KR101796440B1

KR101796440B1 - method for synchronizing slot of GSM signal for signal analyzing equipment

Info

Publication number: KR101796440B1
Application number: KR1020160014651A
Authority: KR
Inventors: 정진섭; 이주형; 임용훈; 서창우
Original assignee: 주식회사 이노와이어리스
Priority date: 2016-02-05
Filing date: 2016-02-05
Publication date: 2017-11-10
Also published as: KR20170093363A

Abstract

The present invention relates to a slot synchronization method of a GSM signal in a signal analyzer capable of detecting slot synchronization of a GSM normal burst more quickly and accurately even in a small amount of calculation without any prior information.
A method for slot synchronization of a GSM signal of a signal analyzer according to an aspect of the present invention includes: capturing a frame of GSM signal, moving the sample from the first sample to a sample unit, comparing the sample energy E _idx with a threshold value T _slot (A) estimating a position of a guard interval by a result; (B) estimating the approximate position of the TSC from the position of the guard interval estimated in the step (a); (C) estimating the obtained maximum correlation position as a precise position of the TSC by calculating a degree of correlation with a previously known TSC while moving in units of a sample based on the estimated position in the step (b) (D) performing slot synchronization on the basis of the precise position estimated in step (a).

Description

A method for synchronizing a GSM signal in a signal analyzer,

The present invention relates to a slot synchronization method of a GSM signal in a signal analyzer, and more particularly, to a slot synchronizing method of a GSM signal in a signal analyzer capable of detecting slot synchronization of a GSM normal burst more quickly and accurately even with a small amount of calculation, Slot synchronization method.

As is well known, Global System for Mobile Communications (GSM) is a personal mobile communication system based on Time Division Multiplexing Access (TDMA). There are many different types of physical and logical channels in this GSM system, and each of these types of channels has a unique physical structure at the slot (burst) level.

Figure 1 shows a total of five burst types employed in a GSM air interface. As shown in Fig. There are five types of bursts in GSM. Here, a burst refers to a bit string transmitted by a base station or a user terminal, and the time slot (hereinafter, simply referred to as a 'slot' And has a real-time, dispersed period that must reach within such a time that it can be decoded.

First, a normal burst carries a traffic channel and all types of control channels. The Frequency Correction Burst carries the FCCH downlink to compensate for the frequency of the local oscillator to be efficiently synchronized with the frequency of the base station. Synchronization Burst carries the SCH downlink for timing synchronization between the base station and the user terminal. Dummy bursts are used to carry dummy information (no information). Finally, an access burst is a burst used when a user terminal attempts to access a base station.

Meanwhile, one GSM radio frame has a time interval of 4.615 ms, and has a total of 8 slots. Here, the slot of the normal burst is a 26-bit-long training sequence used to allow the receiver's equalizer to estimate the transfer characteristic of the physical path between the base station and the user terminal, A Stealing Flag allocated to each of left and right sides, a Stealing Flag allocated to the right and left sides of the Steering Flag, a size of 57 bits each to the left and right, and information (Info) A TB (Tail Bit) of 3 bits each on the left and right used to indicate the start and end of the burst, and a Guard Period (GP), which is a section given by the error margin of the system.

In the above-described configuration, the length of one slot of the normal burst is exactly 0.577 ms, but since the length of the burst is 0.546 ms, a time difference of 0.031 ms (8.25 bits) exists as an error margin.

On the other hand, in a conventional GSM signal analyzer, after demodulating a signal, various measurement information is displayed on a slot basis. To do so, it is necessary to detect a signal in a slot unit. Further, in order to accurately measure the EVM (Error Vector Magnitude), the frequency error, or the phase error of the GSM signal, the starting point of each slot must be accurately detected with a fine resolution.

In order to precisely detect the starting point of each slot, a correlation is calculated using a training sequence code (TSC) having a length of 26 bits previously known by the GSM standard.

2 is a diagram for explaining a slot synchronization method of a GSM signal of a conventional signal analyzer. In analyzing a GSM signal, especially a normal burst in a conventional signal analyzer, a signal of a frame length (length) is usually captured. Since it captures without any prior information, it is not known at any point of a GSM frame at a capture start point. In other words, in the example of FIG. 2, the capture start point is the information (Info) period of the slot but may be the inside of the TSC area, and in some cases, the guard period may be the capture start point.

Therefore, in order to find the GSM slot synchronization of the captured signal in consideration of all the cases described above, a position having a maximum correlation value is calculated by calculating the correlation with TSC, The correlation is calculated from this point on a sample basis to detect the precise starting point of the TSC, and the position which is 61 bits long from the detected starting point is synchronized to the starting point of the slot.

However, according to the slot synchronization method of the GSM signal of the conventional signal analyzer as described above, since the capture start point is unlikely to be the slot starting point as shown in FIG. 2, the correlation is calculated during two slot lengths from the capture start point. There is a problem that the amount of calculation increases. Furthermore, since we do not know what type of TSC is used in advance, we need to calculate the correlation for all 8 types of TSCs and calculate the correlation for 12 times oversampled signals for precise synchronization As a result, not only the amount of computation increases dramatically, but also the time required for synchronization is prolonged.

Prior Art 1: 10-2008-0096498 Disclosure of Invention Problem to be Solved by the Invention (Title of the Invention: Initial Synchronization Method and Apparatus of GSM System and TD-SCDMA System) Prior Art 2: 10-2003-0038170 Disclosure of the Invention Problems to be Solved by the Invention The present invention relates to a mobile communication terminal,

Disclosure of Invention Technical Problem [8] The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a slot synchronization method of a GSM signal in a signal analyzer capable of detecting slot synchronization of a GSM normal burst more quickly and accurately even with a small amount of calculation, And the like.

A method for slot synchronization of a GSM signal of a signal analyzer according to an aspect of the present invention includes: capturing a frame of GSM signal, moving the sample from the first sample to a sample unit, comparing the sample energy E _idx with a threshold value T _slot (A) estimating a position of a guard interval by a result; (B) estimating the approximate position of the TSC from the position of the guard interval estimated in the step (a); (C) estimating the obtained maximum correlation position as a precise position of the TSC by calculating a degree of correlation with a previously known TSC while moving in units of a sample based on the estimated position in the step (b) (D) performing slot synchronization on the basis of the precise position estimated in step (a).

In the above-described configuration, the captured GSM signal is characterized by being oversampled over the original sampling rate.

The threshold T _slot is characterized by the energy mean (E _avg ) of all samples and the required SNR level of the signal analyzer.

In the step (a), the initial sample having the sample energy E _idx that is larger or smaller than the threshold T _slot is estimated as a start point or an end point of the guard interval.

The correlation calculation in the step (c) is performed starting from a sample before a predetermined sample from the estimated position.

According to the slot synchronization method of the GSM signal of the signal analyzer of the present invention, the position of the start point of the TSC is roughly detected from the detected guard interval based on the energy of the sample, The position of the starting point of the TSC is precisely detected. By detecting the synchronization of the slot, the slot synchronization of the GSM signal can be performed quickly and accurately while greatly reducing the amount of calculation.

1 shows a total of five burst types employed in a GSM air interface;
BACKGROUND OF THE INVENTION Field of the Invention [0001]
3 is a flowchart illustrating a slot synchronization method of a GSM signal of the signal analyzer of the present invention.
4 is an illustration of a GSM normal burst with a 25 MHz sampling rate (12 times oversampling) captured in a slot synchronization method of a GSM signal of a signal analyzer of the present invention.

Hereinafter, a preferred embodiment of a slot synchronization method of a GSM signal of the signal analyzer of the present invention will be described in detail with reference to the accompanying drawings.

3 is a flowchart illustrating a slot synchronization method of a GSM signal of the signal analyzer of the present invention. As shown in FIG. 3, according to the slot synchronization method of the GSM signal of the signal analyzer of the present invention, in step S10, the GSM signal of one frame amount is captured in a state in which there is no prior information, It is desirable to oversample the sampling rate of? MHz, i.e., 12 times the original sampling rate.

Next, in step S20 in this energy average of all the samples sampled (E _avg) calculations, and, in step S30 leading to this energy average values (E _avg) energy average limit value (hereinafter simply "threshold value" for the slot detected on the basis of the La and) (T _slot) to calculate the, equation (1) and (2) below is an equation used to calculate the respective average energy (E _avg) and the limit value (T _slot).

In the above Equation 1, N represents the total number of samples of the captured signal, and Re (n) and Im (n) represent the real and imaginary components of the nth sample, respectively. In Equation (2), the threshold value (T _slot ) is a value 10 dB smaller than the energy average value (E _avg ), which is determined in consideration of the condition that the SNR of the conventional signal analyzer is 10 dB or more.

4 is an illustration of a GSM normal burst with a 25 MHz sampling rate (12 times oversampling) captured in a slot synchronization method of a GSM signal of a signal analyzer of the present invention. As shown in FIG. 4, according to the method of the present invention, the energy average value of each captured sample, that is, the magnitude envelope average (E _avg ) of each sample size (refer to the one- The position of the guard interval (see the rectangular point in FIG. 4) is detected with reference to the threshold value T _slot (see the dotted line in FIG. 4).

Returning to Fig. 3, in step S40, the index idx of the first sample of the capture interval is set to 0, and again in step S50, the sample energy E _idx of the current index idx is larger than the limit value T _slot . If it is determined in step S50 that the sample energy E _idx of the current index idx is larger than the threshold T _slot , it is determined that the sample is a sample of the burst period, It is determined that the sample is located in the burst interval, and the process proceeds to step S60. If the sample interval is less than the threshold T _slot , it is determined that the sample of the guard interval, i.e., the capture start point is located in the guard interval.

In step S60 and step S70 to determine if is greater than the sample energy (E _idx) of back current index (idx) from the state in which increase in the current sample index (idx) of by one limit value (T _slot), limit value (T _slot) The process proceeds to step S80 where the current sample position is regarded as the start point of the guard interval. If the guard interval is less than the threshold value T _slot , The flow advances to step S120.

Next, in step S90 and step S100, it is determined whether the sample energy E _idx of the current index idx is again greater than the threshold T _slot in the state where the current sample index idx is increased by one. T _slot ), the steps S90 and S100 are repeated because the corresponding sample is still a sample of the guard interval, whereas if it is larger than the limit value T _slot , the procedure goes to step S110 to set the sample position of the immediately preceding index as the start point And then proceeds to step S120.

In step S120, the starting point of the TSC is estimated based on the starting point or the ending point of the guard interval. For example, if the starting point of the guard interval is found in step S80 (step S80) It is assumed that a sample after a bit of +3 bits (tail bit) +57 bits (information area) + 1 bit (stilling flag)) is estimated as a start point of the TSC, whereas if an end point of a guard interval is found (step S110) 61 (= 3 bits (tail bit) +57 bits (information area) + 1 bit (stilling flag)) bit is estimated as the start point of the TSC.

Next, in step S130, the correlation between a total of eight types of TSC previously known by the standard and a GSM signal of the estimated position of the TSC are calculated in units of samples in order to estimate the precise position of the TSC, Is determined as the starting point of the TSC. It is preferable that the correlation calculation in step S130 is performed from a sample before the bit position of the estimated position of the TSC. Finally, in step S140, the starting point of each slot is synchronized from the starting point of the TSC, that is, 69.25 (= 8.25 bits (guard interval) +3 bits (tail bit) +57 bits Stealing flag)) to the starting point of each slot.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. will be. Accordingly, the scope of the present invention should be determined by the following claims.

Claims

As a result of comparing the sample energy (E _idx ) with the threshold value (T _slot ) determined by the energy average value (E _avg ) of all samples while moving from the first sample to the sample unit after capturing the GSM signal of one frame amount (A) estimating a position of a guard interval;
(B) estimating the approximate position of the TSC from the position of the guard interval estimated in the step (a);
(C) estimating the obtained maximum correlation position as a precise position of the TSC by calculating a degree of correlation with a previously known TSC while moving in units of samples on the basis of the estimated position in the step (b)
And (d) performing slot synchronization based on the precise position estimated in step (c).

The method according to claim 1,
Characterized in that the captured GSM signal is oversampled over the original sampling rate.

3. The method of claim 2,
Wherein the threshold T _slot is determined by further considering the required SNR level of the signal analyzer.

4. The method according to any one of claims 1 to 3,
_{Wherein the} estimating step estimates the first sample having the sample energy E _idx greater than or less than the threshold value T _{slot as} the start point or the end point of the guard interval.

5. The method of claim 4,
Wherein the correlation calculation in the step (c) is performed starting from the sample before the predetermined sample from the estimated position.