KR100293614B1 - Time synchronous tracer for digital mobile communication system using asymmetric smoothing filter - Google Patents

Abstract

PURPOSE: A time synchronous tracer for a digital mobile communication system using an asymmetric smoothing filter is provided to accurately determine a signal transmission timing in a BTS(Base Transceiver Station) by measuring the reliability of a receiving signal using a level of the receiving signal and estimating the reliability of the receiving signal. CONSTITUTION: A sampling clock signal generator(1) receives a system clock signal(CK) and generates a sampling clock signal. A matching filter(2) filters a signal received in a mobile body so that an SN ration of an output is maximized. A signal power calculating unit(3) calculates a signal power of a signal outputted from the matching filter(2) and outputs the calculated signal power. A peak value detector(4) detects a peak value of a signal outputted from the signal power calculating unit(3). A reliability measurer(5) judges the reliability of a signal received in the mobile body using an output signal of the signal power calculating unit(3). A smoother(6) smoothes an output signal of the peak value detector(4) and adjusts a phase of the clock signal outputted from the sampling clock signal generator(1). A BTS determines whether a transmission timing of a transmission signal is updated according to the reliability of the signal received in the mobile body.

Description

Time Synchronous Tracker in Digital Mobile Communication System Using Asymmetric Smoothing Filter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a time synchronization tracker in a time division multiple access (TDMA) mobile communication system. A reliability measurer and a smoothing device that suppresses sudden changes in the output signal to evaluate the reliability of the received signal.As the quality of the received signal is poor, the base station does not update the timing of signal transmission. A time synchronization tracker of a digital mobile communication system using a type smoothing filter.

In general, in order to satisfy the performance of the receiver in a digital mobile communication system, time synchronization between the mobile station and the base station must be accompanied. That is, in the TDMA digital mobile communication system, time synchronization is required for the mobile to satisfy various requirements. Therefore, the mobile must determine the correct transmission timing of the burst between the mobile and the base station, and if the mobile cannot determine the correct transmission timing within the transmission accuracy T / 2 of the mobile, efficient TDMA is impossible.

However, time synchronization, which is mainly used in TDMA digital mobile communication systems, tracks the transmission timing of a transmission signal transmitted from a base station by using a known training signal, which is a reception received by a mobile object to track transmission timing. After up-sampling the signal, the matching timing is used to determine the correlation between the trained signal and the received signal received by the moving object.

The conventional time synchronizer performing this function incorrectly determines the transmission timing by updating the time synchronizer by measuring the correlation between the trained signal and the received signal even when the received signal is poor regardless of the state of the received signal. There was this.

The present invention has been made to solve the problems of the conventional time synchronizer, and includes a signal reliability measurer and a smoother to measure the reliability of the received signal by measuring the reliability of the received signal by the size of the signal received by the mobile from the base station. Therefore, since the base station does not update the signal transmission timing to transmit a signal when the quality of the received signal is poor, the object of the present invention is to provide a time synchronization tracker for a digital mobile communication system using an asymmetric smoothing filter that accurately determines the signal transmission timing at the base station. have.

1 is a block diagram of a time synchronization tracker in a digital mobile communication system using the asymmetric smoothing filter of the present invention.

<Description of the reference numerals for the main parts of the drawings>

1 Sampling Clock Signal Generator 2 Matching Filter

3: signal power calculation unit 4: maximum value detector

5: signal reliability meter 6: smoother

CK: system clock signal

The time synchronous tracker of the digital mobile communication system using the asymmetrical smoothing filter of the present invention for achieving the above object, in the time synchronous tracker to determine the signal transmission timing from the base station to the mobile, by inputting the system clock signal (CK) A sampling clock signal generator 1 for generating a sampling clock signal, a matching filter 2 for filtering the signal received by the moving object to maximize the output SN ratio, and a signal of the signal output from the matching filter 2; A signal power calculator 3 for calculating and outputting power, a peak detector 4 for detecting a maximum value of the signal output from the signal power calculator 3, and an output signal of the signal power calculator 3; The sampling clock signal is generated by smoothing the output signal of the reliability detector 5 and the peak detector 4 for determining the reliability of the received signal received by the moving object. According to (1) the moving object, the reliability of the data received by having a smoothing group (6) for adjusting the phase of the clock signal output from characterizes in determining whether to update transmission timing of a signal transmitted from the base station.

Hereinafter, with reference to the accompanying drawings will be described in detail the operation and effect of the present invention.

1 is a block diagram of a time synchronization tracker in a digital mobile communication system using the asymmetric smoothing filter of the present invention. The synchronization tracker shown in FIG. 1 is used to determine symbol timing from a training sequence of synchronization bursts and normal bursts, and the signal power calculation section 3 performs a sequence of received symbols. Find the desired training sequence by generating a correlation peak, such as a pulse, when is equal to the coefficient of the matched filter (2).

The output i of the sampling clock signal generator 1 is weighted at a ratio of 4 / T, and is set to a modulated value of the repetition rate of the training sequence, so that the output of the sampling clock signal generator 1 is completely timing. (i) Pulses always have the same value. However, since the timing is not perfect and has a time offset, the present time synchronous tracker measures the time offset by recording the value of the output (i) of the sampling clock signal generator 1 at the moment of the peak to measure the time offset of the sampling clock signal generator 1. It is used to estimate the time offset, and once the offset is known, the timing phase can be adjusted.

The reliability measurer 5 of the signal checks the timing reliability of the correlation maximum by determining whether the magnitude of the received signal is within the set range, and when the signal-to-noise ratio is low, that is, when the magnitude of the received signal is a signal outside the set range, the timing is determined. Preventing updates ensures accurate time synchronization even in low signal-to-noise ratio areas.

The time synchronization tracker shown in FIG. 1 does not operate continuously. This is because it requires too many processor cycles. Instead, it is used to determine the tracking period by estimating the initial time provided by the frequency synchronizer within the time determined by the accuracy of the frequency corrected burst position and the number of taps of the matching filter 2.

Since the time-synchronous tracker of the present invention uses T / 4 sampling, the tracking window must be four times the initial accuracy plus the number of taps, and the synchronization burst and normal burst contain a known data sequence. Therefore, the coefficient of matched filter 2 is the inverse time conjugate complex number of the ideal training sequence sampled at intervals of T / 4. Therefore, the output of the matched filter 2 is calculated as follows.

····(One)

here Is the complex input sample received at time i, c _k is the coefficient of the second matched filter 2. The input of the definitive filter 2 is T / 4 interval, but the input signal is T interval. In theory, three zero samples should be inserted before being input into the matched filter (2). However, in this case unnecessary multiplication by zero occurs. Therefore, in the present invention, the matching filter 2 is treated as four different filters, each of length N / 4, and the T interval output is multiplexed to generate a T / 4 interval sample.

The sampling clock signal generator 1 provides a time synchronizer with a time index that is sampled at the moment of arrival of a trained sequence of synchronous bursts or normal bursts, the function of the peak detector 4 being at the output of the signal power calculator 3. Determine the time index for the peak of. These peaks occur when the trained sequence is shifted to the matched filter 2, and the sampling clock signal generator 1 reads the instantaneous value of the highest output. This value is in units of T / 4 for the nth burst. It is called. The index n is incremented each time the sync burst or normal burst is counted and the output i of the sampling clock signal generator 1 reaches zero.

The function of the smoother 6 is performed by using a first order smoothing filter with an asymmetric step size. When is denoted as the smoothed output of the filter, that is, the output of the smoother 6, the operation of filtering is expressed as follows.

····(2)

Where β is a time constant, and as β increases, the smoothing increases, and the length of the memory increases, so that the change in input is slowly tracked. If α = 1-β, the above formula (2) can be rewritten as follows.

(3)

Is a small amount Is updated by Using asymmetric adjustment And previous estimates according to Update the value of, the error term function In step size α is used.

Therefore, for the first run of the synchronization circuit, we initialize the estimate for the highest index.

For the other continuous bursts, the following timing recovery update equation shown in equation (5) is used.

Where n is the burst index and L (Δi) is the limit function

As such, the timing phase of the clock signal output from the sampling clock signal generator 1 is adjusted by the output i _ave (n) of the smoother 6 to update the transmission timing of the transmission signal transmitted from the base station. When the magnitude of the received signal received by the moving object is within the set range, that is, when the received signal determined by the signal reliability measuring device 5 is of good quality, the smoothing device 6 is output by the output i _max of the peak detector 4. ) Is synchronized with a new output by updating the transmission timing of the signal, and having a low signal-to-noise ratio outside the set range of the size of the received signal received by the moving object, i.e., the received signal determined by the signal reliability measurer 5 is of high quality. In a bad situation, since i _ave (n) time increases a lot, it is not converged due to an error in time estimation. Therefore, the signal reliability measurer 5 detects such a situation. If there is no reliability, the output i _max of the peak detector 4 is discarded without input to the smoother 6.

Therefore, the smoother 6 has no signal input from the peak detector 4 so that the transmission timing of the signal is determined and synchronized by the existing output without updating the transmission timing of the signal with the new output.

The time synchronous tracker of the present invention, which operates as described above, is used as a time synchronous tracker in a TDMA digital mobile communication system, so that the timing of transmission of the base station transmission signal is updated according to the reliability of the received signal of the mobile. There is an advantage that the transmission timing of the transmission signal can be accurately determined.

Claims (3)

In the time synchronization tracker for determining the signal transmission timing from the base station to the mobile, A sampling clock signal generator 1 for inputting a system clock signal CK to generate a sampling clock signal, a matching filter 2 for filtering a signal received by a moving object to maximize the output SN ratio, and the matching filter A signal power calculator 3 for calculating and outputting signal power of the signal output from (2), a peak detector 4 for detecting the highest value of the signal output from the signal power calculator 3, and the signal; The sampling clock signal generator 1 by smoothing the output signal of the signal detector 5 and the reliability detector 5 for determining the reliability of the received signal received by the moving object as the output signal of the power calculator 3. And a smoothing device 6 for adjusting the phase of the clock signal output from the mobile station, and determining whether to update the transmission timing of the signal to be transmitted from the base station according to the reliability of the received signal received by the moving object. Time synchronization of the tracer digital mobile communication system using a symmetrical smoothing filter. The signal detector (5) according to claim 1, wherein the reliability measurer (5) of the signal judges whether the magnitude of the signal received by the moving object is within a set range, evaluates the reliability of the received signal, and outputs it from the peak detector (4) according to the evaluated reliability. A time synchronization tracker in a digital mobile communication system using an asymmetric smoothing filter, characterized in that it controls the input of the signal to the smoother (6). 2. A time synchronous tracker in a digital mobile communication system using an asymmetric smoothing filter as claimed in claim 1, characterized in that the smoothing (6) is a first order smoothing filter having an asymmetric step size.