阅读说明：本技术 一种测井电缆上数据传输系统 (Data transmission system on logging cable ) 是由 张涛 田恒 张波 于 2020-06-04 设计创作，主要内容包括：本发明公开了一种测井电缆上数据传输系统,包括通过电缆通信的地面设备和井下设备,电缆中的信道包括主信道、若干辅信道和若干耦合信道；其中,主信道：在上行时隙,与辅信道共同传输上行数据；在下行时隙,单独传输下行数据；辅信道：在上行时隙,与主信道共同传输上行数据；在下行时隙,不传送任何数据；耦合信道：在上行时隙,耦合其他信道上传输的信号以辅助解调上行数据。本发明利用主信道传输下行数据,多信道共同传输上行数据,有效提高了数据传输的速率和可靠性。(The invention discloses a data transmission system on a logging cable, which comprises ground equipment and underground equipment which are communicated through the cable, wherein channels in the cable comprise a main channel, a plurality of auxiliary channels and a plurality of coupling channels; wherein, the main channel: in the uplink time slot, uplink data is transmitted together with the auxiliary channel; in the downlink time slot, independently transmitting downlink data; auxiliary channels: in the uplink time slot, uplink data is transmitted together with the main channel; in the downlink time slot, no data is transmitted; coupling the channels: in the uplink time slot, signals transmitted on other channels are coupled to assist in demodulating the uplink data. The invention utilizes the main channel to transmit the downlink data, and the multi-channel transmits the uplink data together, thereby effectively improving the speed and the reliability of data transmission.)

1. A system for transmitting data on a wireline, comprising surface equipment and downhole equipment communicating via the wireline, characterized by: the channels in the cable comprise a main channel, a plurality of auxiliary channels and a plurality of coupling channels;

wherein the content of the first and second substances,

main channel: in the uplink time slot, uplink data is transmitted together with the auxiliary channel; in the downlink time slot, independently transmitting downlink data;

auxiliary channels: in the uplink time slot, uplink data is transmitted together with the main channel; in the downlink time slot, no data is transmitted;

coupling the channels: in the uplink time slot, signals transmitted on other channels are coupled to assist in demodulating the uplink data.

2. The system of claim 1, wherein: the downhole equipment comprises a transmitting unit and a receiving unit; a receiving unit of the underground equipment receives one path of downlink data through a main channel, and a sending unit of the underground equipment sends multiple paths of uplink data through the main channel and an auxiliary channel;

the ground equipment comprises a transmitting unit and a receiving unit; a sending unit of the ground equipment sends one path of downlink data through a main channel, and a receiving unit of the ground equipment receives multiple paths of uplink data through the main channel, an auxiliary channel and a coupling channel.

3. A system for data transmission on a wireline according to claim 1 or 2, characterized in that: the cable core and the shell in the cable form a communication loop; wherein, the communication loop with the minimum interference is a main channel; according to the principle of maximizing the capacity of the uplink channel, a plurality of communication loops are selected as auxiliary channels, and a plurality of communication loops are selected as coupling channels.

4. The system of claim 1, wherein: the way in which data is transmitted in a channel is time division multiplexing.

5. The system of claim 1, wherein: the uplink time slot is larger than the downlink time slot.

6. The system of claim 1, wherein: the communication frame preamble sequences for data transmission on each channel are different from each other, and each preamble sequence is formed by modulating a plurality of same basic preamble symbols through different orthogonal sequences.

7. The system of claim 6, wherein: the orthogonal modulation sequence of the main channel preamble sequence has one and only one symbol jump.

Technical Field

The invention relates to a data transmission system on a logging cable, and belongs to the field of signal transmission.

Background

In the oil well logging process, the data transmission system comprises surface equipment and downhole equipment. The surface equipment supplies power to the downhole equipment (various motors and equipment) through the armored 7-core cable shown in figure 1, any pair of cable cores or any cable core and the metal shell in the armored cable can form a communication loop, and therefore the cable is also used for data communication between the surface equipment and the downhole equipment. The surface equipment sends various instructions (namely downlink data) to the underground equipment through a cable; the various data (namely uplink data) collected by the downhole equipment according to the instructions in the lifting or lowering process are transmitted to the ground through a cable for recording, analyzing and displaying. The existing system adopts a channel to transmit uplink and downlink data, and has the defect of low data transmission rate.

Disclosure of Invention

The invention provides a data transmission system on a logging cable, which solves the problems disclosed in the background technology.

In order to solve the problems, the technical scheme adopted by the invention is as follows:

a logging data transmission system on a cable comprises surface equipment and downhole equipment which communicate through the cable, wherein channels in the cable comprise a main channel, a plurality of auxiliary channels and a plurality of coupling channels;

wherein the content of the first and second substances,

main channel: in the uplink time slot, uplink data is transmitted together with the auxiliary channel; in the downlink time slot, independently transmitting downlink data;

auxiliary channels: in the uplink time slot, uplink data is transmitted together with the main channel; in the downlink time slot, no data is transmitted;

coupling the channels: in the uplink time slot, signals transmitted on other channels are coupled to assist in demodulating the uplink data.

The downhole equipment comprises a transmitting unit and a receiving unit; a receiving unit of the underground equipment receives one path of downlink data through a main channel, and a sending unit of the underground equipment sends multiple paths of uplink data through the main channel and an auxiliary channel;

the ground equipment comprises a transmitting unit and a receiving unit; a sending unit of the ground equipment sends one path of downlink data through a main channel, and a receiving unit of the ground equipment receives multiple paths of uplink data through the main channel, an auxiliary channel and a coupling channel.

The cable core and the shell in the cable form a communication loop; wherein, the communication loop with the minimum interference is a main channel; according to the principle of maximizing the capacity of the uplink channel, a plurality of communication loops are selected as auxiliary channels, and a plurality of communication loops are selected as coupling channels.

The way in which data is transmitted in a channel is time division multiplexing.

The uplink time slot is larger than the downlink time slot.

The communication frame preamble sequences for data transmission on each channel are different from each other, and each preamble sequence is formed by modulating a plurality of same basic preamble symbols through different orthogonal sequences.

The orthogonal modulation sequence of the main channel preamble sequence has one and only one symbol jump.

The invention achieves the following beneficial effects: 1. the invention adopts the main channel to transmit the downlink data and adopts the multi-channel to transmit the uplink data, thereby effectively improving the speed and the reliability of the uplink data transmission; 2. the invention adopts a time division multiplexing data transmission mode, avoids the mutual crosstalk between uplink and downlink communication in the existing space division and frequency division modes, and greatly simplifies the underground communication terminal.

Drawings

FIG. 1 is a cross-sectional view of an armored 7-core cable;

FIG. 2 is a schematic diagram of the system of the present invention;

FIG. 3 is a schematic diagram of a communication frame structure;

fig. 4 is a schematic structural diagram of a downlink communication transmitting end;

FIG. 5 is a schematic diagram of an IFFT modulation module;

fig. 6 is a schematic diagram of a downlink communication receiving end structure;

fig. 7 is a schematic structural diagram of an uplink communication transmitting end;

fig. 8 is a schematic diagram of a structure of an uplink communication receiving end.

Detailed Description

The invention is further described below with reference to the accompanying drawings. The following examples are only for illustrating the technical solutions of the present invention more clearly, and the protection scope of the present invention is not limited thereby.

As shown in fig. 2, a logging data transmission system on cable includes a surface device and a downhole device communicating through a cable, the cable is an armored 7-core cable as shown in fig. 1, the cable core and the housing can form 7 communication loops, each communication loop is a channel, the surface device and the downhole device transmit uplink and downlink data through the channel, wherein the downlink data is sampled in a traditional single-input single-output manner, and the uplink data is in a MIMO multiple-input multiple-output manner, so the channel includes a main channel, a plurality of auxiliary channels and a plurality of coupling channels; the number of each channel is selected according to different communication rate requirements and cost considerations, and only one main channel is in the minimum configuration.

Main channel: in the uplink time slot, uplink data is transmitted together with the auxiliary channel; and in the downlink time slot, the downlink data is transmitted independently.

In the armored cable, the channel quality of the communication loop formed by the central cable core (i.e. the cable core 7) and the outer shell is the best, namely the capacitance reactance, the inductance reactance and the resistance of the channel are all suitable for the transmission of broadband high-speed signals, and the interference to the channel is the least. According to our practical tests, the capacity of the channel is about 3 times that of the loop (loaded) formed by the cable cores 1 and 4, in the case of a cable length of 7 km and full load operation of all downhole equipment. Therefore, the communication loop formed by the central cable core and the outer shell is generally used as a main channel. Due to different configurations of the equipment at the surface and downhole, it is possible that some other communication loop is less disturbed. Other communication loops may be used as the primary channel. Of course, if the system does not need high communication speed, the loop formed by other cable cores can be used as the main channel.

Auxiliary channels: in the uplink time slot, uplink data is transmitted together with the main channel; in the downlink time slot, no data is transmitted. According to the principle of maximizing the capacity of the uplink channel, according to the requirements of communication rate and cost, a plurality of channels except the main channel are selected as auxiliary channels.

Coupling the channels: and coupling uplink data transmitted on other channels in the uplink time slot. And selecting a plurality of channels from the rest channels except the main channel and the auxiliary channel as coupled channels, wherein the coupled channels have no connecting equipment at a transmitting end, and the coupled signals can provide assistance for multi-signal demodulation at a ground part.

The data is transmitted in a time division multiplexing mode in the channel, so that the uplink main channel and the downlink channel share the same transmission loop with better channel parameters and share a frequency band with good transmission performance. When the allocated downlink time slot is smaller and the uplink time slot is larger, namely the uplink time slot is larger than the downlink time slot, the main channel and the auxiliary channel are utilized to transmit uplink data in the uplink time slot.

As shown in fig. 3, a communication frame for data transmission on a channel includes a preamble series, a plurality of control symbols, and a plurality of data payload symbols, where a Symbol is an OFDM Symbol (generated by 1024-point IFFT). Depending on the requirements of the communication system, a frame may have only a preamble sequence, or a preamble sequence + control symbols + payload symbols. The preamble sequence is used to implement the functions of the communication module such as synchronization timing, AFC (automatic frequency control), AGC (automatic gain control), channel estimation, etc. Wherein, the synchronous timing can be completed by adopting sequence correlation operation in a time domain; in order to carry out channel estimation of a plurality of channels at the same time of uplink communication, different preamble sequences which are modulated by the same basic preamble symbol through different orthogonal sequences are transmitted on each channel; the orthogonal modulation sequence of the main channel leader sequence has one and only one symbol jump so as to facilitate the frame synchronization of the receiving end.

The preamble sequence is composed of 8 preamble symbols, each symbol is composed of 1024 real number elements, and no guard interval and no cyclic prefix exist between the symbols. The preamble symbols are divided into positive preamble symbols and negative preamble symbols, which are obtained by multiplying a basic preamble symbol by 1 or-1, respectively. The preamble sequences in the downlink channel and the uplink main channel are the same. The first 4 are positive leading symbols and the last 4 are negative leading symbols. This sequence can be expressed asA₁Is an 8-element sequence [ 1111-1-1 ═ 1]B is a sequence of 1024 real elements, called basic preamble symbols,representing the corelnk product, the result is an 8192 real signal sequence. The basic preamble symbol is composed of 1024 real numbers and can be generated by IFFT from a frequency domain signal, which must be a complex signal with even symmetry in real part and odd symmetry in imaginary part. The frequency domain signal has a value of non-0 only on the sub-carrier corresponding to the frequency band used by the channel and the image frequency band, and is 0 on other sub-carriers. For the convenience of synchronization, the autocorrelation characteristic of the time domain is required to be good. The main preamble sequence has one and only one symbol jump, which is beneficial for the frame synchronization of the receiving end.

For the purpose of channel estimation, the preamble modulation sequences on the respective channels are orthogonal, i.e. the preamble sequence on the mth channel is denoted as

All a are orthogonal, i.e.:

A*A^T＝8*I

where I is an M identity matrix.

Sequence A can be represented by a row vector of an 8 × 8Hadamard matrix, e.g., A of the primary channel₁＝W₈(4)＝[1 1 11 -1 -1 -1 -1]If the total number of main and auxiliary channels in the system is less than or equal to 4, the preamble sequence can also be composed of 4 preamble symbols to increase the channel communication rate on the premise of meeting the requirements of AFC, AGC, frame synchronization and channel estimation, then A can be represented by the row vector of 4 × 4Hadamard matrix, for example, A of the main channel₁＝W₄(2)＝[1 1 -1 -1]Other row vectors may be used for other secondary channels. If the system needs to increase the performance of AFC, AGC, frame synchronization and channel estimation, more preamble symbols can be added before or after the 8 orthogonal preamble symbols.

The underground equipment comprises a transmitting unit (comprising a plurality of IFFT conversion modules and an analog front end) and a receiving unit; a receiving unit of the underground equipment receives one path of downlink data through a main channel, and a sending unit of the underground equipment sends multiple paths of uplink data through the main channel and an auxiliary channel; the ground equipment comprises a transmitting unit and a receiving unit (comprising a plurality of analog front ends and an FFT (fast Fourier transform) module); a sending unit of the ground equipment sends one path of downlink data through a main channel, and a receiving unit of the ground equipment receives multiple paths of uplink data through the main channel, an auxiliary channel and a coupling channel.

The downlink communication of the system adopts a traditional single-input single-output OFDM modulation method, in the uplink and downlink communication, the lengths of FFT and IFFT are 1024 points, the clock frequencies of ADC and DAC are 5MHz, and the used frequency range is configured in the range of 10KHz to 1 MHz. As shown in fig. 4, the payload bits or control bits of a frame of downlink data are first calculated and inserted by CRC check codes, then TURBO encoded, and encoded and output at 1/2 coding rate, and then channel interleaved, and bit copied (the bit copy has two functions, one is to repeat the input bits to increase the signal-to-noise ratio of information bits, and the other is to adjust the coded bits according to the physical rate of the channel), and the data output by bit copy is modulated in a manner of BPSK, QPSK, 16QAM, 64QAM, etc., the result of modulation is a complex signal, and the complex signal and its conjugate signal are IFFT transformed together, and the result of transformation is a real signal, and after inserting a guard interval, the complex signal and its conjugate signal are coupled to the channel and sent out by analog front-end devices such as DAC, amplification, etc.

As shown in fig. 5, a preamble sequence needs to be transmitted before the control symbols and the payload symbols are transmitted. The basic preamble symbols in the preamble sequence may be stored in the memory in advance in the form of a time domain signal. The preamble sequence formed by modulating a series of basic preamble symbols by orthogonal sequence is coupled to the channel by analog front-end devices such as DAC and amplifier, and is transmitted. As shown in fig. 6, the receiving unit of the downlink communication employs a conventional OFDM receiver.

As shown in fig. 7, the difference between the uplink communication and the downlink communication is that the uplink communication has a plurality of channels to transmit data and the amount of data is large. The bit copy/allocation function in the upstream communication replaces the bit copy function in the downstream communication. Bit copying/allocation requires not only repeated copying of bits but also allocation according to the physical rate of different channels. The modulation scheme on each channel is also different and adaptive to the channel quality.

As shown in fig. 8, the difference of the upstream and downstream communications is that the upstream communication receiving unit can receive data on a plurality of channels. Since the signals on all channels in the uplink communication are synchronous, the synchronous detection only needs to be carried out on the main channel. The output after signal detection and demodulation is processed by bit superposition/combination, and finally output after channel de-interleaving or inverse channel interleaving, TURBO decoding and CRC check.

The downlink channel is a single-input single-output communication, which is relatively simple, and the channel estimation algorithm and the demodulation algorithm thereof are not described in detail here.

Channel estimation for uplink channel transmission: since IFFT is a linear transform, the complex sequences of 8 frequency domain symbols constituting each channel preamble sequence are also orthogonal to each other on the same subcarrier. Assuming that C is the frequency domain value of the basic preamble symbol, the 8 frequency domain preamble sequences of the k-th subcarrier of the uplink main channel can be represented as a₁*c_k，c_kIs a known scalar, all preamble frequency domain sequences on all M channels can be represented as a c_k(is a matrix of M × 8), so

(A*c_k)*(A*c_k)^T＝8*I*|c_k|²

The uplink channel transmission is a multiple-input multiple-output communication if the channel of the k-th subcarrier (including the IFFT transformation of the transmitting unit and the FFT transformation of the receiving unit) is in matrix H_kIndicating (is an N × M matrix), the preamble frequency domain sequence transmitted by the transmitting unit is known, and the signal Y output on the k-th subcarrier after FFT transformation by the receiving unit_k(matrix N × 8), noise and interference matrix Z observed by the receiving unit_k(is a matrix of N × 8), i.e.:

wherein h is_k,n,mThe channel response, which represents that the frequency domain signal on the mth transmitting channel on the kth subcarrier reaches the nth receiving channel through the IFFT transformation, the communication loop, and the receiving end FFT transformation, is a complex number.

Then

Y_k＝H_k*(A*c_k)+Z_k

In the case of high signal-to-noise ratio, the LS method can be used to estimate H_kThe channel estimated at the receiving end is:

further, in the present invention,

the channel estimation method is quite simple, and other methods such as minimum mean square MMSE and the like can be adopted to calculate the channel estimation accuracy.

And in the uplink communication receiving, the traditional Linear MMSE is adopted for signal demodulation. When the uplink channel transmits data, if the data transmitted by all M channels on the kth carrier wave of the transmitting end is recorded as S_k(column vector of M elements before IFFT), and marking the signal after FFT of all N channels (main channel, auxiliary channel and coupling channel) on the kth carrier wave of the receiving end as R_k(column vector of N elements), noise or interference is denoted W_k(column vector of N elements) then there are:

R_k＝H_k*S_k+W_k

according to the Linear MMSE algorithm, the demodulated signal is obtained as follows:

wherein, C_s、C_nAre each S_kAnd W_kThe autocorrelation matrix of (a).

The system works in an asymmetric half-duplex mode, the carrier frequency range is 100KHz to 300KHz, and the adjustment can be carried out according to the interference of actual load and the performance of the cable. When the system works, 90% of the running time of the system is used for upstream communication, 10% of the running time of the system is used for downstream communication, and the distribution of the time intervals is adjustable.

The system adopts a transmission mode of transmitting downlink data by a main channel and transmitting uplink data by multiple channels, thereby effectively improving the speed and reliability of data transmission; the data transmission mode adopted by the system is time division multiplexing, so that the problem of mutual crosstalk between uplink and downlink communication in the existing space division and frequency division transmission modes is avoided, the communication system can multiplex part of software and hardware, and the communication terminal is greatly simplified.

The above description is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several modifications and variations can be made without departing from the technical principle of the present invention, and these modifications and variations should also be regarded as the protection scope of the present invention.