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

Abstract

The present invention discloses a visible light communication dimming system based on Polar codes and M-PAM technology, relating to the field of optical communication technology. The system comprises a transmitter and a receiver. The transmitter comprises a Polar encoder, a scrambler, an M-PAM modulator, a dimming rate controller, and a light source. The receiver comprises a photodetector, an M-PAM demodulator, a descrambler, and a Polar decoder. The transmitter's source sequence is encoded with polarization code error correction by the Polar encoder, scrambled by the scrambler, and modulated by the M-PAM modulator before being output to the light source and emitting a visible light signal. The dimming rate controller participates in the polarization code error correction encoding of the Polar encoder, thereby controlling the transmit power of the light source. The visible light signal received by the photodetector is then passed through the M-PAM demodulator, descrambler, and Polar decoder to output a recovery sequence. The present invention introduces Polar codes as an efficient error correction code, uses a scrambler for scrambling, and combines M-PAM technology to achieve flexible dimming, thereby achieving efficient transmission of indoor visible light communication while taking into account both lighting and dimming functions.

Description

Technical Field

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

[0002] Indoor visible light communication (VLC) based on LEDs (Light Emitting Diodes) has garnered widespread attention in recent years due to its unique advantages, including security and confidentiality, abundant spectrum resources, low power consumption, environmental friendliness, and dual functionality for both communication and lighting. VLC is undoubtedly a promising method for future short-range wireless communications.

[0003] Dimming is one of the main challenges facing VLC. Dimming refers to the ability of VLC to control the brightness of a light source based on user requirements. Dimming can effectively save energy and provide a more comfortable user experience. Numerous dimming solutions have been proposed, including pulse-width modulation dimming using rectangular signals, amplitude modulation dimming, and digital dimming based on modulation techniques such as ACO-OFDM and MIMO, as proposed in the IEEE 802.15.7-2011 standard. These technologies achieve brightness changes by inserting compensation symbols. In recent years, numerous researchers have also explored dimming schemes using forward error correction codes, which not only achieve dimming but also achieve certain coding gain. Dimming schemes employed include RM code concatenation and interleaving, LDPC code concatenation and RLL code concatenation, Turbo code concatenation and scrambling, and polar code concatenation and RLL code concatenation. Polar codes are error correction codes with excellent error performance and low complexity. It adopts channel merging and splitting construction. When the code length tends to infinity, the transmission capacity can approach the Shannon limit. It has been included in the 5G standard as a coding scheme for the control channel in the 5G enhanced mobile broadband scenario. Summary of the Invention

[0004] To address the above issues, the present invention proposes a visible light communication dimming system based on Polar codes and M-PAM technology, which achieves efficient transmission of indoor visible light communication, takes into account both lighting and dimming functions, solves the problem of difficult balance between communication and lighting in traditional VLC systems, and significantly improves the overall performance of the system and user experience.

[0005] A visible light communication dimming system based on Polar code and M-PAM technology 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] The transmitter's source sequence is encoded with polar code error correction by the Polar encoder, then output to the scrambler for scrambling, then to the M-PAM modulator for M-PAM modulation, and finally 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 polar code error correction encoding of the Polar encoder by setting the dimming rate, thereby controlling the transmit power of the light source.

[0007] 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 polar code error correction decoding to output a recovery sequence.

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

[0009] Preferably, the error detection code encoding is CRC encoding; correspondingly, the error detection code check is CRC check.

[0010] Preferably, 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. K+r represents the K+r information bit length obtained after CRC encoding of the input source sequence, K represents the information bit length of the input source sequence, and r represents a check bit. The output of the polar encoder is expressed as:

[0011] ;

[0012] in, Represents the output of the Polar encoder; represents the information bit generator matrix, represents the set of information bit positions; represents the frozen bit generator matrix, represents the set of frozen bit positions; Represents a sequence of information bits; Indicates a frozen bit sequence.

[0013] Preferably, the amplitude of each constellation point in the constellation diagram of the M-PAM modulator is expressed as:

[0014] ;

[0015] in, 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; Indicates dimming rate; represents the probability of intensity shift.

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

[0017] ;

[0018] 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.

[0019] Preferably, the mutual information calculation formula between the visible light signal emitted by the emitter and the electrical signal output by the photodetector is expressed as:

[0020] ;

[0021] ;

[0022] in, express and 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.

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

[0024] 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;

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

[0026] S3, increasing the set intensity offset probability by a fixed amount;

[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 based on the set intensity offset probability to 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 probabilities of each constellation point under the optimal intensity offset probability is also the optimal probability of the occurrence of the signal at each constellation point.

[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] 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; Indicates the maximum acceptance angle of the photodetector.

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

[0034] The present invention introduces polarization codes (i.e., Polar codes) as efficient error-correcting codes, significantly improving communication reliability and reducing bit error rates. A scrambler is used for scrambling operations to effectively suppress light flicker and improve lighting quality. This technology is combined with M-PAM technology to achieve flexible dimming, meeting user needs for brightness adjustment. This technology combination not only achieves efficient transmission of indoor visible light communication, but also takes into account lighting and dimming functions, resolving the difficulty of balancing communication and lighting in traditional VLC systems, significantly improving the overall system performance and user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The present invention will be described in further detail below with reference to the accompanying drawings;

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

[0037] Figure 2 This is a step for solving the optimal intensity offset probability of a visible light communication dimming system based on Polar codes and M-PAM technology in an embodiment of the present invention. DETAILED DESCRIPTION

[0038] The present invention is further described below through specific embodiments.

[0039] like Figure 1 As shown in FIG, a visible light communication dimming system based on Polar codes and M-PAM technology includes a transmitter 1 and a receiver 2. 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. Receiver 2 includes a photodetector 21, an M-PAM demodulator 22, a descrambler 23, and a Polar decoder 24.

[0040] The source sequence received by transmitter 1 is encoded with polarization code error correction by polar encoder 12 and then output to scrambler 13 for scrambling. It is then output to M-PAM modulator 14 for M-PAM modulation and then to LED light source 15. LED light source 15 transmits a visible light signal based on the M-PAM modulated signal. A dimming rate controller 16 controls the transmit power of LED light source 15 by setting the dimming rate. A photodetector 21 converts the received visible light signal into an electrical signal, which is then output to M-PAM demodulator 22 for M-PAM demodulation. The signal is then output to descrambler 23 for descrambling, and then to Polar decoder 24 for polarization code error correction decoding, which outputs a recovered sequence.

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

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

[0043] exist Figure 1Polar codes are used as error correction codes. To further improve Polar decoding performance at the receiver, the K-length information bits are first CRC-encoded using CRC code 11 (Cyclic Redundancy Check) before entering the Polar encoder. This adds r-length check bits, making the information bits K+r long before encoding. This forms a CRC-SCL (Successive Cancellation List) algorithm. The polar code output rate is (K+r) / N. Among the N polarized channels, K+r error-free channels are selected to transmit the information bits, while the remaining (NKr) channels transmit frozen bits. The output of the Polar code is:

[0044] ;

[0045] Where, is the generator matrix of Polar code; and They represent the information bit position set and the frozen bit position set respectively; and 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 appropriate and .

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

[0047] To suppress optical signal flicker, a scrambler 13, consisting of a pseudorandom code, is introduced after the polar encoder 12 to balance the ratio of "0s" and "1s" in the codeword, resulting in DC-balanced data with limited run length. Accordingly, a descrambler 23 is provided in the receiver 2 to perform the inverse operation of the scrambler 13 on the received scrambled data, recovering the original information. This data is then modulated by M-PAM and transmitted by the LED light source 15. The optical signal X emitted by the LED light source 15 has a value range of (0, A), where A is the maximum transmit power of the LED light source 15. This means that the optical signal must be non-negative and within the safe range for the human eye. Figure 1 The dimming rate controller 16 in the system controls the M-PAM modulator 14 according to the dimming rate required by the user, thereby controlling the transmission power of the LED light source 15. In the dimmable VLC system, the average optical power emitted by the LED light source 15 is required to be stable and adjustable according to the user's needs, which is expressed as:

[0048] ;

[0049] in, It is called dimming rate and its value range is (0, 1).

[0050] When M-PAM modulation is used, the amplitude of each constellation point must also meet , and satisfies the following formula:

[0051] ;

[0052] in, is the probability of occurrence of each constellation point, which satisfies the probability completeness, m is the index of the constellation point (from 1 to M), and M is the modulation order.

[0053] From the above formula, we can see that by changing and The dimming rate required by the user can be obtained by More specifically, the intensity of each constellation point of M-PAM The magnitude of the intensity shift probability can be varied by changing and dimming rate Implementation, specifically expressed as:

[0054] ;

[0055] According to the knowledge of information theory, the probability of each constellation point is It should satisfy the completeness and maximum entropy theorem, that is, when the source entropy H(X) of the sending signal reaches the maximum value, For the best distribution, see the following formula:

[0056] ;

[0057] From the above analysis, we can see that the amplitude and probability of the signal at each constellation point of M-PAM modulation are modulated by the dimming rate output by the dimming controller. That is, at different dimming rates, the amplitude and probability of the signal at 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 the Gaussian white noise (AWGN) channel and reaches the receiving end. The electrical signal detected by the photodetector 21 is , whose expression is:

[0060] ;

[0061] in, 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, which is assumed to have a mean of 0 and a variance of The photodetector 21 of this embodiment adopts PD (Photodiode, photodiode), is the signal gain, i.e., the DC gain between the LED light source 15 at the transmitting end and the photodetector 21 at the receiving end, and is expressed as:

[0062] ;

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

[0064] In the AWGN channel, the mutual information obtained from the sender to the receiver in the VLC system is calculated as follows:

[0065] ;

[0066] Where, is the probability distribution function of the M-PAM signal received by the receiver, expressed as:

[0067] ;

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

[0069] At the set dimming rate The optimal intensity shift probability is according to Figure 2 The steps shown are derived, 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 optimal distribution of each constellation point Mutual information of

[0072] Step 3): according to Increase the offset;

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

[0074] Step 5): According to steps 2) and 3) different Under the mutual information, find the corresponding mutual information when the maximum , at this time The optimal intensity shift probability , corresponding It is also the probability of the best signal appearing at each constellation point.

[0075] The signal output by the photodetector 21 undergoes M-PAM demodulation and then enters the polar decoder 24. In this embodiment, the polar decoder 24 uses the SCL decoding algorithm. After decoding, each output is sequentially checked by a CRC check 25. If the check is correct, the decoded codeword is output. If the check fails, the output with the lowest path metric is selected as the decoding result.

[0076] The above is only a specific implementation of the present invention, but the design concept of the present invention is not limited to this. Any non-substantial changes to the present invention using this concept shall be deemed as an 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 transmitter's source sequence is encoded with polar code error correction by the Polar encoder, then output to the scrambler for scrambling, then to the M-PAM modulator for M-PAM modulation, and finally 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 polar code error correction encoding of the Polar encoder by setting the dimming rate, thereby controlling the transmit 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 polar code error correction decoding and outputting a recovered sequence; The amplitude of each constellation point in the constellation diagram of the M-PAM modulator is expressed as: Among them, x m represents the intensity of the m-th constellation point of M-PAM, x m ∈(0,A), A represents the maximum emission power of the light source; m represents the index of the constellation point, m∈{1,2,…,M}, M represents the modulation order; ρ represents the dimming rate; α represents the intensity offset probability; 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: Among them, p m Satisfy the formula H(X) represents the source entropy, X represents the visible light signal emitted by the transmitter, and X is x m The collection of p m represents the probability of the mth constellation point; Indicates taking the maximum value; 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: Where I(X; Y) represents the mutual information between X and Y; Y represents the electrical signal detected by the photodetector, and y represents a single symbol received by the receiver; f Y (y) represents the probability distribution function of the M-PAM signal received by the receiver; f Z (·) represents the probability distribution function of channel noise AWGN; σ 2 represents the variance of Gaussian white noise; η represents the photoelectric conversion factor of the photodetector in the receiver; G represents the signal gain; Under the set dimming rate, obtaining the optimal intensity offset 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 to obtain the first mutual information; S3, increasing the set intensity offset probability by a fixed amount; S4, determine whether the set intensity offset 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 based on the set intensity offset probability to obtain a second mutual information. Compare the first mutual information with 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 optimal probability of occurrence of the signal at each constellation point.

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, the source sequence is also encoded with an error detection code. After the Polar decoder performs polar code error correction decoding, the output of the Polar decoder is also checked with an error detection code.

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. K+r represents the K+r information bit length obtained after CRC encoding of the input source sequence, 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: Where c represents the output of the Polar encoder; G A represents the information bit generation matrix, A represents the information bit position set; represents the frozen bit generator matrix, A c represents the set of frozen bit positions; u A 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 light source is an LED light source.

6. The visible light communication dimming system based on Polar code and M-PAM technology according to claim 5, characterized in that: The DC gain between the light source in the transmitter and the photodetector in the receiver is expressed as: Where G represents the signal gain; n represents the Lambertian emission order of the light source; A R represents the receiving area of the photodetector; L represents the transmission distance from the light source in the transmitter to the photodetector in the receiver; θ represents the irradiance angle of the light source; represents the angle of incidence to the photodetector in the receiver; and They represent the filter gain and concentrator gain of the photodetector respectively; Φ C Indicates the maximum acceptance angle of the photodetector.

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