KR100193859B1 - Frequency offset measurement device between base station and mobile station in time division multiple access communication system - Google Patents

Abstract

The present invention is to simplify the configuration of an apparatus for measuring the offset of the carrier frequency between the base station and the mobile station for the synchronization of the system in a time division multiple access mobile communication system. The apparatus for measuring frequency offset includes a multiplier for inputting a baseband frequency correction burst to multiply this signal by a predetermined sinusoidal frequency, a low pass filter for low pass filtering the output of the multiplier, and an output of the low pass filter. And a frequency offset calculator for calculating a phase offset from the average phase value calculated by the phase calculator.

Description

Frequency offset measurement device between base station and mobile station in time division multiple access communication system

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time division multiple access digital mobile communication system, and more particularly, to an apparatus for measuring an offset of a carrier frequency between a base station and a mobile station after processing a frequency calibration burst provided from a base station for base station synchronization in a mobile station. will be.

In general, time division multiple access (hereinafter referred to as TDMA) is a multiple access method in mobile communication, in which a base station carries a digitized signal in a time slot to which the base station is assigned to a radio wave of the same frequency in a burst form. It transmits and it is said that a mobile station performs multiple connection between each base station.

Such a TDMA digital mobile communication system (hereinafter referred to as a TDMA communication system) includes a base station and a mobile station. At this time, the base station and the mobile station transmits a frequency correction burst (Frequency Correction Burst) to synchronize the frequency with each other. This frequency correction burst is a sine wave characteristic defined by 148 bits, and the base station periodically transmits the frequency correction burst to the mobile station by using a multiframe. In addition to the frequency correction burst, the mobile station receives other bursts (normal burst, synchronization burst, etc.), and detects only the frequency correction burst and measures the carrier frequency offset to perform the synchronization operation of the carrier frequency for communication between the base station and the mobile station. .

1 is a block diagram of a mobile station processing process for receiving a frequency calibration burst from a base station and performing an operation for synchronizing carrier frequencies in a TDMA communication system according to the prior art. The synchronization device shown in FIG. 1 is a configuration proposed under US Patent No. 5,241,688 (registered August 31, 1993) under the title FREQUENCY AND TIME SLOT SYNCHRONIZATION USING ADAPTIVE FILTERING.

Referring to FIG. 1, a mobile station for synchronizing carrier frequencies may be divided into a portion for detecting a frequency correction burst transmitted from a base station and a portion for measuring a frequency offset of the frequency correction burst after detecting a frequency correction burst. Components for detecting the frequency correction burst correspond to 101 to 107, and components for measuring the frequency offset of the frequency correction burst correspond to 108 to 109.

First, the process of detecting the frequency calibration burst will be described.

In FIG. 1, the adaptive band-pass filter 101 inputs one of a baseband signal I signal and a Q signal modulated by a continuous phase shift keying method, and then outputs a band pass filter. do. POLE ADATATION BLOCK 102 inputs the bandpass filtering output to adaptively adjust and output the pole. The energy calculator 103 calculates energy for the output of the adaptive bandpass filter 101, and the energy calculator 104 calculates energy for the input of the adaptive bandpass filter 101. The result calculated by the two energy calculators 103, 104 is input to a gain adjustment block (GAIN ADAPTATION BLOCK) 105, the gain is adjusted, the tone detector 106 detects the presence or absence of the tone (TONE) in the gain-controlled result. At this time, when the tone is detected, the detection operation of the frequency calibration burst is started. TIMER BLOCK 107 detects the end time index of the frequency calibration burst by measuring the length of time that the current state of the tone continues. The gain regulator 105 and the pole regulator 102 adjust the gain and the pole of the adaptive bandpass filter 101 by feedbacking the gain coefficient and the pole coefficient of the output signal of the adaptive bandpass filter 101. In addition, the output of the pole adjuster 102 is also fed back to the bandpass filter 110 for measuring the frequency offset of the frequency calibration burst to adjust the pole of the filter.

Next, the process of measuring the frequency offset of the frequency calibration burst will be described.

The input signal Xn is input to the adaptive bandpass filter 101 and the buffer 108 (SHIFT REGISTER BUFFER). When the frequency correction burst detection signal is transmitted from the timer block 107 for detecting the frequency correction burst section end index, the buffer 108 in which the frequency correction burst signal is stored applies the signal to the band pass filter 110. The band of the bandpass filter 110 adjusted by the pole coefficient fed back from the pole regulator 102 passes through the frequency calibration burst frequency band. The influence of the bandpass filter 110 results in a good signal to noise index. do. In this case, the band pass filter 110 is formed of an Infinite Impusle Response (IIR) filter and performs a filtering operation according to Equation 1 below.

The output Wn of the bandpass filter 110 has an optimal phase measured by a least square error prediction block 109. In this case, the measured angular frequency of the received frequency calibration burst is calculated by Equation 2 below.

The frequency offset (FREQUENCY OFFSET) value measured and output by the least square error prediction block 109 is obtained from a difference value of π / 2 (67.5 kHz) which is the angular frequency of the ideal frequency calibration burst of Equation 2 above. Is saved. The frequency offset value of the frequency calibration burst thus obtained is inputted to a local oscillator (not shown) of the mobile station to synchronize the carrier frequency between the mobile station and the base station, thereby controlling the oscillation frequency.

On the other hand, according to the prior art as described above, the pole value for the band pass filter 110 used to pass the frequency band of the frequency correction burst is provided from the pole adjuster 102, the band pass filter 110 is implemented in the form of IIR Able to know. In addition, it can be seen that the least square error prediction method is used to measure the frequency offset of the frequency calibration burst. However, this method, i.e., using the IIR filter and the least square error prediction method, is not only very complicated in signal processing but also requires a large amount of calculation.

Accordingly, an object of the present invention is to more simply find the offset of the frequency of the frequency correction burst in the TDMA communication system.

Another object of the present invention is to more quickly measure an offset with respect to a frequency of a frequency calibration burst in a TDMA communication system.

It is another object of the present invention to minimize errors in frequency measurement of frequency calibration bursts in a TDMA communication system.

The present invention for achieving these objectives is to multiply the frequency correction burst signal by the theoretical frequency fcb of the frequency correction burst, and to use the Doppler frequency shift and the mobile station in the mobile communication environment to minimize errors in the frequency offset measurement. We designed a low pass filter considering the error tolerance of local oscillator. Also, we can reduce frequency of digital signal processing using sampler and measure frequency offset faster than conventional technology. The structure and simple frequency offset calculation eliminates the need for a high-performance digital signal processor, reducing the hardware cost.

According to a first aspect of the present invention, an apparatus for measuring an offset of a carrier frequency between a base station and a mobile station after processing a frequency calibration burst provided from a base station in a baseband in a TDMA communication system is provided. Calculating a phase with respect to the frequency correction burst using a multiplier that inputs a burst to multiply the signal by a predetermined sinusoidal frequency, a low pass filter to low pass filter the output of the multiplier, and an output of the low pass filter. And a phase offset calculator for calculating a frequency offset from the average phase value calculated by the phase calculator.

According to a second aspect of the present invention, there is provided a frequency offset measuring apparatus comprising: a multiplier for inputting a baseband frequency correction burst to multiply a predetermined sinusoidal frequency to a low pass filter; and a low pass filter for low pass filtering the output of the multiplier; A phase calculator for calculating a phase with respect to the frequency calibration burst using the output of the low pass filter, and comparing the average phase value calculated by the phase calculator with a preset phase value to determine the characteristics of the frequency offset, It consists of a frequency offset calculator for calculating the frequency offset according to the characteristics.

The frequency offset measuring apparatus according to the third aspect of the present invention multiplies a predetermined sinusoidal frequency by each of an I (nT) signal and a Q (nT) signal for a baseband frequency correction burst, and thus an I1 (nT) signal and a Q1 ( a multiplier for outputting an nT) signal and low pass filtering based on a preset cutoff frequency by inputting the I1 (nT) signal and the Q1 (nT) signal to output an I2 (nT) signal and a Q2 (nT) signal A low pass filter, a sampler for sampling the I2 (nT) signal and the Q2 (nT) signal according to a preset sampling rate M and outputting an I3 (nMT) signal and a Q3 (nMT) signal, and the I3 (n) a phase calculator for calculating an average phase value (Θav) for the nMT) signal and the Q3 (nMT) signal, and comparing the average phase value (Θav) with a preset phase value to determine the characteristics of the frequency offset, And a frequency offset calculator for calculating the frequency offset fo according.

1 is a view showing the configuration of a frequency offset measurement apparatus between a base station and a mobile station according to the prior art.

2 is a view showing the configuration of a frequency offset measuring apparatus according to the present invention.

DETAILED DESCRIPTION A detailed description of preferred embodiments of the present invention will now be described with reference to the accompanying drawings. In the following description of the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted. In addition, the terms to be described below are terms defined in consideration of functions in the present invention, which may vary according to the intention or custom of the user or chip designer, and the definitions should be made based on the contents throughout the present specification.

2 is a view showing the configuration of an apparatus for measuring the frequency offset of the frequency calibration burst in accordance with the present invention. The operation of this device is successful in the baseband section after the frequency calibration burst transmitted from the base station of the TDMA communication system passes through the antenna, duplexer, RF receiver and A / D converter of the mobile station. It is assumed that it is detected.

Referring to FIG. 2, the apparatus according to the present invention inputs an I (Inphase) signal and a Q (Quadrature) signal, which are digital signals of a frequency correction burst (FCB) modulated by a phase continuous shift (CPSK) method. Multipliers 201 and 202 input the I (nT) signal and the Q (nT) signal, respectively, and multiply the sinusoidal frequency fcb of the frequency calibration burst oscillated by the oscillator 203 to multiply the I1 (nT) signal and Q1 (nT). Output the signal. This multiplication result is applied to the low pass filter 204 designed in consideration of the oscillation frequency tolerance and the Doppler frequency shift of the local oscillator used in the RF receiver of the mobile station, and then filtered the I2 (nT) and Q2 (nT) signals. It is output as a signal. A sampler 205 inputs the I2 (nT) signal and the Q2 (nT) signal, samples at appropriate intervals, and outputs the sampled I3 (nMT) signal and Q3 (nMT) signal. The phase calculator 206 calculates a phase of the I3 (nMT) signal and the Q3 (nMT) signal and outputs a calculation result value Θav, and the frequency offset calculator 207 calculates a frequency offset by inputting the calculation result value Θav. Output the result fo. The frequency offset fo thus calculated is converted into an analog value Va by the D / A converter 208, filtered by the low pass filter 209, and output to Vc. The filtering result Vc output from the low pass filter 209 is applied to the voltage controlled oscillator 210 as a voltage capable of correcting the offset of the carrier frequency. As a result, the voltage controlled oscillator 210 oscillates the frequency controlled by the filtering result value Vc and applies it to the RF transmitter / receiver 211 so that the offset of the carrier frequency is corrected.

Referring again to FIG. 2, the input signals I (nT) and Q (nT) are baseband digital signals modulated by a phase-consecutive transition scheme passed through an antenna, a duplexer, an RF receiver, and an A / D converter in a mobile station. It has 1 sample value. The signals I (nT) and Q (nT) are signals corresponding to frequency correction bursts having a pure sine wave frequency (67.5 KHz) characteristic periodically transmitted from the base station for communication with the base station. It is a mixture of multipath fading and additive white gaussian noise. At this time, the I (nT) signal and the Q (nT) signal are the same signal having a phase difference of 90 degrees with each other.

The output signals I1 (nT) and Q1 (nT) of the multipliers 201 and 202 are output after the I (nT) signal and the Q (nT) signal are multiplied by fcb, which is the sinusoidal frequency of the frequency calibration burst, respectively. Has characteristics.

The output signals I2 (nT) and Q2 (nT) of the low pass filter 204 are signals from which out-of-band noise of the I1 (nT) and Q1 (nT) signals is removed, and has a good signal to noise ratio. Has characteristics. In this case, the 3dB cut-off frequency of the low pass filter 204 is r [ppm], the Doppler frequency transition is fp, and the local oscillation frequency is the error tolerance of the local oscillator used in the RF receiver of the mobile station. When we say (r × ) is determined by + fp.

The sampler 205 samples one sample signal I2 (nT) and Q2 (nT) per input bit at a sample rate M value and outputs sampled I3 (nMT) and Q3 (nMT). The sample rate M value can be set within the range of 10 to 20. The sampler 205 is a component provided to reduce the phase calculation and the frequency offset calculation amount of the frequency correction burst.

The phase calculator 206 inputs I3 (nMT) and Q3 (nMT), obtains a phase of each sample according to Equation 3 below, and uses Equation 4 to measure an average phase with respect to the frequency correction burst. In the following, the units of Θ i and Θ av are radians, and values thereof range from −π ≦ Θi, Θav <π.

The frequency offset calculator 207 represents a negative frequency offset characteristic when the average phase Θav for the input frequency calibration burst is larger than π, and a positive frequency offset characteristic when smaller than π. In the former case, the value of the frequency offset calculated by the frequency offset calculator 207 is determined according to Equation 5 below, and in the latter case, the value of the frequency offset calculated by the frequency offset calculator 207 is determined according to Equation 6 below. do. In the following, T represents a time period of one bit.

The digital frequency offset value fo measured by the frequency offset calculator 207 is converted into an analog signal value Va by the D / A converter 208 and then applied to the low pass filter 209. The low pass filter 209 inputs the analog signal value Va and outputs the filtered voltage value Vc. This voltage value Vc is applied to the voltage controlled oscillator 210 of the mobile station as described above, controlled to correct the measured frequency offset, and then applied to the RF transmitter / receiver 211. Therefore, the RF transmitter / receiver 211 transmits and receives a signal synchronized with the carrier frequency of the base station through the antenna Ant according to the output from the voltage controlled oscillator 210.

As described above, the present invention uses the Doppler frequency shift and the mobile station in the mobile communication environment to multiply the frequency correction burst signal by the theoretical frequency fcb of the frequency correction burst, and to minimize errors in the frequency offset measurement. We designed a low pass filter considering the error tolerance of the local oscillator and also used a sampler. Accordingly, by significantly reducing the amount of computation of digital signal processing, frequency offsets can be measured at a higher speed than in the prior art, and a high performance digital signal processor is not required due to the relatively uncomplicated filter structure and simple frequency offset calculation. The cost of hardware is also reduced.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications may be made without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be defined not only by the scope of the following claims, but also by the equivalents of the claims.

Claims (14)

An apparatus for measuring an offset of a carrier frequency between a base station and a mobile station after processing a frequency correction burst provided from a base station as a baseband in a time division multiple access communication system, A multiplier for inputting the baseband frequency correction burst and multiplying the signal by a predetermined sine wave frequency; A low pass filter for low pass filtering the output of the multiplier; A phase calculator for calculating a phase with respect to the frequency calibration burst using the output of the low pass filter; And a frequency offset calculator for calculating a frequency offset from the average phase value calculated by the phase calculator. The frequency offset measurement apparatus of claim 1, wherein the low pass filter is connected between the phase calculator and the output of the low pass filter is sampled according to a preset sampling rate and output to the phase calculator. The frequency offset measurement apparatus of claim 1, wherein the multiplier multiplies the baseband frequency correction burst by the sine wave frequency with respect to the frequency correction burst transmitted from the base station. An apparatus for measuring an offset of a carrier frequency between a base station and a mobile station after processing a frequency correction burst provided from a base station as a baseband in a time division multiple access communication system, A multiplier for inputting the baseband frequency correction burst and multiplying the signal by a predetermined sine wave frequency; A low pass filter for low pass filtering the output of the multiplier; A phase calculator for calculating a phase with respect to the frequency calibration burst using the output of the low pass filter; And a frequency offset calculator for determining a frequency offset characteristic by comparing the average phase value calculated by the phase calculator with a preset phase value and calculating a frequency offset according to the determined characteristic. The frequency offset calculator of claim 4, wherein when the average phase value calculated by the phase calculator is smaller than the set phase value, the frequency offset calculator determines a positive frequency offset and calculates a frequency offset accordingly. If the phase value is greater than the frequency offset measurement device characterized in that it is determined by the negative frequency offset and the frequency offset accordingly. 5. The apparatus of claim 4, wherein the multiplier multiplies the baseband frequency correction burst by the sine wave frequency with respect to the frequency correction burst transmitted from the base station. The low pass filter is connected between the low pass filter and the phase calculator, and the output of the low pass filter is sampled according to a preset sample rate and output to the phase calculator. Frequency offset measuring device. An apparatus for measuring an offset of a carrier frequency between a base station and a mobile station after processing a frequency correction burst provided from a base station as a baseband in a time division multiple access communication system, A multiplier for outputting an I1 (nT) signal and a Q1 (nT) signal by multiplying a predetermined sinusoidal frequency by each of an I (nT) signal and a Q (nT) signal for the baseband frequency correction burst; A low pass filter for inputting the I1 (nT) signal and the Q1 (nT) signal to low pass filtering based on a preset cutoff frequency and outputting an I2 (nT) signal and a Q2 (nT) signal, respectively; A sampler for sampling the I2 (nT) signal and the Q2 (nT) signal according to a preset sampling rate M and outputting an I3 (nMT) signal and a Q3 (nMT) signal; A phase calculator for calculating an average phase value Θ av for the I 3 (nMT) signal and a Q 3 (nMT) signal; And a frequency offset calculator for determining a characteristic of the frequency offset by comparing the average phase value Θav with a preset phase value and calculating a frequency offset fo according to the determined characteristic. The frequency offset of claim 8, wherein the multiplier multiplies and outputs the I (nT) signal and the Q (nT) signal by multiplying the sinusoidal frequency fcb with respect to the frequency correction burst transmitted from the base station. Measuring device. 9. The method of claim 8, wherein the cut-off frequency of the low pass filter is r [ppm] the error tolerance of the local oscillator of the RF receiver of the mobile station, fp the Doppler frequency transition, and the local oscillation frequency. When we say (r × ) Frequency offset measurement apparatus characterized in that it is determined as + fp. The frequency offset measurement apparatus of claim 8, wherein the average phase value Θav of the I3 (nMT) signal and the Q3 (nMT) signal is determined by the following equation. [Equation 3] [Equation 4] In Equations 3 and 4, −π <Θi and Θav <π. The frequency offset calculator of claim 8, wherein when the average phase value Θav is smaller than the set phase value, the frequency offset calculator determines a positive frequency offset, calculates a frequency offset accordingly, and sets the set phase value. If larger, the frequency offset measurement apparatus, characterized in that the frequency offset is determined according to the negative (offset). The frequency offset calculator of claim 12, wherein the frequency offset calculator determines a positive frequency offset when the average phase value Θav is smaller than the set phase value π, and determines a negative frequency offset when it is larger than the set phase value π. After that, the frequency offset measuring apparatus, characterized in that for calculating the frequency offset accordingly. 15. The method of claim 13, wherein the frequency offset calculator calculates a frequency offset according to Equation 5 below when the frequency offset calculator is determined as a positive frequency offset for the average phase value Θ av, and when the frequency offset calculator is determined as a negative frequency offset. Frequency offset measurement apparatus, characterized in that for calculating the frequency offset according to equation (6). [Equation 5] [Equation 6] In Equations 5 and 6, T is a bit time.