JP2621005B2 - End code transmission / reception method for voice coded communication - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transmitting and receiving an end code when speech coding communication is applied to a half-duplex communication system.

[0002]

2. Description of the Related Art When applying voice coded communication to half-duplex communication, an end code (end code) is transmitted at the end of transmission to notify the receiving side of the end of transmission. On the receiving side, upon receiving the end code, the standby process for the next transmission, that is, the decoding of the voice is ended, and the process enters the start code detecting process. If the end code is not detected due to a bit error due to deterioration of the line or the like, the receiving side will continue to decode the voice even though data is not transmitted, generating annoying noise, and Since the process does not start the process of detecting the start code of the next transmission, noise is continuously output until the end of the next transmission, that is, the end code at the end of the next transmission is detected. In addition, since the process of detecting the start code of the next transmission is not performed, the voice of one transmission is lost. This phenomenon is rare in the case of a wired line,
Such a phenomenon frequently occurs in mobile communication in which the line state fluctuates greatly. In order to reduce the occurrence rate of such a phenomenon, conventionally, an end code is provided in a plurality of frames (for example, 3 to 5 frames).
In general, it is determined that the transmission is completed when the end code of one frame is transmitted.

[0003]

However, a similar phenomenon occurs when voice coded communication such as a digital car phone or a mobile phone is adopted and the communication is advanced, and deterioration due to a change in the state of a wireless line is large in an urban area or the like. Occurs frequently. Hereinafter, the problems of the conventional technology will be analyzed in detail. It is considered that there are the following cases in the detection error of the end code. (1) A voice frame is mistaken for an end code. (2) Misdetection of an end code caused by an error in the end code due to line condition deterioration. As a countermeasure against the above (1), there is a method of adopting a code that does not theoretically occur in a voice frame as an end code, but it is not sufficient considering that a bit error occurs due to a change in a line state. Therefore, it is necessary to make the length of the end code sufficiently long to reduce the probability that the same code occurs in a voice frame. For example, if the end code is 50 bits, the probability P of occurrence of the same code is P = 1/2 ⁵⁰ = 8.888178 × 1
Shown as ^0-16 . Therefore, if the encoding speed of the audio encoder is 2400 bps, the interval at which the same code occurs in the audio frame is 1 / (2400 × P) = 4.69.
It is 12 × 10 ¹¹ seconds, that is, once every 130 million hours, and it is considered that this does not occur first. However, there is a drawback that if the end code length is long, the transmission efficiency is poor. next,
As a countermeasure for the above (2), the end code should be several
〜5 frames) There is a method of transmitting continuously, but it is not enough.

FIG. 3 is a time chart when three frames of an end code having 50 bits as one frame are transmitted. For example, as shown in FIG. 3, it is considered that a random bit error of 2% has occurred in the end code due to the deterioration of the line state (an error rate of land mobile communication often becomes 1 to 3%). In the example of FIG.
When three 0-bit end codes are transmitted (a total of 150 bits), a random bit error of 2% occurs due to deterioration of the line condition, that is, an average of three 150-bit errors occurs, and the receiving side detects any end code. This is the case where it is not possible (end code detection omission). In this example, the end code cannot be detected because bit errors have occurred in all three frames. Under the condition of a random bit error rate of 2%, that is, a three-bit error
Assuming that it occurs during 0 bits, the probability Pn that the end code is not detected is Pn = (2/3) × (1/3) = 2 /
In other words, the end of the transmission cannot be detected once every 4.5 transmissions. This is a disadvantage that cannot be ignored in practical use.

An object of the present invention is to improve the above-mentioned problems,
It is an object of the present invention to provide an end code transmission / reception method in speech coding communication in which end code detection omission due to bit errors is reduced.

[0006]

The present invention is characterized in that the length of an end code to be transmitted and the length of an end code detected on a receiving side are changed. That is, the voice coded communication is applied to the half-duplex communication system, and an end code in which a predetermined number of bits indicating that the transmission from the transmission side is completed is set to one frame is continuously transmitted in a plurality of frames, and the reception side is transmitted. Detecting the end code received through the transmission line in the end code transmission / reception method in the voice coded communication configured to enter a standby process for the next transmission. In order to reduce errors, the end code of the one frame transmitted from the transmission side is 1 / N (where N is an end code length of 3 to 1).
(Ends of 6 bits) are continuously transmitted in units of a bit length end code so as to be substantially equal to the total number of bits of the plurality of frames. It is characterized in that the code is detected by shifting the code in the unit of one frame and one end code at a time.

[0007]

In transmission, the end code length is set to 1 / N (N
Is an integer whose end code length is 3 to 16 bits)
Then, the end code is continuously transmitted by N times. Therefore, the number of bits of the entire end code to be transmitted is the same as the conventional total number of bits. On the other hand, on the receiving side, N times this end code is regarded as one frame, and code coincidence is detected by shifting one code at a time.
FIG. 1 is a time chart showing a configuration example of the end code of the present invention. In FIG. 1, end codes E (1), E
(2),... Each of E (30) is 5 bits (N = 1
0), and transmit a total of 150 bits of 30 codes (the number of transmission bits is the same as the conventional one). On the receiving side, the end code is detected by shifting 50 bits (10 codes) into one frame, which is the same as the conventional method, in units of one code. By adopting such a configuration, the end code performs the match detection for every 5 bits, which has the effect of reducing the omission of the end code detection due to a bit error. FIG. 2 is a time chart showing an example in which the end code is not detected on the receiving side in the configuration of the present invention. In this example, if 10 error-free codes are not consecutive, for example, 8 in the first frame
Th end code E (8) is a case where not detected, the probability P _p of such an error pattern is generated is expressed by the following equation.

[0008]

(Equation 1) Compared with the conventional case of FIG. 3, the end omission code detection omission is about one fifth, and it can be seen that the end code omission detection can be reduced. The same reduction effect can be expected when the number of bit errors is further increased.

On the other hand, the probability that a voice frame is mistaken for an end code has the same performance as the conventional one because the detection frame length on the receiving side is the same as the conventional one. However, if the end code to be transmitted is too short, for example, in the case of 1 to 2 bits, there is a possibility that the code matches a code pattern unique to the audio coding method (a pattern which is likely to be generated when there is no sound).

FIG. 4 is a block diagram showing an example of a circuit configuration for implementing the method of the present invention. FIG. 4A shows a configuration example of an encoding device, and FIG. 4B shows a configuration example of a decoding device.
In FIG. 4A, an audio signal a is converted into a digital signal b by an analog / digital converter 1 and is input to an audio encoder 2. The audio encoding unit 2 converts the digitized signal b into a frame (eg, one frame 20 m
s) and information compression (speed conversion to a low bit rate), and sends out an encoded signal c. The end code generator 3 generates an end code d having a pattern set according to the present invention. The output signal switching unit 4 sends out the encoded audio signal c as digital data f when the transmission control signal e indicates the start of transmission, and outputs the end code d as digital data f when the transmission control signal e indicates the end of transmission. , The transmission of the digital data f is stopped.

In the decoding device shown in FIG. 4B, the digital data g received via the radio line is
, And is output as digital data h for each frame. The digital data h is information-decompressed in the audio decoder 6 and output as a decoded signal i. The end code detecting section 7 detects whether or not the digital data h input by the method shown in FIG. 1 is an end code, and outputs the result j. The synchronization processing unit 5 outputs a signal n indicating whether synchronization is achieved, and the silence signal generation unit 8 outputs digital data k such that the output p of the digital / analog conversion unit 10 becomes silent. doing. The output signal switching unit 9 outputs the decoded signal i from the decoding unit 6 when the synchronization signal n indicates that synchronization is achieved, and when the end code detection signal j indicates that the end code has been detected, and When the synchronization signal n indicates that synchronization has not been achieved, an unvoiced signal k is output. The signal m output from the output signal switch 9 is converted into an analog signal by the digital / analog converter 10 and output as an audio signal p.

[0012]

As described above in detail, by implementing the present invention, the effect of reducing omission of end code detection in half-duplex communication of voice coded communication is great, and it is extremely useful in practical use.

[Brief description of the drawings]

FIG. 1 is a time chart showing an embodiment of the present invention.

FIG. 2 is a time chart showing an example of detection omission in the method of the present invention.

FIG. 3 is a time chart of a conventional end code.

FIG. 4 is a block diagram of an apparatus for implementing the method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 A / D conversion part 2 Encoding part 3 End code generation part 4 Output signal switching part 5 Synchronization processing part 6 Decoding part 7 End code detection part 8 Silence signal generation part 9 Output signal switching part 10 D / A conversion part

Claims (1)

(57) [Claims] 1. An end code in which a predetermined number of bits indicating that transmission from a transmission side has been completed is defined as one frame by applying speech coded communication to a half-duplex communication system, and a plurality of frames are continuously transmitted. An end code transmission / reception method in voice-encoded communication configured to detect the end code received via a transmission line on a receiving side and to enter a standby process for a next transmission, wherein: To reduce end code detection errors, the end code of the one frame transmitted from the transmission side is 1 / N (where N is an integer such that the end code length is 3 to 16 bits). The transmission is continuously performed so that the number of bits of the end code is substantially equal to the total number of bits of the plurality of frames. A method for transmitting and receiving an end code in voice coded communication, wherein the detection is performed by shifting one end code at a time in units of one frame.