KR100686130B1 - Tracker of mobile broadcasting receiver - Google Patents

Abstract

The present invention relates to a tracker in a mobile broadcast receiver.

The present invention relates to a mobile broadcast receiver having a plurality of fingers configured to extract a CDM symbol of a specific channel through PN despreading and WALSH despreading after synchronizing a signal received through a corresponding path in a tracker. A digital resampler that compensates the digital signal by resampling to a sampling frequency corresponding to a timing error, a DLL that estimates a timing error using a correlation characteristic of a PN code from the digital signal compensated by the digital resampler, and outputs from the DLL The first filter unit and the first filter unit to output the final timing error signal in addition to the integrally filtered signal and generate a sampling frequency corresponding to the first filter unit. An NCO output to the digital resampler is configured for each finger, And a second filter unit configured to receive and synthesize a timing error signal output from the first filter unit of the finger, and then integrally filter and output the integrated filter to the first filter unit of each finger. to provide. Therefore, the phenomenon of lowering the SNR of the output signal can be overcome.

Tracker, Integral Filter, Differential Filter, Timing Error Signal

Description

Tracker of mobile broadcasting receiver

1 is a diagram illustrating a tracker in a conventional mobile broadcast receiver.

2 is a view for explaining a tracker in the mobile broadcast receiver according to the present invention.

* Explanation of symbols for main parts of the drawings

120: digital resampler 130: DLL

140: proportional filter unit 150: NCO

160: integral filter unit 170: timing error synthesizer

180: despreader 190: SRG

200: first filter unit 210: second filter unit

The present invention relates to a tracker in a mobile broadcast receiver, and more particularly, to a mobile broadcast having a new structure having a digital resampler applicable to a satellite digital multimedia broadcasting (DMB) receiver using code division modulation. A tracker in a receiver.

DMB (Digital Multimedia Broadcasting) may be classified into terrestrial DMB and satellite DMB. Terrestrial DMB provides audio and video services on the move based on Orthogonal Frequency Division Multiplexing (OFDM), and satellite DMB uses audio and video services on the move using satellites and complementary terrestrial gap fillers based on CDM. To make it possible

In a satellite DMB receiver, a received signal input to an antenna is converted into a baseband through a tuner, and an automatic gain controller (AGC) of the received signal is used to maintain a constant size of the signal input to the A / D. The power is measured and multiplied by a gain value calculated. The ADC converts an analog signal into a digital signal by sampling a signal having a relatively constant magnitude by the AGC. In order to demodulate a signal in the CDM transmission scheme, the acquisition of a pseudo-noise sequence used for signal spreading should be prioritized. This process consists of two stages: signal acquisition and tracking. .

     The division unit of the pseudo noise sequence is called a chip, and the acquisition is a process of securing signal synchronization within ± 1/2 chips at a receiver, and is performed by a searcher. Signal tracking is a fine tuning of the signal found and is performed in the tracker. In this way, the synchronized signal is despread by multiplying the pseudo-noise sequence generated by the receiver, and the symbol of the desired CDM channel is extracted by multiplying the WALSH code used to distinguish the CDM channels.

The process is performed in all the multiple paths searched by the searcher, each of which is called a finger.

1 is a view for explaining a tracker in a conventional mobile broadcast receiver.

In FIG. 1, the conventional tracker is composed of an analog part 10, an ADC 11, and a voltage controlled crystal oscillator (VCXO) 13, and the digital part 20 includes a selector 21 and a delayed locked loop (DLL). 23), Shift Register Generater (SRG) (25)
And a despreader 27, a loop filter 29, and a digital-analog converter (DAC) 31.

First, an input of a clock having a frequency higher than the chip rate generated in the voltage controlled crystal oscillator (VCXO) 13 is oversampled by the ADC 11.

Over sampled data generated by the VCXO 13 and oversampled by the ADC 11 is input to the selector 21 to be drawn. For example, if the input signal is over sampled 8 times, the selector 21 selects one for every eight input signals. In this case, the selector 21 operates based on a timing error signal generated by the DLL (Delayed Locked Loop, hereinafter referred to as a 'DLL') 23 and passed through the loop filter 29.

The selector 21 outputs not only the chip rate data in position but also 1/2 chip faster data and 1/2 chip slow data while deciding. In this case, the chip data output from the correct position is called main path data, and the data output from the 1/2 chip fast position is called early path data, and the data output from the 1/2 chip slow position. Is defined in the present invention as late path data.

In addition, the SRG 25 outputs the PN code generated by the SRG 25 to the DLL 23 and the despreader 27 by a PN code generator.

Early path data and late path data output from the selector 21 are input to the DLL 23 to generate a timing error signal, and further, the selector ( Main path data output from 21 is input to the despreader 27 to output a despreading signal.

In addition, early path data and late path data output from the selector 21 and input to the DLL 23 generate a timing error signal, and the timing error signal is a Loop Filter ( 29) and a signal converted into an analog signal from a digital-analog converter (DAC) 31 is outputted, and a timing frequency offset component is inputted to the VCXO 12 to provide an analog-to-digital converter (ADC). The clock speed of (11) is adjusted and frequency correction is performed in the ADC (11).

The timing phase offset component output from the loop filter 29 is input to the selector 21 to perform phase compensation to select data corresponding to the most appropriate phase. That is, the conventional tracker is different in frequency compensation and phaser compensation.

As the closed loop is formed in the above manner, tracking is performed in the tracker.

However, the tracker in the above-described conventional mobile broadcast receiver has a problem of signal degradation when synthesizing an output signal of each finger of a digital multimedia receiver to which a multi-power signal having a small power is applied.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a tracker that prevents the output of a finger to which a low multipath signal is applied to act as noise of the output signal during synthesis.

Another object of the present invention is to provide a tracker that contributes to maximizing the SNR of the output signal by MRC (Maximum Ration Combining) effect by applying weak power multipath signal at the time of synthesis by stable and accurate selection. .

In order to achieve the above object, the present invention is a mobile broadcast receiver comprising a plurality of fingers to extract the CDM symbol of a specific channel through PN despreading and WALSH despreading after synchronizing the signal received through the path in the tracker A digital resampler for compensating the digital signal by resampling a received digital signal at a sampling frequency corresponding to a timing error, and estimating timing error using a correlation characteristic of a PN code from the digital signal compensated by the digital resampler. A first filter unit for outputting a final timing error signal in addition to an integrally filtered signal after the proportional filtering by receiving the timing error signal output from the DLL, and receiving the tie type error signal from the first filter unit. NCO generating corresponding sampling frequency and outputting to digital resampler And a second filter unit configured to receive the synthesized timing error signal outputted from the first filter unit of each finger, and then integrate and filter the received timing error signal to the first filter unit of each finger. A tracker in a mobile broadcast receiver is provided.

The first filter unit includes a proportional filter unit for proportionally filtering the timing error signal output from the DLL, an adder for adding the timing error signal output from the proportional filter and the timing error signal output from the second filter unit. It is preferable to comprise.

The second filter unit may include a timing error synthesizer for synthesizing a timing error signal output from the DLL of each finger, an integral filter for receiving an integrated timing error signal synthesized by the timing error synthesizer, and outputting the integrated filter to the first filter unit. It is preferable to comprise a filter part.

Therefore, according to the present invention, a distorted timing frequency offset occurs in a finger to which a multipath with low signal power is allocated in a conventional tracker system, and digital data selected by the timing frequency offset value acts as a noise during Rake synthesis. Solution It is possible to overcome the phenomenon of lowering the SNR of the final output signal, and because all the finger data have the same timing frequency offset value, all of them are applied during Rake synthesis without any discarded data. The output signal has better SNR, and all the fingers share the delay element and the adder constituting the integral filter unit, thereby reducing the size of the digital system, reducing power consumption, and timing frequency offset. Tracker and timing phaser offset Other it is possible to be applied to the tracker structure.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention that can be specifically realized for the above purpose.

Referring to FIG. 2, a first embodiment of a tracker in a mobile broadcast receiver according to the present invention will be described.

In the satellite digital multimedia broadcasting receiver, the signal received through the corresponding path is synchronized in the tracker, and the part which extracts CDM symbols of a specific channel through PN despreading and WALSH despreading is called a finger. 2 illustrates a system having four fingers, but the present invention is applicable to a case where a plurality of fingers are provided.

In the mobile broadcast receiver according to the present invention, the tracker includes a digital resampler 120, a DLL 130, a first filter unit 200, a normally controlled oscillator (NCO) 150, and a second filter unit 201. It is configured by.

The digital resampler 120 receives a digital signal from the ADC 110 for converting the input signal into a digital signal. The digital resampler 120 resamples the digital signal sampled at a constant frequency from the ADC 110 and extracts data corresponding to the position of the transmission signal.

In addition to the digital resampler 120, an interpolator may be used to configure another embodiment of a tracker in the mobile broadcast receiver according to the present invention.

The signal output from the digital resampler 120 is input to the DLL 130. The DLL 130 estimates a timing error signal using a PN correlation characteristic from the digital signal compensated by the digital resampler 120. (estimation)

The DLL 130 receives a PN code from the SRG 190, which is a PN code generator, receives a signal output from the digital resampler 120, and signals the SRG 190, the despreader 180, and a loop filter. Outputs

Therefore, the timing error signal output from the DLL 130 is inputted to the loop filter to perform the cumulative correction. A PI loop filter is used as the loop filter.

However, the biggest difference between the present invention and the tracker structure of the conventional CDM receiver is that the PI loop filter is divided into two parts.

The timing error signal output from the DLL 130 is input to two parts, and is input to the first filter part 200 and the second filter part 210.

First, the first filter unit 200 proportionally filters the timing error signal output from the DLL 130, the timing error signal output from the proportional filter 140, and the second filter unit. And an adder 145 for adding the timing error signal filtered and output at 210. In this case, the first filter unit 200 is configured for each finger.

The second filter unit 210 receives a timing error signal output from the DLL 130, and includes a timing error synthesizer 170 and an integral filter unit 160.

The timing error synthesizer 170 synthesizes a timing error signal output from the DLL 130 of each finger and outputs the synthesized signal to the integrating filter unit 160.

The timing error synthesizer 170 also has a number of methods for synthesizing the timing error, the embodiment will be described.

In a first embodiment of the method of synthesizing the timing error, delta modulation is applied after adding timing error signals of all fingers.

The charging agent in the case of applying the delta modulation has a lower timing error value of a finger having a lower signal power than a timing error value of a finger having a different high power. Even in the case of addition, the assumption is made that the total timing error value does not affect the sign of whether it is positive (+) or negative (-).

In a second embodiment of the method of synthesizing the timing error, the timing signal T from the unlocked finger is locked by using a lock signal generated at a part other than the tracker such as a channel estimation lock. There is a method that does not apply to error synthesis.

The signal synthesized by the timing error synthesizer 170 is input to the integral filter unit 160 to undergo integral filtering. The integral filter unit 160 operates using the delay element 161 and the adder 162 as components. In addition, the signal output from the integration filter unit 160 is input to each finger.

As described above, in the tracker according to the present invention, all the fingers share the timing error synthesizer 170 and the integral filter unit 160 constituting the second filter unit 210 in the mobile broadcast receiver structure. As a result, all the fingers share the delay element 161 and the adder 162 constituting the integral filter unit 160, thereby reducing the size of the digital system and reducing power consumption.

The signal output from the proportional filter unit 140 of each finger and the signal output from the integration filter unit 160 are added by the adder 145 of the first filter unit 200 to perform loop filtering to perform NCO. Is input to 150.

In this case, the signal filtered by the integrating filter unit 160 is an estimated timing frequency offset. Therefore, since all the fingers share the same timing frequency offset, it is possible to solve the problem caused by the timing frequency offset being changed during the Raker Combining of the signal output from each finger.

In addition, a distorted timing frequency offset occurs in a finger to which a multipath with low signal power is allocated, and digital data selected by the timing frequency offset value acts as a noise during Rake synthesis, thereby lowering the SNR of the final output signal. It can be overcome.

When performing a field test with the system proposed in the present invention, it was confirmed that the timing frequency offset of the multipath signals across all fingers is uniform regardless of whether the power of the multipath is large or small.

     Once the timing frequency offset values have converged in the integrating filter unit 160, the tracker of each finger operates as a primary PLL structure that filters only in the proportional filter unit 140, thereby remaining residual that may be different for each finger. The timing frequency offset and timing phase offset are compensated for.

Therefore, the problem of frequency offset of a finger assigned in a gap filler having different timing frequency offsets is also solved by applying this structure. In general, the gap filler is transmitted based on a signal generated from a crystal oscillator having a very low error so that the frequency offset between the gap fillers is very small.

Accordingly, after the timing frequency offset between the mobile broadcast receiver and the gap filler is corrected through the integration filter unit 160, the timing frequency offset between the gap fillers converges to a first order PLL structure having a fixed integral filter unit 160 output. do. Therefore, even if a timing gap offset of a different gap filler is applied to each finger, this structure can be solved.

The signals output from the proportional filter unit 140 and the integral filter unit 160 are added to the NCO 150.

The NCO 150 generates the sampling frequency corresponding to the timing error signal from the loop filtered input signal and outputs the sampling frequency to the digital resampler 120.

The present invention can also be applied to other tracker structures that compensate for both timing frequency offset and timing phase offset in the tracker.

The present invention is not limited to the above-described embodiments, and can be modified by those skilled in the art as can be seen from the appended claims, and such modifications are within the scope of the present invention.

The effects of the tracker in the digital multimedia broadcasting receiver according to the present invention described above are as follows.

First, in a conventional tracker system, a distorted timing frequency offset is generated on a finger to which a multipath with low signal power is allocated, and the digital data selected by the timing frequency offset value acts as a noise during Rake synthesis, so that The phenomenon of lowering the SNR can be overcome.

Second, in the present invention, since all finger data have the same timing frequency offset value, all of them are applied at the time of Rake synthesis without discarding data, so that the final output signal has better SNR in terms of maximum ratio combining.

Third, all the fingers share the delay element and the adder constituting the integral filter, thereby reducing the size of the digital system and reducing power consumption.

Claims (5)

In the mobile broadcast receiver having a plurality of fingers to extract the CDM symbol of a specific channel through the PN despreading and WALSH despreading after synchronizing the signal received through the path in the tracker, A digital resampler for compensating the digital signal by resampling the received digital signal to a sampling frequency corresponding to a timing error; A DLL estimating a timing error using a correlation characteristic of a PN code from the digital signal compensated by the digital resampler; A first filter unit which receives the timing error signal output from the DLL, performs proportional filtering, and outputs a final timing error signal in addition to the integral filtered signal; An NCO configured to receive a timing error signal from the first filter unit and generate a sampling frequency corresponding to the timing error signal, and output the same to the digital resampler. And a second filter unit for inputting and synthesizing the timing error signal output from the DLL of each finger, and integrating and outputting the filtered filter to the first filter unit of each finger. The method of claim 1, wherein the first filter unit, And a adder for proportionally filtering the timing error signal output from the DLL, and an adder for adding the timing error signal output from the proportional filter and the timing error signal output from the second filter unit. Tracker in a mobile broadcast receiver. The method of claim 1, wherein the second filter unit, A timing error synthesizer for synthesizing the timing error signal outputted from the DLL of each finger, and an integral filter unit configured to receive the integrally filtered timing error signal from the timing error synthesizer and to output the filtered result to the first filter unit. A tracker in a mobile broadcast receiver, characterized by the above-mentioned. The method of claim 3, wherein And a timing error signal output from the second filter part and input to the first filter part of each finger is the same timing error signal. The method of claim 3, wherein The tracker in the mobile broadcast receiver, characterized in that all fingers share the delay element and the adder constituting the integral filter unit.

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