CN103840886B

CN103840886B - Based on the method for precoding of multiple light courcess in a kind of visible light communication

Info

Publication number: CN103840886B
Application number: CN201410035504.7A
Authority: CN
Inventors: 董昊; 张洪明; 郎凯
Original assignee: Tsinghua University
Current assignee: Tsinghua University
Priority date: 2014-01-24
Filing date: 2014-01-24
Publication date: 2016-02-24
Anticipated expiration: 2034-01-24
Also published as: CN103840886A

Abstract

Based on the method for precoding of multiple light courcess in a kind of visible light communication, the data bit flow of serial is after mapping through planisphere, be N channel parallel data through serioparallel exchange, N number of orthogonal sub-carriers is used to modulate N channel parallel data respectively, according to the channel fading characteristic recorded in advance, draw the flat fading gains σ of each subchannel _i, i=0,1 ..., N-1, if the received power that subchannel i expects is P _i, the flat fading gains of channel is σ _i, then, when adopting precoding, the transmitting power of subchannel i is P _iˊ=P _i/ σ _idivide into groups according to the transmitting power of each subchannel afterwards, then often Signal averaging will be organized, be loaded on different LED light sources, the present invention not only can reduce the higher PAPR of OFDM symbol to the impact of transmission of visible light system, improve power utilization, and reversed by the channel fading of transmitting terminal, the signal to noise ratio of receiving terminal can be improved.

Description

Based on the method for precoding of multiple light courcess in a kind of visible light communication

Technical field

The invention belongs to technical field of visible light communication, particularly in a kind of visible light communication based on the method for precoding of multiple light courcess.

Background technology

The later stage nineties 20th century, the semi-conductor LED illuminating technical development being described as green illumination is swift and violent, the low-carbon (LC) possessed due to white light LEDs, green and the feature such as efficient, government also releases policy and approaches and encourages it to develop, in recent years, along with the maturation of LED technology and the reduction of cost, its application is sprawled rapidly and is come.The Novel Communication technology that visible light communication grows up just nearly ten years in this context, utilize the high speed electro-optical response characteristic of white light LEDs, information is by injecting its utilizing emitted light power of Current Control of LED, use photodetector to complete the conversion of photosignal at receiving terminal, complete the demodulation of information further.

The single-carrier modulated modes such as OOK, PPM are in high rate data transmission situation, and intersymbol interference will cause system performance degradation, become the principal element affecting speed and promote.Therefore, in visible ray high-speed communication system, OFDM (OFDM) technology becomes the focus of current research.The low speed data that principle Shi Jiang mono-tunnel of OFDM technology converting serial data streams at a high speed becomes N road parallel, go respectively afterwards to modulate the orthogonal subcarrier in N road, N subcarriers is launched with the form of base band or radio frequency after superimposing.When number of sub carrier wave N is enough large, the intersymbol interference that the temporal dispersion that can effectively reduce channel brings, the use of orthogonal sub-carriers simultaneously also makes its availability of frequency spectrum have the lifting of nearly a times compared with single carrier transmission.In addition the modulation /demodulation of quadrature modulation can the very ripe IFFT/FFT of operation technique, and the system of which greatly simplifies realizes difficulty.

Tradition OFDM is applied to the typical structure of visible light communication system as shown in Figure 1, because OFDM symbol is that the superposition of multiple sub-carrier signal generates, when multiple sub-carrier signal phase place is consistent, the instantaneous power of signal is by the average power much larger than signal, so OFDM symbol exists the higher problem of papr (PAPR).Consider non-linear (the non-linear and cut-off characteristics of transmission characteristic) of LED light source, current visible ray ofdm system needs to use power attenuation to avoid signal generation slicing usually, this can cause the reduction of power efficiency, and therefore the transmission rate of system and coverage also can be affected.And additive method such as restricted coding, selected mapping method can increase the implementation complexity of system.

Summary of the invention

In order to overcome the shortcoming of above-mentioned prior art, the object of the present invention is to provide the method for precoding based on multiple light courcess in a kind of visible light communication, not only can reduce the higher PAPR of OFDM symbol to the impact of transmission of visible light system, improve power utilization, and reversed by the channel fading of transmitting terminal, the signal to noise ratio of receiving terminal can be improved.

To achieve these goals, the technical solution used in the present invention is:

Based on the method for precoding of multiple light courcess in a kind of visible light communication, the data bit flow of serial is after mapping through planisphere, be N channel parallel data through serioparallel exchange, N number of orthogonal sub-carriers is used to modulate N channel parallel data respectively, according to the channel fading characteristic recorded in advance, draw the flat fading gains σ of each subchannel _i, i=0,1 ..., N-1, if the received power that subchannel i expects is P _i, the flat fading gains of channel is σ _i, then, when adopting precoding, the transmitting power of subchannel i is P _i'=P _i/ σ _i, divide into groups according to the transmitting power of each subchannel afterwards, then often will organize Signal averaging, be loaded on different LED light sources.

Consider more general situation, according to the relation between each sub-channel transmission power, suitable value P' can be chosen, carry out subchannel grouping.As when each sub-channel transmission power difference is less, as subchannel maximum transmission power and the ratio of minimum emissive power are less than or equal to k (k desirable scope be 9 to 16), here P' can be the maximum two or several sub-channel transmission power sums of transmitting power, then divide into groups from low sequence number subcarrier, grouping standard is that the transmitting power sum often organizing comprised subcarrier is about P'.As when each sub-channel transmission power difference is larger, as subchannel maximum transmission power and the ratio of minimum emissive power are more than or equal to k(k desirable about 16), now desirable P' is the maximum sub-channel transmission power of transmitting power, divide into groups from low sequence number subcarrier, grouping standard often organizes comprised subcarrier transmitting power sum to be about P'.

Compared with prior art, the total transmitting power often organizing signal due to the present invention is consistent, and often organize subchannel number limited (artificially often will organize subcarrier number as the selection by P' to control within 4), therefore by control signal power, its amplitude is strict controlled in the linear operating region of LED light source.

Through flat decline σ _iafterwards, received power remains P _iσ _i/ σ _i=P _i.Channel is reversed in transmitting terminal and completes, and receiving terminal noise power is still N ₀b _n, serve the effect improving receiving terminal signal to noise ratio.

Accompanying drawing explanation

Fig. 1 is visible ray ofdm communication system exemplary block diagram.

Fig. 2 is the pre-coding scheme system configuration schematic diagram that the present invention is based on multiple light courcess.

Fig. 3 is the channel frequency response curve using one of impulse response method test gained normalized typical visible ray direct-view link.

Embodiment

Embodiments of the present invention are described in detail below in conjunction with drawings and Examples.

As shown in Figure 2, the present invention is the method for precoding based on multiple light courcess in a kind of visible light communication, and the data bit flow of serial, after mapping through planisphere, is N channel parallel data through serioparallel exchange, use N number of orthogonal sub-carriers to modulate N channel parallel data respectively, namely use cos2 π f ₀t modulates first via data, uses cos2 π f ₁t modulates the second circuit-switched data ..., use cos2 π f _n-1t modulates N circuit-switched data.

Relative to wireless radiofrequency channel, the decline of visible light communication channel is metastable, so can carry out test evaluation to channel fading characteristic in advance, as used the frequency response of frequency sweep method or impulse response method test channel.Be illustrated in figure 3 the channel frequency response curve using one of impulse response method test gained normalized typical visible ray direct-view link.

According to the channel fading characteristic recorded, the flat fading gains σ of each subchannel can be drawn _i, i=0,1 ..., N-1, if the received power that subchannel i expects is P _i, the flat fading gains of channel is σ _i, then, when adopting precoding, the transmitting power of subchannel i is P _i'=P _i/ σ _i.

Divide into groups according to the transmitting power of each subchannel afterwards, consider more general situation, according to the relation between each sub-channel transmission power, suitable value P' can be chosen, carry out subchannel grouping.When each sub-channel transmission power difference is less, as subchannel maximum transmission power and the ratio of minimum emissive power are less than or equal to k (k desirable scope be 9 to 16), desirable P' is the maximum two or several sub-channel transmission power sums of transmitting power, then divide into groups from low sequence number subcarrier, grouping standard is that the transmitting power sum often organizing comprised subcarrier is about P'.When each sub-channel transmission power difference is larger, as subchannel maximum transmission power and the ratio of minimum emissive power are more than or equal to k(k desirable about 16), now desirable P' is the maximum sub-channel transmission power of transmitting power, divide into groups from low sequence number subcarrier, grouping standard often organizes comprised subcarrier transmitting power sum to be about P'.

Often will organize Signal averaging afterwards, be loaded on different LED light sources, because the total transmitting power often organizing signal is consistent, and often organizing subchannel number, limited (artificially often will organize subcarrier number as the selection by P' controls within 4, prevent high-power peaks), therefore by control signal power, its amplitude is strict controlled in the linear operating region of LED light source.

Wherein digital-to-analogue conversion is completed by digital to analog converter (DAC), and direct current biasing can use bias-T device or complete through the analog circuit of design, and direct current biasing point needs meticulously to select to ensure that signal is operated in the range of linearity of LED transmission curve.

At receiving terminal, by photoelectric detector, light signal is converted to the signal of telecommunication, by analog to digital converter, by analog electrical signal, it is converted to digital electric signal afterwards, in digital device (FPGA/DSP), settling signal is synchronous, remove Cyclic Prefix, FFT operates, planisphere inverse mapping and parallel-serial conversion, exports decoding bit stream.

Claims

1. in a visible light communication based on the method for precoding of multiple light courcess, the data bit flow of serial is after mapping through planisphere, be N channel parallel data through serioparallel exchange, it is characterized in that, N number of orthogonal sub-carriers is used to modulate N channel parallel data respectively, according to the channel fading characteristic recorded in advance, draw the flat fading gains σ of each subchannel _i, i=0,1 ..., N-1, if the received power that subchannel i expects is P _i, the flat fading gains of channel is σ _i, then, when adopting precoding, the transmitting power of subchannel i is P _i'=P _i/ σ _i, divide into groups according to the transmitting power of each subchannel afterwards, then often will organize Signal averaging, be loaded on different LED light sources;

As subchannel maximum transmission power and the ratio of minimum emissive power are less than or equal to k, the span of k is 9 to 16, then getting P' is the maximum two or several sub-channel transmission power sums of transmitting power, then divide into groups from low sequence number subcarrier, grouping standard is that the transmitting power sum often organizing comprised subcarrier is about P';

As subchannel maximum transmission power and the ratio of minimum emissive power are greater than k, the value 16 of k, then getting P' is the maximum sub-channel transmission power of transmitting power, and divide into groups from low sequence number subcarrier, grouping standard often organizes comprised subcarrier transmitting power sum to be about P'.