Visible light communication dimming system based on Polar code and M-PAM technology

Abstract

The invention discloses a visible light communication dimming system based on a Polar code and an M-PAM technology, and relates to the technical field of optical communication. The emitter comprises a Polar encoder, a scrambler, an M-PAM modulator, a dimming rate controller and a light source; the receiver comprises a photoelectric detector, an M-PAM demodulator, a descrambler and a Polar decoder; after polar code error correction coding is carried out on an information source sequence of the transmitter through the Polar encoder, scrambling operation is carried out on the information source sequence through the scrambler, M-PAM modulation is carried out on the information source sequence through the M-PAM modulator, then the information source sequence is output to the light source, and visible light signals are transmitted. The dimming rate controller participates in polarization code error correction coding of the Polar encoder so as to control the sending power of the light source; a visible light signal received by the photoelectric detector passes through the M-PAM demodulator, the descrambler and the Polar decoder, and then a recovery sequence is output. According to the invention, a Polar code is introduced as a high-efficiency error correction code, a scrambler is used for scrambling, flexible dimming is realized by combining an M-PAM technology, high-efficiency transmission of indoor visible light communication is realized, and illumination and dimming functions are considered at the same time.

Description

Technical Field

[0001] The present invention relates to the field of optical communication technologies, and particularly to a visible light communication dimming system based on Polar code and M-PAM technologies. Background Art

[0002] Indoor visible light communication (VLC) based on LEDs (Light Emitting Diodes) has received extensive attention in recent years due to its unique advantages such as security and confidentiality, abundant spectrum resources, low power consumption and environmental friendliness, and dual functions of communication and lighting. Undoubtedly, VLC will become a very promising communication method in future short-distance wireless communication.

[0003] The dimming function is one of the main challenges faced by VLC. Dimming refers to VLC controlling the brightness of the light source according to user requirements. Dimming can effectively save energy and provide a more comfortable user experience. So far, numerous dimming schemes have been proposed. For example, the pulse width modulation dimming, amplitude modulation dimming using rectangular signals proposed by the IEEE 802.15.7-2011 standard, and digital dimming based on modulation technologies such as ACO-OFDM and MIMO. They achieve the change in brightness by inserting compensation symbols. In recent years, many researchers have also studied dimming schemes using forward error correction codes, which not only achieve dimming but also obtain a certain coding gain. The dimming schemes adopted include RM code concatenated interleaving technology, LDPC code concatenated RLL code, Turbo code concatenated scrambler, Polar code concatenated RLL code, etc. Among them, the Polar code is an error correction code with excellent error performance and low complexity. It adopts a channel combining and splitting construction method. When the code length approaches infinity, the transmission capacity can approach the Shannon limit and has been incorporated into the 5G standard as the coding scheme for the control channel in the 5G enhanced mobile broadband scenario. Summary of the Invention

[0004] In view of the above problems, the present invention proposes a visible light communication dimming system based on Polar code and M-PAM technologies, which realizes the efficient transmission of indoor visible light communication, takes into account both lighting and dimming functions, solves the problem that it is difficult to balance communication and lighting in traditional VLC systems, and significantly improves the overall performance and user experience of the system.

[0005] The visible light communication dimming system based on Polar code and M-PAM technologies includes a transmitter and a receiver. The transmitter includes a Polar encoder, a scrambler, an M-PAM modulator, a dimming rate controller, and a light source; the receiver includes a photodetector, an M-PAM demodulator, a descrambler, and a Polar decoder;

[0006] After the source sequence of the transmitter undergoes polar code error correction coding by a Polar encoder, it is output to a scrambler for scrambling operation, and then output to an M-PAM modulator for M-PAM modulation, and then output to a light source; the light source emits a visible light signal to a receiver based on the signal after M-PAM modulation; the dimming rate controller participates in the polar code error correction coding of the Polar encoder by setting the dimming rate, so as to control the transmission power of the light source.

[0007] The photodetector converts the received visible light signal into an electrical signal, outputs it to an M-PAM demodulator for M-PAM demodulation, then outputs it to a descrambler for descrambling operation, and then outputs it to a Polar decoder for polar code error correction decoding and then outputs a recovered sequence.

[0008] Preferably, before the Polar encoder performs polar code error correction coding, it further includes performing error detection code coding on the source sequence; after the Polar decoder performs polar code error correction decoding, it further includes performing error detection code verification on the output of the Polar decoder.

[0009] Preferably, the error detection code coding is CRC coding; correspondingly, the error detection code verification is CRC verification.

[0010] Preferably, the Polar encoder selects K + r error-free channels among N polarization channels to transmit information bits, and transmits frozen bits in the remaining N - K - r channels; where K + r represents the length of K + r information bits obtained after the input source sequence undergoes CRC coding, K represents the length of the information bits of the input source sequence, and r represents the parity bits; the output of the Polar encoder is expressed as:

[0011] ;

[0012] Among them, represents the output of the Polar encoder; represents the information bit generation matrix, represents the information bit position set; represents the frozen bit generation matrix, represents the frozen bit position set; represents the information bit sequence; represents the frozen bit sequence.

[0013] Preferably, the amplitudes of the constellation points in the constellation diagram of the M-PAM modulator are expressed as:

[0014] ;

[0015] Among them, represents the intensity of the m-th constellation point of M-PAM, , represents the maximum emission power of the light source; m represents the index of the constellation point, , M represents the modulation order; represents the dimming rate; represents the intensity offset probability.

[0016] Preferably, by maximizing the source entropy of the visible light signal transmitted by the light source, the optimal distribution of the probabilities of each constellation point is obtained, which is expressed as:

[0017] ;

[0018] wherein, satisfies the formula ; represents the source entropy, represents the visible light signal transmitted by the transmitter, is a set of; represents the probability of the m-th constellation point; represents taking the maximum value.

[0019] Preferably, the formula for calculating the mutual information between the visible light signal transmitted by the transmitter and the electrical signal output by the photodetector is expressed as:

[0020] ;

[0021] ;

[0022] wherein, represents and the mutual information of; represents the electrical signal after detection by the photodetector, represents a single symbol received by the receiver; represents the probability distribution function of the M-PAM signal received by the receiver; represents the probability distribution function of the channel noise AWGN; represents the variance of the Gaussian white noise; represents the photoelectric conversion factor of the photodetector in the receiver.

[0023] Preferably, under the set dimming rate, the acquisition of the optimal intensity offset probability includes the following steps:

[0024] S1, initialize the intensity offset probability, and set the intensity offset probability to 0; use the initialized intensity offset probability as the set intensity offset probability;

[0025] S2, according to the set intensity offset probability, calculate the mutual information of each constellation point under the optimal distribution to obtain the first mutual information;

[0026] S3. Increase the offset by a fixed amount according to the set intensity offset probability;

[0027] S4. Determine whether the set intensity offset probability is less than 1. If so, execute S2 and S3; if not, execute S5;

[0028] S5. Calculate the mutual information of each constellation point under the optimal distribution according to the set intensity offset probability to obtain the second mutual information. Compare the magnitudes of the first mutual information and the second mutual information. The intensity offset probability corresponding to the larger mutual information is the optimal intensity offset probability. The distribution of the probabilities of each constellation point under the optimal intensity offset probability is also the best probability of the appearance of each constellation point signal.

[0029] Preferably, the light source is an LED light source.

[0030] Preferably, the DC gain between the light source in the transmitter and the photodetector in the receiver is expressed as:

[0031] ;

[0032] wherein, represents the signal gain; represents the Lambert emission order of the light source; represents the receiving area of the photodetector; represents the transmission distance from the light source in the transmitter to the photodetector in the receiver; represents the irradiance angle of the light source; represents the incident angle of the photodetector in the receiver; and respectively represent the filter gain and the concentrator gain of the photodetector; represents the maximum receiving angle of the photodetector.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] The present invention introduces the polar code (i.e., Polar code) as an efficient error correction code, significantly improving the reliability of communication and reducing the bit error rate; uses a scrambler for scrambling operations to effectively suppress optical flicker and improve the lighting quality; and combines with the M-PAM technology to achieve flexible dimming to meet the user's demand for brightness adjustment. This technology combination not only realizes the efficient transmission of indoor visible light communication but also takes into account the lighting and dimming functions, solving the problem that it is difficult to balance communication and lighting in traditional VLC systems and significantly improving the overall performance and user experience of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The following further describes the present invention in detail with reference to the drawings;

[0036] Figure 1 Schematic diagram of the visible light communication dimming system based on Polar code and M-PAM technology according to an embodiment of the present invention;

[0037] Figure 2 Optimal intensity offset probability solving steps of the visible light communication dimming system based on Polar code and M-PAM technology according to an embodiment of the present invention. Detailed implementation manners

[0038] The present invention will be further described below through specific implementation manners.

[0039] As Figure 1 shown, the visible light communication dimming system based on Polar code and M-PAM technology includes a transmitter 1 and a receiver 2. The transmitter 1 includes a Polar encoder 12, a scrambler 13, an M-PAM modulator 14, a dimming controller 16, and an LED light source 15. The receiver 2 includes a photodetector 21, an M-PAM demodulator 22, a descrambler 23, and a Polar decoder 24.

[0040] After the source sequence received by the transmitter 1 is subjected to Polar code error correction coding by the Polar encoder 12, it is output to the scrambler 13 for scrambling operation, and then output to the M-PAM modulator 14 for M-PAM modulation, and then output to the LED light source 15; the LED light source 15 emits a visible light signal based on the M-PAM modulated signal; the dimming rate controller 16 controls the transmission power of the LED light source 15 by setting the dimming rate; the photodetector 21 converts the received visible light signal into an electrical signal, outputs it to the M-PAM demodulator 22 for M-PAM demodulation, then outputs it to the descrambler 23 for descrambling operation, and then outputs it to the Polar decoder 24 for Polar code error correction decoding and outputs the recovered sequence.

[0041] Among them, the visible light signal emitted by the LED light source 15 passes through the AWGN channel and is transmitted to the photodetector 21; the transmitter 1 is the sending end, and the receiver 2 is the receiving end.

[0042] In this embodiment, the Polar coding scheme of the Polar encoder 12 is as follows:

[0043] In Figure 1In it, the Polar code is adopted as the error correction code. To further improve the Polar decoding performance at the receiving end, before the K-bit information bits enter the Polar encoder, they are first CRC-encoded using CRC-11 (Cyclic Redundancy Check), with r-bit parity bits added. After the information bits become K + r bits, they are encoded, thus forming the CRC-SCL (Successive Cancellation List) algorithm. At this time, the code rate of the polar code output is (K + r) / N. Among the N polar channels, K + r error-free channels are selected to transmit information bits, and frozen bits are transmitted in the remaining (N - K - r) channels. The output of the Polar encoding is:

[0044] ;

[0045] In the formula, is the generating matrix of the Polar code; the subscripts and represent the information bit position set and the frozen bit position set respectively; and represent the information bit sequence and the frozen bit sequence respectively. In the binary AWGN channel, the Gaussian approximation method GA is used to estimate the error probability of each sub-channel, so as to construct the most suitable and .

[0046] In this embodiment, the M-PAM dimming technical solution of the M-PAM modulator 14 is as follows:

[0047] To suppress the flicker of the optical signal, a scrambler 13 composed of a pseudo-random code is introduced after the Polar encoder 12 to balance the ratio of "0" and "1" in the codeword, so as to obtain data with DC balance and limited run length; correspondingly, a descrambler 23 is set in the receiver 2 to perform the inverse operation of the scrambler 13 on the received scrambled data to restore the original information. This data is then modulated by M-PAM and used to control the LED light source 15 to send. The value range of the optical signal X emitted by the LED light source 15 is (0, A), where A is the maximum emission power of the LED light source 15, that is, it is required that the optical signal is non-negative and its value is within the safe range of the human eye. Figure 1 The dimming rate controller 16 in

[0048] ;

[0049] Among them, is called the dimming rate, and its value range is (0, 1).

[0050] When using M-PAM modulation, the amplitudes of each constellation point also need to satisfy , and satisfy the following formula:

[0051] ;

[0052] Among them, is the probability of each constellation point appearing. It satisfies probability completeness. m is the index of the constellation point (from 1 to M), and M is the modulation order.

[0053] It can be seen from the above formula that by changing and , the dimming rate required by the user can be obtained. More specifically, the intensity of each constellation point of M-PAM can be achieved by changing the intensity offset probability and the dimming rate , and is specifically expressed as:

[0054] ;

[0055] According to information theory knowledge, the value of the probability of each constellation point should satisfy completeness and the maximum entropy theorem, that is, when the source entropy H(X) of the transmitted signal reaches the maximum value, the at this time is the optimal distribution, as shown in the following formula:

[0056] ;

[0057] It can be seen from the above analysis that the amplitudes and probabilities of the signals of each constellation point in M-PAM modulation are modulated by the dimming rate output by the dimming controller. That is, at different dimming rates, the amplitudes and probabilities of the signals of each constellation point are different.

[0058] In this embodiment, the demodulation and decoding scheme of the receiver 2 is as follows:

[0059] The signal emitted by the LED light source 15 is transmitted through an AWGN (Additive White Gaussian Noise) channel and reaches the receiving end. The electrical signal after being detected by the photodetector 21, and its expression is:

[0060] ;

[0061] Among them, is the photoelectric conversion factor of the photodetector 21 at the receiving end; is the optical signal at the transmitting end; Z is the noise, assumed to have a mean of 0 and a variance of Gaussian white noise. In this embodiment, the photodetector 21 uses a PD (Photodiode). is the signal gain, that is, the DC gain between the LED light source 15 at the transmitting end and the photodetector 21 at the receiving end, and the expression is:

[0062] ;

[0063] Where, is the Lambert emission order of the LED; is the receiving area of the PD; is the transmission distance from the transmitting end to the receiving end; is the irradiance angle of the LED; is the incident angle at the receiving end; and are the filter gain and concentrator gain of the PD respectively; is the maximum receiving angle of the PD.

[0064] In the AWGN channel, the calculation formula for the mutual information obtained from the transmitting end to the receiving end in the VLC system is as follows:

[0065] ;

[0066] In the formula, is the probability distribution function of the M-PAM signal received at the receiving end, expressed as:

[0067] ;

[0068] In the formula, is the probability distribution function of the channel noise AWGN.

[0069] At the set dimming rate , the optimal intensity offset probability is derived according to the steps shown in Figure 2 , and the specific steps are as follows:

[0070] Step 1): Initialize the intensity offset probability, let ;

[0071] Step 2): According to the given , calculate the mutual information of each constellation point under the optimal distribution ;

[0072] Step 3): According to increase the offset;

[0073] Step 4): Judge Is it less than 1? If yes, repeat steps 2) and 3); if not, go to step 5).

[0074] Step 5): Obtain the mutual information under different and find the one corresponding to the maximum mutual information . At this time, is the optimal intensity offset probability , and the corresponding is also the probability of the appearance of the best signal at each constellation point.

[0075] The signal output by the photodetector 21 enters the Polar decoder 24 after M-PAM demodulation. In this embodiment, the Polar decoder 24 adopts the SCL decoding algorithm. After the decoding is completed, each output is sequentially subjected to CRC verification by the CRC checker 25. If the verification is correct, the decoded codeword is output; if the verification fails, the output with the lowest path metric is selected as the decoding result.

[0076] The above is only the specific implementation manner of the present invention, but the design concept of the present invention is not limited thereto. Any non-substantive modification of the present invention using this concept shall fall within the scope of infringement of the protection scope of the present invention.

Claims

1. A visible light communication dimming system based on Polar code and M-PAM technology, comprising a transmitter and a receiver, characterized in that: The transmitter includes a Polar encoder, a scrambler, an M-PAM modulator, a dimming rate controller and a light source; the receiver includes a photodetector, an M-PAM demodulator, a descrambler and a Polar decoder; The source sequence of the transmitter is encoded with polarization code error correction by the Polar encoder, then output to the scrambler for scrambling operation, then output to the M-PAM modulator for M-PAM modulation, and then output to the light source; the light source transmits a visible light signal to the receiver based on the M-PAM modulated signal; the dimming rate controller participates in the polarization code error correction encoding of the Polar encoder by setting the dimming rate, thereby controlling the transmission power of the light source; The photodetector converts the received visible light signal into an electrical signal, outputs it to the M-PAM demodulator for M-PAM demodulation, then outputs it to the descrambler for descrambling, and then outputs it to the Polar decoder for polarization code error correction decoding and then outputs a recovery sequence.

2. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 1, characterized in that: Before the Polar encoder performs polar code error correction encoding, it also includes performing error detection code encoding on the source sequence; after the Polar decoder performs polar code error correction decoding, it also includes performing error detection code verification on the output of the Polar decoder.

3. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 2, characterized in that: The error detection code encoding is CRC encoding; accordingly, the error detection code check is CRC check.

4. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 3, characterized in that: The Polar encoder selects K+r error-free channels from N polarized channels to transmit information bits, and transmits frozen bits in the remaining NKr channels; wherein K+r represents the K+r information bit length obtained after the input source sequence is CRC encoded, K represents the information bit length of the input source sequence, and r represents the check bit; the output of the Polar encoder is expressed as: ； in, Represents the output of the Polar encoder; represents the information bit generator matrix, represents a set of information bit positions; represents the frozen bit generator matrix, represents a set of frozen bit positions; represents a sequence of information bits; Indicates a frozen bit sequence.

5. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 1, characterized in that: The amplitude of each constellation point in the constellation diagram of the M-PAM modulator is expressed as: ； in, represents the strength of the m-th constellation point of M-PAM, , represents the maximum emission power of the light source; m represents the index of the constellation point, , M represents the modulation order; Indicates the dimming rate; represents the probability of intensity shift.

6. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 5, characterized in that: By maximizing the source entropy of the visible light signal sent by the light source, the optimal distribution of the probability of each constellation point is obtained, which is expressed as: ； in, Satisfy the formula ; represents the source entropy, Represents the visible light signal emitted by the transmitter, yes A collection of; represents the probability of the mth constellation point; Indicates taking the maximum value.

7. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 6, characterized in that: The mutual information calculation formula between the visible light signal emitted by the transmitter and the electrical signal output by the photodetector is expressed as: ； ； in, express and The mutual information of Represents the electrical signal detected by the photodetector, Represents a single symbol received by the receiver; represents the probability distribution function of the M-PAM signal received by the receiver; represents the probability distribution function of channel noise AWGN; represents the variance of Gaussian white noise; represents the photoelectric conversion factor of the photodetector in the receiver; Indicates signal gain.

8. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 7, characterized in that: Under the set dimming rate, obtaining the optimal intensity shift probability includes the following steps: S1, initialize the intensity offset probability, set the intensity offset probability to 0; use the initialized intensity offset probability as the set intensity offset probability; S2, calculating the mutual information of each constellation point under the optimal distribution according to the set intensity offset probability, and obtaining the first mutual information; S3, increasing the set intensity offset probability by a fixed amount; S4, determine whether the set intensity deviation probability is less than 1; if so, execute S2 and S3; if not, execute S5; S5, calculate the mutual information of each constellation point under the optimal distribution according to the set intensity offset probability, obtain the second mutual information, compare the first mutual information and the second mutual information, the intensity offset probability corresponding to the larger mutual information is the optimal intensity offset probability; the distribution of the probability of each constellation point under the optimal intensity offset probability is also the optimal probability of occurrence of the signal of each constellation point.

9. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 1, characterized in that: The light source is an LED light source.

10. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 9, characterized in that: The DC gain between the light source in the transmitter and the photodetector in the receiver is given by: ； in, Indicates signal gain; Indicates the Lambertian emission order of the light source; represents the receiving area of ​​the photodetector; It represents the transmission distance from the light source in the transmitter to the photodetector in the receiver; Indicates the irradiance angle of the light source; represents the angle of incidence to the photodetector in the receiver; and denote the filter gain and concentrator gain of the photodetector, respectively; Represents the maximum acceptance angle of the photodetector.

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