KR100710321B1 - Timing Recovery Device for Mobile Broadcasting Receiver - Google Patents

Abstract

The present invention relates to a timing recovery apparatus of a mobile broadcast receiver for accurately recovering timing errors.

The present invention relates to a timing recovery apparatus of a mobile broadcast receiver for extracting CDM symbols of a specific channel by despreading a PN and despreading a received signal, and an A / D converter for digitizing the received signal and the A / D. A tracker that receives the digitized received signal from the converter and estimates a timing error during an initial operation, and a timing error estimator and the tracker that receives the digitized received signal from the A / D converter and estimates the timing error using a Gardner TED algorithm. And a sampling frequency generator for generating a sampling frequency corresponding to the timing error estimated by the timing error estimate and the timing error value estimated by the timing error estimator, and recovering the timing error of the mobile broadcast receiver. Provide the device.

Therefore, it is possible to quickly capture the timing offset of the satellite DMB receiver in a high speed mobile environment and a channel environment in which the transmission channel is severely changed, and it is possible to accurately recover the timing error.

Gardner TED, Tracker, VCXO, A / D Converter, Error Controller,

Description

 Timing Recovery Device for Mobile Broadcasting Receiver

1 is a conceptual block diagram of a mobile broadcast receiver

2 is a pilot frame structure of a mobile broadcast receiver

Figure 3 is a Gardner TED block diagram

4 is a block diagram of a first embodiment of a timing recovery apparatus for a mobile broadcast receiver according to the present invention;

5 is a block diagram of a second embodiment of a timing recovery apparatus for a mobile broadcast receiver according to the present invention;

6 is a block diagram of a third embodiment of a timing recovery apparatus for a mobile broadcast receiver according to the present invention;

7 is a block diagram of a fourth embodiment of a timing recovery apparatus for a mobile broadcast receiver according to the present invention;

<Description of the symbols for the main parts of the drawings>

110: AGC (automatic gain control unit) 120: A / D conversion unit

130: SEARCHER 160: RAKE synthesizer

170: frequency offset measuring instrument 410: timing error estimation unit

412: Front filter 414: Gardner TED

416: loop filter 420: VCXO

500: Resampler 510: NCO

520: Oscillator 600: Tracker

610: error controller

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to digital multimedia broadcasting (hereinafter referred to as DMB), and more particularly, to a timing recovery apparatus of a mobile broadcast receiver.

The DMB can be roughly divided into terrestrial DMB and satellite DMB. The terrestrial DMB provides audio and video services while moving based on OFDM, and the satellite DMB enables audio and video services while moving based on CDM.

Orthogonal Frequency Multiplexing (OFDM) is a type of multi-carrier transmission using multiple carriers, and the transmission period in each channel is increased by the number of carriers, and the code division multiplexing (CDM) refers to a protection division multiplexing scheme. .

Currently, the technical standard of the satellite DMB adopted in Korea is the system E method defined by the International Telecommunication Union (ITU), which basically adopts the CDM transmission method, and uses CD quality sound and weather, traffic and video using various channels. It is a new concept service of representative communication and broadcasting convergence that broadcasts information, etc.

The satellite DMB uses frequencies in the upward 13.824-13.883 GHz band and the downward 2.630-2.655 GHz and 12.21-12.23 GHz bands, supports up to 64 channels, and has broad coverage with national broadcasting.

The transmission channel of the satellite DMB is a wireless mobile reception channel and has a magnitude of a received signal.

Not only is Amplitude time-varying, but Doppler shift of the received signal spectrum occurs due to the influence of mobile reception.

In consideration of the transmission and reception under such a channel environment, the satellite DMB transmission scheme adopts the CDM scheme, and interleaves the time domain signals to correct errors occurring in the transmission channel.

The CDM method multiplies the data to be transmitted by a pseudo noise signal having a data rate much faster than that of the data, thereby spreading and transmitting the frequency, so that signals exist over a wide band, so that narrow-band interference ), And the receiver of the RAKE structure can reduce the deterioration of reception performance due to the multipath.

Referring to Figure 1, a conventional satellite DMB receiver will be described. The received signal input to the antenna is converted into a baseband through the tuner 100 and output to the AGC (auto gain control unit) 110.

The AGC multiplies the gain value calculated by measuring the power of the received signal in order to maintain a constant magnitude of the signal input to the A / D converter 120 and converts the result into the A / D converter 120. ).

The A / D converter 120 converts an analog signal into a digital signal by sampling a signal having a relatively constant size by the AGC 110.

In the CDM transmission method, in order to demodulate a signal, the acquisition of a pseudo noise signal used for spreading the signal has to be prioritized. This process consists of two stages of signal acquisition and tracking.

The division unit of the pseudo-noise signal is called a chip, and the acquisition is a process of securing signal synchronization within ± 1/2 chips at the receiver, and is performed by the SEARCHER 130.

Signal tracking refers to fine synchronization of the found signal and is performed in the trackers 140 to 14n.

The synchronized signal is despread by multiplying the pseudo-noise signal generated by the inverse converting units 150 to 15n of FIG. 1, and multiplying the WALSH code used to distinguish the CDM channels to obtain the desired symbol of the CDM channel. Extract.

This process is performed in all the multipaths found by the SEARCHER 130, each of which is called a finger.

The frequency offset estimator 170 estimates the frequency offset for each finger, synthesizes the feedback, and feeds back the tuner to correct the frequency offset.

The extracted symbols are synthesized by the RAKE synthesizer 160. In this case, the received performance may be improved by estimating and compensating the reception channel environment.

RAKE synthesis is performed for all CDM channels to be demodulated, and the pilot channel, which is the control channel, contains information on the interleaver size and convolutional coding rate and must be demodulated.

2 illustrates the structure of a pilot channel, and extracts timing of a frame and a superframe using the pilot channel.

In general, when using a digital modem such as quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) for wireless communication including high-speed satellite communication, synchronization of data symbols and sampling positions is performed. A symbol timing recovery circuit is needed.

In particular, in the case of the satellite DMB, a timing recovery circuit that can operate properly in a high speed mobile environment, a channel environment in which the transmission channel changes, and a Doppler environment is required.

The Gardner method has a relatively simple structure, as shown in FIG. 3, and estimates a sampling clock error by calculating a symbol timing component from general data. Therefore, the Gardner method converges relatively quickly and operates well in a changing channel environment.

General showed the structure of a Gardner timing error detector in Figure 3, the Gardner algorithm in the satellite DMB system uses the QPSK transmission system is the timing error TED _err as shown in Equation 1 to a two-times oversampled signal of the symbol rate Estimate.

TED _err = y _I (r-1 / 2) {y _I (r) -y _I (r-1)} + y _Q (r-1 / 2) {y _Q (r) -y _Q (r-1 )}

Wherein r is the symbol number, y (r) is twice shows a sampling a received signal and, y _Ⅰ (r) and y _Q (r) is in-phase component of the signal input to the TED block each (par component) And quardrature components (orthogonal components), respectively. In addition, Equation 1 estimates the timing error by detecting how symmetrical or cross the zero point the signal takes.

However, the conventional timing recovery method for satellite DMB has the following problems.

First, since the tracker is performing timing restoration during the initial operation, it may take up to several hundred ms depending on the good and bad channel environment, and there is a case that the timing restoration is not achieved when the timing offset increases by a certain limit or more.

Second, in the case of Gardner using frequency components, it is difficult to recover the timing when it is impossible to extract frequency components from the received signal due to effects of multipath and fading.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to accurately recover a timing error by detecting a timing error and estimating a frequency offset by interworking a Gardner timing error detection method and an existing detection algorithm. It is to provide a timing recovery method of a satellite DMB receiver.

In order to achieve the above object, the present invention provides a timing recovery apparatus of a mobile broadcast receiver comprising a Gardner Timing Error Detector (hereinafter referred to as TED) for estimating timing error.

According to another embodiment of the present invention, the present invention includes a tracker for estimating a timing error and an error controller configured to add a weighted value to the timing error estimated from the tracker and the timing error estimated from the timing error detector. A timing restoring apparatus for a broadcast receiver is provided.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can specifically realize the above object will be described.

The same components as in the prior art are given the same names and the same reference numerals for convenience of description, and detailed description thereof will be omitted.

A first embodiment of a timing recovery apparatus for a mobile broadcast receiver according to the present invention will be described with reference to FIG.

The first embodiment of the present invention shows a timing recovery apparatus to which the Gardner timing error estimation algorithm is applied, and illustrates a case where the A / D converter 400 receives a sampling frequency from the timing recovery unit.

The timing recovery apparatus includes an A / D converter 400, a VCXO 420, and a timing error estimator 410 (front filter 412, Gardner TED 414, and loop filter 416).

The band-limited reception signal is sampled by the A / D converter 400 and converted into a digital signal, and then input to the front filter 412 located in front of the Gardner TED 414.

The band-limited received signal is input to an antenna and then converted to a baseband through a tuner, and multiplied by a gain value calculated by measuring the power of the received signal by an AGC. Therefore, the magnitude of the signal input to the A / D converter 400 is kept constant.

The band-limited reception signal digitized by the A / D converter 400 is input to the front filter 412 of the timing error estimator.

The front filter 412 reduces the self-noise of the band-limited received signal, removes the dc component, and then supplies it to the Gardner TED 414.

The Gardner TED 414 estimates a timing error, inputs the estimated timing error to the loop filter 146, and passes the band component of the timing error to the VCXO 420. .

The voltage controlled crystal generator 420 (hereinafter referred to as a VCXO) generates a sample frequency proportional to the signal filtered by the loop filter 416 and reflects the result back to the A / D output unit 400. Feedback loop system.

A second embodiment of a timing recovery apparatus for a mobile broadcast receiver according to the present invention will be described with reference to FIG.

In the second embodiment of the present invention, the A / D converter receives a fixed clock from an oscillator 520 (hereinafter referred to as a generator) instead of the VCXO in the first embodiment.

The digitized signal according to the fixed clock is input to a resampler 500 to convert the symbol rate, and then the front filter 412, the Gardner TED 414, and the loop filter 416 of FIG. Supplied to.

The received signal filtered by the loop filter is supplied to an NCO 510 (Number Controlled Oscillator), and the NCO 510 feeds back a basement index and a fractioal interval to the resampler 500 again.

The resampler 500 serves as a filter that interpolates the index of an interpolation filter by using a basement index and a fractional interval fed back from the NCO 520 to precisely adjust the sampling timing.

Referring to FIG. 6, a third embodiment of a timing recovery apparatus for a mobile broadcast receiver according to the present invention will be described.

In the third embodiment, the first embodiment is constructed in conjunction with the timing error detection method in the tracker 600 currently being used.

The band-limited reception signal is digitized by the A / D converter and input to the front filter of the timing error estimator, and is also input to the tracker 600.

The timing error estimated by the tracker and the timing error estimated through the front filter, the Gardner TED, and the loop filter are weighted by an error controller 610 (Error Controllr), and the A / D conversion is performed again through the VCXO. Is reflected in wealth.

Referring to FIG. 7, a fourth embodiment of a timing recovery apparatus for a mobile broadcast receiver according to the present invention will be described.

The configuration of the fourth embodiment of the present invention is basically the same as that of the second embodiment.

However, as in the third embodiment, a tracker and an error controller are used, and the timing error estimated by the tracker and the timing error estimated through the front filter, the Gardner TED, and the loop filter are weighted by an error controller. After the addition, the NCO is supplied to the resampler through NCO.

That is, the NCO supplies a basement index and a fractioal interval back to the resampler.

The resampler serves as a filter that interpolates by changing the index of an interpolation filter by using a basement index and a fractional interval fed back from the NCO, thereby accurately adjusting the sampling timing.

An effect of the timing restoration method of the satellite DMB receiver according to the present invention described above is as follows.

First, in performing the timing restoration in the satellite DMB receiver, it is possible to accurately restore the timing error by linking the Gardner timing error detection method with an existing detection algorithm.

Second, it enables fast acquisition of the timing offset of the satellite DMB receiver in a high speed mobile environment and a channel environment in which the transmission channel is severely changed.

Claims (5)

In the timing recovery apparatus of the mobile broadcast receiver for extracting the CDM symbols of a specific channel by despreading the PN signal and WALSH despreading, An A / D converter for digitizing the received signal; A tracker that receives a digitized received signal from the A / D converter and estimates a timing error during an initial operation; A timing error estimator which receives the digitized received signal from the A / D converter and estimates a timing error by a Gardner TED algorithm; And And a sampling frequency generator configured to add a weighted timing error value estimated by the tracker and a timing error value estimated by the timing error estimator and generate a sampling frequency corresponding thereto. Restoration device. The method of claim 1, When the A / D converter receives and receives a fixed frequency, A resampler for converting the symbol rate of the input signal to the output terminal of the A / D converter further, Sampling frequency of the sampling frequency generating unit is a timing error recovery device of a mobile broadcast receiver, characterized in that provided to the resampler. The method of claim 2, An error controller that adds weights to the timing error estimated from the tracker and the timing error estimated from the timing error estimator; And And an NCO for feeding back a base index and a fractional interval. The method of claim 1, When the A / D converter receives and samples the sampling frequency of the sampling frequency generator, The sampling frequency generator includes an error controller adding weighted timing errors estimated from the tracker and timing errors estimated from the timing error estimator; And And a VCXO which generates a sample frequency proportional to the signal filtered by the loop filter and reflects the A / D converter back to the A / D converter. The method of claim 1, The timing error estimator includes: a front filter which reduces self-noise of the band-limited waveform of the digitized signal and removes a dc component to supply the gardner TED; Gardner TED for detecting timing errors using two received samples and one intermediate sample; And And a loop filter for filtering the timing error.

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