KR20050063155A - Apparatus and method for transmission mode detecting in dmb receiver - Google Patents

Abstract

The present invention relates to an apparatus and method for determining a transmission mode by estimating a NULL symbol length in a digital multimedia broadcasting (DMB) receiver. In particular, an energy value of each sample is accumulated during an integration period to obtain an average energy value. Calculate the average energy ratio from the average energy value of the integral section, detect the position in the time domain when the energy ratio becomes the maximum and minimum, and measure the difference between the detected maximum energy ratio position and the minimum energy ratio position value. By estimating and determining the transmission mode using the estimated NULL symbol length, the transmission mode can be estimated regardless of the amount of noise on the channel. In addition, the circuit configuration may be simplified by using a multiplier and a comparator instead of a divider in the process of finding the position where the energy ratio is maximum and minimum.

Description

Apparatus and method for transmission mode detecting in DMB receiver

The present invention relates to a digital multimedia broadcasting (DMB) receiver, and more particularly, to an apparatus and method for determining a transmission mode by detecting a start position and an end position of a NULL symbol in a DMB receiver.

Digitalization of broadcasts has also affected existing analog radio broadcasts, which has led to the advent of digital radio broadcasts. In addition to existing voice radio services, digital multimedia broadcasting (DMB), which includes data transmission and multimedia services, has become possible. The DMB is robust against noise and distortion on a transmission channel, has a high transmission efficiency, and has various advantages of enabling various multimedia services.

Digital multimedia broadcasting (DMB), adopted in Korea, is based on Eureka-147 digital radio broadcasting (DAB), which has been adopted as the European terrestrial radio standard. Added to improve multimedia broadcasting performance, RS-code (Reed-Solomon Code) and convolutional interleaver, which are robust against burst errors that may occur on a transmission channel, are added. The two additional blocks are applied to the DAB Ensemble input signal at the transmitter and provide an error rate low enough to enable video service even in a mobile reception environment. In addition, the transmission channel of the DMB broadcast is a wireless mobile reception channel, and the amplitude of the received signal is not only time-varying, but also the Doppler Spreading of the spectrum of the received signal due to the influence of the mobile receiver. Occurs. In consideration of the transmission and reception in such a channel environment, the DMB transmission scheme is based on Orthogonal Frequency Division Multiplexing (OFDM). Since the OFDM scheme uses a plurality of multicarriers, it is very resistant to ghosts generated by the multipath channel, and channel estimation based on a pilot signal is easy.

That is, in the DMB transmitter, each service signal (audio, video, data service) is individually encoded for error prevention and then interleaved in the time domain, and each service signal interleaved in the time domain is multiplexed and is a main service which is a data channel. Merged into the Channel (Main Service Channel (MSC)). The multiplexed signal is interleaved in the frequency domain together with multiplexing configuration information (MCI) and service information (Service Informaton (SI)) transmitted through a fast information channel (FIC), which is a control channel. At this time, since information transmitted to the FIC does not allow time delay, time domain interleaving is not performed. The frequency interleaved bit string is mapped to a differential quaternary phase shift keying (DQPSK) symbol, and then an OFDM symbol is generated through an inverse fast Fourier transform (IFFT). The OFDM symbol is modulated into an RF signal and transmitted.

At this time, the transmission standard defines four transmission modes of transmission modes 1,2,3,4 that vary according to the frequency band and the reception region.

Parameters according to each transmission mode are shown in Table 1 below.

       Transmission mode item      One      2      3      4 Applications Terrestrial (SFN)   Terrestrial Satellite / cable   Terrestrial Carrier frequency  <375 MHz  <1.5 GHz  <3 GHz  <1.5 GHz Subcarriers    1536    384    192    768 Subcarrier spacing    1 KHz    4 KHz    8 KHz    4 KHz Guard section length    246 yen    62㎲    31㎲    123 yen Effective symbol length    1 ms    250 ㎲    125 ㎲    500㎲ Frame length    96ms (196608T)    24ms (49152T)    24ms (49152T)    48ms (98304T) Null symbol length    1.297ms (2656T)    324㎲ (664T)    168㎲ (345T)    648㎲ (1328T) Symbols per frame    76    76    153    76 Relative frame length (based on mode 1)    One    1/4    1/4    1/2

That is, the transmission standard is transmission mode 1 for local broadcasting of band 1,2,3 of terrestrial single frequency network (SFN), transmission modes 2 and 4 for band 1,2,3,4,5 and L band, and 3GHz or less Terrestrial, satellite, cable and terrestrial / satellite broadcasts are defined as transmission mode 3. Referring to Table 1, it can be seen that subcarriers, frame lengths, guard interval lengths, effective symbol lengths, and null symbol lengths vary according to transmission modes.

1 shows a frame structure for transmission mode 1 of the above-described transmission modes. The beginning of the transmission frame is the synchronization channel (SC) with null symbols and Phase Reference Symbol (PRS) for DQPSK modulation and demodulation is allocated. The SC is followed by the FIC, followed by the MSCs carrying the audio, data and video services. Data transfer consists of FIC and MSC, which consists of 256-bit fast information blocks (FIBs) and controls the MSC arrangement. At the heart of the control information is the MCI transmitted over the FIC, which is rearranged as needed.

In FIG. 1, the OFDM symbol is composed of a valid period of 1 ms and a guard period of 0.246 ms. The transmission frame of transmission mode 1 is composed of a null symbol, three symbols for PRS and FIC, and 72 symbols for MSC. The total length is 96ms.

In this case, interleaving the signals in the time domain and the frequency domain in the DMB transmission scheme is to correct an error occurring in the transmission channel. That is, the DMB transmission signal is transmitted with a much smaller signal strength than the conventional analog radio broadcast signal. Considering the mobile reception like in a car in a severe fading channel environment such as downtown, the signal strength of the actual received signal is Very small

Therefore, the DMB receiver should be able to correct the transmission error by receiving the received signal as much as possible in such a poor reception environment. In addition, considering the fact that it is a mobile receiving terminal, it is a key requirement of the DMB receiver configuration that the maximum reception performance is achieved at a limited cost.

FIG. 2 is a conceptual block diagram of a DMB receiver according to the DMB transmission scheme as shown in FIG. 1 scheduled to be serviced in Korea, and the tuner 201 tunes only an RF signal of a specific channel among the RF signals received by the antenna 200. The signal is converted into a pass-band signal of an intermediate frequency (IF) and then output to an AGC (Auto gain control) unit 202. The AGC unit 202 multiplies the IF signal by a gain value calculated according to a reference signal size for A / D conversion of the IF signal to make the size of the IF signal constant, and then to the A / D converter 203. Output

The A / D converter 203 performs sampling on the gain-adjusted IF signal irrespective of the magnitude of the received signal, converts it into a digital signal, and outputs the digital signal to the I / Q divider 204. The I / Q divider 204 converts the digital signal into a complex component signal which also has a quadrature component (Q) because the input digital signal has only a real component (I). ) Is output to the signal synchronizer 206 and the OFDM demodulator 207.

The mode detector 205 detects a transmission mode of the received signal, and the OFDM demodulator 207 removes an unnecessary guard interval, and then uses a fast fourier transform (FFT) to frequency-domain a signal in a frequency domain. After conversion to the signal feed back to the signal synchronizer 206 and output to the frequency deinterleaving unit 208.

The signal synchronizer 206 extracts information necessary for synchronization in the time / frequency domain of the signal using the input and output signals of the OFDM demodulator 207. That is, the signal synchronizer 206 performs frame synchronization, OFDM symbol synchronization, and carrier frequency synchronization.

The frequency de-interleaving unit 208 restores the positions of the frequency interleaved sub-carrier signals at the transmitter and outputs the positions of the sub-carrier signals to the first channel distributor 209. The first channel divider 209 separates the FIC channel as the control channel and the MSC channel as the data channel, and then outputs the signal of the separated FIC channel to the FIC decoder 210, and the signal of the MSC channel is a time deinterleaving unit. Output to (211).

Here, since the signal of the FIC channel is not time-domain interleaved at the transmitter, the receiver does not perform time-domain deinterleaving. The FIC decoder 210 receives the FIC channel signal as an input, extracts information necessary to decode the MSC channel, and outputs the information to the FIC data decoder 217. In this case, the separate control data transmitted through the FIC channel is recovered by the FIC data decoder 217.

Meanwhile, the time deinterleaving unit 211 restores 16 logical frames of the MSC channel interleaved in the time domain by the DMB transmitter in the original frame order. The time deinterleaved MSC channel signal is input to a convolutional decoder 212, and the convolutional decoder 212 corrects a random error generated in a transmission channel included in the MSC channel. If the random error corrected data is scrambled, it is descrambled by the original data in the energy descramble 213, and then output to the second channel distributor 214, and if not, the data is scrambled to the second channel distributor 214. Passed.

The second channel splitter 214 distinguishes whether the transmitted data channel is a data / audio signal for a DAB service or a video signal for a DMB service, and then separates the separated audio / data signal into an audio / data decoder ( 218, and the separated video signal is output to the convolutional de-interleaving unit 215.

The convolutional deinterleaving unit 215 rearranges the data additionally interleaved by the transmitter in the original order and outputs the RS decoder 216 to the RS decoder 216. The RS decoder 216 transmits RS-encoded data by the transmitter. After reconstruction, the video decoder 219 outputs the video decoder 219. The video decoder 219 recovers the video signal for the DMB service.

In FIG. 2, all the signal processing performed after the A / D conversion until the final transport stream is recovered is determined by the transmission mode detected by the mode detector 205. At this time, the DMB transmission mode is not transmitted on the signal and should be automatically detected by the DMB receiver. Therefore, the detection performance of the mode detector 205 is a very important factor in determining whether the entire DMB receiver is operating properly.

There are many ways to implement such a mode detector.

In general, a method of using a NULL symbol interval, which is the first symbol, in the transmission frame structure of the DMB signal as shown in FIG. 1 is used. That is, the DMB transmission system transmits a NULL symbol in which no signal exists during the first symbol period of every frame for the purpose of acquiring signal synchronization in the time domain. In this case, since the length of the NULL symbol varies depending on four DMB transmission modes, the DMB receiver can determine the transmission mode by detecting the NULL symbol and estimating the length of the symbol.

3 is a block diagram illustrating a general configuration of a mode detector using the NULL symbol section described above. That is, the energy detector 302 squares and adds the real part I signal and the imaginary part Q signal, which are the outputs of the I / Q divider 301, respectively, to produce an energy sample, and output the result to the integrator 303. The integrator 303 integrates the output value of the energy detector 302 for a predetermined period, calculates an average energy of the received input signal, and outputs the average energy to the NULL symbol detector 304. The NULL symbol detector 304 compares a predetermined reference energy magnitude with an average energy magnitude of the received signal output from the integrator 303, detects the position of the NULL symbol among the received signals, and then estimates a symbol length estimator 305. ) At this time, the reference energy magnitude value should theoretically be 0, but it is set to an appropriate value considering the noise on the channel.

The symbol length estimator 305 detects a received signal section having an average energy lower than a reference energy size, estimates a NULL symbol length, and outputs the NULL symbol length to the mode determiner 306. The mode determiner 306 finally determines a transmission mode by comparing the estimated NULL symbol length with a reference NULL symbol length determined according to four transmission modes. For example, if the estimated NULL symbol length is in the range of 1.297 ms, the transmission mode 1 is determined.

This method uses a very simple structure, which makes the system easy to implement and shows good performance in a channel environment with a constant noise level. However, in order to detect the NULL symbol section, the receiver must first know the magnitude of the noise flowing on the channel and use it as a reference energy magnitude value. In the general transmission channel environment where the magnitude of the noise varies, the detection performance is greatly reduced. Have.

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 an apparatus and method for detecting a transmission mode irrespective of the magnitude of noise on a channel by estimating a null symbol length using a signal energy ratio. have.

A transmission mode detection apparatus in a DMB receiver according to the present invention for achieving the above object, DMB for detecting the transmission mode after receiving and demodulating a transmission frame consisting of a NULL symbol, a phase reference symbol, and a plurality of data symbols An apparatus for detecting a transmission mode in a receiver, the apparatus comprising: an average energy calculator configured to calculate an average energy value of a received signal by integrating a demodulated signal to obtain an energy value of each sample and integrating for a predetermined period; A delayer for delaying an average energy value of the received signal output from the average energy calculator by an integration period of the average energy calculator; The average energy ratio is calculated by receiving the average energy value of two consecutive integration sections output from the average energy calculator and the retarder, and the ratio / position for obtaining and outputting the position in the time domain when the energy ratio becomes maximum and minimum. A calculator; A NULL symbol length estimator for estimating a NULL symbol length from a maximum energy ratio position and a minimum energy ratio position value output from the ratio / position calculator; And a mode determiner for finally determining a transmission mode by comparing the NULL symbol length estimated by the NULL symbol length estimator with a reference NULL symbol length determined according to a transmission mode.

The average energy calculation unit is composed of an energy detector and an integrator, and the integration section for integrating the energy values of each sample calculated by the energy detector is set to the NULL symbol length of transmission mode 1 having the shortest NULL symbol length.

The ratio / position calculator includes a counter for counting during a preset search period in synchronization with the output signal of the average energy calculator and the delay unit, a multiplier, a comparator, and a register, and includes an average of the integral section output from the delay unit. A maximum position detector which calculates the average energy ratio of the integral section output from the energy to the average energy calculator, and outputs the position in the time domain where the energy ratio becomes the maximum using the count value of the counter, a multiplier and a comparator, The average energy ratio of the integral section outputted from the delay section output from the delay unit to the average section of the output section calculating unit is calculated, and the count value of the counter is used to calculate the average energy ratio in the time domain. Consists of minimum position detector to output position And that is characterized.

The search section for finding the position of the maximum value and the minimum value of the energy ratio may be set to one frame section of transmission mode 1 having the maximum frame period.

The maximum position detector may include a first multiplier that multiplies the output of the delay unit and a first feedback value with each other, a second multiplier that multiplies the output of the average energy calculator with a second feedback value, and the first and second multipliers. A comparator for comparing output magnitudes, a first selector configured to select an output of the average energy calculator when the comparator determines that the output of the first multiplier is large, and to select and output a first feedback value when it is determined not to be large; A first register for storing the output of the first selector and outputting the first multiplier to the first selector as a first feedback value; and if the comparator determines that the output of the first multiplier is large, selects the output of the delayer And a second selector for selecting and outputting a second feedback value, and storing the output of the second selector if it is determined not to be large. A second register that outputs a second feedback value to the selection unit and is only enabled when the comparator determines that the output value of the first multiplier is greater than the output value of the second multiplier, and stores the count value of the counter; And a third register for outputting the maximum ratio position value.

The minimum position detector may include a first multiplier that multiplies the output of the delay unit and a first feedback value with each other, a second multiplier that multiplies the output of the average energy calculator with a second feedback value, and the first and second multipliers. A comparator for comparing output magnitudes, a first selector configured to select an output of the average energy calculator when the comparator determines that the output of the first multiplier is small, and to select and output a first feedback value when determined to be not small; A first register for storing the output of the first selector and outputting the first multiplier to the first selector as a first feedback value; and if the comparator determines that the output of the first multiplier is small, the output of the delay unit is selected And a second selector for selecting and outputting a second feedback value, and storing the output of the second selector if it is determined to be not small. A second register that outputs a second feedback value to the selection unit and is only enabled when the comparator determines that the output value of the first multiplier is smaller than the output value of the second comparator, and stores the count value of the counter; It is characterized by consisting of a third register for outputting a to the minimum ratio position value.

The NULL symbol length estimator may compare the estimated NULL symbol lengths with a plurality of preset thresholds, respectively, and compensate for the NULL symbol length according to a comparison result to determine a final NULL symbol length.

Transmission mode detection method in a DMB receiver according to the present invention,

(a) calculating an average energy value of the received signal by squared the demodulated signal to obtain an energy value of each sample and then integrating for a predetermined period;

(b) delaying the average energy value of the received signal calculated in step (a) by the integral period;

(c) Calculate the average energy ratio by inputting the average energy value of two successive integration intervals output in the above steps (a) and (b), and find the position in the time domain when the energy ratio becomes maximum and minimum. Outputting; And

(d) estimating a NULL symbol length from the difference between the maximum energy ratio position and the minimum energy ratio position value, and finally determining the transmission mode by comparing the estimated NULL symbol length with a reference NULL symbol length determined according to the transmission mode. Characterized in that comprises a.

In step (d), the estimated NULL symbol length is compared with each of a plurality of preset threshold values, and the final NULL symbol length is determined by compensating for the NULL symbol length according to a comparison result.

Other objects, features and advantages of the present invention will become apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings.

Hereinafter, with reference to the accompanying drawings illustrating the configuration and operation of the embodiment of the present invention, the configuration and operation of the present invention shown in the drawings and described by it will be described as at least one embodiment, By the technical spirit of the present invention described above and its core configuration and operation is not limited.

4 is a block diagram illustrating an apparatus for detecting a transmission mode through null symbol length estimation according to an embodiment of the present invention, wherein an energy sample is generated by squaring and adding each real part I signal and an imaginary part Q signal from an I / Q divider to generate an energy sample. An integrator 403 that calculates an average energy value of a received input signal by integrating a detector 402, an output value of the energy detector 402 for a predetermined period, and an average energy of a received signal output from the integrator 403. The average energy ratio is calculated by receiving an average energy value between two consecutive integrating sections output from the delay unit 404 and the integrator 403 and the delay unit 404, which delays the value by an integration period, and the energy ratio is maximum. And a ratio / position calculator 405 that calculates and outputs a position in the time domain when the minimum is reached, and the maximum energy ratio position and minimum that are output from the ratio / position calculator 405. The symbol length estimator 406 estimates the NULL symbol length from the ratio ratio position value, and the NULL symbol length estimated by the symbol length estimator 406 is compared with a reference NULL symbol length determined according to the transmission mode. And a mode determiner 407 for determining.

In the present invention configured as described above, the energy detector 402 squares and adds the real part I signal and the imaginary part Q signal output from the I / Q divider 401 to obtain the energy value of each sample, and then outputs the result to the integrator 403. do. The integrator 403 integrates the output value of the energy detector 402 for a predetermined period, calculates the average energy of the received input signal, and outputs the average energy to the delayer 404 and the ratio / position calculator 405.

That is, the integrator 403 accumulates the energy value of each sample obtained by the energy detector 402 for a predetermined period, and then divides the cumulative value into a cumulative interval to obtain an average energy value of the received signal. In this case, the length of the integral section is proportional to the performance of the system and inversely proportional to the complexity. However, since the receiver does not know the transmission mode, the integral section of the integrator 403 cannot be determined using the symbol length.

Accordingly, in the present invention, the length of the shortest NULL symbol, that is, the length of the NULL symbol of transmission mode 3, among the lengths of the NULL symbols according to the four transmission modes is determined as an integration section. This is the maximum integration interval that can achieve the maximum performance in detecting the energy of the NULL symbol without knowing the transmission mode.

The delay unit 404 delays the average energy value output from the integrator 403 by the integration period and outputs the result to the ratio / position calculator 405. In other words, the input and output of the retarder 404 represents the average energy value during two consecutive integration periods. In this case, the output of the delayer 404 becomes the average energy value of the first integrating section that is temporally advanced, and the input of the delayer 404 becomes the average energy value of the second integrating section that is behind in time.

5A shows an average energy value in the time domain including a NULL symbol. In this case, in the case of the data symbol interval, the average energy value has a substantially constant value. However, when the integral section begins to include the NULL symbol, the average energy begins to decrease. When only the NULL section is used as the integration section, only the energy level of the noise signal remains.

Accordingly, the ratio / position calculator 405 receives the average energy values of two consecutive integration sections, calculates the average energy ratio of the first integration section to the average energy ratio of the second integration section, and the energy ratio is the maximum and the minimum. Outputs the position in the time domain when

At this time, the search period for finding the position of the maximum value and the minimum value of the energy ratio is one period of the DMB frame, and it should be able to search for all four transmission modes. Therefore, the ratio / position calculator 405 selects one frame section of the transmission mode I having the maximum frame period as the search section.

5B shows an energy ratio of two consecutive integration sections in a time domain including a NULL symbol. If the two integration intervals contain only data symbols, the energy ratio has a constant value of nearly one. However, when the first integration section begins to include a NULL symbol, the average energy of the first integration section decreases and the energy ratio starts to increase. When the first integration section corresponds to the NULL symbol section, the energy ratio becomes maximum. If the integral section proceeds and the NULL symbol section is included only in the second integration section, the energy ratio is reduced to 1 or less. If the NULL symbol section is included in the second integration section, the energy ratio has a minimum value close to zero. .

Therefore, the position value in the time domain when the energy ratio is minimum is the start point of the NULL symbol, and the position value in the time domain when the energy ratio is maximum corresponds to the end point of the NULL symbol. In this case, a division operation is required to obtain an energy ratio between two integration sections, which increases the complexity of the system. Accordingly, the ratio / position calculator 405 of the present invention compares the energy ratio through a multiplication operation and a comparison operation instead of a division operation.

If this is expressed mathematically, Equation 1 below.

In Equation 1, E denotes an average energy, an index n denotes an index of an integral section, and w denotes an integral section. That is, w1 means the first integration section and w2 means the second integration section. As shown in Equation 1, it can be seen that the comparison of the two energy ratios is equivalent to a multiplication using four average energy values. In this case, it is assumed that the average energy is not zero.

FIG. 6 is a detailed block diagram of the ratio / position calculator 405 based on Equation 1, and includes a counter 600, a maximum position detector 610, and a minimum position detector 620.

The maximum position detector 610 outputs the delay unit 404. And the first feedback value The first multiplier 611 to multiply, the output of the integrator 403 And second feedback value The second multiplier 615 to multiply, the comparator 612 to compare the output of the first, second multipliers (611, 615), the output of the integrator 403 and one of the first feedback value of the comparator 612 A first feedback unit 613 for selecting and outputting an output signal according to an output signal and storing the output of the first selection unit 613, and then outputting a first feedback value to the first multiplier 611 and the first selection unit 613; A second selector 616 that selects one of an output of the delayer 404 and a second feedback value according to an output signal of the comparator 612, and outputs the first register 614 and the second feedback value; A second feedback value to the second multiplier 615 and the second selector 616 after storing the output of the second selector 616; A second register 617 outputting a second register 617 and a third register 618 enabled by the output of the comparator 612 to store an output value of the counter 600 and outputting the stored value as a maximum ratio position value. It consists of.

First, the operation of the maximum position detector 610 will be described in detail.

That is, the average energy value of the received signal of the second integration section obtained by the integrator 403 is input to the delay unit 404, the second multiplier 615, and the first selector 613. The average energy value of the received signal of the first integration section delayed by the integration section by the delay unit 404 is input to the first multiplier 611 and the second selector 616.

The first multiplier 611 multiplies the output value of the delay unit 404 by the first feedback value of the first register 614 and outputs the result to the comparator 612. The second multiplier 615 outputs the output value of the integrator 403. Multiplies the second feedback value of the second register 617 and outputs the result to the comparator 612. The comparator 612 compares two multiplication results and satisfies BOOLEAN TRUE as the selection signals of the first and second selectors 613 and 616 and the enable signal of the third register 618 when the inequality relation of Equation 1 is satisfied. Output According to the output of the comparator 612, the first selector 613 maintains a value stored in the register 614 as a previous value or updates a new value.

That is, the comparator 612 outputs '1' if the output of the first multiplier 611 is greater than the output of the second multiplier 615, and outputs '0'.

The first selector 613 selects and stores the first feedback value of the first register 614 in the first register 614 when the output of the comparator 612 is 0, and outputs the integrator 403 when the output is 1. Is selected and stored in the first register 614.

That is, if the output of the comparator 612 is 0, the value stored in the first register 614 becomes the previous value, and if the output of the comparator 612 is 0, the new value, that is, the output value of the integrator 403 is updated.

Similarly, if the output of the comparator 612 is 0, the value stored in the second register 617 becomes the previous value, and if the value is 1, the new value, that is, the output value of the delay unit 404, is updated.

In this way, the first and second selectors 613 and 616 maintain the values stored in the two registers according to the output of the comparator 612 as the old values or the new values, that is, the integrator 403 and the delayer 404. Update to the output of.

Then, the first and second multipliers 611 and 615 also multiply the newly updated values with the values output from the integrator 403 and the delay unit 404 and output the multipliers to the comparator 612.

In addition, the value of the counter 600 is increased by one in accordance with the input / output ratio of the delay unit 404, and the counter 600 is initialized at the end of one frame period of the transmission mode 1. Accordingly, the value of the third register 618 output at the end of the frame period is a time position when the energy ratio searched during the frame period is maximum.

Meanwhile, the configuration of the minimum position detector 620 is the same as that of the maximum position detector 610 described above. The only difference is that only the condition of the comparator 622 needs to be changed to the inverse of the condition of the comparator 612 of the maximum position detector 610. That is, the comparator 622 may set '0' if the output of the first multiplier 621 is greater than the output of the second multiplier 625, and otherwise output '1'.

Then, when the output of the comparator 622 is 0, the first selector 623 selects and stores the first feedback value of the first register 624 in the first register 624. Select the output of and store it in the first register 624.

That is, if the output of the comparator 622 is 0, the value stored in the first register 624 becomes the previous value, and if 1, the value of the comparator 622 is updated to the new value, that is, the output value of the integrator 403.

Similarly, if the output of the comparator 622 is 0, the value stored in the second register 627 is the old value, and if it is 1, the new value is updated to the output value of the delay unit 404.

Then, the value of the third register 628 output at the end of one frame period in transmission mode 1 becomes a time position when the energy ratio searched during the frame period is minimum.

The maximum ratio position value and the minimum ratio position value output from the ratio / position calculator 405 are output to the NULL symbol length estimator 406.

The NULL symbol length estimator 406 may estimate the length of a NULL symbol by using a difference between two position values. In other words, subtracting the minimum ratio position value from the maximum ratio position value gives the NULL symbol length.

However, as shown in Table 1, the length of one DMB frame varies depending on the transmission mode. Therefore, in the case of transmission mode 4, two frames of the DMB signal are transmitted in the case of transmission mode 2 or 3 during the transmission mode 1 frame length. Four frames will be included. Therefore, if the maximum and minimum values of the energy ratio are found during the frame length of the transmission mode 1, the transmission mode finds the maximum and minimum values for several frame intervals instead of one frame interval in the other transmission modes. This soon degrades the performance of determining the transmission mode.

Therefore, the NULL symbol length estimator 406 needs to compensate for this and then output the result to the mode determiner 407 to determine the transmission mode.

7 illustrates positions of frames and NULL symbols of DMB transmission signals according to four transmission modes. For example, when receiving a DMB signal of transmission mode 4, two NULL symbol sections are included during a frame section of transmission mode 1, which is a search section. Therefore, if the maximum and minimum values are searched, one of the positions corresponding to the start and end points of the two NULL symbols is detected. Therefore, the length of the NULL symbol cannot be determined simply by obtaining the difference between the two position values.

A flowchart of estimating the NULL symbol length by compensating for this is shown in FIG. 8. 8, the length of the received NULL symbol can be estimated regardless of the transmission mode.

That is, in step 801, the NULL symbol length D is temporarily estimated by subtracting the minimum ratio position value from the maximum ratio position value. The value of D is then compared to-(frame length of transmission mode 1-NULL symbol length of transmission mode 1-error range) (step 802). For example, if the error range is set to 504, the value compared with the D value is -193448 (= 196608-2656-504).

If it is determined in step 802 that the final NULL symbol length is determined by the value of D value + frame length of transmission mode 1 (= 196608), and if large, the process proceeds to the next step 803. That is, in step 802, the value of D is less than -193448, since a null symbol spans the beginning and the end of a search period (that is, one frame period of transmission mode 1) in transmission mode 1, and thus corresponds to transmission mode 1. Add the frame length to estimate the final NULL symbol length.

In step 803, if it is determined that the value of D is smaller than -146666 by comparison, the final NULL symbol length is determined as D value + (frame length of transmission mode 1-frame length of transmission modes 2 and 3). Proceed to step 804.

In step 804, if it is determined that the value D is greater than 147675 by comparison, the final NULL symbol length is determined as D value-(frame length of transmission mode 1-frame length of transmission mode 2). Proceed.

In step 805, if it is determined that the value D is smaller than -96724 by comparison, the final NULL symbol length is determined as D value + (frame length of transmission mode 4).

In step 806, if it is determined that the value of D is greater than 98397 by comparison, the final NULL symbol length is determined as D value-(frame length of transmission mode 4).

In step 807, if it is determined that the value D is smaller than -48362 by comparison, the final NULL symbol length is determined as D value + (frame length of transmission modes 2 and 3).

In step 808, if it is determined that the value of D is greater than 49371 by comparison, the final NULL symbol length is determined as D value-(frame length of transmission modes 2 and 3). All.

That is, the frame lengths of the transmission modes 2 and 3 correspond to 1/4 based on the transmission mode 1. Therefore, there are at least four null symbols in transmission modes 2 and 3 in one frame period of transmission mode 1. At this time, the minimum ratio position value and the maximum ratio position value may be detected anywhere in the four null symbols. Therefore, each null symbol must be considered.

In this case, in step 803, if the value of D is less than -146666, the maximum ratio position value is detected in the first null symbol in the search interval in transmission modes 2 and 3, and the minimum ratio position value is detected in the fourth null symbol. to be. In this case, the final NULL symbol length is determined based on the above-described D value + (frame length of transmission mode 1-frame length of transmission modes 2 and 3).

In step 804, the value of D is greater than 147675 when the minimum ratio position value is detected in the first null symbol and the maximum ratio position value is detected in the fourth null symbol in transmission modes 2 and 3. At this time, the final NULL symbol length is determined by the above-described D value (frame length of transmission mode 1-frame length of transmission modes 2 and 3).

In addition, in case of transmission modes 2 and 3, the maximum ratio position value of two NULL symbols (for example, the first null symbol and the third null symbol, or the second null symbol and the fourth null symbol) that exist across one another, respectively. And minimum ratio position values may be detected and steps 805 and 806 confirm this.

That is, in step 805, the value of D is less than -96724 when the minimum ratio position value is detected in the rear null symbol section and the maximum ratio position value is detected in the null symbol section in front of one another. In this case, the final NULL symbol length is determined by the D value + (frame length of transmission mode 4).

In the step 806, the value of D is greater than 98397 when the maximum ratio position value is detected in the rear null symbol section and the minimum ratio position value is detected in the front null symbol section. In this case, the final NULL symbol length is determined by the value D (frame length of transmission mode 4).

Meanwhile, in transmission modes 2 and 3, the maximum ratio position value and the minimum ratio position value may be detected in two neighboring null symbol intervals (for example, the first null symbol interval and the second null symbol interval). Steps 807 and 808 confirm this.

That is, in step 807, if the value of D is less than -48362, the minimum ratio position value is detected in the null symbol interval located at the rear of two neighboring null symbol intervals, and the maximum ratio position value in the immediately preceding null symbol interval This is the case when it is detected. In this case, the final NULL symbol length is determined by the D value + (frame length of transmission modes 2 and 3).

Further, in step 808, if the value of D is greater than 49371, the maximum ratio position value is detected in the null symbol section located at the rear of two neighboring null symbol sections, and the minimum ratio position value is detected in the immediately preceding null symbol section. If it is. In this case, the final NULL symbol length is determined by the D value (frame length of transmission modes 2 and 3).

In step 808, the value of D is less than 49371 in the case where the maximum ratio position value and the minimum ratio position value are detected in the same null symbol interval of transmission modes 1, 2, 3, and 4, in which case the D value is the final NULL. It is determined by the symbol length.

Meanwhile, the frame length of transmission mode 4 corresponds to 1/2 based on transmission mode 1. Therefore, there are at least two null symbol intervals in transmission mode 4 in one frame interval in transmission mode 1. In this case, the minimum ratio position value and the maximum ratio position value may be detected in any one of the two null symbol intervals, and thus, the above-described steps 805 and 806 are steps of confirming this.

That is, in step 805, the value of D is less than -96724 when the minimum ratio position value is detected in the rear null symbol section and the maximum ratio position value is detected in the front null symbol section. In this case, the final NULL symbol length is determined by the D value + (frame length of transmission mode 4).

In the step 806, the value of D is greater than 98397 when the maximum ratio position value is detected in the rear null symbol section and the minimum ratio position value is detected in the front null symbol section. In this case, the final NULL symbol length is determined by the value D (frame length of transmission mode 4).

The final NULL symbol length thus obtained is output to the mode determiner 407. The mode determiner 407 finally determines the transmission mode by comparing the estimated final NULL symbol length with the reference NULL symbol length determined according to four transmission modes. Done. For example, if the estimated NULL symbol length is in the range of 1.297 ms, the transmission mode 1 is determined.

The numbers presented in each step of FIG. 8 are thresholds for determining the above-described conditions, and the thresholds may vary according to an error range, and thus the numbers shown in the above examples will not be limited.

As described above, according to the apparatus and method for detecting a transmission mode in a DMB receiver according to the present invention, by comparing energy ratios of two integration intervals, estimating a NULL symbol length and determining a transmission mode with an estimated NULL symbol length, The transmission mode can be estimated regardless of the amount of noise.

In addition, by using a multiplier and a comparator instead of a divider in the process of finding a position where the energy ratio is maximum and minimum, the circuit configuration is simplified.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the spirit of the present invention.

Therefore, the technical scope of the present invention should not be limited to the contents described in the embodiments, but should be defined by the claims.

1 shows an example of a transmission frame structure in transmission mode 1

2 is a configuration block diagram of a typical DMB receiver

3 is a block diagram illustrating an example of a conventional transmission mode detector;

4 is a block diagram showing an example of a transmission mode detection unit according to the present invention;

5A shows an example of an average energy value in a NULL symbol region.

5B shows an example of an energy ratio value in a NULL symbol region.

6 is a detailed block diagram illustrating an example of the ratio / position calculator of FIG. 4.

7 (a) to 7 (d) show an example of a position of a frame structure and a null symbol according to a transmission mode

8 is a flowchart illustrating an example of a NULL symbol length compensation process according to the present invention.

Explanation of symbols for main parts of the drawings

200: antenna 201: tuner

202: AGC part 203: A / D converter

204: I / Q distributor 205: mode detector

206: signal synchronizer 207: OFDM demodulator

208: frequency deinterleaving unit 209: channel divider 1

210: FIC decoder 211: time deinterleaving unit

212: convolutional decoder 213: energy descrambler

214: channel distributor 2 215: weaving deinterleaving unit

216 RS decoder 217 FIC data decoder

218 audio / data decoder 219 video decoder

402: energy detector 403: integrator

404: delayer 405: ratio / position calculator

406: NULL symbol length estimator 407: mode determiner

Claims (14)

A transmission mode detection apparatus in a DMB receiver for detecting a transmission mode after receiving and demodulating a transmission frame including a NULL symbol, a phase reference symbol, and a plurality of data symbols, An average energy calculating unit calculating an average energy value of the received signal by integrating the demodulated signal to obtain an energy value of each sample and integrating for a predetermined period; A delayer for delaying an average energy value of the received signal output from the average energy calculator by an integration period of the average energy calculator; The average energy ratio is calculated by receiving the average energy value of two consecutive integration sections output from the average energy calculator and the retarder, and the ratio / position for obtaining and outputting the position in the time domain when the energy ratio becomes maximum and minimum. A calculator; A NULL symbol length estimator for estimating a NULL symbol length from a maximum energy ratio position and a minimum energy ratio position value output from the ratio / position calculator; And And a mode determiner for finally determining a transmission mode by comparing the NULL symbol length estimated by the NULL symbol length estimator to a reference NULL symbol length determined according to a transmission mode. . The method of claim 1, wherein the average energy calculation unit The demodulated signal is separated into a real component signal and an imaginary component signal, and then squared and added to each of the real component signal and the imaginary component signal to calculate an energy value of each sample. Device. The method of claim 1, wherein the average energy calculation unit An integration section for integrating the energy values of each sample is set to the NULL symbol length of the transmission mode with the shortest NULL symbol length. The method of claim 3, wherein An integration section for integrating the energy values of each sample is set to a NULL symbol length of transmission mode 3, the transmission mode detection apparatus in the DMB receiver. The method of claim 1, wherein the ratio / position calculator A counter for counting during a preset search period in synchronization with the output signals of the average energy calculator and the delay unit; Calculating the average energy ratio of the integral energy output from the delay section output from the delay unit to the average energy calculation section output from the delay section, and using the count value of the counter to output the position in the time domain of the maximum energy ratio A maximum position detection section, Computing the average energy ratio of the integral energy output from the delay section output from the delay unit to the average energy calculation unit, and outputs the position in the time domain where the energy ratio is the minimum using the count value of the counter Transmission mode detection apparatus in a DMB receiver, characterized in that it comprises a minimum position detector. The method of claim 5, And a search section for finding positions of the maximum and minimum values of the energy ratio is set to one frame section of a transmission mode having a maximum frame period. The method of claim 1, wherein the NULL symbol length estimation unit The maximum ratio position value output from the ratio / position calculator is determined as the end point of the NULL symbol section, the minimum ratio position value is the start point of the NULL symbol section, and the difference between the maximum ratio position value and the minimum ratio position value is NULL. Transmission mode detection apparatus in a DMB receiver, characterized in that estimated by the symbol length. The method of claim 7, wherein the NULL symbol length estimation unit And comparing the estimated null symbol length with a plurality of preset threshold values, and compensating for the null symbol length according to a comparison result to determine a final NULL symbol length. A transmission mode detection method in a DMB receiver for detecting a transmission mode after receiving and demodulating a transmission frame including a NULL symbol, a phase reference symbol, and a plurality of data symbols, (a) calculating an average energy value of the received signal by squared the demodulated signal to obtain an energy value of each sample and then integrating for a predetermined period; (b) delaying the average energy value of the received signal calculated in step (a) by the integral period; (c) Calculate the average energy ratio by inputting the average energy value of two successive integration intervals output in the above steps (a) and (b), and find the position in the time domain when the energy ratio becomes maximum and minimum. Outputting; And (d) estimating a NULL symbol length from the difference between the maximum energy ratio position and the minimum energy ratio position value, and finally determining the transmission mode by comparing the estimated NULL symbol length with a reference NULL symbol length determined according to the transmission mode. Transmission mode detection method in a DMB receiver, characterized in that comprises a. The method of claim 9, wherein step (a) The demodulated signal is separated into a real component signal and an imaginary component signal, and then squared and added to each of the real component signal and the imaginary component signal to calculate an energy value of each sample. Way. The method of claim 9, wherein step (a) The integration section for integrating the energy values of each sample is set to the NULL symbol length of transmission mode 3 having the shortest NULL symbol length. The method of claim 9, wherein step (c) Performing counting for a preset search period in synchronization with the output signals of steps (a) and (b); Calculate the average energy ratio of the first integration period to the average energy of the second integration section output in the step (a), (b), and use the count value to determine the position in the time domain where the energy ratio becomes the maximum. Outputting, Calculate the average energy ratio of the first integration period to the average energy of the second integration section output in the step (a), (b), and use the count value to determine the position in the time domain where the energy ratio becomes the minimum. A transmission mode detection method in a DMB receiver, characterized in that comprising the step of outputting. The method of claim 12, The search section for finding the position of the maximum value and the minimum value of the energy ratio is set to one frame section of transmission mode 1 having the maximum frame period. The method of claim 8, wherein step (d) And comparing the estimated NULL symbol length with a plurality of preset threshold values, and compensating for the NULL symbol length according to a comparison result to determine a final NULL symbol length.