CN109450538B - Visible light communication square synchronization system suitable for power transmission line inspection in high-altitude area - Google Patents
Visible light communication square synchronization system suitable for power transmission line inspection in high-altitude area Download PDFInfo
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- CN109450538B CN109450538B CN201811457635.9A CN201811457635A CN109450538B CN 109450538 B CN109450538 B CN 109450538B CN 201811457635 A CN201811457635 A CN 201811457635A CN 109450538 B CN109450538 B CN 109450538B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/11—Arrangements specific to free-space transmission, i.e. transmission through air or vacuum
- H04B10/114—Indoor or close-range type systems
- H04B10/116—Visible light communication
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
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Abstract
The first square ring carrier synchronization unit and the second square ring carrier synchronization unit are used for respectively carrying out phase synchronization processing on the received signals, and the output signals processed by the first square ring carrier synchronization unit and the output signals processed by the second square ring carrier synchronization unit are added through an adder to form an integral digital output signal. The invention fully utilizes the signal resources of the non-line-of-sight link part, realizes carrier synchronization in the field of visible light communication, is not interfered by complex electromagnetic environment of a high-voltage line in the line inspection process, is easy to realize a linear network topological structure, is suitable for networking of a power transmission line, and can be applied to the inspection of the power transmission line in a high-altitude area.
Description
Technical Field
The invention relates to a visible light communication square synchronization system. In particular to a visible light communication square synchronization system suitable for routing inspection of transmission lines in high altitude areas.
Background
High altitude, more mountainous areas and severe natural environment in areas such as Qinghai-Tibet plateau, high-voltage transmission lines are mostly built according to mountains in order to save precious land resources, and the traditional manual inspection mode of the high-voltage transmission lines is greatly restricted. New technologies such as unmanned aerial vehicle routing inspection play an important role in power grid maintenance and inspection. Because unmanned aerial vehicle is when high-speed flight, its channel environment is constantly changeing, and its transmission speed can not be changed according to the channel situation of difference in real time to the communication system of single speed, is unfavorable for the promotion of transmission efficiency. In addition, when the unmanned aerial vehicle flies at a high speed, a relatively serious Doppler effect can be generated to cause relatively large intersymbol interference, and meanwhile, strong electromagnetic interference exists nearby a high-voltage transmission line, so that the limitation of the traditional communication mode is relatively large.
At the core of visible light communication technology, the transmission mode of visible light channel and the carrier synchronization closely related to the transmission mode are always the key areas of research. The link scheme of the indoor communication system can be divided into two points. The first point is to see if the transmitter and receiver are directional. Orientation, which is actually an angular problem, is called a directional transmitter if the divergence angle of the emitted light beam is small and the emitted light beam is nearly parallel; if the field angle range of the receiver is small, the receiver is called a directional receiver. If both are oriented, a link is established when the two ends of the receiving and sending are aligned, and the link is called as an oriented link. And the non-directional link uses a large angle receiver and transmitter. There is also a link where one of the transmitter and receiver is non-directional and the other is directional, which is known as a hybrid link. The second point is that the two ends are classified according to whether there is an undisturbed line of sight (LOS) between the transmitter and the receiver. Light received by a receiver in a line of sight (LOS) link is stored in unreflected light transmitted by a transmitter; instead of a line of sight (NLOS) link, a transmitter typically transmits a light signal against a ceiling, via a series of reflections off walls, to a receiver. In summary, the link schemes of the wireless optical communication are generally classified into the following six types: a directional line-of-sight link; a non-directional line-of-sight link; a hybrid line-of-sight link; a directional non-line-of-sight link; a non-directional non-line-of-sight link; hybrid non-line-of-sight links.
In a digital communication system, synchronization is an important technical problem and a difficult point in implementation, and the quality of synchronization performance directly determines the performance of the communication system.
In a communication system, after information is mapped in a specific mode, a transmitter modulates the information and transmits the information through a channel at a certain frequency, a signal received by a receiver is interfered by noise in the channel, and in order to accurately recover transmitted data, the receiver mainly works to provide a synchronous system for a decision device so as to realize estimation and correction of data parameters. When a receiver demodulates a signal, a coherent carrier with the same frequency and phase as a received signal carrier needs to be extracted from the signal, the extraction process of the coherent carrier is carrier synchronization, and the carrier synchronization is the basis of coherent demodulation. Digital information in a communication system is a continuous sequence of symbols, and when symbol decision is made on a demodulated signal, the optimal sampling time in a symbol period, that is, the position where an eye pattern is maximally opened, is generally selected. The receiving end must generate a bit timing pulse sequence that is synchronized with the symbol clock of the received modulated signal for symbol sampling decisions.
The carrier synchronization can be divided into two categories, namely a pilot method and a direct method, the pilot sequence needs to be inserted into a transmitted information sequence by the pilot insertion method, and a system needs to allocate certain power to a pilot signal, so that the power allocated to the information sequence is correspondingly reduced. The square-loop method is one of direct carrier synchronization methods, and the traditional square-loop carrier synchronization method consists of a square law device, a phase-locked loop and a two-frequency divider. The phase-locked loop is equivalent to a very narrow-band filter, can well extract a required carrier component, and has good tracking, narrow-band filtering and memory functions.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a square synchronization system which makes full use of frequency spectrum resources of an LOS channel and an NLOS channel, improves the frequency band utilization rate of a visible light system and is suitable for routing inspection of a transmission line in a high-altitude area.
The technical scheme adopted by the invention is as follows: the first square ring carrier synchronization unit and the second square ring carrier synchronization unit are used for respectively carrying out phase synchronization processing on the received signals, and the output signals processed by the first square ring carrier synchronization unit and the output signals processed by the second square ring carrier synchronization unit are added through an adder to form an integral digital output signal.
The first square ring carrier synchronization unit and the second square ring carrier synchronization unit have the same structure and both comprise: the square law module, the band-pass filter, the phase-locked loop and the frequency divider are sequentially connected in series, wherein the input end of the square law module receives a line-of-sight signal or a non-line-of-sight signal and is used for squaring the received signal and outputting a group of time domain signals, and the output end of the frequency divider forms the output end of the first square ring carrier synchronization unit or the second square ring carrier synchronization unit.
The phase-locked loop including phase detector, loop filter and the numerically controlled oscillator of series connection in proper order, the output of band pass filter is connected to the input of phase detector, the input of phase detector and the input of two frequency dividers are connected respectively to the output of numerically controlled oscillator, wherein, the phase detector carries out the phase discrimination to the output signal of numerically controlled oscillator and band pass filter's output signal, produces a phase error signal, loop filter filtering receive signal in high frequency signal and noise, take out the frequency of slowly changing direct current component control numerically controlled oscillator to through the double-linear transformation with received analog signal mapping to the digital domain, numerically controlled oscillator produces the changeable sine of ideal frequency and cosine signal with loop filter's output.
The numerically controlled oscillator comprises a phase accumulator, a phase register, a phase adder and a CORDIC algorithm module which are sequentially connected in series, wherein the input end of the phase accumulator is respectively connected with the output end of the loop filter and the output end of the phase register, the input end of the phase adder is also connected with a phase control word, and the output end of the CORDIC algorithm module is respectively connected with the input end of the phase discriminator and the input end of the frequency divider.
The invention is suitable for the transmission line routing inspection visible light communication square synchronization system in the high altitude area, fully utilizes the signal resource of a Non-line of sight (Non-LOS) part, and realizes the carrier synchronization in the field of visible light communication. The invention has the following advantages:
1. based on the visible light communication technology, a two-way carrier synchronization method is adopted, and signals passing through an NLOS channel part are fully utilized. The frequency band utilization rate is improved.
2. Compared with the traditional numerically-controlled oscillator based on a lookup table, the numerically-controlled oscillator part adopts a novel numerically-controlled oscillator based on a cordic algorithm, and improves the reaction speed and the working efficiency.
3. Compared with the traditional visible light communication synchronization module, the complexity of the synchronization system is not increased.
In conclusion, the visible light communication square synchronization system suitable for power transmission line inspection in the high-altitude area has a good application prospect.
Drawings
FIG. 1 is an overall block diagram of a visible light communication square synchronization system for power transmission line inspection in high altitude areas;
FIG. 2 is a block diagram showing the structure of a square-loop carrier synchronization unit according to the present invention;
fig. 3 is a block diagram of a configuration of a numerically controlled oscillator according to the present invention.
In the drawings
1: first square ring carrier synchronization unit 2: second square ring carrier synchronization unit
3: adder 4: square law module
5: band-pass filter 6: phase-locked loop
61: the phase detector 62: loop filter
63: digitally controlled oscillator 631: phase accumulator
632: phase register 633: phase adder
634: CORDIC algorithm block 635: phase control word
7: frequency divider
Detailed Description
The following describes details of the visible light communication square synchronization system suitable for power transmission line inspection in high altitude areas according to the embodiments and the accompanying drawings.
As shown in fig. 1, the visible light communication square synchronization system suitable for routing inspection of power transmission lines in high altitude areas of the present invention is characterized by comprising a first square ring carrier synchronization unit 1 and a second square ring carrier synchronization unit 2, wherein the first square ring carrier synchronization unit 1 and the second square ring carrier synchronization unit 2 simultaneously and respectively receive line-of-sight signals (LOS) and non-line-of-sight signals (NLOS), the first square ring carrier synchronization unit 1 and the second square ring carrier synchronization unit 2 are used for respectively performing phase synchronization processing on received signals, and an output signal processed by the first square ring carrier synchronization unit 1 and an output signal processed by the second square ring carrier synchronization unit 2 are added by an adder 3 to form an integral digital output signal.
As shown in fig. 2, the first square ring carrier synchronization unit 1 and the second square ring carrier synchronization unit 2 have the same structure, and both include: the square law module 4, the band-pass filter 5, the phase-locked loop 6 and the frequency divider 7 are connected in series in sequence, wherein the input end of the square law module 4 receives a line-of-sight signal or a non-line-of-sight signal and is used for squaring the received signal and outputting a group of time domain signals, and the output end of the frequency divider 7 forms the output end of the first square ring carrier synchronization unit 1 or the second square ring carrier synchronization unit 2.
The phase locked loop 6 comprises a phase detector 61, a loop filter 62 and a numerically controlled oscillator 63 which are connected in series in sequence, the input end of the phase detector 61 is connected with the output end of the band-pass filter 5, the output end of the numerical control oscillator 63 is respectively connected with the input end of the phase detector 61 and the input end of the frequency divider 7, wherein, the phase discriminator 61 discriminates the phase of the output signal of the digital controlled oscillator 63 and the output signal of the band-pass filter 5 to generate a phase error signal, the loop filter 62 filters out the high frequency signal and noise in the received signal, extracts the slowly changing dc component to control the frequency of the digitally controlled oscillator 63, and maps the received analog signals to the digital domain through bi-linear transformation, and the numerically controlled oscillator 63 generates ideal variable frequency sine and cosine signals through fixed frequency control words and the output of the loop filter 62.
As shown in fig. 3, the digital controlled oscillator 63 includes a phase accumulator 631, a phase register 632, a phase adder 633 and a CORDIC algorithm module 634, which are sequentially connected in series, wherein an input end of the phase accumulator 631 is respectively connected to an output end of the loop filter 62 and an output end of the phase register 632, an input end of the phase adder 633 is further connected to a phase control word 635, and an output end of the CORDIC algorithm module 634 is respectively connected to an input end of the phase detector 61 and an input end of the divide-by-two divider 7.
The invention is suitable for the transmission line polling visible light communication square synchronization system in the high altitude area by the following examples.
The visible light channel is divided into LOS and NLOS, so that the impulse response of the channel forms two peaks with a certain phase difference. The luminous flux of visible light communication is mainly concentrated on an LOS channel, so the traditional synchronization mode mainly synchronizes the LOS channel part, and the invention adopts a synchronization unit in a double-carrier synchronization mode as shown in fig. 1 to synchronize two parts of signals in different phase intervals respectively.
According to fig. 2, firstly, two square ring carrier synchronization units at the receiving end of the signal respectively perform synchronization operation on corresponding phase regions. Now, assuming that the input signal is a BPSK signal, after the BPSK signal is input to the synchronization unit, the BPSK signal is firstly squared by the square law module to obtain:
when the input signal is a rectangular pulse
Suppose the phase-locked loop is phase-locked at 2 omegacAt a frequency of the digitally controlled oscillator
Wherein
Is an estimate of the phase of the input signal.
The phase error signal obtained by the phase detector is as follows because the phase detector is realized by a multiplier
The signals obtained after the loop filter filters the high-frequency components are as follows:
it follows that the output of the loop filter is only phase dependent. The system function of the loop filter is:
the key to this part is the value of C1 and C2, whereby the analog quantity of the phase difference is mapped to a digital quantity that can be recognized by the numerically controlled oscillator.
The traditional numerically controlled oscillator adopts a table look-up method to generate sine and cosine signals, needs to occupy a large amount of hardware storage resources under the condition of higher requirement on output precision, and the output speed is restricted by the reading speed of a chip RAM. The CORDIC algorithm adopted by the invention can decompose sine and cosine calculation into a series of addition, subtraction and shift operations, has a simpler algorithm structure, is suitable for hardware realization, and occupies less hardware storage resources.
Claims (3)
1. The visible light communication square synchronization system is characterized by comprising a first square ring carrier synchronization unit (1) and a second square ring carrier synchronization unit (2), wherein the first square ring carrier synchronization unit (1) and the second square ring carrier synchronization unit (2) simultaneously and respectively receive line-of-sight signals, the first square ring carrier synchronization unit (1) and the second square ring carrier synchronization unit (2) are used for respectively carrying out phase synchronization processing on the received signals, and output signals processed by the first square ring carrier synchronization unit (1) and output signals processed by the second square ring carrier synchronization unit (2) are added through an adder (3) to form an integral digital output signal; the first square ring carrier synchronization unit (1) and the second square ring carrier synchronization unit (2) have the same structure and both comprise: the square law module (4), band-pass filter (5), phase-locked loop (6) and divide-by-two ware (7) that series connection in proper order, wherein, the input of square law module (4) of art receives line-of-sight signal or non-line-of-sight signal for square the signal received, export a set of time domain signal, the output of divide-by-two ware (7) constitutes the output of first square ring carrier synchronization unit (1) or second square ring carrier synchronization unit (2).
2. The system for the visual communication square synchronization for the routing inspection of the power transmission lines in the high altitude areas according to claim 1, wherein the phase-locked loop (6) comprises a phase detector (61), a loop filter (62) and a numerical control oscillator (63) which are sequentially connected in series, the input end of the phase detector (61) is connected with the output end of the band-pass filter (5), the output end of the numerical control oscillator (63) is respectively connected with the input end of the phase detector (61) and the input end of the frequency divider (7), wherein the phase detector (61) performs phase discrimination on the output signal of the numerical control oscillator (63) and the output signal of the band-pass filter (5) to generate a phase error signal, the loop filter (62) filters out high-frequency signals and noise in the received signal and takes out slowly-varying direct-current components to control the frequency of the numerical control oscillator (63), the received analog signals are mapped to a digital domain through bilinear transformation, and a digital controlled oscillator (63) generates ideal sine and cosine signals with variable frequency through fixed frequency control words and the output of a loop filter (62).
3. The system for visual communication square synchronization for power transmission line inspection in high altitude areas according to claim 2, wherein the numerically controlled oscillator (63) comprises a phase accumulator (631), a phase register (632), a phase adder (633) and a CORDIC algorithm module (634) which are sequentially connected in series, wherein an input end of the phase accumulator (631) is respectively connected with an output end of the loop filter (62) and an output end of the phase register (632), an input end of the phase adder (633) is further connected with a phase control word, and an output end of the CORDIC algorithm module (634) is respectively connected with an input end of the phase detector (61) and an input end of the frequency halver (7).
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Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN101150343A (en) * | 2006-09-20 | 2008-03-26 | 华为技术有限公司 | A MIMO mobile communication method and system |
| CN107359935A (en) * | 2017-07-11 | 2017-11-17 | 中国科学技术大学 | A kind of ultraviolet scatter communication system of non line of sight based on step-by-step counting and its method |
| CN108494714A (en) * | 2018-03-22 | 2018-09-04 | 桂林电子科技大学 | A method of quickly overcoming the GMSK coherent demodulations of Doppler frequency shift |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN101150343A (en) * | 2006-09-20 | 2008-03-26 | 华为技术有限公司 | A MIMO mobile communication method and system |
| CN107359935A (en) * | 2017-07-11 | 2017-11-17 | 中国科学技术大学 | A kind of ultraviolet scatter communication system of non line of sight based on step-by-step counting and its method |
| CN108494714A (en) * | 2018-03-22 | 2018-09-04 | 桂林电子科技大学 | A method of quickly overcoming the GMSK coherent demodulations of Doppler frequency shift |
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