DCO-OFDM visible light communication system research method based on software radio

Abstract

The invention discloses a DCO-OFDM visible light communication system research method based on software radio, and particularly relates to a DCO-OFDM visible light communication system, DCO-OFDM visible light communication equipment, a DCO-OFDM visible light communication modulation method and a DCO-OFDM visible light communication signal processing method. The visible light signal is processed at the transmitting end in combination with the DCO-OFDM modulation mode, and the video data can be clearly and smoothly played at the receiving end, so that the real-time effective transmission of the visible light to the video is realized, and the transmission rate is further improved. The visible light communication system established by the invention has feasibility and effectiveness.

Description

Technical Field

[0001] The present application relates to the field of communication technology, and in particular to a DCO-OFDM visible light communication system, equipment, modulation and signal processing method. Background Art

[0002] Nowadays, wireless communication is developing rapidly. Various emerging services such as mobile Internet and streaming media have penetrated into every corner of people's lives and work, bringing great convenience to people. However, at the same time, traditional wireless radio frequency (RF) communication technology has gradually revealed many problems and shortcomings.

[0003] The demand for high-speed wireless communication continues to grow, while traditional wireless radio frequency spectrum resources are on the verge of exhaustion and have become one of the most scarce public resources in contemporary society. At the same time, with the development of solid-state lighting technology, light emitting diodes (LEDs) have rapidly replaced most incandescent and fluorescent lamps with their advantages of low power consumption, low cost and long service life, becoming the mainstream lighting device. Against this background, visible light communication (VLC), which combines the dual functions of lighting and communication, came into being and can effectively solve the above problems.

[0004] The basis of the visible light communication system is a lighting system composed of LED and other equipment. It can achieve high-speed wireless communication in the visible light spectrum range (380-790THz) with huge bandwidth and free of charge, which helps to alleviate the shortage of traditional wireless radio frequency spectrum resources and is a powerful supplement to the existing radio frequency technology. Compared with traditional wireless radio frequency communication equipment, it is low-cost, more low-carbon and green, and has no electromagnetic radiation problems and safety concerns. It is suitable for hospitals, cabins, nuclear power plants, banks, confidentiality agencies and other scenes that require radio frequency signals, and has broad application prospects in the fields of Internet of Things, smart cities, smart homes, subways, indoor positioning and navigation, and underground operations.

[0005] The transmission efficiency of the VLC communication system based on the BPSK modulation scheme of USRP is not high. The system platform built based on software radio and LabVIEW uses non-open source software, and the design cost is high. OFDM modulation technology has high spectrum utilization, can increase data rate, and can effectively combat inter-symbol interference caused by multipath distortion. Since the visible light emitted by LED is non-correlated light, the modulation method adopts intensity modulation / direct detection, requiring that the signal transmitted by visible light can only be a non-negative real signal. This type of OFDM modulation is called optical OFDM (O-OFDM) modulation technology. The DCO-OFDM modulation method based on USRP and GNU Radio has high spectrum utilization and low design implementation cost.

[0006] In summary, there are many problems with previous modulation technologies, and the DCO-OFDM visible light communication system based on USRP and GNU Radio improves spectrum utilization and effectively combats inter-symbol interference. Summary of the invention

[0007] In view of the above problems, the present invention proposes a research method for a DCO-OFDM visible light communication system based on software radio, which has both high transmission rate and cost saving.

[0008] The DCO-OFDM visible light communication system based on software radio mainly consists of two parts: software subsystem and hardware subsystem. Figure 1 The overall structure diagram of the visible light communication system in the invention example. The software subsystem uses the open source GNURadio software. Figure 2 This is a structural block diagram of the software subsystem in the invention example. GNU Radio was developed by Eric Blossom. GNU Radio uses a mixed programming of C++ and Python scripting languages. The highly efficient C++ language is used to develop complex signal processing modules (called blocks) to ensure real-time performance. Figure 3 This is an example of a GNU Radio flow chart in an example of the invention. The hardware subsystem uses a low-cost software radio device USRP X310, an LED module, and a photodiode (PD) module. The present invention is further described below.

[0009] Furthermore, the software subsystem at the transmitter uses the open source GNU Radio software to process the video signal and generate a DCO-OFDM baseband signal which is then transmitted to the USRP X310 equipped with the LFTX daughterboard via an Ethernet cable.

[0010] Furthermore, the baseband signal sent by the software subsystem drives the LED module, and the hardware subsystem is responsible for the transmission of the modulated signal.

[0011] Furthermore, the PD module is used as a receiver at the receiving end to convert the optical signal into an electrical signal. Then, the software subsystem at the receiving end uses the open source GNU Radio software to process the data signal, and transmits the processed data part through the UDP port. The media stream is received through UDP at the application layer, and the received video is decoded and played through VLC through port 1234. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the existing technical solutions, a brief introduction will be given below to the drawings required for use in the examples or the description of the prior art. Obviously, the drawings described below are only some examples of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0013] Figure 1 The overall structure diagram of the visible light communication system in the invention example

[0014] Figure 2 The software subsystem structure diagram in the invention example

[0015] Figure 3 This is an example of the GNU Radio flow graph in the invention example.

[0016] Figure 4 The DCO-OFDM system block diagram in the invention example

[0017] Figure 5 The information sequence with CRC in the invention example

[0018] Figure 6 The structure diagram of the data packet at the sending end in the invention example

[0019] Figure 7 The time domain waveform of the transmitter in the invention example

[0020] Figure 8 The frequency domain waveform of the transmitting end in the invention example

[0021] Fig. 9 The time domain waveform of the receiving end in the invention example

[0022] Fig.10 The frequency domain waveform of the receiving end in the invention example

[0023] Fig.11 This is the video playback screen captured by the receiving end in the invention example DETAILED DESCRIPTION

[0025] 1. Implementation process

[0026] The method provided by the present invention has the following specific steps: using the open source GNU Radio software to process the data signals at the transmitting end and the receiving end, and the modulation mode of the specific transmitting end is combined with the appended claims of the present invention. Figure 4 .Generate DCO-OFDM data and transmit the signal via Ethernet cable to the USRP X310 equipped with the LFTX daughter board, which is responsible for transmitting the modulated signal.

[0027] Step S201: At the transmitting end, DCO-OFDM modulation and demodulation are implemented in GNU Radio software. First, the File Source module is used as the source file of the transmitting end in the form of a video stream, and the data stream Payload is packaged using the Stream To Tagged Stream module to form a frame data stream with a data frame length of 96 bytes, and a 4-byte CRC check code is formed for each frame of data and attached to the end of each frame of data ( Figure 5 The information sequence with CRC in the invention example) is used, so the length of a frame of data is 100 bytes, and a frame header is created for each frame of data, and the length of the frame header is 6 bytes. Figure 6 This is a diagram of the data packet structure at the sending end in the invention example.

[0028] Step S202: symbol mapping is performed on the frame header and the data respectively, the frame header is modulated by BPSK, and the data is modulated by QPSK to realize the conversion from data block to symbol stream, and then the frame header and data signals are combined by the Tagged Stream Mux module to obtain a frame of data.

[0029] Step S203: Perform Hermitian symmetric transformation on the data. After the Hermitian symmetric frequency domain signal is transformed by IFFT, a time domain signal is generated. After adding a cyclic prefix and DA conversion, a time domain analog signal can be obtained. By DC biasing the signal, the bipolar signal is converted to a unipolar signal to obtain a baseband signal.

[0030] Step S204: The baseband signal can drive the LED to emit light to realize the conversion of the electrical signal into the optical signal, and the LED optical carrier reaches the receiving end through the channel.

[0031] Step S205: At the receiving end, the PD acts as a receiver at the receiving end to convert the optical signal into an electrical signal.

[0032] Step S206: In the demodulation at the receiving end, the UHD USRP Source module is first used to transmit the signal received by the hardware USRP X310 to the host.

[0033] Step S207: The signal is de-DC processed, and the output data is divided into two paths. One path of data is synchronized, i.e., the Schmidl&Cox OFDM synch module and the frequency modulation, i.e., the Frequency Mod module, and then enters the multiplication module.

[0034] Step S208: the other data is delayed by one DCO-OFDM symbol and then enters the multiplication module. After the two signals enter the multiplication module, they enter the effective load separator module to separate the header part and the data part in a frame of data.

[0035] Step S209: Since the receiving end does not know the frame structure of the received signal at the beginning, the frame header part and the data part must be demodulated separately. The frame header information must be demodulated first before the received signal can be demodulated normally. The frame header part first enters the FFT module for Fourier transform, and then enters the OFDM Channel Estimation module. After passing through this module, two parameters, integer frequency offset and system frequency domain response, are obtained. Then the data stream enters the OFDM FrameEqualizer module with these two parameters to correct the integer frequency offset and equalize the signal. Then, the OFDM Serializer module is used to realize the conversion from parallel data to serial data, and the information after BPSK demapping is returned to the frame header and data separation module as a label.

[0036] Step S210: After the frame header and data separation module receives the decoded frame header information, it processes the data information. The data part first enters the FFT module for Fourier transform, then enters the OFDM Frame Equalizer module and the OFDM Serializer module to implement frame equalization and parallel-to-serial conversion processing, then QPSK demodulates the data information, and then removes the CRC check word, and the demodulated data part passes the UDP port, receives the media stream through UDP at the application layer, and decodes and plays the received video through VLC through port 1234.

[0037] The step S201 of adding a CRC check code to each frame of data and creating a frame header is further described as follows:

[0038] 1) The frame header contains different contents such as the source address and destination address of the frame. The MAC layer payload contains the data and information to be transmitted. The frame tail check sequence contains error detection and error correction bits. The present invention adopts the CRC-32 check method. The CRC algorithm is to add an r-bit binary sequence after a d-bit binary information sequence to form a binary sequence with a total length of n=d+r bits.

[0039] The generator polynomial specified by the CRC-32 protocol is:

[0040] GCRC-32 =10000010011000001000111011011011=0x104C11DB7

[0041] 2) Take the d-bit frame header and MAC layer payload as the input sequence D, and use the modulo-2 division operation with G, that is, D and G are bit-wise XORed, and the remainder is the r-bit CRC-32 check code R. The calculation formula of R is

[0042]

[0043] 3) The receiving end performs a modulo-2 division operation on the received D again. If the remainder is 0, the test passes and the data is received normally. If the remainder is not 0, it is considered that an error has occurred. At the sending end, the MAC packetizer only needs to package the data to be sent according to the above structure and then modulate it. At the receiving end, the MAC packetizer only needs to unpack the data to be sent according to the above structure, perform a CRC check, and restore the valid data.

[0044] The calculation process of "performing Hermitian symmetric transformation on data" in step S203 includes:

[0045] 1) Hermitian symmetry conditions:

[0046] X={X 0 , X 1 , X 2 , ..., X N-1}

[0047] ={0, X 1 , X 2 , ..., X N / 2-1 ,0,X * N / 2-1 , ..., X * 1}

[0048] X k =X * N-k And X 0 =X N / 2

[0049] Where: X * is the complex conjugate of X, and k is the kth subcarrier.

[0050] 2) Calculate the number of valid data subcarriers as (N / 2-1).

[0051] 3) After the Hermitian symmetric frequency domain signal X is transformed by IFFT, a time domain signal x is generated. The nth time domain value x of x is n It is expressed as:

[0052]

[0053] 4) Apply DC bias to the signal to realize the conversion from bipolar signal to unipolar signal, that is:

[0054] x DCO (t) = x(t) + I DC

[0055] Where: I DC is the bias current

[0056] 5) After adding DC bias, there are still a few negative signals, so for x DCO The part of (t) that is still less than 0 is cut off and expressed as:

[0057]

[0058] 2. Simulation Results and Analysis

[0059] The video is modulated and demodulated by DCO-OFDM, and the signal is transmitted. The average transmission efficiency is 1753Kb / s. The time domain and frequency domain waveforms of the transmission and reception are shown in the attached figure. Figure 7-10 .From the observation results, it can be found that the video stream can be played smoothly without any delay. If the network does not fluctuate during the transmission process, there will be no packet loss. The captured video playback screen is attached. Fig.11 .

Claims

1. A research method for a DCO-OFDM visible light communication system based on software radio, which has both high transmission rate and cost saving. Its characteristics are: It includes the system software subsystem GNU Radio, VLC media player and the hardware subsystem USRP X310, LED module, and PD module. The software subsystem demonstration uses VLC media player to send and receive data through the UDP interface, which can conveniently and intuitively demonstrate the real-time transmission of video.

2. The method for studying a DCO-OFDM visible light communication system based on software radio according to claim 1, characterized in that: The transmitting end of the software subsystem includes a CRC check code adding module, a digital modulation module, a serial-to-parallel conversion module, a Hermitian transform module, an IFFT transform, a cyclic prefix adding module, a DC bias module, a signal amplification and current limiting module, which are connected in sequence, and then generate a baseband signal so that the baseband signal drives the LED through analog modulation.

3. The method for studying a DCO-OFDM visible light communication system based on software radio according to claim 1, characterized in that: The sending end of the software subsystem includes a DC removal module, a cyclic prefix removal module, an FFT module, an inverse Hermitian symmetric transform module, a parallel-to-serial conversion module, a digital demodulation module, and a CRC check code removal module, which are connected in sequence, and then processes the received signal to view the transmitted video in real time.

4. The method for studying a DCO-OFDM visible light communication system based on software radio according to claim 1, characterized in that: The transmitting end of the hardware subsystem includes USRP X310 and LED module, and the baseband signal sent by the software subsystem drives the LED module.

5. The method for studying a DCO-OFDM visible light communication system based on software radio according to claim 1, characterized in that: The receiving end of the hardware subsystem includes a photodiode (PD) module, which serves as a receiver at the receiving end and is used to convert optical signals into electrical signals.

Images