CN104539363A - Self-adaptive transmission method for multicolor LED visible light communication - Google Patents

Self-adaptive transmission method for multicolor LED visible light communication Download PDF

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CN104539363A
CN104539363A CN201510019678.9A CN201510019678A CN104539363A CN 104539363 A CN104539363 A CN 104539363A CN 201510019678 A CN201510019678 A CN 201510019678A CN 104539363 A CN104539363 A CN 104539363A
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sequence
receiver
subcarrier
transmitter
channel
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CN201510019678.9A
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CN104539363B (en
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赵春明
吴满
黄鹤
梁霄
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东南大学
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Abstract

The invention discloses a self-adaptive transmission method for multicolor LED visible light communication. The self-adaptive transmission method comprises the steps that a system enters a configuration negotiation status under the condition that multicolor LED available transmission bandwidth is unknown and the change of signal to interference ratio exceeds a threshold value during normal communication; in the configuration negotiation status, unequal bandwidth transmission on different colors is achieved by transmitting estimated available bandwidth and an effective signal to interference ratio of a leader sequence and by adopting an orthogonal frequency division multiplexing virtual subcarrier method, an error correction coding code rate is selected according to an equivalent signal to interference ratio of the system, and a suitable modulation method is selected according to equivalent signal to interference ratios of all subcarriers in available bandwidth of all the colors, so self-adaptive transmission approaching channel capacity is achieved; after configuration negotiation is completed, the system enters a normal communication status and performs communication transmission. According to the self-adaptive transmission method, by introducing the virtual subcarriers, OFDM modulation with the same subcarrier spacing is adopted on different colors, so the implementation complexity is lowered; the coding code rate of subcarrier modulation is selected through the equivalent signal to interference ratio, and therefore bandwidth efficiency and power efficiency are effectively improved.

Description

A kind of multi-colored led visible light communication adaptive transmission method
Technical field
The present invention relates to a kind of multi-colored led visible light communication adaptive transmission method, belong to visible light communication technology.
Background technology
Wireless light communication (OWC) because of its frequency spectrum resource abundant and unrestricted, transmitting power can improve greatly and accepts signal to noise ratio, advantages such as electromagnetic radiation level is low, and fail safe is good and obtain the concern of communications field researcher, and becomes study hotspot gradually.In recent years, visible light communication technology obtains and develops rapidly, IEEE has formulated IEEE802.15.7 standard, to its physical layer (PHY, Physics) and media access control layer (MAC, Medium Access Control) implementation method and parameter index carried out standardization.In order to improve the transmission rate of radio optical communication system, to anti-multipath jamming, OFDM modulation mode is introduced, and researcher finds that OFDM is a kind of mode of effective raising radio optical communication system performance from theory and experiment.And the wireless optical ofdm communication system occurred at present is mostly for specific channel design, ensureing under the poorest channel condition also can proper communication, but traffic rate does not have difference under severe channel circumstance and good channel circumstance, such system can not change good channel condition into transmission rate gain.
Because current radio optical communication system generally adopts intensity modulated/direct-detection (IM/DD), the positive solid of OFDM time-domain signal therefore to be ensured.Two the optical communication OFDM structures be widely adopted now are non-symmetrical clipping light OFDM (ACO-OFDM) and direct current biasing light OFDM (DCO-OFDM).ACO-OFDM is the improvement transmitted at optical communication special channel traditional OFDM, proposed in 2006 by Australian Scientists Jean Armstrong, its basic thinking is exactly to be exchanged for by the properties that Fourier converts with more subcarrier to launch symbol to meet optical channel characteristic in time domain, its frequency domain symbol meets conjugate symmetry and value in even subcarriers is 0 entirely, only have the subcarrier of 1/4 for sending significant character, therefore the availability of frequency spectrum is lower; But it does not add direct current biasing, capacity usage ratio can be improved.The frequency domain symbol of DCO-OFDM also meets conjugate symmetry, but do not ask the value in even subcarriers to be 0, there is the subcarrier of 1/2 for transmitting significant character, the availability of frequency spectrum is high, but its in order to make time-domain signal be on the occasion of, need the signal to IFFT exports to add extra direct current biasing, reduce capacity usage ratio.
White light LEDs can be divided into monocrystalline type and polymorphic according to the difference of light-emitting diode quantity.Common monocrystalline type white light LEDs utilizes monolithic blue-ray LED deexcitation yellow fluorescent powder to produce white light, and its technology is simple, low price, and the white light LEDs of present stage is all mainly adopt this technology, but its color rendering index and luminous efficiency are all lower.Common polymorphic white light LEDs red, green, blue, Huang etc. is planted the LED of color carry out colour mixture thus produce white light, and its color rendering index and luminous efficiency all have a distinct increment relative to monocrystalline type white light LEDs, but its technology relative complex, present stage cost higher.These two kinds of LED etc. can be used for visible light communication, and can also modulate respectively the diode of the multiple color of polymorphous LED and add filter at receiving terminal again and obtain multiple relatively independent channel, realize the communication of visible ray multiband, improve transmission rate.But the characteristic of channel of the subchannels such as the red, green, blue of polymorphic LED, Huang is different, can be made full use of the bandwidth of these subchannels by adaptive modulation technology.
Summary of the invention
Goal of the invention: in order to overcome the deficiencies in the prior art, the invention provides a kind of adaptive transmission scheme being applicable to multi-colored led visible light communication system, this system according to the different adaptively modifying modulation of each color of light channel, thus can improve transmission rate while guaranteeing system communication reliability.
Technical scheme: for achieving the above object, the technical solution used in the present invention is:
A kind of multi-colored led visible light communication adaptive transmission method, system comprises configuring negotiation and proper communication two kinds of operating states, under the change of generation signal interference ratio exceedes threshold condition when the multi-colored led available transmission bandwidth of the unknown and proper communication, enter configuring negotiation state; In configuring negotiation state, available bandwidth and effective signal interference ratio is estimated by sending targeting sequencing, OFDM (OFDM) virtual subnet carrier method is adopted to realize not homochromy upper different-bandwidth transmission, follow and select error correction coding code check according to system equivalence signal interference ratio, and select suitable modulator approach according to subcarrier equivalence signal interference ratio each in each color available bandwidth, realize the Adaptive Transmission of approaching channel capacity; After configuring negotiation completes, system enters normal communication state, carries out communications.
The present invention makes by introducing virtual subnet carrier wave the OFDM modulation that not homochromy upper employing subcarrier spacing is identical, enormously simplify implementation complexity, selects encoder bit rate and subcarrier-modulated, effectively improve band efficiency and power efficiency by equivalent signal interference ratio.
In configuring negotiation state, comprise the steps: first, transmitter sends the known pilot frequency sequence of specific receiving terminal to receiver; Then, receiver, according to the pilot frequency sequence received, estimates the signal interference ratio on each subcarrier, obtains the transformation parameter under adaptation current system channel condition, and this transformation parameter is sent to receiver; Then, after transmitter receives transformation parameter, according to transmission parameter settings transmitter, ACK is sent after arranging successfully to receiver; Again, after receiver receives ack signal, according to transmission parameter settings receiver, send ACK after arranging successfully to transmitter, transmitter receives ACK, and represent that parameter configuration terminates, system enters normal communication state; Finally, Receiver And Transmitter carries out normal data transfer.
The method specifically comprises the steps:
(1) configuring negotiation state is entered after system boot, first specific, that receiving terminal is known ZC sequence is placed on each subcarrier by transmitter on each color (as RGB tri-look) subchannel, and ZC sequence is converted to ZC sequence time-domain signal and sends after conjugation symmetry and fast Fourier transform (IFFT conversion); Wherein ZC sequence is targeting sequencing, and its expression formula is:
In formula: r is the radical exponent of ZC sequence, with the length N of ZC sequence zCcoprime; K=0,1 ..., N zC-1, q is arbitrary integer; For the sake of simplicity, q can value be 0, N zCcan value be the sub-carrier number N of ofdm system sC;
(2) each color subchannel of receiver goes to do relevant to the burst received with same ZC sequence time-domain signal respectively, and the relevant peaks obtained is synchronous peak, and formula is as follows:
p ( d ) = Σ n = d N + d - 1 y ( n ) · x ZC ( n - d )
In formula: y (n) represents the burst received, x zCn () represents known ZC sequence time-domain signal, p (d) is y (n) and x zCthe cross-correlation function of (n), d is the independent variable of cross-correlation function, and N is the length of ZC sequence, and n represents the position of Received signal strength; Because ZC sequence has good autocorrelation performance, therefore using the peak value of p (d) as ZC sequence synchronization head, from the burst received, extract the ZC sequence time-domain signal y after channel according to synchronous head zC(n);
(3) to the y that each color subchannel of receiver receives zCn () is the frequency-region signal Y that fast Fourier transform (FFT conversion) obtains ZC sequence zCn (), obtains the frequency domain response of channel with LS algorithm:
H ( n ) = Y ZC ( n ) X ZCn ( )
In formula: H (n) is the channel coefficients that the n-th subcarrier is corresponding, X zCand Y zCrepresent without channel and the frequency domain ZC sequence through channel respectively;
(4) according to channel parameter H, X of each color subchannel zCthe estimated value of reconstructed reception sequence:
Y ~ ZC ( n ) = H ( n ) · X ZC ( n )
Noise jamming variance then on each subcarrier is the estimated value obtaining the signal interference ratio of each subcarrier is there is a certain distance between the estimated value of this SINR and actual value, need to carry out correction according to prior information and obtain SINR estimated value more accurately; The order of modulation selecting each subcarrier is required according to the bit error rate of predetermined chnnel coding code check, SINR value is set to virtual subnet carrier wave lower than the subcarrier of predetermined SINR lower limit, namely do not transmit data on these sub-carriers, then configuration information signaling channel is sent to transmitter by receiver;
(5) transmitter receives configuration information and after CRC confirms that configuration information is correct, sends ack signal to receiver;
(6) receiver returns an ACK to transmitter after receiving ACK, and transmitter confirms after receiving ACK that the configuring negotiation of both sides completes, and enters normal communication periods, starts to send user data with the configuration consulted;
(7) receiving terminal normally receives user data, and the signal interference ratio SINR of tracking and monitoring system, if significant change appears in SINR, then reenter configuring negotiation state, again consult configuration, realize the adaptive updates of transformation parameter and channel.
The present invention had both been applicable to multi-colored led visible light communication and had also been applicable to monochromatic LED and infrared visible light communication system, gets the program be for the moment automatically turned into monochromatic LED adaptive transmission scheme when the color participating in transmitting simultaneously.
Beneficial effect: multi-colored led visible light communication adaptive transmission method provided by the invention, has following advantage: 1, bandwidth self-adaption, obtain the transmission rate close to channel capacity; 2, decide transmission bandwidth by virtual subnet ZAP, do not need to change hardware, greatly simplify system; 3, different LED and different application scenarioss can be adapted to, expand the scope of application of visible light communication; 4, when the characteristic of channel changes, automatically can re-start configuring negotiation, recover proper communication, what enhance system exerts rod.
Accompanying drawing explanation
Fig. 1 is the working state of system transition diagram being applicable to the adaptive transmission scheme of multi-colored led visible light communication system that the present invention proposes;
Fig. 2 is that time diagram replied by the transmitter of the adaptive transmission scheme being applicable to multi-colored led visible light communication system and receiver;
Fig. 3 is the input and output schematic diagram of auto-adaptive parameter selection algorithm of the present invention;
Fig. 4 is the Signal to Interference plus Noise Ratio testing one group of RGB tri-look obtained on a hardware platform, and in figure, Frequency represents frequency; Wherein 4 (a) represents red, and 4 (b) represents green, and 4 (c) represents blue.
Embodiment
Below in conjunction with accompanying drawing, the present invention is further described.
Be illustrated in figure 1 a kind of multi-colored led visible light communication adaptive transmission method, system comprises configuring negotiation and proper communication two kinds of operating states, under the change of generation signal interference ratio exceedes threshold condition when the multi-colored led available transmission bandwidth of the unknown and proper communication, enter configuring negotiation state; In configuring negotiation state, available bandwidth and effective signal interference ratio is estimated by sending targeting sequencing, OFDM (OFDM) virtual subnet carrier method is adopted to realize not homochromy upper different-bandwidth transmission, follow and select error correction coding code check according to system equivalence signal interference ratio, and select suitable modulator approach according to subcarrier equivalence signal interference ratio each in each color available bandwidth, realize the Adaptive Transmission of approaching channel capacity; After configuring negotiation completes, system enters normal communication state, carries out communications.
Fig. 2 gives the detailed transmitter of system and sequential chart replied by receiver: first, and transmitter sends the known pilot frequency sequence of specific receiving terminal to receiver; Then, receiver, according to the pilot frequency sequence received, estimates the signal interference ratio on each subcarrier, obtains the transformation parameter under adaptation current system channel condition, and this transformation parameter is sent to receiver; Then, after transmitter receives transformation parameter, according to transmission parameter settings transmitter, ACK is sent after arranging successfully to receiver; Again, after receiver receives ack signal, according to transmission parameter settings receiver, send ACK after arranging successfully to transmitter, transmitter receives ACK, and represent that parameter configuration terminates, system enters normal communication state; Finally, Receiver And Transmitter carries out normal data transfer.
As shown in Figure 1, the method specifically comprises the steps:
(1) configuring negotiation state is entered after system boot, first specific, that receiving terminal is known ZC sequence is placed on each subcarrier by transmitter on each color (as RGB tri-look) subchannel, and ZC sequence is converted to ZC sequence time-domain signal and sends after conjugation symmetry and fast Fourier transform (IFFT conversion); Wherein ZC sequence is targeting sequencing, and its expression formula is:
In formula: r is the radical exponent of ZC sequence, with the length N of ZC sequence zCcoprime; K=0,1 ..., N zC-1, q is arbitrary integer; For the sake of simplicity, q can value be 0, N zCcan value be the sub-carrier number N of ofdm system sC;
(2) each color subchannel of receiver goes to do relevant to the burst received with same ZC sequence time-domain signal respectively, and the relevant peaks obtained is synchronous peak, and formula is as follows:
p ( d ) = Σ n = d N + d - 1 y ( n ) · x ZC ( n - d )
In formula: y (n) represents the burst received, x zCn () represents known ZC sequence time-domain signal, p (d) is y (n) and x zCthe cross-correlation function of (n), d is the independent variable of cross-correlation function, and N is the length of ZC sequence, and n represents the position of Received signal strength; Because ZC sequence has good autocorrelation performance, therefore using the peak value of p (d) as ZC sequence synchronization head, from the burst received, extract the ZC sequence time-domain signal y after channel according to synchronous head zC(n);
(3) to the y that each color subchannel of receiver receives zCn () is the frequency-region signal Y that fast Fourier transform (FFT conversion) obtains ZC sequence zCn (), obtains the frequency domain response of channel with LS algorithm:
H ( n ) = Y ZC ( n ) X ZCn ( )
In formula: H (n) is the channel coefficients that the n-th subcarrier is corresponding, X zCand Y zCrepresent without channel and the frequency domain ZC sequence through channel respectively;
(4) according to channel parameter H, X of each color subchannel zCthe estimated value of reconstructed reception sequence:
Y ~ ZC ( n ) = H ( n ) · X ZC ( n )
Noise jamming variance then on each subcarrier is the estimated value obtaining the signal interference ratio of each subcarrier is there is a certain distance between the estimated value of this SINR and actual value, need to carry out correction according to prior information and obtain SINR estimated value more accurately; The order of modulation selecting each subcarrier is required according to the bit error rate of predetermined chnnel coding code check, SINR value is set to virtual subnet carrier wave lower than the subcarrier of predetermined SINR lower limit, namely do not transmit data on these sub-carriers, then configuration information signaling channel is sent to transmitter by receiver;
(5) transmitter receives configuration information and after CRC confirms that configuration information is correct, sends ack signal to receiver;
(6) receiver returns an ACK to transmitter after receiving ACK, and transmitter confirms after receiving ACK that the configuring negotiation of both sides completes, and enters normal communication periods, starts to send user data with the configuration consulted;
(7) receiving terminal normally receives user data, and the signal interference ratio SINR of tracking and monitoring system, if significant change appears in SINR, then reenter configuring negotiation state, again consult configuration, realize the adaptive updates of transformation parameter and channel.
Fig. 3 provides a kind of flow chart using RGB tri-look transmission system.As shown in Figure 3, adaptive modulation parameter optimized algorithm is limited by the BER of the SINR on each subcarrier, system, specified through-put power and RGB colour mixture require to determine, RGB colour mixture requires that referring to the light that transmitting terminal sends after ovennodulation mixed light should ensure or white light, and this is also the basic demand of visible light communication.
What Fig. 4 showed is the Signal to Interference plus Noise Ratio testing one group of RGB tri-look obtained on a hardware platform, if the bandwidth of operation that now we arrange system is that (actual samples frequency is 100M to 50M, the working band of front 50M, 50M is the symmetrical frequency band of conjugation below), suppose that modulation system is restricted to 256QAM, 64QAM, 16QAM, 4QAM.System has 128 subcarriers, and realize for simplifying system hardware, subcarrier is divided into 8 groups, often group has 16 subcarriers, can affect the performance of the several subcarrier of low frequency because analog circuit existing capacitance, and being fixedly installed 0th ~ 3 sub carriers is virtual subnet carrier wave.The modulation scheme that the present invention obtains is as shown in table 1.This is because the low-frequency range Signal to Interference plus Noise Ratio of ruddiness channel is apparently higher than green glow and blue light, the modulation system of more high-order can be used, and the frequency band SINR of 40M to 50M is too low, should be set to virtual subnet carrier wave.
Table 1 RGB tri-sub-channels modulation scheme
Subcarrier sequence number 0~3 4~15 16~63 64~95 96~111 112~127
Red Virtual subnet carrier wave 256QAM 64QAM 16QAM 4QAM Virtual subnet carrier wave
Green Virtual subnet carrier wave 64QAM 64QAM 16QAM 4QAM Virtual subnet carrier wave
Blue Virtual subnet carrier wave 64QAM 64QAM 16QAM 4QAM Virtual subnet carrier wave
The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (3)

1. a multi-colored led visible light communication adaptive transmission method, it is characterized in that: system comprises configuring negotiation and proper communication two kinds of operating states, under the change of generation signal interference ratio exceedes threshold condition when the multi-colored led available transmission bandwidth of the unknown and proper communication, enter configuring negotiation state; In configuring negotiation state, available bandwidth and effective signal interference ratio is estimated by sending targeting sequencing, OFDM virtual subnet carrier method is adopted to realize not homochromy upper different-bandwidth transmission, follow and select error correction coding code check according to system equivalence signal interference ratio, and select suitable modulator approach according to subcarrier equivalence signal interference ratio each in each color available bandwidth, realize the Adaptive Transmission of approaching channel capacity; After configuring negotiation completes, system enters normal communication state, carries out communications.
2. multi-colored led visible light communication adaptive transmission method according to claim 1, is characterized in that: in configuring negotiation state, comprises the steps: first, and transmitter sends the known pilot frequency sequence of specific receiving terminal to receiver; Then, receiver, according to the pilot frequency sequence received, estimates the signal interference ratio on each subcarrier, obtains the transformation parameter under adaptation current system channel condition, and this transformation parameter is sent to receiver; Then, after transmitter receives transformation parameter, according to transmission parameter settings transmitter, ACK is sent after arranging successfully to receiver; Again, after receiver receives ack signal, according to transmission parameter settings receiver, send ACK after arranging successfully to transmitter, transmitter receives ACK, and represent that parameter configuration terminates, system enters normal communication state; Finally, Receiver And Transmitter carries out normal data transfer.
3. multi-colored led visible light communication adaptive transmission method according to claim 1, is characterized in that: the method specifically comprises the steps:
(1) configuring negotiation state is entered after system boot, first specific, that receiving terminal is known ZC sequence is placed on each subcarrier by transmitter on each color subchannel, and ZC sequence is converted to ZC sequence time-domain signal and sends after conjugation symmetry and fast Fourier transform; Wherein ZC sequence is targeting sequencing, and its expression formula is:
In formula: r is the radical exponent of ZC sequence, with the length N of ZC sequence zCcoprime; K=0,1 ..., N zC-1, q is arbitrary integer;
(2) each color subchannel of receiver goes to do relevant to the burst received with same ZC sequence time-domain signal respectively, and the relevant peaks obtained is synchronous peak, and formula is as follows:
p ( d ) = Σ n = d N + d - 1 y ( n ) · x ZC ( n - d )
In formula: y (n) represents the burst received, x zCn () represents known ZC sequence time-domain signal, p (d) is y (n) and x zCthe cross-correlation function of (n), d is the independent variable of cross-correlation function, and N is the length of ZC sequence, and n represents the position of Received signal strength; Using the peak value of p (d) as ZC sequence synchronization head, from the burst received, extract the ZC sequence time-domain signal y after channel according to synchronous head zC(n);
(3) to the y that each color subchannel of receiver receives zCn () is the frequency-region signal Y that fast Fourier transform obtains ZC sequence zCn (), obtains the frequency domain response of channel with LS algorithm:
H ( n ) = Y ZC ( n ) X ZC ( n )
In formula: H (n) is the channel coefficients that the n-th subcarrier is corresponding, X zCand Y zCrepresent without channel and the frequency domain ZC sequence through channel respectively;
(4) according to channel parameter H, X of each color subchannel zCthe estimated value of reconstructed reception sequence:
Y ~ ZC ( n ) = H ( n ) · X ZC ( n )
Noise jamming variance then on each subcarrier is the estimated value obtaining the signal interference ratio of each subcarrier is there is a certain distance between the estimated value of this SINR and actual value, need to carry out correction according to prior information and obtain SINR estimated value more accurately; The order of modulation selecting each subcarrier is required according to the bit error rate of predetermined chnnel coding code check, SINR value is set to virtual subnet carrier wave lower than the subcarrier of predetermined SINR lower limit, namely do not transmit data on these sub-carriers, then configuration information signaling channel is sent to transmitter by receiver;
(5) transmitter receives configuration information and after CRC confirms that configuration information is correct, sends ack signal to receiver;
(6) receiver returns an ACK to transmitter after receiving ACK, and transmitter confirms after receiving ACK that the configuring negotiation of both sides completes, and enters normal communication periods, starts to send user data with the configuration consulted;
(7) receiving terminal normally receives user data, and the signal interference ratio SINR of tracking and monitoring system, if significant change appears in SINR, then reenter configuring negotiation state, again consult configuration, realize the adaptive updates of transformation parameter and channel.
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