KR101007271B1 - Method for detecting time synchronization - Google Patents

Abstract

PURPOSE: A time sync detecting method is provided to improve a receiving performance in a multi path channel of a wireless communication system by detecting the exact time sync. CONSTITUTION: A correlation measuring unit(410) measures a correlation feature of preamble of receiving signals as correlation. A maximum correlation calculator(420) calculates an maximum correlation sample location of largest correlation among the measured correlation. Based on the maximum correlation sample location, an effective candidate group calculator(430) determines a valid candidate group. A final time sync estimator(440) determines a final time synch timing among the valid candidate group.

Description

Method for detecting time synchronization

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting time synchronization in a signal received at a receiving end of a communication system, and more particularly, to a method for detecting accurate time synchronization in a mobile communication system in a multipath channel environment.

Single Carrier-Frequency Domain Equalizer (SC-FDE) and Orthogonal Frequency Division Multiplexing (OFDM) transmissions are the next generation of wireless LANs because of their high frequency efficiency and ease of coupling with Multi Input Multi Output (Multi-Input Output) technology. It is considered as a transmission method for 4G mobile communication. To achieve this advantage, the receiver performs Fast Fourier Transform (FFT) operation on the received signal at an appropriate position to recover the signal. Therefore, it is important to find an appropriate FFT time synchronization time point for accurate signal recovery in SC-FDE and OFDM transmission.

SC-FDE and OFDM transmission methods include a method of using a signal (hereinafter, referred to as a preamble) promised at a transmitter and a receiver for time synchronization, and a time synchronization method using time signal synchronization using signal characteristics of the transmitted signal itself. .

In the method of detecting time synchronization using the preamble, the time synchronization is estimated using the correlation characteristics of the preamble received at the receiving end. That is, the conventional time synchronization method determines the time synchronization point based on the measured correlation degree after measuring the correlation characteristics of the received preamble. Because of the design characteristics of the correlation measurement, the time point having the largest value in the measured correlation is determined as the time synchronization time point.

However, the conventional time synchronization timing determination method using the preamble has a problem in that its performance deteriorates rapidly in a multipath channel environment. In other words, the correlation measured in the multipath channel environment has the same type of correlation as the impulse response of the channel.In the multipath channel environment, the impulse response always has the largest value. There was a problem that can not determine the exact time synchronization point.

For example, referring to FIG. 1, which shows a correlation of impulse response types in a multipath channel environment, when the impulse response in the multipath channel environment is the largest in the third channel tap, the position of the first channel tap is precisely time synchronized. In spite of the viewpoint, the conventional method determines the third channel tap position as the time synchronization point, causing an error in the time synchronization point estimation.

An object of the present invention is to provide a synchronization method capable of accurately detecting time synchronization even in a multipath channel environment by overcoming a problem of deterioration of time synchronization time detection performance in a multipath channel. In addition, the present invention provides a method for detecting an accurate time synchronization point by selecting a candidate group group in advance in detecting the time synchronization point. Another object of the present invention is to provide a synchronization method for variably determining a time synchronization time point in consideration of a signal-to-noise ratio in detecting a time synchronization time point.

In accordance with another aspect of the present invention, there is provided a method of measuring correlation, which is a preamble correlation feature of received signals, finding a maximum correlation sample having the largest correlation among the correlations, and the maximum correlation sample. Determining a valid candidate group that is a candidate sample group at a time synchronization point based on a position of, and selecting a location of a specific sample from the valid candidate group to determine a time synchronization point.

The valid candidate group is characterized in that the samples in the interval from the time point located to the left of the predetermined interval than the time point where the maximum correlation sample is located to the time point where the maximum correlation sample is located.

Selecting the position of a particular sample from the valid candidate group selects the position of the sample having the earliest point in time among samples in the valid candidate group having a correlation greater than a specific threshold value T _{th , SNR} .

The threshold values T _{th and SNR} vary according to the signal-to-noise ratio SNR of the received signal.

When the threshold value (T _{th , SNR} ), ρ is the value of the signal-to-noise ratio (SNR), χ _ρ is a variable applied to each communication system when determining the threshold value according to the signal-to-noise ratio (SNR),

임을 특징으로 한다.

It is characterized by that.

According to an embodiment of the present invention, the present invention has an effect of detecting accurate time synchronization even in a multipath channel environment. In addition, due to the accurate time synchronization detection, the reception performance is greatly improved in a multipath channel environment of a wireless communication system such as SC-FDE and OFDM. In addition, SC-FDE and OFDM systems as well as a single carrier system requiring accurate time synchronization has an effect of improving the reception performance. In addition, when applied to the time synchronization method of the MIMO (Multi Input Multi Output) system, the performance can be improved.

1 is a correlation diagram of an impulse response type in a multipath channel environment.
2 is a block diagram schematically illustrating an example of a communication system.
3 is a block diagram illustrating a configuration of a receiving end in a communication system.
4 is a block diagram illustrating an operation process of a time synchronization detection module applied at a receiving end of a communication system according to an exemplary embodiment of the present invention.
5 is a diagram illustrating a correlation measurement result appearing in the form of an impulse at an accurate synchronization point.
6 illustrates a frame having a preamble.
7 is a diagram illustrating an embodiment of a timing metric.
8 is a diagram illustrating performance improvement when the time synchronization determiner, which is an embodiment of the present invention, is actually applied to a multipath channel environment.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention in more detail. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you. Like numbers refer to like elements in the figures.

2 is a block diagram schematically illustrating an example of a communication system.

The illustrated transmitting end 10 and receiving end 20 provide a communication service using a frame. Therefore, it is necessary for the transmitter 10 and the receiver 20 to acquire time synchronization points (synchronization information) of each other for transmission and reception of a frame. In order to obtain a time synchronization point (synchronization information), the transmitter 10 transmits a synchronization signal for identifying a start position of a frame transmitted to the receiver 20 to the receiver 20. The receiving end 20 receiving the synchronization signal and the frame transmitted from the transmitting end 10 checks the start position of the frame, that is, the frame timing, using the synchronization signal. At this time, the receiving end 20 demodulates the received frame using the confirmed frame timing. In this case, as a synchronization signal, a specific preamble sequence previously promised by the transmitter 10 and the receiver 20 is used.

3 is a block diagram illustrating a configuration of a receiving end in a communication system.

The frame transmitted from the transmitter is received through the receive antenna 600. The frame received by the receiving antenna 600 is transmitted to the time synchronization detection module 400 and the demultiplexing module 500. The time synchronization detection module 400 detects synchronization information and channel estimation information by analyzing a preamble among the received frames. At this time, the time synchronization detection module 400 determines the start position of the received frame using the synchronization information.

When the start position of the frame is determined, the demultiplexing module 500 performs Fourier transform (FFT) on the transmission data of the received frame with reference to the start position of the frame to distinguish the PHY header, the MAC header, and the data. The divided signals are input to the PHY header analysis module 100, the MAC header analysis module 200, and the data recovery module 300, respectively.

The PHY header analysis module 100 analyzes the PHY header transmitted from the demultiplexing module 500 and transmits the result information to the data recovery module 300. The MAC header analysis module 200 analyzes the MAC header transmitted from the demultiplexing module 500 and transmits the result information to the data recovery module 300. Accordingly, the data restoration module 300 finally restores the data transmitted from the demultiplexing module 500 by using the analysis result information of each header transmitted from the PHY header analysis module 100 and the MAC header analysis module 200. do.

An embodiment of the present invention provides an accurate time synchronization point in a wireless communication system using a transmission scheme such as Single Carrier-Frequency Domain Equalizer (SC-FDE) and Orthogonal Frequency Division Multiplexing (OFDM) in the time synchronization detection module 400. To be detected. Hereinafter, the time synchronization detection module described in the embodiment of the present invention can be applied to all communication systems requiring time synchronization as well as the wireless communication system. In particular, it can be effectively used for time-synchronous detection to provide an appropriate fast Fourier transform (FFT) viewpoint under multipath channels of communication systems using SC-FDE and OFDM transmission schemes.

4 is a block diagram illustrating an operation process of a time synchronization detection module applied at a receiving end of a communication system according to an exemplary embodiment of the present invention.

Time synchronization detection module according to an embodiment of the present invention, the correlation measuring unit 410 for measuring the correlation characteristics of the received signal, the maximum correlation calculation unit 420 for finding the sample position having the largest correlation among the measured correlations ), A valid candidate group calculating unit 430 for determining a valid candidate group based on the maximum correlation calculation unit output value, and a time synchronous estimating unit 440 for determining a final time synchronization time point among valid candidate groups to determine a final time synchronization point. Have

Hereinafter, the operation of the respective functional units of the time synchronization detection module will be described as respective processes.

The correlation measurer 410 has a process of measuring a correlation feature of a preamble in the received signals as a correlation degree (S410). The correlation measurer 410 measures correlation characteristics with respect to a preamble designed in advance to measure an accurate correlation in an environment in which noise, channel, and interference exist, and provides the correlation to a maximum correlation calculator and an effective candidate group calculator. do. If there is no noise and interference in the frequency environment, it has an impulse characteristic only at the exact synchronization time point as shown in FIG. 5.

Correlation measurement is performed by measuring correlation characteristics of a preamble. An example of such a preamble is illustrated in FIG. 6. 6 is a diagram showing the structure of a frame used in a general communication system. As shown, the frame consists of a preamble and data. The preamble is used for synchronization of frames and channel estimation. The information included in the data may be data selected by a user and requested to be transmitted and / or control information of a communication system. The structure of the frame may be a fixed format according to the communication system as shown in FIG. 6, but in other communication systems, the preamble may be located at the middle or the end of the data. That is, in the frame, the preamble may be arranged at various locations according to the communication system.

The correlation measurer 410 measures correlation characteristics using a preamble in the frame shown in FIG. 6, and this method of measuring correlation has been suggested in many papers and patents. In the description of an embodiment of the present invention, a cross-correlation method, which is a representative technique of correlation measurement, will be described as an example.

The cross-correlation measurement method is represented by the following [Formula 1].

[Equation 1]

Where y _n represents a sample of the sampled received signal. n is a sample index of the received signal, and makes sample index 0 an accurate time synchronization point. P _k represents the k th sample of the preamble. () ^* Represents the conjugate complex number of an arbitrary signal. In the absence of noise and interference, the output of the correlation measurer using the method of Equation 1 has an impulse characteristic as shown in FIG. 5. In general, the correlation value R _n measured by the correlation measurer as shown in FIG. 5 is referred to as a timing metric. Hereinafter, the correlation measurement result as shown in FIG. 5 will be referred to as a timing metric in an embodiment of the present invention. .

The maximum correlation calculator 420 performs a process of finding the maximum correlation sample position having the largest correlation among the correlations measured by the correlation measurer (S420). To this end, the maximum correlation calculating section 420, the correlation among values of the measured output R _n unit, R _n the position of the sample index of the sample (n _max when the greatest; hereinafter referred to as maximum correlation sample index Output). That is, the maximum correlation sample index n _max , which is an output value of the maximum correlation calculation unit, may be expressed as shown in [Formula 2]. In the following, the argmax function points to the sample index when R _n has the maximum value.

[Equation 2]

n _max = argmax (R _n )

The valid candidate group calculator 430 determines a valid candidate group based on the position of the maximum correlation sample (maximum correlation sample index) in order to determine the final time synchronization point (S430).

The valid candidate group calculating unit 430 receives an output value R _n of the correlation measurer and a maximum correlation sample index n _max , which is an output of the maximum correlation calculator, as an input, and based on this, an accurate time synchronization point is obtained. Constitute a valid candidate group. That is, in order to compensate for the problem of the conventional method of directly estimating the sample position having the largest correlation as the time synchronization time point, a valid candidate group is formed by collecting the time points that can be accurate time synchronization time points.

The configuration of the effective candidate group Cn _max consists of a total of M samples as samples from the sample index having the maximum correlation among the timing metrics to before the M-1 sample when the total number of the valid candidate groups is designed to M. . The effective candidate group Cn _max is expressed by the following formula.

[Equation 3]

FIG. 7 is a diagram showing an example of a timing metric. The valid candidate group configured in the valid candidate group calculating unit includes M samples to the left including n _max , which is the maximum correlation position. That is, the valid candidate group includes samples in the interval from the time point n _ma xM-1 located to the left of the predetermined interval than the time point n _max at which the maximum correlation sample is located to the time point n _max at which the maximum correlation sample is located. Is done.

The reason for configuring the effective candidate group as samples from the sample index having the maximum correlation among the timing metrics to before the M-1 sample is that in the multipath channel environment, the point of time having the maximum correlation is always accurate due to the characteristics of the timing metric. This is because they appear the same or later than time synchronization. In other words, the exact time synchronization point exists on the left side of the maximum correlation point (the sample index is smaller) in the timing metric. Therefore, the valid candidate group is composed of M R _n values present on the left side of the sample index having the maximum correlation among the timing metrics. Here, the determination of M is a value determined by the system parameter and the application channel environment of the SC-FDE system and the OFDM system to which the present invention is applied, and this value is generally optimal through an empirical test method. You can find the value.

The final time synchronization estimator 440 determines a final time synchronization time point among the valid candidate groups, that is, receives a valid candidate group Cn _{max that} is an output of the valid candidate group calculation unit 430 (S440). ). Determining a final time synchronization point of time is the last time synchronization with the time a certain threshold (T _{th, SNR),} the index of more than R _n the left hand side of the R _n (that is, over the threshold value R _n the smallest index of) from the effective candidate (n _final )

Expressed by the equation, it is possible to determine the final time synchronization time point as shown in [Equation 4] below, the argmax function indicates the smallest index of R _n over the threshold in the valid candidate group Cn _max .

[Equation 4]

n _final = argmin (R _n > T _{th, SNR} ) (where Rn ∈ Cn _max )

In the above, the reason for setting the threshold values T _{th and SNR} may generally include a noise section for samples on the left side among samples of the valid candidate group. Therefore, the threshold value is used as a reference value for finding an accurate time synchronization point without determining a sample of such a noise period as the final time synchronization point. In this relationship, the performance of the present invention may vary depending on the setting of the threshold. Thus, the threshold may be set to a specific fixed value, and in another embodiment, is adaptive as the Signal to Noise Ratio (SNR) changes without using the threshold as a fixed value for improved performance. It can be set to the threshold value changed to. The threshold can be set to a value that changes as the signal-to-noise ratio (SNR) changes rather than a fixed value, thereby enabling optimal time synchronization estimation.

In detail, when the threshold value is set to a threshold value that can be adaptively changed as the signal-to-noise ratio (SNR) changes, the threshold values T _{th and SNR} may be defined as shown in Equation 5 below.

[Equation 5]

In the above, ρ is a power value adaptively changed according to an actual radio channel environment, and in this embodiment, may be an SNR value measured by a receiver. Also, χ _ρ is a variable for adaptively determining the threshold value according to the SNR. χ _ρ is defined differently according to the system to which the embodiment of the present invention is applied, and its value can be found empirically through simulation. As described above, the threshold value in the embodiment of the present invention may be adaptively changed according to the SNR change, thereby enabling optimal time synchronization.

For reference, referring to FIG. 7, the leftmost sample among the samples exceeding the set threshold in the valid candidate group is determined as a time synchronization time point.

FIG. 8 shows the performance improvement when the time synchronization determiner, which is an embodiment of the present invention, is actually applied to a multipath channel environment. As shown in FIG. 8, when the embodiment of the present invention is applied, almost accurate time synchronization can be performed even in a multipath channel environment such that the average is nearly zero and the variance is 10 ⁻² . It can be confirmed. Performing accurate time synchronization can greatly improve the reception performance of SC-FDE and OFDM systems. In addition, the embodiment of the present invention can achieve the same performance when applied to a single carrier system requiring accurate time synchronization as well as SC-FDE and OFDM scheme, and likewise MIMO (Multi Input Multi Output) In case of applying to the time synchronization method of the system, the performance improvement can be obtained greatly.

While the invention has been described above with reference to the accompanying drawings and the preferred embodiments described above, the invention is not limited thereto, but is defined by the claims that follow. Accordingly, one of ordinary skill in the art may variously modify and modify the present invention without departing from the spirit of the following claims.

400: time synchronization detection module 410: correlation measurer
420: maximum correlation calculator 430: effective candidate group calculator
440: final time synchronization estimation unit

Claims (7)

Measuring a correlation that is a preamble correlation feature of the received signals;
Finding a maximum correlation sample having the largest correlation among the correlations;
Determining an effective candidate group which is a candidate sample group at a time synchronization point based on the position of the maximum correlation sample;
Selecting a location of a specific sample from the valid candidate group and determining a time synchronization point;
Measuring the correlation, time synchronization detection method characterized in that to have a correlation value of the output value of the impulse (impulse) characteristics in an environment free from noise and interference. delete The method of claim 1, wherein the valid candidate group is determined by an experimental result by a parameter of a communication system and a channel environment. The method of claim 3, wherein the valid candidate group is samples located in a section from a time point located to the left of the predetermined interval to a time point in which the maximum correlation sample is located from the time point at which the maximum correlation sample is located. The method of claim 1, wherein selecting a location of a specific sample from among the valid candidate groups comprises selecting a location of a sample having the earliest viewpoint among samples in the valid candidate group having a correlation greater than a specific threshold value T _{th, SNR} . Time synchronization detection method. The method of claim 5, wherein the threshold values (T _{th, SNR} ) vary according to a signal-to-noise ratio (SNR) of a received signal. The method according to claim 6, wherein the threshold value (T _{th, SNR} ), ρ is a value of the signal-to-noise ratio (SNR), χ _ρ is a variable applied to each communication system when determining the threshold value according to the signal-to-noise ratio (SNR). time,

Time synchronization detection method calculated by.

Images