KR0177882B1 - Frequency offset measuring apparatus and method of the same in digital mobile communication system - Google Patents

Abstract

The present invention discloses a frequency offset measuring apparatus and a measuring method thereof of a digital mobile communication system. Means for inputting a frequency correction burst through an antenna, separating it into analog I and Q signals, converting it into a digital signal, mixing with a predetermined frequency to move to the baseband, respectively, and a frequency offset for inputting and correcting the measured frequency offset The offset measuring apparatus of the mobile station system having correction means inputs digital I and Q signals, samples at a predetermined multiple of the bit sampling rate of the frequency correction burst, extracts any sampled signals, obtains a phase, and Means for outputting a phase average value, and means for calculating a frequency offset by comparing the phase average value with π, and outputting the calculated frequency offset to the frequency offset correction means. Accurate frequency with minimal noise and excellent thermal stability The offset can be measured and the phase calculation amount can be reduced to shorten the frequency offset correction time.

Description

Frequency offset measurement device and method of measurement in digital mobile communication system

1 is a block diagram of a device for measuring and correcting a conventional frequency offset.

2 is a schematic block diagram of a mobile station in a digital mobile communication system for explaining a frequency offset measuring apparatus according to the present invention.

3 is a detailed block diagram of the frequency offset measuring unit according to the present invention shown in FIG.

4 is a flowchart for explaining a frequency offset measuring method according to the present invention performed in FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to frequency synchronization of digital mobile communication, and more particularly, to measure a frequency offset of a digital mobile communication system of a time division multiple access (TDMA) system. And a measuring method thereof.

In a TDMA digital cellular mobile communication system, a base station repeatedly transmits a frequency correction burst in accordance with the TDMA multi-frame communication protocol for frequency synchronization between a base station and a mobile station. The mobile station repeatedly transmits such a frequency correction burst in accordance with the multi-frame communication protocol of TDMA. The mobile station receives this frequency correction burst and synchronizes it with the frequency of the base station.

In the TDMA scheme, the frequency correction burst is an analog radio signal in which specific data is modulated. In particular, in the case of the European TDMA system (SGM, DCS), the frequency correction burst is composed of a total of 148 bits, and all of the 148 bits are defined as binary data '0'. '0' is modulated by Gaussian Minimum Shift Key (GMSK) and wirelessly transmitted from the base station to the mobile station. If the symbol transmission rate is T, at the carrier frequency fca As many as transitioned Has a frequency spectrum characteristic. In addition, the frequency correction burst in the baseband from which the carrier frequency, which is a radio frequency (RF), is removed Sinusoidal characteristics with a period of

A conventional frequency offset measurement and correction apparatus will be described below with reference to FIG.

FIG. 1 is a block diagram of a conventional frequency offset measurement and correction device, and includes an RF receiver 20, a low band passband 30, a phase meter 40, and a frequency offset correction unit from an antenna 10 for receiving an airwave. A mixer 52 constituting 50, a loop filter 54, and a voltage controlled oscillator (VCO) 56 are sequentially formed.

When the frequency correction burst transmitted from the base station of the TDMA digital mobile communication passes through the antenna 10 and the RF receiver 20 of the mobile station shown in FIG. It has sinusoidal characteristics with a period of. This frequency correction burst Is input to the phase meter 40 via a low pass passband 30 having a low pass cutoff frequency of. The phase measuring unit 40 measures the phase of the signal input from the low band passband 30 based on the reference frequency f _R , and then outputs the phase to the frequency offset correcting unit 50. In the frequency offset corrector 50, the phase is input to the VCO 56 through a modulo 2π subtracter 52 and a loop filter 54. At this time, the output frequency of the VCO 56 is controlled according to the magnitude of the output signal of the loop filter 54. If the output signal of the loop filter 54 is '0', the frequency synchronization is stabilized. This is a case where the frequency offset difference is larger as it deviates from the value. The loop continues to run so that this difference is zero. As a result, the signal whose frequency offset is corrected is output from the VCO 56 and applied to the RF transceiver to achieve frequency synchronization.

The hardware implementation of the conventional frequency offset measurement and correction unit described above is mainly a phase-locked loop using a mixer 52, a low pass pass-through 30, a VCO 56, etc. PLL (Phase Locked Loop) technique is used, and there is a problem in that the frequency offset cannot be accurately measured and corrected according to the error tolerance and temperature characteristics of the devices used.

In addition, under a rapidly changing mobile communication channel environment such as multipath fading or handover of a base station to another base station, it is unable to actively measure a fine frequency offset according to the state of a received signal. There is a problem.

An object of the present invention is to provide an apparatus for measuring frequency orset in a digital mobile communication system that measures the frequency offset digitally for accurate correction of the frequency offset in order to solve the conventional problems as described above.

Another object of the present invention is to provide a frequency offset measuring method performed in the frequency offset measuring apparatus of the digital mobile communication system according to the present invention.

Signal separation means for inputting a frequency correction burst through an antenna according to the present invention to achieve the above object, and separating the analog I signal and the Q signal, an analog / digital converter for converting the I signal and the Q signal into a digital signal, The apparatus for frequency offset measurement of a mobile station system comprising mixers for mixing I and Q signals to a baseband, respectively, and mixers for mixing with a predetermined frequency, and frequency offset correction means for inputting and correcting a measured frequency offset. Sampling means for inputting the output I and Q signals, sampling at a predetermined multiple of the bit sampling rate of the frequency correction burst, and outputting the sampled In and Qn signals; And phase calculating means for outputting phase average values of the phases, and the phase averages. The frequency offset is calculated by comparing the value with π to calculate the frequency offset, and outputting the calculated frequency offset to the frequency offset correction means.

In order to achieve the above another object, the frequency correction burst according to the present invention receives the I signal and the Q signal, converts it into a digital signal, calculates a frequency offset from the converted signal, and the calculated frequency offset measuring method includes: Sampling the I signal and the Q signal at a predetermined multiple of the bit sampling rate of the frequency correction burst to obtain a sampled In signal and a Qn signal, and using the following equation: phase (θ _i of the frequency correction burst) ), And the average value of the phases θ _i ( ) Step.

Step, and the average value ( Is greater than π to obtain the frequency offset f _o using the following second equation, and if the average is less than π, to obtain the frequency offset f _o using the following third equation:

(Where T denotes a symbol rate).

Hereinafter, the configuration and operation of a mobile station in a TDMA digital mobile communication system will be described with reference to FIG.

2 is a schematic block diagram of a mobile station in a digital mobile communication system for explaining a frequency offset measuring apparatus according to the present invention, from the antenna 60 to the duplexer 70, the RF transceiver 80, analog / digital (Analogue / Digital) converter 90, mixers 100 and 102, frequency offset corrector 110, and frequency offset corrector 120 in turn.

The frequency correction bust wirelessly transmitted from the base station of the TDMA digital mobile communication system using the RF carrier is received by the mobile station of the digital mobile communication system through the antenna 60 and input to the RF transceiver 80 through the duplexer 70. do.

Here, the RF transceiver 80 performs a reception function when receiving a frequency correction burst through the antenna 60, and transmits a signal to the base station when the frequency is synchronized between the mobile station and the base station. Perform the function.

At this time, the signal output from the RF transceiver 80 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 Has a phase difference characteristic.

The A / D converter 90 converts the analog I and Q signals into digital I and Q signals and outputs them to the mixers 100 and 102. At this time, the output digital I and Q signals on the frequency spectrum As the shifted signal, the first mixer 100 and the second mixer 102 input the I and Q signals through the input terminal IN1. And each of the baseband characteristics of the frequency correction burst The sine wave of the period is output to the frequency offset measuring unit 110 as a signal that is almost a direct current component.

The frequency offset measurement unit 110 calculates and outputs a phase average value from the I signal and Q signal input from the mixers 100 and 102 and the sample rate M input through the input terminal IN2, and outputs the frequency offset correction unit 120. ) Is inputted to the control suppression input terminal of the local oscillator of the RF transmitter / receiver 80 after inputting a phase average value and converting it into an analog, then filtering by a low pass filter composed of an RC network. At this time, the output frequency of the local oscillator is applied to the RF transceiver 80 of the mobile station according to the magnitude of the input voltage, and the frequency offset is corrected. As a result, frequency synchronization between the mobile station and the base station is achieved, thereby enabling transmission and reception.

The configuration and operation of the frequency offset measurement unit 100 according to the present invention will be described in detail with reference to FIGS. 3 and 4 as follows.

FIG. 3 illustrates the configuration and operation of the frequency offset measuring unit 110 according to the present invention shown in FIG. 2 with reference to FIGS. 3 and 4 as follows.

FIG. 3 is a detailed block diagram of the frequency offset measuring unit 110 according to the invention of the ball shown in FIG. 2, and the sampling unit 114, the phase calculating unit 116, and the frequency offset calculation are performed from the filter unit 112. Part 118 is sequentially configured.

4 is a flowchart for explaining a frequency offset measuring method according to the present invention, which is performed in FIG. 3, by sampling a signal to obtain an average phase value (steps 200 and 202), and from the average phase value. Computing the frequency offset (steps 204 to 208).

The filter unit 112 shown in FIG. 3 inputs the I signal and the Q signal through the input terminals IN3 and IN4, respectively, and minimizes and outputs noise outside the signal band. At this time, the filter section 112 has a 3dB cut-off frequency fr = r × 10 ⁻⁶ ) f ₁₀ + f _d or more.

Where r is the tolerance of the local oscillator of the RF transceiver 80, 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 transceiver 80, respectively. The sampling unit 114 inputs the I signal and the Q signal output from the filter unit 112 to sample at M times the bit sampling rate T [kbps] of the frequency correction buster, and the sampling value is within the range of M values among the sampled signals. According to the present invention, arbitrary signals are extracted (step 200), and the extracted I and Q signals In and Qn are output. At this time, the sample rate (M) is input through the input terminal IN5 and the range is about 10 to 20. For example, the sampling unit 114 samples the signals I and Q, and extracts 7-14 from the sampled signals for a frequency correction burst composed of a total of 148 bits according to the sampling rate range. Output to the phase calculator 116 to measure the frequency offset.

The phase calculator 116 inputs In and Qn output from the sample extractor 114 to input phases θ _i and phase average values such as the following equations (1) and (2). ) (Step 202).

Here, -πQ _i π and I is a natural number from 1 to n.

here, to be.

After step 202, the frequency offset calculator 118 inputs a phase average value to determine whether the phase average value is greater than [pi] (step 204). If greater than π, the negative frequency offset is calculated by the following equation (3) (step 206), and if less than π, the positive frequency offset is calculated by the following equation (4) (first Step 208).

As described above, the frequency offset measuring apparatus and the measuring method of the digital mobile communication system according to the present invention is a low-pass filter considering the noise of the signal to measure the frequency offset, the local oscillator error tolerance of the receiver and the Doppler frequency transition, etc. Minimize the error rate by using the digital signal processing method and measure the frequency offset by the digital signal processing method. By using the sampling unit, the amount of phase calculation can be reduced, thereby reducing the frequency offset correction time.

Claims (4)

Signal separation means for inputting a frequency correction burst through an antenna to separate analog I and Q signals, an analog / digital converter for converting the I and Q signals into digital signals, and the I and Q signals to baseband, respectively. A frequency offset measuring apparatus of a mobile station system having mixers mixing with a predetermined frequency to move, and frequency offset correction means for inputting and correcting a measured frequency offset, wherein the I and Q signals output from the mixers are adjusted. Sampling means for inputting and sampling at a predetermined multiple of the bit sampling rate of the frequency correction burst, extracting arbitrary signals according to the predetermined number of sampled signals, and outputting an In signal and a Qn signal; Phase calculation means for inputting the In signal and the Qn signal to obtain a phase, and outputting a phase average value of the phases; And a frequency offset calculating means for comparing the phase average value with π, calculating the frequency offset according to the comparison result, and outputting the calculated frequency offset to the frequency offset correction means. Frequency offset measuring device of the system. The apparatus of claim 1, wherein the frequency offset measuring apparatus further comprises a filter unit which outputs a signal by minimizing noise outside the signal bands of the input I and Q signals. . 2. The apparatus of claim 1, wherein the frequency offset calculating means comprises: first calculating means for calculating the frequency offset using a following first equation when the phase average value is larger than [pi]; And And a second calculating means for calculating the frequency offset by using the following second equation when the phase average value is smaller than [pi]. (Where T represents symbol rate) Receives a frequency correction burst, converts it into an I signal and a Q signal, converts it into a digital signal, calculates a frequency offset from the converted signal, and corrects the calculated frequency offset. In the measuring method, the I and Q signals are sampled at a predetermined multiple of the bit sampling rate of the frequency correction burst, and arbitrary signals are extracted according to the predetermined number of the sampled signals to obtain an In signal and a Qn signal. step; The phase θ _i of the frequency correction burst is obtained by using the following first equation, and the average value of the phase θ _i ( Obtaining; (Where i = 1, 2, 3, ...., n and -πQ _i π) The average value ( Determining whether is greater than π; And the average value ( Is greater than π to obtain the frequency offset fo using the following second equation; And obtaining the frequency offset fo by using the following third equation when the average value is smaller than π. (Where T represents symbol rate)