JP2015103931A - Ofdm transmitter, receiver and transmission and reception system for wireless microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide OFDM transmitter and receiver for wireless microphone which can be used in a plurality of transmission modes, while reducing the delay time due to transmission and reception of audio signals.SOLUTION: An OFDM transmitter for wireless microphone includes an information source coding section including a voice compression unit and an additional information addition unit, and a transmission path coding section including an OFDM modulation unit. The additional information adding section adds the additional information so that the output from the information source coding section has a predetermined information bit rate. An OFDM receiver for wireless microphone includes an audio signal extraction unit for processing the additional information, and an audio data decompression unit. The OFDM transmitter and receiver can deal with a plurality of modes by switching the clock frequency.

Description

  The present invention relates to an OFDM transmitter, receiver, and transmission / reception system for a wireless microphone that transmits and receives digital audio signals using an OFDM (Orthogonal Frequency Division Multiplexing) modulation scheme.

  Conventionally, there are an analog method and a digital method as a transmission method of a wireless microphone. Non-Patent Document 1 describes the standards established for “radio equipment for land mobile stations of specific radio microphones”, and Non-Patent Document 2 describes “radio equipment for specific low-power radio stations radio microphones”. Standards written are written.

  In addition, a standard for transmission bandwidth is also set for wireless microphones, and Non-Patent Document 3 describes a standard for wireless microphones in the 25 MHz to 3 GHz band of the European Telecommunications Standards Institute (ETSI) of less than 1 GHz. In the frequency band, the maximum transmission bandwidth is set to 200 kHz, and the transmission bandwidth that can be used only in the frequency band of 1 GHz or more is defined as 250 kHz, 300 kHz, 400 kHz, and 600 kHz.

  An analog wireless microphone has a short delay time and is currently widely used, but has a problem that it is easily interrupted by an obstacle, has a short transmission distance, and easily interferes. Therefore, it is necessary to use a digital wireless microphone to provide high-quality sound outdoors or at a concert hall.

  For example, Patent Literature 1 discloses a wireless microphone system that compresses and encodes and transmits audio in a digital manner. FIG. 10 is a block diagram showing the configuration of such a conventional wireless microphone system. The wireless microphone transmission device 60 includes a microphone 61, an A / D conversion unit 62, a compression encoding unit 63, an interleave / error correction unit 64, a modulation unit 65, a D / A conversion unit 66, and a transmission frequency conversion. A unit 67 and a transmission antenna 68 are provided. The wireless microphone transmission device 60 converts an analog audio signal input from the microphone 61 into a digital signal by the A / D conversion unit 62, compresses and encodes the digital signal by the compression encoding unit 63, and performs an interleaving / error correction unit 64. Interleave and error correction. Subsequently, in the wireless microphone transmission device 60, the modulation unit 65 modulates, for example, in the π / 4 shift DQPSK modulation method, the D / A conversion unit 66 converts the modulated signal into an analog signal, and the transmission frequency conversion unit 67 transmits the transmission frequency. And output to the transmission antenna 68.

  The wireless microphone receiver 70 includes a reception antenna 71, a reception frequency conversion unit 72, an A / D conversion unit 73, a demodulation unit 74, a deinterleave / error correction unit 75, a decompression decoding unit 76, a D / A A conversion unit 77 and a speaker 78 are provided. The wireless microphone receiver 70 converts the frequency of the signal input from the reception antenna 71 by the reception frequency converter 72, converts it to a digital signal by the A / D converter 73, and modulates the signal by the demodulator 74 on the transmission side. The modulated signal is demodulated, and the deinterleave / error correction unit 75 performs deinterleave and error correction. Subsequently, the wireless microphone receiver 70 expands the signal compressed on the transmission side by the expansion decoding unit 76, converts the expanded signal to an analog signal by the D / A conversion unit 77, and outputs the analog signal to the speaker 78.

Japanese Patent Laid-Open No. 10-150692

“Radio equipment of land mobile stations with specific radio microphones”, ARIB RCR STD-22, The Japan Radio Industry Association "Radio equipment for specified low-power radio stations radio microphones", ARIB RCR STD-15, Japan Radio Industry Association European Telecommunications Standards Organization “ETSI EN300 422-1” [online], [retrieved November 22, 2013], Internet <URL: http://www.etsi.org/deliver/etsi_en/300400_300499/30042201/01.03. 02_60 / en_30042201v010302p.pdf>

  However, in the conventional digital wireless microphone system, in order to save the frequency band, the compression encoding unit 63 performs compression processing, and the expansion decoding unit 76 performs expansion processing on the compressed signal. There is a delay time due to the process. In the conventional digital wireless microphone system shown in FIG. 10, a delay time of about 3 ms occurs in the wireless microphone transmission device 60 and the wireless microphone reception device 70 in total. Among them, the delay time due to the compression processing of the compression encoding unit 63 and the expansion processing of the expansion decoding unit 76 is said to be about 1 ms in total.

  In addition, when using a wireless microphone outdoors or while moving, fading due to multipath occurs and the quality deteriorates.

  Accordingly, an object of the present invention is to provide a wireless microphone OFDM transmitter, receiver, and transmitter / receiver system that reduce delay time due to transmission / reception of audio signals and prevent deterioration of reception quality due to multipath fading. .

  In the past, when designing a wireless microphone, various transmission parameter settings and circuit designs have been made in accordance with the frequency band and transmission bandwidth of the wireless microphone, so that each was a dedicated transmission / reception device for each transmission mode. If a device that selects and uses a plurality of transmission modes is manufactured, the circuit scale is large.

  Accordingly, another object of the present invention is to provide a compact wireless microphone OFDM transmitter, receiver, and transmission / reception system that can be used in a plurality of transmission modes.

  In order to solve the above problems, an OFDM transmitter for a wireless microphone according to the present invention is an OFDM transmitter for a wireless microphone that transmits an audio signal by an OFDM modulation method, and includes an audio compression unit for a digital audio signal, and additional information A transmission path encoding unit including an information source encoding unit, an error correction encoding unit, and an OFDM modulation unit, wherein the additional information adding unit is an output of the information source encoding unit. Is characterized in that the additional information is added so that becomes a predetermined information bit rate.

  Also, in the OFDM transmitter for wireless microphone of the present invention, the information source encoding unit includes two systems of digital audio signal processing means, and the data processed by the two systems of digital audio signal processing means are processed in parallel / It is desirable to perform the processing of the transmission path encoding unit after serial conversion.

  Also, in the OFDM transmitter for wireless microphone of the present invention, by enabling selection of the clock frequency for OFDM modulation processing, a plurality of OFDM modulation schemes having different information compression rates and / or transmission bandwidths can be switched and used. It is desirable to do.

  In the wireless microphone OFDM transmitter of the present invention, it is preferable that the additional information is used as a parity bit or other control information.

  In the wireless microphone OFDM transmitter of the present invention, it is desirable that the transmission bandwidth is 600 kHz or less, 288 kHz or less, or 192 kHz or less.

  In the wireless microphone OFDM transmitter of the present invention, the information compression of the audio signal may be instantaneous compression based on a companding law or ADPCM (adaptive differential pulse code modulation) encoding processing. desirable.

  In the wireless microphone OFDM transmitter of the present invention, it is preferable that the OFDM modulation section includes a time interleaving section.

  In order to solve the above problems, an OFDM receiver for a wireless microphone according to the present invention is an OFDM receiver for a wireless microphone that receives an OFDM signal transmitted by the above-described OFDM transmitter for a wireless microphone, and is an OFDM signal. An OFDM demodulator that demodulates the signal, an error correction decoder that performs error correction decoding on the demodulated signal, an audio signal extractor that processes additional information after the decoding, and a compressed audio signal And an audio data restoring unit that restores the audio signal and outputting an audio signal.

  Further, in the OFDM receiver for wireless microphone of the present invention, two systems of digital audio signal processing means including the audio data restoration unit are provided, and after the data processed by the error correction decoding unit is serial / parallel converted, the 2 systems It is desirable to perform processing by the digital audio signal processing means.

  In addition, in the wireless microphone OFDM receiver of the present invention, it is desirable that it is an ear monitor OFDM receiver.

  Further, in the wireless microphone OFDM receiver of the present invention, by enabling selection of the clock frequency for OFDM demodulation processing, a plurality of OFDM modulation schemes having different information compression rates and / or transmission bandwidths can be switched and used. It is desirable to do.

  In the wireless microphone OFDM receiver of the present invention, the OFDM demodulator preferably includes a time deinterleaver.

  In order to solve the above problem, an OFDM transmission / reception system for a wireless microphone that transmits and receives an audio signal according to the present invention by an OFDM modulation method includes an OFDM transmitter for a wireless microphone, an audio compression unit for a digital audio signal, and additional information The wireless microphone OFDM receiver includes an OFDM demodulation unit, an error correction decoding unit, and an audio signal extraction unit that processes the additional information. And an audio data restoration unit for restoring the compressed audio signal, and the additional information is adjusted so that a transmission signal including the audio signal has a predetermined information bit rate.

  Also, in the wireless microphone OFDM transmission / reception system of the present invention, the wireless microphone OFDM transmitter comprises two digital audio signal processing means, and the data processed by the two digital audio signal processing means are parallel / serial. After the conversion, the OFDM modulation processing is performed, and the OFDM receiver for wireless microphone includes two systems of digital signal processing means including an audio data recovery unit for recovering the compressed digital signal, and the OFDM demodulated data is serial / After the parallel conversion, it is desirable to process with two systems of digital audio signal processing means.

  Moreover, in the OFDM microphone transmission / reception system of the present invention, it is desirable that the ear monitor OFDM transmission / reception system.

  In the OFDM transceiver system for a wireless microphone according to the present invention, it is desirable that a plurality of OFDM modulation schemes having different information compression rates and / or transmission bandwidths can be switched and used by enabling selection of a clock frequency. .

  Moreover, it is desirable to use time interleaving in the wireless microphone OFDM transmission / reception system of the present invention.

  According to the present invention, it is possible to reduce a delay time due to transmission / reception of an audio signal and to prevent a reduction in reception quality due to multipath fading.

  In addition, according to the present invention, a LPCM (Linear Pulse Code Modulation) low-delay radio microphone with a transmission bandwidth of 600 kHz (meaning 600 kHz or less, the same applies to other bandwidths), and a transmission bandwidth with a large number of 288 kHz and 192 kHz. Since the circuit of the transmission / reception unit of the channel low delay radio microphone can be shared, the circuit scale can be greatly reduced when a plurality of transmission modes are selected and used. Furthermore, a stereo wireless microphone (ear monitor) can be realized with a common circuit.

1 is a block diagram illustrating a configuration of an OFDM transmitter for wireless microphone according to Embodiment 1. FIG. 1 is a block diagram illustrating a configuration of an OFDM receiver for wireless microphone according to Embodiment 1. FIG. 6 is a block diagram showing a configuration of an OFDM transmitter for stereo wireless microphone according to Embodiment 2. FIG. 6 is a block diagram illustrating a configuration of an OFDM receiver for stereo wireless microphone according to Embodiment 2. FIG. It is a figure which shows the example of a time interleaving process. It is a figure which shows the example of a transmission parameter of a low-delay wireless microphone (transmission bandwidth of 600 kHz or less). It is a figure which shows the example of a transmission parameter of a low delay wireless microphone (transmission bandwidth of 288 kHz or less). It is a figure which shows the example of a transmission parameter of a low-delay wireless microphone (transmission bandwidth of 192 kHz or less). It is a figure which shows the transmission parameter example of a low-delay stereo wireless microphone (transmission bandwidth of 600 kHz or less). It is a block diagram which shows the structure of the conventional wireless microphone system.

  The OFDM modulation method has been used for digital television broadcasting as a modulation method that enables high-speed and wide-band transmission, and is known as a method that can add an advanced error correction function and is resistant to radio interference. Yes.

  However, even if there is an idea to use this OFDM modulation method for various signal transmissions, how to optimize the modulation method and demodulation method when using the OFDM modulation method in a wireless microphone system In addition, the circuit configuration has not been sufficiently studied so far.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
In this specification, the wireless microphone includes both monaural and stereo, and the transmission device includes a microphone main body used with a microphone head, a small transmitter directly connected to an electronic musical instrument, and the like. Further, the receiving device includes not only a fixed device but also various forms such as a headphone and an ear monitor.

(Embodiment 1)
As Embodiment 1, a monaural wireless microphone OFDM transceiver apparatus will be described.

[OFDM transmitter for wireless microphone]
FIG. 1 is a block diagram illustrating a configuration of an OFDM transmitter 1 for a wireless microphone according to a first embodiment of the present invention. The OFDM transmitter 1 according to the first embodiment includes an information source encoding unit A and a transmission path encoding unit B.

  As shown in FIG. 1, the OFDM transmitter 1 includes an A / D conversion unit 11, a voice compression unit 12, an additional information addition unit 13, an energy spreading unit 21, an error correction coding unit 22, and a carrier modulation. Unit 23, frequency interleaving unit 24, time interleaving unit 25, OFDM frame configuration unit 26, IFFT (Inverse Fast Fourier Transform) unit 27, and guard interval adding unit 28. Among these configurations, the A / D conversion unit 11, the audio compression unit 12, and the additional information addition unit 13 constitute an information source encoding unit A. Further, a transmission path encoding unit B is configured from the energy spreading unit 21 to the guard interval adding unit 28. The carrier modulation unit 23, the frequency interleaving unit 24, the time interleaving unit 25, the OFDM frame configuration unit 26, the IFFT unit 27, and the guard interval addition unit 28 constitute an OFDM modulation unit. Although not shown in the figure, the modulation signal output from the OFDM modulation unit is then converted to an analog signal by the D / A conversion unit, and further modulated to the transmission frequency by the transmission frequency conversion unit, thereby amplifying the power. It is obvious in the technical field to transmit from the transmitting antenna.

  Each component will be described. The A / D conversion unit 11 converts an analog audio signal input from the microphone into a digital signal and outputs the digital signal to the audio compression unit 12. For information source coding (sampling) of an audio signal, for example, 48 kHz is used as a sampling frequency and 24 bits are used as a quantization bit length. Note that 32 kHz may be used as the sampling frequency, and 20 bits, 18 bits, or 16 bits may be used as the quantization bit length.

  The audio compression unit 12 compresses audio data at a predetermined information compression rate, and generally represents various audio data compression means. For example, the voice compression unit is an instantaneous compression unit, an ADPCM (adaptive differential pulse code modulation) encoding unit, or from an instantaneous compression unit, an ADPCM encoding unit, and a selection unit. The compression part which can select the information compression means comprised may be sufficient. Moreover, you may employ | adopt another suitable information compression means. Furthermore, when the transmission bit rate of the transmission path is high, the compression rate may be 1/1 (that is, information compression is not performed), and includes a case where the compression rate is substantially uncompressed. The signal compressed by the audio compression unit 12 is output to the additional information adding unit 13.

  The audio data compression means will be briefly described. Instantaneous compression is a method of compressing data according to the correspondence relationship by predetermining a 24-bit → 12-bit companding rule in advance when processing at a compression ratio of 1/2, for example, and immediately compressing information with a very small time delay Can do. Alternatively, after quantization with 24 bits, unnecessary lower 8-bit information may be deleted, and then the data may be compressed according to a companding rule of 16 bits → 12 bits. Note that the data compression rate is not limited to ½, and the data amount can be compressed at an appropriate compression rate.

  Further, data compression (encoding) and decompression (decoding) may be performed by ADPCM processing as means for compressing / restoring the data amount of a digital signal processed with a very small time delay. ADPCM is an improved method of differential pulse code modulation (DPCM, differential PCM) that encodes a differential signal between a past signal sample and a current signal sample, and uses adaptive prediction and adaptive quantization to quantize Efficient information compression is performed by changing the width. Since this is a general information compression technique in this technical field, detailed description is omitted, but information compression can be performed with an extremely small time delay by using the ADPCM encoding process.

  The additional information adding unit 13 adds additional information for making the information bit rate constant to the audio data so that the transmission line encoding unit B in the subsequent stage can perform common processing. For example, when a transmission path encoding process assuming a 1248 kbps information bit rate is scheduled in the transmission path encoding unit B, digital audio data having a quantization bit number of 24 bits and a sampling frequency of 48 kHz is represented by an information compression rate 1 / 1 voice compression, i.e. it can be transmitted without compression. At this time, 2-bit additional information is selected and added per 24-bit audio data. As a result, the audio rate is 1152 kbps, the additional information rate is 96 kbps, and the overall information bit rate is 1248 kbps. If the audio rate matches the target information bit rate, the additional information may be 0 bits.

  This additional information may be used simply for adjusting the information bit rate. However, for example, the additional information may be used as a parity bit or other information (for example, compression mode, transmission power, battery remaining) that can be used for control. It is also possible to provide data having various information, such as information on the amount and the number of data repetitions. Further, the additional information adding unit 13 also performs data blocking as necessary. The processing up to this point is the processing of the information source encoding unit A.

  Next, the configuration of the transmission path encoding unit B will be described. The energy spreading unit 21 randomizes the output signal of the additional information adding unit 13 using a pseudo-random signal or the like so that energy is not concentrated on a specific carrier of OFDM due to the deviation of the voice information.

  The error correction encoding unit 22 performs, for example, convolutional encoding or the like on the signal input from the energy spreading unit 21, and thereafter encodes the signal so that it can be corrected even if a data error occurs. For example, 1/2 or 2/3 can be selected as the coding rate of the error correction coding unit 21. The encoded data is output to the carrier modulation unit 23.

The carrier modulation unit 23 includes a bit rotation unit 231 and a mapping unit 232 therein. The bit rotation unit 231 performs bit rotation on the signal input from the error correction encoding unit 22 as data rearrangement (bit interleaving) in units of bits within an OFDM symbol that does not cause a large time delay. Bit rotation is to change the bit arrangement of a group of bit strings so that a predetermined number of bits at the beginning of the bit string are moved to the end of the bit string and the bits are rotated sequentially. For example, a 78-bit data as one block, QPSK when employing a modulation scheme (Quadrature Phase Shift Keying), the bit sequence _{(b 0, b 1, b} 2 ··· b 77) are two in serial / parallel conversion It is converted into a bit string (each bit number is 39). After that, for example, 30-bit shift rotation is performed on one bit string, and then the two bit strings are output to the mapping unit 232. The mapping unit 232 performs mapping on the IQ plane according to a predetermined modulation scheme (modulation multilevel number M) for each carrier, generates a carrier modulation signal, and outputs the carrier modulation signal to the frequency interleaving unit 24.

  The frequency interleaving unit 24 rearranges carrier numbers in the same symbol and distributes data in frequency in order to improve tolerance when a specific carrier wave is disturbed such as frequency selective fading. For frequency interleaving, when the total number of carriers is 46 (number of data carriers 39), for example, the following equation is used.

Carrier number after interleaving = (carrier number before interleaving × 20 + symbol number) mod 39 (1)

  The frequency interleave unit 24 outputs the rearranged data to the time interleave unit 25.

The time interleaving unit 25 improves the transmission characteristics at the time of mobile reception, for example, in a flat fading environment where the entire band of the OFDM signal is attenuated at the same time, the frequency interleaving effect cannot be obtained. By performing time interleaving for dispersion, strong transmission line coding is achieved. Although signal processing delay may occur, it is effective to perform time interleaving within an allowable range. Time interleaving uses convolutional interleaving. FIG. 5A shows the configuration of the time interleave circuit. In the circuit, time-interleaved data is obtained by sequentially switching input and output to each buffer.

In FIG. 5A, _mi is, for example, _mi = (i × 5) mod 39. nc is the number of data carriers (39 in this example), and i is the intra-symbol carrier number. When the value of I × m _{i in} the symbol buffer is not an integer, the decimal part is rounded up to an integer.

  As the time interleave length, six types of parameters can be selected by changing the value of the cell length (I) as shown in FIG. When time interleaving is not performed, I = 0 may be selected, or the time interleaving unit 25 may be omitted. The head of the frame after time interleaving is the head of the symbol containing the most delayed data. The data rearranged by the time interleave unit 25 is output to the OFDM frame configuration unit 26.

  The OFDM frame configuration unit 26 generates an OFDM frame by inserting and arranging a pilot signal or the like with respect to the signal input from the time interleaving unit 25, and outputs the OFDM frame to the IFFT unit 27. Since the pilot signal has a known amplitude and phase at the time of signal generation, the transmission path characteristics can be estimated on the receiving side. The OFDM frame configuration unit 26 may insert a CP (Continual Pilot) signal continuously arranged in the symbol direction in addition to SP (Scattered Pilot) signals arranged in a distributed manner as a pilot signal. Further, the OFDM frame configuration unit 26 inserts a TMCC (Transmission and Multiplexing Configuration Control) signal that is a signal for transmitting control information. As the OFDM frame configuration, for example, one having a total number of carriers of 46 (number of data carriers of 39) is used. Also, other frame configurations such as a total number of carriers 31 (26 data carriers) may be used.

  The IFFT unit 27 performs an IFFT (Inverse Fast Fourier Transform) process on the OFDM frame input from the OFDM frame configuration unit 26 to generate an IFFT output signal in an effective symbol period.

  The guard interval adding unit 28 inserts a guard interval obtained by copying the latter half of the IFFT output signal in the effective symbol period at the head of the IFFT output signal in the effective symbol period input from the IFFT unit 27. Thereby, an OFDM symbol signal to be transmitted is generated. The processing from the energy spreading unit 21 to the guard interval adding unit 28 can be shared as the transmission path encoding unit B.

  After that, digital / analog conversion is performed on the created OFDM symbol signal by a D / A conversion unit (not shown), and data converted into an analog signal by a frequency conversion unit (not shown) is converted into a transmission frequency. To do. Thereafter, the signal converted into the transmission frequency is power-amplified and transmitted from the transmission antenna. As described above, the OFDM transmitter 1 according to the first embodiment is configured to perform signal processing.

  Next, typical numerical values (bandwidth 600 kHz) in the information encoding process of the first embodiment will be exemplified. As described above, by selecting and adding additional information of 2 bits per audio data having an information compression rate of 1/1, 24 bits, data with an overall information bit rate of 1248 kbps is output from the additional information adding unit 13. Yes (mode 4). Also, digital audio data having a quantization bit number of 24 bits and a sampling frequency of 48 kHz is converted into 19-bit audio data by performing audio compression with an information compression ratio of 19/24, and 0.5-bit additional information is selected per 19-bit audio data. To add. As a result, the audio rate becomes 912 kbps, the additional information rate becomes 24 kbps, and the overall information bit rate becomes 936 kbps (mode 3).

  Also, digital audio data having a quantization bit number of 24 bits and a sampling frequency of 48 kHz is subjected to audio compression at an information compression rate of 13/24 to obtain 13-bit audio data, and additional information is set to 0 bits. As a result, the audio rate is 624 kbps, the additional information rate is 0 kbps, and the overall information bit rate is 624 kbps (mode 2). Also, audio compression is performed at an information compression rate of 9/24 to obtain 9-bit audio data, and 0.75-bit additional information is selected and added per 9-bit audio data. As a result, the audio rate is 432 kbps, the additional information rate is 36 kbps, and the overall information bit rate is 468 kbps (mode 1).

  The typical numerical value in the transmission-line encoding process of the present Example 1 is illustrated. The error correction code is a convolutional code, the coding rate is 2/3 or 1/2, and the carrier modulation is 16QAM or QPSK. By changing the OFDM carrier modulation scheme and error correction coding rate, it is possible to cope with four transmission parameters (mode4, mode3, mode2, and mode1). In OFDM modulation, parameters such as FFT size 128, FFT clock frequency 1.632 MHz, symbol length 83.33 μs, effective symbol length 78.43 μs, carrier interval 12.75 kHz, number of carriers 46 (number of data carriers 39) can be used.

  The commonality of the transmission path encoding process will be described. When the transmission path coding processing is OFDM modulation with an occupied bandwidth of 600 kHz, transmission with a carrier modulation of 16 QAM and a transmission bit rate of 1872 kbps, or transmission with a transmission bit rate of 936 kbps with carrier modulation QPSK is possible.

  Therefore, for each mode, data (mode 4) having an information bit rate of 1248 kbps can be encoded at a coding rate of 2/3, and OFDM modulation can be performed with 16QAM as a transmission bit rate of 1872 kbps. Further, data (mode 3) having an information bit rate of 936 kbps can be encoded at a coding rate of 1/2, and OFDM modulation can be performed with 16QAM as a transmission bit rate of 1872 kbps. Similarly, data (mode 2) having an information bit rate of 624 kbps can be encoded at a coding rate of 2/3, and OFDM modulation can be performed with QPSK as a transmission bit rate of 936 kbps. Also, data (mode 1) having an information bit rate of 468 kbps can be encoded at a coding rate of 1/2, and OFDM modulation can be performed with QPSK as a transmission bit rate of 936 kbps. In this way, it is possible to share transmission path encoding processing such as subsequent OFDM modulation processing for audio signals having different information compression rates. Note that the numerical values of the information source encoding process and the transmission path encoding process correspond to the respective transmission parameters described in FIG.

  Furthermore, in the OFDM modulation of the transmission line encoding process of the first embodiment, the FFT size 128, the FFT clock frequency 0.7532 MHz, the symbol length 180.56 μs, the effective symbol length 169.93 μs, the carrier interval 5.88 kHz, the number of carriers A parameter such as 46 (number of data carriers 39) can be used, and a transmission bandwidth of 288 kHz can be realized by this numerical value. As described above, by multiplying or dividing the clock frequency without changing the OFDM frame configuration, it is possible to cope with transmission path encoding processing of different transmission bandwidths. Also in this case, a convolutional code is used as an error correction code, a coding rate is 2/3 or 1/2, a carrier modulation is 16QAM or QPSK, and an OFDM carrier modulation scheme and an error correction coding rate are changed. It is possible to cope with transmission parameters (mode 4, mode 3, mode 2, and mode 1).

  Therefore, the OFDM transmission apparatus 1 according to the first embodiment can perform transmission processing corresponding to various transmission modes by making it possible to select the information compression rate and the clock frequency in the audio compression unit.

[OFDM receiver for wireless microphone]
FIG. 2 is a block diagram showing a configuration of a monaural wireless microphone OFDM receiver 2 according to a second embodiment of the present invention. The OFDM receiving apparatus 2 according to the second embodiment is a receiving apparatus for receiving a signal transmitted from the OFDM transmitting apparatus 1 according to the first embodiment.

  As shown in FIG. 2, the OFDM receiver 2 includes at least one reception system, and includes a guard interval removing unit 31, an FFT (Fast Fourier Transform) unit 32, a waveform equalizing unit 33, a time demultiplexing unit, and the like. Interleave unit 34, frequency deinterleave unit 35, carrier demodulation unit 36, error correction decoding unit 37, energy despreading unit 38, audio signal extraction unit 39, audio data restoration unit 40, and D / A conversion Part 41. Among these configurations, the guard interval removing unit 31, the FFT unit 32, the waveform equalizing unit 33, the time deinterleaving unit 34, the frequency deinterleaving unit 35, and the carrier demodulating unit 36 constitute an OFDM demodulating unit. To do. Although not shown in the figure, the reception signal received from the antenna is converted to an intermediate frequency by the reception frequency conversion unit, converted to a digital signal by the A / D conversion unit, and input to the guard interval removal unit 31. This is obvious in the art. In FIG. 2, only one reception system is described, but diversity reception is performed by a plurality of reception systems, and each received signal is weighted and combined according to the level by a maximum ratio combining unit. Also good.

  Each component will be described. First, the guard interval removing unit 31 removes the guard interval from the received signal converted into the digital signal, creates an effective symbol signal, and outputs the effective symbol signal to the FFT unit 32.

  The FFT unit 32 performs FFT (Fast Fourier Transform) processing on the signal from which the guard interval has been removed.

  The waveform equalizing unit 33 obtains a transfer function of the transmission path using a pilot signal or the like for the signal changed due to the influence of the transmission path, and returns the original signal waveform by processing with the inverse characteristic of the transfer function. Process.

  The time deinterleave unit 34 performs time deinterleave processing on the signal subjected to FFT processing and waveform equalization processing, and restores the temporally rearranged data. When time interleaving is not performed on the transmission side, I = 0 may be selected by the time deinterleaving unit 34, or the time deinterleaving unit 34 may be omitted.

  The frequency deinterleave unit 35 performs frequency deinterleave processing on the signal subjected to FFT processing and waveform equalization processing, and restores the data rearranged in terms of frequency.

  The carrier demodulator 36 demodulates the signal input from the frequency deinterleaver 35 for each carrier and outputs the demodulated signal to the error correction decoder 37. The carrier demodulating unit 36 includes a demapping unit 361 and an inverse bit rotation unit 362 therein, and after obtaining the I signal value and the Q signal value by the demapping unit 361 and demodulating the data in bit units, In the inverse bit rotation unit 362, the data rearranged in units of bits in the carrier modulation unit on the transmission side is returned to the original arrangement.

  The error correction decoding unit 37 performs a predetermined decoding process such as Viterbi decoding on the signal input from the carrier demodulation unit 36 to perform data error correction.

  Next, the energy despreading unit 38 performs energy despreading to restore the original signal. Up to this point, the encoding process performed by the transmission-side encoding unit B on the transmission side is decoded.

  The audio signal extraction unit 39 receives the data signal for which the data demodulation processing has been completed from the energy despreading unit 38, and extracts the audio signal therefrom. This audio signal extraction process corresponds to an inverse conversion process corresponding to the process of the additional information adding unit 13 on the transmission side. In addition to simply removing the additional information, when a parity bit is added as additional information on the transmission side, an error correction decoding process using the parity bit may be further added. Although not shown, the error data that could not be corrected by the error correction decoding unit is further concealed, for example, by performing linear interpolation on the preceding and succeeding data or holding the value immediately before the error occurs. May be performed.

  The voice data restoration unit 40 restores the voice compression processing on the transmission side, and generally represents various voice data expansion / decoding means. That is, the audio data restoration unit is an instantaneous decompression unit, or an ADPCM decoding unit, or a restoration unit that can be selected by a data decompression / decoding unit including an instantaneous decompression unit, an ADPCM decoding unit, and a selection unit. There may be. Further, other appropriate audio data restoration means may be employed. The signal restored by the audio data restoration unit 40 is output to the D / A conversion unit 41.

  The audio data restoration process will be briefly described. The instantaneous decompression unit can perform data decompression processing with a very small time delay by using a preset companding law. The ADPCM decoding unit decodes the input digital signal (for example, 12 bits) into the original 24-bit digital signal by ADPCM decoding processing. This decoding process is an inverse process of ADPCM encoding, and data decoding process can be performed with a very small time delay by using known means. Further, the instantaneous extension unit and the ADPCM decoding unit may be selectable using a selection unit.

  The D / A conversion unit 41 performs digital / analog conversion on the expanded digital data and outputs an analog audio signal.

  Thus, according to the OFDM receiver of the second embodiment, a voice signal can be output from the received OFDM signal.

  The OFDM receiving apparatus according to the second embodiment is designed corresponding to the transmission parameters used in the OFDM transmitting apparatus according to the first embodiment. Therefore, by making it possible to select the information expansion rate in the audio data restoration unit and the clock frequency used for the FFT processing and the like, it is possible to perform reception processing corresponding to various transmission modes.

(Embodiment 2)
As a second embodiment, a stereo wireless microphone OFDM transmitter / receiver (ear monitor) will be described.

[OFDM transmitter for stereo wireless microphone]
FIG. 3 is a block diagram showing the configuration of the stereo wireless microphone OFDM transmitter 3 according to the third embodiment of the present invention. Here, the same components as those in the first embodiment are denoted by the same reference numerals, and the description is simplified.
The stereo wireless microphone OFDM transmitter 3 according to the third embodiment is different from the configuration according to the first embodiment in that there are two audio inputs (stereo transmission). It is possible to share the apparatus with the wireless microphone of the first embodiment by adopting transmission parameters compatible with the wireless microphone (radio microphone) that transmits the monaural signal of the first embodiment.

As shown in FIG. 3, the OFDM transmitter 3 includes two systems of A / D converters 11 (11 ₁ , 11 ₂ ), an audio compressor 12 (12 ₁ , 12 ₂ ), and an additional information adder 13 ( 13 ₁ , 13 ₂ ) and a parallel / serial (P / S) converter 14, and these constitute the information source encoder A. Furthermore, an energy spreading unit 21, an error correction coding unit 22, a carrier modulation unit 23, a frequency interleaving unit 24, a time interleaving unit 25, an OFDM frame configuration unit 26, and an IFFT (Inverse Fast Fourier Transform) unit 27. The transmission path encoding unit B is configured by the guard interval adding unit 28 as in the first embodiment. The carrier modulation unit 23 includes a bit rotation unit 231 and a mapping unit 232. Among these configurations, the carrier modulation unit 23, the frequency interleaving unit 24, the time interleaving unit 25, the OFDM frame configuration unit 26, the IFFT unit 27, and the guard interval addition unit 28 constitute an OFDM modulation unit. Although not shown in the figure, the modulation signal output from the OFDM modulation unit is then converted to an analog signal by the D / A conversion unit, and further modulated to the transmission frequency by the transmission frequency conversion unit, thereby amplifying the power. It is obvious in the technical field to transmit from the transmitting antenna.

Each component will be described. The A / D converter 11 (11 ₁ , 11 ₂ ) converts analog audio signals (right audio signal and left audio signal) input from the microphone into digital signals, respectively. It is equivalent to the D conversion unit 11. The A / D converter 11 (11 ₁ , 11 ₂ ) outputs digital signals to the audio compressors 12 (12 ₁ , 12 ₂ ), respectively.

The audio compression unit 12 (12 ₁ , 12 ₂ ) performs information compression (reduction of information amount) on the input digital signal (for example, 24 bits) with an extremely small time delay. Convert to bit digital signal.

  For example, instantaneous compression or data compression (encoding) by ADPCM processing can be used as a means for compressing the data amount of a digital signal with an extremely small time delay. In addition, the compression unit may be selectable by the instantaneous compression unit, the ADPCM encoding unit, and the selection unit, and similarly, another data compression unit having a low processing time may be used.

The additional information adding unit 13 (13 ₁ , 13 ₂ ) adds additional information for each signal of the two stereo systems and outputs it to the parallel / serial (P / S) conversion unit 14. The additional information adding unit 13 adds additional information for making the information bit rate constant to the audio data. This process is the same as in the first embodiment. It should be noted that the additional information adding unit 13 and the P / S converting unit 14 may be arranged in the opposite manner, and additional information adding processing may be performed on the serial data after P / S conversion.

  The additional information may be simply used for adjusting the information bit rate, but further, for example, may be used as a parity bit or other information that can be used for control (for example, compression mode, transmission power, remaining battery capacity). It is also possible to provide data having various information, such as information on the number of data repetitions).

  The parallel / serial (P / S) conversion unit 14 performs parallel / serial conversion processing on the signals processed by the above-described two systems of digital audio signal processing means to form a serial signal, and then outputs the serial signal to the energy diffusion unit 21. The processing up to this point is the processing of the information source encoding unit A.

  The processing of the transmission path encoding unit B is the same as in the first embodiment. From the energy spreading unit 21, an error correction coding unit 22, an OFDM modulation unit (carrier modulation unit 23, frequency interleaving unit 24, time interleaving unit 25, OFDM frame configuration unit 26, IFFT unit 27, and guard interval addition unit 28). Then, an OFDM signal is generated. After that, the signal is converted into an analog signal by the D / A conversion unit, further modulated to the transmission frequency by the transmission frequency conversion unit, power amplified and transmitted from the transmission antenna in common with the OFDM transmission apparatus of the first embodiment. . Bit rotation and frequency interleaving can be performed in the same manner as in the first embodiment.

  When representative numerical values of the information source encoding process in the stereo wireless microphone of the third embodiment are exemplified, the information source encoding (sampling) of the audio signal is performed with a quantization bit length of 24 bits for each of the left and right systems, and a sampling frequency fs = 48 kHz. In this way, by compressing this to 12 bits by instantaneous compression, the total (two systems total) audio bit rate becomes 1152 kbps (12 bits × 2 [stereo] × 48 kHz), as in the first embodiment. As additional information, 2 bits are added per audio bit number (12 + 12) bits. As a result, the additional information rate is 96 kbps, and the overall information bit rate is 1248 kbps (mode 4).

  In the stereo wireless microphone of the third embodiment, the information source coding (sampling) of the audio signal is performed for each of the left and right systems with a quantization bit length of 24 bits and a sampling frequency of fs = 48 kHz. By compressing to 9 bits by instantaneous compression, the total (two systems total) audio bit rate becomes 864 kbps (9 bits × 2 [stereo] × 48 kHz). As additional information, 1.5 bits are added per audio bit number (9 + 9) bits. As a result, the additional information rate is 72 kbps, and the overall information bit rate is 936 kbps (mode 3).

  In the stereo wireless microphone according to the third embodiment, the information source coding (sampling) of the audio signal is performed for each of the left and right systems with a quantization bit length of 24 bits and a sampling frequency of fs = 48 kHz. By compressing to 6 bits by instantaneous compression, the total (two systems total) audio bit rate becomes 576 kbps (6 bits × 2 [stereo] × 48 kHz). As additional information, 1 bit is added per audio bit number (6 + 6) bits. As a result, the additional information rate is 48 kbps, and the overall information bit rate is 624 kbps (mode 2). Similarly, by compressing each system to 4 bits by instantaneous compression with an information compression rate of 1/8, the total (two systems total) audio bit rate becomes 384 kbps (4 bits × 2 [stereo] × 48 kHz). As additional information, 1.75 bits are added per audio bit number (4 + 4) bits. As a result, the additional information rate is 84 kbps, and the overall information bit rate is 468 kbps (mode 1).

  Next, typical numerical values in the transmission path encoding process of the third embodiment will be exemplified. The error correction code is a convolutional code, the coding rate is 2/3 or 1/2, and the carrier modulation is 16QAM or QPSK. In OFDM modulation, parameters such as FFT size 128, FFT clock frequency 1.632 MHz, symbol length 83.33 μs, effective symbol length 78.43 μs, carrier interval 12.75 kHz, number of carriers 46 (number of data carriers 39) can be used. This is the same as the parameter of the transmission path encoding process with the bandwidth of 600 kHz in the first embodiment.

  The commonality of the transmission path encoding process will be described. As described in the first embodiment, transmission with a transmission bit rate of 187 kbps can be performed with carrier modulation 16QAM, or transmission with a transmission bit rate of 936 kbps can be performed with carrier modulation QPSK, using the above-described transmission path coding parameters. Therefore, for each mode, data (mode 4) having an information bit rate of 1248 kbps can be encoded at a coding rate of 2/3, and OFDM modulation can be performed with 16QAM as a transmission bit rate of 1872 kbps. Further, data (mode 3) having an information bit rate of 936 kbps can be encoded at a coding rate of 1/2, and OFDM modulation can be performed with 16QAM as a transmission bit rate of 1872 kbps. Similarly, data (mode 2) having an information bit rate of 624 kbps can be encoded at a coding rate of 2/3, and OFDM modulation can be performed with QPSK as a transmission bit rate of 936 kbps. Also, data (mode 1) having an information bit rate of 468 kbps can be encoded at a coding rate of 1/2, and OFDM modulation can be performed with QPSK as a transmission bit rate of 936 kbps. In this way, transmission path encoding processing such as subsequent OFDM modulation processing can be made common. Note that the numerical values of the information source encoding process and the transmission path encoding process all correspond to the respective transmission parameters described in FIG.

  By adopting such transmission parameters, not only can the parameters of the stereo microphone be shared, but also the parameters can be shared with the monaural wireless microphone OFDM transmitter of the first embodiment. Therefore, the wireless microphone (radio microphone) of the first embodiment and the circuit configuration after the transmission path encoding unit B can be shared.

[OFDM receiver for stereo wireless microphone]
FIG. 4 is a block diagram illustrating a configuration of an OFDM receiver for stereo wireless microphones according to a fourth embodiment of the present invention. As a specific example of the OFDM receiver for stereo wireless microphone, there is an ear monitor used on a stage or stage. Here, the same reference numerals are given to the same components as those of the second embodiment (receiving device of the first embodiment), and the description thereof is simplified. The stereo wireless microphone OFDM receiver 4 according to the fourth embodiment is different from the configuration according to the second embodiment in that there are two audio outputs (stereo transmission).

As shown in FIG. 4, the OFDM receiver 4 has at least one reception system, and includes a guard interval removal unit 31, an FFT unit 32, a waveform equalization unit 33, a time deinterleaving unit 34, a frequency A demodulator 35; a carrier demodulator 36 including a demapping unit 361 and an inverse bit rotation unit 362; an error correction decoding unit 37; and an energy despreading unit 38; and a serial / parallel (S / P) conversion unit 42, two-line audio signal extraction unit 39 (39 ₁ , 39 ₂ ), audio data restoration unit 40 (40 ₁ , 40 ₂ ), and D / A conversion unit 41 (41 ₁ , 41) ₂ ). Among these configurations, the guard interval removing unit 31, the FFT unit 32, the waveform equalizing unit 33, the time deinterleaving unit 34, the frequency deinterleaving unit 35, and the carrier demodulating unit 36 constitute an OFDM demodulating unit. To do. Although not shown in the figure, the received signal received from the antenna is modulated to an intermediate frequency by the reception frequency converter, converted to a digital signal by the A / D converter, and input to the OFDM demodulator. Is obvious in the art. In FIG. 4, only one receiving system is described. However, diversity reception is performed by a plurality of receiving systems, and each received signal is weighted and combined according to the level by a maximum ratio combining unit. Also good.

  Signal processing from the guard interval removing unit 31 to the FFT unit 32, the waveform equalizing unit 33, the time deinterleaving unit 34, the frequency deinterleaving unit 35, the carrier demodulating unit 36, the error correction decoding unit 37, and the energy despreading unit 38 This is the same as the OFDM receiver 2 of the second embodiment. Up to the process of the energy despreading unit 38, the encoding process performed by the transmission side encoding unit B on the transmission side is decoded.

  The energy despreading unit 38 performs energy despreading and outputs a signal (serial signal) to the serial / parallel (S / P) conversion unit 42.

The serial / parallel (S / P) conversion unit 41 separates the signal after energy despreading into two systems of signals by serial / parallel conversion processing, and each signal is an audio signal extraction unit 39 (39 ₁ , 39 ₂ ). Output to.

The audio signal extraction unit 39 (39 ₁ , 39 ₂ ) extracts an audio signal from each signal sequence and outputs it to the audio data restoration unit 40 (40 ₁ , 40 ₂ ). This audio signal extraction process corresponds to an inverse conversion process corresponding to the process of the additional information adding unit 13 on the transmission side. In addition to simply removing the additional information, when a parity bit is added as additional information on the transmission side, an error correction decoding process using the parity bit may be further added. Further, although not shown in the drawing, concealment such as performing linear interpolation on the previous and subsequent data on error data that could not be corrected by the error correction decoding unit, or holding a value immediately before an error occurs, etc. May be performed. In addition, when additional information is added to the serial data after P / S conversion on the transmission side, the audio signal extraction unit 39 and the S / P conversion unit 42 are arranged oppositely to extract the audio signal. After processing, the signal is separated into two systems.

The audio data restoration unit 40 (40 ₁ , 40 ₂ ) performs data restoration (reconstruction of the amount of compressed information) on the input digital signal (for example, 12 bits) with an extremely small time delay, and for example, 24-bit digital Convert to signal. As this data restoration with a very small time delay, for example, instantaneous extension using a companding law or ADPCM decoding processing can be used as in the second embodiment. Signal restored (decompressed) by the data recovery unit 40 ₍₄₀ 1, 40 ₂₎ is output to the respective D / A converter 41 ₍₄₁ 1, 41 _2).

The D / A converter 41 (41 ₁ , 41 ₂ ) performs digital / analog conversion on the expanded digital data and outputs an analog audio signal. By providing two systems of digital audio signal processing means, the output becomes a stereo audio signal. Thus, according to the OFDM receiver 4 of the fourth embodiment, a stereo audio signal can be output from the received OFDM signal.

  The stereo wireless microphone OFDM receiving apparatus 4 according to the fourth embodiment can cope with OFDM signals in various stereo modes by employing the transmission parameters described in the third embodiment. Furthermore, the wireless microphone OFDM receiver 2 of the second embodiment and the circuit configuration from the receiving antenna to the energy despreading unit 38 can be shared.

  In FIG. 9, only a parameter with a transmission bandwidth of 600 kHz is shown, but it goes without saying that if the number of audio bits is further reduced by information compression, an OFDM transmission / reception system for a stereo wireless microphone can be realized with a narrower transmission bandwidth. In order to make the transmission bandwidth variable, it is the same as in the first and second embodiments that the FFT clock frequency is made variable in the transmission device and the reception device.

  6 to 9 are examples of transmission parameters that can be used in each embodiment of the present invention. FIG. 6 shows transmission parameters of a standard microphone with a low delay with a bandwidth of 600 kHz, FIG. 7 shows transmission parameters of a multi-channel microphone with a low delay with a bandwidth of 288 kHz, and FIG. 8 shows a transmission parameter with a low delay of a bandwidth of 192 kHz. This is a transmission parameter of a multi-channel microphone. FIG. 9 shows transmission parameters of a stereo microphone (ear monitor) with a bandwidth of 600 kHz and a low delay. All transmission schemes use an OFDM frame configuration with a total number of carriers of 46 (39 data carriers), and can be supported with the same system configuration by changing the FFT clock frequency. The system can be shared. Note that transmission schemes with different transmission bandwidths can be set as necessary, and the transmission parameters are not limited to these.

  Although the present invention has been described based on the drawings and examples, it should be noted that those skilled in the art can easily make various modifications and corrections based on the present disclosure. Therefore, it should be noted that these variations and modifications are included in the scope of the present invention. For example, functions and the like included in each means, each configuration, etc. can be rearranged so as not to be logically contradictory, and a plurality of means, configurations, etc. can be combined into one or divided. .

DESCRIPTION OF SYMBOLS 1,3 OFDM transmitter for wireless microphones 2,4 OFDM receiver for wireless microphones 11 A / D conversion unit 12 Voice compression unit 13 Additional information addition unit 14 P / S conversion unit 21 Energy diffusion unit 22 Error correction coding unit 23 Carrier modulation unit 231 Bit rotation unit 232 Mapping unit 24 Frequency interleaving unit 25 Time interleaving unit 26 OFDM frame configuration unit 27 IFFT unit 28 Guard interval adding unit 31 Guard interval removing unit 32 FFT unit 33 Waveform equalizing unit 34 Time deinterleaving unit 35 Frequency deinterleaving unit 36 Carrier demodulation unit 361 Demapping unit 362 Inverse bit rotation unit 37 Error correction decoding unit 38 Energy despreading unit 39 Audio signal extraction unit 40 Audio data restoration unit 41 D / Conversion unit 42 S / P conversion unit

Claims (17)

An OFDM transmitter for a wireless microphone that transmits an audio signal by an OFDM modulation method,
An information source encoding unit including an audio compression unit for digital audio signals and an additional information adding unit;
A transmission path encoding unit including an error correction encoding unit and an OFDM modulation unit;
The wireless microphone OFDM transmission device, wherein the additional information adding unit adds additional information so that an output of the information source encoding unit becomes a predetermined information bit rate.   The OFDM transmitter for a wireless microphone according to claim 1, wherein the information source encoding unit includes two systems of digital audio signal processing means, and the data processed by the two systems of digital audio signal processing means are processed in parallel / An OFDM transmitter for a wireless microphone, which performs processing of the transmission path encoding unit after serial conversion.   The OFDM transmitter for a wireless microphone according to claim 1 or 2, wherein a plurality of OFDM modulation schemes having different information compression rates and / or transmission bandwidths are used by enabling selection of a clock frequency for OFDM modulation processing. An OFDM transmitter for a wireless microphone, characterized in that it can be used.   4. The wireless microphone OFDM transmitter according to claim 1, wherein the additional information is used as a parity bit or other control information. 5.   2. The wireless microphone OFDM transmitter according to claim 1, wherein the transmission bandwidth is any one of 600 kHz or less, 288 kHz or less, or 192 kHz or less.   6. An OFDM transmitter for a wireless microphone according to claim 1, wherein information compression of the audio signal is performed by instantaneous compression based on a companding law or ADPCM (adaptive differential pulse code modulation). ) OFDM transmitter for wireless microphone, characterized by encoding processing.   The wireless microphone OFDM transmitter according to any one of claims 1 to 6, wherein the OFDM modulation section includes a time interleaving section. An OFDM receiver for a wireless microphone that receives an OFDM signal transmitted by the OFDM transmitter for a wireless microphone according to claim 1,
An OFDM demodulator for demodulating an OFDM signal;
An error correction decoding unit that performs error correction decoding processing on the demodulated signal;
An audio signal extraction unit for processing additional information after the decoding process;
An audio data restoration unit for restoring the compressed audio signal,
An OFDM receiver for a wireless microphone, which outputs an audio signal.   9. The OFDM receiver for a wireless microphone according to claim 8, comprising two systems of digital audio signal processing means including said audio data restoring unit, and after serial / parallel conversion of the data processed by said error correction decoding unit, 2 systems A wireless microphone OFDM receiving apparatus, wherein the digital audio signal processing means performs processing.   10. The wireless microphone OFDM receiver according to claim 9, wherein the wireless microphone OFDM receiver is an ear monitor OFDM receiver.   The OFDM receiver for a wireless microphone according to any one of claims 8 to 10, wherein a plurality of OFDM modulations having different information compression rates and / or transmission bandwidths by enabling selection of a clock frequency for OFDM demodulation processing. An OFDM receiver for a wireless microphone, which can be used by switching a method.   12. The wireless microphone OFDM receiver according to claim 8, wherein the OFDM demodulator includes a time deinterleave unit. An OFDM transmission / reception system for a wireless microphone that transmits and receives an audio signal by an OFDM modulation method,
An OFDM transmitter for a wireless microphone includes an audio compression unit for a digital audio signal, an additional information addition unit for adding additional information, an error correction coding unit, and an OFDM modulation unit,
The OFDM receiver for a wireless microphone includes an OFDM demodulator, an error correction decoder, an audio signal extractor that processes additional information, and an audio data recovery unit that recovers a compressed audio signal,
The wireless transceiver OFDM transmission / reception system, wherein the additional information is adjusted so that a transmission signal including an audio signal has a predetermined information bit rate. The OFDM transceiver system for a wireless microphone according to claim 13,
The OFDM transmitter for wireless microphone includes two systems of digital audio signal processing means, performs parallel / serial conversion on the data processed by the two systems of digital audio signal processing means, and then performs OFDM modulation processing,
The wireless microphone OFDM receiver includes two systems of digital signal processing means including an audio data recovery unit that recovers a compressed digital signal, and after serial / parallel conversion of OFDM demodulated data, the two systems of the digital signal Processed by audio signal processing means,
An OFDM transmission / reception system for a wireless microphone.   The OFDM transmission / reception system for a wireless microphone according to claim 14 is an OFDM transmission / reception system for an ear monitor.   The OFDM transmission / reception system for a wireless microphone according to any one of claims 13 to 15, wherein a plurality of OFDM modulation schemes having different information compression rates and / or transmission bandwidths can be switched by selecting a clock frequency. An OFDM transmission / reception system for a wireless microphone, characterized in that it can be used. The OFDM transceiver system for a wireless microphone according to any one of claims 13 to 16, wherein time interleaving is used.

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