JP2003198517A - Receiver and radio transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove distortion depending on jitter or the responsiveness of PLL on a radio transmission line. <P>SOLUTION: On the basis of a digital modulated signal and a first reference signal from a first reference signal source 64, a signal processing part 62 reproduces a transmission clock signal and reproduces digital audio data on the basis of this reproduced transmission clock signal. Synchronously with the reproduced transmission clock signal, the digital audio data are inputted to a sampling rate converter 66. Synchronously with a second reference signal from a second reference signal source 70, the digital audio data are outputted from the sampling rate converter 66 and the outputted digital audio data are converted into analog signals by a digital/analog converter 72. The first and second reference signal sources 64 and 70 mutually independently output the first and second reference signals. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless transmission system having a wireless transmitter and a wireless receiver and a wireless receiver used for the same, and more particularly to digital wireless communication.

[0002]

2. Description of the Related Art FIG. 3 shows a basic digital wireless transmission system. This system consists of a transmitter 2 and a receiver 4. The transmitter 2 comprises a signal source 6 of an audio frequency signal, for example a microphone. An audio frequency signal, for example, an analog audio signal from the signal source 6 is amplified by an amplifier 8 and then converted by an analog / digital converter 10 into a digital audio signal having a predetermined number of bits. This digital conversion is performed in synchronization with each clock signal generated from the reference signal source 12. The digital audio signal is supplied to the signal processing unit 14. Here, using the clock signal from the reference signal source 12, the frame synchronization signal is added to each digital audio signal to form a digital modulation signal. These digital modulation signals are transmitted to the high frequency section 1
6 and modulates the high frequency carrier signal. The high frequency signal generated thereby is transmitted from the antenna 18.

On the other hand, in the receiver 4, the high frequency signal received by the antenna 20 is demodulated by the high frequency unit 22,
The signal is supplied to the signal processing unit 24. The signal processing unit 24 detects a frame synchronization signal from the demodulated digital modulation signal and extracts a predetermined number of bits following the frame synchronization signal as a digital audio signal. The clock signal from the reference signal source 26 is used to extract the digital audio signal. The extracted digital audio signal is supplied to the digital / analog converter 28, converted into an analog signal, amplified by the amplifier 30, and then amplified by the speaker 32. The analog conversion is also performed in synchronization with the clock signal of the reference signal source 26.

In this wireless transmission system, the clock signal of the reference signal source 12 used in the transmitter 2 and the clock signal of the reference signal source 26 used in the receiver 4 are asynchronous. Therefore, duplication or loss of data occurs. For example, the clock signal supplied from the reference signal source 26 to the digital-analog converter 28 is faster than the transfer rate of the digital audio signal supplied from the signal processing unit 24 of the receiver 4 to the digital-analog converter 28. If it is fast, the output analog signal will have data duplication, and if it is slow, data will be lost.

In order to improve this point, for example, in the signal processing section 24 of the receiver 4a shown in FIG. 4, the demodulated digital modulation signal and the clock signal from the reference signal source 26 are
The signal is supplied to the PLL circuit 34, the transmission clock signal synchronized with the demodulated digital modulation signal is reproduced by the phase synchronization method, the frame is synchronized from the digital modulation signal and the reproduction transmission clock signal, and each digital audio signal is reproduced. ing. The reproduced digital audio signal is supplied to the digital-analog converter 28 in synchronism with the sample clock based on the reproduction transmission clock signal, and is digital-analog converted.

With this configuration, since the digital-analog converter 28 synchronizes the digital audio signal received from the signal processing unit 24 with the reproduction transmission clock signal received from the PLL circuit 34, the output analog signal. There is no duplication or loss of data.

[0007]

However, since the digital modulation signal is affected by fading that occurs in the radio transmission line between the antennas 18 and 20, and jitter is generated, P
Jitter also occurs in the reproduction transmission clock signal by the LL circuit 34. The accuracy of the output signal of the PLL circuit 34 depends on the response speed of the PLL circuit 34. When these are combined, the reproduction transmission clock signal which is the output signal of the PLL circuit 34 does not have a constant cycle. As a result, the conversion cycle of the digital / analog converter 28 is not constant,
The analog conversion cycle is also not constant, and the analog signal output from the digital-analog converter 28 is subject to phase distortion.

According to the present invention, the jitter and the PLL in the wireless transmission line are
It is an object of the present invention to provide a wireless transmission system that eliminates distortion depending on the response of a circuit and a receiver used for the wireless transmission system.

[0009]

A receiver according to the present invention comprises:
Based on the received data signal and the first reference signal of the first reference signal source, the transmission clock reproduction means reproduces the reproduction transmission clock signal synchronized with the data signal. The receiver is
A demodulation unit for demodulating a signal received by the antenna, for example, a high frequency signal into a data signal is provided. The data signal is
It is input to the input / output means in synchronization with the reproduced transmission clock signal. This data signal is output from the input / output means in synchronization with the second reference signal of the second reference signal source. The first and second reference signal sources output the first and second reference signals independently of each other. The second reference signal source outputs a reference signal having a constant cycle.

In the receiver thus constructed, the transmission clock signal is regenerated from the data signal by the transmission clock regenerating means. At this time, the data signal and the reproduction transmission clock signal are synchronized. However, as described above, neither the cycle of the data signal nor the cycle of the reproduction transmission clock signal is constant due to the influence of the jitter generated in the wireless transmission path. Therefore, the data signal is input to the input / output unit in synchronization with the reproduced clock signal, but is output from the input / output unit in synchronization with the second reference signal.
Since the second reference signal is independent of the clock signal,
It is not affected by jitter and its period is constant. Therefore, the output signal read from the input / output means also has a constant cycle, and even if this is converted into an analog audio signal, a distortion-free analog audio signal unaffected by phase noise can be obtained. .

The data signal may be an audio frequency signal, for example, a digital audio frequency signal obtained by digitally converting an audio signal. In the digitized audio frequency signal, if this is converted into an analog signal,
If the cycle is not constant, it is largely affected by distortion, but when output from the input / output means, it is not affected by distortion because the cycle is constant.

Further, digital / analog conversion means for converting the output signal of the input / output means into an analog signal in synchronization with the second reference signal may be provided. In this case, the analog signal output from the digital-analog conversion means is also synchronized with the second reference signal, is output at a constant cycle, and does not include distortion.

A wireless transmission system can be constituted by these receivers and transmitters. The transmitter transmits a modulated signal in which a carrier wave is modulated with a data signal,
The receiver has demodulation means for receiving the modulated signal and demodulating it into a data signal.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, a wireless transmission system according to an embodiment of the present invention includes a transmitter 40 and a receiver 42.
It has and.

The transmitter 40 is, for example, a digital wireless microphone and includes an analog signal source, for example, an audio frequency signal source, specifically, a microphone 44. The analog audio signal from the microphone 44 is
The signal is amplified by the amplifier 46 and supplied to the analog / digital converter 48. This analog-digital converter 4
At 8, the analog audio signal is converted into a data signal, for example a digital audio frequency signal, specifically a digital audio signal of a predetermined number of bits. This conversion is performed in synchronization with each generation of the reference clock signal from the reference signal source 50. That is, the sampling is performed according to the frequency of the reference clock signal. This digital audio signal is supplied to the signal processing unit 52.

The signal processing unit 52 outputs the frame synchronization signal generated based on the reference clock signal from the reference signal source 50.
A digital modulation signal is generated by adding to each digital audio signal. These digitally modulated signals are supplied to the high frequency section 54, where they modulate a predetermined high frequency carrier signal.
A high frequency signal which is an output signal of the high frequency unit 54 is output from the antenna 56.

The receiver 42 is arranged at a position distant from the transmitter 40. The receiver 42 has an antenna 58. A wireless transmission path is formed between the antenna 58 and the antenna 56 of the transmitter 40. While the high frequency signal is being transmitted through this wireless transmission path, the modulated signal is affected by jitter and the like.

The high frequency signal received by the antenna 58 is
The demodulation means, for example, the high frequency unit 60, demodulates each digital modulation signal. The demodulated digital modulation signal is
It is supplied to the signal processing means, for example, the signal processing unit 62. By the phase synchronization method using the PLL circuit 68 to which the demodulated digital modulation signal and the reference signal from the first reference signal source 64 are input, the transmission clock signal synchronized with the demodulation digital modulation signal is reproduced, The signal processing unit 62 detects a frame synchronization signal from the digital modulation signal and the reproduction transmission clock signal, extracts a predetermined number of bits following the frame synchronization signal as a data signal, for example, a digital audio signal, and outputs the digital audio data. To play.

The reproduced digital audio data is PLL
The sample clock based on the transmission clock reproduced by the circuit 68 is supplied to the input / output means, for example, the sampling rate converter (SRC) 66. Since the digital audio data is input to the sampling rate converter 66 in synchronization with the reproduction transmission clock signal, data duplication or loss does not occur.

The sampling rate converter 66 includes
A second reference signal is also supplied from the second reference signal source 70. The second reference signal source 70 is provided independently of the first reference signal source 64. The second reference signal of the second reference signal source 70 and the first reference signal of the first reference signal source 64 can have the same frequency or different frequencies. Since the second reference signal is provided independently of the first reference signal source 64,
It has a fixed period without being affected by jitter. A digital audio signal is output from the sampling rate converter 66 in synchronization with the second reference signal.
That is, the digital audio signal input to the sampling rate converter 66 in synchronization with the reproduction transmission clock signal is
The frequency of the second reference signal is converted into a digital audio signal having a sampling frequency, which is output from the sampling rate converter 66.

For example, if the digital audio signal of the signal processing unit 62 is affected by jitter or the like in the radio transmission path and its cycle is not constant, the reproduction transmission clock signal from the PLL circuit 68 is affected by the influence. However, the period is not constant as shown in FIG. Alternatively, the cycle of the reproduced transmission clock signal of the PLL circuit 68 may not be constant due to the influence of the response speed of the PLL circuit 68. On the other hand, since the reference signal of the second reference signal source 70 is independent of the PLL circuit 68 and the first reference signal source 64, it is not affected by the jitter or the like and is shown in FIG. As described above, it is always generated in a constant cycle.

As shown in FIG. 2B, a digital audio signal is input to the sampling rate converter 66 in synchronization with the rising edge of the reproduction transmission clock signal of the PLL circuit 68, and as shown in FIG. If the digital audio signal is output from the sampling rate converter in synchronization with the rising of the second reference signal of the second reference signal source 70, the output digital audio signal always has a constant cycle. . Therefore, it is not affected by the phase noise and has no distortion. The second reference signal source 7
The frequency of the second reference signal of 0 is the first of the first reference signal source 64.
If the frequency is different from that of the reference signal, a so-called sampling rate converted digital audio signal is output from the sampling rate converter 66. Since the configuration of the sampling rate converter is known, the detailed description of the configuration is omitted.

The digital audio signal output from the sampling rate converter 66 is supplied to the digital / analog converter 72. This digital-analog converter 7
2 is also supplied with the reference signal of the second reference signal source 70, and the digital-analog converter 72 converts the digital audio signal into an analog audio signal in synchronization with the second reference signal. Therefore, this analog audio signal is also converted into an analog signal in the same cycle as the digital audio signal having a constant cycle, and is not affected by the phase distortion.

This analog audio signal is amplified by the amplifier 74 and then amplified by the speaker 76. The analog audio signal from the speaker 76 is naturally not affected by the phase distortion.

Although the sampling rate converter 66 is used as the input / output means in the above embodiment,
The present invention is not limited to this. For example, writing to a shift register having a plurality of stages can be performed by the output signal of the PLL circuit 68, and reading from the shift register can be performed by the reference signal of the reference signal source 70. In the above-described embodiment, the output signal of the sampling rate converter 66 is converted into an analog audio signal by the digital / analog converter 72. However, when the signal is recorded as it is on a recording medium or the like, the digital / analog converter 72 is unnecessary. Is. Further, although the microphone 44 is used in the above-described embodiment, the present invention is not limited to this, and an analog signal source of audio frequency, such as a cassette tape or a CD, is used.
Etc. can also be used.

[0026]

As described above, according to the present invention, the phase caused by the jitter in the wireless transmission path from the transmitter to the receiver and the responsiveness of the transmission clock recovery means included in the receiver, for example, the PLL circuit. The distortion can be removed, and the analog signal can be reproduced with good sound quality.

[Brief description of drawings]

FIG. 1 is a block diagram of a wireless transmission system according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of the wireless transmission system of FIG.

FIG. 3 is a block diagram of an example of a conventional wireless transmission system.

FIG. 4 is a block diagram of another example of a conventional wireless transmission system.

[Explanation of symbols]

40 transmitter 42 receiver 62 signal processing unit (signal processing means) 64 First reference signal source 66 Sampling rate converter (input / output means) 68 PLL circuit (transmission clock recovery means) 70 Second reference signal source 72 Digital-to-analog converter

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takako Shibuya             72-1 Minatojima Nakamachi, Chuo-ku, Kobe City, Hyogo Prefecture             No. In TOA Co., Ltd. (72) Inventor Nobuyuki Keigami             72-1 Minatojima Nakamachi, Chuo-ku, Kobe City, Hyogo Prefecture             No. In TOA Co., Ltd. F-term (reference) 5K047 AA06 BB01 GG43 LL01

Claims (4)

[Claims] 1. A transmission clock reproducing means for reproducing a transmission clock signal synchronized with the data signal based on the received data signal and a first reference signal of a first reference signal source, and the data signal, An input / output unit that is input in synchronization with the reproduced transmission clock signal and is output in synchronization with the second reference signal of the second reference signal source, wherein the first and second reference signal sources are: A receiver that outputs the first and second reference signals independently of each other. 2. The receiver according to claim 1, wherein the data signal is a digital audio frequency signal obtained by digitally converting an audio frequency signal. 3. The receiver according to claim 2, further comprising digital-analog conversion means for converting the output signal of the input / output means into an analog signal in synchronization with the second reference signal. 4. The receiver according to claim 1, further comprising a transmitter that transmits a modulated signal modulated by the data signal, wherein the receiver receives the modulated signal, A wireless transmission system for converting the data signal.