CN111636865B - Data transmission system on logging cable - Google Patents

Abstract

The invention discloses a data transmission system on a well logging cable, which includes ground equipment and downhole equipment through cable communication, and the channels in the cable include a main channel, several auxiliary channels and several coupling channels; wherein, the main channel: in the uplink time slot , transmit uplink data together with the auxiliary channel; in the downlink time slot, transmit downlink data alone; auxiliary channel: in the uplink time slot, transmit uplink data together with the main channel; in the downlink time slot, no data is transmitted; coupling channel: in the uplink Time slots, coupled with signals transmitted on other channels to assist demodulation of uplink data. The present invention utilizes the main channel to transmit downlink data and multiple channels to jointly transmit uplink data, thereby effectively improving the rate and reliability of data transmission.

Description

A Data Transmission System on Well Logging Cable

technical field

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

Background technique

In the oil drilling logging process, the data transmission system includes surface equipment and downhole equipment. The ground equipment supplies power to the downhole equipment (various motors and equipment) through the armored 7-core cable shown in Figure 1. Any pair of cores in the armored cable or any one core and the metal shell can form a communication loop, so The cable is also used for data communication between surface equipment and downhole equipment. The surface equipment sends various instructions (that is, downlink data) to the downhole equipment through the cable; the various data (that is, the uplink data) collected by the downhole equipment according to the instructions during the lifting or lowering process are transmitted to the ground through the cable for recording, analysis and For display. The existing system uses one channel for uplink and downlink data transmission, which has the defect of low data transmission rate.

Contents of the 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 above problems, the technical solution adopted in the present invention is:

A data transmission system on a well logging cable, including surface equipment and downhole equipment communicating through the cable, the channels in the cable include a main channel, several auxiliary channels and several coupling channels;

in,

Main channel: In the uplink time slot, transmit uplink data together with the auxiliary channel; in the downlink time slot, transmit downlink data alone;

Auxiliary channel: In the uplink time slot, transmit uplink data together with the main channel; in the downlink time slot, no data is transmitted;

Coupling channel: In the uplink time slot, couple signals transmitted on other channels to assist demodulation of uplink data.

The downhole equipment includes a sending unit and a receiving unit; the receiving unit of the downhole equipment receives one channel of downlink data through the main channel, and the sending unit of the downhole equipment sends multiple channels of uplink data through the main channel and the auxiliary channel;

The ground equipment includes a sending unit and a receiving unit; the sending unit of the ground equipment sends one channel of downlink data through the main channel, and the receiving unit of the ground equipment receives multiple channels of uplink data through the main channel, auxiliary channel and coupling channel.

The cable core and the outer shell in the cable form a communication loop; among them, the communication loop with the least interference is the main channel; according to the principle of maximizing the capacity of the uplink channel, select some of the remaining communication loops as auxiliary channels, and then select from the remaining communication loops. Several serve as coupling channels.

The way to transmit data in the channel is time division multiplexing.

Uplink time slots are larger than downlink time slots.

The preamble sequences of the communication frame for data transmission on each channel are different, and each preamble sequence is modulated by the same multiple basic preamble symbols through different orthogonal sequences.

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

The beneficial effects achieved by the present invention: 1. The present invention adopts the main channel to transmit downlink data, and adopts multiple channels to transmit uplink data, which effectively improves the rate and reliability of uplink data transmission; 2. The present invention adopts the data transmission mode of time division multiplexing , which avoids the mutual crosstalk between the uplink and downlink communications in the existing space division and frequency division methods, and at the same time greatly simplifies the underground communication terminal.

Description of drawings

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

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

Fig. 3 is a schematic structural diagram of a communication frame;

FIG. 4 is a schematic structural diagram of a downlink communication sending end;

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

FIG. 6 is a schematic structural diagram of a downlink communication receiving end;

FIG. 7 is a schematic structural diagram of an uplink communication sending end;

FIG. 8 is a schematic structural diagram of an uplink communication receiving end.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings. The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

As shown in Figure 2, a data transmission system on a logging cable, including surface equipment and downhole equipment through cable communication, the cable is an armored 7-core cable as shown in Figure 1, and the cable core and shell can form 7-way communication Loop, each communication loop is a channel, and the surface equipment and downhole equipment transmit uplink and downlink data through the channel. Among them, the downlink data sampling adopts the traditional single-input single-output method, and the uplink data adopts the MIMO multiple-input multiple-output method, so the channel here Specifically, it includes a main channel, several auxiliary channels, and several coupling channels; among them, the selection of the number of each channel needs to be based on different communication rate requirements and cost considerations, and there is only one main channel in the minimum configuration.

Main channel: In the uplink time slot, it transmits uplink data together with the auxiliary channel; in the downlink time slot, it transmits downlink data alone.

In armored cables, the channel quality of the communication loop composed of the central cable core (i.e. cable core 7) and the outer shell is usually the best, that is, the capacitive reactance, inductive reactance and resistance of the channel are suitable for the transmission of broadband high-speed signals, and it is subjected to There is also minimal disruption. According to our actual test, when the cable length is 7 kilometers and all downhole equipment is fully loaded, the capacity of this channel is about 3 times that of the loop (with load) formed by cable cores 1 and 4. Therefore, the communication loop composed of the central cable core and the outer shell is generally used as the main channel. Due to the different equipment configurations on the surface and downhole, it is also possible that some other communication loop will be less disturbed. At this time, other communication circuits can also be used as the main channel. Of course, if the system does not require a high communication rate, the loop formed by other cable cores can also be used as the main channel.

Auxiliary channel: In the uplink time slot, it transmits uplink data 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 speed and cost, select some of the other channels except the main channel as auxiliary channels.

Coupling channel: In the uplink time slot, it couples uplink data transmitted on other channels. Select some of the remaining channels except the main channel and the auxiliary channel as the coupling channel. The coupling channel is not connected to the device at the sending end, and the coupling signal on the ground can provide assistance for multi-signal demodulation.

Time-division multiplexing is used to transmit data in the channel, so that the uplink main channel and the downlink channel share the same transmission circuit with better channel parameters and a frequency band with good transmission performance. The assigned downlink time slot is smaller and the uplink time slot is larger, that is, when the uplink time slot is larger than the downlink time slot, the uplink data is transmitted in the uplink time slot by using the main channel and the auxiliary channel.

As shown in Figure 3, the communication frame of data transmission on the channel includes a preamble series, several control symbols and several data load symbols, where the symbol refers to an OFDM Symbol (generated by 1024-point IFFT). According to different requirements of the communication system, a frame may only have a preamble sequence, or a preamble sequence + a control symbol, or a preamble sequence + a control symbol + a payload symbol. The preamble sequence is used to realize synchronous timing, AFC (automatic frequency control), AGC (automatic gain control), channel estimation and other functions of the communication module. Among them, synchronous timing can be completed by sequence correlation operation in the time domain; in order to perform channel estimation of multiple channels simultaneously in uplink communication, each channel transmits different signals modulated by the same basic preamble symbols through different orthogonal sequences. Preamble sequence; the orthogonal modulation sequence of the preamble sequence of the main channel has one and only one symbol hopping, so as to facilitate frame synchronization at the receiving end.

A₁是一个8元素的序列＝[1 1 1 1 -1 -1-1 -1]，B是一个由1024个实数元素组成的序列，被称作基本前导符号，

表示科罗内克乘积，其结果是一个8192个实数信号序列。基本前导符号由1024个实数组成，可以由频域信号经过IFFT产生，该频域信号必须是实部偶对称，虚部奇对称的复信号。而该频域信号只是在信道所使用的频段和镜像频段所对应的子载波上有非0值，而在其他子载波上为0。为便于同步，要求其时域的自相关特性比较好。主前导序列有且只有一次符号跳变，这有利于接收端进行帧同步。The preamble sequence is composed of 8 preamble symbols, and each symbol is composed of 1024 real number elements. There is no guard interval between symbols and no cyclic prefix. Leading symbols are divided into positive leading symbols and negative leading symbols, which are respectively obtained by multiplying a basic leading symbol by 1 or -1. 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 as

A ₁ is a sequence of 8 elements = [1 1 1 1 -1 -1-1 -1], B is a sequence consisting of 1024 real elements, called the basic leading symbol,

Represents the Coroneck product, the result of which is a sequence of 8192 real numbers. The basic preamble symbol is composed of 1024 real numbers, and can be generated by IFFT from a frequency domain signal. The frequency domain signal must be a complex signal with an even symmetric real part and an odd symmetric imaginary part. The frequency domain signal only has a non-zero value on the subcarrier corresponding to the frequency band used by the channel and the image frequency band, and is 0 on other subcarriers. In order to facilitate synchronization, the autocorrelation characteristics of the time domain are required to be relatively good. The main preamble sequence has one and only one symbol hopping, which is beneficial for the receiving end to perform frame synchronization.

所有的A是正交的，即：To facilitate channel estimation, the preamble modulation sequences on each channel are orthogonal, that is, the preamble sequence on the mth channel is expressed as

All A's are orthogonal, ie:

A*A ^T ＝8*I

where I is an M×M identity matrix.

Sequence A can be represented by a row vector of an 8×8 Hadamard matrix, for example, A ₁ =W ₈ (4)=[1 1 11 -1 -1 -1 -1] of the main channel, and other auxiliary channels can use other Row vector representation. If the total number of main channels 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 under the premise of meeting the requirements of AFC, AGC, frame synchronization and channel estimation. At this time, A can be represented by a row vector of a 4×4 Hadamard matrix, for example, A ₁ =W ₄ (2)=[1 1 -1 -1] of the main channel, and other auxiliary channels can be represented by other row vectors. 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 downhole equipment includes a sending unit (including multiple IFFT transformation modules and analog front ends) and a receiving unit; the receiving unit of the downhole equipment receives one channel of downlink data through the main channel, and the sending unit of the downhole equipment sends multiple channels of uplink data through the main channel and the auxiliary channel; The ground equipment includes a sending unit and a receiving unit (including multiple analog front-ends and FFT transformation modules); the sending unit of the ground equipment sends one downlink data through the main channel, and the receiving unit of the ground equipment receives multiple downlink data through the main channel, auxiliary channel and coupling channel. row data.

The downlink communication of the above system adopts the traditional single-input single-output OFDM modulation method. In the uplink and downlink communication, the length of FFT and IFFT is 1024 points, the clock frequency of ADC and DAC is 5MHz, and the frequency band is configured within the range of 10KHz to 1MHz. As shown in Figure 4, the load bits or control bits of a frame of downlink data are first calculated and inserted through the CRC check code, and then TURBO encoded, using a 1/2 encoding rate, and the encoded output is channel interleaved, followed by bit copying ( Bit copy has two functions, one is to repeat the input bits, increase the signal-to-noise ratio of information bits, and the other is to adjust the number of encoded bits according to the physical rate of the channel), and the output data of bit copy is modulated and modulated The method can be BPSK, QPSK, 16QAM, 64QAM, etc. The result of modulation is a complex signal. The complex signal and its conjugate signal are subjected to IFFT transformation. The result of the transformation is a real signal. After inserting the guard interval, it is amplified by DAC and Wait for the analog front-end device to couple to the channel and send it out.

As shown in FIG. 5 , a preamble sequence needs to be transmitted before the control symbol and the payload symbol are sent. The basic preamble symbols in the preamble sequence can be pre-stored in the memory in the form of time domain signals. The preamble sequence formed by a series of basic preamble symbols modulated by the orthogonal sequence is coupled to the channel by DAC, amplifier and other analog front-end devices and sent out. As shown in Figure 6, the receiving unit for downlink communication uses a traditional OFDM receiver.

As shown in FIG. 7 , the difference between uplink and downlink communication is that uplink communication has multiple 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 not only needs to repeatedly copy bits, but also needs to be allocated according to the physical rate of different channels. And the modulation mode on each channel is also different, and it is adaptive to the channel quality.

As shown in FIG. 8 , the difference between uplink and downlink communication is that the uplink communication receiving unit can receive data on multiple channels. Since the signals on all channels in the uplink communication are synchronized, the synchronization detection only needs to be performed on the main channel. The output after signal detection and demodulation is subjected to bit superimposition/combination processing, and finally output after channel de-interleaving or reverse channel interleaving, TURBO decoding, and CRC checking.

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

Channel estimation for uplink channel transmission: Since IFFT is a linear transformation, on the same subcarrier, the complex sequences of 8 frequency-domain symbols that make up the preamble sequence of each channel are also orthogonal to each other. Assuming that C is the frequency domain value of the basic preamble symbol, the 8 frequency domain preamble sequences of the kth subcarrier of the uplink main channel can be expressed as A ₁ *c _k , where c _k is a known scalar, then all preambles on all M channels The frequency domain sequence can be expressed as A*c _k (a matrix of M×8), so

(A*c _k )*(A*c _k ) ^T ＝8*I*|c _k | ²

Uplink channel transmission is multiple-input multiple-output communication. If the channel of the kth subcarrier (including the IFFT transformation of the sending unit and the FFT transformation of the receiving unit) is represented by a matrix H _k (an N×M matrix), the preamble sent by the sending unit The domain sequence is known, the signal Y _k (which is a matrix of N×8) output on the kth subcarrier after the FFT transformation of the receiving unit, the noise and interference matrix Z _k (which is a matrix of N×8) observed by the receiving unit ),Right now:

Among them, h _k,n,m represent the channel response of the frequency domain signal on the mth transmission channel on the kth subcarrier to the nth receiving channel after IFFT transformation, communication loop, and receiving end FFT transformation, which is a complex number.

but

Y _k ＝H _k *(A*c _k )+Z _k

In the case of high SNR, the LS method can be used to estimate H _k , and the channel estimated at the receiving end is:

further,

The above-mentioned channel estimation method is quite simple. In order to improve the estimation accuracy, other calculation methods, such as the least mean square MMSE, can also be used.

The traditional Linear MMSE is used for signal demodulation in uplink communication reception. When the uplink channel transmits data, if the data transmitted by all M channels on the kth carrier at the sending end is denoted as S _k (column vector of M elements before IFFT transformation), all the data on the kth carrier at the receiving end The signal after FFT transformation of N channels (main channel, auxiliary channel and coupled channel) is denoted as R _k (column vector of N elements), and the noise or interference is denoted as W _k (column vector of N elements), then:

R _k ＝H _k *S _k +W _k

According to the Linear MMSE algorithm, the demodulated signal is:

Among them, C _s and C _n are the autocorrelation matrices of S _k and W _k respectively.

The above-mentioned system works in an asymmetric half-duplex mode, and the carrier frequency band is 100KHz to 300KHz, and can be adjusted according to the interference of the actual load and the performance of the cable. When the system is working, 90% of its running time is used for uplink communication, and 10% of its running time is used for downlink communication, and the allocation of time slots is adjustable.

The above-mentioned system adopts the transmission method of the main channel to transmit downlink data and multi-channel transmission of uplink data, which effectively improves the rate and reliability of data transmission; the data transmission method adopted by the above-mentioned system is time division multiplexing, which avoids the existing space division and frequency division. The problem of mutual crosstalk between uplink and downlink communications in the transmission method enables the communication system to reuse part of the software and hardware, which greatly simplifies the communication terminal.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. It should also be regarded as the protection scope of the present invention.

Claims (7)

1. A data transmission system on a well logging cable, comprising surface equipment and downhole equipment through cable communication, characterized in that: the channels in the cable include main channels, some auxiliary channels and some coupling channels; in, Main channel: In the uplink time slot, transmit uplink data together with the auxiliary channel; in the downlink time slot, transmit downlink data alone; Auxiliary channel: In the uplink time slot, transmit uplink data together with the main channel; in the downlink time slot, no data is transmitted; Coupling channel: In the uplink time slot, couple signals transmitted on other channels to assist demodulation of uplink data. 2. A data transmission system on a well logging cable according to claim 1, characterized in that: the downhole equipment includes a sending unit and a receiving unit; the receiving unit of the downhole equipment receives one path of downlink data through the main channel, and the downhole equipment’s sending unit Send multiple channels of uplink data through the main channel and the auxiliary channel; The ground equipment includes a sending unit and a receiving unit; the sending unit of the ground equipment sends one channel of downlink data through the main channel, and the receiving unit of the ground equipment receives multiple channels of uplink data through the main channel, auxiliary channel and coupling channel. 3. A data transmission system on a well logging cable 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 that is least disturbed is the main channel; according to the uplink The principle of channel capacity maximization is to select some of the remaining communication circuits as auxiliary channels, and then select some of the remaining communication circuits as coupling channels. 4. A data transmission system on a logging cable according to claim 1, characterized in that: the way of transmitting data in the channel is time division multiplexing. 5. A data transmission system on a logging cable according to claim 1, wherein the uplink time slot is larger than the downlink time slot. 6. The data transmission system on a kind of well logging cable according to claim 1, characterized in that: the preambles of the communication frames for data transmission on each channel are different, and each preamble is passed through by the same plurality of basic preamble symbols Modulated by different orthogonal sequences. 7. A data transmission system on a well logging cable according to claim 6, wherein the orthogonal modulation sequence of the preamble sequence of the main channel has one and only one symbol jump.

Images