CN101179356A - Data transmitting, receiving method and device - Google Patents
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Abstract
A method and a device for transmitting and receiving data are provided. The method comprises the following steps: A: data to be transmitted are interleaved after being divided, randomized and conducted forward error correction coding on the transmitting terminal. B: QAM maps the interleaved data into corresponding QAM constellation points according to the sub-channel bit and energy distribution parameter. C: after the QAM mapping treatment, the data are generated into frequency field data frame, which are then conducted IFFT transformation and generated into OFDM signals. D: insert cyclic prefix into the OFDM signals, which are then generated into baseband analog signals after digital to analog conversion; the baseband analog signals are transmitted to the receiving terminal in the service sub-channel of the logging cable. By adopting the method and device of the invention, data transmission rate in present logging cable is greatly improved, which in turn meets requirements of the large data amount transmission of under-well instruments.
Description
Technical Field
The invention relates to a data transmitting and receiving method and device, in particular to a data transmitting and receiving method and device for a logging cable.
Background
Logging systems typically include two parts, a surface facility (surface end facility) and a downhole tool (downhole end facility), which are connected by a wireline. The underground instrument needs to transmit acquired data to ground equipment through a logging cable; the surface equipment also needs to transmit data such as control commands to downhole tools.
Logging operations began in the twenties to the thirty of the 20 th century, and logging systems have undergone a transition from analog to digital. It has now progressed to the fifth generation imaging logging stage. With the development of logging instruments, the demand for data transmission rates has increased.
In order to meet the demand for ever-increasing data transmission rates, a large number of researchers have studied well logging transmission techniques. In the sixties, analog modulation modes such as frequency modulation and amplitude modulation are basically adopted to transmit analog quantity, the transmitted data quantity is small, and the transmission rate is low. In the eighties, the logging transmission technology began to adopt a large number of digital modulation modes, but the data transmission rate still cannot meet the requirements.
For example, the company atlas developed a 3502 PCM (pulse code Modulation) modulator in the mid eighties, with a transmission rate of only 7.5 kbps. Then, the modem technology of the company starts to adopt the manchester coding mode, and the transmission rate is increased to 93.35kbps (model number WTC 3510).
Schlumberger has used Phase Shift Keying (PSK) modulation to transmit data. Before the mid eighties, two models of digital transmission nipples, namely CCS and CTS, were developed, wherein the transmission rate of CCS is 80kbps, and the transmission rate of CTS is 100 kbps. Both CCS and CTS use BPSK (Binary Phase Shift Keying) modulation technique. In the nineties, an imaging logging system with the model number of MAX-500 was developed for the first time, wherein 500 in the MAX-500 represents that the uplink transmission rate of the telemetry system data can reach 500 kb/s. A telemetry system of the Schlumberger company is called a DTS digital telemetry system, adopts a QAM (Quadrature amplitude modulation) technology, can reach a data transmission rate of 500kbps, and can basically meet the requirement of information quantity transmission of an imaging measuring instrument. In the imaging logging system EXCELL-2000, introduced by Haributton corporation, its telemetry system (model DITS) uses modulated binary code transmission at an upload rate of 217.6 kbps. In an imaging logging system with the model of ECLIPS-2000, which is introduced by Beck-Atlas, a remote transmission system (with the model of WTC) adopts Manchester code transmission, and the uploading speed is 230 kbps.
However, with the higher real-time requirement of modern logging systems, the more data volume needs to be transmitted between surface equipment and downhole instruments, and the transmission rate of the existing logging systems cannot meet the requirement.
Disclosure of Invention
The technical problem to be solved by the invention is to overcome the defects of the prior art and provide a high-speed data transmitting and receiving method and device for a logging cable.
In order to solve the above problems, the present invention provides a data transmission method applied to a logging communication system including a transmitting end and a receiving end connected by a logging cable, the method comprising the steps of:
a: the data to be transmitted is subjected to interleaving processing after being subjected to segmentation, randomization and forward error correction coding at the transmitting end;
b: carrying out QAM mapping processing on the data after the interleaving processing according to the sub-channel bit and the energy distribution parameter to map the data into corresponding QAM constellation points;
c: generating a frequency domain data frame by using the data subjected to QAM mapping processing, and performing IFFT (inverse fast Fourier transform) on the frequency domain data frame to generate an OFDM (orthogonal frequency division multiplexing) signal;
d: and inserting a cyclic prefix into the OFDM signal, performing digital-to-analog conversion to generate a baseband analog signal, and transmitting the baseband analog signal to the receiving end in a service sub-channel of the logging cable.
In addition, the step a further comprises the following steps: and the transmitting end and the receiving end carry out channel initialization and determine bit and energy distribution parameters of the sub-channels.
In addition, the step a further comprises the following steps: determining OFDM basic parameters according to the transmission characteristics of the logging cable channel; the OFDM basic parameters comprise: subchannel interval, total number of subchannels, effective symbol time, guard interval time, and FFT processing bandwidth.
Further, the subchannel interval is 1.220703125 kHz; the total number of subchannels is 256; the valid symbol time is 819.2 us; the guard interval time is 204.8 us; the FFT processing bandwidth is 312.5 kHz.
In addition, among the 256 subchannels, n1 th subchannel through n1+ m1 th subchannel from low frequency to high frequency are used as an uplink subchannel; using the (n) 1+ m2 th sub-channel to the 256 th sub-channel from low frequency to high frequency as a downlink sub-channel;
wherein n1, m1 and m2 are positive integers, and n1 is more than or equal to 3 and less than or equal to 7; m2-m1 is more than or equal to 3 and less than or equal to 7; n1+ m2 < 256;
the data transmission direction of the uplink sub-channel is from the underground end to the ground end of the logging communication system; and the data transmission direction of the downlink sub-channel is from the ground end to the underground end of the logging communication system.
In addition, 1 subchannel is selected as a pilot channel from the uplink subchannel and/or the downlink subchannel; the pilot signal transmitted by the pilot channel is a sine wave.
In addition, 1 first synchronization signal SYNC is inserted every 128 OFDM symbols, and 1 second synchronization signal SYNC is inserted between the 64 th and 65 th OFDM symbols of the 128 OFDM symbols
SYNC and
are signals that are in opposite phase.
In addition, the SYNC is formed by BPSK modulation by PRBS, and the mapping rule of a BPSK constellation is 1 → -1, 0 → + 1; the generator polynomial of the PRBS is: x is the number of8+x6+x5+x4+1。
In addition, in the step A,
dividing the data to be transmitted into data packets with the length of 112 bytes;
the randomization is a modulo-2 addition of the 112 byte long data packet using a PRBS sequence; the generator polynomial of the PRBS sequence isx15+x14+1；
The forward error correction coding adopts RS codes; the RS algorithm adopts a parameter with error correction capability t being 8; total data length 128; the field generating polynomial of the RS code is: p (x) x8+x4+x3+x2+ 1; the code generator polynomial of the RS code is:
g(x)＝(x+λ0)(x+λ1)(x+λ2)...(x+λ15)＝g16x16+…+g1x+g0；
the interleaving processing adopts the parameters as follows: and the interleaving width I is 8, and the interleaving depth M is 16.
The invention also provides a data receiving method, which is applied to a logging communication system comprising a sending end and a receiving end which are connected through a logging cable, and is characterized by comprising the following steps:
a) the receiving end carries out analog-to-digital conversion sampling on the baseband analog signal, then carries out time domain equalization and synchronous correction processing to remove a time guard interval and then outputs the baseband analog signal;
b) performing FFT (fast Fourier transform) on data output after the time protection interval is removed through synchronous correction processing, and then performing frequency domain equalization processing;
c) carrying out QAM demapping on the data after the frequency domain equalization processing according to the sub-channel bit and the energy distribution parameter;
d) and performing de-interleaving and RS decoding on the data output after QAM de-mapping and then performing de-randomization to obtain original user data.
In addition, the step a) also comprises the following steps before: and the transmitting end and the receiving end carry out channel initialization and determine bit and energy distribution parameters of the sub-channels.
In addition, the step a) also comprises the following steps before: determining OFDM basic parameters according to the transmission characteristics of the logging cable channel; the OFDM basic parameters comprise:
subchannel interval, total number of subchannels, effective symbol time, guard interval time, and FFT processing bandwidth.
Further, the subchannel interval is 1.220703125 kHz; the total number of subchannels is 256; the valid symbol time is 819.2 us; the guard interval time is 204.8 us; the FFT processing bandwidth is 312.5 kHz.
In addition, the time domain equalizer coefficient obtained in the channel initialization stage is adopted to carry out the time domain equalization; the time domain equalization enables the time delay expansion caused by channel impulse response to fall within the time protection interval range;
the synchronization correction is carried out by adopting the synchronization information obtained in the channel initialization stage;
performing the frequency domain equalization by using the frequency domain equalizer coefficient obtained in the channel initialization stage;
performing the de-interleaving by adopting a convolution de-interleaving method with parameters of interleaving width I being 8 and interleaving depth M being 16;
the RS decoding adopts the following parameters: the error correction capability t is 8; total data length 128; the original length of the data is 112;
the field generator polynomial of the RS code adopted by the RS decoding is as follows: p (x) x8+x4+x3+x2+1；
The code generator polynomial of the RS code is:
g(x)＝(x+λ0)(x+λ2)(x+λ2)...(x+λ15)＝g16x16+…+g1x+g0。
the invention also provides a data sending device which is connected with the receiving device through the logging cable; the transmitting device is provided with a modulator; the modulator comprises a randomization unit, an RS coding unit, an interleaving unit and a DAC; characterized in that said modulator further comprises: a QAM mapping unit; wherein:
the QAM mapping unit is used for randomizing the randomizing unit according to the subchannel bit and energy distribution parameters, the RS encoding unit performs forward error correction encoding, the data interleaved by the interleaving unit performs QAM mapping processing, and the data is output after being mapped into corresponding QAM constellation points;
the frequency domain framing unit is used for outputting the generated frequency domain data frame output by the QAM mapping unit;
the IFFT unit is used for carrying out IFFT transformation on the frequency domain data frame to generate OFDM signals and then outputting the OFDM signals;
the guard interval insertion unit is used for inserting a cyclic prefix into the OFDM signal, then sending the OFDM signal into the DAC for digital-to-analog conversion to generate a baseband analog signal, and sending the baseband analog signal to the receiving device in a service sub-channel of the logging cable.
Further, the modulator transmits data using the following parameters: the subchannel interval is 1.220703125 kHz; the total number of subchannels is 256; the valid symbol time is 819.2 us; the guard interval time is 204.8 us; the FFT processing bandwidth is 312.5 kHz.
In addition, among the 256 subchannels, n1 th subchannel through n1+ m1 th subchannel from low frequency to high frequency are used as an uplink subchannel; using the (n) 1+ m2 th sub-channel to the 256 th sub-channel from low frequency to high frequency as a downlink sub-channel;
wherein n1, m1 and m2 are positive integers, and n1 is more than or equal to 3 and less than or equal to 7; m2-m1 is more than or equal to 3 and less than or equal to 7; n1+ m2 < 256;
the data transmission direction of the uplink sub-channel is from the underground end to the ground end of the logging communication system; and the data transmission direction of the downlink sub-channel is from the ground end to the underground end of the logging communication system.
In addition, the modulator transmits a pilot signal in 1 subchannel of the uplink subchannel or the downlink subchannel, and the pilot signal is a sine wave.
In addition, the modulator inserts 1 first synchronization signal SYNC every 128 OFDM symbols and 1 second synchronization signal SYNC between the 64 th and 65 th OFDM symbols of the 128 OFDM symbols
SYNC and
are signals that are in opposite phase.
In addition, the SYNC is formed by BPSK modulation by PRBS, and the mapping rule of a BPSK constellation is 1 → -1, 0 → + 1; the generator polynomial of the PRBS is: x is the number of8+x6+x5+x4+1。
The invention also provides a data receiving device which is connected with the transmitting device through the logging cable; the transmitting device is provided with a demodulator; the demodulator comprises: ADC, time domain equalizing unit, synchronous correcting unit; wherein said demodulator further comprises: the device comprises an FFT unit, a frequency domain balancing unit, a QAM demapping unit, a deinterleaving unit, an RS decoding unit and a derandomizing unit; wherein:
the FFT unit is used for carrying out time domain equalization on the data which is subjected to analog-to-digital conversion sampling by the ADC and is output after time domain equalization by the time domain equalization unit and synchronous correction processing by the synchronous correction unit and time protection interval removal, and carrying out FFT conversion on the data;
the frequency domain equalizing unit is used for carrying out frequency domain equalizing processing on the data output by the FFT unit and then outputting the data;
the QAM demapping unit is used for carrying out QAM demapping on the data output by the frequency domain balancing unit according to the subchannel bits and the energy distribution parameters;
the de-interleaving unit is used for de-interleaving the data output by the QAM de-mapping unit and then outputting the data;
the RS decoding unit is used for carrying out RS decoding processing on the data output by the de-interleaving unit and then outputting the data;
and the derandomizing unit is used for derandomizing the data output by the RS decoding unit to obtain the original user data.
Further, the demodulator performs reception of data using the following parameters: the subchannel interval is 1.220703125 kHz; the total number of subchannels is 256; the valid symbol time is 819.2 us; the guard interval time is 204.8 us; the FFT processing bandwidth is 312.5 kHz.
In addition, among the 256 subchannels, n1 th subchannel through n1+ m1 th subchannel from low frequency to high frequency are used as an uplink subchannel; using the (n) 1+ m2 th sub-channel to the 256 th sub-channel from low frequency to high frequency as a downlink sub-channel;
wherein n1, m1 and m2 are positive integers, and n1 is more than or equal to 3 and less than or equal to 7; m2-m1 is more than or equal to 3 and less than or equal to 7; n1+ m2 < 256;
the data transmission direction of the uplink sub-channel is from the underground end to the ground end of the logging communication system; and the data transmission direction of the downlink sub-channel is from the ground end to the underground end of the logging communication system.
In addition, the demodulator receives a pilot signal in 1 subchannel of the uplink subchannel or the downlink subchannel, and the pilot signal is a sine wave.
Furthermore, the demodulator receives 1 first synchronization signal SYNC every 128 OFDM symbols and 1 second synchronization signal SYNC between the 64 th and 65 th of the 128 OFDM symbolsSYNC andare signals that are in opposite phase.
In addition, the SYNC is formed by BPSK modulation by PRBS, and the mapping rule of a BPSK constellation is 1 → -1, 0 → + 1; the generator polynomial of the PRBS is: x is the number of8+x6+x5+x4+1。
In summary, the data transmission rate is greatly improved on the existing logging cable by adopting the OFDM-based data transmitting and receiving method and device, and the transmission requirement of large data volume of the underground instrument is met.
Drawings
FIG. 1 is a schematic diagram of a logging system configuration employing the channel initialization and data transmission method of the present invention;
FIG. 2 is a schematic diagram of channel division according to OFDM basic parameters corresponding to a logging cable;
FIG. 3 is a flow chart of a channel initialization method for a wireline according to an embodiment of the present invention;
fig. 4 is a schematic system diagram of a modulator in a data transmission apparatus according to an embodiment of the present invention;
fig. 5 is a flowchart of a modulation method in a data transmission method according to an embodiment of the present invention;
fig. 6 is a diagram illustrating a superframe structure formed by a data transmission method according to an embodiment of the present invention;
fig. 7 is a schematic system diagram of a demodulator in the data transmission apparatus according to the embodiment of the present invention;
fig. 8 is a flowchart of a data transmission demodulation method according to an embodiment of the present invention.
Detailed Description
The basic idea of the present invention is to apply a multi-carrier technology, especially an OFDM (Orthogonal Frequency Division Multiplexing) technology, to data transmission of a logging cable in order to improve the data transmission rate.
The multi-carrier technology is to realize parallel data transmission and multi-channel data transmission by Frequency Division Multiplexing (FDM) of overlapping frequency spectrums, etc. to increase the transmission rate of data. Therein, the FDM scheme is typically implemented using a Discrete Fourier Transform (DFT).
Among the various FDM techniques, the OFDM technique based on the multi-carrier scheme is one of the most promising modulation and demodulation techniques in the field of communication technology. The OFDM divides the information code stream with high speed into a plurality of low speed code streams, and carries out parallel transmission on a group of orthogonal sub-channels. The use of OFDM techniques can extend the width of the subchannel transmission symbols, thereby greatly simplifying the design of the equalizer in the receiver. Meanwhile, the OFDM technology adopts a time guard interval (TGI for short) to effectively remove intersymbol interference (ISI for short), and overcomes the channel time delay expansion smaller than the TGI. On the other hand, by utilizing the orthogonality among the subcarriers, the OFDM technology effectively improves the frequency spectrum utilization rate. Compared with the traditional single carrier technology, the OFDM has higher spectrum utilization rate, the spectrum utilization rate approaches to Nyquist limit along with the increase of the number of sub-channels, and adaptive bit and energy (power) distribution can be carried out according to the transmission condition of each sub-channel so as to fully utilize the channel capacity and improve the transmission rate.
The present invention will be described in detail below with reference to the drawings and examples.
FIG. 1 is a schematic diagram of a logging system architecture employing the channel initialization and data transmission method of the present invention. As shown in fig. 1, the system comprises: the system comprises a ground end, a downhole end and a logging cable connecting the ground end and the downhole end.
The ground terminal includes: the system comprises a ground terminal, a ground terminal interface, a Coded Orthogonal Frequency Division Multiplexing (COFDM) modulator B, a COFDM demodulator B and a ground cable interface.
The downhole end comprises: the device comprises a downhole instrument, a downhole instrument interface, a COFDM modulator A, a COFDM demodulator A and a downhole cable interface.
And the ground terminal is connected with the COFDM modulator B and the COFDM demodulator B through a ground terminal interface and used for sending and receiving data.
And the COFDM modulator B receives data to be sent from a ground terminal interface, and after modulation, the data is carried on the logging cable through a ground cable interface and sent to the downhole end.
And the COFDM demodulator B receives data sent by the downhole end carried on the logging cable through a ground cable interface, and sends the demodulated data to a ground terminal through a ground terminal interface.
The COFDM modulator B and the COFDM demodulator B may directly perform data interaction. COFDM modulator B and COFDM demodulator B may be referred to collectively as COFDM modem B.
The downhole instrument is connected with the COFDM modulator A and the COFDM demodulator A through a downhole instrument interface and sends and receives data.
The COFDM modulator A receives data to be sent from an underground instrument interface, and the data to be sent is carried on a logging cable through an underground cable interface after modulation and is sent to a ground end.
The COFDM demodulator A receives data sent by a ground end carried on a logging cable through an underground cable interface, and sends the data to an underground instrument through an underground instrument interface after demodulation.
Similarly, COFDM modulator a and COFDM demodulator a may interact directly. COFDM modulator a and COFDM demodulator a may also be referred to collectively as COFDM modem a.
Wireline cables typically employ armored wireline cables. According to the data transmission method based on the OFDM, part of OFDM system parameters are determined according to the transmission characteristics of an armored logging cable channel.
Taking 7000 m armored logging cable as an example, the following OFDM basic parameters can be determined according to the transmission characteristics of the cable channel:
the Up channel (Up Link, downhole to surface) contains the total number of available sub-channels: 195;
the downlink channel (Down Link, surface to downhole) contains the total number of available sub-channels: 7 pieces of the Chinese herbal medicines are used.
And on the armored logging cable, carrying out channel division according to the OFDM basic parameters. FIG. 2 is a schematic diagram of channel division according to OFDM basic parameters corresponding to a logging cable. As shown in figure 2 of the drawings, in which,
The pilot signal transmitted on the pilot subchannel is a sine wave and is used for clock synchronization between the transmitting end and the receiving end.
The data transmission method of the invention comprises the following steps: a channel initialization phase and a data transmission phase.
It needs to be done in the channel initialization phase: communication link establishment, transmit power control, receiving AGC parameters, clock synchronization, symbol synchronization, frame synchronization, time domain equalizer training, frequency domain equalizer training, subchannel performance estimation, subchannel bit allocation, and energy allocation.
FIG. 3 is a flow chart of a channel initialization method for a wireline according to an embodiment of the present invention. As shown in fig. 3, the method comprises the following steps:
101: the COFDM modulator A sends a training sequence 0 to a COFDM modem B;
the signal corresponding to the training sequence 0 is formed by BPSK modulation by a PRBS (pseudo random binary sequence), and the mapping rule of the BPSK constellation is 1 → -1, 0 → + 1. The generator polynomial of the PRBS is: x is the number of8+x6+x5+x4+1。
102: after receiving the training sequence 0, the COFDM modem B completes channel activation, multi-carrier clock synchronization, multi-carrier symbol synchronization, multi-carrier frame synchronization, AGC parameter setting, transmission power adjustment, training of a time domain equalizer and a frequency domain equalizer.
Through AGC parameter setting, the COFDM demodulator B controls AGC to be at an optimal receiving level; through the synchronization of multi-carrier symbols, the COFDM demodulator B adjusts the FFT window to the optimal position, so that the received signal has no interference among sub-channels; through the training of the time domain equalizer and the frequency domain equalizer, the COFDM demodulator B obtains the equalization coefficients of the time domain equalizer and the frequency domain equalizer, and prepares for subsequent training sequences and data transmission.
By calculating the channel attenuation, the COFDM modulator B performs power adjustment to optimize the transmission power.
103: the COFDM modulator B sends a training sequence 0 to the COFDM modem A;
the training sequence 0 is generated in the same manner as in step 101.
Similarly, the training sequence 0 may be transmitted using all the subchannels of the downlink channel, or may be transmitted using one or more subchannels of the downlink channel.
104: after receiving the training sequence 0, the COFDM modem a completes channel activation, multi-carrier clock synchronization, multi-carrier symbol synchronization, multi-carrier frame synchronization, AGC parameter setting, channel response estimation, transmission power adjustment, time domain equalizer and frequency domain equalizer training.
Through AGC parameter setting, the COFDM demodulator A controls AGC at an optimal receiving level; through the synchronization of multi-carrier symbols, the COFDM demodulator A adjusts an FFT window to an optimal position, so that the received signal has no interference among sub-channels; through the training of the time domain equalizer and the frequency domain equalizer, the COFDM demodulator A obtains the equalization coefficients of the time domain equalizer and the frequency domain equalizer, and prepares for subsequent training sequences and data transmission.
The channel attenuation is calculated through channel response estimation, and the COFDM modulator A adjusts the power to enable the sending power to reach the optimal state.
105: COFDM modem a sends an ACK (ACKnowledgement) sequence 0 to COFDM modem B;
by sending ACK sequence 0, COFDM modem B knows that COFDM modem a has completed receiving training sequence 0 and the corresponding settings, and may proceed to the next phase.
106: the COFDM modem B sends an ACK sequence 0 to the COFDM modem A;
by sending ACK sequence 0, COFDM modem a knows that COFDM modem B has completed receiving training sequence 0 and the corresponding setup, and can proceed to the next phase.
The ACK sequence 0 is generated in the same manner as in step 105.
107: the COFDM modulator A sends a training sequence 1 to a COFDM modem B;
108: after receiving the training sequence 1, the COFDM modem B performs sub-channel SNR (Signal to Noise Ratio) estimation according to the training sequence, and performs bit and energy allocation on each sub-channel according to the estimated SNR value.
And in the subsequent data transmission stage, determining which constellation each subchannel is modulated by according to the bit and energy distribution result of the subchannel and how much power each subchannel is transmitted.
In this embodiment, the range of bit allocation for each subchannel: 0 to 10 bits.
109: the COFDM modulator B sends a training sequence 1 to the COFDM modem A;
110: after receiving the training sequence 1, the COFDM modem a performs subchannel SNR estimation according to the training sequence, and performs bit and energy allocation on each subchannel according to the estimated SNR value.
Similarly, in the subsequent data transmission stage, it is determined what constellation each subchannel is modulated with and how much power each subchannel is transmitted with according to the above subchannel bit and energy allocation results.
111: the COFDM modem A sends an ACK sequence 1 to a COFDM modem B;
by sending ACK sequence 1, COFDM modem B knows that COFDM modem a has completed receiving training sequence 1 and the corresponding settings, and may proceed to the next phase.
The ACK sequence 1 in this step is the same as the ACK sequence 0.
112: the COFDM modem B sends an ACK sequence 1 to the COFDM modem A;
by sending ACK sequence 1, COFDM modem a knows that COFDM modem B has completed receiving training sequence 1 and the corresponding setup, and can proceed to the next phase.
The ACK sequence 1 in this step is the same as the ACK sequence 0.
113: the COFDM modem A sends system information to a COFDM modem B;
the system information includes: subchannel bit allocation information and subchannel energy allocation information.
The system information is transmitted by using one or more sub-channels of an uplink channel in a QPSK modulation mode.
In this embodiment, the system information is transmitted using 4 subchannels of the lowest frequency (good channel condition) of the uplink channel to improve reliability.
114: the COFDM modem B sends system information to the COFDM modem A;
similarly, the system information includes: subchannel bit allocation information and subchannel energy allocation information.
The system information is transmitted by using one or more sub-channels of a downlink channel in a QPSK modulation mode.
In this embodiment, the system information is transmitted using 4 subchannels of the lowest frequency (good channel condition) of the downlink channel to improve reliability.
115: the COFDM modem A sends an ACK sequence 2 to a COFDM modem B;
by sending ACK sequence 2, COFDM modem B knows that COFDM modem a has completed receiving system information and corresponding setting, and can enter a data transmission phase.
116: the COFDM modem B sends an ACK sequence 2 to the COFDM modem A;
by sending ACK sequence 2, COFDM modem a knows that COFDM modem B has completed receiving system information and setting accordingly, and can enter a data transmission phase.
From the above, the present invention completes the setting of each communication parameter through the transmission of 2 training sequences; that is, the setting of the parameters is performed in two stages, and the setting of the parameters in the second stage may refer to the result of the setting of the parameters in the first stage. In this way, the communication parameters can be set more accurately.
In the data transmission stage, data to be transmitted is modulated by a modulator of a transmitting end and then transmitted to a demodulator of a receiving end; the receiving end identifies and receives the modulation signal, demodulates the modulation signal by the demodulator and transmits the demodulation signal to the terminal. The modulation and demodulation methods and the devices thereof according to the present invention will be described below with reference to the accompanying drawings and examples.
Hereinafter, modulators refer to COFDM modulator a and COFDM modulator B; the demodulators refer to COFDM demodulator a and COFDM demodulator B.
The modulator of the present invention will be briefly described with reference to the accompanying drawings.
Fig. 4 is a schematic system diagram of a modulator in a data transmission apparatus according to an embodiment of the present invention. As shown in fig. 4, the modulator includes: the device comprises a randomization unit, an RS coding unit, an interleaving unit, a QAM mapping unit, a frequency domain framing unit, an IFFT unit, a guard interval inserting unit and a DAC. Wherein:
the randomization unit is used for randomizing the input data and outputting the randomized input data;
the RS coding unit is used for carrying out FEC (forward error correction coding) coding on the data output by the randomization unit and then outputting the data;
the interleaving unit is used for interleaving the data output by the RS coding unit and then outputting the data;
the QAM mapping unit is used for carrying out QAM mapping on the data output by the interleaving unit according to the bit and the sub-channel bit and the energy distribution information in the energy distribution table and then outputting the data;
the frequency domain framing unit is used for generating and outputting a frequency domain data frame by using the data output by the QAM mapping unit;
the IFFT unit is used for carrying out IFFT transformation on the frequency domain data frame output by the frequency domain framing unit and outputting a time domain OFDM signal;
the guard interval insertion unit is used for adding a cyclic prefix to the time domain OFDM signal output by the IFFT unit to serve as a time domain guard interval and outputting a baseband transmission signal;
the DAC is used for carrying out digital-to-analog conversion on the baseband sending signal output by the guard interval inserting unit and outputting a baseband analog signal.
The modulation method used by the modulator of the present invention will be described in detail with reference to the accompanying drawings.
Fig. 5 is a flowchart of a modulation method in a data transmission method according to an embodiment of the present invention. As shown in fig. 5, the modulation method includes the following steps:
201: after entering a modulator, data to be transmitted is divided into physical layer data packets with the length of 112 bytes, and the physical layer data packets are sent into a randomization unit for randomization and then output randomized data packets;
the randomizer generates a PRBS sequence from a PRBS generator, which is randomized modulo-2 addition to the incoming physical layer packet.
The generator polynomial of the PRBS sequence is: x is the number of15+x14+1。
202: sending the randomized data packet to an RS (Reed-Solomon ) coding unit for FEC (forward error correction coding) coding, and outputting a 128-byte-long RS coded data packet;
the RS encoding unit uses the following parameters: the error correction capability t is 8; total data length 128; the original length of the data is 112.
The field generator polynomial of the RS code is: p (x) x8+x4+x3+x2+1；
The code generator polynomial of the RS code is:
g(x)＝(x+λ0)(x+λ1)(x+λ2)...(x+λ15)＝g16x16+…+g1x+g0。
203: the RS coded data packet is sent to an interleaving unit for interleaving processing, and an interleaving data packet is output;
the interleaving unit adopts convolution interleaving, and the parameters are as follows: the interleaving width I is 8, and the interleaving depth M is 16.
The RS coded data packet can enhance the RS code error correction performance through the interleaving processing.
204: the interleaved data packets are sent to a QAM mapping unit for mapping processing;
the mapping unit distributes the data in the interleaved data packet to each sub-channel according to the corresponding bit number according to the sub-channel bit and energy distribution information (stored in a bit and energy distribution table) obtained in the channel initialization stage, maps the data into corresponding QAM constellation points, and outputs the frequency domain data after QAM modulation.
205: the data output by the QAM mapping unit is sent to a frequency domain framing unit to generate a frequency domain data frame.
206: the frequency domain data frame is sent to an IFFT (Inverse Fast Fourier Transform) unit to be IFFT-transformed, i.e., OFDM-modulated, to generate a time domain OFDM signal (including a number of OFDM symbols).
207: sending the OFDM signal generated after IFFT conversion into a guard interval insertion unit, adding a cyclic prefix as a time domain guard interval (TGI) and forming a time domain baseband transmission signal; the time domain baseband sending signal is converted by a Digital-to-Analog converter (DAC) to generate a baseband Analog signal, and then the baseband Analog signal is sent to a logging cable channel for transmission.
Fig. 6 is a diagram illustrating a superframe structure formed by a data transmission method according to an embodiment of the present invention; as shown in fig. 6, one superframe is composed of 128 OFDM symbols and 2 synchronization frames.
1 OFDM symbol is composed of 1 CP and 1 IFFT block; the length of the CP is 1/4 of the IFFT block length.
2 synchronization frames: SYNC and
respectively located between the 64 th OFDM symbol (Data 63) and the 65 th OFDM symbol (Data 64) before the 1 st OFDM symbol (Data 0). The length of SYNC is 256, which is the same as training sequence 0;
is the inverse of SYNC.
The demodulator of the present invention will be briefly described with reference to the accompanying drawings.
Fig. 7 is a schematic system configuration diagram of a demodulator in the data transmission apparatus according to the embodiment of the present invention. As shown in fig. 7, the demodulator includes: ADC, time domain equalization unit, channel information acquisition unit, AGC unit, synchronous correction unit, FFT (Fast Fourier Transform) unit, frequency domain equalization unit, QAM demapping unit, deinterleaving unit, RS decoding unit and derandomizing unit. Wherein,
the ADC is used for performing analog-to-digital conversion on the input baseband analog signal and outputting a digital signal;
the time domain equalization unit is used for extracting the time domain equalizer coefficient obtained in the channel initialization stage from the channel information acquirer, and performing time domain equalization on the digital signal output by the ADC by using the coefficient to shorten the channel impulse response so as to enable the time delay expansion caused by the channel impulse response to fall within the TGI range;
the AGC unit is used for setting and adjusting AGC parameters according to the digital signals output by the ADC;
the synchronous correction unit is used for extracting the synchronous information obtained in the channel initialization stage from the channel information acquirer, and outputting the data output by the time domain equalization unit after the data enter the synchronous correction unit to remove TGI by using the information;
the FFT unit is used for carrying out FFT conversion on the data output by the synchronous correction unit and then outputting the data;
the frequency domain equalization unit is used for extracting the frequency domain equalizer coefficient obtained in the channel initialization stage from the channel information acquirer and carrying out frequency domain equalization processing on the data output by the FFT unit by using the coefficient;
the QAM demapping unit is used for extracting bit allocation information obtained in the initialization stage from the channel information acquirer and carrying out QAM demapping on data output by the frequency domain equalization unit by using the information;
the de-interleaving unit and the RS decoding unit are used for performing de-interleaving and RS decoding processing on the data output by the QAM de-mapping unit and then outputting the data;
and the de-randomizing unit is used for de-randomizing the data output by the de-interleaving unit and the RS decoding unit and then outputting the user data.
The demodulation method used by the demodulator of the present invention will be described in detail below with reference to the accompanying drawings.
Fig. 8 is a flowchart of a data transmission demodulation method according to an embodiment of the present invention. As shown in fig. 8, the demodulation method includes the following steps:
301: the baseband Analog signal is sampled by an ADC (Analog Digital converter) and then sent to a time domain equalization unit for time domain equalization to truncate the channel impulse response, so that the time delay spread caused by the channel impulse response falls within the TGI range.
And the time domain equalization unit extracts the time domain equalizer coefficient obtained in the channel initialization stage from the channel information acquirer to perform time domain equalization.
In addition, the data sampled by the ADC is also sent to an AGC unit for setting and adjusting AGC parameters.
302: the data output by the time domain equalization unit enters a synchronous correction unit to remove TGI and then is output;
the synchronization correction unit extracts the synchronization information obtained in the channel initialization stage from the channel information obtainer to perform synchronization correction.
303: the data output from the synchronization correcting unit is sent to an FFT (Fast Fourier Transform) unit to be FFT-transformed.
304: the data output after FFT enters a frequency domain equalization unit for frequency domain equalization processing;
and the frequency domain equalization unit extracts the frequency domain equalizer coefficient obtained in the channel initialization stage from the channel information acquirer to perform frequency domain equalization.
305: the data output by the frequency domain balancing unit enters a QAM demapping unit to carry out QAM demapping;
the QAM demapping unit extracts the bit allocation information obtained in the initialization stage from the channel information acquirer and performs QAM demapping.
306: the data output by the QAM demapping unit enters a deinterleaving unit and an RS decoding unit to be deinterleaved and RS decoded and then output;
the deinterleaving unit adopts convolutional deinterleaving, and the parameters are as follows: the interleaving width I is 8, and the interleaving depth M is 16.
The RS decoding unit uses the following parameters: the error correction capability t is 8; total data length 128; the original length of the data is 112.
The field generator polynomial of the RS code is: p (x) x8+x4+x3+x2+1；
The code generator polynomial of the RS code is:
g(x)＝(x+λ0)(x+λ1)(x+λ2)...(x+λ15)＝g16x16+…+g1x+g0。
307: the data output after being processed by the de-interleaving unit and the RS decoding unit enters the de-randomizing unit for de-randomization so as to obtain original user data;
the de-randomizing unit generates a PRBS sequence from a PRBS generator, and the PRBS sequence performs modulo-2 addition with the input physical layer data packet to complete de-randomization.
The generator polynomial of the PRBS sequence is: x is the number of15+x14+1。
In summary, the invention provides the logging cable high-speed data transmission method based on the OFDM technology according to the superiority of the OFDM technology in data transmission and by combining the characteristics of the logging system. By using the method and the device, high-speed data transmission with the uploading speed of 800kbps and the downloading speed of 30kbps can be realized on the armored logging cable 7000 m.
Claims (26)
1. A data sending method is applied to a logging communication system comprising a sending end and a receiving end which are connected through a logging cable, and is characterized by comprising the following steps:
a: the data to be transmitted is subjected to interleaving processing after being subjected to segmentation, randomization and forward error correction coding at the transmitting end;
b: carrying out QAM mapping processing on the data after the interleaving processing according to the sub-channel bit and the energy distribution parameter to map the data into corresponding QAM constellation points;
c: generating a frequency domain data frame by using the data subjected to QAM mapping processing, and performing IFFT (inverse fast Fourier transform) on the frequency domain data frame to generate an OFDM (orthogonal frequency division multiplexing) signal;
d: and inserting a cyclic prefix into the OFDM signal, performing digital-to-analog conversion to generate a baseband analog signal, and transmitting the baseband analog signal to the receiving end in a service sub-channel of the logging cable.
2. The data transmission method according to claim 1, wherein the step a further comprises the following steps: and the transmitting end and the receiving end carry out channel initialization and determine bit and energy distribution parameters of the sub-channels.
3. The data transmission method according to claim 1, wherein the step a further comprises the following steps: determining OFDM basic parameters according to the transmission characteristics of the logging cable channel; the OFDM basic parameters comprise:
subchannel interval, total number of subchannels, effective symbol time, guard interval time, and FFT processing bandwidth.
4. The data transmission method as claimed in claim 3, wherein the subchannel interval is 1.220703125 kHz; the total number of subchannels is 256; the valid symbol time is 819.2 us; the guard interval time is 204.8 us; the FFT processing bandwidth is 312.5 kHz.
5. The data transmission method as claimed in claim 4, wherein among the 256 subchannels, n1 to n1+ m1 subchannels from a low frequency to a high frequency are used as an uplink subchannel; using the (n) 1+ m2 th sub-channel to the 256 th sub-channel from low frequency to high frequency as a downlink sub-channel;
wherein n1, m1 and m2 are positive integers, and n1 is more than or equal to 3 and less than or equal to 7; m2-m1 is more than or equal to 3 and less than or equal to 7; n1+ m2 < 256;
the data transmission direction of the uplink sub-channel is from the underground end to the ground end of the logging communication system; and the data transmission direction of the downlink sub-channel is from the ground end to the underground end of the logging communication system.
6. The data transmission method of claim 5, wherein 1 subchannel is selected as a pilot channel from an uplink subchannel and/or a downlink subchannel; the pilot signal transmitted by the pilot channel is a sine wave.
7. The data transmission method of claim 1, wherein 1 first synchronization signal SYNC is inserted every 128 OFDM symbols, and 1 second synchronization signal SYNC is inserted between 64 th and 65 th OFDM symbols of the 128 OFDM symbolsSYNC and
are signals that are in opposite phase.
8. The data transmission method according to claim 7, wherein the SYNC is BPSK modulated by PRBS, and a mapping rule of a BPSK constellation is 1 → -1, 0 → + 1; the generator polynomial of the PRBS is: x is the number of8+x6+x5+x4+1。
9. The data transmission method according to claim 1, wherein, in the step A,
dividing the data to be transmitted into data packets with the length of 112 bytes;
the randomization is a modulo-2 addition of the 112 byte long data packet using a PRBS sequence; the generator polynomial of the PRBS sequence is x15+x14+1；
The forward error correction coding adopts RS codes; the RS algorithm adopts a parameter with error correction capability t being 8; total data length 128; the field generating polynomial of the RS code is: p (x) x8+x4+x3+x2+ 1; the code generator polynomial of the RS code is:
g(x)＝(x+λ0)(x+λ1)(x+λ2)...(x+λ15)＝g16x16+…+g1x+g0；
the interleaving processing adopts the parameters as follows: and the interleaving width I is 8, and the interleaving depth M is 16.
10. A data receiving method is applied to a logging communication system comprising a sending end and a receiving end which are connected through a logging cable, and is characterized by comprising the following steps:
a) the receiving end carries out analog-to-digital conversion sampling on the baseband analog signal, then carries out time domain equalization and synchronous correction processing to remove a time guard interval and then outputs the baseband analog signal;
b) performing FFT (fast Fourier transform) on data output after the time protection interval is removed through synchronous correction processing, and then performing frequency domain equalization processing;
c) carrying out QAM demapping on the data after the frequency domain equalization processing according to the sub-channel bit and the energy distribution parameter;
d) and performing de-interleaving and RS decoding on the data output after QAM de-mapping and then performing de-randomization to obtain original user data.
11. The data receiving method as claimed in claim 10, wherein said step a) further comprises the steps of: and the transmitting end and the receiving end carry out channel initialization and determine bit and energy distribution parameters of the sub-channels.
12. The data receiving method as claimed in claim 10, wherein said step a) further comprises the steps of: determining OFDM basic parameters according to the transmission characteristics of the logging cable channel; the OFDM basic parameters comprise:
subchannel interval, total number of subchannels, effective symbol time, guard interval time, and FFT processing bandwidth.
13. The data transmission method as claimed in claim 12, wherein the subchannel interval is 1.220703125 kHz; the total number of subchannels is 256; the valid symbol time is 819.2 us; the guard interval time is 204.8 us; the FFT processing bandwidth is 312.5 kHz.
14. The data receiving method as claimed in claim 10,
performing the time domain equalization by using the time domain equalizer coefficient obtained in the channel initialization stage; the time domain equalization enables the time delay expansion caused by channel impulse response to fall within the time protection interval range;
the synchronization correction is carried out by adopting the synchronization information obtained in the channel initialization stage;
performing the frequency domain equalization by using the frequency domain equalizer coefficient obtained in the channel initialization stage;
performing the de-interleaving by adopting a convolution de-interleaving method with parameters of interleaving width I being 8 and interleaving depth M being 16;
the RS decoding adopts the following parameters: the error correction capability t is 8; total data length 128; the original length of the data is 112;
the field generator polynomial of the RS code adopted by the RS decoding is as follows: p (x) x8+x4+x3+x2+1；
The code generator polynomial of the RS code is:
g(x)＝(x+λ0)(x+λ1)(x+λ2)...(x+λ15)＝g16x16+…+g1x+g0。
15. a data transmitting device is connected with a receiving device through a logging cable; the transmitting device is provided with a modulator; the modulator comprises a randomization unit, an RS coding unit, an interleaving unit and a DAC; characterized in that said modulator further comprises: a QAM mapping unit; wherein:
the QAM mapping unit is used for randomizing the randomizing unit according to the subchannel bit and energy distribution parameters, the RS encoding unit performs forward error correction encoding, the data interleaved by the interleaving unit performs QAM mapping processing, and the data is output after being mapped into corresponding QAM constellation points;
the frequency domain framing unit is used for outputting the generated frequency domain data frame output by the QAM mapping unit;
the IFFT unit is used for carrying out IFFT transformation on the frequency domain data frame to generate OFDM signals and then outputting the OFDM signals;
the guard interval insertion unit is used for inserting a cyclic prefix into the OFDM signal, then sending the OFDM signal into the DAC for digital-to-analog conversion to generate a baseband analog signal, and sending the baseband analog signal to the receiving device in a service sub-channel of the logging cable.
16. The data transmission apparatus of claim 15, wherein the modulator performs the transmission of the data using the following parameters: the subchannel interval is 1.220703125 kHz; the total number of subchannels is 256; the valid symbol time is 819.2 us; the guard interval time is 204.8 us; the FFT processing bandwidth is 312.5 kHz.
17. The data transmission apparatus of claim 16, wherein among the 256 subchannels, from an n 1-th subchannel to an n1+ m 1-th subchannel, from a low frequency to a high frequency, is used as an uplink subchannel; using the (n) 1+ m2 th sub-channel to the 256 th sub-channel from low frequency to high frequency as a downlink sub-channel;
wherein n1, m1 and m2 are positive integers, and n1 is more than or equal to 3 and less than or equal to 7; m2-m1 is more than or equal to 3 and less than or equal to 7; n1+ m2 < 256;
the data transmission direction of the uplink sub-channel is from the underground end to the ground end of the logging communication system; and the data transmission direction of the downlink sub-channel is from the ground end to the underground end of the logging communication system.
18. The data transmitting apparatus of claim 17, wherein the modulator transmits a pilot signal in 1 subchannel of the uplink subchannel or the downlink subchannel, the pilot signal being a sine wave.
19. The data transmission apparatus of claim 15, wherein the modulator inserts 1 first synchronization signal SYNC every 128 OFDM symbols and 1 second synchronization signal SYNC between 64 th and 65 th OFDM symbols of the 128 OFDM symbols
SYNC and
are signals that are in opposite phase.
20. The data transmission apparatus according to claim 19, wherein the SYNC is BPSK modulated by a PRBS, and a mapping rule of a BPSK constellation is 1 → -1, 0 → + 1; the generator polynomial of the PRBS is: x is the number of8+x6+x5+x4+1。
21. A data receiving device is connected with a transmitting device through a logging cable; the transmitting device is provided with a demodulator; the demodulator comprises: ADC, time domain equalizing unit, synchronous correcting unit; wherein said demodulator further comprises: the device comprises an FFT unit, a frequency domain balancing unit, a QAM demapping unit, a deinterleaving unit, an RS decoding unit and a derandomizing unit; wherein:
the FFT unit is used for carrying out time domain equalization on the data which is subjected to analog-to-digital conversion sampling by the ADC and is output after time domain equalization by the time domain equalization unit and synchronous correction processing by the synchronous correction unit and time protection interval removal, and carrying out FFT conversion on the data;
the frequency domain equalizing unit is used for carrying out frequency domain equalizing processing on the data output by the FFT unit and then outputting the data;
the QAM demapping unit is used for carrying out QAM demapping on the data output by the frequency domain balancing unit according to the subchannel bits and the energy distribution parameters;
the de-interleaving unit is used for de-interleaving the data output by the QAM de-mapping unit and then outputting the data;
the RS decoding unit is used for carrying out RS decoding processing on the data output by the de-interleaving unit and then outputting the data;
and the derandomizing unit is used for derandomizing the data output by the RS decoding unit to obtain the original user data.
22. The data receiving apparatus of claim 21, wherein the demodulator performs reception of data using the following parameters: the subchannel interval is 1.220703125 kHz; the total number of subchannels is 256; the valid symbol time is 819.2 us; the guard interval time is 204.8 us; the FFT processing bandwidth is 312.5 kHz.
23. The data receiving apparatus according to claim 22, wherein among the 256 subchannels, from an n 1-th subchannel to an n1+ m 1-th subchannel from a low frequency to a high frequency is used as an upstream subchannel; using the (n) 1+ m2 th sub-channel to the 256 th sub-channel from low frequency to high frequency as a downlink sub-channel;
wherein n1, m1 and m2 are positive integers, and n1 is more than or equal to 3 and less than or equal to 7; m2-m1 is more than or equal to 3 and less than or equal to 7; n1+ m2 < 256;
the data transmission direction of the uplink sub-channel is from the underground end to the ground end of the logging communication system; and the data transmission direction of the downlink sub-channel is from the ground end to the underground end of the logging communication system.
24. The data receiving apparatus of claim 23, wherein the demodulator receives a pilot signal in 1 subchannel of the uplink subchannel or the downlink subchannel, the pilot signal being a sine wave.
25. The data receiving apparatus of claim 21, wherein the demodulator receives 1 first synchronization signal SYNC every 128 OFDM symbols and 1 second synchronization signal SYNC between 64 th and 65 th OFDM symbols of the 128 OFDM symbols
SYNC andare signals that are in opposite phase.
26. The data receiving apparatus according to claim 25, wherein the SYNC is BPSK modulated by PRBS, and a mapping rule of a BPSK constellation is 1 → -1, 0 → + 1; the generator polynomial of the PRBS is: x is the number of8+x6+x5+x4+1。
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