KR0157012B1 - Frequency correction burst detecting device of digital mobile telecommunications - Google Patents

Abstract

The present invention discloses an apparatus for detecting frequency correction burst in digital mobile communication and a method of detecting the same. The frequency correction burst detection apparatus of the mobile station, comprising means for receiving an analog signal expected from the frequency correction burst transmitted from the base station, separating the I signal and the Q signal, and converting the signal into a digital signal. Mixers for outputting by mixing with a predetermined frequency to move to the band, the first signal size calculation means for calculating the size to minimize the noise of the I and Q signals output from the input mixers, and outputs from the mixers Second signal size calculating means for calculating and outputting the magnitudes of the I and Q signals, a signal size adjusting means for dividing an output of the first signal size calculating means to an output of the second signal size calculating means, and a signal And frequency correction determining means for inputting the output of the scale adjusting means to determine whether the frequency correction burst is applied. It does not depend on the size of the signal input to the frequency baseband unit, to detect the start and end points of a more accurate frequency correction burst signal than using the signal level regulator there is an effect that it is possible to accurately detect a correct burst signal period.

Description

Frequency corrected burst detection device and detection method thereof in digital mobile communication

1 is a block diagram of a conventional frequency correction detection apparatus.

2 is a block diagram of a frequency correction burst detection apparatus of digital mobile communication according to the present invention.

3 is a waveform diagram of a signal input to the mixers shown in FIG.

4 is a waveform diagram of signals output from the mixers shown in FIG.

5 is a waveform diagram of a signal Ep output from the first signal calculator.

6 is a waveform diagram of a signal output from the signal size control unit shown in FIG.

FIG. 7 is a waveform diagram of a signal input to a frequency correction determination unit for explaining a frequency correction burst detection method performed by the frequency correction determination unit shown in FIG.

FIG. 8 is a flowchart for explaining a frequency correction burst detection method performed in the frequency correction determining unit shown in FIG.

9 (a) to (b) are flowcharts for explaining in detail the steps 132 to 134 shown in FIG.

* Explanation of symbols for main parts of the drawings

52: When receiving RF 54: Sampler

56: D / A converter 58,60: mixers

62: filter unit 64: first size signal calculation unit

66: second size signal calculation section 68: signal size adjustment section

70: frequency correction discriminating unit

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division multiple access (TDMA) digital mobile communication system, and more particularly, to an apparatus for detecting frequency correction burst (FCB) in the system and a detection method thereof.

In the TDMA digital mobile communication system, the TDMA multiframe communication protocol transmits an analog radio signal, that is, a frequency correction burst, in which predetermined data is modulated for frequency synchronization between a base station and a mobile station. In response to this, the base station repeatedly transmits radio waves.

The mobile station of the digital mobile communication system receives this frequency correction burst to synchronize with the frequency of the base station and measures the frequency offset. To this end, the receiver of the mobile station must first detect a corresponding time, which is a period of time corresponding to the frequency corrected burst signal and the frequency corrected burst signal, among various burst signals received.

Hereinafter, the configuration and operation of a conventional apparatus for detecting a frequency correction burst will be described as follows with reference to FIG.

FIG. 1 is a block diagram of a conventional frequency correction detecting apparatus, and from the antenna 5, a duplexer 10, an RF receiver 20, an analog / digital converter 30, and a frequency correction burst detection unit 40 are shown. A band pass filter 42 and a frequency correction burst comparison discriminator 44 are configured in this order.

In the conventional frequency detection apparatus shown in FIG. 1, the radio burst signal received through the antenna 5 is converted into a digital baseband signal through the duplexer 10, the RF receiver 20, and the analog / digital converter 30. And input to the frequency correction burst detector 40. In addition to the frequency correction burst signal, various types of burst signals are input to the signal input to the frequency correction burst detection unit 40. That is, the frequency corrected burst detector detects only the frequency corrected burst signal among the input burst signals.

On the other hand, since the frequency correction burst signal has a characteristic that binary data of '1' or '0' is continuously configured, the baseband modulation method of the continuous phase frequency shift keying (CPFSK) class is used. In the TDMA mobile communication system, the peak value of the spectrum of the frequency correction burst signal appears at a frequency shifted by fcb due to the characteristics of CPFSK modulation. Here, fcb means the frequency of the frequency correction burst signal from which the RF carrier is removed from the baseband, (Where T _B represents the transmission time of one bit in the frequency correction burst).

In order to detect the frequency correction burst using the frequency correction burst signal characteristic, the frequency correction burst detection unit 40 first includes a bandpass filter having a characteristic of fcb, a bandwidth of 2Δf, and a 3dB cutoff frequency (fcf) of fcb + Δf. Use 42 to pass only the frequency correction burst signal. Here, the error tolerance (unit: ppm) of the local generator used in the RF receiver 20 of the mobile station to determine Δf, which determines the bandwidth of the bandpass filter 42, the reception frequency of the local oscillator and the moving speed of the mobile station. Factors causing frequency shifts, such as Doppler frequency shifts, should be considered.

The frequency corrected burst comparison discriminator 44 sets As / 2, which is 1/2 of the average size As of the signal input from the bandpass filter 42, to determine the time interval of the frequency corrected burst signal, as a comparison reference value. Input through 1N1, and determine the time when the frequency correction burst signal starts when a signal larger than As / 2 is input, and when the magnitude of the continuous signal is less than As / 2, the end of the frequency correction burst signal The time interval corresponding to the frequency correction burst and the frequency correction burst is determined by determining the time.

The As / 2 value used here is set experimentally. For example, in the case of the European TDMA mobile communication system, 0.5 can be set to the As / 2 value.

In the above-described conventional frequency correction burst detection apparatus, the determination of the start time and the end time of the frequency correction burst signal section is not accurate, and the signal-to-noise ratio (SNR) of the signal input to the frequency correction burst detection unit 40 is In the case where the change in the signal size As is large according to the ratio, a large number of errors occur, which makes it difficult to accurately detect the frequency correction burst received signal.

SUMMARY OF THE INVENTION An object of the present invention is to provide a frequency correction burst detection apparatus of a digital mobile communication system which detects a frequency correction burst using a baseband signal characteristic of a frequency correction burst in a digital mobile communication system. have.

Another object of the present invention is to provide a frequency correction burst detection method performed in the frequency correction burst detection apparatus of digital mobile communication according to the present invention.

In order to achieve the above object, an analog signal expected from a frequency correction burst transmitted from a base station of a digital mobile communication system according to the present invention is received and an I (in phase) signal and a Q (quadrature phase: 90 ° transition phase) are received. A device for frequency correction burst detection in a mobile station of the mobile communication system, comprising means for separating into signals and means for converting the I and Q signals into digital signals, respectively, to move the I and Q signals to baseband, respectively. Calculate the mixers mixing and outputting a predetermined frequency, the filter means for minimizing the noise of the I and Q signals output from the input mixers and the magnitude of the I and Q signals output from the filter means First signal size calculating means for outputting the calculated magnitude and magnitudes of the I and Q signals output from the mixers; Dividing the output of the first signal magnitude calculating means by the output of the second signal magnitude calculating means in order to calculate and adjust the second signal magnitude calculating means for outputting the calculated magnitude and the level of the frequency correction burst, And signal frequency adjusting means for outputting the divided value, and frequency correction determining means for inputting the output of the signal size adjusting means to determine whether a frequency correction burst is applied.

And means for receiving an expected burst expected from a frequency correction burst transmitted from a base station of the digital mobile communication system according to the present invention, separating the I signal from the Q signal, and converting the signal into a digital signal. A frequency corrected burst detection method of a frequency corrected burst detection device of a mobile communication system mobile station includes a ratio of the magnitudes of the I and Q signals from which the noise is removed and the magnitudes of the I and Q signals from which the noise is removed as data. A storing step of storing, a first detecting step of finding a start of the expected burst, a second detecting step of finding an end of the expected burst, and determining whether the expected number of bits of the expected burst is greater than a predetermined reference number of bits. Determining, and if the expected number of bits is greater than the reference number of bits, frequency prediction bursts the estimated bursts. And a second burst determining step of determining the expected burst as a burst other than the frequency correction burst if the expected number of bits is less than the reference number of bits.

EMBODIMENT OF THE INVENTION Hereinafter, with reference to the accompanying drawings, the frequency correction burst detection apparatus and its detection method of digital mobile communication by this invention are demonstrated as follows.

The frequency correction burst in the TDMA scheme is composed of specific data types already determined. In particular, for example, in the case of the European TDMA digital mobile communication system (GSM, DCS1800), the frequency correction burst is composed of a total of 148 bits, all of which are defined as binary data '0'. In the European TDMA scheme, 148-bit binary data '0' constituting the frequency correction burst is modulated by Gaussian Minimum Shift Key (GMSK) and wirelessly transmitted from the base station to the mobile station. At this time, the carrier frequency (Carrier) The frequency corrected burst signal has a peak power spectral characteristic at the frequency fca + fcb [Hz] shifted by the frequency fca by a predetermined frequency fcb (where fcb is as described above). In addition, the frequency correction burst signal in the baseband from which a radio frequency (RF) carrier is removed exhibits a sinusoidal characteristic having a frequency of fcb [Hz].

2 is a block diagram of a frequency correction burst detection device for digital mobile communication according to the present invention, from the antenna 50 to the duplexer 50, the RF receiver 52, the sampler 54, and the analog / digital converter 56 ), Mixers 58 and 60, filter unit 62, first and second signal size calculation units 64 and 66, signal size adjustment unit 68 and frequency correction determination unit 70, The RF band portion from the duplexer 50 to the analog-to-digital converter 56 represents the base band portion from the mixes 58 and 60 to the frequency correction determining portion 70, respectively.

The frequency correction burst transmitted wirelessly from the base station of the TDMA digital mobile communication system using the RF carrier is input to the duplexer 50 together with the other burst signal through the antenna 48 and output to the RF receiver 52. The RF receiver 52 outputs I (t) and Q (t) signals, which are GMSK modulated analog signals from which RF carriers and frequencies have been removed, to the sampler 54. At this time, the signal output from the RF receiver 52 is the carrier frequency is removed, the ISK (In-phase) signal and Q (Quadrature) signal, which is a GMSK modulated analog signal, the Q signal is 90 ° compared to the I signal It has a phase difference characteristic. The sampler 54 samples the input signal and outputs the sampled signals I (nT) and Q (nT) to the analog-to-digital converter 56.

FIG. 3 is a waveform diagram of a signal input to the mixers 58 and 60 shown in FIG. 2, wherein the periods 80 and 84 are I (nT) or Q (nT) of bursts other than frequency correction bursts. ) Shows the general waveform of the signal, and the section 82 indicates the general waveform of the I (nT) and Q (nT) signals of the frequency correction burst.

On the other hand, the I (nT) and Q (nT) signals shown in FIG. 3 converted from the analog / digital converter 56 into digital signals are input to the mixers 58 and 60. As can be seen from the waveform diagram shown in Fig. 3, when a frequency correction burst of 82 sections is received, the I (nT) or Q (nT) signal is The sinusoidal wave has a frequency of, and the I (nT) or Q (nT) signals of the other bursts show waveform characteristics having an arbitrary period when compared with the frequency correction burst signal. Therefore, the frequency correction burst Using the sinusoidal characteristics of the frequency, the first mixer 58 and the second mixer 60 transfer the fcb input through the input terminal IN to the I (nT) and Q (nT) signals to the baseband. ) And Q (nT) signals are respectively mixed and output to the filter unit 62, which may be implemented as a low pass filter.

4 shows the waveform of the signal output from the mixers 58 and 60 shown in FIG. 2, and the waveform diagram of the I ₁ (nT) and Q ₁ (nT) signals of the frequency correction burst is shown in the section 92. FIG. Section 90 and 94 show waveform diagrams of I ₁ (nT) and Q ₁ (nT) signals of other bursts than the frequency correction burst, respectively.

The signal of the frequency correction burst shown in FIG. 4 exhibits a nearly direct current waveform characteristic including AWGN Additive White Gaussian Noise and signal fading due to the characteristics of the mobile communication channel. Depending on the change in the negative (negative) may also exhibit a direct current characteristic.

The filter unit 62 shown in FIG. ₂ inputs the I ₁ (nT) signal and the Q ₁ (nT) signal respectively shown in FIG. 4 to minimize and output noise outside the signal band. At this time, the 3 dB cutoff frequency fr of the filter unit 62 is equal to or greater than (r × 10 ⁻⁶ ) f _L0 + f _D. Where r is the tolerance of the local oscillator of the RF receiver 52, the unit is ppm, f _D is the difference in the Doppler frequency, f _L0 is the frequency of the local oscillator of the RF receiver 52, respectively.

5 is a waveform diagram of the signal Ep output from the first signal calculator 64, where sections 100, 104 and 108 are signal sizes of frequency correction bursts, and numbers 102, 106 and 110 are other bursts. Indicates the signal magnitude of each.

The first signal calculator 64 calculates the magnitude Ep shown in FIG. 5 of the I ₂ (nT) and Q ₂ (nT) signals output from the filter unit 62 using the following equation (1). The second signal calculator 66 calculates the magnitude Eq of the I ₁ (nT) and Q ₁ (nT) signals output from the mixers 58 and 60 using the following equation (2). Do this.

That is, the signal size can be calculated by obtaining the instantaneous energy E of the signal.

As can be seen from the waveform diagram of the signal shown in Fig. 5, the frequency correction burst can be detected by the difference between the signal sizes of the frequency correction bursts (sections 104 and 108) and the signal sizes of the other bursts, The signal size of is not different from the signal size of the other bursts in the interval 102 due to the severe signal size fading of the mobile communication channel, so that only the Ep signal can be detected and the frequency correction burst cannot be accurately detected. In order to overcome this problem, the magnitude Eq of the signal not passing through the filter 62 and the magnitude Ep of the signal passed through the filter 62 are calculated and output to the signal magnitude adjusting unit 68. Therefore, the difference in signal size between frequency correction bursts and other bursts is further adjusted. That is, the signal magnitude adjusting unit 68 further differentiates the magnitude of the signal of the frequency correction burst from the magnitude of the other burst signal as shown in FIG. 6 by using the following equation (3).

Here, G represents the signal shown in FIG. 6 output from the signal magnitude adjusting unit 68. As shown in FIG.

As can be seen from the waveform diagram shown in FIG. 6, the difference in signal magnitude when the frequency correction burst is received and when the other burst is received is shown in FIG. 5, which is output from the first signal size calculation section 64. FIG. Compared with the proposed signal, it is larger, so that frequency correction bursts can be detected even in a multipath fading channel environment of mobile communication.

FIG. 7 is a waveform diagram of a signal input to the frequency correction determination unit 70 for explaining the frequency correction burst detection method performed by the frequency correction determination unit 70 shown in FIG. ST is a variable indicating the start point of the expected burst expected by the frequency correction burst, and END is a variable indicating the end point of the expected burst.

FIG. 8 is a flowchart for explaining a frequency correction burst detection method performed by the frequency correction determining unit 70 shown in FIG. 2, and storing the input signal to find a start point and an end point of an expected burst (130). Step 134) and determining the frequency correction burst by calculating the number of bits of the expected burst and comparing it with the number of reference bits (steps 136 to 140).

9 (a) to (b) are flowcharts for explaining in detail the steps 132 to 134 shown in FIG. 8, where the starting point of the expected burst is found (steps 150 to 166), and the end point of the expected burst is shown. (Step 168 to 178) and calculating the expected number of frequency correction bits (step 180).

The frequency correction determining unit 70 shown in FIG. 2 inputs and stores the signal shown in FIG. 7 from the signal magnitude adjusting unit 68 (step 130), and finds the start point and the end point of the expected burst from the stored data. (Steps 132 and 134), the number of bits of the expected burst is calculated by subtracting the starting point from the end point, and then it is determined whether the number of bits is greater than or equal to the existing number of bits (step 136). This reference number of bits means the minimum number of bits to be a frequency correction burst.

If the number of bits of the anticipated burst is larger than the number of reference bits, the burst is determined as a frequency correction burst (step 138), and if less, it is determined as another burst (step 140).

The above-described frequency correction burst detection method will be described in detail with reference to FIGS. 8, 9 (a) and 9 (b) as follows.

Variable i shown in Figs. 9 (a) to (b) indicates the number of data to be stored, L1 is a variable indicating a first reference value, L2 is a variable indicating a second reference value having a large size L1q, and CO_L1 Is a variable that is incremented by 1 when the size of the data is less than l1, CO_L2 is a variable that is incremented by 1 when the size of the data is greater than or equal to L2, NO1 is a variable that represents the number of bits of the expected burst, and NO2 is Defined as a variable representing the number of reference bits.

First, step 132 of detecting the starting point of the expected burst will be described in detail as follows.

After operation 130, the frequency correction determination unit 70 initializes the variables i, CO_L1, CO_L2, ST, END, and NO1 (step 150). After step 150, the variable i is increased by one (step 152), and it is determined whether the stored data is greater than or equal to the variable L1 shown in FIG. 7 (step 154). If again, proceed to step 153 to increase the variable i by one again.

After step 156, it is determined whether the stored data is 1 or 2 or more shown in FIG. 7 (step 158), and if it is abnormal, the variable CO_L2 is increased by 1 (step 162). In step 160 (step 160), the variable i is increased by one.

After step 162, the frequency correction determining unit 70 determines whether the variable CO_L2 is 20 or more (step 164). If the value is equal to or higher, the frequency correction determining unit 70 sets the value of the variable i as the value of the variable ST shown in FIG. (Step 166), if less, proceed to step 156 to increase the variable i by one.

Next, step 134 of detecting an end point of the expected burst will be described.

After step 166, ST is increased to n as a variable n (step 168). In order to detect an endpoint, it is determined whether the data is less than or equal to the variable L1 (step 170). n is increased by 1 (step 172), and then, variable CO_L1 is increased by 1 (step 174). After step 174, it is determined whether the variable CO_L1 is 20 or more (step 176), and if it is not abnormal, the variable n is increased by 1; if it is 20 or more, the expected burst is made by using the value of the variable n as the variable END value shown in FIG. The endpoint of is detected (step 178).

Finally, in order to determine whether the expected burst is a frequency correction burst, the start point is subtracted from the detected end point of the detected burst to obtain the number of bits of the expected burst (step 180), and the flow proceeds to step 136 shown in FIG.

The above-described variables L1 and L2 are 20 or less, and 0 or more, which may be referred to as the most preferable range of L1 and L2, and other predetermined values may be used.

As described above, the frequency corrected burst detection device and its detection method in digital mobile communication do not depend on the magnitude of the signal input to the frequency baseband portion, and start the frequency corrected burst signal more accurately by using a signal size adjuster. And the end point can be detected to accurately detect the correction burst signal section.

Claims (5)

Means for receiving an analog signal expected from a frequency correction burst transmitted from a base station of a digital mobile communication system and separating the signal into an in phase (I phase) signal and a quadrature phase (Q) signal; A frequency corrected burst detection apparatus for a mobile station of the mobile communication system, comprising means for converting a Q signal into a digital signal, comprising: mixers for mixing and outputting a predetermined frequency to shift the I and Q signals to baseband, respectively ; Filter means for minimizing and outputting noise of the I and Q signals output from the input mixers; First signal size calculating means for calculating magnitudes of the I and Q signals output from the filter means and outputting the calculated magnitudes; Second signal size calculating means for calculating magnitudes of the additive I and Q signals output from the mixers and outputting the calculated magnitudes; Signal size adjusting means for dividing the output of the first signal size calculating means to the output of the second signal size calculating means and adjusting the level of the frequency correction burst; And frequency correction determining means for inputting the output of said signal size adjusting means to determine whether or not a frequency correction burst is applied. Means for receiving an expected burst expected from a frequency correction burst transmitted from a base station of a digital mobile communication system, separating the signal into an I signal and a Q signal, and converting the signal into a digital signal. A frequency corrected burst detection method, comprising: a storing step of storing, as data, a ratio of the magnitudes of the I and Q signals from which noise has been removed and the magnitudes of the I and Q signals from which the noise has been removed; A first detecting step of finding a start of the expected burst; A second detection step of finding an end portion of the expected burst; A determination step of determining whether an expected number of bits of the expected burst is greater than a predetermined reference number of bits; A first burst determination step of determining the expected burst as a frequency correction burst when the expected number of bits is greater than the reference number of bits; And a second burst determining step of determining the expected burst as a burst other than the frequency correction burst when the number of expected bits is less than the reference number of bits. The method of claim 2, wherein i is a variable representing the number of data to be stored, L1 is a variable representing a first reference value, L2 represents a second reference value, and is a variable having a larger size than the variable l1, and CO_L1 is CO_L2 is a variable that is increased by 1 when the size of the data is smaller than L1, CO_L2 is a variable that is increased by 1 when the size of the data is greater than or equal to L2, ST is a variable indicating a starting point of the frequency correction burst, and END is a value of the expected burst. A variable representing an endpoint, NO1 is a variable representing the number of bits of the expected burst, NO2 is a variable representing the number of threshold bits of the frequency correction burst, the first detection step is the variable i, CO_L1, CO_L2, A first initialization step of initializing ST, END, and NO1 after the storing step; A first increasing step of increasing the variable i; A first judging step of determining whether the data is equal to or greater than L1 and proceeding to the first increasing step if it is not satisfied; A second increasing step of increasing i by one if the first determination step is satisfied; A second judging step of determining whether the data is equal to or greater than the L2; A second initialization step of initializing the CO_L2 and proceeding to the first increase step if the second determination step is not satisfied; A third increasing step of increasing the CO_L2 by 1 when the second judging step is satisfied; A third judging step of determining whether or not the CO_L2 is equal to or greater than a predetermined value and proceeding to the second increasing step; And a burst start point determining step of setting the value of i to the value of ST if the third judging step is satisfied. 4. The method of claim 3, wherein the second detecting step comprises: a fourth increasing step of increasing the ST by one after the burst start point determining step; A fourth judging step of determining whether the size of the data is equal to or less than the L1; A third initialization step of initializing the CO_L1 and proceeding to the fourth increase step if the fourth determination step is not satisfied; A fifth increasing step of increasing the CO_L1 by 1 when the fourth judging step is satisfied; A fifth determination step of determining whether the CO_L1 is equal to or greater than the predetermined value and proceeding to the fourth increasing step if it is not satisfied; And a burst endpoint determining step of setting the value of i to the value of END if the fifth determination step is satisfied. The method of claim 4, wherein the determining step comprises: calculating a number of bits by subtracting the ST from the END to obtain the NO1; And a sixth judging step of judging whether or not the NO1 is equal to or greater than the NO2, and proceeding to the first burst determining step and, if not satisfied, to the second burst determining step. Frequency correction burst detection method.