JP3386668B2 - Receiver for digital audio broadcasting - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for digital audio broadcasting (DAB), and in particular, it automatically identifies the transmission mode of a DAB broadcasting station and receives the DAB broadcasting according to the transmission mode. The present invention relates to a receiving device in digital audio broadcasting that can perform.

[0002]

2. Description of the Related Art An audio signal is digitized into serial data, the serial data is divided into 2N pieces, and the 2N pieces of digital data are divided into N groups of 2 bits each, each of which is a combination of 1 and 0 of 2 bits. Digital audio in which N carriers having different frequencies are 4-phase PSK-modulated, frequency-multiplexed with each modulated signal, and transmitted from a transmitting station, and a receiver receives the frequency-multiplexed phase-modulated signal, demodulates and outputs voice. Broadcasting (DAB) has been proposed and is being considered for practical use in Europe and the like.

In this DAB system, in order to reduce the influence of selective fading, information is divided in parallel and modulation is performed using a large number of carriers, and even if any carrier receives fading, the influence is reduced as a whole. Basically, frequency division multiplexing (FDM: Frequent)
ncy Division Multiplex) method. By the way, in the case of simple FDM, it is necessary to take a sufficient space between carriers in order to avoid spectrum overlap, and frequency utilization efficiency is not so good. Therefore, OF
A DM (Orthogonal Frequency Division Multiplex) method has been proposed. In the case of this OFDM, each carrier is arranged so as to satisfy the orthogonal condition, spectrum overlap is allowed, frequency utilization efficiency is high, and the modulator and demodulator use IDFT (Inverse Discrete Fourier Tra
nsform: Inverse Discrete Fourier Transform, DFT (Discrete Fouri)
er Transform: Discrete Fourier Transform) operations can be used, which has the advantage of greatly simplifying the hardware.

(A) Principle of OFDM-based digital audio broadcasting FIG. 6 is a diagram showing the basic configuration of a transmitter for digital audio broadcasting. 1 is serial data d (n) (a (0), b (0), a (1), b (1), ...) Inputted at the transmission rate fs (= 2 / Δt).
·) The serial-parallel converter for converting parallel data of 2N bits (S / P converter), 2 ₀ to 2 _N-1 in the N carriers multiplication unit, two bits parallel data 2 × N bits A set of a (0), b (0); a (1), b (1);
1), b (N-1), and the first bit a (0), a (1),
..A (N-1) carrier (cosω) with frequency f _{0 to} f _N-1
n t) and the second bits b (0), b (1), ... b (N-1) are multiplied by carriers (−sinω _n t) of frequencies f _{0 to} f _N−1 , 3 is the output signal a (n) cosω of the carrier multiplication unit of each set
_n t, −b (n) sin ω _n t (n = 0 to N−1) is combined and frequency-multiplexed to transmit a signal D (t) (M).
UX).

The frequency multiplexing unit 3 synthesizes the output signals of the carrier multiplying units of each set, so that the carriers of the frequencies f _{0 to} f _{N -1} are four-phased in each set of 2-bit 1 and 0 combinations. Since the PSK modulation is performed, the output D (t) of the frequency multiplexing unit 3 is D (t) = Σ {a (n) cosω _n t−b (n) sin _{ω n} t} (n = 0 to N-
1) If the frequency interval of each carrier is Δf,
The (n + 1) th carrier frequency fn is fn = f ₀ + nΔf, and the transmission time of 2-bit data is Δt (transmission speed f
If s = 2 / Δt), the frequency interval Δf becomes Δf = 1 / NΔt.

FIG. 7 is an explanatory view of the function of the frequency multiplexing unit 3.
, Each of the N carriers f at Δf intervals ₀~ F_N-12 bits
N sets of data a (0), b (0); a (1), b (1);
・ ； 4φPSK modulation with a (N-1) and b (N-1), each modulated signal
Are frequency-multiplexed and transmitted. Figure 8 is an explanatory diagram of symbols
Yes, 2 × N bits make up one symbol, and one symbol
If the time length of Le is Ts, Ts = NΔt Δf = 1 / Ts Becomes 4φPS for each symbol (2 × N bits)
Frequency modulation of K modulation and modulation signals is performed to
The multiple signals D (t) are sequentially transmitted.

FIG. 9 shows a receiver for digital audio broadcasting.
It is a principle block diagram. Four₀~ 4_N-1Is N carrier multiplication
The frequency f to the received signal D (t)₀~ F_N-1Career (c
osω _nt, −sinω_nt, n = 0 to N-1)
Of 5₀~ 5_N-1Returns the data by integrating the output of each multiplier.
The integrator 6 adjusts the parallel data of 2 × N bits in serial
Parallel-to-serial converter (P / S conversion)
Vessel). Each integrator 5₀~ 5_N-1Is the input signal D (t)
Then the following formula

[Equation 1] And data a (0), b (0); a (1), b
(1); ...; demodulates a (N-1) and b (N-1).

(B) OFDM Modulation / Demodulation System Using DFT In the meantime, N 4φPSK modulators are required to generate the OFDM baseband signal D (t), and
To demodulate, N 4φPSK demodulators are required.
Becomes larger, it is not practical. Therefore, a method of easily performing modulation / demodulation using DFT will be described next.

(B-1) Configuration of modulator The baseband signal of OFDM is

[Equation 2] Is expressed as If d (k) = a (k) + jb (k), then equation (1) becomes

[Equation 3] Is represented. Where * means a complex number and R [] is
Represents the real part of [].

[0010]

[Equation 4] Therefore, it is clear from the equation (3) that D (t) is represented by the equation (2). In equation (2), if t = mΔt,

[Equation 5] Becomes Note that D (m) is the real part of the IDFT (Inverse Discrete Fourier Transform) of d (k).
When D (m) is output as D (0), D (1), ... D (N-1) for each Δt, it becomes as shown in FIG. This signal is nothing but the sample of equation (2) for each Δt. Therefore,
When the ideal filter having the frequency characteristic shown in FIG. 11 (a) and the impulse characteristic shown in FIG. 11 (b) is passed through, the same thing as the expression (2) is obtained.

From the above, as the modulator, the input data d (k) (complex) is IDFTed, and its real part D (0) to D (0)
By outputting up to (N-1) every Δt and passing through an ideal filter, a modulated wave (baseband signal) can be obtained. FIG. 12 is a main part configuration diagram of a transmitter configured by focusing on this point. 11 is N bits of data a (k), b (k) (k
= 0 to N), an IDFT unit that performs an inverse discrete Fourier transform on the input data d (k) represented by a complex representation, 12a is a DA converter that converts the real number part output from the IDFT unit to analog, 13a
Is an ideal filter, and 14a is a cos of the ideal filter output D (t).
by multiplying the omega _c t is a multiplier unit for frequency conversion.

(B-2) Configuration of demodulation section When only D (t) is obtained in reception frequency conversion, 2
The original information cannot be extracted without sampling N points. This is because D (t) is only the real part of the N-point IDFT. It is also clear from the sampling theorem as shown in FIGS. 13 (a) and 13 (b). According to the sampling theorem, the signal in the band N · Δf is 1 / (2 · N · Δ
Must be sampled at the frequency of f). Since 1 / (2 · N · Δf) = Δt / 2, it is necessary to sample at Δt / 2 intervals instead of Δt intervals. Therefore, Ts section (N · Δt)
2N points need to be sampled at. But,
When the real part D (t) and the imaginary part I (t) are obtained, the original signal can be extracted by sampling at N points as shown below. Equation (5) shows the complex baseband signal after the reception frequency conversion.

[0013]

[Equation 6] The real part and imaginary part on the right side are D due to the transmission line and noise, respectively.
(t) and I (t) are modified, and in an ideal transmission line, D
(t) and I (t).

[0014]

[Equation 7] If equation (6) is sampled with mΔt (m = 0,1,2, ... N-1),

[Equation 8] Then, equation (7) becomes

[Equation 9] Therefore, d (k) is obtained by the DFT of equation (8) as follows.

[0015]

[Equation 10] From this, an estimate of the original signal d (k) is obtained. For reference, the relational expression of DFT and IDFT is as follows.

[0016]

[Equation 11] From the above, if the complex baseband signal obtained by frequency-converting the received signal S (t) is converted to digital through a low-pass filter and DFT is performed in the DFT section, an estimated value of the original signal d (k) can be obtained. To be FIG. 14 is a main part configuration diagram of a receiver configured by focusing on such a point, and 15 is a frequency conversion unit and 1
6a and 16b are low-pass filters, 17a and 17b are A
The D converter, 18 is a DFT unit.

(C) The quadrature balanced modulation method using the transmission side frequency conversion D (t) and I (t) is the same as the frequency conversion method used in the SSB method, as shown in FIG. In the figure, 11 is an IDFT unit, and 12a and 12b are A.
D converter, 13a, 13b is a low-pass filter, 14 is a frequency converter, cos .omega _c t, is constituted by a multiplier 14a, 14b and multiplier hybrid circuit 14c that outputs synthesized and output of multiplying sin .omega _c t ing.

The output signal S (t) of the frequency converter 14 is

[Equation 12] And does not include the lower sideband. Therefore, the band is halved as compared with the double sideband system, and the transmission efficiency is improved.

(D) Frequency conversion method on receiving side Figure 16 is cosω_ct, sinω_cThe structure of the orthogonal frequency converter by t
It is a diagram. 15a is the next to the received signal s (t) (see equation (11))
Noise signal n (t) n (t) = n_c(k) cos2π (f_c+ f_k) T-n_s(k) sin2π (f_c+
f_k) T Adder that outputs the signal r (t) (actually
No), 15b is a bandpass filter, 15c, 15
d is cosω in the bandpass filter output_ct, −sinω _csquared t
It is a multiplication unit that calculates. There is no amplitude attenuation or noise, and
In an ideal transmission line with no phase delay, r (t) = s (t)
It In the description below, r (t) = s (t). This orthogonal
The output signals D '(t) and I' (t) of the frequency converter are
formula

[Equation 13] Expressed by Incidentally, (12), it is ignored section 2f _c in (13). These Eqs. (12) and (13) match the real and imaginary parts of Eq. (3), which represents the transmitting-side complex baseband signal, respectively. Therefore, the original signal can be extracted by performing the N-point sampling DFT operation as described above.

(E) In the differential encoding (d), the frequency conversion method on the receiving side has been described, but it is very difficult to create a receiving local frequency synchronized with the transmitting local frequency ω _c in the OFDM method. Also, if there is a frequency error in the received local frequency (in the case of non-synchronization), the result will be rotation of the demodulation vector, and demodulation by the absolute phase will be difficult. Therefore, instead of expressing the information by the absolute phase on the transmitting side, the information is expressed by the magnitude of the phase rotation. This is called differential encoding, and demodulation is possible even if there is some frequency error.

(E-1) Differential Encoder FIG. 17 is an explanatory diagram of the transmission side differential encoder, and the logical expression of the differential encoder 21 is

[Equation 14] Is. The differential encoder 21

[Equation 15] The data D _l (k) represented in complex form is converted into d _l (k) by the above logical expression.

The differential code is (1) [A _l (k), B _l (k)] = (1,1)

[Equation 16] Then, substituting into equation (14)

[Equation 17] And the phase does not change.

(2) When [A _l (k), B _l (k)] = (-1, -1),

[Equation 18] And phase inversion, that is, π shift.

(3) When [A _l (k), B _l (k)] = (1, -1)

[Formula 19] And shifts clockwise by π / 2.

(4) When [A _l (k), B _l (k)] = (-1,1),

[Equation 20] And shifts counterclockwise by π / 2.

(E-2) Differential decoder From equation (14),

[Equation 21] Is obtained. The differential decoder 22 converts the data d _l (k) into D _l (k) according to the logical formula (15) as shown in FIG. Therefore, the following differential decoding results (1) to (4) are output corresponding to the above (1) to (4) of the differential encoder.

[0027]

[Equation 22]

(F) Blocks of transmission system and reception system From the above, the transmission system and the reception system in digital audio broadcasting by the OFDM system have the configurations shown in FIGS. 19 (a) and 19 (b). In the frequency converter 14 of the transmission system,
d is an oscillator for outputting a cos signal (cosω _c t) of frequency f _c,
14e is a phase shifter for outputting a -sinω _c t to -90 ⁰ phase shift the cos signal. Also, the frequency converter 15 in the receiving system, 15e oscillator for outputting a cos signal of frequency _{f c (cosω c t),} 15f is -sinω _c t to -90 ⁰ phase shift the cos signal
Is a phase shifter that outputs Cos waves and sin waves (carriers) of the transmission system are called transmission local signals, and cos waves and sin waves of the reception system are called reception local signals. On the transmission side, a DAB frame is composed of known phase reference symbols and M data symbols, each symbol is divided into N groups of 2 bits, and the first data of each group is the real part and the second data is the imaginary part. Is differentially encoded, the real number part and the imaginary number part of the differential code are sequentially input to the inverse Fourier transform unit 11, the real number part and the imaginary number part output from the inverse Fourier transform unit are converted into analog signals, and the analog signals are transmitted. The cos wave and the sin wave of the local frequency fc are multiplied, the multiplication results are combined, and the result is radiated into space.

On the receiving side, the signal radiated into space is received, the received signal is multiplied by the cos wave and sin wave of the received local frequency, and the respective multiplication results are converted into digital signals and input to the Fourier transform section 18, The real number part and the imaginary number part output from the Fourier transform unit are differentially decoded and sequentially output as first data and second data that are original data. The Fourier transform unit 18 executes the Fourier transform process based on the generation timing of the DFT window signal. That is, a window signal generation unit (not shown) detects a null signal portion provided between frames and outputs a DFT window signal which is the Fourier transform execution timing of each symbol, and the Fourier transform unit 18 generates the DFT window signal generation timing. Perform a Fourier transform based on.

FIG. 20 is an explanatory diagram of DAB frames and window signals. The head portion of the DAB frame is called a synchronization channel, and is composed of a null signal portion NULL and a phase reference symbol portion PRS (Phase Reference Symbol), and before the phase reference symbol portion PRS, in order to reduce the influence of multipath. A guard interval GIT of 62 μs (for mode 2) is provided. A predetermined number (= m) of symbols are arranged after the synchronization channel, and before each symbol, in order to reduce the influence of multipath as well.
A guard interval of 62 μs is provided, and the same content as the latter half of the corresponding symbol is repeatedly inserted in each guard interval.

The null signal portion NULL is used to find the beginning of the frame, and the phase reference symbol portion PRS is used as a reference signal for differential decoding. A unique pattern (known) fixed for each frame is sent. come. The PRS window is a window provided at a predetermined time position based on the null signal portion NULL detected, and the DFT window shows the DFT operation timing for each symbol. Actually, the positions of the PRS window and the DFT window are shifted to a position that is not affected by the adjacent symbol due to the multipath depending on the situation of occurrence of the multipath.

[0032]

In DAB broadcasting, there are modes I to IV as transmission modes, and the DAB frame length T _F and the null signal width T in each transmission mode.
_NULL , symbol length T _S , and guard interval length Δ are different. FIG. 21 (a) is a block diagram of a DAB frame, FIG.
(B) shows (1) DAB frame length T in each transmission mode
_{It is F} , (2) null signal width T _{N ULL} , (3) symbol length T _S , (4) guard interval length Δ, (5) sum of symbol length and guard interval T _U. As is clear from FIG. 21B, the frame length T _F is different between mode I, mode II / III, and mode IV. Further, the frame length T _F (= 24 msec) of the mode II and the mode III is the same, but the symbol length T
_S , guard interval length Δ, symbol length and sum of guard intervals T _U are different. That is, mode II,
The frame period of III is a minimum of 24 ms, but mode I
Frame period is 96 ms, which is four times the minimum frame period, and mode IV frame period is 48 ms, which is 2 times the minimum frame period.
Double.

From the above, in order to correctly demodulate the DAB broadcast signal, it is necessary to identify the transmission mode and perform the DFT demodulation processing according to the transmission mode. At present, there is no effective means for determining the transmission mode, the transmission mode is identified when all the modes have been successfully demodulated, and the transmission mode is identified after that. ing. However, in such a conventional method, there is a problem that the process of identifying the transmission mode becomes complicated and a considerable time is required until the DAB broadcast audio is output. From the above, it is an object of the present invention to easily perform the mode identification processing, shorten the mode identification time, and output the DAB broadcast sound in a short time after the DAB broadcast reception operation.

[0034]

According to the present invention, there is provided a null signal detecting section for detecting a null signal portion, and a DAB releasing section.
By the first null detection signal after transmission / reception operation is performed,
The minimum frame rate among the frame periods of multiple transmission modes
Generates a signal of a certain width (null window) with a periodic period
The number of occurrences of the null window and the width of the null window
A first transmission mode identification unit for identifying a transmission mode of a DAB broadcasting station based on a ratio with the number of null signals generated in a corresponding null window period, and a Fourier transform of each symbol based on the identified transmission mode. This is achieved by a receiving device in digital audio broadcasting that includes a DFT window generation unit that generates a DFT window that is execution timing and inputs the DFT window to the Fourier transform unit.

According to the present invention, the first problem is that the two transmission modes having the same frame cycle exist.
When the transmission mode identification unit of the above cannot identify the transmission mode of the DAB broadcasting station, it is assumed that the DAB broadcasting radio wave is transmitted in one of the two transmission modes.
The correlation between the demodulation result obtained by performing the T demodulation process and the known phase reference symbol is calculated, and if the correlation value is equal to or higher than the set level, it is determined that the transmission mode of the DAB broadcasting station is the one transmission mode. If the correlation value is below the set level, D
The transmission mode of the AB broadcasting station is achieved by the receiving device in the digital audio broadcasting, which includes the second transmission mode identifying unit that determines the other transmission mode.

[0036]

DETAILED DESCRIPTION OF THE INVENTION

(A) As is apparent from the schematic diagram 21 of the present invention, mode I, mode II / III,
The frame length T _F is different from that in mode IV, and the frame length T _F (= 24 msec) in mode II and mode III is the same, but the symbol length T _S is different. Therefore, in order to determine the transmission mode in the DAB receiver, first the frame length T _F is measured. This makes it possible to determine the modes I and IV. However, in both modes II and III, the frame length is 2
Since it is 4 ms, the mode cannot be determined only by measuring the frame length T _F. Therefore, the frame length T _F is 24m
When s is found, the received signal is temporarily demodulated in mode II, and the correlation value between the demodulation result obtained by demodulation and the phase reference symbol PRS of mode II that the receiver has in advance. And calculate the mode based on the correlation value
Distinguish between II and III. That is, if the correlation value is larger than the set value, the DAB broadcast station transmission mode is determined to be mode II, and if the correlation value is smaller than the set value, the DAB broadcast station transmission mode is determined to be mode III. This is D
When the transmission mode of the AB broadcasting station is the mode II, the result demodulated in the mode II is correlated with the phase reference symbol PRS of the mode II and the correlation value increases, but when the transmission mode of the DAB broadcasting station is the mode III. This is because the correlation cannot be obtained and the correlation value becomes small.

(B) Configuration of DAB Receiver FIG. 1 is a configuration diagram of the DAB receiver of the present invention. 6 in the figure
0 is a receiving antenna, 61 is a received signal of carrier frequency
Baseband analog signal D by multiplying cos wave and sin wave
A DAB RF signal demodulation unit that outputs (t) and I (t), and 62 converts baseband analog signals D (t) and I (t) into digital data D (m) and I (m) at a predetermined sampling frequency. Convert A
D converter, 63 is a sampling pulse generator that outputs sampling pulses, and 64 is DAB based on received power.
Null signal portion between frames is detected to detect null signal ND
A null signal detection unit that outputs T, 65 outputs a DFT window signal (including a PRS window signal) that is the Fourier transform execution timing of each symbol that constitutes the DAB frame based on the transmission mode of the DAB broadcasting station.
It is an FT window generator.

66 is a PRS window, D for each symbol
A Fourier transform / differential decoding unit for performing Fourier transform processing on the digital data D (m) and I (m) in the FT window and differentially decoding the coded audio data (for example, MPEG audio data), 67 is an MPEG Audio signal decoding unit for decoding audio data into PCM audio data, 68 DA conversion unit for converting PCM audio data into analog, 69 amplifier, 70 speaker, 71 operation key unit of DAB receiver, 72 display unit , 73 are control units for performing tuning control and other controls. Reference numeral 81 indicates the transmission mode (mode I, mode II / II) of the DAB broadcasting station based on the difference in the frame cycle T _F of the transmission mode.
I, mode IV), a first transmission mode determination unit, 82
Are transmission modes with the same frame period (mode II, mode II
The second transmission mode determination unit determines the transmission mode of the DAB broadcasting station by correlation calculation when two or more I) exist.

(C) First Transmission Mode Determining Section FIG. 2 is a block diagram of the first transmission mode determining section, and FIG. 3 is an operation explanatory diagram of the first transmission mode determining section. In the first transmission mode determination unit 81, reference numeral 81a denotes a null window generation unit, which is a minimum window period (= 24 msec) of a plurality of transmission modes (modes I to IV) and has a predetermined width of null window ( A null window signal NWD is generated, and the null window NWD is generated by the first null detection signal NDT after the DAB broadcast receiving operation is performed. 81b is a counter unit, and two counters 9
1 and 92 are provided. The counter 91 counts the input null window NWD and outputs the counted value as the null window number a, and the counter 92 outputs the null detection signal NDT generated when the null window NWD is at the high level (during the null window period). It counts and outputs the count value as the number b of null detection signals. The counter 92 does not count the null detection signal NDT generated when the null window NWD is at the low level. The reason is that the reception power of the portion other than the normal null signal portion becomes weak due to the reception state of the DAB broadcast and the null detection signal NDT is generated, so that the counting of the null detection signal is excluded.

Reference numeral 81c is a transmission mode identification unit for identifying the transmission mode (mode I, mode II / III, mode IV) of the DAB broadcasting station based on the ratio of the number of null windows a and the number of null detection signals b. FIG. 4 is a mode determination processing flow of the first transmission mode determination unit 81. When the operation key unit 71 instructs reception of a predetermined DAB broadcasting station, the control unit 73 performs tuning control. As a result, the DAB RF signal demodulation unit 61 tunes to the selected DAB broadcasting station and outputs the baseband analog signals D (t) and I (t), and the AD converter 62 outputs from the sampling pulse generation unit 63. The baseband analog signals D (t) and I (t) are converted into digital data D (m) and I (m), respectively, based on the sampling pulse generated by the null signal detection unit 64 and the Fourier transform / differential decoding unit. Enter 66. The null signal detector 64 confirms that the received power has once exceeded the set level, and thereafter,
The null detection signal NDT is output every time the received power becomes equal to or less than the set value. The null window generation unit 81a (FIG. 2) of the first transmission mode determination unit 81 monitors whether the null detection signal NDT is input (step 101), and the null detection signal NDT is detected at time t ₁ (see FIG. 3). Once entered,
Thereafter, a null window NWD having a predetermined width W is generated in the minimum frame period of 24 msec among the frame periods of the transmission mode (mode I to mode IV) (step 102).

Thereafter, the counter 91 displays the null window NW.
Each time D occurs, the count value (initial value is 0) is incremented and the generated null window number a is output (step 103). Also, the counter 92 has a null window NWD.
When the null detection signal NDT is input when is high level (step 104), the count value (initial value is 0) is incremented and the null detection signal number b is output (step 10).
5). The counter 92 does not count even if the null detection signal NDT is generated when the null window NWD is at the low level. The transmission mode identification unit 81c checks whether or not the null window number a has reached the set value (step 106), and if it has not reached the set value, the counters 91 and 92 set the null window number a and The null detection signal number b is incremented.

When the null window number a reaches the set value, the transmission mode identifying unit 81c checks whether a / 4−b = 0 (step 107). The reason why the number of null windows a is divided by 4 in the judgment formula is that the frame period of mode I is 96 ms, which is four times the minimum frame period (null window period) of 24 ms. The allowable error ε is determined in consideration of the counting error, and it is checked whether | a / 4-b | <ε. If | a / 4-b | <ε, the frame length T _F is about 4 times the null window period of 24 ms, so it is determined that the transmission mode is mode I (step 108). If not | a / 4-b | <ε, the transmission mode identification unit 81c checks whether a / 2−b = 0 (step 109). In the judgment formula, the number of null windows a is divided by 2 because the frame period of mode IV is 48 ms and the minimum frame period (null window period) is 24.
This is because it is twice ms. The allowable error ε is determined in consideration of the counting error, and it is checked whether | a / 2-b | <ε. If | a / 2−b | <ε, the frame length T _F is about twice the null window period of 24 ms, so it is determined that the transmission mode is mode IV (step 110).
Unless | a / 2-b | <ε, the transmission mode is Mode II.
Alternatively, it is determined that the mode is Mode III (step 11).
1).

(D) Second Transmission Mode Determining Section FIG. 5 is a processing flow for determining the transmission mode when the first transmission mode determining section 81 determines that the transmission mode is the mode II or the mode III. The transmission mode determined by the first transmission mode determination unit 81 is Mode II or Mode III.
If it is determined that the DFT window is generated (step 201), the DFT window generation unit 65 (FIG. 1) determines that the DFT window (including the PRS window) is transmitted in the predetermined transmission mode, for example, the mode II in which DAB broadcast radio waves are transmitted. Occur. As a result, the Fourier transform / differential decoding unit 66
Digital data D in S window and DFT window
(m) and I (m) are Fourier-transformed, then differentially decoded and output.

The second transmission mode determining section 82 uses the mode II.
The correlation value between the demodulation result demodulated in step S1 and known PRS data is calculated. That is, N sets of differentially decoded 2-bit data sequences are set as v _m (m = 0 to N−1), and a known P
A correlation value between v _m and d _m is calculated by setting N _m data series with 2 bits in the RS data as one set (m = 0 to N−1) (step 202). If the transmission mode of the DAB broadcasting station is mode 2, the correlation value between v _m and d _m becomes the maximum and becomes the set value or more. Therefore, the second transmission mode determination unit 82 checks whether the correlation value is greater than or equal to the set value (step 203), and if it is greater than or equal to the set value, the transmission mode is determined to be mode II (step 204), and the setting is performed. If it is less than or equal to the value, it is determined that the mode is III (step 20
5).

(E) Operation after Mode Determination When the transmission mode is the mode I or the mode IV, the first transmission mode determination unit 81 sets the identified transmission mode to DF.
Input to the T window generation unit 65, and the transmission mode is
In the case of II or mode III, the fact is input to the second transmission mode determination unit 82. Second transmission mode determination unit 8
2 identifies the transmission mode and inputs the identified mode (mode II or mode III) to the DFT window generator 65. The DFT window generator 65 generates a DFT window signal based on the input transmission mode and inputs it to the Fourier transform / differential decoder 66. The Fourier transform / differential decoding unit 66 performs a Fourier transform process on the digital data D (m) and I (m) in the DFT window for each symbol,
Differential decoding is performed to demodulate audio code data (MPEG audio data) and output. The audio signal decoding unit 67 decodes the MPEG audio data into PCM audio data, and the DA conversion unit 68 converts the PCM audio data into analog, inputs it into the speaker 70 through the amplifier 69, and outputs DAB sound.

In the above, the case where there are transmission modes (mode II, mode III) having the same DAB frame cycle has been described. However, when they do not exist, the transmission mode is determined only by the first transmission mode determination unit. You can Although the present invention has been described above with reference to the embodiments, the present invention can be variously modified according to the gist of the present invention described in the claims, and the present invention does not exclude these.

[0047]

As described above, according to the present invention, paying attention to the fact that the DAB frame period (null signal portion interval) differs depending on the transmission mode, and among the frame periods of a plurality of transmission modes,
A signal of a certain width (null win
Dow) is generated, and the number of occurrences of the null window and the null
The number of nulls that occurred during the null window period, which corresponds to the window width.
Since the transmission mode of the DAB broadcasting station is identified based on the ratio with the number of the digital signals, it is possible to identify the transmission mode and output the DAB broadcasting voice in a short time by a simple process and configuration.

Further, there are two transmission modes having the same frame cycle.
The presence of two DAs based on the difference in the frame period.
If the transmission mode of station B cannot be specified, demodulation results obtained by performing DFT demodulation processing and a known phase reference symbol assuming that DAB broadcast radio waves are being transmitted in one of these two transmission modes. If the correlation value is above the set level, it is determined that the DAB broadcast station transmission mode is one of the above transmission modes. If the correlation value is below the set level, the DAB broadcast station transmission mode is Since it is determined that the transmission mode is the other transmission mode, even if there are two modes having the same frame cycle, it is only necessary to perform the correlation calculation once. Can be output.

[Brief description of drawings]

FIG. 1 is a block diagram of a DAB receiver of the present invention.

FIG. 2 is a configuration diagram of a first transmission mode determination unit.

FIG. 3 is an operation explanatory diagram of a first transmission mode determination unit.

FIG. 4 is a processing flow of a first transmission mode determination unit.

FIG. 5 is a processing flow of a second transmission mode determination unit.

FIG. 6 is a principle configuration diagram of a transmitter of digital audio broadcasting.

FIG. 7 is a functional explanatory diagram of a frequency multiplexing unit.

FIG. 8 is an explanatory diagram of symbols.

FIG. 9 is a principle configuration diagram of a receiver for digital audio broadcasting.

FIG. 10 is an explanatory diagram of D (m).

FIG. 11 is a characteristic of an ideal filter.

FIG. 12 is a configuration diagram of a main part of a transmitter using IDFT.

FIG. 13 is an explanatory diagram of a sampling theorem.

FIG. 14 is a main-part configuration of a receiver using DFT.

FIG. 15 is a configuration of a quadrature balanced modulation system.

FIG. 16 is a configuration of an orthogonal frequency conversion system.

FIG. 17 is an explanatory diagram of a differential encoder.

FIG. 18 is an explanatory diagram of a differential decoder.

FIG. 19 is a configuration of a transmission system and a reception system.

FIG. 20 is an explanatory diagram of a DAB frame.

FIG. 21 is an explanatory diagram of a frame length, a symbol length and the like in each transmission mode.

[Explanation of symbols]

60 ... Reception antenna 61 ... DAB RF signal demodulator 62 ... AD converter 63..Sampling pulse generator 64. Null signal detector 65 ··· DFT window generator 66 ... Fourier transform / differential decoding unit 67 ... Audio signal decoding section 81 ... First transmission mode determination unit 82 ... Second transmission mode determination unit

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H04J 11/00

Claims (2)

(57) [Claims] 1. A frame is composed of a known phase reference symbol and a plurality of data symbols, and a null signal part is inserted between the frames to divide 2N digital data forming the symbol into N groups of 2 bits each. The first data of the set is sequentially input to the inverse Fourier transform unit as the real part and the second data as the imaginary part, the real part and the imaginary part output from the inverse Fourier transform unit are converted into analog signals, and the carrier frequencies are respectively set. fc cos wave, sin wave are multiplied, the multiplication results are combined and radiated into space, the signal radiated into space is received, the received signal is multiplied by the cos wave and sin wave of the carrier frequency,
Each multiplication result is converted into digital at a predetermined sampling frequency in an AD converter and input to the Fourier transform unit, and the real number part and the imaginary number part output from the Fourier transform unit are output as the first data and the second data. In the receiver for digital audio broadcasting, the null signal detection part that detects the null signal part and outputs the null detection signal and the first null detection signal after the DAB broadcast reception operation are performed.
Therefore, among the frame periods of multiple transmission modes, the minimum
A signal of a predetermined width (null window) that has a frame period
Occurrence, the number of occurrences of the null window and the null window
A first transmission mode identifying unit identifies a transmission mode of DAB broadcasting station based on the ratio of the <br/> number of null signals generated null window period corresponding to the width, based on the identified transmission mode A receiver for digital audio broadcasting, comprising a DFT window generator that generates a DFT window, which is the Fourier transform execution timing of each symbol, and inputs the DFT window to the Fourier transformer. 2. When the transmission mode of the DAB broadcasting station cannot be specified by the first transmission mode identification section due to the existence of two transmission modes having the same frame period, one of the two transmission modes is selected. The correlation between the demodulation result obtained by performing the DFT demodulation process and the known phase reference symbol is calculated assuming that the DAB broadcast radio wave is transmitted, and if the correlation value is equal to or higher than the set level, the transmission mode of the DAB broadcast station is the above-mentioned. It is characterized by further comprising a second transmission mode identifying section that determines one transmission mode and determines that the transmission mode of the DAB broadcasting station is the other transmission mode if the correlation value is equal to or lower than the set level. A receiver for digital audio broadcasting according to claim 1.