JPH0662039A - Cell forming and encoding system - Google Patents

Abstract

PURPOSE:To provide a cell forming and encoding system for an ATM transmission line provided with cell abandonment compensation for which the degradation of transmission efficiency is less with a simple circuit by multiplexing two cells constituted of bits whose importance is different and transmitting them. CONSTITUTION:The upper 8 bits of a 9-bit PVM signal are made into the cells by a cell forming circuit 12, the upper 7 bits and the lowest 1 bit are made into the cells by the cell forming circuit 15 and the output signals of the two cell forming circuits are multiplexed by a multiplex circuit 14 and outputted to a transmission line 20. The 9-bit PCM is outputted from the two cell signals when there is no cell abandonment on the transmission line in the selection circuit 24 of a reception example and when either of the cell signals is abandoned, 8-bit PCM signal is outputted from the other cell signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coding system for voice and image signals, and more particularly to an ATM (Asynchronous T
The present invention relates to a cell coding system which is used in a device of a transfer mode (asynchronous transfer mode) system and corresponds to a case where a signal undergoes cell discard during transmission.

[0002]

2. Description of the Related Art Conventionally, as a cell discard compensation measure, this type of cell coding method is a method in which the same cell is repeatedly transmitted twice or divided in a frequency domain called hierarchical coding. A method of transmitting cells in the low frequency range and cells in the high frequency range is used.

[0003]

When a voice signal or an image signal is transmitted using an ATM transmission line, when the cell discard, which is a feature of the ATM transmission line, occurs, information about the discarded cells is lost. There is a problem that the same cell is repeatedly transmitted to compensate for the cell loss, or a low frequency region is designated as a priority cell (cell with a low probability of cell loss) by using hierarchical coding. However, the method of repeatedly transmitting the same cell twice has the drawback of being inefficient, and the layered coding method is complicated in coding and requires a large amount of hardware when simple coding is performed. There is a problem that the addition becomes too large, and when the priority cell is used but the priority cell itself is also discarded, it becomes invalid.

[0004]

According to the cell coding system of the present invention, a voice or image signal is coded into a PCM signal,
In a device for constructing and transmitting a cell by combining a plurality of PCM signals, a first cell that PCM-encodes an input signal at time T with N bits (N is a natural number) to compose M cells to form a cell; PCM the same input signal at the same time T as the first cell with (N + n) bits (n is a natural number, N> n)
Encoded and the upper (N-n) of the (N + n) bits
The first cell and the second cell are multiplexed and transmitted by performing cell formation into two cells, that is, a second cell forming a cell by combining M bits and lower n bits.

[0005]

An embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a cell coding device according to the present invention. The input signal 101 input from the input terminal A is input to the A / D converter 11. The A / D converter 11 converts the input signal 101 into a 9-bit PCM signal. Of the 9-bit PCM signal, the PCM signal 102 of the higher 7 bits (in this case, the higher order means the bit importance order) is output to the cell assembling circuit 12 and the cell assembling circuit 15, and the PCM signal 103 of the 8th bit is outputted. To the cell assembling circuit 12 and the least significant 9th bit PCM signal 104 as the cell assembling circuit 1
Output to 5 respectively.

In the cell assembling circuit 12, the input PCM signal 102 and PCM signal 103 form the first cell signal shown in FIG. 2, and the first cell signal 105 is output to the buffer 13. In FIG. 2, the first cell signal 105 is M 8-bit PCM signals (b8 is the most significant bit, and is hereinafter referred to as b7, b.
6 bits, b5, b4, b3, b2, b1).

On the other hand, in the second cell conversion circuit 15, the input PCM signal 102 and PCM signal 104 constitute a second cell signal as shown in FIG.
Is output to the buffer 16. In FIG. 2, the second cell signal is composed of M 8-bit PCM signals (b8 is the most significant bit, and b7, b6, b5, b4, b3, b2 and 8 bits of the least significant bit are b0 below). .

The buffer 13 converts the input first cell signal 105 into a signal having a double speed for multiplexing, and outputs it as a first cell signal 106 to the multiplexing circuit 14. On the other hand, the buffer 16 converts the input second cell signal into a signal having a double speed for multiplexing and outputs it as the second cell signal 108 to the multiplexing circuit 14. In the multiplexing circuit 14, the input first cell signal 106 and the second cell signal 106
And the cell signal 108 is output as a multiplexed signal 109, and the multiplexed signal 109 is output from the transmission line output terminal B to the transmission line 20.

The multiplexed signal 201 input from the transmission line input terminal C is input to the separation circuit 21. The demultiplexing circuit 21 converts the input multiplexed signal 201 into the first cell signal 202.
And the second cell 203 signal, and outputs the first cell signal 202 to the cell disassembly circuit 22 and the second cell signal 203 cell disassembly circuit 23, respectively.

In the cell disassembly circuit 22, the input first cell signal 202 is combined with the PCM signal 204 of the higher 7 bits and the eighth PCM signal 204.
It is converted into a bit PCM signal 205 and both are output to the selection circuit 24. On the other hand, in the cell disassembly circuit 23, the input second cell signal 203 is transferred to the PCM signal 20 of the higher 7 bits.
6 and the least significant 9th bit PCM signal 207 and both are output to the selection circuit 24.

In the selection circuit 24, the first cell signal 202
If neither the second cell 203 nor the second cell 203 receives the cell discard, the PCM signal 204 (or either 205 may be used), the PCM signal 205 and the PCM signal 207 are selected and the D / A converter 25 is used as the PCM signal 208. Output to. At this time, the most significant bit of the PCM signal 208 is b8.
In the following, 9 bits of b7, b6, b5, b4, b3, b2, b1 and b0 of the least significant bit.

When only the second cell signal 203 has undergone cell discard, the selection circuit 24 selects the PCM signal 13 and the PCM signal.
The signal 14 is selected, a "0" level is inserted in the 9th bit, and the PCM signal 208 is output to the D / A converter 205. The most significant bit of the PCM signal 208 at this time is b8, and the following bits b7, b6, b5, b4, b3, b2,
Following b1, the least significant bit is 9 bits of "0".

When only the first cell signal 202 receives the cell discard, the selection circuit 24 selects the PCM signal 13,
A "0" level is inserted in the 8th bit and a "0" level is inserted in the 9th bit as well, so that the PCM signal 208 is D / A.
Output to the converter 25. The most significant bit of the PCM signal 208 at this time is b8, and the following bits b7, b6, b5, b4,
Continued with b3 and b2, the 8th bit and the least significant bit are "00"
Of 9 bits.

First cell signal 202 and second cell signal 2
If both 03 receive the cell discard, the selection circuit 20
4 is a PCM signal 17 and all "0" from b8 to b0
The signal of is output to the D / A converter 25. D / A converter 2
In 5, the input PCM signal 208 is D / A converted and an output signal 209 is output. Output signal 209 is output terminal D
Is output from.

In this manner, even if a cell is dropped due to cell discard, a PCM signal with a precision of at least 7 bits can be transmitted unless two cells are discarded at the same time, and a PCM signal with a precision of 9 bit is normally used when cell discard does not occur. The signal can be transmitted.

In this embodiment, in order to simplify the explanation, the number of PCM coded bits is set to 9 bits, the 8th bit is set to the first cell, and the 9th bit (least significant bit) is set to the second cell. The upper 7 bits are assigned to both the first cell and the second cell, but these numbers are not limited.

[0018]

As described above, according to the present invention, since two cells composed of bits of different importance are multiplexed and transmitted, even if cell loss occurs due to cell discard, the two cells are simultaneously transmitted. P with at least 7-bit precision unless discarded
The CM signal can be efficiently generated, and the PCM signal can be transmitted with 9-bit accuracy in the normal state where cell discard does not occur.

That is, there is an effect that a simple circuit configuration almost the same as the one in which simple double repetition is performed and the transmission efficiency is not lowered due to cell discard compensation.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a configuration diagram of a cell in FIG.

[Explanation of symbols]

 A input terminal B transmission path output terminal C transmission path input terminal D output terminal 11 A / D converter 12 first cell assembly circuit 13 buffer 14 multiplexing circuit 15 second cell assembly circuit 16 buffer 21 separation circuit 22 cell disassembly Circuit 23 Cell disassembly circuit 24 Selection circuit 25 D / A converter

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H04Q 11/04

Claims (1)

[Claims] 1. A device for encoding a voice or image signal into a PCM signal, forming a plurality of the PCM signals to form a cell, and transmitting the cells, wherein the input signal at time T is PCM encoded with N bits (N is a natural number). The same input signal at the same time T as that of the first cell, which is formed by assembling M cells, and (N + n) bits (n is a natural number, N>
(n) performs PCM coding to perform cell formation into two cells, that is, a second cell that constitutes a cell by combining M pieces of upper (N−n) bits and lower n bits of the (N + n) bits. A cell coding system, wherein the first cell and the second cell are multiplexed and transmitted.