Optical communication systems, transmitters, receivers

Abstract

This technology improves the success rate of timing synchronization in visible light communication. [Solution] The transmitter 10 blinks the light source 20 in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence, and the data that follows the synchronization signal. The synchronization code is a code that can detect timing synchronization by autocorrelation, and the spread sequence is a sequence that includes polarity reversal. The receiver 50 receives light from the transmitter 10 using an event camera 60. The event camera 60 outputs a positive event when the change in the brightness value of the received light exceeds a positive threshold, and outputs a negative event when it exceeds a negative threshold. The receiver 50 detects timing synchronization based on the autocorrelation between the synchronization code and a pattern obtained by arranging the positive or negative events output from the event camera 60 in time series.

Description

Technical Field

[0001] The present disclosure relates to optical communication technology, and particularly to an optical communication system, a transmitter, and a receiver that perform data communication by blinking light.

Background Art

[0002] In visible light communication using an event camera, the change in luminance caused by blinking an LED (Light-Emitting Diode) according to data is utilized. However, since the background also has a change in luminance, it is difficult to separate the LED blinking and the background noise. In order to separate this, the LED is blinked by data spread by a Walsh-Hadamard code, which is a kind of orthogonal code, so that the LED blinks at a high speed compared to the background noise. As a result, since the number of alternations of the change in luminance due to the LED blinking is different from the number of alternations of the change in luminance due to the background noise, it is possible to separate the LED blinking and the background noise (see, for example, Non-Patent Document 1).

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In visible light communication using event cameras, timing synchronization between the transmitter and receiver is necessary. For example, if the transmitter turns off an LED for a certain period after each packet, the receiver can establish timing synchronization by detecting the start of blinking. However, this method cannot be used for the more practical transmission of continuous packets without any blackout period.

[0005] This disclosure is made in light of these circumstances and aims to provide a technology that improves the success rate of timing synchronization in visible light communication. [Means for solving the problem]

[0006] To solve the above problems, an optical communication system in one embodiment of the present disclosure comprises a transmitter that blinks a light source in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence and data following the synchronization signal, and a receiver that receives light from the transmitter using an event camera. The synchronization code is a code that can detect timing synchronization by autocorrelation, the spread sequence is a sequence that includes polarity reversal, the event camera outputs a positive event when the change in the brightness value of the light received from the transmitter exceeds a positive threshold and a negative event when it exceeds a negative threshold, the receiver detects timing synchronization based on the autocorrelation between a pattern obtained by arranging the positive or negative events output from the event camera in time series and the synchronization code, and the receiver demodulates the data after detecting timing synchronization.

[0007] Another aspect of the present disclosure is a transmitter, which flashes a light source in response to a synchronization signal obtained by spreading a synchronization code in a spread sequence and data following the synchronization signal, wherein the synchronization code is a code in which timing synchronization can be detected by autocorrelation, and the spread sequence is a sequence that includes polarity reversal.

[0008] Another aspect of this disclosure is a receiver. This receiver includes an event camera that receives light from a transmitter that blinks a light source in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence and data following the synchronization signal, and outputs a positive event when the change in the brightness value of the light received from the transmitter exceeds a positive threshold and a negative event when it exceeds a negative threshold; a detection unit that detects timing synchronization based on the autocorrelation between a pattern obtained by arranging the positive or negative events output from the event camera in time series and the synchronization code; and a demodulation unit that demodulates the data after the detection unit has detected timing synchronization. The synchronization code is a code that can detect timing synchronization by autocorrelation, and the spread sequence is a sequence that includes polarity reversal.

[0009] Furthermore, any combination of the above components, as well as any conversion of the expressions of this disclosure between methods, apparatus, systems, recording media, computer programs, etc., are also valid forms of this disclosure. [Effects of the Invention]

[0010] According to this disclosure, the success rate of timing synchronization in visible light communication can be improved. [Brief explanation of the drawing]

[0011] [Figure 1] This is a diagram showing the configuration of the optical communication system according to this embodiment. [Figure 2] This diagram shows the format of packets transmitted from the transmitter shown in Figure 1. [Figure 3] Figures 3(a) and 3(b) show the events output from the event camera in Figure 1. [Figure 4] This diagram shows the configuration of the transmitter shown in Figure 1. [Figure 5] Figure 4 shows the autocorrelation characteristics of the synchronization code in the synchronization signal output section. [Figure 6] This diagram shows the configuration of the receiver shown in Figure 1. [Figure 7] Figures 7(a) and 7(b) show an overview of the operation of the event camera and detection unit shown in Figure 6. [Figure 8] Figures 8(a)-(f) show an overview of the operation of the event camera and detection unit shown in Figure 6. [Figure 9] Figures 9(a)-(c) show an overview of the operation of the demodulation unit in Figure 6. [Modes for carrying out the invention]

[0012] Before describing this disclosure in detail, an overview will be provided. This embodiment is a visible light communication system in which a transmitter flashes a light source (LED) according to the data, and a receiver transmits data by capturing the flashing light with an event camera. The event camera has a high response speed and can therefore be used as a receiver for visible light communication. The event camera detects only the change in brightness of each pixel and outputs an event when the change in brightness is large. Visible light communication using an event camera uses brightness change information generated by flashing the LED. If events associated with changes in background brightness are also acquired, it becomes difficult to identify the event of the transmitting LED. Therefore, Walsh-Hadamard coding, a type of orthogonal coding, is effective for visible light communication using an event camera. In order to improve the success rate of timing synchronization in such visible light communication, this embodiment utilizes the autocorrelation characteristics of Barker coding and spreads Barker coding in a bipolar sequence so that an event is generated even if bits of the same polarity are transmitted consecutively.

[0013] Figure 1 shows the configuration of the optical communication system 100. The optical communication system 100 includes a transmitter 10 and a receiver 50. The transmitter 10 includes a light source 20, and the receiver 50 includes an event camera 60. Figure 2 shows the format of a packet transmitted from the transmitter 10. This corresponds to the format of one packet, and multiple packets of the same format may be consecutive. The packet includes a synchronization signal followed by data. The synchronization signal is a signal to cause the receiver 50 to detect timing synchronization with the transmitter 10, and its details will be described later. The data is information to be transmitted from the transmitter 10 to the receiver 50. Return to Figure 1.

[0014] The transmitter 10 causes the light source 20 to blink according to the synchronization signal and the data. Specifically, an ON-OFF keying (OOK) modulation method is used, in which the light source 20 is turned on (ON) when the bits included in the synchronization signal and the data are “+1”, and the light source 20 is turned off (OFF) when the bits included in the synchronization signal and the data are “-1”.

[0015] The receiver 50 receives the light from the transmitter 10 by means of the event camera 60. The event camera 60 detects the difference when the luminance value of the light received from the transmitter 10 changes. The event camera 60 outputs a positive event when the change in the luminance value of a predetermined pixel exceeds a positive threshold value. On the other hand, the event camera 60 outputs a negative event when the change exceeds a negative threshold value. The positive event and the negative event may be collectively referred to as an “event”. This operation is performed independently for each pixel.

[0016] Figs. 3(a)-(b) show the events output from the event camera 60. The horizontal axes indicate time, which is shown as “0”, “1”, ···, “6”. Fig. 3(a) shows the information transmitted from the transmitter 10. As described above, the light source 20 is turned on when the information is “+1”, and the light source 20 is turned off when the information is “-1”. Here, the information “+1”, “-1”, “+1”, “+1”, “+1”, “-1” is transmitted in this order.

[0017] Fig. 3(b) shows the events when the event camera 60 receives the light that has blinked according to the information shown in Fig. 3(a). As described above, a positive event or a negative event is output when the change in the luminance value exceeds a positive threshold value or a negative threshold value. Therefore, a negative event is output at time “1”, a positive event is output at time “2”, and a negative event is output at time “5”. That is, simply transmitting the information as it is does not result in obtaining an event with the same content as the information. In order to obtain an event with the same content as the transmitted information, in this embodiment, the following processing is executed.

[0018] FIG. 4 shows the configuration of the transmitter 10. The transmitter 10 includes an input unit 12, a modulation unit 14, a synchronization signal output unit 16, a control unit 18, and a light source 20. The input unit 12 inputs the data to be transmitted. The data to be transmitted is represented by "+1" or "-1". The input unit 12 outputs the data to the modulation unit 14.

[0019] The modulation unit 14 inputs the data from the input unit 12. The modulation unit 14 encodes (modulates) the data with an orthogonal code. An example of the orthogonal code is the Walsh Hadamard Code. The Walsh Hadamard Code is a code that uses a Hadamard Matrix, and the Hadamard Matrix is a square matrix composed of "±1" as follows, and a matrix in which any two different row vectors are orthogonal.

Equation

[0022] The synchronization signal output unit 16 outputs a synchronization signal to the receiver 50 to detect timing synchronization. For timing synchronization, for example, the low autocorrelation value in the sidelobes of a Barker code is utilized. A Barker code is one of the synchronization codes that can detect timing synchronization by autocorrelation. Figure 5 shows the autocorrelation characteristics of the synchronization code in the synchronization signal output unit 16. The horizontal axis represents timing, and the vertical axis represents the autocorrelation value. This shows the autocorrelation value calculated while shifting the timing for a synchronization code (Barker code) with code length "7". Time "T0" represents the case where there is no timing shift. The autocorrelation value when the timing is shifted is lower than the autocorrelation value when the timing is correct. Therefore, a Barker code can be used as a synchronization code. Return to Figure 4.

[0023] However, as explained in Figures 3(a)-(b), the event camera 60 outputs an event when there is a large change in brightness value, so the receiver 50 cannot obtain the Barker code simply by transmitting the Barker code as is. The synchronization signal in the synchronization signal output unit 16 is generated by spreading the synchronization code as a spread sequence. The spread sequence is a sequence that includes polarity inversion, for example, the bipolar sequence [-1,1]. The detection of timing synchronization using such a synchronization signal will be described later, but for example, the synchronization signal is a 52-bit sequence obtained by concatenating two Barker codes with sequence length "13" and then spreading them as the bipolar sequence [-1,1].

[0024] The control unit 18 receives data from the modulation unit 14 and a synchronization signal from the synchronization signal output unit 16. The control unit 18 generates packets by combining the synchronization signal and data as shown in Figure 2. Multiple packets may be generated consecutively. The control unit 18 blinks the light source 20 according to the synchronization signal and data contained in the packets.

[0025] Figure 6 shows the configuration of the receiver 50. The receiver 50 includes an event camera 60, a detection unit 62, a demodulation unit 64, and an output unit 66. The event camera 60 receives light from the transmitter 10, which causes the light source 20 to blink according to the synchronization signal and data. It outputs a positive event when the change in the brightness value of the light received from the transmitter 10 exceeds a positive threshold, and a negative event when it exceeds a negative threshold.

[0026] The detection unit 62 detects timing synchronization based on the autocorrelation between a pattern of positive or negative events output from the event camera 60 arranged in time series and a synchronization code. Figures 7(a)-(b) show an overview of the operation of the event camera 60 and the detection unit 62. The horizontal axis represents time, and the vertical axis represents a value of "+1" or "-1".

[0027] Figure 7(a) shows information transmitted from transmitter 10, such as a synchronization signal. Here, as an example, let's assume the synchronization code is "+1", "-1", "+1", "+1", "+1", "-1". The synchronization code is switched at the timings "T1", "T2", "T3", ..., "T6". On the other hand, the spread sequence is [-1,+1]. By spreading the synchronization code "+1" with the spread sequence [-1,+1], the synchronization signal becomes [-1,+1]. Also, by spreading the synchronization code "-1" with the spread sequence [-1,+1], the synchronization signal becomes [+1,-1]. In Figure 7(a), the boundary between "-1" and "+1" in the spread sequence [-1,+1] is shown by the times "T1'", "T2'", "T3'", ..., "T6'". For example, time "T2'" ​​is placed between times "T1" and "T2".

[0028] Figure 7(b) shows the events output from the event camera 60 that received the synchronization signal in Figure 7(a). Regardless of whether the polarity of the synchronization code is consecutive or not, events "+1", "-1", "+1", "+1", "+1", and "-1" appear at times "T1'", "T2'", "T3'", ..., "T6'". Event "+1" indicates a positive event, and event "-1" indicates a negative event. In other words, the transmitted synchronization code is output at the timing when the polarity of the spreading sequence changes. Return to Figure 6.

[0029] The detection unit 62 extracts events received from the event camera 60 at intervals equal to the sequence length of the diffusion sequence, and generates a pattern in which positive or negative events that may appear at timings equal to the sequence length of the diffusion sequence are arranged in time. The detection unit 62 calculates the autocorrelation between the generated pattern and the synchronization code. Therefore, the detection unit 62 does not perform despreading when calculating the autocorrelation value. The detection unit 62 detects the timing of the maximum value of the autocorrelation as the synchronization timing.

[0030] The longer the distance between the transmitter 10 and the receiver 50, the lower the brightness value of the light received by the event camera 60 from the light source 20. As a result, the change in brightness value also becomes smaller, and the event camera 60 may fail to output an event even at a time when an event could occur. This corresponds to no event being output at least one of the times "T1'", "T2'", "T3'", ..., "T6'" in Figure 7(b), and below we will refer to this situation as a "missing event".

[0031] Figures 8(a)-(f) show an overview of the operation of the event camera 60 and the detection unit 62. The horizontal axis represents time, and the vertical axis represents the value of "+1" or "-1". First, we will explain the situation in which data loss occurs using Figures 8(a)-(c). Figure 8(a) shows information transmitted from the transmitter 10, such as the synchronization signal. This is the same as Figure 7(a). Figure 8(b) shows the events output from the event camera 60 that received the synchronization signal in Figure 8(a). Here, data loss occurs at time "T5'". In other words, the event that should be output at time "T5'" (a positive event) is not output. As a result, as shown in Figure 8(c), the events "+1", "-1", "+1", "+1", "0", and "-1" are output, which are different from the synchronization code.

[0032] Next, Figures 8(d)-(f) will be used to explain the process for filling in the missing data in the detection unit 62. Figure 8(d) shows the information transmitted from the transmitter 10, for example, the synchronization signal. This is the same as in Figure 8(a). Figure 8(e) shows the event output from the event camera 60 that received the synchronization signal in Figure 8(d). Similar to Figure 8(b), a missing data occurs at time "T5'".

[0033] If an event does not appear at a timing corresponding to the sequence length of the spread sequence, such as time "T5'" in Figure 8(e), the detection unit 62 fills in the missing event based on an event that appeared at a past timing other than the sequence length of the spread sequence, for example, at time "T4". Here, since the polarity of adjacent bits is inverted in the spread sequence [-1,+1], the polarity of the event appearing at time "T4" and the event appearing at time "T5'" are also determined. The detection unit 62 identifies the negative event at time "T4" and fills in time "T5'" with the positive event obtained by inverting it. As a result, as shown in Figure 8(f), the events "+1", "-1", "+1", "+1", "+1", and "-1" are output, which are identical to the synchronization code. Returning to Figure 6, if the detection unit 62 detects timing synchronization, it notifies the demodulation unit 64 of the detected synchronization timing.

[0034] The demodulation unit 64 demodulates the data according to the synchronization timing notified by the detection unit 62 after the detection unit 62 has detected the timing synchronization. The Walsh-Hadamard transform is used for data demodulation. To illustrate the Walsh-Hadamard transform, Figures 9(a)-(c) are also used here. Figures 9(a)-(c) show an overview of the operation of the demodulation unit 64. Figure 9(a) shows events from the event camera 60. As shown, it includes both positive and negative events.

[0035] The Walsh-Hadamard transform evaluates the similarity between events from the event camera 60 and each Walsh-Hadamard code by using Walsh-Hadamard codes as correlators, as shown in Figure 9(b). The Walsh-Hadamard transform is shown as follows:

number

[0036] Therefore, the higher the correlation between the Walsh-Hadamard code and the event, that is, the more the positive and negative signs match, the larger the similarity Iz will be. For this reason, as shown in Figure 9(c), the demodulation unit 64 performs a Walsh-Hadamard transformation, then searches for the wz(tr) that maximizes Ir, estimates wz(tr) as data, and demodulates it. Returning to Figure 6, the output unit 66 outputs the demodulated data from the demodulation unit 64.

[0037] This configuration can be implemented hardware-wise using the CPU (Central Processing Unit), memory, and other LSIs (Large Scale Integrations) of any computer, and software-wise using programs loaded into memory. However, this description focuses on the functional blocks realized through the coordination of these components. Therefore, it will be understood by those skilled in the art that these functional blocks can be implemented in various ways, either solely through hardware or through a combination of hardware and software.

[0038] According to this embodiment, timing synchronization is detected based on the autocorrelation between the event from the event camera, which receives light flashing according to a synchronization signal obtained by spreading the synchronization code in a spread sequence, and the synchronization code. Therefore, the synchronization code can be used for timing synchronization in the event camera. Furthermore, since the synchronization code is used for timing synchronization in the event camera, the success rate of timing synchronization in visible light communication can be improved.

[0039] Furthermore, since the Barker code is spread in a bipolar sequence, the Barker code with high autocorrelation characteristics can be reproduced in events output from the event camera. Also, because the Barker code with high autocorrelation characteristics is reproduced in events output from the event camera, the Barker code can be used for timing synchronization in the event camera.

[0040] Furthermore, since the autocorrelation between events that may occur at the sequence length timing of the spreading sequence and the synchronization code is calculated, despreading at the receiving end becomes unnecessary. Also, because despreading at the receiving end is unnecessary, processing can be simplified. In addition, since events that did not occur are filled in based on events that occurred at past timings other than the sequence length timing of the spreading sequence, the accuracy of reconstructing the synchronization code can be improved. Furthermore, because the accuracy of reconstructing the synchronization code is improved, the success rate of timing synchronization in visible light communication can be improved.

[0041] An overview of one aspect of this disclosure is as follows: (Item 1) A transmitter that flashes a light source in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence, and data following the synchronization signal. The system includes a receiver that receives light from the transmitter via an event camera, The aforementioned synchronization code is a code capable of detecting timing synchronization by autocorrelation, The aforementioned diffusion series is a series that includes a reversal of polarity, The event camera outputs a positive event when the change in the brightness value of the light received from the transmitter exceeds a positive threshold, and outputs a negative event when it exceeds a negative threshold. The receiver detects timing synchronization based on the autocorrelation between the pattern obtained by arranging the positive or negative events output from the event camera in chronological order and the synchronization code. The receiver is an optical communication system that detects timing synchronization and then demodulates the data.

[0042] According to this embodiment, timing synchronization is detected based on the autocorrelation between the event from an event camera that receives light flashing according to a synchronization signal obtained by spreading the synchronization code in a spread sequence, and the synchronization code. This improves the success rate of timing synchronization in visible light communication.

[0043] (Item 2) The aforementioned synchronization code is a Barker code, The aforementioned spreading sequence is a bipolar sequence, as described in item 1 of the optical communication system. In this case, since the Barker code is spread in a bipolar sequence, a Barker code with high autocorrelation characteristics can be used in an event camera.

[0044] (Item 3) The optical communication system according to item 1 or 2, wherein the receiver calculates the autocorrelation between the synchronization code and a pattern obtained by arranging the positive or negative events that may appear at timings equal to the sequence length of the spreading sequence. In this case, since the autocorrelation between events that may occur at the timing of the sequence length of the spread sequence and the synchronization code is calculated, despreading at the receiving end becomes unnecessary.

[0045] (Item 4) The optical communication system described in item 3, wherein if the receiver does not have the positive or negative event at the timing of the sequence length of the spreading sequence, it compensates for the missing positive or negative event based on the positive or negative event that had occurred at a past timing other than the timing of the sequence length of the spreading sequence. In this case, events that did not occur are compensated for based on events that occurred at past timings other than the sequence length timing of the spreading sequence, thus improving the success rate of timing synchronization in visible light communication.

[0046] (Item 5) A transmitter that blinks a light source in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence and data following the synchronization signal, The aforementioned synchronization code is a code capable of detecting timing synchronization by autocorrelation, The aforementioned spreading sequence is a transmitter whose sequence includes a reversal of polarity.

[0047] (Item 6) The aforementioned synchronization code is a Barker code, The aforementioned spreading sequence is a bipolar sequence, as described in item 5 of the transmitter.

[0048] (Item 7) An event camera receives light from a transmitter that blinks a light source in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence and data following the synchronization signal, outputs a positive event when the change in the brightness value of the light received from the transmitter exceeds a positive threshold, and outputs a negative event when it exceeds a negative threshold, A detection unit that detects timing synchronization based on the autocorrelation between a pattern obtained by arranging the positive or negative events output from the event camera in chronological order and the synchronization code, The system includes a demodulation unit that demodulates the data after the detection unit has detected timing synchronization, The aforementioned synchronization code is a code capable of detecting timing synchronization by autocorrelation, The aforementioned spreading sequence is a receiver whose sequence includes a reversal of polarity.

[0049] The present disclosure has been explained above based on examples. These examples are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications are also within the scope of the present disclosure.

[0050] In this embodiment, a Barker code is used as the synchronization code. However, it is not limited to this; for example, a PN sequence (pseudo-random sequence) may be used. For example, an M sequence or a Zadoff-Chu sequence. A multi-user code may also be used. For example, a Gold sequence or a Kasami sequence. This modified example improves the flexibility of the configuration.

[0051] In this embodiment, a bipolar sequence is used as the diffusion sequence. However, it is not limited to this; for example, any sequence with a code length of "3" or more, such as "+1", "-1", "+1" or "+1", "+1", "-1", may be used, as long as it includes polarity reversal. Manchester codes, CMI (Coded Mark Inversion), and DMI (differential mark inversion) may also be used. This modified example improves the degree of freedom in configuration. [Explanation of Symbols]

[0052] 10 Transmitter, 12 Input unit, 14 Modulation unit, 16 Synchronization signal output unit, 18 Control unit, 20 Light source, 50 Receiver, 60 Event camera, 62 Detection unit, 64 Demodulation unit, 66 Output unit, 100 Optical communication system.

Claims

1. A transmitter that flashes a light source in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence, and data following the synchronization signal. The system includes a receiver that receives light from the transmitter via an event camera, The aforementioned synchronization code is a code capable of detecting timing synchronization by autocorrelation, The aforementioned diffusion series is a series that includes a reversal of polarity, The event camera outputs a positive event when the change in the brightness value of the light received from the transmitter exceeds a positive threshold, and outputs a negative event when it exceeds a negative threshold. The receiver detects timing synchronization based on the autocorrelation between the pattern obtained by arranging the positive or negative events output from the event camera in chronological order and the synchronization code. The receiver is an optical communication system that detects timing synchronization and then demodulates the data.

2. The aforementioned synchronization code is a Barker code, The optical communication system according to claim 1, wherein the spreading sequence is a bipolar sequence.

3. The optical communication system according to claim 1 or 2, wherein the receiver calculates the autocorrelation between the synchronization code and a pattern obtained by arranging the positive or negative events that may appear at timings equal to the sequence length of the spreading sequence.

4. The optical communication system according to claim 3, wherein if the receiver does not have the positive event or the negative event at the timing of the sequence length of the spreading sequence, it supplements the positive event or the negative event that did not occur based on the positive event or the negative event that occurred at a past timing other than the timing of the sequence length of the spreading sequence.

5. A transmitter that blinks a light source in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence and data following the synchronization signal, The aforementioned synchronization code is a code capable of detecting timing synchronization by autocorrelation, The aforementioned spreading sequence is a transmitter whose sequence includes a reversal of polarity.

6. The aforementioned synchronization code is a Barker code, The transmitter according to claim 5, wherein the spreading sequence is a bipolar sequence.

7. An event camera receives light from a transmitter that blinks a light source in accordance with a synchronization signal obtained by spreading a synchronization code in a spread sequence and data following the synchronization signal, outputs a positive event when the change in the brightness value of the light received from the transmitter exceeds a positive threshold, and outputs a negative event when it exceeds a negative threshold, A detection unit that detects timing synchronization based on the autocorrelation between a pattern obtained by arranging the positive or negative events output from the event camera in chronological order and the synchronization code, The system includes a demodulation unit that demodulates the data after the detection unit has detected timing synchronization, The aforementioned synchronization code is a code capable of detecting timing synchronization by autocorrelation, The aforementioned spreading sequence is a receiver whose sequence includes a reversal of polarity.

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