OFDM (Orthogonal Frequency Division Multiplexing) waveform design method and system suitable for covered wire transmission

Abstract

The invention provides an OFDM (Orthogonal Frequency Division Multiplexing) waveform design method suitable for covered wire transmission, which comprises the steps of CRC (Cyclic Redundancy Check) check, Turbo coding / rate matching, serial-to-parallel conversion, constellation mapping, OFDM modulation and framing, and utilizes a mode of combining an OFDM transmission technology with high spectrum utilization rate with 16QAM (Quadrature Amplitude Modulation) and 4QAM modulation technologies with high information transmission rate. Compared with a traditional single-carrier frequency domain equalization technology and a PAM constellation mapping mode of covered line transmission, the frequency spectrum utilization rate and the data transmission rate are improved; meanwhile, compared with the traditional grid coding, the Turbo coding further improves the coding gain; the insertion of the CP-UW pilot signals can reduce the difficulty of subsequent receiving end signal processing and improve the channel estimation precision, so that distortion and attenuation signals introduced by covered wire long-distance transmission can be recovered more accurately, large-bandwidth and long-distance communication in a covered wire communication environment is realized, and audio and video transmission services can be supported.

Description

Technical Field

[0001] This invention belongs to the field of communication technology, and specifically discloses an OFDM waveform design method suitable for multiline transmission. Background Technology

[0002] With the development of modern technology, the demand for high-speed data transmission systems is increasing daily. Double-faced cables have a copper-clad steel internal structure, offering high strength and good conductivity. Their external insulation and protective layers can withstand extreme cold and heat. Furthermore, they are easy to install and repair, and flexible in laying, making them widely used in field operations. To achieve high-speed data transmission with double-faced cables, further research is needed on the transmission waveforms suitable for them.

[0003] Chinese patent CN106797288A uses Orthogonal Frequency Domain Multiplexing (OFDM) technology to achieve high-speed data transmission by dividing a high-speed data stream into multiple parallel low-speed substreams and modulating these substreams onto mutually orthogonal subcarriers. However, the OFDM technology used in this patent is only suitable for wireless communication environments and is difficult to implement for long-distance high-speed data transmission in the special transmission environment of multiline communication.

[0004] The challenge of double-wire transmission technology lies in achieving reliable data transmission on copper-clad steel wires with limited bandwidth and high attenuation. Existing copper-clad steel double-wire communication waveforms have low transmission rates, with a maximum transmission rate of only 64kbps over a 5km communication distance, which can only support voice and data services. When the need for self-organizing networks in outdoor environments is added, requiring additional time slot resource allocation, it becomes even more unacceptable for long-distance communication.

[0005] Therefore, there is an urgent need for a new waveform design method suitable for multiline transmission. Summary of the Invention

[0006] Purpose of the invention: The key feature of the multiline transmission waveform described in this patent is the implementation method that combines OFDM transmission technology with 16QAM and 64QAM high-order modulation technology to achieve long-distance communication with large bandwidth.

[0007] Technical solution:

[0008] On the one hand, this invention proposes an OFDM waveform design method suitable for multiline transmission, including:

[0009] Receive raw data, verify the raw data, and transform the raw data that passes the verification to obtain the signal to be processed;

[0010] The signal to be processed is transformed from serial to parallel by constellation mapping and mapped into a point signal on the complex plane. The constellation mapping is performed by frequency band mapping according to the frequency attenuation characteristics of the complex line channel spectrum.

[0011] The point signal is modulated using OFDM transmission technology to obtain a time-domain OFDM signal;

[0012] Take several OFDM signals as a frame of the waveform, and copy the last few samples of each OFDM signal to the beginning of the OFDM signal to form a cyclic prefix;

[0013] Generate a guard interval signal and a pilot sequence. Insert the guard interval signal into the frame header and frame tail respectively, and insert the pilot sequence after the guard interval signal in the frame header.

[0014] The cyclic prefix is ​​inserted between the guard interval signal and the pilot sequence in the frame header, and an all-zero signal is inserted after the guard interval signal in the frame tail to form a physical layer frame, thus completing the waveform design.

[0015] Furthermore, the original data is verified using the CRC check algorithm, and the original data that passes the verification is converted by Turbo encoding and rate matching. The signal to be processed is a binary signal.

[0016] Furthermore, the constellation mapping includes: setting a threshold based on the fading characteristics of the multi-channel; treating signals with frequencies below the threshold as low-frequency bands and using 64QAM modulation; and treating signals with frequencies above the threshold as high-frequency bands and using 16QAM modulation.

[0017] Furthermore, the modulation of the point signal includes:

[0018] The point signal obtained by constellation mapping has a length of N. The point signal is divided into a first half and a second half with a length of N / 2. The positions of the first half and the second half are interchanged, and 7N zeros are inserted in the middle to form a modulation point signal with a length of 8N. The modulation point signal is subjected to inverse fast Fourier transform to obtain a time-domain OFDM signal.

[0019] Furthermore, the generation of the guard interval signal and pilot sequence is based on the ZC sequence, which is represented as:

[0020]

[0021] Where M is the root exponent of the ZC sequence, k is the sequence index. , Set different parameter groups for sequence length. A guard interval signal and a pilot sequence are generated respectively. The guard interval signal is used to equalize the signal transmission power, and the pilot sequence has ideal periodic autocorrelation properties.

[0022] On the other hand, the present invention also proposes an OFDM waveform design system suitable for multiline transmission, comprising:

[0023] The verification encoding module is used to receive raw data, verify the raw data, and convert the raw data that passes the verification to obtain the signal to be processed.

[0024] The constellation mapping module is used to perform serial-to-parallel transformation on the signal to be processed through constellation mapping, mapping it into a point signal on the complex plane. The constellation mapping is performed by frequency band mapping according to the frequency attenuation characteristics of the complex line channel spectrum.

[0025] The signal modulation module is used to modulate the point signal using OFDM transmission technology to obtain a time-domain OFDM signal;

[0026] The physical layer framing module is used to take several OFDM signals as a waveform frame, copy the last few samples of each OFDM signal to the beginning of the OFDM signal to form a cyclic prefix; generate a guard interval signal and a pilot sequence, insert the guard interval signal at the beginning and end of the frame respectively, and insert the pilot sequence after the guard interval signal at the beginning of the frame; insert the cyclic prefix between the guard interval signal and the pilot sequence at the beginning of the frame, and insert an all-zero signal after the guard interval signal at the end of the frame to form a physical layer frame and complete the waveform design.

[0027] Furthermore, the original data is verified using the CRC check algorithm; the conversion of the verified original data includes Turbo encoding and rate matching, and the signal to be processed is a binary signal.

[0028] Furthermore, the constellation mapping includes: setting a threshold based on the fading characteristics of the multi-channel; treating signals with frequencies below the threshold as low-frequency bands and using 64QAM modulation; and treating signals with frequencies above the threshold as high-frequency bands and using 16QAM modulation.

[0029] Furthermore, the modulation of the point signal includes:

[0030] The point signal obtained by constellation mapping has a length of N. The point signal is divided into a first half and a second half with a length of N / 2. The positions of the first half and the second half are interchanged, and 7N zeros are inserted in the middle to form a modulation point signal with a length of 8N. The modulation point signal is subjected to inverse fast Fourier transform to obtain an OFDM signal.

[0031] Furthermore, the generation of the guard interval signal and pilot sequence is based on the ZC sequence, which is represented as:

[0032]

[0033] Where M is the root exponent of the ZC sequence, k is the sequence index. , Set different parameter groups for sequence length. A guard interval signal and a pilot sequence are generated respectively. The guard interval signal is used to equalize the signal transmission power, and the pilot sequence has ideal periodic autocorrelation properties.

[0034] Beneficial effects:

[0035] This invention combines the high spectral efficiency of OFDM transmission technology with the high information transmission rate of 16QAM and 4QAM modulation technology. Compared with the traditional single-carrier frequency domain equalization technology and PAM constellation mapping method in multiline transmission, it improves the spectral efficiency and data transmission rate. At the same time, the Turbo coding used further improves the coding gain compared with the traditional trellis coding.

[0036] The insertion of the CP-UW pilot signal in the frame structure of this invention significantly reduces the difficulty of subsequent signal processing at the receiving end, improves channel estimation accuracy, and thus more accurately recovers the signal distortion and attenuation introduced by long-distance transmission via multiplexing, enabling high-bandwidth, long-distance communication in multiplexing communication environments. Currently, when using copper-clad steel multiplexing for a transmission distance of 5km, the transmission rate at a power of approximately 20dBm is about 64kbps. However, this method can increase the transmission rate to a maximum of 1Mbps. Attached Figure Description

[0037] Figure 1 This is a flowchart of the waveform design method of the present invention;

[0038] Figure 2 This is an information processing flowchart;

[0039] Figure 3 This is a spectrum diagram of the multiline channel;

[0040] Figure 4 The autocorrelation performance of the UW signal is plotted.

[0041] Figure 5 This is a constellation diagram for GP signals;

[0042] Figure 6 This is a structural diagram of the physical layer frame of the present invention. Detailed Implementation

[0043] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments. The present invention discloses a method for designing OFDM waveforms suitable for multiline transmission, such as... Figure 1 The flowchart shown is a method of the present invention, which includes the following steps:

[0044] Step 1: Verify the original data using the CRC check algorithm, and then perform Turbo encoding and rate matching. In this embodiment, the original data is a binary number, the information sampling rate is 2.88MHz, and the bandwidth is 180KHz.

[0045] Turbo encoding with a 1 / 3 code rate is used. For example... Figure 2 The diagram shows the information processing flowchart for each step in this embodiment. The original information rate is 1.004 Mbps. After passing through a 1 / 3 turbo channel coding module, a 16-bit CRC check module, and rate matching processing, a 6144-bit binary signal is obtained.

[0046] Step 2: After the rate-matched signal is serially-to-parallel transformed by constellation mapping, it is mapped into a point signal on the complex plane. Based on the fading characteristics of the complex channel, a specific joint modulation scheme is selected for each frequency band, including 16QAM and 64QAM. The rate-matched binary signal is then subjected to 16QAM and 64QAM constellation mapping respectively. In one embodiment, 682 symbols in the low-frequency band are modulated using 64QAM, and 342 symbols in the high-frequency band are modulated using 16QAM. The reference channel spectrum is as follows: Figure 3 As shown, Figure 3 The horizontal axis represents frequency, and the vertical axis represents spectral density. The channel spectrum is severely attenuated in the high-frequency part.

[0047] Step 3: The point signal is oversampled 8 times and modulated with OFDM using OFDM transmission technology to obtain a time-domain OFDM signal.

[0048] Specifically, in this embodiment, the total number of subcarriers is N=1024. For the 1024 data points obtained after mapping in step 2, the last 512 data points are placed at the beginning and the first 512 data points are placed at the end, with 7168 zeros added in the middle to form 8192 data points. An 8192-point inverse fast Fourier transform (IFFT) is performed on the 8192 data points to convert the frequency domain signal to the time domain to form a time-domain OFDM signal.

[0049] Step 4: Take several modulated OFDM signals as a frame of the physical layer, and copy the samples from the last specific time of each OFDM signal to the beginning of that OFDM signal to form a cyclic prefix. The assembly of physical frames is essentially mapping logical bits to specific time-frequency resources, and this mapping process defines the final generated waveform.

[0050] The physical layer frame in this embodiment contains 6 OFDM symbols. In order to prevent interference between OFDM symbols, the last 20 samples of each OFDM symbol are copied to the front of the OFDM symbol to form a cyclic prefix (CP). At this time, the number of cyclic prefix points is 20.

[0051] Step 5: Generate guard interval signals and pilot sequences. Insert a guard interval signal at the beginning and end of the frame, and insert a pilot sequence after the guard interval signal at the beginning of the frame.

[0052] Due to the spectral characteristics of OFDM symbols, the power values ​​at both ends of the spectrum are relatively low and unsuitable for transmitting useful information. Therefore, guard intervals (GPs) are inserted at the frame header and frame tail, with a GP number of 16 points. Additionally, a pilot sequence (UW) is inserted after the guard interval to facilitate later channel estimation and equalization. The pilot sequence (UW) has 128 points.

[0053] In this embodiment, both the GP signal and the UW signal are selected from ZC sequences that have constant envelopes in the time and frequency domains, perfect autocorrelation characteristics, and good cross-correlation. The ZC sequence can be represented as:

[0054]

[0055] in, It is the root exponent of the ZC sequence. , Set different parameter groups according to the requirements for the length of the sequence. The guard interval signal and pilot sequence are generated separately. The specific parameter configurations selected in this embodiment are shown in Table 1.

[0056] Table 1 GP and UW signal parameter configuration

[0057] signal type Root index M <![CDATA[Sequence length N p > GP 7 16 UW 19 128

[0058] Among them, UW signals have good autocorrelation characteristics, which facilitates signal detection at the receiver, such as... Figure 4 The diagram shown is an autocorrelation performance graph of the UW signal in this embodiment. The horizontal axis represents time delay, and the vertical axis represents the calculated correlation value. When the time delay is 0, the correlation value reaches its absolute peak. Therefore, this characteristic can be used at the receiving end to accurately determine signal arrival. The GP signal is used to ensure balanced signal transmission power, such as... Figure 5 The diagram shows the constellation of the GP signal in this example. The red dots in the diagram represent the ZC sequence, and all the sequences have the same amplitude.

[0059] Step 6: Insert a cyclic prefix between the guard interval signal and the pilot sequence in the frame header, and insert an all-zero signal after the guard interval signal in the frame tail to complete the physical frame assembly. The completion of the framing signifies that the time-frequency distribution of the data on the physical medium has been determined, that is, the waveform design applicable to multiline transmission described in this invention has been completed.

[0060] like Figure 6 The diagram shows the frame structure of the waveform designed in this invention. A burst structure is achieved by adding all-zero bits (ZP) to the end of each frame. A GP signal is inserted at the frame header, which serves both to protect the transmitted data and to implement AGC; a CP signal is inserted before both the UW and OFDM signals; and a GP signal is inserted at the frame tail to protect the data.

Claims

1. A method for designing OFDM waveforms suitable for multiline transmission, characterized in that, include: Receive raw data, verify the raw data, and transform the raw data that passes the verification to obtain the signal to be processed; The signal to be processed is transformed from serial to parallel by constellation mapping and mapped into a point signal on the complex plane. The constellation mapping is performed by frequency band mapping according to the frequency attenuation characteristics of the complex line channel spectrum. The point signal is modulated using OFDM transmission technology to obtain a time-domain OFDM signal; Take several OFDM signals as a frame of the waveform, and copy the last few samples of each OFDM signal to the beginning of the OFDM signal to form a cyclic prefix; Generate a guard interval signal and a pilot sequence. Insert the guard interval signal into the frame header and frame tail respectively, and insert the pilot sequence after the guard interval signal in the frame header. The cyclic prefix is ​​inserted between the guard interval signal and the pilot sequence in the frame header, and an all-zero signal is inserted after the guard interval signal in the frame tail to form a physical layer frame, thus completing the waveform design.

2. The OFDM waveform design method according to claim 1, characterized in that, The original data is verified using the CRC check algorithm. The conversion of the verified original data includes Turbo encoding and rate matching. The signal to be processed is a binary signal.

3. The OFDM waveform design method according to claim 2, characterized in that, The constellation mapping includes: setting a threshold based on the fading characteristics of the multi-channel; treating signals with frequencies below the threshold as low-frequency bands and using 64QAM modulation; and treating signals with frequencies above the threshold as high-frequency bands and using 16QAM modulation.

4. The OFDM waveform design method according to claim 3, characterized in that, The modulation of the point signal includes: the point signal obtained by constellation mapping has a length of N; the point signal is divided into a first half and a second half of length N / 2; the positions of the first half and the second half are interchanged; 7N zeros are inserted in the middle to form a modulation point signal of length 8N; the modulation point signal is subjected to inverse fast Fourier transform to obtain a time-domain OFDM signal.

5. The OFDM waveform design method according to claim 4, characterized in that, The generated guard interval signal and pilot sequence are based on the ZC sequence, which is represented as follows: Where M is the root exponent of the ZC sequence, k is the sequence index. , Set different parameter groups for sequence length. A guard interval signal and a pilot sequence are generated respectively. The guard interval signal is used to equalize the signal transmission power, and the pilot sequence has ideal periodic autocorrelation properties.

6. A waveform design system for OFDM transmission in multiline mode, characterized in that, include: The verification encoding module is used to receive raw data, verify the raw data, and convert the raw data that passes the verification to obtain the signal to be processed. The constellation mapping module is used to perform serial-to-parallel transformation on the signal to be processed through constellation mapping, mapping it into a point signal on the complex plane. The constellation mapping is performed by frequency band mapping according to the frequency attenuation characteristics of the complex line channel spectrum. The signal modulation module is used to modulate the point signal using OFDM transmission technology to obtain a time-domain OFDM signal; The physical layer framing module is used to take several OFDM signals as a waveform frame, copy the last few samples of each OFDM signal to the beginning of the OFDM signal to form a cyclic prefix; generate a guard interval signal and a pilot sequence, insert the guard interval signal at the beginning and end of the frame respectively, and insert the pilot sequence after the guard interval signal at the beginning of the frame; insert the cyclic prefix between the guard interval signal and the pilot sequence at the beginning of the frame, and insert an all-zero signal after the guard interval signal at the end of the frame to form a physical layer frame and complete the waveform design.

7. The OFDM waveform design system according to claim 6, characterized in that, The original data is verified using the CRC check algorithm; the original data that passes the verification is converted by Turbo encoding and rate matching, and the signal to be processed is a binary signal.

8. The OFDM waveform design system according to claim 7, characterized in that, The constellation mapping includes: setting a threshold based on the fading characteristics of the multi-channel; treating signals with frequencies below the threshold as low-frequency bands and using 64QAM modulation; and treating signals with frequencies above the threshold as high-frequency bands and using 16QAM modulation.

9. The OFDM waveform design system according to claim 8, characterized in that, The modulation of the point signal includes: the point signal obtained by constellation mapping has a length of N; the point signal is divided into a first half and a second half of length N / 2; the positions of the first half and the second half are interchanged; 7N zeros are inserted in the middle to form a modulation point signal of length 8N; the modulation point signal is subjected to inverse fast Fourier transform to obtain a time-domain OFDM signal.

10. The OFDM waveform design system according to claim 9, characterized in that, The generated guard interval signal and pilot sequence are based on the ZC sequence, which is represented as follows: Where M is the root exponent of the ZC sequence, k is the sequence index. , Set different parameter groups for sequence length. A guard interval signal and a pilot sequence are generated respectively. The guard interval signal is used to equalize the signal transmission power, and the pilot sequence has ideal periodic autocorrelation properties.

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