different drawings. However, even in such a case, it does not mean that the corresponding components have different functions according to embodiments, or does not mean that they have the same functions in different embodiments. Judgment should be made based on the description of each component in.

IEEE 802.11 is a technology used in computer wireless networks for wireless local area networks, commonly referred to as Wi-Fi, and is the 11th working group of the IEEE's LAN / MAN Standards Committee (IEEE 802). Means the standard technology developed by.

The terms 802.11 and Wi-Fi are sometimes used interchangeably, but the Wi-Fi Alliance defines the term "Wi-Fi" as another set of standards. So 802.11 and Wi-Fi are not synonymous.

IEEE 802.11p is an approved revision of the IEEE 802.11 standard that adds wireless access in vehicular environments (WAVE).

Recently, with the development of vehicles and information communication, research on next-generation intelligent traffic systems is actively conducted, and the importance of V2X (Vehicle to Everything), which can improve driver stability by forming a network between vehicles, is emerging.

V2X refers to the technology by which cars communicate with various elements on the road for autonomous driving. It is composed of V2V (vehicle to vehicle) communication to inform traffic conditions and vehicle-to-vehicle traffic, vehicle to infrastructure (V2I) communication to traffic infrastructure such as traffic lights, and vehicle to pedestrian (V2P) communication to support pedestrian information.

In the highway environment of 100Km / h or more, the data transmitted between vehicles must be reliable, and IEEE 802.11p, which defines the physical layer and the media access control layer of WAVE communication, has been standardized to support such traffic safety services.

Currently, channel estimation techniques for estimating time-varying channel changes without changing the IEEE 802.11p standard have been studied. For example, LS (Least Square), Space-Time Averaging (STA), Constructed Data Pilots (CDP), and TRFI (Time domain Reliable test Frequency domain Interpolation) techniques have been published in an academic paper.

The present invention is an update weighting matrix based channel estimation method and system using the same in an OFDM system.

OFDM refers to a modulation scheme for multiplexing a high-speed transmission signal into a plurality of orthogonal narrowband carriers.

Many modulation schemes have advantages and disadvantages, and one of the great advantages of OFDM is spread spectrum technology. It distributes data over a large number of carriers at regular intervals away from the correct frequency. This spacing provides "Orthogonal" within the technique of preventing the demodulator from referring to a frequency other than its own.

It is to divide data streams having a high data rate into a large number of data streams having a low data rate and transmit them simultaneously using a plurality of subcarriers. That is, OFDM is regarded as a special form of a multi-carrier transmission method in which data streams are simultaneously transmitted side by side on a plurality of sub-channels. Therefore, the OFDM technique is a "multiplexing technique" in terms of simultaneously transmitting a high-speed source data stream of one channel in multiple channels, and is a kind of "modulation technique" in terms of splitting and transmitting the multiple carriers. The waveform of each subcarrier is orthogonal on the time axis, but overlaps on the frequency axis.

The present invention can be applied to an OFDM system, and its utility is great when there are few pilots such as IEEE 802.11p.

1 is a flowchart illustrating a method of estimating a channel in a time and frequency domain based on an update weight matrix in an OFDM system according to the present invention.

An i-th channel estimate S110 and an update matrix S120 which are channel estimates of the i th (where i is a natural number of 1 or more) OFDM data symbols in the packet using a reliability test using correlation of a plurality of adjacent data symbols in the time domain. (S100), if the sum of the values passed through the reliability test among the vectors of the update matrix is less than the reference value (NO in S200), determining the i-th channel estimate as a new channel estimate (S400). And a sum of the i-th channel estimates weighted using the i-th estimate and the weighted sum included in the update matrix when the sum of the values that pass the reliability test among the vectors of the update matrix is equal to or greater than a reference value (YES in S200). And a step S300 of determining a new channel estimate value.

Computing the i-th channel estimate S110 and the update matrix S120, which are channel estimates of the data symbols, may be performed by using channels of adjacent symbols in the time and frequency domain with similar characteristics and pilots on the frequency axis. The channel estimation method of the time and frequency domain, characterized in that to calculate.

3 is an overall configuration diagram of a channel estimator in time and frequency domain according to the present invention.

를 얻을 수 있으며 이를 이용하여 패킷에 포함되어 있는 모든 데이터 심볼을 복구할 수 있는 OFDM 시스템을 다룬다. In the present invention, the initial channel estimate from the long training symbols of each packet.

This paper deals with an OFDM system that can recover all the data symbols contained in the packet.

혹은 과거 시간의 채널 추정 값

를 이용해 수신 신호를 다음과 같이 등화한다.Initial channel estimate

Or channel estimate of past time

Use E to equalize the received signal as

는 복구된 i번째 송신 데이터 심볼을 의미한다.In Equation 1, R _i (k) means all data symbols received in the packet, H _{i- 1} (k) is the i-th (where i means a natural number of 1 or more) channel estimate value,

Denotes the recovered i th transmission data symbol.

는 등화된 신호

를 해당하는 변조 방식으로 디매핑하는 연산(D(x))을 수행한 변수로 디매핑된 변조 심볼을 의미하며 하기 수학식 3에서 사용되는 데이터 파일럿으로 간주될 수 있다. In Equation 2

Is an equalized signal

Denotes a modulation symbol demapped by a variable that performs a demapping operation (D (x)) in a corresponding modulation scheme, and may be regarded as a data pilot used in Equation 3 below.

을 구한다.I-th channel estimation candidate value updated using the LS channel estimation scheme as shown in Equation 3 above.

Obtain

)에 대한 신뢰도 테스트를 연속된 OFDM 심볼의 시간 영역의 높은 상관 특성을 이용하여 수행한다.Like the conventional CDP method, the channel estimation candidate value of Equation 3

Reliability test is performed using the high correlation property of the time domain of consecutive OFDM symbols.

)과 이전 시간 심볼인 i-1번째 채널 추정값(

)을 이용하여 패킷내 i-1번째 수신 데이터 심볼(R_i-1(k))을 등화(Equalization)한다(수학식 4 및 수학식 5). 그리고

와

는 디매핑 연산(D(x))을 통해

와

로 디매핑 된다(수학식 6 및 수학식 7).The channel estimation candidate value (

) And the i-1th channel estimate (the previous time symbol)

) Equalizes the i-1 th received data symbol Ri _i (k) in the packet (Equations 4 and 5). And

Wow

Is the demapping operation (D (x))

Wow

Demapping to Equation (6) and (7).

By using the high correlation of two adjacent data symbols in the time domain, the channel estimation value (Equation 8) and the update matrix value (Equation 9) of the i-th received symbol may be determined through the following comparison process.

의 경우, 현재 채널 추정 후보값

가 신뢰할만하기 때문에

가 되며,

의 경우, k번째 반송파의 채널 추정 후보값

가 부정확함을 의미한다. 따라서 상대적으로 이전 시간의 채널 추정 값이 신뢰할만한 채널 추정 값이라 판단하여

가 된다.

, The current channel estimation candidate value

Because it is reliable

Becomes

, The channel estimation candidate value of the k th carrier

Implies inaccuracy. Therefore, it is determined that the channel estimation value of the previous time is a reliable channel estimation value.

Becomes

‘는 k번째 부반송파가 송수신기가 서로 알고 있는 파일럿 심볼임을 의미하고 이 경우 파일럿 심볼을 이용한 채널 추정 값을 신뢰할 수 있으므로

가 된다. Also in Equations 8 and 9

'Means that the k-th subcarrier is a pilot symbol that the transceiver knows from each other. In this case, we can trust the channel estimate using the pilot symbol.

Becomes

은 k번째 부반송파의 채널 추정값이 이전 시간의 추정 값과 다르게 새로운 값으로 업데이트 되었다는 것을 의미한다.The same condition determines the value of the update metric.

Means that the channel estimate of the k-th subcarrier is updated with a new value different from the previous time estimate.

The conventional CDP technique ends in (8).

‘의 조건을 사용하지 않는다. 즉, 파일럿 심벌을 사용하지 않는다. However, in the conventional CDP technique,

Do not use the condition of '. That is, no pilot symbol is used.

The method proposed in the present invention obtains a new channel estimate through a weighted sum in the frequency domain by using the update matrix value of Equation 9 as shown in Equation 10 below.

를 이용하고, 여기서, m은

이상

이하에 해당하는 자연수, k는 부반송파의 차수,

은 주파수 축 가중치, 및

는 수학식 9의 업데이트 매트릭스 값을 의미하고, 기준값 N 이상인지 여부를 판단하는 것을 특징으로 한다. The method of determining whether the sum of the values passing the reliability test among the vectors of the update matrix is equal to or greater than the reference value corresponds to the conditional expression of Equation 10 above.

, Where m is

More than

K is the order of subcarriers,

Is the frequency axis weight, and

Denotes an update matrix value of Equation 9 and is characterized by determining whether or not the reference value N or more.

,

및

로 설정되어 있다. 다만 이는 사용자가 채널 환경에 따라 다른 값으로 설정할 수 있다.Here in one embodiment of the present invention

,

And

Is set to. However, this value can be set by the user according to the channel environment.

,

및

는 종래의 CDP 방법과 동일하다. 그러므로 수학식 10의 본 발명은 종래의 CDP 기법을 포함하는 일반화된 기법이라 할 수 있다.Also one embodiment of the present invention

,

And

Is the same as the conventional CDP method. Therefore, the present invention of Equation 10 may be referred to as a generalized technique including a conventional CDP technique.

로, 여기서

는 종래의 CDP 기법에 따른 i번째(여기서, i는 1 이상의 자연수) 채널 추정값,

는 업데이트 매트릭스 값 및 k는 부반송파의 차수를 의미하며, 상기 업데이트 매트릭스의 벡터들 중 신뢰도 테스트를 통과한 값의 합이 기준값 이상인 경우 (즉,

을 만족할 경우), 상기 산출된 가중치 합으로 새로운 채널 추정값으로 결정하는 것을 특징으로 한다.In addition, the weighted sum is expressed by Equation 10

Where,

Is the i-th channel where i is a natural number of 1 or more according to the conventional CDP technique,

Is the update matrix value and k is the order of the subcarriers, and if the sum of the values that passed the reliability test among the vectors of the update matrix is greater than or equal to the reference value (that is,

If satisfactory), the new channel estimate is determined based on the calculated weighted sum.

를 구한다(수학식 10). 수학식 10에서

이고

인 경우, 조건

를 만족할 때에만 k번째 채널 추정값인

와 주파수 도메인에서 인접한 두 개의 채널 추정 값의 가중치를

과

을 고려하여

를 결정한다. 반면에

를 만족하지 않는 경우는 주파수축 상에 새롭게 업데이트된 채널 추정값이 없다고 판단하여 과거에 추정된 채널값

를 사용한다.In more detail, the correlation between subcarriers adjacent to the frequency axis

(Eq. 10). In equation (10)

ego

If is a condition

The k-th channel estimate only when

The weights of two adjacent channel estimates in the and

and

Considering

Determine. On the other hand

If does not satisfy, it is determined that there is no newly updated channel estimate on the frequency axis,

Use

5 is an IEEE 802.11p WAVE packet structure.

2 is a block diagram of a system using a method for estimating a time and frequency domain based on an update weight matrix in an OFDM system according to the present invention.

Each configuration relates to a channel estimation system in a time and frequency domain, and includes an i-th (where i is a natural number of 1 or more) OFDM in a packet using a reliability test using correlation of a plurality of adjacent data symbols in the time domain. A calculation unit for determining an i-th channel estimate value and an update matrix, which are channel estimates of the data symbols, a determination unit that determines whether the sum of the update matrix that has passed the reliability test corresponds to a reference value or more, and a determination result of the determination unit In accordance with the present invention, the channel estimation system of the time and frequency domain, characterized in that it comprises a decision unit for determining a new channel estimate value.

The calculation unit 100 of the present invention is characterized in that the channel of a plurality of adjacent symbols in the time and frequency domain calculates a channel estimate using similar characteristics and pilots on the frequency axis together.

The channel estimation method according to the present invention is superior to the conventional CDP channel estimation scheme because it can utilize more accurate channel estimates by using the similarity between the channels of two adjacent symbols in the time and frequency domain and the pilots on the frequency axis. Shows performance. In addition, a technique for weighting the channel estimates of reliable data pilots using an update matrix is used.

This results in higher performance than CDP, which uses the existing channel estimates for unreliable data pilots.

The embodiments described above are just one example, and various modifications and changes may be made by those skilled in the art without departing from the essential characteristics of the present invention. Therefore, the embodiments disclosed in the present invention are not intended to limit the technical idea of the present invention but to describe the present invention, and the scope of the technical idea of the present invention is not limited thereto. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

100: output unit
200: judgment
300: decision

Claims (8)

Calculating an i-th channel estimate and an update matrix, which are channel estimates of the i-th (where i is a natural number of 1 or more) OFDM data symbols in the packet using a reliability test using correlation of a plurality of adjacent data symbols in the time domain;
Determining the i-th channel estimate as a new channel estimate when the sum of values passed through a reliability test among the vectors of the update matrix is less than a reference value; And
When the sum of the values that pass the reliability test among the vectors of the update matrix is equal to or greater than a reference value, the weighted sum of the i-th channel estimate is determined as the new channel estimate using the i-th channel estimate and the weighted sum included in the update matrix. Comprising;
The method of determining whether the sum of the values passed through the reliability test among the vectors of the update matrix is equal to or greater than a reference value may include:
Using the following equation,

Where m is

More than

K is the order of subcarriers and

Denotes an update matrix value, and determines whether the equation is equal to or greater than a reference value. The method of claim 1,
The calculating of the i th channel estimate value and the update matrix may include:
A channel estimation method in a time and frequency domain, wherein a channel of a plurality of adjacent symbols in the time and frequency domain uses a similar characteristic and pilots on the frequency axis together to calculate a channel estimate. delete The method of claim 1,
The weighted sum is equal to the following equation,

here

Is the i-th channel where i is a natural number of 1 or more according to the conventional CDP technique,

Is the update matrix value, and k is the order of subcarriers,
If the sum of the values that pass the reliability test among the vectors of the update matrix is greater than or equal to the reference value (that is,

If satisfied), the channel estimation method of the time and frequency domain characterized in that it is determined as a new channel estimate value using the calculated weighted sum. A calculation unit for determining an i-th channel estimate and an update matrix, which are channel estimates of the i-th (where i is a natural number of 1 or more) OFDM data symbols in a packet by using a reliability test using correlation of a plurality of adjacent data symbols in the time domain. ;
A determination unit that determines whether the sum of the values passing the reliability test among the vectors of the update matrix is equal to or greater than a reference value; And
And a determination unit determining a new channel estimate value according to the determination result of the determination unit.
The determination unit,
Using the following equation,

Where m is

More than

K is the order of subcarriers and

Denotes an update matrix value and determines whether the equation is equal to or greater than a reference value. The method of claim 5,
The calculation unit,
A channel estimation system in the time and frequency domain, wherein a channel of a plurality of adjacent symbols in the time and frequency domain calculates a channel estimate using similar characteristics and pilots on the frequency. delete The method of claim 5,
The weighted sum in the determination unit is equal to the following equation,

here

Is the i-th channel where i is a natural number of 1 or more according to the conventional CDP technique,

Is the update matrix value and k is the order of the subcarriers, and if the sum of the values that passed the reliability test among the vectors of the update matrix is greater than or equal to the reference value (that is,

If satisfied, the new channel estimation value is determined by using the calculated weighted sum.

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