KR101373667B1 - A device and method for channel estimation - Google Patents

Abstract

According to an aspect of the present invention, there is provided a method for estimating a channel that changes over time in a WLAN system, the method comprising: selecting a data symbol to be used as a co-pilot based on a position of a constellation in a received signal; Estimating a channel using the method.

Description

Channel estimation method and apparatus that changes with time in a WLAN system

The present invention relates to a method for estimating a channel in a wireless LAN system.

Recently, telematics technology that provides safety information and additional services using vehicle-to-vehicle or vehicle-to-frafra communication has been in the spotlight. The IEEE 802.11p standard, which is a standard for this, is designed to support high-speed packet transmission in a vehicular mobile environment based on WLAN. What is different from the existing IEEE 802.11a standard is that the bandwidth is lowered by 10 MHz to reduce the Doppler effect on the move, and the transmission rate is also cut in half.

When considering only the indoor environment, such as the service of the IEEE 802.11a standard, since there is almost no channel change, using the channel estimated until the end of a packet using the channel estimated by the long preamble is not a big problem. Therefore, the IEEE 802.11a receiving end has no function of updating the channel estimation result. However, to support high-speed movement, as in the IEEE 802.11p standard, it is necessary to estimate a channel that changes over time.

An object of the present invention is to provide a channel estimation method that changes rapidly with time in the IEEE 802.11p standard.

In one embodiment of the present invention, a method for estimating a channel that changes over time in a WLAN system, the method comprising: selecting a data symbol to be used as a co-pilot based on a position of a constellation in a received signal; Estimating a channel using the selected data symbol.

In one embodiment of the present invention, the received signal may be a channel estimation method, characterized in that the signal based on the IEEE 802.11p standard.

In an embodiment of the present invention, the selecting of the data symbol may include selecting a data symbol having a large signal strength (located outside, far from the origin) on an M-QAM based constellation; It may be a channel estimation method.

In the embodiment of the present invention, the selecting of the data symbol may include selecting a data symbol having an M-QAM based constellation of 16-QAM based constellation and an amplitude of a data symbol of the received signal of 0.8 or more. It may be a channel estimation method characterized in that;

In the embodiment of the present invention, the selecting of the data symbol may include: the M-QAM based constellation is 16-QAM based constellation, and the bit of the received signal is one of 0101, 0111, 1101, 1111. Selecting a data symbol which is any one of 0001, 0011, 0100, 0110, 1001, 1011, 1100, and 1110; It may be a channel estimation method characterized in that.

In an embodiment of the present invention, an apparatus for estimating a channel that changes over time in a WLAN system includes: data selection for selecting a data symbol to be used as a co-pilot based on a constellation position of a received signal part; And a channel estimator for estimating a channel using the selected data symbol.

In one embodiment of the present invention, the received signal may be a channel estimation device, characterized in that the signal based on the IEEE 802.11p standard.

In one embodiment of the present invention, the channel estimating unit may be a channel estimating apparatus for selecting a data symbol having a large signal strength (outwardly located, far from the origin) on an M-QAM-based constellation.

In one embodiment of the present invention, the channel estimating unit may be a channel estimating apparatus for selecting a data symbol whose M-QAM based constellation is 16-QAM based constellation and whose amplitude of the data symbol of the received signal is 0.8 or more. have.

In one embodiment of the present invention, the channel estimator is the M-QAM based constellation is 16-QAM based constellation, and the bit of the received signal is one of 0101, 0111, 1101, 1111, or 0001, 0011 , 0100, 0110, 1001, 1011, 1100, and 1110. The channel estimation apparatus may select a data symbol.

In one embodiment of the present invention, a WLAN system using the IEEE 802.11p communication standard, comprising: a receiving unit for receiving a transmitted signal; An FFT unit for fast Fourier transforming the received signal; A reconstruction unit for demodulating the fast Fourier transformed signal; A data selector which selects a data symbol to be used as a co-pilot based on the constellation position of the demodulated signal; And a channel estimator for estimating a channel by using the selected data symbol.

According to an embodiment of the present invention, the mobility of the transmitting end and the receiving end can be further increased based on the improved channel estimation in a channel that changes rapidly with time as compared with the prior art.

According to an embodiment of the present invention, it is possible to receive more reliable data by improving the performance of channel estimation when moving in car-to-car or car-to-car communication.

1 shows a packet structure of the IEEE 802.11p standard.
2 illustrates a conventional channel estimation method using a pilot.
3 (a) illustrates a method of selecting a data symbol to be used as a co-pilot in a channel estimation method according to an embodiment of the present invention.
3 (b) illustrates a method of selecting a data symbol to be used as a co-pilot in a channel estimation method according to an embodiment of the present invention.
4 (a) shows mapping bits of constellations based on 8-QAM in the channel estimation method according to an embodiment of the present invention.
4 (b) shows mapping bits of constellations based on 16-QAM in the channel estimation method according to an embodiment of the present invention.
4 (c) shows mapping bits of constellations based on 32-QAM in the channel estimation method according to an embodiment of the present invention.
4 (d) shows mapping bits of constellations based on 64-QAM in a channel estimation method according to an embodiment of the present invention.
Figure 5 shows the amplitude of each signal in the 16-QAM based constellation in the channel estimation method according to an embodiment of the present invention.
6 is a diagram illustrating a method of selecting a data symbol to be used as a co-pilot in the channel estimation method according to an embodiment of the present invention.
7 illustrates a configuration diagram of an apparatus for estimating a channel according to an embodiment of the present invention.

Other advantages and features of the present invention and methods of achieving them will become apparent with reference to the embodiments described below in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims.

Unless defined otherwise, all terms (including technical or scientific terms) used herein have the same meaning as commonly accepted by the generic art in the prior art to which this invention belongs. Terms defined by generic dictionaries may be interpreted to have the same meaning as in the related art and / or in the text of this application, and may be conceptualized or overly formalized, even if not expressly defined herein I will not.

The terminology used herein is for the purpose of illustrating embodiments and is not intended to be limiting of the present invention. In the present specification, the singular form includes plural forms unless otherwise specified in the specification. As used herein, the terms' comprise 'and / or various forms of use of the verb include, for example,' including, '' including, '' including, '' including, Steps, operations, and / or elements do not preclude the presence or addition of one or more other compositions, components, components, steps, operations, and / or components.

The term 'and / or' as used herein refers to each of the listed configurations or various combinations thereof.

It should be noted that the terms such as '~', '~ period', '~ block', 'module', etc. used in the entire specification may mean a unit for processing at least one function or operation. For example, a hardware component, such as a software, FPGA, or ASIC. However, '~ part', '~ period', '~ block', '~ module' are not meant to be limited to software or hardware. Modules may be configured to be addressable storage media and may be configured to play one or more processors. ≪ RTI ID = 0.0 > Thus, by way of example, the terms 'to', 'to', 'to block', 'to module' may refer to components such as software components, object oriented software components, class components and task components Microcode, circuitry, data, databases, data structures, tables, arrays, and the like, as well as components, Variables. The functions provided in the components and in the sections ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ' , '~', '~', '~', '~', And '~' modules with additional components.

The packet structure of IEEE 802.11p is shown in FIG. Here, the first ten short training signals t ₁ to t ₁₀ are used for synchronization, and the following long training symbols T ₁ and T ₂ are used for channel estimation. Each data symbol following the training symbol includes a guard interval. The SIGNAL section, which is the first data symbol, contains information on the modulation scheme and length of the packet.

The most widely used channel estimation method in the existing WLAN standard is as follows. This method, called Least Square channel estimation, uses a preamble only at the beginning of a packet to estimate the channel and then compensates for later signals based on the result. The pilot signal in the packet is also used to compensate for the remaining frequency offset. This channel compensation method is widely used in IEEE 802.11a because it is intuitive and easy to implement.

When each of the long training symbols on the time axis is T ₁ [n] and T ₂ [n], the Least Square channel estimation method using the long training signals is as follows.

Where Y ₁ (k) and Y ₂ (k) are the N-point DFTs of T ₁ [n] and T ₂ [n], respectively, X (k) is the pre-scheduled long training symbol and H (k) is estimated Channel. A method of 1-tap compensation on each subcarrier for a received signal using the estimated channel as described above is as follows.

Where S _R (k) is the received signal and S _T '(k) is the compensated signal.

In the above-described Least Square channel estimation method, there is a problem in that the estimated channel H (k) becomes inaccurate as the actual channel changes toward the second half of the packet.

2 illustrates a method of estimating a channel using a pilot signal to compensate for this. The IEEE 802.11p standard packet contains four pilot subcarriers. A method of estimating a channel using this is as follows.

Where Y _p (k) and X _p (k) are respectively a received pilot signal and a predetermined pilot signal, and H _p and m _Hp are average values of the estimated pilot channel and pilot channel, respectively. The estimated H _p 'is increased by linear interpolation and the final channel is estimated using the estimated channel of the previous symbol.

Where H (k) is the estimated channel of the k th symbol, H _p ″ is the result of linear interpolation of the channel of the pilot signal. The estimated channel is used to correct the signal as shown in Equation 4.

3 illustrates a decision directed channel estimation method. Instead of pilot, the data is used as a co-pilot to find an estimate and periodically estimate the channels for all subcarriers to adapt to changing channels. In the decision-oriented channel estimation method, the channel is estimated using the following equation.

는 수신된 신호이고,

는 이전에 추정한 채널이다. 수신된 신호를 이전에 추정한 채널로 나누어서 보상된 신호인

를 구할 수 있다.here

Is the received signal,

Is the previously estimated channel. The received signal divided by the previously estimated channel

Can be obtained.

를 복조(demodulation)하여 복조된 비트(detected bits)를 구하고 이를 다시 재변조(re-modulation) 하여 추정된 실제 신호인

를 구할 수 있고, 수신된 신호인

를 추정된 실제 신호인

로 나누어서 현재 채널인

를 추정할 수 있다.
Compensated signal

Is demodulated to obtain the detected bits and re-modulated again to obtain the estimated actual signal.

Is obtained, and the received signal

Is the estimated actual signal

Divided by the current channel,

Can be estimated.

를 추정한 후 코 파일럿(Co-Pilot)을 이용한 채널 추정은 수학식 9에 따라 이루어진다.

After estimating, channel estimation using a co-pilot is performed according to Equation 9.

는 데이터 심볼의 매핑 인덱스를 의미하고

는 매핑 인덱스가

일 때 코 파일럿(Co-Pilot)을 이용하여 추정된 채널을 의미한다.

는 매핑 인덱스가

인 데이터 심볼로부터

만큼 떨어진 데이터 심볼을 채널 추정에 이용함에 있어서 가중치를 의미한다.

가 작을수록 큰 값을 지니게 된다.

는

를 추정할 때 이용될 앞뒤의 데이터 심볼의 수를 의미한다. 예를 들어, 도 3의 (a)에서 보는 바와 같이 코 파일럿(Co-Pilot)이 7번째 마다 반복되는 경우 사이에 데이터 심볼은 6개 이므로 코 파일럿(Co-Pilot)을 이용하여 채널을 추정할 때 코 파일럿(Co-Pilot) 앞뒤로 3개의 데이터 심볼을 이용하여 채널을 추정하게 되므로

는 3이 된다.From here

Means the mapping index of the data symbol

Has a mapping index

In this case, the channel is estimated by using a co-pilot.

Has a mapping index

From data symbols

It means a weight in using data symbols spaced apart by channel estimation.

The smaller is, the larger the value is.

The

Means the number of data symbols before and after to be used. For example, as shown in (a) of FIG. 3, since six co-pilots are repeated every seventh time, six data symbols are used to estimate a channel using a co-pilot. In this case, the channel is estimated using three data symbols before and after the co-pilot.

Becomes 3.

이고

을 구한다면

가 될 것이다.
if,

ego

If you get

.

This method also takes advantage of the high correlation between adjacent symbols, assuming that the channel changes relatively slowly. Therefore, when used in the IEEE 802.11p standard that can communicate at speeds of 200km / h or more, if there is an error in the data will cause severe performance degradation. Therefore, lowering the data error rate is an important factor in improving channel estimation performance.

이 되어 M 값에 따라 심볼의 비트수가 결정되게 된다. 예를 들어, 16-QAM은 4비트가 한 심볼로 변조되어 전송되는 방식이다.
Quadrature Amplitude Modulation (QAM) is an orthogonal amplitude modulation that modulates using the amplitudes of the real and imaginary parts. M is the number of constellations in the constellation, and the number of bits per symbol is

The number of bits of the symbol is determined according to the M value. For example, 16-QAM is a method in which four bits are modulated into one symbol and transmitted.

4 (a) to 4 (d) show respective constellations based on M-QAM. 4 (a) is an 8-QAM based constellation, FIG. 4 (b) is a 16-QAM based constellation, FIG. 4 (c) is a 32-QAM based constellation, and FIG. 4 (d) is 64- It represents a position mapped according to a bit of a symbol on a QAM-based constellation. QAM-based constellations use gray codes to minimize bit errors. As shown in Figure 4 (a) to 4 (d) it can be seen that the bit difference between the upper, lower, left and right of each constellation point by one bit.

As described above, in the decision-oriented channel estimation method of estimating a channel using data as a pilot, an error of data affects channel estimation performance. Therefore, in an embodiment of the present invention, channel estimation performance may be improved by selecting a signal having a low probability of error of data based on a position on the constellation of the received signal. The farther the position on the constellation of the received signal is from the origin of the constellation, the greater the intensity (amplitude) of the signal, so that the probability of error of the received signal is lowered. Therefore, in an embodiment of the present invention, when the amplitude of the received signal is greater than a certain value or the received signal is more than a certain distance in the constellation and is at the edge, it is modulated again and used for channel estimation.

Hereinafter, a method of selecting a data symbol according to an embodiment of the present invention in a 16-QAM based constellation will be described. Although only the 16-QAM-based constellation is described herein, this is shown as an example for clarity, and M-QAM such as 8-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM, etc. Based or other modulation scheme based.

5 illustrates constellations and amplitudes based on 16-QAM in the channel estimation method according to an embodiment of the present invention. In 16-QAM, when the data symbol is 4 bits and 4 bits are each Q ₁ Q ₂ I ₁ I ₂ , the first bit (Q ₁ ) and the third bit (I ₁ ) determine the polarity, and the second bit (Q ₂ ) and the fourth bit (I ₂ ) represent the amplitude. If the first bit (Q ₁ ) and the third bit (I ₁ ) are 1 (+), if the 0 is (-), if the second bit (Q ₂ ) and the fourth bit (I ₂ ) are 1, 0.821V, 0 means 0.22V. In sum, these truth tables are determined.

I channel




Q channel I ₁ I ₂ Output (V) Q ₁ Q ₂ Output (V) 0 0 -0.22 0 0 -0.22 0 One -0.821 0 One -0.821 One 0 +0.22 One 0 +0.22 One One +0.821 One One +0.821

이고 진폭은

, 위상은

가 된다. 이에 따라 진폭은 0.311, 0.850. 1.161로 세 가지 경우가 생기게 된다. 따라서, 0000~1111까지 모두 대입하면 표 2와 같은 진리표가 만들어진다.Since there are four cases each for the I and Q channels, the result is 16 cases. The general formula is

And amplitude is

, Phase is

. As a result, the amplitude is 0.311, 0.850. There are three cases with 1.161. Therefore, substituting all the numbers from 0000 to 1111 produces the truth table shown in Table 2.

Binary input 16-QAM output Q ₁ Q ₂ I ₁ I ₂ 0 0 0 0 0.311V -135 ° 0 0 0 One 0.850 V -165 ° 0 0 One 0 0.311V -45 ° 0 0 One One 0.850 V -15 ° 0 One 0 0 0.850 V -105 ° 0 One 0 One 1.161 V -135 ° 0 One One 0 0.850 V -75 ° 0 One One One 1.161 V -45 ° One 0 0 0 0.311V 135 ° One 0 0 0 0.850 V 165 ° One 0 One 0 0.850 V 45 ° One 0 One One 0.311V 15 ° One One 0 0 0.850 V 105 ° One One 0 One 1.161 V 135 ° One One One 0 0.850 V 75 ° One One One One 1.161 V 45 °

FIG. 6 illustrates a method of selecting a data symbol to be used as a co-pilot on a 16-QAM based constellation in a channel estimation method according to an embodiment of the present invention. If the received signal has a pilot signal, the channel is first estimated using a known pilot signal. In addition, in an embodiment of the present invention, data is classified based on the strength (amplitude) of the received signal in the 16-QAM based constellation. When grouping four signals of 1.161V located in the outermost group into Group I, and eight signals of 0.850V into Group II and four signals of Group II and 0.311V into Group III, First and foremost, select the data you want to use as a Co-Pilot, then select it in Group II. The channel may be estimated using Equations 8 to 9 using the selected data signal.

By using data with a large signal strength, the influence of Additive White Gaussian Noise (AWGN), which is a major factor in performance degradation, can be reduced, and more reliable data can be obtained.

In the case of 32-QAM and 64-QAM based on FIGS. 4 (c) and 4 (d), the signals located at the edges are classified based on the strength (amplitude) of the received signal on the constellation map. -Pilot) can improve channel estimation performance.

7 exemplarily illustrates a configuration diagram of a channel estimating apparatus 400 and a receiver 1000 using a channel estimating method according to an embodiment of the present invention. The receiver 1000 may include a receiver 100, an FFT unit 200, a restorer 300, and a channel estimator 400. The channel estimator 400 may include a data selector 420 and a channel estimator. It may include the government 440.

When the transmitter transmits a signal through a channel, the receiver 100 receives the signal, performs fast Fourier transform on the FFT unit 200, and restores the converted signal on the restorer 300. The data selector 420 checks the position of the constellation in the reconstructed signal, selects a data symbol to be used as a co-pilot, and the channel estimation unit 440 estimates a channel using the selected data symbol and pilot. Done. The estimated channel is fed back to the receiver and used to receive the next signal.

It is to be understood that the above-described embodiments are provided to facilitate understanding of the present invention, and do not limit the scope of the present invention, and it is to be understood that various modified embodiments may be included within the scope of the present invention. For example, each component shown in the embodiment of the present invention may be distributed and implemented, and conversely, a plurality of distributed components may be combined. Therefore, the technical protection scope of the present invention should be determined by the technical idea of the claims, and the technical protection scope of the present invention is not limited to the literary description of the claims, The invention of a category.

1000: receiver
100:
200: FFT part
300: restoration unit
400: channel estimation device
420: data selector
440: channel estimation

Claims (10)

delete delete delete A method for estimating a channel that changes over time in a WLAN system,
Selecting a data symbol to be used as a co-pilot based on a constellation phase position based on a modulation method of the received signal;
Estimating a channel using the selected data symbol;
Lt; / RTI >
Selecting the data symbol is
The modulation scheme of the received signal is 16-QAM,
Selecting a data symbol whose amplitude is equal to or greater than 0.8 in a 16-QAM based constellation;
And a channel estimation method.
A method for estimating a channel that changes over time in a WLAN system,
Selecting a data symbol to be used as a co-pilot based on a constellation phase position based on a modulation method of the received signal;
Estimating a channel using the selected data symbol;
Lt; / RTI >
Selecting the data symbol is
The modulation scheme of the received signal is 16-QAM,
In 16-QAM based constellation, the bit of the received signal is any one of 0101, 0111, 1101, 1111, or
Selecting a data symbol which is any one of 0001, 0011, 0100, 0110, 1001, 1011, 1100, 1110;
And a channel estimation method. delete delete delete An apparatus for estimating a channel that changes with time in a WLAN system,
A data selector which selects a data symbol to be used as a co-pilot based on a constellation position of the received signal; And
A channel estimator for estimating a channel using the selected data symbol;
Lt; / RTI >
The modulation method of the received signal is 16-QAM,
The channel estimator selects a data symbol whose amplitude of the data symbol of the received signal is 0.8 or more on a 16-QAM based constellation.
An apparatus for estimating a channel that changes with time in a WLAN system,
A data selector which selects a data symbol to be used as a co-pilot based on a constellation position of the received signal; And
A channel estimator for estimating a channel using the selected data symbol;
Lt; / RTI >
The modulation method of the received signal is 16-QAM,
The channel estimator may be any one of bits 0101, 0111, 1101, and 1111 on the 16-QAM based constellation,
A channel estimating apparatus for selecting a data symbol which is any one of 0001, 0011, 0100, 0110, 1001, 1011, 1100, and 1110.

Images