RU2426249C1 - Method of transmitting data over communication channel with fixed operating speed when messages arrive from source in random time instants - Google Patents

Abstract

FIELD: information technology.

SUBSTANCE: invention can be used in data transmission systems, primarily without a feedback channel, to match the varying speed of information coming from a source of messages with a fixed operating transmission speed in a communication channel when information comes from the source of messages in form of blocks of equal size but at random time instants. Information redundancy resulting from the difference in operating transmission speed in the channel and speed of data coming from the source of messages is almost completely spent on raising the degree of reliability message reception.

EFFECT: avoiding the need to use a feedback channel and introduction of a housekeeping instruction system.

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Description

The invention relates to communication technology and can be used in data transmission systems, mainly without a feedback channel, to coordinate the changing speed of information from the message source with a fixed technical transmission speed in the communication channel in cases where information comes from the message source in the form of blocks of the same size, but at random times.

When developing communication systems in which the information to be transmitted has the property of rapid aging, such as, for example, synchronous data transmission equipment, the problem arises of ensuring a minimum delay in the communication channel. If the message source continuously delivers data at a given speed, the data coming from the data source through the communication channel, in most existing systems, is carried out continuously at the same speed as they arrive, or if noise-resistant coding is used, with a correspondingly higher but also constant speed.

In the case when the data from the source arrives at random times, the problem arises of matching the data rate in the communication channel with the speed of data from the message source.

A known method of transmitting information with an improved message format [1]. In a multinodal data network via voice channels from each modem of the local station, the final part of the message is transmitted, before which user data, modem identifier and serial number (before each initial and checksum) are transmitted. The receiver’s measurement of the interval between successive message numbers transmitted from a particular modem is used to accurately calculate the message rate of this modem.

The disadvantage of this method is the operational change of the technical transmission speed in the channel, which requires a feedback channel and the introduction of information redundancy for the exchange of service commands.

The prototype of the proposed method is a method of transmitting data over a communication channel [2], which consists in the fact that data packets are transmitted over the communication channel at random times, as they arrive from the message source. In the intervals between messages, information is not transmitted over the communication channel. In this case, to receive each message, it is necessary to re-solve the problem of detecting a signal, establishing clock synchronization, which is responsible for determining the time boundaries for each elementary parcel, and the task of establishing cyclic synchronization, which is used to determine the beginning of the content part in a message, for which a certain type of message is transmitted before the message sync sequences. If the data from the message source comes in blocks of different sizes, additional commands are entered to determine the boundaries of the useful information. At the same time, the technical transmission rate in the channel is initially set based on the maximum intensity of data input from the source, taking into account the redundancy added to the data packets. An example is the method of transmitting data in the Binary Synchronous Communications (BSC) format, in which each channel block consists of a clock sequence (PAD), two cyclic sequences (SYN), a start header symbol (SOH), a header containing various service commands (OH), the start of text character (STX), the text with data received from the message source (TX), and the end of text character (ETX).

The disadvantage of the prototype is that for the possibility of separation on the receiving side of the useful information from the entire stream of received data on the transmitting side, it is necessary to introduce additional service sequences to indicate the beginning and end for each block with useful information.

This goal is achieved by the fact that in the proposed method, on the transmitting side, the number of information blocks arriving from the message source is calculated at a predetermined time interval corresponding to the duration of the channel block, and then the received blocks are collected into a single data array for which a cyclic control sum (CRC), and the data array with CRC is encoded by an error-correcting code, the redundancy and corrective power of which is higher, the smaller the information block c is contained in the generated array, while the generated channel data block is modulated, passes through the communication channel and, on the receiving side, after demodulation, it enters the decoding device, where the decoding operation is performed for all possible codes, depending on the possible number of source information blocks, and for all decoding implementations, the data is divided into information blocks and the CRC is calculated, if, for some of the decoding options, the control If the sum is the same, then the information blocks received from this decoding option are transmitted to the message receiver, if the checksums do not match for all the options, the information is not transmitted to the message receiver, and this operation is performed cyclically for each time interval corresponding to the channel length block.

The proposed method of data transmission does not require a reverse communication channel for adaptation according to the data transfer rate, and also does not require the introduction of redundancy associated with the transmission of service commands to change the demodulator operating mode or the introduction of sequences indicating the beginning or end of the information part in the message.

The drawing shows a structural diagram of a method of transmitting data.

It contains: 1 - a source of information; 2 - memory module; 3 - timer counter packets; 4 - device add CRC; 5 - an encoding device consisting of a generator and encoders; 6 - modulator; 7 - communication channel; 8 - demodulator; 9 - a device for establishing and holding cyclic synchronization; 10 - memory module; 11 is a decoding device consisting of decoders; 12 — CRC verification device; 13 - information receiver.

Suppose that from a source of information at random times, data packets of a fixed length of K bits are received. For a given packet length, a set of M error-correcting codes with parameters (N, K _m ) is selected, where:

N is the number of data bits received from the output of the encoder;

K _m - the number of source data bits at the input of the encoder,

K _m = K · m + C, m = 1 ... M;

C is the number of bits allocated for the cyclic checksum.

The length of the code block N is selected from the relation N> K · M + C. The time of information accumulation T is defined as the minimum time for which M packets of data can arrive from the information source. The required technical speed in the communication channel is defined as V = N / T.

Data packets of size K bits coming from information source 1 are stored in memory module 2. Packet timer 3 generates time segments of duration T, and also records the arrival of each data packet and counts the number of packets m received from information source 1 during time period T.

In the event that, at the end of the time interval T, the number of packets m> 0, then the packet timer 3 sends a signal to memory module 2 to transmit a data block of m packets accumulated over time period T to the CRC 4 add-on device, where a data block of K · m bits is formed and a cyclic checksum of size C bits is added. To calculate the cyclic sum, it is proposed to use the widespread algorithm that uses the cyclic redundancy code - Cyclic Redundancy Code (CRC), which is a highly efficient error detection tool that allows you to determine whether data is distorted by the cyclic checksum both when one or more bits are distorted in the information sequence .

The data block thus formed from K · m + C bits goes to the encoding device 5, where for it, depending on the value of m received from the timer counter of packets 3, the corresponding encoding algorithm is launched, as a result of which a closed cyclic checksum is formed and is noise-resistant code channel data block size N bits. The data packets transmitted to the encoding device 5 are deleted from the memory module 2, and the packet timer 3 counter is reset and starts to count again the number of incoming data packets for the next time interval T.

If during the time interval T no data packets were received, i.e. m = 0, then the encoding device 5 generates some pseudo-random sequence (PSP) of N bits, indicating the absence of useful information, which serves to maintain cyclic synchronization on the receiving side in the absence of information from the message source.

Thus formed channel data block or SRP size N bits is fed to the modulator 6, after which the analog signal generated by the modulator 6 is fed into the communication channel 7.

At the receiving side, the analog signal from the communication channel 7 is supplied to the demodulator 8. It is assumed that earlier, in the process of organizing the communication session, the cyclic synchronization responsible for determining the data stream of the beginning of arrival of the next channel block of length N bits. The data coming from the demodulator 8 is accumulated in the memory module 10. As soon as the cyclic synchronization signal corresponding to the completion of the reception of the channel data block with a length of N bits is received from the output of the device for establishing and holding cyclic synchronization 9, this data block is sent to the decoding device 11, and the memory module 10 is cleared and will begin to accumulate data for the next channel block. In the decoding device 11, M operations are performed for decoding the received information of size N bits in accordance with the decoding algorithm for each of the M used codes.

From the output of the decoding device 11, all M obtained as a result of decoding sequences of size K · m + C bits each, where m takes values from 1 to M, are simultaneously sent to the verification device according to CRC 12, where each of them is divided into m packets data of size K bits each, and a cyclic checksum of C bits, and then a CRC check is performed. If for one of the M variants of the received sequences of size K · m bits, the CRC check does not reveal any distortions, then m data packets of size K bits each corresponding to this option are transmitted to the information receiver 13. If the check detects CRC errors in all M options, the data is not transmitted to the information receiver 13.

The additional delay in transmitting information blocks from the correspondent to the subscriber due to data storage operations corresponds to T _D ≤2 · T.

A method of transmitting data over a communication channel can be used in data acquisition and transmission systems using asynchronous information sources and non-adaptive communication channels.

A positive result of the method is the lack of the need to use the feedback channel and the introduction of a system of service commands both for adaptive changes during the communication session of the operating modes of the modulator - demodulator, and for indicating the boundaries of blocks with useful information. The information redundancy generated due to the difference in the technical transmission rate in the channel and the data arrival rate from the message source is almost completely spent on increasing the degree of reliability of message reception.

Information sources

1. Patent EPO (EP) No. 890705, cl. H04L 11/00.

2. Sipser R. Communication architecture in distributed systems (translation into Russian). Moscow, Mir, 1981, v. 1, v. 2. (see vol. 1, p. 386).

Claims (1)

A method of transmitting data at a fixed speed, consisting in the fact that at random times, data packets of a fixed length of K bits are received from the source, characterized in that a set of M error-correcting codes with parameters (N, K _m), where N - number of data bits received from the output of the encoder, K _m - number of source data bit on the input of the encoder, the data size K stored in the memory module, and the timer-counter performs packet formation temporal x segments of duration T, captures the arrival of each data packet and counts the number of packets t coming from the information source over a period of time T, for a data block of K · m bits, a cyclic checksum of size C bits is generated and added, and the data block thus formed from K · m + C, the bit goes to the encoding device, where for it, depending on the value of m received from the packet timer-counter, the corresponding encoding algorithm is launched, while the generated channel data block modulate, the analog signal enters the communication channel, the incoming demodulated data is stored in memory, and after the reception of the channel data block of length N is decoded, M performs decoding operations of the received channel data block of size N bits in accordance with the decoding algorithm for each of the M noise-resistant codes, all M received as a result of decoding sequences of size K · m + C bits each, where m takes a value from 1 to M, simultaneously arrive at the device CRC checks, where each of them is divided into m data packets of size K bits each and a cyclic checksum of C bits, and then CRC checks are performed, and the data accumulation operation is performed cyclically for each time interval corresponding to the channel length block.

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