KR100530262B1 - An apparatus for Phase Noise Suppression in the Wireless LAN Systems, and a method thereof - Google Patents

Abstract

The present invention relates to an apparatus and method for removing phase noise of a wireless LAN system.

An apparatus for canceling phase noise in an orthogonal frequency division multiplexing (OFDM) wireless LAN system using several tens of gigabytes, comprising: an adder for adding channel added noise to a transmitted / received OFDM signal; A multiplier multiplying the OFDM signal to which the channel additional noise is added by the phase noise generated in the oscillators of the transmitter and the receiver; And a phase noise removing unit for estimating a phase noise power initial value and a phase noise change rate from the OFDM signal to which the channel additional noise and the phase noise are added to remove phase noise by a minimum mean square error (MMSE) method. Phase Noise Suppression (PNS).

According to the present invention, it is possible to prevent performance degradation caused by phase noise in a 60 GHz OFDM WLAN system.

Description

An apparatus for phase noise suppression of a wireless LAN system and a method thereof

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and method for canceling phase noise for a wireless LAN system. More particularly, in an orthogonal frequency division multiplexing (OFDM) wireless LAN system using tens of gigabytes, The present invention relates to a phase noise canceling apparatus and method for a wireless LAN system that efficiently removes phase noise generated at a transmitting end and a receiving end resulting in performance degradation.

Under the assumption that the phase noise is very small in the conventional OFDM system If the phase noise is analyzed by using, but the phase noise of the oscillator of the transmitter / receiver has a value that cannot be ignored, more accurate analysis should be performed.

In other words, both the phase noise of the transceiver and the additional noise of the channel should be considered. In the conventional noise reduction method, reliability and stability are inferior in estimating various necessary parameters. Therefore, there is a need for a phase noise cancellation method based on a more accurate noise cancellation analysis.

On the other hand, as a prior art, a paper entitled "A phase noise suppression algorithm for OFDM-based WLANs" was published by S. Wu et al. In December 2002 on pages 6, 535 to 537 of IEEE Communication Letters. In order to eliminate phase noise in a system, a MMSE-based phase noise canceller based on an attenuation factor of an approximated SNR is disclosed, and it is disclosed that phase noise can be eliminated in an OFDM WLAN system in a 5 GHz band.

However, according to the previous paper, an MMSE-based phase noise canceller based on the attenuation factor of the approximated SNR under the assumption that the phase noise is very small, the OFDM WLAN system using several tens of giga bands with more phase noise The problem is serious to apply.

Therefore, the technical problem to be achieved by the present invention is to solve the conventional problems, and to overcome the performance degradation caused by the phase noise in a wireless LAN system, in particular 60 GHz wireless LAN system and a phase noise removing device and method thereof It is to provide.

Another object of the present invention is to provide an apparatus and method for removing phase noise of a wireless LAN system that can be easily implemented.

In order to achieve the above technical problem, a phase noise removing apparatus of a wireless LAN system according to an aspect of the present invention, in the OFDM (Orthogonal Frequency Division Multiplexing) wireless communication system using several tens of gigabytes, adding a channel to the transmitted and received OFDM signal An adder for adding noise; A multiplier multiplying the OFDM signal to which the channel additional noise is added by the phase noise generated in the oscillators of the transmitter and the receiver; And a phase noise removing unit for estimating a phase noise power initial value and a phase noise change rate from the OFDM signal to which the channel additional noise and the phase noise are added to remove phase noise by a minimum mean square error (MMSE) method. Phase Noise Suppression (PNS).

The phase noise canceller may include: a channel estimator estimating a channel from the OFDM signal to which the channel additive noise and the phase noise are added; A CPE estimator estimating a common phase error (CPE) from the OFDM signal to which the channel additive noise and the phase noise are added; An ICI and noise power estimator for estimating inter-carrier interference (ICI) and noise power components from the OFDM signal to which the channel additional noise and phase noise are added; And an MMSE equalizer for correcting a distortion characteristic of the channel in a minimum mean square error (MMSE) scheme with respect to the estimated OFDM signal of the channel.

In this case, the initial phase noise power value may be obtained using a preamble of a periodically generated broadcast signal, and may be estimated using pilot symbols included in one OFDM symbol. In addition, the phase noise change rate may be estimated by approximating the energy of the inter-carrier interference (ICI) when the signal-to-noise ratio (SNR) is large.

On the other hand, the phase noise removal method for a wireless LAN system according to another aspect of the present invention, in the phase noise removal method of an OFDM wireless communication system using several tens of gigabytes, adding the channel addition noise to the transmitted and received OFDM signal ; Multiplying the OFDM signal to which the channel additional noise is added by the phase noise generated in the oscillators of the transmitter and the receiver; And estimating a phase noise power initial value and a phase noise change rate from the OFDM signal to which the channel additional noise and the phase noise are added to remove phase noise by a minimum mean square error (MMSE) method.

According to the present invention, in order to reduce the complexity and improve the performance of the conventional scheme, by constructing a MMSE-based phase noise canceller based on the precise analysis of the attenuation factor of the SNR, it is possible to stably remove phase noise in an OFDM WLAN system. It becomes possible.

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

In general, an OFDM system is robust to a multipath environment, and thus many researches and applications have been made in a communication system. However, due to the non-ideal characteristics of the RF stage, such as phase noise, frequency offset, and peak to averaged power ratio (PAPR), performance deteriorates a lot. Among them, the phase noise generated in the local oscillator of the transmitting and receiving end acts as a factor to increase the ICI which damages the orthogonality between subcarriers of the OFDM system.

The present invention analyzes the theoretical analysis of phase noise in a 60 GHz wireless LAN system and analyzes SNR degradation in terms of SNR in an OFDM system, and proposes a method for overcoming the SNR degradation.

1 is a block diagram showing the configuration of a 60 GHz OFDM wireless LAN system, and FIG. 2 is a block diagram showing the configuration of an OFDM system simplified in consideration of phase noise in a 60 GHz OFDM wireless LAN system according to the present invention.

As shown in FIG. 1, a typical 60 kHz OFDM wireless LAN system, as a transmitter, first includes a scrambling / FEC coding / interleaving block 111, a QAM mapping block 112, and a pilot insertion block in front of the IFFT block 120. 133, a serial / parallel converter (S / P: 134) is provided, and after passing through the IFFT 120, a parallel / serial converter (P / S: 131), a CP (Cyclic Prefix) additional block 132 The transmission is made via the DAC 133, the IQ demodulator 134, the multiplier 136, and the HPA 138, where reference numerals 135 and 137 denote local oscillators that generate phase noise.

In addition, as a receiver, an LNA 141, a multiplier 142, an automatic gain adjusting unit (AGC) 144, an analog / digital converter (ADC: 145), a timing and frequency synchronization block 146, are provided at the front end of the FFT block 120. Cyclic Prefix (CP) removal block 147, S / P block 148 is provided, and after passing through the FFT block 120, P / S 151, channel correction block 152, QAM demapping ( 153 and descrambling / FEC decoding / deinterleaving block 154, where reference numeral 143 denotes a local oscillator that generates phase noise.

In order to theoretically analyze phase noise in the present invention, it is assumed that frequency offset estimation, timing synchronization, channel estimation, and the like are completely performed. Considering only the phase noise discussed in the present invention, FIG. It can be reconfigured to a simplified OFDM system.

Referring to FIG. 2, the OFDM system simplified by considering only phase noise in the 60 kHz OFDM wireless LAN system according to the present invention includes a serial / parallel converter (S / P: 210), an IFFT 220, a multiplier 230, F (240), x (n) denotes an OFDM signal, r (n) denotes a received signal in consideration of phase noise. First, the theoretical interpretation of phase noise is described first, and then the components are described. It will be described later.

Referring back to FIG. 2, in the OFDM system simplified by considering only phase noise in the 60 GHz OFDM wireless LAN system according to the present invention, the OFDM signal may be represented by Equation 1 below.

At this time, the phase noise at the receiving end Considering this, the received signal is expressed by Equation 2 below.

If phase noise Assuming this is very small It can be simplified by using the fast Fourier transform (FFT) of the received signal as follows.

Is an error term of the equation (3) Consider two cases as follows. First, If is

It can be expressed as, which is a common phase error (CPE) component that causes phase rotation on all subcarriers.

Secondly, If is

This means that one subcarrier signal receives ICI from another subcarrier under the influence of phase noise. This acts as a factor that inhibits orthogonality between subcarriers in an OFDM system. FIG. 3 illustrates the effect of ICI.

3 is a view for explaining the effect of the ICI in the 60 kHz OFDM wireless LAN system, it can be seen that the orthogonality is severely impaired by the ICI.

The existing analysis method assumes that the phase noise is very small. If the phase noise of the oscillator of the transmitter / receiver is large enough to be negligible, a more accurate analysis must be performed.

Therefore, considering both the phase noise of the transceiver and the additional noise of the channel, Equation 2 may be represented by Equation 6 below.

In addition, the signal after the FFT operation of the received signal is as follows.

if, Considering two cases, the following two cases are divided.

One) : Common phase error (CPE)

2) : Intercarrier Interference (ICI)

And if we define the SNR attenuation factor as

Is equal to, and in Equation 10 Denotes the power of the noise component generated by the power of the desired signal, the power of the noise, and the phase noise, respectively.

The power of each noise component of Equation 10 is obtained as follows.

The SNR attenuation factor is expressed as follows.

In addition, the SNR value of the OFDM system with phase noise is as follows.

In the same manner, the SNR attenuation factors and SNR values for phase noise considering the receiver are shown in Equations 15 and 16.

Meanwhile, the rate of change of phase noise for an SNR given to an OFDM system according to the related art and the present invention ( The relationship of the SNR attenuation factor with respect to) is shown in FIGS. 4A and 4B, respectively.

4A and 4B show the rate of change of phase noise at a given SNR in accordance with the prior art and the invention, respectively. As a diagram showing the relationship of the SNR attenuation factor to), it can be seen that according to the present invention, the attenuation width of the SNR attenuation factor decreases.

In addition, a method for removing phase noise in terms of minimum mean square error (MMSE) may be designed as shown in FIG. 5.

5 is a diagram illustrating a configuration of an MMSE phase noise canceller for a 60 kHz OFDM wireless LAN system according to an exemplary embodiment of the present invention.

Referring to FIG. 5, the MMSE phase noise canceller for a 60 kHz OFDM wireless LAN system according to an exemplary embodiment of the present invention includes a serial / parallel converter (S / P) 510 and a cyclic prefix (CP) for the parallel and parallel signals. ) CP addition and IDFT conversion unit 520 for adding and processing IDFT (Inverse Discrete Fourier Transform), and channel unit 530 for channeling and outputting the signal output from the CP removal and DFT conversion unit. An adder 540 for adding channel added noise to the signal output from the multiplier, a multiplier 550 for multiplying the signal added with the channel added noise by the phase noise generated in the oscillators of the transmitter and the receiver, and removing the CP from the signal output from the multiplier. CP removal and DFT conversion 560 for performing DFT processing, and a synchronization unit 57 and a phase noise suppression block (PNS) block 580 for synchronizing and outputting a signal output from the CP removal and DFT conversion unit. to Is done.

Here, the phase noise canceller block 580 is composed of an MMSE equalizer 581, a channel estimator 582, a CPE estimator 583, and an ICI and noise power component estimator 584, the operation of which other components are known to those skilled in the art. Obviously, only the phase noise canceller block 580 according to the present invention will be described in detail.

The phase noise canceller block 580 includes: a channel estimator 582 estimating a channel from the OFDM signal to which the channel additive noise and the phase noise are added; A CPE estimator 583 estimating a common phase error (CPE) from the OFDM signal to which the channel additive noise and the phase noise are added; An ICI and noise power estimator 584 for estimating inter-carrier interference (ICI) and noise power components from the OFDM signal to which the channel additive noise and phase noise are added; And an MMSE equalizer 581 that corrects the distortion characteristics of the channel with a minimum mean square error (MMSE) method for the estimated OFDM signal of the channel.

Considering only the phase noise covered by the present invention FIG. 5 can be simplified to FIG. 6 as follows. FIG. 6 shows a schematic configuration of an MMSE phase noise removing device considering only phase noise in FIG. 5 according to the present invention. Drawing.

Referring to FIG. 6, the MMSE phase noise removing apparatus considering only phase noise according to an embodiment of the present invention includes an S / P 610, an IFFT 620, a channel unit 630, an adder 640, and a multiplier 650. ) And PNS 660, and the principle of the MMSE phase noise removing apparatus and method will be described below with reference to FIG.

First, the n th sample of the m th OFDM symbol May be expressed as in Equation 17 below.

here, Refers to the convolution operator. In this case, if the CP is removed and the fast Fourier transform (FFT) is performed, Equation 18 is obtained.

In addition, by using the MMSE equalizer 581 according to the present invention, the received signal can be restored as shown in Equation 19 below.

here, Is obtained by the MMSE standard, which is expressed by Equation 20 below.

In order to implement a phase noise canceller for a 60 ㎓ WLAN system according to the present invention, ) And phase noise change rate ( ) Should be estimated. first, In order to estimate, since the TDMA TDD system uses the preamble of the broadcast signal periodically generated Is obtained by the following equation (21).

And using eight pilot symbols included in one OFDM symbol Equation 22 is as follows.

Where α is the loop factor and w is the weighting value.

In addition, according to the present invention In order to estimate, we first consider using 56 null subchannels.

remind Can be approximated with ICI energy when the SNR is large. The ICI energy Equation 23 can be expressed by Equation 23, and the approximation of Equation 23 shows when only receiver phase noise is considered.

If the SNR is large, the ICI energy will be quite large, so a null subchannel is used to estimate the phase noise change rate due to ICI energy. Can be approximated as

The estimated value for the ICI energy is also expressed by the following equation (25) using a loop filter to remove the phase noise according to the present invention.

On the other hand, the phase noise of the typical Lorentz spectrum is generated for the simulation according to the embodiment of the present invention. At this time, the level of the phase noise is 75 kHz / 10 @, the phase noise flow is 115 kHz / 1 MHz. At this time, it is assumed that the delay spread of the channel model is 50 ms. In addition, 16QAM signals are used for modulation, and when the SNRs are 20 and 30 dB, respectively, the ICI and the noise power spectrum are obtained as shown in FIGS. 7A and 7B.

7A and 7B show the estimation of the ICI and noise power spectrum when the SNR is 20 Hz and 30 Hz, respectively, according to the present invention, in which there is no phase noise, when there is typical phase noise, and 22 The ICI and noise power spectrum are shown when the phase noise of c / k is added.

8 is a diagram illustrating performance analysis of a symbol error rate when the phase noise canceling method according to an exemplary embodiment of the present invention is applied to 22 dB / s. When no phase noise is present and typical phase noise exists, FIG. When the phase noise cancellation method according to the present invention is applied to the phase noise of ㏈c / ㎐ and 22㏈c / ㎐ phase noise, the performance for each symbol error rate is shown. It can be seen that the improvement.

As a result, the present invention can overcome the performance degradation caused by phase noise in a 60 GHz wireless LAN system.

While the invention has been described above, these examples are intended to illustrate rather than limit this invention. It will be apparent to those skilled in the art that various changes, modifications, or adjustments to the above embodiments are possible without departing from the technical details of the present invention. Therefore, the protection scope of the present invention will be limited only by the appended claims, and should be construed as including all such changes, modifications or adjustments.

As described above, according to an embodiment of the present invention, it is possible to effectively prevent the performance degradation caused by phase noise in a 60 GHz wireless LAN system.

In addition, the receiving end can demodulate the signal with high reliability and further increase the transmission / reception capacity of the entire WLAN system.

In addition, it is easy to implement a function for removing phase noise, and it is possible to reduce the cost of manufacturing an integrated circuit for such a function. In addition, when applied to a wireless terminal sensitive to power consumption it can further reduce power consumption.

1 is a block diagram showing the configuration of a 60 GHz OFDM wireless LAN system.

2 is a block diagram illustrating a configuration of a simplified OFDM system in consideration of phase noise in a 60 GHz OFDM wireless LAN system according to an exemplary embodiment of the present invention.

3 is a view for explaining the effect of the ICI in the 60 kHz OFDM wireless LAN system.

4A and 4B are diagrams illustrating phase noise changes in a given SNR according to an embodiment of the present invention, respectively. Is a diagram showing the relationship of the SNR attenuation factor with respect to

5 is a diagram illustrating a configuration of an MMSE phase noise canceller for a 60 kHz OFDM wireless LAN system according to an exemplary embodiment of the present invention.

6 is a diagram illustrating a schematic configuration of an MMSE phase noise removing apparatus considering only phase noise in FIG. 5 according to an exemplary embodiment of the present invention.

7A and 7B are diagrams illustrating the estimation of the ICI and the noise power spectrum when the SNRs are 20 dB and 30 dB, respectively, according to an embodiment of the present invention.

8 is a diagram illustrating performance analysis of a symbol error rate when the phase noise removing method according to an exemplary embodiment of the present invention is applied to 22 dB / s.

Claims (17)

In an orthogonal frequency division multiplexing (OFDM) wireless LAN system using several tens of gigabytes, An adder for adding channel additive noise to the transmitted and received OFDM signal; A multiplier multiplying the OFDM signal to which the channel additional noise is added by the phase noise generated in the oscillators of the transmitter and the receiver; And A phase noise canceller (PNS) for estimating a phase noise power initial value and a phase noise change rate from the OFDM signal to which the channel additional noise and the phase noise are added to remove phase noise by a minimum mean square error (MMSE) method. : Phase Noise Suppression Phase noise removing device of a wireless LAN system comprising a. The method of claim 1, wherein the phase noise removing unit, A channel estimator estimating a channel from the OFDM signal to which the channel additive noise and the phase noise are added; A CPE estimator estimating a common phase error (CPE) from the OFDM signal to which the channel additive noise and the phase noise are added; An ICI and noise power estimator for estimating inter-carrier interference (ICI) and noise power components from the OFDM signal to which the channel additional noise and phase noise are added; And An MMSE equalizer for correcting the distortion characteristics of the channel with a minimum mean square error (MMSE) method for the estimated OFDM signal of the channel Phase noise removing device of a wireless LAN system comprising a. The method of claim 1, The phase noise power initial value is obtained using a preamble of a periodically generated broadcast signal, and is estimated by using eight pilot symbols included in one OFDM symbol phase noise removing apparatus of a wireless LAN system. The method of claim 1, The phase noise change rate is estimated by approximating the sub-carrier interference (ICI) energy when the signal-to-noise ratio (SNR) is large. The method of claim 4, wherein The phase noise change rate estimation value due to the inter-carrier interference (ICI) energy is calculated using a root filter. The method of claim 1 A serial / parallel converter for converting the OFDM signal into a parallel signal; A CP addition and IDFT converter configured to add a cyclic prefix (CP) to the parallel-parallel OFDM signal and process the inverse discrete fourier transform (IDFT); A channel unit providing a signal output to the adder to the CP removal and DFT converter; A CP removal and DFT converter for removing the CP from the signal output from the multiplier and performing DFT processing to output the CP; A synchronizer for synchronizing the signal output from the CP remover and the DFT converter and outputting the signal to the phase noise remover Phase noise removing device of the wireless LAN system further comprising. A method for canceling phase noise of an OFDM (orthogonal frequency division multiplexing) wireless LAN system using several tens of giga bands, Adding channel additive noise to the transmitted and received OFDM signal; Multiplying the OFDM signal to which the channel additional noise is added by the phase noise generated in the oscillators of the transmitter and the receiver; And Estimating a phase noise power initial value and a phase noise change rate from the OFDM signal to which the channel additional noise and the phase noise are added to remove phase noise by a minimum mean square error (MMSE) method. Phase noise removal method of a wireless LAN system comprising a. The method of claim 7, wherein The phase noise power initial value is obtained by using a preamble of a periodically generated broadcast signal, and estimated by using eight pilot symbols included in one OFDM symbol. The method of claim 7, wherein The phase noise change rate is estimated by approximating the subcarrier interference (ICI) energy when the signal-to-noise ratio (SNR) is large. The method of claim 7, wherein Phase noise at the receiving end Considering the received signal In this case, the signal after the FFT operation of the received signal is Phase noise removal method of the WLAN system represented by. The method of claim 10 remind = Common phase error (CPE) , : Intercarrier Interference (ICI) SNR attenuation factor , The power of each noise component ( )this How to remove phase noise of a WLAN system that satisfies. The method of claim 11, The SNR Attenuation Factor How to remove phase noise of a WLAN system that satisfies. The method of claim 11, SNR value of OFDM system with phase noise How to remove phase noise of a WLAN system that satisfies. The method of claim 11, SNR Attenuation Factor for Phase Noise Considering Receiver Where the SNR value is How to remove phase noise of a WLAN system that satisfies. The method of claim 7, The phase noise power initial value silver And α is a loop factor and w is a weighting value. The method of claim 7, The phase noise change rate estimation value silver How to remove phase noise of a WLAN system that satisfies. Phase Noise Reduction Method of Orthogonal Frequency Division Multiplexing (OFDM) Wireless LAN System Using Tens of Giga Bands Adding channel additive noise to the transmitted and received OFDM signal; Multiplying the OFDM signal to which the channel additional noise is added by the phase noise generated in the oscillators of the transmitter and the receiver; And And a program for implementing a function of removing phase noise by a minimum mean square error (MMSE) method by estimating a phase noise power initial value and a phase noise change rate from the OFDM signal to which the channel additional noise and the phase noise are added.