KR0157951B1 - Method for transmitting cell unit interleaving of asynchronous transfer mode - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cell-based interleaving transmission method of an asynchronous transmission method (ATM) in which cell header bits can be distributed and transmitted in a data interval in order to improve a cell loss rate for a burst error mainly occurring in a wireless transmission channel. In the block-based interleaving transmission method, when an unexpected long burst error occurs, several cells may be lost at the same time, and the processing time may be long. In view of this, by applying interleaving to an asynchronous cell (ATM) cell itself, the header bits of the cell are arranged at regular intervals in the entire cell area, and the interleaved signal is received at the receiving end and rearranged as it is. The cell loss rate can be greatly improved, and can be applied to both synchronous digital hierarchy (PDH) based, synchronous digital hierarchy (SDH) based, and cell based physical layer.

Description

Cell-based interleaving transmission method of asynchronous transmission method

1 is an explanatory diagram showing an interleaving method of an asynchronous transmission (ATM) cell according to the present invention.

2 is a comparison graph showing the cell loss rate when the cell interleaving of the present invention is applied to the channel where the burst error occurs and when it is not applied.

3 is an exemplary explanatory diagram showing a method of applying the cell-based interleaving transmission method of the present invention to each physical layer protocol of a BISDN.

* Explanation of symbols for main parts of the drawings

1: Asynchronous Cell (ATM) Cell 2: Interleaving Cell

3: transmitting cell 4, 7: cell buffer

5: new cell 8: receiving cell

9: interleaver 10: deinterleaver

The present invention relates to a cell-based interleaving transmission method that can improve a cell loss rate, which is a problem when introducing an asynchronous transmission method (ATM), a transmission technique of a broadband information communication network (BISDN), into a wireless network. In particular, the present invention relates to a cell-based interleaving transmission method of an asynchronous transmission method in which cell head bits are distributed and transmitted in a data interval in order to improve a cell loss rate for a burst error mainly occurring in a wireless transmission channel.

In general, an asynchronous cell (ATM) cell consists of a header section of 5 bytes and a data section of 48 bytes, the header is a path between links when the cell is transmitted between the end (end-to-end) Virtual Path Identifier (VPI) and Virtual Channel Identifier (VCI) bits to distinguish, Effective Load Type (PT) bits to indicate the type of data on the cell, and Cell to indicate cell abandonment when congested in the network Loss priority (CLP) bits, header error correction (HEC) bits, reserved reserved (RES) bits, and general flow control (GFC) bits that control the flow between user and manganese in case of user manganese interface (UNI). Consists of. When transmitting such an asynchronous transmission cell, noise generated in the channel may cause errors in bits in the cell. In this case, an error of a data bit carried in a pay load is merely an information loss of the bit, and does not affect cell loss and cell inflow in the wrong direction. However, if an error occurs in the header bit, the information in the header may be misunderstood and the cell may flow in the wrong direction or the entire cell may be lost. The header error correction (HEC) may correct a 1-bit error that may occur in the header, and the cell may be lost when a 2-bit error occurs. Therefore, when an error of 1 bit or less occurs in the cell header, the cell can be transmitted exactly to the destination.

This asynchronous transmission protocol (ATM) protocol is suitable for the case of the optical transmission path that can maintain the transmission error of 10E-9 or less, and the broadband information communication network (BISDN) uses the optical fiber for the transmission path Is most of them. However, asynchronous transmission (ATM) technology has been widely used due to the advantages of being able to efficiently use a transmission channel by a statistical multiplexing method and delivering various services having different speeds and characteristics to one transmission medium. In particular, with the rise of personal mobile communication services, asynchronous transmission (ATM) cell transmission is required in satellite and wireless transmission environments. However, unlike the optical transmission line, in the line-of-sight environment, the bit error rate (BER) is relatively poor and the probability of burst error is increased, and when a burst error occurs in the header, only one bit can be corrected. Error correction (HEC) cannot recover the error, resulting in cell loss and cell inflow in the wrong direction. Therefore, cell bursting is a serious problem in the environment where burst error occurs in itself, and only the 1-bit error of the header is recovered.

In view of these problems, efforts have been made in various ways to improve asynchronous cell loss (ATM), and a typical method is to recover a lost cell by sending an extra cell by a forward error correction (FEC) method. There is a method of improving the error correction function to 2 bits by reinforcing the header error correction (HEC) bit, and a method of preventing cell loss by distributing the burst error by interleaving.

However, the cell loss rate improvement method according to the forward error correction (FEC) method is difficult to apply when the load is large because extra cells may increase and cause an increase in load, and also reinforces the header error correction (HEC) bit. Therefore, the method of improving cell loss does not conform to the existing protocol, so the interface is a big problem to apply to the broadband information network (BISDN).

In addition, the interleaving method requires little additional overhead so that the overload effect can be ignored, and cell loss rate and cell insertion rate can be improved when a burst error occurs. Asynchronous Link Enhancement (ATM) Link Enhancement technology, which is described above, provides interleaving between cell headers in block units (DS ₃ to 12 cell units) when an ATM cell is transmitted through a DS ₃ satellite transmission channel. Block formation) to improve cell loss rate. This method, however, has the disadvantage of losing multiple cells simultaneously if an unexpected long burst error occurs (more than 14 bits in error burst length).

Accordingly, an object of the present invention is to provide a cell-by-cell interleaving transmission method that can solve the disadvantages of the conventional methods described above in an environment where cell loss due to a burst error is a problem, and also provides a cell-by-cell interleaving transmission method similar to a synchronous digital layer. The present invention provides a method that can be applied to a structure (PDH) based, a synchronous digital layer structure (SDH) based, and a cell-based physical layer.

The present invention having the above object requires less overhead than the forward error correction (FEC) method, can be easily applied to the existing protocol, and has the advantage of reducing the number of cells to the unexpected long burst error which is a disadvantage of block-by-block interleaving. At the same time, there are no side effects that are lost, and the processing delay time required for blocking a cell is shorter than that of block interleaving. Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is an explanatory diagram illustrating an interleaving method of arranging header bits of an asynchronous transmission (ATM) cell in an entire cell area at 10-bit intervals. As shown in FIG. 1, an asynchronous transmission (ATM) cell 1 is illustrated. Interleaving is applied to itself to show an interleaving cell 2 in which the header bits of the asynchronous transfer cell (ATM) cell 1 are arranged at intervals of 10 bits in the entire cell area.

The asynchronous cell (ATM) cell 1 has a total of 53 bytes consisting of a 48-byte data section and a 5-byte header section. As described above, since the header includes information on a path through which the cell is delivered, when an error occurs in the header, information of the entire cell may be lost. In the BISDN physical layer protocol, a header error correction (HEC) bit can be used to correct an error of one bit in the header. However, if an error of two or more bits occurs in the header section, cell loss occurs. do. Thus, burst errors are most common in wireless transmission links and are caused by fading, multipath, jamming pulses, and so on. In addition, forward error correction (FEC) coding is used to improve the quality of the wireless transmission link, which causes a burst error. In addition, Convolutional Coding and Viterbi Decoding are mainly used to improve error correction in satellite channels and digital microwave radios for data transmission. If a wind occurs when the path is selected, the burst length of the error tends to increase according to the constraint length of the coder Coder.

In this burst error situation, if the header of the cell is distributed before transmission and restored at the receiving end, the characteristics of the random error appear in the header. Accordingly, the cell loss rate is the same as that of the random error. Can be improved.

Accordingly, the present invention distributes a burst error occurring in a header to a random error form, and provides a method of improving a cell loss rate at the same level as a random error even with a conventional header error correction (HEC). The method for distributing the header bits is performed as shown in FIG. 1 described above. In other words, the 5-byte header corresponds to 40 bits, and the 48-byte data corresponds to 384 bits, so that the asynchronous cell (ATM) cell 1 is composed of a total of 424 bits. Is distributed in 10-bit intervals over the entire 424-bit cell, and 383-bit data is sequentially filled in the remaining empty space.

The receiver collects the distributed header bits and arranges them in the first 40-bit period of the cell. The 384 data bits are rearranged in the original form from the 41st bit to the 424th bit. In this case, the header error correction (HEC) corrects an error occurring in the rearranged header. In this case, only one error is corrected, but since the burst error is distributed, the probability of occurrence of two or more errors in the header is reduced. Results. As a result, the cell loss rate can be significantly improved in a burst error environment.

2 is a graph demonstrating the effect of improving cell loss rate when a burst (when burst size is 2) error occurs through equations and simulations. FIG. 2A shows the cell loss rate when cell interleaving is not applied. FIG. 2B shows the cell loss rate when the cell interleaving is applied. As shown in FIG. 2, the lower the bit error rate (BER), the more the cell loss rate is improved. The burst loss occurs in the same cell loss rate as when a random error occurs. Is improved. On the other hand, as a result of simulating and comparing the burst error of 2, 3, 4, and 5 with and without the present invention, the burst length had little effect on the cell loss rate improvement effect. As a result, when the burst size is not large (at a burst length of 10 or less), intercell interleaving improves the cell loss rate to a random error level regardless of the burst length.

However, when the burst length of the error is less than 10, the cell loss rate is significantly improved, but the cell loss rate improvement effect becomes smaller for the burst error of 11 or more, and the cell loss rate is slightly increased when a burst error of 20 or more occurs. However, in non-fading channels, the burst length by Viterbi decoding is less than 10, and even in faded channels, if the signal-to-noise ratio remains above 5, the burst length is almost no more than 10. In addition, even if a cell having 10 or more errors completely reaches its destination, the error cannot be recovered from a higher layer. Therefore, cell propagation for an error with a very long burst length is not meaningful.

Therefore, the present invention can improve the cell loss rate, and because processing is performed in one cell, processing delay time is small, and burst cell loss that simultaneously loses multiple cells does not occur even when an unexpected long burst error occurs. Does not work.

In addition, in the case of block interleaving, since headers are interleaved in units of 12 cells, if a burst error of 14 bits or more occurs, several cells may be lost at a time. However, in the cell interleaving of the present invention, a long burst error may occur. Only that cell is lost. Therefore, in an environment where unexpected long burst errors may occur, the cell interleaving method is excellent.

When this interleaving method is applied to an asynchronous transmission (ATM) cell, it must be interworked with a protocol of a broadband information communication network (BISDN). It should be applicable to each physical layer, with reference to FIG. 3, which is an exemplary explanatory diagram showing how to apply the cell-based interleaving transmission method of the present invention to each physical layer protoco of a broadband information communication network (BISDN). Explain how.

The pseudo-synchronous digital layer structure (PDH) based physical layer includes DS ₁ (1.544 Mbps), DS ₂ , DS ₃ , DS ₄ , DS _1E , DS _2E, and the like. Among them, the method of transmitting asynchronous transmission (ATM) cells using DS ₁ and DS _1E is specified as a standard in the ITU-T physical layer recommendation. This recommendation requires cell boundary identification to use header error correction (HEC). However, in case of DS ₃ , a separate frame is required to transmit an Asynchronous Cell, and the cell boundary can be identified by the frame discrimination function unique to the frame.

In addition, two methods of identifying a cell boundary are used in the synchronous digital layer structure (SDH) based physical layer. One method uses a header error correction (HEC) of an asynchronous cell (ATM) cell. Another method is to use H ₄ , which is an overhead of the synchronous digital hierarchy (SDH). In the case of the cell-based physical layer, cell boundary identification is performed using header error correction (HEC).

Did not require a separate overhead when using the similar H ₄ upon identification of a cell boundary in the DS ₃ or synchronous digital hierarchy (SDH) synchronous digital hierarchy (PDH), the receiving end after applying interleaving in the cell and transmitting De-interleaving at will naturally restore the original interface without the need for an extra interface. Therefore, when transmitting an asynchronous cell (ATM) cell over the DS ₃ link, the transmitting cell 3 passes through the interleaver 9 only in FIG. ₃ to perform inter-cell interleaving and transmits according to the DS ₃ format. In addition, in case of synchronous digital layer structure (SDH) using H ₄ for cell boundary identification, asynchronous transmission (ATM) cells are passed through the interleaver 9 of FIG. 3 to perform inter-cell interleaving, and the lower 48 bytes of the cells are mixed. (Scrambling) is carried on the effective load interval of the synchronous digital hierarchy (SDH) to transmit. In both cases, the remaining functions in Figure 3 do not apply.

In addition, since the hybridization process when transmitting a cell using a DS ₃ link is performed by a DS ₃ unique format instead of cell-by-cell, it does not need to be considered when applying interleaving.

The interleaver 9 refers to a functional block that performs the same operation as that of FIG. 1 described above, and the de-interleaver 10 of FIG. 3 refers to a functional block that undergoes the reverse process of FIG. 1 described above. . That is, the interleaver 9 distributes the header bits in 10-bit intervals in the entire cell area and sequentially arranges data in the remaining sections. The deinterleaver 10 stores the header bits scattered in the entire cell area. It collects the data in the upper 5 byte section of the cell and places the remaining data bits in the lower 48 byte section of the cell.

In addition, when using header error correction (HEC) for cell boundary identification, all of the interface processes as shown in FIG. 3 are required. 3 illustrates a process for interfacing cell-based interleaving to a physical layer protocol, and the principle thereof will be described.

A 53-byte transmit cell 3 is created by adding a header error correction (HEC) to the 4-byte header and 48-byte data transmitted from the Asynchronous Transfer Layer (ATM) layer, and the interleaver for the 53-byte transmit cell 3 (9) interleaves 40 bits and stores in the cell buffer (4). A new header 5 is created by adding a virtual header error correction (V-HEC) to the first 52 bytes stored in the cell buffer 4.

On the other hand, there is a mixing process before transmission. The process is different for each physical layer protocol. In the cell-based case, the entire cell is mixed, and the virtual header error (V-HEC) after the mixing is obtained with the first 4 bytes of the virtual cell. Also, in case of synchronous digital hierarchy (SDH), headers are not mixed but only data are mixed. Therefore, virtual header error correction (V-HEC) is made before mixing, and is obtained with the first 4 bytes of a 52-byte virtual cell as in cell-based.

The receiver may identify the cell boundary by using the virtual header error correction (V-HEC), perform an error check of the header if necessary, and, if the cell boundary is found, de-mixing process (6). The demixing process is different for each physical layer as in transmission. That is, in the case of cell-based, the entire cell is demixed, and in the case of synchronous digital hierarchy (SDH), the header is not mixed but only the data is demixed. In this manner, 53 bytes of the transferred cell are stored in the cell buffer 7 after the reverse mixing process, and when 52 bytes arrive, the 53 bytes are taken from the upper part of the cell buffer 7 and decoded through the deinterleaver 10. Interleave to restore the original cell. The header of this restored cell is checked for errors using header error correction (HEC), and a receiving cell 8 having corrected the header error is created.

This process is based on similar synchronous digital hierarchy (PDH), synchronous digital hierarchy (SDH), and cell-based methods using interleaving while complying with ITU-T Recommendation I.432 physical layer protocol. Applicable to the physical layer.

On the other hand, in the process of applying the present invention to the physical layer requiring header error correction (HEC) in cell boundary identification, one additional cell per 52 cells is generated, but not only an increase of about 2% (1/52).

As described in detail above, the present invention provides a method of interleaving on a cell basis. Even if a burst error occurs by distributing header bits in all areas of a cell, only one error appears in the header. Complements header error correction (HEC), which is vulnerable to burst errors of more than two bits, requires fewer additional cells, and greatly improves cell loss rate when errors occur bursts.

In addition, compared to block interleaving, which blocks 12 cells and interleaves, it has a strong side against unexpected long bursts, has a low latency problem, and is in the process of interfacing with the physical layer. Since the 432 physical layer protocol is faithfully adhered, it can be applied to both synchronous digital layer structure (PDH) based, synchronous digital layer structure (SDH) based, and cell based physical layer.

In addition, the process of interfacing depends on the cell boundary identification method of the physical layer, and cell boundary identification using H ₄ in DS ₃ or synchronous digital hierarchical structure (SDH) where cell boundary identification is found as a frame-specific function. In this case, the interface process can be easily applied without the need for a separate interface process. Also, when using the header error correction (HEC) for cell boundary identification, the interface process as shown in FIG. 3 is required. This increases, but requires less overhead than other methods for improving cell loss rates.

The cell loss rate for the burst error in the present invention as described above is 14dB when the bit error rate (BER) is 10E-3 and 23.9dB when the bit error rate (BER) is 10E-4 based on the cell loss rate before interleaving. When the bit error rate (BER) is 10E-5, it improves by 33.9dB.

Claims (12)

Asynchronous transmission method (ATM) cell unit of the asynchronous transmission method characterized in that the interleaving is applied to the cell itself by interleaving and then transmitting, and receiving and rearranging the received signal at the receiving end of the cell unit Interleaving Transmission Method. The method of claim 1, wherein the interleaving is performed by arranging header bits of an asynchronous transmission (ATM) cell in an entire cell area at predetermined intervals. The method of claim 2, wherein the interleaving is performed by distributing 40 bits of the header of the asynchronous cell (ATM) cell by 1 bit at 10-bit intervals in 424 bits of the entire cell interval, and 384 bits of data are sequentially arranged in the remaining empty space. Cell-based interleaving transmission method of the asynchronous transmission method characterized in that made. The method of claim 1, wherein the cell-based interleaving transmission method is applied to a DS ₃ physical layer protocol of a pseudo-synchronous digital layer structure (PDH), and then transmitted according to the DS ₃ format after cell-based interleaving. . The synchronous digital layer structure (SDH) according to claim 1, wherein the lower 48 bytes of the cell are mixed by performing inter-cell interleaving after applying to a physical layer protocol using H ₄ to identify the cell boundary of the synchronous digital layer structure (SDH). A cell-based interleaving transmission method of the asynchronous transmission method characterized in that the transmission in the effective load interval. The method of claim 1, wherein the header error correction is applied to a 4-byte header and a 48-byte data transmitted by an asynchronous transmission method (ATM) layer by applying to a physical layer protocol using header error correction (HEC). And a 53-byte cell by adding HEC), interleaving the cell, creating a new cell, and transmitting the cell through a hybridization process. 7. The cell-based interleaving transmission method according to claim 6, wherein each interleaved bit is stored in a 105-byte cell buffer and processed. The method of claim 6, wherein the new cell is made by cutting an interleaved 53-byte cell into 52-byte units. The method of claim 6 or 8, wherein a virtual header error correction (V-HEC) is added to the new cell to identify the boundary of the new cell. 10. The method of claim 9, wherein the virtual header error correction (V-HEC) is obtained by adding the first 4 bytes of the virtual cell of 52 bytes. 7. The inter-cell interleaving transmission method according to claim 6, wherein the mixing process mixes the entire cell when it is cell-based. 7. The method of claim 6, wherein the mixing process mixes only the data without the headers when the synchronous digital hierarchy (SDH) is based.