JP2984216B2 - Spread spectrum communication method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a spread spectrum communication method and apparatus, and more particularly, to a reception C / N (C:
The present invention relates to a spread spectrum communication method and apparatus for automatically adjusting a processing gain when a carrier (N: noise) changes and maintaining a predetermined communication quality (S / N).

[0002]

2. Description of the Related Art In a radio communication system using spread spectrum modulation, as shown in FIG. 2, a spread code obtained by a spread code generator 16 is applied to transmission data supplied to an input terminal 15 by a spread modulator 17. Multiply by Here, the multiplication of digital data is exclusive OR (E
xclusive OR). That is, if the value of the spreading code is 0
If so, the value of the transmission data (1 or 0) is left as it is, and if the value of the spreading code is 1, the polarity of the transmission data is inverted. Referring to FIG. 3, if the transmission data is (A) and the spreading code is (B), the signal obtained by spreading the transmission data is as shown in (C). That is, during the period when the transmission data is 1, the polarity of the data of (C) with respect to (B) is inverted. Here, the spreading code is random data having a data rate that is an integral multiple of the data rate of the transmission data, and for example, an M-sequence code is used. The M-sequence code has a finite-length repetition period (for example, 10
(About 00 bits) and can be regarded as a pseudo random code.

As a result of multiplication of the transmission data (A) and the spreading code (B), the transmission data is converted into a random code having a data rate of the spreading code as shown in FIG.
Here, assuming that the data rate of the transmission data is f _T and the data rate of the spreading code is f _D , f _D / f _T = g is called a spreading gain. Further, the occupied band of the transmission data depends on the content (information amount) of the data. When the data is random including many high-frequency components, it has a frequency band substantially corresponding to f _T. Furthermore, the occupied band of the data after multiplying the transmission data by the spread code has a frequency band substantially corresponding to f _D without depending on the content of the transmission data.

[0004] The spread modulation output of the spread modulator 17 is
In the modulator 18, for example, BPSK (binary phase shif)
t keying), and is converted into a high-frequency signal by the frequency converter 19. In wireless transmission by spread spectrum modulation, ISM (industr
2.4GH of ial scientific and medical equipment)
z is used. This high-frequency signal is transmitted from the transmitting antenna 20. On the other hand, the high-frequency signal transmitted from the transmitting antenna 20 is received by the receiving antenna 21 on the receiving station side, and is converted into an intermediate frequency signal by the frequency converter 22. Then, for example, in the demodulator 23 of the BPSK system,
It is demodulated into the random data of the data rate f _D.

More specifically, the despreading code generator 24
Generates the same spreading code as the spreading code on the transmitting side (hereinafter referred to as despreading code). The despread code is multiplied by the despread demodulator 25 with the demodulated random data. As a result of this multiplication, if the value of the despreading code is 0, the value of the demodulated data is left as it is, and if the value of the despreading code is 1, the polarity of the demodulated data is inverted. That is, when the same received data as the spread-modulated transmission data (C) shown in FIG. 3 is multiplied by the same despreading code as the spreading code (B), the same received data as the transmission data (A) is obtained. Become. Therefore, if the repetition period and phase are the same between the spread code in transmission and the despread code in reception, received data equal to the transmitted data is obtained at the output terminal 26.

[0006] In the spread spectrum method, S / N (S: signal, N: noise) on the receiving side is spread gain by expanding data originally having only the band of f _{T to} the band of f _D and transmitting the data. G times, and transmission is possible even on a transmission line with a low S / N. By the way, in the spread spectrum communication system, when another spread spectrum transmitter approaches a receiving receiver, C / N (C: carrier, N:
Noise). That is, when the approached another spread spectrum transmitter of the carrier (input frequency into the communicating receiver) and C _1, becomes the noise N is increased to N + C _1, C / N is, C / (N + C ₁ ). Therefore,
Other transmitters will interfere with the communicating receiver. U.S. Pat. No. 5,056,109 discloses that in a cellular mobile telephone system, the transmission power is adjusted according to the communication distance to prevent the above-mentioned interference by the transmitter carrier. .

[0007]

As the conventional transmission power control system, there are various systems such as open-loop control and closed-loop control, but there is a problem that the apparatus and system become complicated. An object of the present invention is to solve this problem and to provide a spread spectrum communication method and apparatus capable of obtaining a predetermined reception S / N without complicating the configuration.

[0008]

In order to achieve the above object, the present invention transmits received C / N information to a transmitter,
By controlling the data rate of the transmission code transmitted from the transmitter in accordance with / N, the processing gain is adjusted to maintain a predetermined S / N. In the spread spectrum communication method according to the present invention, at least one of the stations measures a parameter indicating a C / N value of a received signal during communication between stations separated from each other by a spread spectrum communication method. Then, when the measured C / N value changes by a predetermined value or more, the data rate of the transmission signal of the other station is changed.
Further, a spread spectrum communication system according to the present invention is provided.
A first communication station including a unit for performing spread spectrum modulation on an input signal with a spread code, and a unit for converting a spread spectrum modulated signal into a radio frequency signal and transmitting the signal;
A receiving unit for receiving a radio frequency signal from the first communication station to reproduce a spread-spectrum modulated signal, and a spread-spectrum demodulation of the spread-spectrum modulated signal with a despreading code having the same period and phase as the spreading code A second unit that includes a demodulation unit that performs a demodulation unit, a unit that detects a parameter indicating a C / N value of a received signal in a receiving unit, and a unit that transmits information of the detected C / N value to a first communication station.
The first communication station receives the information of the C / N value and changes the data rate of the transmission signal of the first communication station when the C / N value changes by a predetermined value or more. It further has a control unit. As a result, in the present invention, by lowering the data rate of the transmission signal, the C /
Even if the N value (or the S / N value) deteriorates, a predetermined C / N value can be maintained. Also, C of the received signal
When the / N value is excessively high, by increasing the data rate of the transmission signal, it becomes possible to transmit more information at the same time while maintaining the predetermined C / N value.

Hereinafter, the principle will be briefly described. In the spread spectrum communication method, as described above, the ratio between the data rate f _D of the transmission band, that is, the data rate f _T of the transmission code, and the data rate f _T of the transmission code is the spread gain g. Conventionally, f _D and f _T are fixed in the system, so that the spread gain g is operated in a constant state. Also, C / N,
The S / N and the spreading gain have the following relationship. S / N = C / N + spread gain (unit: dB) ("Spread spectrum communication system": Jatec Publishing, 1
(See page 1.) Therefore, even if the C / N value deteriorates, a predetermined S / N can be obtained by increasing the spreading gain. To change the spreading gain, change the data rate of the spreading code or
Alternatively, it is necessary to change the data rate of the transmission code. However, if the data rate of the spread code is changed, the transmission band changes and there is a practical problem. Therefore, in the present invention, the amount of information that can be transmitted per unit time increases or decreases by changing the data rate of the transmission code according to the detected C / N value, but the transmission bandwidth is fixed and the predetermined S / N Can be obtained. As a result, a predetermined communication quality can be maintained with a simple configuration without using a complicated system such as a system for controlling transmission power.

[0010]

FIG. 1 is a block diagram of a spread spectrum wireless communication system according to an embodiment of the present invention. In the figure, 1 is an input terminal of a digitized transmission code, 2 is a data rate conversion unit of a transmission code built in a data terminal device described later, 3 is a spread spectrum radio transmitter, 4 is a transmission antenna, 5 Is a receiving antenna, 6 is a receiver of received C / N information described later, 7 is this received C / N information, and these are simplified representations of the configuration provided on the transmitting station side. Reference numeral 8 denotes a receiving antenna, 9 denotes a spread spectrum radio receiver, 10 denotes a data rate conversion unit of a reception code built in a data terminal device as described later, 11 denotes an output terminal, 12 denotes detected C / N information, and 13 denotes This C / N
An information transmitter 14 is a transmitting antenna, which is a simplified illustration of the configuration provided on the receiving station side.

On the transmitting side, the transmission code input to the input terminal 1 is converted by the data rate conversion unit 2 into a predetermined data rate. Further, this transmission code is multiplied (spread modulation) by the spread code of a predetermined data rate in the spread spectrum radio transmitter 3. In one example, the transmission code is BPSK-modulated, converted to a transmission frequency band (for example, 2.4 GHz band), and transmitted from the antenna 4. On the receiving side, a transmission signal from the transmitting side is received by the spread spectrum wireless receiver 9 via the antenna 8. This received signal is subjected to frequency conversion, B
After PSK demodulation, it is despread demodulated and output from terminal 11 via data rate converter 10. At the same time, the receiver 9 receives the C / N signal based on the received signal.
Detect information. Then, the C / N information is transmitted to the transmitting side through a transmission path from the receiving side to the transmitting side, that is, through the transmitter 13 and the antenna 14.

On the transmitting side, a receiver 6
Receives C / N information on the receiving side. Then, the C / N information 7 from the receiving side is sent to the data rate conversion unit 2, and it is determined whether the C / N value on the receiving side is within a predetermined level range. If it is outside the predetermined level range, the data rate conversion unit 2 changes the data rate of the transmission code based on the C / N information 7. In this case, the data rate conversion unit 2 sets the data rate to a data rate determined according to the content of the C / N information 7. For example, when the data indicating the C / N value is equal to or less than a predetermined value, the transmission data rate is adjusted in a lowering direction. Also,
When the data indicating the C / N value is larger than a predetermined value, the transmission data rate can be increased.

Here, when a data terminal device on the receiving side, which will be described later, uses a transmission / reception independent synchronization system, for example, an asynchronous system, it is necessary to match the reception clock (data rate) with the transmission clock. Therefore, when the data rate is changed on the transmission side as described above, the reception C / N information is also sent to the data rate conversion unit 10 at the same time, and the data of the reception code is adjusted according to the data rate conversion of the transmission code on the transmission side. Perform rate conversion. Note that the data terminal device on the receiving side
In the case of a transmission / reception dependent synchronization system that operates based on the transmission side clock, the processing in the data rate conversion unit 10 is not required. In addition, the detection of the C / N value on the receiving side is performed, for example, in connection with the C / N, the S / N after the spread spectrum modulation.
It can also be performed by detecting N or the bit error rate of the received data. If the C / N is not satisfied even after changing the data rate, the data rate of the transmission code is reduced again in a predetermined step, and the above operation is repeated until the received C / N value satisfies a desired condition. When synchronization is lost due to a sudden decrease in C / N and communication becomes impossible, the data rate of the transmission code may be reduced to, for example, a settable minimum value to prioritize synchronization recovery. .

The embodiment of FIG. 1 is one-way communication in which one side is a transmitting side and the other side is a receiving side. However, both communication stations are provided with a transmitting device and a receiving device so that bidirectional communication is performed. In the case of a system, both reception C / N information can be inserted into a spread spectrum transmission signal and transmitted to a partner station. In that case, the dedicated transmitter 13 and receiver 6 for transmitting and receiving the C / N information become unnecessary. In the case of such a two-way communication system, the reception C /
When N decreases, the data rate of the transmission code may be sequentially reduced at predetermined steps on both sides, and mutual communication may be performed at steps at which a predetermined C / N is obtained. For example, if the reception C / N is not improved even after a predetermined time has passed after transmitting a signal for lowering the data rate to the other party, a procedure for changing to a lower transmission data rate is automatically executed. It can be programmed as follows. The above description of the embodiment has been made on the assumption that the C / N changes during communication. According to the present invention, when a predetermined C / N cannot be secured immediately after the start of communication operation, a desired communication quality can be obtained by reducing the data rate of a transmission code to a predetermined value.

FIG. 4 shows a block diagram of a specific embodiment of the present invention, which will be described in detail below. FIG. 4 shows a system for transmitting an image signal to a receiving side by spread spectrum communication. On the transmitting side, an image signal obtained by imaging with the TV camera 31 is converted to an image encoding device 3 constituting a data terminal device.
2. The image encoding device 32 is configured to change the data rate by changing the clock speed when encoding an image. The image signal encoded here is transmitted to the spread spectrum modulator 3.
3 is multiplied by the spread code 34, and is converted into spread spectrum transmission data as described above.
5, at a transmission band of -2.4 GHz and a transmission output per band of -10 mW / MHz, for example, transmitted from the transmission antenna 36. The device of the present invention aims to send a quasi-moving image of 2 frames / sec to 12 frames / sec.
As the spreading code 34, for example, for a video signal digitally encoded to a data rate of 1 to 2 Mbps,
A spreading code having a data rate of 60 to 10 times is used.

On the receiving side, the reception data transmitted from the wireless transmitter 35 via the antenna 36 is received by the antenna 37. This received signal is frequency-converted by a radio receiver 38 and supplied to a spread spectrum demodulator 39.
In the spread spectrum demodulator 39, the despreading code 4 having the same repetition frequency and phase as the spreading code 34 on the transmitting side is used.
It is multiplied by 0 and demodulated. The demodulated signal is decoded into the original image signal by the image decoding device 41 constituting the data terminal device, and is displayed on the monitor 42. On the other hand, S / N
The detector 43 detects the C / N value of the received signal from the S / N value detected from the spread spectrum demodulated signal.
A signal indicating the detected C / N value is transmitted from the wireless transmitter 44 to the image data transmitting side via the antenna 45. For transmission of the detected C / N value, for example, a specific low power data radio having a frequency of 430 MHz and a power of 10 mW can be used. The transmitted C / N value signal is received by the wireless receiver 47 via the antenna 46. Here, the C / N value signal is applied to the image encoding device 32, and the data rate of the encoding of the image data to be transmitted is changed according to the level of the C / N value signal.

For example, the image encoding device 32 has a function of 1.53.
The data rate can be switched stepwise like 6, 0.768, 0.384 Mbps. When the C / N detection level becomes, for example, 6 dB or less, the data rate is reduced by one step. I do. As a result, the spreading gain g increases, and as a result, the S / N is improved. On the other hand, on the receiving side, as described above, the image decoding device 4 is synchronized with the data rate change of the image coding device 32 on the transmitting side.
It is necessary to change the data rate in the decoding in 1. That is, the S / N detected by the S / N detector 43
The C / N value signal converted from / N is applied to the image decoding device 41, and the data rate of the image decoding device 41 is changed according to the level of the C / N value signal.

Next, as an example of a method other than the S / N detection,
A case will be described in which it is detected that communication has become difficult or communication has become impossible based on clock disappearance information, loss of synchronization information, and bit error information. FIG. 5 is a block diagram showing an embodiment of a spread spectrum receiver according to the present invention. The data sent from the transmitting side includes an antenna 51,
It is received by the wireless receiver 52 and converted into an intermediate frequency signal,
After the amplification, it is supplied to the phase demodulator 53. Phase demodulator 5
In 3, the received signal is subjected to, for example, BPSK demodulation. The despreading demodulator 55 is supplied with the despreading code generated by the despreading code generator 54, and the received signal is subjected to spectrum despreading demodulation. The signal subjected to the spectrum despread demodulation is supplied to an error correction unit 57 and to a synchronization detection / clock generation unit 56. The synchronization detection / clock generation unit 56 generates a clock signal and a frame synchronization signal from the signal subjected to the spectrum despread demodulation. This clock signal is supplied to a despreading code generator 54 to make the clock speed of the despreading code match that of the transmitting side.

The frame synchronization signal is supplied to a phase demodulator 53.
And used as a reference for phase demodulation. The signal despread demodulated by the despread demodulator 55 is output to the error correction unit 5.
After a code error is detected in 7, it is sent to the data terminal 58, subjected to processing such as image decoding, and displayed on the monitor 59. Here, when the synchronization signal or the clock signal cannot be normally generated from the signal subjected to the despread demodulation, the synchronization detection / clock generation unit 56 detects the synchronization signal or the clock signal, and detects the loss of synchronization information (a) and the clock disappearance information ( b) is output to the control unit 60. The bit error information (c) is supplied from the error correction unit 57 to the control unit 60. The threshold value of the bit error information is set in the control unit 60. The bit error information is, for example, the number of bits 10 ⁶
, The bit error rate 1
This is data corresponding to / 10 ⁶ .

Here, when the C / N value decreases and the bit error increases and exceeds the set threshold, the control unit 60 changes the data rate to the data terminal 58 so as to reduce the data rate by a predetermined value. Give a command. The control unit 60
If either the out-of-synchronization information or the clock disappearance information is supplied, the communication becomes impossible, and the data terminal 58 is instructed to reduce the data rate until the generation of the synchronization signal and the clock signal becomes possible. give. The control unit 60 sends a data rate change command to the data terminal 58 and, at the same time, transmits data for instructing the transmission side to similarly change the data rate of the transmission data from the wireless transmitter 61 to the antenna. The transmission is performed via the transmission line 62, and the transmission side also changes the data rate at the same time as in the above embodiment. By setting the threshold value to, for example, a limit value at which a received image can be reproduced, the minimum receivable data transmission can be performed.

[0021]

According to the present invention, when the reception C / N value changes, the data rate of the transmission code on the transmission side is controlled according to this value to change the gain, so that the reception side has a predetermined S / N value. / N can be maintained. Therefore, the problem of distance between communication stations can be solved in spread spectrum communication without using a complicated power control device.

[Brief description of the drawings]

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

FIG. 2 is a block diagram for explaining a conventional spread spectrum wireless communication system.

FIG. 3 is a waveform chart for explaining spread spectrum modulation.

FIG. 4 is a block diagram of a spread spectrum wireless communication system according to another embodiment of the present invention.

FIG. 5 is a block diagram of a receiving apparatus of the spread spectrum wireless communication system according to the present invention.

[Explanation of symbols]

2 Data rate converter for transmission code, 3 spread spectrum radio transmitter, 6 receiver, 7, 12 C / N information, 9
Spread spectrum radio receiver, 10 Received code data rate converter, 13 Transmitter, 31 TV camera, 3
2 image encoding device, 33 spread spectrum modulator,
34 spreading code, 35, 44 radio transmitter, 38, 47
Radio receiver, 39 Spread spectrum demodulator, 40
Despreading code, 41 image decoding device, 42 monitor, 4
3 S / N detector.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H04J 13/00 H04B 1/40

Claims (6)

(57) [Claims] A transmitting device and a receiving device;
Wirelessly transmits the image-encoded video signal between the
In the spread spectrum communication method for transmission , the transmitting side converts the encoded video signal into a predetermined data rate.
And converts the transmission code to a predetermined data rate.
Spread spectrum modulation by the spread code of the
The modulated transmission code is further converted and modulated into a predetermined frequency band.
After transmitting, the receiving side converts and modulates to the predetermined frequency band
And demodulates the transmitted transmission signal to a predetermined frequency.
And the received signal converted to the predetermined frequency is
Cram despread demodulation, data rate conversion,
And demodulates it into a video signal.
Received C / N (C: carrier, N: noise) value information from transmitted signal
And transmits the C / N value information to the transmitting side.
Side receives the C / N value information and determines whether the C / N value is a specified value.
If the communication quality deteriorates and the communication quality deteriorates,
The data rate of the transmission code according to the variation of the C / N value.
While the communication quality is controlled to a predetermined value.
In the case where the above has been improved, a change in the C / N value
A spread spectrum communication method characterized by maintaining a predetermined communication quality by increasing the data rate of the transmission code . 2. The spread spectrum communication system according to claim 1,
The detection of the reception C / N value on the reception side of the signal includes the S / N value after spread spectrum demodulation, the code error rate of the reception data.
A spread spectrum communication method performed by at least one of the following . 3. A transmitting device comprising a transmitting device and a receiving device.
Wirelessly transmits the image-encoded video signal between the
In the spread spectrum communication method for transmission , the transmitting side converts the encoded video signal into a predetermined data rate.
And converts the transmission code to a predetermined data rate.
Spread spectrum modulation by the spread code of the
After the modulated transmission code is further phase-modulated, transmit and receive
The side converts and modulates to the predetermined frequency band and transmits
The transmission signal is phase demodulated and converted to the predetermined frequency.
Despread spectrum demodulation of the received signal
And then demodulates it into the encoded video signal.
Then, synchronization detection is performed from the received signal, and the detected synchronization signal is detected.
Signal based on the synchronization signal for despreading
Performs the spectrum despread demodulation of
Despread demodulated signal is bit error corrected and encoded
Outputs a video signal, and outputs the information of the synchronization detection or
Detects the bit error information as C / N value information
Then, the C / N information is transmitted to the transmitting side, and the transmitting side transmits the C / N information.
Upon receiving the C / N information, the C / N value fluctuates from a predetermined value,
When the communication quality is degraded, the C
/ N lower data rate of transmission code according to fluctuation of information
The communication quality is improved by a predetermined value or more.
If the C / N information is changed, the transmission is performed according to the change of the C / N information.
A spread spectrum communication method characterized by maintaining a predetermined communication quality by increasing a code data rate . 4. The method according to claim 3, wherein the synchronization detection information is
Indicates that synchronization has been lost.
Signal data rate is reduced by a predetermined value to restore synchronization
A spread spectrum communication method characterized by the above-mentioned. 5. An image encoding means for encoding a video signal, means for performing spread spectrum modulation on a signal encoded by the image encoding means with a predetermined spreading code, and a method for transmitting the spread modulated signal to a predetermined radio signal. A video signal transmitting apparatus having means for converting the signal to a frequency signal and transmitting the signal, a means for receiving and demodulating a transmission signal from the video signal transmitting apparatus, and a means for demodulating the demodulated signal with the spreading code, repetition period and phase shift A video signal receiving apparatus having means for performing spectrum despread demodulation with the same despreading code and image decoding means for decoding the demodulated signal into the original video signal,
At least means for detecting an S / N (S: signal, N: noise) value of the demodulated video signal of the video signal receiving apparatus to obtain corresponding C / N value information, and information obtained by the means; And a means for changing a data rate of the image encoding means in accordance with the image coding means. 6. The spread spectrum communication apparatus according to claim 5, wherein a data rate of the spread code is set in a range of 10 to 60 times a data rate of the video signal.