OCC transmitter, OCC receiver, OCC signal generation method, OCC signal reception method, and program

Abstract

The present invention provides an OCC transmitter comprising a dimmer and an on–off keying modulation unit. The dimmer converts a high-rate signal on the basis of a low-rate signal by m-out-of-n encoding, and generates a superimposed signal that gives two desired dimming levels. Provided that Y0 and Y1 denote the two dimming levels, respectively, m and n are related by m = Y0n and m = Y1n. The on–off keying modulation unit converts the signal outputted by the dimmer into an optical signal. An OCC receiver comprises a low-speed camera, a RoI identification unit, a high-speed camera, an on–off keying demodulation unit, and an inverse dimmer. The low-speed camera captures an image of the OCC signal and outputs a low-rate signal. The RoI identification unit identifies a RoI from the low-rate signal. The high-speed camera extracts the RoI from the camera field of view and outputs a RoI image capture signal. The on–off keying demodulation unit demodulates the RoI image capture signal and acquires a superimposed signal. The inverse dimmer uses a codebook to decode the superimposed signal into a high-rate signal.

Description

OCC transmitter, OCC receiver, OCC signal generation method, OCC signal reception method, and program

[0001] The disclosed technology relates to dimming control and encoding techniques for optical camera communication.

[0002] Optical camera communication (OCC) is a visible light communication method that uses a light source, such as an LED display, as the transmitting means and a camera as the receiving means. The transmitting side modulates the light emitted by a light source such as an LED to transmit a digital signal. Modulation is performed by controlling the light source on and off.

[0003] The IEEE 802.15.7 m group (TG 7 m) introduced visible light Region-of-Interest (RoI) signaling to vehicular OCC systems (Non-Patent Document 1), which allows OCC systems to transmit low-rate and high-rate data streams simultaneously.

[0004] While the low-rate stream is used for Route of Interconnect (RoI) identification, the high-rate stream is used for high-speed data communication over the selected Route of Interconnect (ROI). Hybrid modulation schemes such as Twinkle Variable Pulse Position Modulation (VPPM) and Hybrid Spatial Phase-Shift Keying (HS-PSK) are often used to modulate the low-rate and high-rate streams.

[0005] Specifically, the high-rate stream is modulated by Twinkle VPPM (Non-Patent Document 2) or Dimming Spatial-8 Phase-Shift Keying (DS8-PSK) (Non-Patent Document 1), and the low-rate stream is modulated by Undersampled Frequency-Shift On-Off Keying (UFSOOK), Undersampled Phase-Shift On-Off Keying (UPSOOK), or Spatial-2 Phase-Shift Keying (S2-PSK).

[0006] Both streams transmitted from the RoI are decoded by a dual-camera receiver, where the high-speed (HS) camera demodulates the high-rate stream and the low-speed (LS) camera demodulates the low-rate stream, thereby reducing the computational load of the high-speed camera-based receiver.

[0007] MD Thieu et al, "Optical RoI-signaling for vehicular communications", IEEE Access, vol. 7, pp.69873 - 69891, 2019. R. Roberts, "Intel OCC Proposal", IEEE Standards Assoc., Jan. 2016, [Retrieved July 25, 2020], Internet<https: / / bit.ly / 3dUL7ZK> D.-P. Nguyen et al., "A probabilistic shaping approach for optical region-of-interest signaling", IEEE Photonics Technology Letters, vol. 34, no. 6, pp.309 - 312, Mar. 2022.T. Fehenberger et al., "Multiset-partition distribution matching", IEEE Transactions on Communications 67, no. 3 (2018), pp.1885 - 1893.

[0008] Dimming control is one of the key issues in OCC and visible light communication (VLC) systems. Traditional approaches to dimming control use correction symbol insertion and puncturing, which adds a large number of redundant bits to the frame, reducing the achievable transmission rate.

[0009] The dimming level can be managed by adjusting the percentage of the optical bit stream that is OFF (hereinafter referred to as "logic 0") or ON (hereinafter referred to as "logic 1") between 0% and 100%. Dimming control in HS-PSK and Twinkle VPPM involves changing the duty cycle (length of ON or OFF) of the high-rate pulses. Therefore, demodulation is difficult for DS8-PSK and Twinkle VPPM signals, which require strict synchronization, sampling, and decoding of each optical pulse.

[0010] Furthermore, in traditional VLC systems, long sequences of logic 1s or 0s are to be avoided because they cause flicker and clock data recovery (CDR) problems. Therefore, run-length-limited (RLL) codes maintain a direct current (DC) balance by equalizing the number of logic 1s and logic 0s in each symbol.

[0011] There is a trade-off between rate loss and ease of implementation for RLL codes such as Manchester, 4B6B, and 8B10B. Furthermore, when it comes to forward error correction (FEC), systems that use both FEC and RLL only support hard-decision (HD) FEC decoders because most RLL decoders generate hard output information, which results in poor error correction performance.

[0012] The soft-input soft-output (SISO) RLL decoder introduced by Kim et al. improves system reliability by generating soft outputs for soft-decision (SD) FEC decoding algorithms. However, the decoding algorithm for SISO RLL codes is complex and cannot be integrated into a VLC receiver.

[0013] Instead of using hybrid modulation techniques with the drawbacks mentioned above, Nguyen et al. proposed stochastic shaping for RoI signaling applications (Non-Patent Document 3), but implementation still presents challenges.

[0014] To solve the above problems, the OCC transmitter according to the disclosed technology includes a dimmer and an on-off keying modulator. The dimmer converts a high-rate signal based on a low-rate signal using m-out-of-n encoding to generate a superimposed signal that provides two desired dimming levels. The m and n in the m-out-of-n encoding are Y0 and Y1, respectively, and have the relationship m = Y0n and m = Y1n. The codebook for the m-out-of-n encoding is generated using Cm, a set of bit sequences with m logical 1s or logical 0s in n bits, and pairs Cm-l and Cm+l (l is a natural number). The on-off keying modulator converts the signal output by the dimmer into an optical signal. Furthermore, an OCC receiver according to the disclosed technology, which receives an OCC signal transmitted by an OCC transmitter, includes a low-speed camera, an RoI determination unit, a high-speed camera, an on-off keying demodulation unit, and an inverse dimmer. The low-speed camera captures the OCC signal and outputs a low-rate signal. The RoI determination unit determines the RoI from the low-rate signal. The high-speed camera extracts the RoI from the camera's field of view and outputs an RoI capture signal. The on-off keying demodulation unit demodulates the RoI capture signal to obtain a superimposed signal. The inverse dimmer uses a codebook to decode the superimposed signal into a high-rate signal.

[0015] Thanks to the non-RLL feature, soft-decision forward error correction algorithms can be applied, thereby increasing system reliability. The disclosed 4p-EMDPM dimmer-based visible light RoI signaling technology enables easier clock tracking and synchronization compared to conventional twinkle VPPM approaches. The disclosed 4p-EMDPM method reduces rate loss (bit redundancy) due to stochastic shaping compared to conventional methods.

[0016] 1. Functional block diagrams of an OCC transmitter and an OCC receiver according to an embodiment. 2. A diagram comparing rate losses of different distribution matching methods. 3. A diagram comparing rate losses of MPDM, EMPDM, 2p-EMPDM, and 4p-EMPDM. 4. Functional block diagram and codebook structure diagram of a 4p-EMPDM dimmer. 5. A diagram showing the codebook structures of MPDM, EMPDM, and 4p-EMPDM. 6. A diagram showing the binary tree structure of 4p-EMPDM. 7. A diagram explaining the details of the digital signal processing flow of an OCC transmitter and an OCC receiver according to an embodiment. 8. A photograph showing an OCC transmitter, a low-speed camera, and a video monitor in the slow RoI signaling-high-speed OCC demonstration system. 9. A photograph showing an OCC transmitter, a high-speed camera, and an OCC receiver in the slow RoI signaling-high-speed OCC demonstration system. 10. Exposure time and pixel Eb / N ０ The relationship between I and A is measured by varying the distance between the transmitter and receiver. A diagram showing how noise affects the intensity I and area A of a 50% dimmed symbol. A diagram showing how noise affects the intensity I and area A of a 30% dimmed symbol and a 70% dimmed symbol. A diagram showing two-class classification by intensity area threshold. Υ ０ = 41%, γ １ 1. A diagram showing the codebook size of a 4p-EMPDM dimmer and an EMPDM dimmer with a BER of 59%. 2. A diagram showing the overhead of 4p-EMPDM dimming and FEC coding. 3. A diagram showing the output probability distribution of 100,000 information words shaped by a 4p-EMPDM dimmer and coded by an SPE according to the LPS architecture. 4. A diagram showing the setup of a low-rate experimental system and a high-rate experimental system. 5. A flowchart explaining the operation of an OCC transmitter 1. 6. A flowchart explaining the operation of an OCC receiver 2. 7. A diagram showing an example of the functional configuration of a computer.

[0017] Hereinafter, embodiments of the disclosed technology will be described in detail. Note that components having the same functions are assigned the same numbers, and duplicated descriptions will be omitted.

[0018] The disclosed technology provides a binary extended multiset-partition distribution matching (EMPDM) with four composition pairs (4p), and a dimmer based on 4p-EMPDM for visible light RoI signaling applications. We first explain the disclosed technology through an overview of the proposed system in which 4p-EMPDM is used, followed by a theoretical analysis of the proposed algorithm and experimental optimization to find the optimal parameters of a 4p-EMPDM dimmer dedicated to RoI signaling applications.

[0019] [Overview of the proposed system] The functional block diagram of the proposed system is shown in Figure 1. The two inputs to the system are a low-rate signal v and a high-rate signal μ = (μ １ ,μ ２ ,...,μ ｋ ) where v and μ ｊ (1≦j≦k) takes the value 0 or 1. The proportion of logic 1 in the n-bit 4p-EMPDM dimming codeword u and the z-bit FEC codeword y is defined as type PA(1) (%) and ω (%), respectively. In the OCC transmitter, the 4p-EMPDM dimmer converts the information word μ with a Bernoulli (1 / 2) distribution into the codeword u=(u １ , u ２ ,..., u ｎ )

[0020] In fact, when the message u is encoded by a systematic FEC encoder, ω will have a slightly different value than PA(1). Following the Layered Probabilistic Shaping (LPS) architecture, a systematic polar encoder (SPE) is used to preserve the probabilistic shape of ω, generating two dimming levels in a non-RLL VLC transmitter. Furthermore, rather than using RLL coding to limit the run length as in conventional VLC systems, the 4p-EMPDM dimmer shapes the information word μ so that there is no significant difference between the occurrence of logic 1s and logic 0s. As a result, the run length of y is limited to a range that does not cause flicker at the minimum optical clock rate. The frequency of occurrence of logic 1s and logic 0s in the codeword u (e.g., "1011101011" has "3 0s and 7 1s") is referred to as a "composition" in this specification. The composition with a logic 1 occurrence frequency of i is referred to as γ. ｉ For example, the sequence "1011101011" is represented by γ ７ Belongs to.

[0021] In the dual-camera receiver (OCC receiver), a low-speed global shutter camera with a frame rate of 30 fps and a long exposure time detects the dimming level of a light-emitting diode (LED). This camera decodes the logic 0s and 1s of the low-rate bit stream used for Route of Interest (ROI) identification. A high-speed camera with a high frame rate (e.g., 10,000 fps) decodes the high-rate data stream on the Route of Interest (ROI) detected by the low-speed camera. A SD consecutive cancellation SPD (SD-SPD) decodes the codeword y' into u'. Finally, an inverse 4p-EMPDM dimmer decodes the message u' to reconstruct the high-speed binary sequence μ', assuming that all transmission errors have been corrected by the SD-SPD.

[0022] OOK was chosen as the modulation technique due to its simplicity and popularity in VLC systems. Note that since codeword u is a composite of a low-rate signal and a high-rate signal, codeword u and the codeword u' before decoding (de-dimming) are sometimes referred to as the "superimposed signal" in this specification.

[0023] [Binary Extended MPDM (EMPDM)] The matching rate R indicates how many bits of information are transmitted with each bit coded in binary DM. ＤＭ is defined by the following equation (1). where is an inequality The largest k that satisfies the above is output.

[0024] Alphabet B = {0,1}, Type P Ａ The entropy of a discrete random variable A is given by equation (2). The maximum matching rate that can be achieved by binary DM is given by equation (3). The rate loss of binary DM is defined as in equation (4).

[0025] The rate loss of Constant Composition Distribution Matching (CCDM) increases with decreasing block length (Reference 1).

[0026] Reference 1: P. Schulte et al., "Constant composition distribution matching", IEEE Trans. Inf. Theory, vol. 62, no. 1, pp.430 - 434, Jan. 2016.

[0027] MPDM was introduced as a method to reduce rate loss (especially when block lengths are short) and is suitable for practical implementation (Non-Patent Document 4). The rate loss reduction of MPDM comes from including multiple composition pairs (CPs) in addition to a typical composition (TC) to generate a non-constant composition DM. The compositions used in a pair are complementary to each other, such that the stochastic means of the sequences generated by both compositions achieve the desired distribution.

[0028] Non-Patent Document 4 introduced a binary tree structure in which each information word is divided into a payload that is mapped to a binary CCDM sequence and a prefix that selects a composition. Unlike conventional MPDM, which requires the number of sequences in a specific composition to be rounded to the nearest power of two (power-of-two constraint), the disclosed technology proposes binary EMPDM, which removes the power-of-two constraint for each composition and expands the codebook used in conventional matching. To enable EMPDM to be implemented using a binary tree structure, we propose sharing codebooks between the TC and the leading CP, and between adjacent compositions.

[0029] Cm represents an n-element binary group of weight m, forming the codebook of TC. For low-level dimming, m=Y ０ ・n, m=Y for high level dimming １ ・n. |C ｉ | is C ｉ The composition pair {γ ｍ－ｌ , γ ｍ＋ｌ The number of permutations in the codebook for}(l>0) can be calculated as follows: The total number of permutations in the EMPDM codebook including TC and all CPs is given by: where N ｐａｉｒｓ is the constraint {γ ｍ－ｌ , γ ｍ＋ｌ}=2{γ ｍIndicates the number of valid CPs that satisfy}(l is a natural number), and the maximum is m when m < n / 2 and n - m when m > n / 2.

[0030] Υ ０ <0.5, min(|C ｍ－ｌ |, |C ｍ＋ｌ |) = |C ｍ－ｌ |, and from equations (5) and (6), Similarly, for Υ １ >0.5, min(|C ｍ－ｌ |, |C ｍ＋ｌ |) = |C ｍ＋ｌ |, and equation (8) is obtained from equations (5) and (6). Low-level shaping Υ ０ and high-level shaping Υ １ The number of sequences in the EMPDM codebook is as follows.

[0031] Since EMPDM is a fixed-length reversible mapping, the input bit number k and the output sequence length n are fixed. Constraint Υ ０ = 1 - Υ １ Imposing this leads to an implementation that supports two symmetric shaping levels for Rol signaling applications. By imposing this constraint on equation (9), the following equation is obtained.

[0032] From (1) and (9), the matching rates of EMPDM at the two shaping levels can be written as follows.

[0033] The rate loss Δ ＥＭＰＤＭ of EMPDM is estimated by replacing R ＥＭＰＤＭ in equation (10) with R ＤＭ in equation (4). Figure 2 shows the rate losses of different distribution matching methods. The sequences are shaped for different output distributions PA(1) from 1% to 99%. It can be seen that the rate loss of EMPDM is much lower than that of other shaping methods for all output distributions. Furthermore, Υ ０ = 1 - Υ １The rate loss is symmetric about PA(1)=50% under the constraint that the matching rate and rate loss symmetry are important in designing a DM-based dimmer that allows two dimming levels with the same rate loss.

[0034] However, if the EMPDM codebook contains all CPs, it would appear difficult to implement EMPDM using look-up tables (LUTs). Furthermore, because flicker is a fundamental problem in non-RLL VLC systems, shaped sequences with long free runs of logic 1 or 0 must be avoided. Therefore, the remainder of the disclosure optimizes EMPDM to make it compatible with VLC-based RoI signaling applications.

[0035] [4p-EMPDM dimmer and its implementation] Two dimming levels γ for RoI signaling applications ０ and Y １ We propose a 4p-EMPDM dimmer that supports Υ ０ and Y １ are the typical output distributions of the dimmer for logic 0 and logic 1 of the low-rate stream, respectively. For 1 ≤ m < n, C ｍ C ｍ－１ To see how many times larger it is, calculate the following formula:

[0036] <Example> When n=100, C ２５ is C ２０ 452.5 times larger than C １５ 957293 times larger than C １５ < <C ２０ < <C ２５ is.

[0037] According to equation (11), most of the non-uniform sequences in the EMPDM codebook are ｍ ) and the leading CP{γ ｍ－ｌ , γ ｍ＋ｌIt has {}. Note that l is a small positive value. FIG. 3 shows the rate losses for some examples of MPDM and EMPDM. The examples of EMPDM are when the codebook has TC and two leading CPs (2p - EMPDM), four leading CPs (4p - EMPDM), and all CPs (EMPDM). 4p - EMPDM is a compact version of EMPDM and generates only run - length - aware codewords (codewords with the maximum value of the run - length suppressed to a predetermined value) for the purpose of reducing flicker in VLC applications. Arrow 31 indicates the empirical shaping range for low - level dimming (logical 0), and arrow 32 indicates the empirical shaping range for high - level dimming (logical 1).

[0038] The gap around PA(1) = 50% is provided so that the state detection of logical 0 and logical 1 of the low - rate signal is not ambiguous. The shaping range (run - length - aware range) aware of the run - length of the VLC application is marked with surrounding diagonal lines. Comparing EMPDM in FIG. 2 and 4p - EMPDM in FIG. 3, it can be seen that the rate loss of 4p - EMPDM is equivalent to that of EMPDM. In particular, there is no inferiority in the range of PA(1)<45% for low - level dimming and the range of PA(1)>55% for high - level dimming.

[0039] On the other hand, the rate loss of 2p - EMPDM increases as a penalty for not including the third and fourth CPs in the codebook. In a non - RLL VLC system, the codewords need to be shaped so that there is no large difference in the occurrence ratio of logical 1 and logical 0. If the two dimming levels are around 50% (for example, Υ ０ = 41%, Υ １ = 59%), there should be little difference in the occurrence ratio of logical 1 and logical 0. Therefore, the lowest rate loss and DC balance become two criteria for determining the restricted shaping range of the 4p - EMPDM dimming device. Experimental evaluation was carried out to determine two run - length - aware shaping ranges. They are 37%<PA(1)<45% and 55%<PA(1)<63% (see FIG. 3).

[0040] Figure 4 shows a detailed functional block diagram and codebook structure of the 4p-EMPDM dimmer 11 in Figure 1. The 4p-EMPDM dimmer supports two dimming levels with the same rate loss through symmetry about type PA(1) = 50%, as explained in the section on Binary Extended MPDM (EMPDM). The low-level 4p-EMPDM dimmer 41 and the high-level 4p-EMPDM dimmer 42 operate at dimming level Y. ０ , Υ １ According to the m determined from ｍ－ｌ , C ｍ＋ｌ ) (where l={1, 2, 3, 4}) and a typical composition (C ｍ ) codebook, and its rate loss is smaller than that of CCDM.

[0041] Figure 5 shows the codebook structures of conventional MPDM, EMPDM, and 4p-EMPDM. 4p-EMPDM uses the typical composition γ ｍ and four composition pairs {γ ｍ－ｌ , γ ｍ＋ｌ} (l = {1, 2, 3, 4}). EMPDM is a codebook extension of MPDM because its composition codebook does not have a power-of-two constraint, as explained in the section on Binary Extended MPDM (EMPDM). The codebook of 4p-EMPDM has a binary tree structure, and adjacent compositions share the codebook. In addition, the codebook of 4p-EMPDM contains only four CPs in addition to the TC. The codebook size of the remaining CPs is insignificant compared to the codebook size of the four CPs.

[0042] From (7) and (8), the total number of output sequences of the two-level 4p-EMPDM dimmer is: however, represents the rounding function to the nearest power of two.

[0043] Figure 6 shows the binary tree structure of 4p-EMPDM. Huffman coding is used to determine prefixes that identify subset pairs. ｌOne or two bits are used for the prefix. The next bit (the first bit of the payload) selects the shared subset within the subset pair. In this specification, the prefix and the first bit of the payload are sometimes collectively referred to as the "selection code."

[0044] There are two types of shared subsets: (i) Shared typical-pairwise subsets: The codebook of a TC is shared with the codebook of its paired composition element. For example, (C ｍ , C ｍ－１ ) and (C ｍ , C ｍ＋１ ) (ii) Shared Pairwise Subset: A codebook is shared between two paired composition elements. For example, (C ｍ－１ , C ｍ－２ ), (C ｍ＋１ , C ｍ＋２ ), (C ｍ－２ , C ｍ－３ ,C ｍ－４ ), and (C ｍ＋２ , C ｍ＋３ ,C ｍ＋４ ) is the subset with the remaining k ｌ Binary CCDM based on m-out-of-n codes is applied for one-to-one mapping of bit payload to shaped sequences.

[0045] [OCC Transmitter] Here, an OCC transmitter of the disclosed technology and its operation will be described with reference to Figures 1 and 18. The OCC transmitter 1 includes a dimmer 11 (4p-EMPDM dimmer), an FEC encoder 12 (systematic polar encoder), an OOK modulator 13, and an LED 14. Two dimming levels Y are preset. ０ , Υ １ and set the dimming level Υ ０ Then m = Y ０ n, dimming level γ １ Then m = Y １ As n, C ｍ And, C ｍ－ｌ and C ｍ＋ｌA codebook for m-out-of-n encoding is created from pairs (l = 1, 2, 3, 4). A low-rate signal v and a high-rate signal μ are input to the dimmer 11 (steps S1801 and S1802). Based on the low-rate signal and the high-rate signal, the dimmer 11 converts the high-rate signal into an m-out-of-n code using the codebook and outputs a superimposed signal (step S1803). The FEC encoder 12 encodes the superimposed signal using, for example, a systematic polar code and outputs an FEC code (step S1804). The OOK modulator 13 modulates the FEC code to drive the LED 14 and outputs an OCC signal (step S1805).

[0046] [OCC Receiver] Next, the OCC receiver and its operation of the disclosed technology will be described using Figures 1 and 19. The OCC receiver 2 includes a low-speed camera 21, a high-speed camera 22, an RoI determination unit 23, an OOK demodulation unit 24, an FEC decoding unit 25 (systematic polar decoding unit), and an inverse dimmer 26 (4p-EMPDM inverse dimmer). The low-speed camera 21 captures the entire camera field of view and outputs the captured image to the RoI determination unit 23 (step S1901). The RoI determination unit 23 detects a low-rate signal from the camera field of view (step S1902). The RoI determination unit 23 determines the RoI in the field of view from the detected low-rate signal (step S1903) and outputs the RoI information to the high-speed camera 22. Based on the RoI information, the high-speed camera 22 extracts the RoI portion from the captured signal (camera field of view) and outputs the RoI captured signal (step S1904). The OOK demodulator 24 demodulates the RoI imaging signal and outputs an FEC code (step S1905). The FEC decoder 25 decodes the superimposed signal from the FEC code (step S1906). The inverse dimmer 26 decodes the superimposed signal into a high-rate signal using the m-out-of-n encoding codebook generated in the same manner as the dimmer 11 (step S1907).

[0047] The details of the codebook construction of the 4p-EMPDM dimmer and its binary tree structure are as follows: 1: Output distribution Y that generates two desired dimming levels. ０ ,Y １ 2: Typical composition γ for each dimming levelｍ For low level dimming, m = Υ ０ ・n, m=Y for high level dimming １ n. The low-rate signal v determines the dimming level. 3: Constraint {γ ｍ－１ , γ ｍ＋１}=2{γ ｍ} (where l>0). 4: Composition pairs (C ｍ－ｌ , C ｍ＋ｌ ) are deleted. The number of sequences after this deletion is |(C ｍ－ｌ , C ｍ＋ｌ )|=2・min (|C ｍ－ｌ |, |C ｍ＋ｌ |), where l={1, 2, 3, 4}. 5: The main codebook is limited to TC and four CPs. The total number of sequences in the codebook is given by the following formula: 6: Sort the TC and four CPs in descending order according to the number of sequences in the codebook. 7: Divide the total number of sequences into the nearest power of 2 (2 ｋ ) where k is the number of input bits of the dimmer. 8: The total number of sequences is 2 ｋ The codebooks are divided into pairs of subsets of varying sizes. For example, the shared representative pairwise subsets are divided into pairs of subsets of 2. ｉ k powers of 2 are divided into shared pairwise subsets. ｉ+1 9: To identify pairs of subsets, p ｌ A bit is reserved as a prefix bit. The bit following the prefix bit is used to identify the subset within the pair. (i) Shared Typical - Pairwise Subset: p ｌ =1 (ii) For shared pairwise subsets: p ｌ =2 10: Using m-out-of-n code, k ｌ The bit payload is mapped to a shaped sequence within each subset.

[0048] Experimental Optimization This section presents a method to optimize the shaping level of the 4p-EMPDM dimmer through experimental evaluation. This system supports two dimming levels, representing logic 0 and logic 1 levels for low-rate communication in Roll of I / O signaling applications. Each time the dimmer changes the power distribution PA(1), the LED dimming level reflects the change. A low-speed camera-based receiver decodes the low-rate stream to identify the Roll of I / O by detecting the dimming level.

[0049] In experimental optimization, there are three criteria for finding the optimal dimmer shaping level: (1) the rate loss is lowest, (2) the power distribution is within the run-length sensitive range of non-RLL VLC (see Figure 3), and (3) the corresponding dimming level can be easily detected and demodulated by a low-speed camera-based receiver.

[0050] Figure 7 shows the digital signal processing (DSP) flow and experimental setup for the proposed transmitter and receiver. Figures 8 and 9 show the low-rate RoI signaling-high-rate OCC demonstration system. Figure 17 summarizes the setups for the low-rate and high-rate experimental systems. The low-rate RoI signal receiver uses a 30-fps low-speed global-shutter camera (LS global-shutter camera) to detect the dimming level and decode the low-rate bitstream. An Atmos Shogun 7 with SSD mini-storage serves as the video capture and monitoring device. VLC transmitters equipped with low-power LEDs are placed at distances of 1.7 m, 2.9 m, and 4.2 m from the receiver.

[0051] On the other hand, we use a high-speed camera / OCC receiver (HS camera / OCC receiver) operating at 10,000 fps with an exposure time of 50 μs. Images captured by the high-speed camera are sent to a field-programmable gate array (FPGA) for processing. In addition, to evaluate the performance of the proposed method, we built a simulation system of the high-speed OCC system on the OCC channel.

[0052] How noise affects image quality has been widely studied in the literature. In general, the impact of noise varies depending on the imaging system. In OCC systems, noise is modeled as a Gaussian distribution. The main noise sources are thermal noise generated by the readout circuitry and shot noise due to background illumination. The variance of the shot noise is proportional to the area of ​​the received pixel and the received light intensity. The pixel noise of a charge-coupled device / complementary metal-oxide semiconductor (CCD / CMOS) camera can be approximated as follows, assuming one bit per symbol: where N ０ is the noise density, E ｂ is the bit energy, θ=T ｅ / T is the ratio of the camera exposure time to the bit interval, a is the amplitude of the mark and space, and α and β are fitting parameters. Using α = 0.01529 and β = 0.1973 experimentally estimated in Non-Patent Document 1, pixel Eb / N ０ In addition, a camera with a long exposure time can be considered as a low-pass filter that attenuates high-frequency signals. Therefore, adjusting the exposure time can reduce pixel Eb / N ０ has a significant impact on

[0053] As shown in Figure 10, pixel Eb / N ０ changes, but T ｅ When the time exceeds 4500 μs, pixel Eb / N ０ The saturation point is about 39.7 dB. At a Tx clock rate of 20 kHz, the average luminance of a 128-bit frame needs 6.4 ms to be fully sensed by a slow camera. Therefore, to find the optimal shaping level of the 4p-EMPDM dimmer, we set the T ｅ = 6400μs. When this is the case, pixel Eb / N ０ is 39.74 dB.

[0054] Figure 11 shows how noise affects the intensity I of the 50% dimming symbol and region A. An intensity variance |maxI - minI| of 14.5 and a region variance |maxA - minA| of 10 were obtained. The variance at the 50% dimming level was adopted as the within-class variance for determining the threshold range for demodulating the low-rate bit stream.

[0055] Conventional OCC systems determine the on and off states of LEDs by comparing with the intensity threshold. To determine the threshold, the VLC transmitter sent 100,000 symbols shaped by a 4p-EMPDM dimmer with 30% < PA(1) < 70%. Figure 12 shows that logic 0 is Υ ０ = 30%, and logic 1 is Υ １ = 70% for the received symbols shaped by the dimmer. Only intensity information is used to determine the logic 0 / logic 1 decision threshold. The exposure time of the camera sensor is T ｅ = 6400 μs. The camera-based receiver was placed 4.2 m away from the VLC transmitter. It can be seen that the pixel intensity of the symbols shaped by the Υ １ = 70% dimmer does not change significantly. The receiver can only detect the difference in pixel area for symbols shaped with different compositions.

[0056] On the other hand, for the symbols shaped by the Υ ０ = 30% dimmer, the intensity variation is quite large. The reason is that at dimming levels close to 70%, the pixel intensity reaches saturation. It was confirmed that VPPM shows the best performance at this dimming level (Non-Patent Document 1). This discovery reveals that in addition to pixel intensity, the pixel area of the received signal is useful for data demodulation. Therefore, our low-speed camera-based receiver uses the intensity and area information of the captured signal for data demodulation and threshold determination.

[0057] Specifically, to determine a threshold range that is within the range between a low threshold and a high threshold, a low threshold, a central threshold, and a high threshold are used. The within-class scatter value due to the noise effect determines the width of the range. The threshold range is defined to avoid ambiguity when detecting adjacent dimming levels. The central threshold is given by the following equation (14). Here, s and b represent the slope and y-intercept of the threshold line, respectively, and can be calculated using the following equations (15) and (16). Here, A and I represent the area (width × height) and average intensity of the captured pixel, respectively.

[0058] The high and low threshold lines can be determined using a linear equation. However, b ｈ and b ｌ are determined by replacing with the coordinates of the farthest points above and below the central threshold of equation (14).

[0059] To check whether an arbitrary point (X ｉ , Y ｉ ) is above or below the central threshold, the coordinates of the point (X ｉ , Y ｉ ) are inserted into the threshold line equation (14). Then, Yi is compared with s.X + b. If Y ｉ < s.X + b, the point is below the line. Otherwise, if Yi > s.X + b, the point is above the threshold.

[0060] Figure 13 shows a two-class classification by the intensity-region threshold. The camera captures a dimming symbol shaped by a 4p-EMPDM dimmer. The typical shaping ratio is Υ ０ = 41% for logic 0 and Υ １ = 59% for logic 1. Both the intensity and area of the captured pixels are used to determine the intensity-region threshold. The exposure time of the camera sensor is T ｅ= 6400 μs. The camera-based receiver is placed 4.2 m away from the VLC transmitter. Using the intensity-area threshold, the typical shaping level is close to 50%; specifically, 30% to 41% is logic 0, and 70% to 59% is logic 1. As a result, the rate loss of the dimmer decreases from 0.031 to 0.0165 (Figure 3), which means that the matching rate increases with the proposed area-intensity threshold.

[0061] FIG. 14 shows Y ０ =41%, γ １ Figure 3 shows the codebook sizes of the 4p-EMPDM and EMPDM dimmers at 59%. These optimal power distributions were experimentally determined using an intensity-area threshold to determine the low-rate logic levels. Because the majority of the codebook belongs to the TC and four CPs, the codebook size of the 4p-EMPDM dimmer is 90.88% of that of the EMPDM dimmer. In the ranges PA(1) = [37%, 45%] and PA(1) = [55%, 63%], the rate loss of the 4p-EMPDM dimmer is comparable to that of the EMPDM dimmer (Figure 3). As explained in the section "4p-EMPDM Dimmer and Its Implementation," the 4p-EMPDM dimmer generates only sequences with similar proportions of logic 0 and logic 1. Therefore, compared to other binary distribution matching techniques, 4p-EMPDM is suitable for non-RLL VLC systems because the run length of its output sequence is constrained to mitigate flicker.

[0062] Figure 15 shows the overhead of 4p-EMPDM dimmer and FEC coding. Coding overhead is the ratio of the number of redundant bits to the number of information bits, and can be expressed as a percentage. The overhead of 4p-EMPDM is 4.16%, and the overhead of SPE(FEC) is 28%.

[0063] Although systematic FEC encoders better preserve the output probability distribution of 4p-EMPDM dimmers compared to non-systematic FEC encoders, logical operations on the generator and parity matrices of systematic FEC encoders typically alter the output distribution of the dimmer codewords. Therefore, we investigated the output distribution of LPS output sequences using Monte Carlo simulations. Figure 16 shows the output probability distribution of 100,000 information words shaped by a 4p-EMPDM dimmer and encoded by an SPE following the LPS architecture. We observe that the SPE slightly shifts the output distribution of the dimmer closer to PA(1) = 50%. For Roll signaling applications, low-rate logic levels are created from two dimming levels. Therefore, the output distributions of LPS symbols corresponding to the two dimming levels must not overlap in order to be recognized by a low-speed camera-based receiver.

[0064] [Program, Recording Medium] The various processes described above can be implemented by loading a program that executes each step of the above method into the recording unit 2020 of the computer 2000 shown in FIG. 20 and operating the control unit 2010, input unit 2030, output unit 2040, display unit 2050, etc.

[0065] The program describing the processing contents can be recorded on a computer-readable recording medium, which may be, for example, a magnetic recording device, an optical disk, a magneto-optical recording medium, a semiconductor memory, or any other suitable recording medium.

[0066] The program may be distributed by, for example, selling, transferring, lending, etc. portable recording media such as DVDs and CD-ROMs on which the program is recorded. Furthermore, the program may be stored in a storage device of a server computer, and then transferred from the server computer to other computers via a network, thereby distributing the program.

[0067] A computer that executes such a program may first temporarily store the program recorded on a portable recording medium or transferred from a server computer in its own storage device. Then, when executing a process, the computer reads the program stored on its own recording medium and executes the process in accordance with the read program. Alternatively, the computer may read the program directly from a portable recording medium and execute the process in accordance with the program. Furthermore, the computer may execute the process in accordance with each program transferred from the server computer. Alternatively, the server computer may not transfer the program to the computer, but may instead execute the process through a so-called ASP (Application Service Provider) service, which realizes the processing function by issuing an execution instruction and obtaining the results. In this embodiment, the program includes information used for processing by a computer that is equivalent to a program (e.g., data that is not a direct instruction to the computer but has properties that define computer processing).

[0068] Furthermore, in this embodiment, the device is configured by executing a predetermined program on a computer, but at least a part of the processing contents may be realized by hardware.

[0069] 1 OCC transmitter 11 dimmer 12 FEC encoding unit 13 OOK modulation unit 14 LED 15 memory unit 2 OCC receiver 21 low-speed camera 22 high-speed camera 23 RoI determination unit 24 OOK demodulation unit 25 FEC decoding unit 26 inverse dimmer 27 memory unit 2000 computer 2010 control unit 2020 recording unit 2030 input unit 2040 output unit 2050 display unit

Claims

1. An OCC transmitter that generates an OCC signal in which a low-rate signal and a high-rate signal are superimposed, comprising: a dimmer that converts a high-rate signal based on a low-rate signal by m-out-of-n coding to generate a superimposed signal that provides two desired dimming levels; and an on-off keying modulation unit that converts the signal output from the dimmer into an optical signal, wherein the dimmer sets the two dimming levels to Υ ０ , Υ １ respectively, and at dimming level Υ ０ , m = Υ ０ n, and at dimming level Υ １ , m = Υ １ n, and converts the high-rate signal by m-out-of-n coding to output an n-bit signal. Let the set of bit sequences having m logical 1s or logical 0s among n bits be Cm. The codebook of the m-out-of-n coding is generated using Cm and a pair of Cm-l and Cm+l (l is a natural number that is at most m when m < n / 2 and at most n-m when m > n / 2). OCC transmitter.

2. An OCC transmitter that generates an OCC signal in which a low-rate signal and a high-rate signal are superimposed, comprising: a dimmer that converts the high-rate signal based on the low-rate signal by m-out-of-n coding to generate a superimposed signal that provides two desired dimming levels; and an on-off keying modulation unit that converts the signal output by the dimmer into an optical signal, and the dimmer converts the two dimming levels into Υ ０ , Υ １ and the dimming level is Υ ０ Then m = Y ０ n, dimming level Υ １ Then m = Y １ an OCC transmitter for converting the high-rate signal using m-out-of-n encoding to output an n-bit signal, where Cm is a set of bit sequences having m logical 1s or logical 0s in n bits, and the codebook for the m-out-of-n encoding is generated using Cm and a pair of Cm-l and Cm+l (l = 1, 2, 3, 4).

3. An OCC transmitter as claimed in claim 2, wherein the codebooks are created as one codebook CB0 from Cm, Cm-1 and Cm+1, one codebook CB100 from Cm-1 and Cm-2, one codebook CB101 from Cm+1 and Cm+2, one codebook CB110 from Cm-2, Cm-3 and Cm-4, and one codebook CB111 from Cm+2, Cm+3 and Cm+4.

4. An OCC transmitter as claimed in claim 3, wherein the high rate signal has a selection code for selecting the codebook, and the dimmer selects the codebook CB0 when the selection code is 0, selects the codebook CB100 when the selection code is 100, selects the codebook CB101 when the selection code is 101, selects the codebook CB110 when the selection code is 110, and selects the codebook CB111 when the selection code is 111.

5. An OCC receiver that receives an OCC signal generated by the OCC transmitter described in claim 1 and decodes it into a low rate signal and a high rate signal, comprising: a low speed camera, a RoI determination unit, a high speed camera, an OOK demodulation unit, and an inverse dimmer, wherein the RoI determination unit obtains the low rate signal from the low speed camera and determines the RoI, the high speed camera extracts the RoI from the camera field of view and outputs an RoI shooting signal, the OOK demodulation unit obtains the superimposed signal from the RoI shooting signal, and the inverse dimmer decodes the high rate signal from the superimposed signal using the codebook.

6. A method for generating an OCC signal having two dimming levels with a low-rate signal and a high-rate signal superimposed thereon, wherein a set of bit sequences having m logical 1s in n bits is C ｍ is defined as such, and the dimmer is C ｍ and C ｍ－ｌ and C ｍ＋ｌ pairs (where l is a natural number that is at most m when m < n / 2 and at most n - m when m > n / 2) are used to generate a codebook for m-out-of-n encoding; the dimmer sets the two dimming levels to Υ ０ , Υ １ such that at dimming level Υ ０ , m = Υ ０ n, and at dimming level Υ １ , m = Υ １ n, and a k-bit signal is converted by m-out-of-n encoding to generate a superimposed signal; an on-off keying modulation unit converts the signal output by the dimmer into an optical signal; and an OCC signal generation method including the above steps.

7. An OCC signal receiving method for receiving an OCC signal generated by the OCC signal generating method according to claim 6 and decoding a high-rate signal, comprising the steps of: a low-speed camera capturing an OCC signal and outputting a low-rate signal; a RoI identifying unit identifying an RoI from the low-rate signal; a high-speed camera extracting the RoI from the camera's field of view and outputting an RoI capturing signal; an OOK demodulating unit demodulating the RoI capturing signal and acquiring the superimposed signal; and an inverse dimmer decoding the high-rate signal from the superimposed signal using the codebook.

8. A program for causing a computer to function as the OCC transmitter according to any one of claims 1 to 4.

9. A program for causing a computer to function as the OCC receiver according to claim 5.

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