WO2015152513A1

WO2015152513A1 - Apparatus for compensating center frequency in wireless lan

Info

Publication number: WO2015152513A1
Application number: PCT/KR2015/000872
Authority: WO
Inventors: 황용석; 장한용
Original assignee: 주식회사 아이앤씨테크놀로지
Priority date: 2014-04-01
Filing date: 2015-01-28
Publication date: 2015-10-08
Also published as: KR101444275B1

Abstract

The purpose of the present invention is to enable the center frequency of a primary upper frequency channel to be more accurately corrected by, when the center frequency is estimated and compensated in a wireless LAN, estimating the center frequency of a primary frequency channel and correcting an error and thereafter compensating the center frequency on the basis of the correction result. To this end, the present invention comprises: a center frequency estimator for estimating a center frequency error in a signal of the primary frequency channel outputted from a second low-pass filter; a center frequency corrector for correcting a correction value depending on the center frequency position in the center frequency error estimated by the center frequency estimator, calculating a correction value for each position of a primary lower frequency channel, and correcting, on the basis of the correction value, an offset resulting from a sampling frequency error; and a center frequency compensator for compensating a center frequency error for a signal of the primary upper frequency channel outputted from a first low-pass filter, using the center frequency error in the center frequency corrector.

Description

Center frequency compensation device of WLAN

The present invention relates to a technique for estimating and compensating a center frequency in a wireless LAN. In particular, when receiving a 40 MHz, 80 MHz, or 160 MHz signal, the center frequency error of the primary frequency channel is estimated, and the center frequency error value is sampled. The present invention relates to a center frequency compensation device of a wireless LAN capable of compensating for a center frequency of a 40 MHz, 80 MHz, and 160 MHz signal based on a correction result after an error.

In general, in a system using 802.11a / g / ac wireless LAN (WLAN), the center frequency error is estimated and compensated at the time of signal reception. For example, the center frequency error is estimated from a short train field (STF) symbol and a long train field (LTF) symbol, and the center frequency error is compensated from the LTF symbol. The LTF symbol is used for channel estimation, where the estimated channel value is then used to compensate the channel in the symbol. Therefore, the channel estimate is affected by the estimation accuracy for the center frequency error.

The correlation value of the repeated section in the STF and LTF symbols is used to estimate the center frequency error. The STF symbol repeats 16 samples 10 times, and the LTF symbol repeats 64 samples twice. For reference, as shown in Table 1 below, t _k corresponds to 16 samples, and T ₁ and T ₂ correspond to 64 samples.

Table 1

802.11ac uses bandwidths such as 20 MHz, 40 MHz, 80 MHz, and 160 MHz. For example, when using an 80 MHz band in 802.11ac, it is divided into 20 MHz and one of the four bandwidths is set as a primary 20 MHz channel.

The position of the primary channel may be recognized in advance by using the received beacon signal. There may be a signal on the primary 20 MHz channel, but no signal on the remaining channels. At the time of receiving the STF and LTF signals, it is not known through which bandwidth. Therefore, only the bandwidth of the primary 20 MHz channel should be considered, and the frequency estimation method can be used for the 20 MHz signal as in the 802.11a / g case.

However, in the conventional system, when compensating the center frequency of the primary channel, the center frequency is compensated using the compensation information obtained on the corresponding primary channel. For example, when compensating the center frequency of a primary 80 MHz channel, the center frequency of the 80 MHz channel is compensated using the compensation information obtained on the primary 20 MHz channel.

As described above, in the conventional WLAN system, when the center frequency of the received signal is compensated, the center frequency error of the received signal is compensated by using the center frequency error obtained from the primary channel. There is this.

The problem to be solved by the present invention is to estimate the frequency error in the primary channel when the signal is received, to compensate for the offset due to the sampling frequency error, and then to compensate the center frequency of the primary received signal using the result value .

In accordance with another aspect of the present invention, there is provided an apparatus for compensating a center frequency of a wireless LAN, comprising: an analog-to-digital converter for converting an analog intermediate frequency signal supplied through an antenna and a high frequency processing unit into a digital signal; A first low pass filter for low pass filtering the signal output from the analog to digital converter; A second low pass filter for low-pass filtering the signal of the primary frequency channel from the signal output from the analog-to-digital converter; A center frequency estimator estimating a center frequency error in the signal of the primary frequency channel output from the second low pass filter; A center frequency corrector for calculating a correction value using the position of the primary frequency channel and the sampling frequency error from the center frequency error estimated by the center frequency estimator, and correcting the center frequency error based on the correction value; And a center frequency compensator configured to compensate for a center frequency error with respect to the signal output from the first low pass filter using the center frequency error in the center frequency corrector.

The present invention estimates the center frequency error of the primary frequency channel when the signal of the primary channel is received, corrects the offset due to the sampling frequency error, and then compensates the center frequency of the received signal using the correction information, thereby receiving the received signal. There is an effect that can be corrected more precisely the center frequency error of.

1 is a block diagram of a center frequency compensation device of a wireless LAN according to an embodiment of the present invention.

2 is a diagram illustrating a section of a primary 20 MHz channel.

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

1 is a block diagram of a center frequency compensator of a wireless LAN according to an embodiment of the present invention. As shown in FIG. 1, the center frequency compensator 100 includes an analog-to-digital converter (ADC) 110 and a first low pass filter. 120, a second low pass filter 130, a center frequency estimator 140, a center frequency corrector 150, a center frequency compensator 160, and a fast Fourier transform (FFT) 170. do.

The analog-to-digital converter 110 converts an analog signal supplied through an antenna and a radio frequency (RF) processor (not shown) into a digital signal. The sampling frequency of the analog to digital converter 110 may be twice the bandwidth.

The first low pass filter 120 low-pass filters a signal having a predetermined frequency, for example, an 80 MHz signal, from among the signals output from the analog-to-digital converter 110.

When the signal of a predetermined frequency is output from the analog-to-digital converter 110, for example, when the primary 80 MHz signal is output, the second low pass filter 130 may output a signal of the primary frequency channel, for example, primary. Low-pass filtering the signal of 20MHz channel.

The center frequency estimator 140 estimates a center frequency error in the signal of the primary 20 MHz channel output from the second low pass filter 130.

The center frequency corrector 150 corrects a correction value according to the center frequency position in the center frequency error estimated by the center frequency estimator 140. In this case, the center frequency corrector 150 calculates a position-specific correction value of the primary 20 MHz channel and corrects an offset due to a sampling frequency error based on the correction value.

The center frequency compensator 160 compensates for the center frequency error of the signal of the 80 MHz channel output from the first low pass filter 120 using the center frequency error of the center frequency corrector 150.

As described above, in an 802.11ac WLAN to which the present invention is applied, a frequency error of a symbol subsequent to a long train field (LTF) symbol is compensated for by using a center frequency error obtained from a primary 20 MHz channel. do. When compensating for an errored frequency error estimate, an error appears in the channel estimate. In practice, there is an offset in the center frequency error estimate depending on the position of the primary 20 MHz channel. The section of the primary 20MHz channel may be located as shown in FIG.

In FIG. 2, when the first channel section D1 or the fourth channel section D4 is the primary 20 MHz channel section, the second channel section D2 or the third channel section D3 is the primary 20 MHz channel section. Compared to this, there is a larger offset in the center frequency error estimate. This is because the offset is determined by the sampling frequency along with the center frequency error. Because.

An example of the case where there is no center frequency error but only a sampling frequency error will be described below.

Since the center frequency and the sampling frequency are generated from the same oscillator, the center frequency error can be expressed as a constant product of the sampling frequency errors. For example, if the sampling frequency error is Δf _s when sampling the signal received from the antenna at 160 MHz, the center frequency error of the 20 MHz channel sections D1, D2, D3, and D4 in FIG. 2 is −Δf _s. * 3/8,-DELTA f _s / 8, DELTA f _s / 8, DELTA f _s * 3/8 can be estimated to exist.

At this time, when a center frequency error Δf _c is present, the center frequency error Δf _c is Δf _c -Δf _s * 3/8, Δf _c -Δf _s / 8, Δf _c It can be estimated as + Δf _s / 8, Δf _c + Δf _s * 3/8.

In this case, for example, when the primary 20MHz channel is located in the first channel section D1 in FIG. 2, Δf _c -Δf _s * 3/8 is estimated as the center frequency error, and the compensation is performed. The residual center frequency errors in each channel section D1, D2, D3, and D4 may be estimated as 0, Δf _s * 2/8, Δf _s * 4/8, and Δf _s * 6/8.

For another example, when the primary 20MHz channel is located in the second section D2, Δf _c -Δf _s / 8 is estimated as the center frequency error, and each channel is corrected after the center frequency error is corrected. interval remaining center frequency error in the (D1, D2, D3, D4 ) , respectively - may be estimated by _{△ f s * 4/8 -} △ f s * 2/8, 0, △ f s * 2/8,.

In particular, when the center frequency error is large, the signal-to-noise ratio (SNR) is high, and the received signal is modulated using a high modulation rate, performance loss may occur due to the residual center frequency error Δf _s * 6/8.

For this reason, it can be concluded that compensating the frequency error in the received signal after correcting the sampling frequency error in the estimated center frequency error as described in FIG. 1 has a good effect on the reception performance improvement.

Table 2 below shows an example of correction values for the center frequency channel sections D1, D2, D3, and D4 in an 80 MHz received signal. Even for a 160 MHz received signal, a correction value for each center frequency channel section D1, D2, D3, or D4 can be calculated in the same manner as in the 80 MHz received signal.

TABLE 2

Accordingly, in the embodiment of the present invention, when receiving a received signal, for example, an 80 MHz signal in the 802.11ac receiver, as shown in FIG. 1, the center frequency error is estimated after separating the signal of the primary 20 MHz channel therefrom. By correcting the offset due to sampling frequency error, the center frequency error of the 80MHz channel is compensated for.

Although the preferred embodiment of the present invention has been described in detail above, the scope of the present invention is not limited thereto, and may be implemented in various embodiments based on the basic concept of the present invention defined in the following claims. Such embodiments are also within the scope of the present invention.

Claims

An analog to digital converter for converting an analog intermediate frequency signal supplied through an antenna and a high frequency processing unit into a digital signal;

A first low pass filter for low pass filtering the signal output from the analog to digital converter;

A second low pass filter for low-pass filtering the signal of the primary frequency channel from the signal output from the analog-to-digital converter;

A center frequency estimator estimating a center frequency error in the signal of the primary frequency channel output from the second low pass filter;

Correct the correction value according to the center frequency position from the center frequency error estimated by the center frequency estimator, calculate the correction value for each position of the primary frequency channel, and correct the offset due to the sampling frequency error based on the correction value. A center frequency corrector; And

And a center frequency compensator for compensating for a center frequency error with respect to a signal output from the first low pass filter using the center frequency error in the center frequency corrector.
The apparatus of claim 1, wherein the primary frequency channel signal is a primary 20MHz channel signal.
The apparatus of claim 1, wherein the signal of the primary frequency channel is a signal of an 80 MHz channel.
2. The center frequency error of claim 1, wherein the center frequency estimator sets the sampling frequency error as Δf s when sampling the signal received through the analog-to-digital converter at 160 MHz. s * 3/8, - △ f s / 8, △ f s / 8, △ f s * 3/8 exists, the wireless LAN device of the center frequency compensation, characterized in that the estimated that as much.
The method of claim 4, wherein when said center frequency estimator is the center frequency offset △ f c present, △ f c - △ f s * 3/8, △ f c - △ f s / 8, △ f c + △ f and a center frequency error of s / 8, Δf c + Δf s * 3/8.