RU71198U1 - MODEM - Google Patents

Abstract

The utility model relates to telecommunication technology and can be used, in particular, in data transmission systems providing duplex operation on switched and non-switched two-wire and four-pass telephone lines and physical connected lines. The aim of the proposed technical solution is to increase the efficiency of the modem by increasing the noise immunity to disturbing environmental factors and the most efficient use of the channel frequency band. The essence of the utility model contains an encoder, modulator, test signal generator, digital-to-analog converter, analog-to-digital converter, echo canceller, complex corrector, demodulator, interpolating filter, in-phase and quadrature shaping filters, carrier oscillator, phase shifter, functional converter, decoder with a decoding device, descrambler, a synchronization system with blocks of the carrier oscillation and clock oscillation, and a complex corrector, made in the form of long-term and short of adaptive filters and the corrector of the connecting line, as well as a block for storing error syndromes, a block for classifying errors and defects, a block for correcting defects, and a block for maintaining clock synchronization when the channel is broken. 4 IL

Description

The utility model relates to telecommunication technology and can be used, in particular, in data transmission systems providing duplex operation on switched and non-switched two-wire and four-wire telephone lines and physical connected lines.

Known two-wire duplex digital transmission system with time division according to patent No. 2037966, IPC ⁶ H04L 5/14, H04J 3/06, containing scrambler, transmission buffer memory unit, encoder, high-pass filter, transmission amplifier, keys, automatic gain control unit , variable corrector, correction amplifier, receiving high-pass filter, decision block, decoder, buffer memory block, descrambler, master oscillator, receiving frequency generation block, packet synchronization block, analysis block, balanced circuit, co transformer, low pass filter.

The disadvantage of this two-wire time-division duplex digital transmission system is the insufficient reliability of duplex operation on two-wire lines.

The closest (prototype) is a duplex modem according to patent No. 2177791 MPK ⁷ H04L 5/14, Н04В 3/00, containing an encoder, modulator, transmitter output unit, differential system,

input unit, test signal generator, control unit, echo canceller, harmonic detector, signal corrector, demodulator, decoder, switch, delay line, subtraction unit, carrier estimate unit, two averaging units, channel amplitude-frequency characteristic calculators, complex channel frequency response, impulse characteristics of the corrector, complex characteristics of the corrector, group deceleration of the channel, matched and corrective filters, the input unit of the receiver.

The prototype does not implement the function of an integrated corrector, which does not provide the required noise immunity. The implementation of the synchronization system does not allow long-term clock synchronization, which also does not provide the requirements for noise immunity.

Thus, a disadvantage of the known duplex modem is the lack of noise immunity due to the inability to track and correct channel parameters for a long time.

The aim of the proposed technical solution is to increase the efficiency of the modem by increasing the noise immunity to disturbing environmental factors and the most efficient use of the channel frequency band.

This is achieved by the fact that the modem containing the encoder, modulator. test signal generator, digital-to-analog converter, analog-to-digital converter, echo canceller, corrector, demodulator, including an interpolating filter connected to in-phase and quadrature shaping filters through a carrier oscillator, and a phase shifter associated with

a functional converter, a decoder containing a decoding device associated with a descrambler, a synchronization system with blocks of the carrier wave and clock oscillation introduced a complex corrector made in the form of long-term and short-term adaptive filters and a corrector for the connecting line connected to the interpolating filter, in-phase and quadrature shaping filters, a phase shifter and a decoder, wherein a block for storing error syndromes, a block for classifying errors and defects, a block and board defects and synchronization system is included in a block when preservation clock channel is broken.

To ensure operation on poor communication channels, a utility line corrector (KSL) is introduced in the utility model, which performs the function of compensating for the attenuation and skew of the amplitude-frequency characteristic of the signal introduced by the connecting lines. KSL is able to amplify the output signal by 20 dB and compensate for the distortion of the amplitude-frequency characteristic to 15 dB.

A short-term adaptive filter provides intersymbol distortion correction functions and uses a solution-driven tuning method, which provides continuous analysis and adjustment of the filter during operation. To implement this method, feedback from the output of the deciding device is implemented.

The long-term adaptive filter provides automatic control of gain and correction of slow changes in the frequency response of the channel associated with changes in the time of day, weather, and other factors.

Thus, there is a separation of functions of the adaptive filter in accordance with the tasks that it solves. This provides a simpler setup and implementation, as well as better performance compared to a single adaptive equalizer implementation. Due to the introduction of a complex corrector, the amplitude-frequency characteristics are compensated due to subscriber line attenuation and frequency response dips, automatic gain control and correction of slow changes in the frequency response of the channel, correction of intersymbol distortions.

Figure 1 shows the structural diagram of the proposed device, figure 2 presents a functional diagram, figure 3 is a structural diagram of a demodulator 22, figure 4 is a structural diagram of a decoder 23.

The structural diagram of the proposed device includes a digital signal processor 1 (DSP), external random access memory 2 (RAM), reprogrammable read-only memory 3 (EPROM), audio codec 4, programmable logic integrated circuit 5 (FPGA), differential system 6 (DS ), microcontroller 7 (MK), digital interfaces 8 (CI), analog interfaces 9, 10 (AI-2, AI-4), digital intercom interface 11 (CISS), power supply 12 (IP).

DSPC 1, is connected via FPGA 5 to a sound codec 4 connected to a differential system 6 connected to an analog interface 9, to a digital intercom interface 11 through a microcontroller 7. The sound codec 4 is interconnected with the analog AI-410 interface. EPROM 3 is associated with

microcontroller 7. microcontroller 7 is connected to RAM 2 and DSP 1 through FPGA 5.

FPGA 5 implements circuit logic and digital joints. C1-I, C2. FPGA 5 provides interaction and collaboration on common data buses and the address of DSPC 1, MK 7, RAM 2.

DSPC 1 programmatically implements modulation / demodulation, coding / decoding, echo cancellation, synchronization, scrambling / descrambling, data flow control and interaction with terminal equipment algorithms. The executable code and data are stored in the internal (fast) RAM of the DSP. External (slow) RAM 2 is intended for buffering data from the terminal equipment (OOD). In EPROM 3, the executable code of DSPC 1 of the control program-monitor is stored, as well as modem protocols, such as ITU-T V.21, ITU-T V.22 / V.22bis, ITU-T V.23, ITU-T V .32 / V.32bis, ITU-T V.26 / V.26ter / V.26bis fax protocols, ITU-T V.27 / V.27ter / V.27bis, ITU-T V.17, as well as specialized modem protocols ШС-126, АТ-3002М, АТ-3002М1. Implementation of specialized modem protocols in the modem provides the possibility of counter-operation with the corresponding products.

The audio codec 4 performs analog-to-digital and digital-to-analog conversion and digital filtering. The microcontroller 7 performs the functions of the initial testing and loading memory PCOS1.

Digital interfaces 8 implement the necessary set of interfaces for working with OOD both in synchronous and asynchronous joints. The logic of the digital joints is implemented in FPGA 5, physical

The interface is implemented using specialized microcircuits and matching transformers. The synchronous joint C1-I provides interaction with OOD via a physical four-wire line at speeds from 1.2 kBa / s to 64 kBa / s. Joint C2 (V.24 / RS-232) provides a mode of operation both in synchronous and in asynchronous mode at speeds from 1.2 kBa / s to 115.2 kBa / s. The modem is controlled by the asynchronous interface C2 with a standard set of “AT commands” (V.25ter). The mode (ACSD - asynchronous commands - synchronous data) of switching from the asynchronous joint C2 to the synchronous joint C2 at the time of establishing a connection is implemented. Transferring the modem to V.54 testing modes is possible both by commands and by installing specialized C2 interface circuits. The fax modem modem belongs to the 3rd group of ITU-T fax machines. Management commands and service messages satisfy the EIA Class 2 and 2.0 command system.

Analog interfaces 9 and 10 provide connection to the communication channel via 2 and 4 wire lines.

The digital intercom interface 11 serves to enable intercom with a remote subscriber. The interface provides the exchange of voice information according to the specification ITU-T G.711, A-law. The functions of establishing and maintaining official communications are provided by DSP 1.

Functionally, the modem contains: digital interfaces with OOD 13, 24 (reception and transmission, respectively); encoder 14; modulator 15; digital-to-analog converter 16; low-pass filter 17, 20; analog joint with 2 and 4 wire lines 18, 19 (transmission and reception, respectively); differential system 6 (in the mode

work with a 2-wire line); analog-to-digital Converter 21; echo canceller 27; demodulator 22; decoder 23; synchronization system 25; the generator of test signals 26. The key K1 provides the inclusion of the generator 26, the key K2 provides the inclusion of a 2 or 4-wire line.

The demodulator 22 (Fig. 3) contains an interpolating filter 29, a complex corrector 46, consisting of a corrector for a connecting line 30 (KSL) connected to an adaptive long-term filter 33 and an adaptive short-term filter 34 through in-phase 31 and quadrature 32 shaping filters, a carrier oscillator 28 , a phase shifter 35 connected to a decoder 23 and a functional converter 36 connected to a carrier oscillation synchronization system 37 and a clock oscillation synchronization unit 38-1 and a clock oscillation when the channel 38-2 is broken connected to the interpolation filter 29.

The decoder 23 contains (Fig. 4) an error syndrome decoder 39 connected to an error and classification classification unit 40 and an error syndrome memory unit 45, a random error correction unit 41 connected to a resolver 43 and a descrambler 44, a defect correction unit 42 connected to a unit for classifying errors and defects 40 and a unit for storing error syndromes 45 and connected to a resolver 43.

Encoder 14 and decoder 23 are intended for encoding and decoding of transmitted digital data, carried out in order to increase noise immunity and error correction.

In the modulator 15, the spectrum of the transmitted signal is formed and it is paired with the passband of the telephone channel (transfer of the spectrum to the frequency range 300-3400 Hz).

The echo canceller 27 generates near and far echo signals and delays and subtracts them from the linear signal.

In the demodulator 22, the signal is inversely converted from analog to digital.

The generator of test signals 26 and the complex corrector 46 perform the functions of preliminary testing the communication channel, adjust the shaping filter and provide correction of phase-frequency distortions at the stage of testing the channel and during the transmission of information.

Over time, channel characteristics change. In this case, both quick and long-term changes take place. A comprehensive corrector 46 is used to compensate for these changes.

The initial adjustment of the filter weights is carried out by the training sequence at the stage of establishing the connection. For ITU-T recommendations, the appropriate synchronization sequence defined in these recommendations is used as a training sequence.

The synchronization system 25 contains synchronization blocks of the carrier 37 and the oscillation clock 38-1, while the clock synchronization conservation unit 38-2 performs the additional function of maintaining the clock synchronization for 90 seconds when the channel is interrupted.

At the same time, parameters are stored and taken into account for a long time by the device for storing the syndromes of errors and defects 45.

The work of the proposed utility model is as follows: stage 1 - connection; stage 2 - setting the KCL parameters; stage 3 - synchronization; stage 4 - data transfer; stage 5 - disconnection.

Installation and disconnection is carried out in accordance with generally accepted rules.

In the setting mode of the KSL 30 parameters on the remote modem, the test signal generator 26 is turned on by the key K1 and a sequence of signals is supplied from it. The demodulator 22 receives a distorted and attenuated modem signal. The gain and weight coefficients of the filter KSL 30 are selected in such a way as to compensate for the attenuation and distortion of the amplitude-frequency characteristics of the connecting line.

In the synchronization and data transfer mode, the key K1 is switched to the modulator 15.

At the synchronization stage, a special synchronizing sequence defined in each modulation protocol is supplied to the input of the modulator 15. Based on this sequence, weights of adaptive filters 33 and 34 are adjusted. Also at this stage, parameters of the echo canceller 27 are adjusted.

At the data transfer stage, information from the digital interface 13 enters the encoder 14 and then the modulator 15. After passing through the digital-to-analog converter 16, the filter 17, the analog joint 18, the differential system 6 and the communication channel, the signal enters

remote modem receiver. Through the analog junction 19, the filter 20 and the analog-to-digital converter 21, the signal enters the echo canceller 27, where the echo signal is subtracted from the received signal. Next, the signal enters the demodulator 22 with a complex corrector 46, which provides compensation for amplitude-frequency distortion and changes made by the connecting line.

At the data transfer stage, a continuous analysis of the communication channel and adjustment of the parameters of the complex corrector 46 are performed.

Thus, through the use of a complex corrector and its introduction into the demodulator, the channel is pre-tuned and continuously monitored and the filter parameters are corrected, which provides an increase in the signal-to-noise ratio and, accordingly, increases the noise immunity as a whole.

Claims (1)

A modem comprising an encoder, a modulator, a test signal generator, a digital-to-analog converter, an analog-to-digital converter, an echo canceller, a corrector, a demodulator including an interpolating filter connected to in-phase and quadrature shaping filters through a carrier oscillator and a phase shifter associated with a functional converter, a decoder, comprising a decoding device associated with a descrambler, a synchronization system with blocks of a carrier wave and a clock wave, characterized in that in the demod a moderator was introduced a complex corrector made in the form of long-term and short-term adaptive filters and a corrector for a connecting line connected to an interpolating filter, in-phase and quadrature shaping filters, a phase shifter and a decoder, while a block of storing error syndromes, a block for classifying errors and defects, was introduced into the decoder, defect correction unit, and the clock synchronization block is included in the synchronization system when the channel is broken.