JPH10150692A - Digital wireless microphone device, transmitter and receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve an S/N and strength against interference in using a wireless microphone by housing an acoustic/electric transducer and a digital type radio equipment in a microphone case body. SOLUTION: An A/D converter 1, a compression encoder 2, a code conversion/interleave/error correction circuit 3 and a phase (or frequency) shift keying modulation/amplifier circuit 4 are housed inside the microphone case body and a transmission antenna 5 is attached to the inside or outside of the microphone case body. Then, the bit rate of digital audio signals is compressed in the compression encoder 2. To bit-compressed and encoded signals, interleave is executed in the code conversion/interleave/error correction circuit 3. Error- corrected encoded signals are sent to the phase (or frequency) modulation/ amplifier circuit 4. Also, output (high frequency signals) from the circuit 4 is transmitted from the transmission antenna 5 as radio waves and received in a base station (receiver).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital wireless microphone device (including a receiver) having the advantages of digitalization, small size, light weight, and low power consumption.

[0002]

2. Description of the Related Art Currently, ARIB (Association of Radio Industries and Businesses) is studying the standardization of digitization of radio equipment for transmitting materials used in broadcasting stations.
Among them, radio microphones and wideband radios for transmitting sound are also included in the subject of digitization.
However, radios used for applications such as current small radio microphones (wireless microphones) are difficult to digitize due to their large size.

[0003]

As described above, with the progress of digitalization of radio equipment for broadcasting stations, wireless microphones (especially sound-to-electric conversion) used by performers while holding and moving. (Which houses the transmitter and receiver) is difficult to digitize while maintaining small size, light weight, and low power consumption, and is therefore likely to be left as an analog type. However, the analog type has a drawback that when the electric field is reduced, sufficient S / N cannot be obtained and the antenna is weak against interference.

[0004] It is an object of the present invention to recognize that in a field other than wireless transmission, for example, a field of recording and the like, a sufficiently miniaturized digital apparatus is becoming popular. The digital wireless device (especially the transmitter) contained in the microphone housing is sufficiently miniaturized to realize the digital wireless microphone device based on the above-described technology, and thereby the S of the wireless microphone device in a low electric field region is realized. / N and to improve the strength against interference.

[0005]

In order to achieve the above object, a digital wireless microphone device according to the present invention is housed in a microphone housing and is connected in sequence to an acoustic-electric converter and an A / D converter. A transmitter comprising: an encoder, an error correction circuit, and a modulator; and a transmitting antenna mounted inside or outside the microphone housing for transmitting the output of the modulator to a receiving side. And a receiver comprising a receiving antenna, a demodulator, an error correction circuit, and a decoder, which are sequentially connected, for receiving the radio wave transmitted from the receiver.

Further, the digital wireless microphone device of the present invention comprises an acoustic-electric converter, an AD converter,
A transmitter in which a compression encoder, a code conversion / interleaving / error correction circuit, a modulation / amplification circuit, and a transmission antenna are sequentially connected and arranged, a reception antenna, a high frequency amplification / frequency converter, an intermediate frequency amplifier, a demodulator, It is characterized by comprising a code conversion / deinterleave / error correction circuit and a receiver in which a decompression decoder is sequentially connected.

Further, the transmitter of the digital wireless microphone device of the present invention comprises an acoustic-electric converter, an AD converter,
A converter, a compression encoder, a code conversion / interleave / error correction circuit, a modulation / amplification circuit, and a transmission antenna are sequentially connected and arranged.

Further, the transmitter of the digital wireless microphone device according to the present invention is characterized in that the error correction of the code conversion / interleaving / error correction circuit is performed based on a double coded Reed-Solomon code. .

Further, the transmitter of the digital wireless microphone device according to the present invention is characterized in that the modulation of the modulation / amplification circuit is a phase or frequency shift keying modulation.

The transmitter of the digital wireless microphone device according to the present invention is characterized in that the phase or frequency shift keying modulation is BPSK or BFSK modulation.

Further, the receiver of the digital wireless microphone device of the present invention comprises a receiving antenna, a high-frequency amplifier / frequency converter, an intermediate frequency amplifier, a demodulator, a code converter / code converter.
The deinterleaving / error correction circuit and the decompression decoder are sequentially connected and arranged.

Further, in the receiver of the digital wireless microphone device according to the present invention, a conversion circuit is interposed between the demodulator and the code conversion / deinterleave / error correction circuit. It is something that is.

Further, the digital wireless microphone device of the present invention transmits and receives radio waves using a frequency of 322 MHz or less among those operating with effective radiation power which can be used without a license. is there.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below based on embodiments of the present invention with reference to the accompanying drawings. FIG.
1 shows an embodiment of a digital wireless microphone device according to the invention, in particular a transmitter of the microphone part. In FIG. 1, 1 is A-
A D converter, 2 is a compression encoder, 3 is a code conversion / interleaving / error correction circuit, 4 is a phase (or frequency) shift keying modulation / amplification circuit, and 5 is a transmission antenna.

Next, the operation of the transmitter will be described.
First, an audio signal (analog signal) from a microphone (acoustic-electric converter) is subjected to necessary signal processing such as amplification and filtering (not shown), and is input to the A / D converter 1. In the A / D converter 1, an analog audio signal is converted into a 16-bit digital signal having a sampling frequency of 44.1 KHz. When the microphone has two channels (for stereo sound collection), the two-channel audio signal is digitized using a two-channel 16-bit A / D converter.

As shown in this example, the audio signal is 44.1 KHz,
When sampling at 16 bits, the bit rate is 705.6K for each monaural microphone
bps (= 44.1 (KHz) × 16 bits), and in the case of a stereo microphone, it is 1411.2 Kbps, which is a very high-speed signal. Therefore, in order to reduce the size of the apparatus, the bit rates of these digital audio signals are compressed to a practical level of about 300 Kbps within a range in which the compression encoder 2 does not degrade the sound quality. This compression is performed, for example, by ATRAC (Adaptive Transform Acous).
tic Coding).

The ATRAC compression encoder 2 converts the signal supplied from the converter 1 into a NonUniform Frequency a
Analysis is performed using nd Time Splitting, which is a different analysis method from MPEG, and the modified DCT-converted 512-band 43 Hz width coefficients are compressed according to the analysis results. DC
The data length of T is changed in accordance with the steepness of the rising edge of the audio signal, and the bandwidth is changed according to the frequency, thereby enabling more efficient and high-quality compression. The bit rate after compression is 300 Kbps.

In examining the validity of this 300 Kbps, according to the reference material attached to the report of the Telecommunications Technology Council to 1995 Advisory No. 74, a bit rate of 64 Kbps for monaural (128 Kbps for stereo) Is sufficient (the sound quality is not degraded), and the above-mentioned bit rate of 300 Kbps is a value that can sufficiently satisfy this.

In the compression encoder 2, 300 Kbps
The bit-compressed and coded signal is sent to the next-stage code conversion / interleaving / error correction circuit 3, where it is first 8-14 to minimize the inversion interval and suppress the DC component.
Are performed, and interleaving is performed. The error correction used in this example is a double coded Reed-Solomon code, which is represented by Rs (32,28) (this is represented by an error correction code C1).
), Rs (28, 24) (this is called the error correction code C
2) are connected with an interleave therebetween to perform error correction.

Here, these error correcting codes (Rs (3
2, 28) and the correction capability of Rs (28, 24)) are calculated on the assumption that a bare bit error is about 10 ⁻³ or less and is regarded as a random error. Now, when the pre-correction symbol error rate is Ps, 1 block, when the transmitted n symbols, the probability Pa err is a symbol becomes a binomial distribution represented by the following equation (1) Pa = _n C _a × Ps ^a × (1-Ps) ^na (1) The probability of occurrence of an error exceeding the maximum error correction capability t is
The block error rate Pb is represented by the equation (2).

(Equation 1)

Next, from the corrected block error rate Pb,
The corrected symbol error rate Pc is obtained. Considering that the probability that the number of erroneous symbols in one block is a is Pa, when any one symbol is extracted from one block, the probability that the symbol is erroneous is:

(Equation 2) Given by Therefore, the corrected symbol error rate Pc is
The following equation (3) is obtained.

(Equation 3)

An error is first detected by an error correction code C1 (= Rs
Is corrected by (32, 28)), the error rate P _c1, and the corrected through further error correction code C2 (= Rs (28, 24)), the error rate P _c2. First, it is calculated from the error rate P _c1 . The error correction code C1 has a parity of 4 and can correct up to 2 errors. Therefore, when t = 2, the worst value of the naked error rate is 0.001 (10 ⁻³ ), and when this is substituted, the following equation (4) is obtained.

(Equation 4) Further, by substituting the error rate P _c1 and obtaining the error rate P _c2 ,
The following expression (5) is obtained.

(Equation 5) In the case of a bit rate of 300 Kbps, the bit error is 3 × 10 ⁵ × 3.333039 × 10 ^{-17 at the} worst, so that an error occurs once every 10 ¹¹ seconds. This can be said to be an error rate that does not matter at all for a wireless microphone.

As described above, the bit rate is 300K
The coded signal compressed to bps and subjected to error correction is sent to the phase (or frequency) modulation / amplification circuit 4. The output (high-frequency signal) from the circuit 4 is transmitted as radio waves from the transmission antenna 5 and received by the base station (receiver).

The modulation format of the radio wave is, for example, 322
For wireless microphone devices that do not require a license to use at frequencies below MHz, the BPS with a simple circuit
A modulation scheme of K or BFSK is suitable. At this time, when the energy per bit is represented by Eb, the inter-symbol distance of modulation is 2 for each of BPSK and BFSK.
√Eb and √2Eb. Further, the signal bandwidth (modulation spectrum) required for transmission may be narrower in BPSK, and BPSK is more preferable from this aspect.

Here, a frequency band which does not require a license and which can be used for a digital microphone device will be examined. The condition of a radio station which does not require a license and which is specified in the radio equipment regulations as a related regulation is 500 μV / m or less at a distance of 3 m and 500 μV / m or more over 322 MHz and 10 GHz at a distance of 3 m.
Up to 35 μV / m at a distance of 3 m.

First, the upper limit of the transmission output that does not require a license is calculated. The effective radiated power of the transmitter giving an electric field strength of 500 μV at a distance of 3 m is determined. Since the electric field is defined at a point that is very short from the transmitter, an error occurs in the calculation of only the radiated power used at a long distance, so it is necessary to consider the static electric field and the induced electric field. Now, assuming that the effective radiation power Pe is a distance d from the transmitting antenna, the electric field strength E is given by the following equation (6).

(Equation 6) The first term in [] is the radiation electric field, the second term is the induced electric field, and the third term is
The term is the electrostatic field, and the three fields are equal at a distance of λ / 2π. When equation (6) is solved for Pe, the following equation (7) is obtained.

(Equation 7) The operating frequency is assigned to the material transmission of the broadcasting station, including the conventional analog wireless microphone.
When the calculation is made for the 60 MHz band, the 460 MHz band, and the 800 MHz band as an example, the upper limit effective output power of each frequency band is as shown in Table 1.

[0027]

[Table 1]

Based on the upper limit effective radiated power, the maximum usage distance of 1
An electric field strength up to 00 m (practical distance) will be obtained. The electric field of the practical distance is determined by using the effective radiated power as an intermediary so as not to be affected by the conditions on the transmitting side such as the transmitting antenna gain used. FIG. 2 shows the change in the electric field strength with respect to the distance in the 160 MHz band obtained as described above. As can be seen from FIG. 2, a considerably large received electric field strength is obtained in the 160 MHz band.

Next, in the 460 MHz band and the 800 MHz band, the upper limit radiated power was almost the same, and thus the electric field strength up to 100 m was determined without particular distinction. FIG.
Indicates a change in the electric field strength between the 460 MHz band and the 800 MHz band with respect to the distance. At a distance of 100 m, the electric field intensity is about 1 (dB / 1 μV / m).

The effective length of the receiving antenna is given by the following equation (8), where R is the radiation resistance of the antenna.

(Equation 8) Further, the reception active power Pr is obtained by the following equation (9).

(Equation 9) For each frequency band, the conditions under which the received power and C / N at a receiving distance of 100 m were obtained were as follows:
Except for the 0 MHz band, the receiving antenna gain G = 2 (3 dB)
And the received radiation resistance was calculated as R = 73.13.
On the other hand, the noise power is N = KTB and B = 400 KH
Assuming that z, T = 293 degrees and the noise figure of the receiver NF = 1.5, N = 2.4 × 10 ⁻¹⁵ W. Table 2 shows received power and C / N for each used frequency.

[0031]

[Table 2]

In digital transmission, the bit error rate is an important factor influencing the transmission performance. When the modulation scheme is BPSK, the bit error rate is approximately (1)
It is shown by the equation (0).

(Equation 10) FIG. 4 shows the change of the bit error rate with C / N (dB) on the horizontal axis. Assuming that an error correction code is used, a bare bit error rate of 10 ^-4 is sufficient. Therefore, the required C / N is 9 dB.

Summing up the above results, a digital wireless microphone device that can be used without a license is:
This can be realized only when the 160 MHz band is used. 160MHz because there is no license requirement
The frequency is not limited to the band and can be realized if the frequency is 322 MHz or less.

On the other hand, in the case of a wireless microphone device requiring a license, its modulation spectrum is 10
Since there is a restriction of the radio equipment rules that the bandwidth must be within 0 KHz bandwidth, BPSK as described above
BFSK modulation cannot be performed, and multi-level modulation equal to or higher than QPSK must be performed.

Next, the power amplification stage of the phase (or frequency) modulation / amplification circuit 4 will be discussed. After up-conversion of the phase-modulated (or frequency-modulated) signal as necessary, the amplifier that amplifies the power is configured by a transistor amplifier that operates in class AB.

At this time, 1 mW including the loss of the coupling circuit
Output power. Assuming that the power supply voltage is 3 V, the load resistance RL is expressed by the following equation (11).

[Equation 11] Now, the efficiency of the class AB amplifier is estimated on the inner ring, and 0.5
Then, the DC input power Pdc is given by the following equation (12).

(Equation 12) The collector current Ic is expressed by the following equation (13).

(Equation 13) Since the collector loss is about 1 mW, a high-frequency amplifying transistor for reception (with low power consumption) can be used.

Next, a receiver constituting a base station of the digital wireless microphone device according to the present invention will be described. As a matter of course, the base station does not move with a microphone, unlike a microphone, so it is not so restricted to small size, light weight, and low power consumption. The circuit configuration of the digital receiver required for a small digital transmitter incorporated in the microphone as a digital wireless microphone device, which is not provided, is characteristic.

FIG. 5 shows a receiver of a digital wireless microphone device according to the present invention. In FIG. 5, 6 is a receiving antenna, 7 is a high-frequency amplifier / frequency converter, 8 is an intermediate frequency amplifier, 9 is a demodulator, 1
0 is a code conversion / deinterleaving / error correction circuit, 11
Is a decompression decoder, and 12 is a DA converter.

Next, the operation of the receiver will be described.
The antenna 6 can also be used for diversity reception as desired, such as by increasing the directivity. The high-frequency amplifier / frequency converter 7 and the intermediate-frequency amplifier 8 which are sequentially connected to the antenna 6 may be ordinary ones, and a signal for diversity reception control is applied from the latter to the former (in the case of diversity reception). The output of the intermediate frequency amplifier 8 is supplied to a demodulator 9 where a baseband bit stream is demodulated.

The demodulated bit stream is supplied to a code conversion / deinterleave / error correction circuit 10 corresponding to the code conversion / interleave / error correction circuit 3 in the transmitter shown in FIG. Of 14
-8 conversion is performed, and error correction is performed. This circuit 10
Is supplied to a decompression decoder 11, where the bit rate is expanded in the opposite manner to that at the transmitter, and the original digital signal is decoded and taken out as a digital output signal. When an analog signal is required, the output (digital output signal) of the decompression decoder 11 is supplied to the DA converter 12, and the analog output signal is extracted from the output side.

The basic configuration of the digital wireless microphone system according to the present invention and the specifications thereof have been described above. The present invention also relates to a commercially available audio recording / reproducing system. The fact that the circuit elements of the mini-desk (MD) can be directly incorporated into a part of the microphone device of the present invention will be described below. In this case, there is a merit that it is not necessary to redesign all the circuit blocks constituting the present invention from the beginning.

First, in the digital transmitter shown in FIG. 1, the components from the A / D converter 1 to the code conversion / interleave / error correction circuit 3 are the circuit elements on the MD recording side (actually, they are implemented as LSIs). Replaced). Also,
In the case of the digital receiver shown in FIG. 5, a circuit element on the reproduction side of the MD receives a bit rate of 1.
Since it is necessary to accept a 4 Mbps burst bit stream, the circuit configuration of FIG. 5 cannot be used as it is. Therefore, in this case, as shown in FIG. 6, a new 300K is provided between the demodulator 9 and the code conversion / deinterleaving / error correction circuit 10 in FIG.
A conversion circuit (functional block) 13 for converting a bps demodulated signal into a 1.4 Mbps burst bit stream.
Is interposed.

[0043]

According to the present invention, a digital-to-analog converter and a small, lightweight, low-power digital radio device (particularly, a transmitter) are housed in a microphone housing. For the first time, a wireless microphone device of the type is realized, and the S / N and the strength against interference when using the wireless microphone can be remarkably improved as compared with the conventional analog type wireless microphone.

Further, according to the present invention, a digital wireless microphone device can be constructed more easily by incorporating existing circuit elements used in the MD into a part of the microphone device of the present invention. it can.

According to the present invention, it is possible to realize an unlicensed digital wireless microphone device for the first time by using radio waves of 322 MHz or less.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a transmitter for a digital wireless microphone according to the present invention.

FIG. 2 shows a change in electric field strength with respect to a distance in a 160 MHz band.

FIG. 3 shows a change in electric field strength with respect to a distance between a 460 MHz band and an 800 MHz band.

FIG. 4 shows a change in a bit error rate with respect to C / N.

FIG. 5 illustrates an embodiment of a digital wireless microphone receiver according to the present invention.

FIG. 6 shows another embodiment of a digital wireless microphone receiver according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 A / D converter 2 Compression encoder 3 Code conversion / interleave / error correction circuit 4 Phase (or frequency) shift keying modulation / amplification circuit 5 Transmitting antenna 6 Receiving antenna 7 High frequency amplifier / frequency converter 8 Intermediate frequency amplifier 9 Demodulator 10 Code conversion / deinterleave / error correction circuit 11 Decompression decoder 12 DA converter 13 Conversion circuit (functional block)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04L 27/10 H04L 27/10 B 27/18 27/18 B

Claims (9)

[Claims] 1. An audio-to-electric converter, an A / D converter, an encoder, an error correction circuit, and a modulator housed in a microphone housing and connected sequentially, and an output of the modulator is received on a receiving side. A transmitter comprising a transmitting antenna mounted inside or outside the microphone housing for transmitting to the microphone housing, a receiving antenna and a demodulator sequentially connected for receiving radio waves transmitted from the transmitter , Error correction circuit,
A digital wireless microphone device comprising a receiver comprising a decoder. 2. An audio-electric converter, an A / D converter 1, a compression encoder 2, a code conversion / interleave / error correction circuit 3, a modulation / amplification circuit 4, and a transmission antenna 5 are sequentially connected and arranged. Transmitter, receiving antenna 6, high frequency amplifier / frequency converter 7, intermediate frequency amplifier 8, demodulator 9,
A digital wireless microphone device comprising: a code conversion / deinterleave / error correction circuit 10; and a receiver in which a decompression decoder 11 is sequentially connected. 3. The transmitter of the digital wireless microphone device comprises an acoustic-electric converter, an A / D converter 1,
A transmitter for a digital wireless microphone device, wherein a compression encoder 2, a code conversion / interleave / error correction circuit 3, a modulation / amplification circuit 4, and a transmission antenna 5 are sequentially connected and arranged. 4. A digital wireless microphone device according to claim 3, wherein the error correction of said code conversion / interleave / error correction circuit 3 is performed based on a double coded Reed-Solomon code. Transmitter. 5. The transmitter according to claim 3, wherein the modulation of the modulation / amplification circuit is phase or frequency shift keying modulation. 6. The transmitter of claim 5, wherein the phase or frequency shift keying modulation is BPSK or BFSK modulation. 7. The receiver of the digital wireless microphone device includes a receiving antenna 6, a high-frequency amplifier / frequency converter 7, an intermediate frequency amplifier 8, a demodulator 9, a code conversion / deinterleave / error correction circuit 10, and a decompression decoder. A receiver for a digital wireless microphone device, wherein the receivers 11 are sequentially connected and arranged. 8. A digital receiver according to claim 7, wherein a conversion circuit is interposed between said demodulator and said code conversion / deinterleave / error correction circuit. -Type wireless microphone device receiver. 9. The microphone device according to claim 1 or 2, wherein radio waves are transmitted and received using a frequency of 322 MHz or less among those operating with effective radiation power that can be used without a license. Digital wireless microphone device.