JP6770494B2 - Optical receiver and known signal detection method - Google Patents

Description

The present invention relates to an optical receiver and a known signal detection method.

In an optical communication system, an optical receiver uses a known signal sequence added to a frame of a received signal for initial convergence. The optical receiver synchronizes the received signal with the timing of signal processing based on the cross-correlation between the standby signal and the received signal. The standby signal is a signal of the same sequence as the known signal sequence. The optical receiver can improve the convergence characteristics of the adaptive equalization filter by extracting a known signal sequence based on the cross-correlation of the standby signal and the received signal and using this sequence for initial convergence (patented). Reference 1).

International Publication No. 2015/141658

However, the synchronization characteristics of the received signal are deteriorated by the distortion generated in the received signal in the transmission line. The conventional optical receiver has a problem that the deterioration of the synchronization characteristics of the received signal cannot be reduced.

In view of the above circumstances, it is an object of the present invention to provide an optical receiver and a known signal detection method capable of reducing deterioration of synchronization characteristics of received signals.

One aspect of the present invention is an acquisition unit that acquires a known signal sequence including a plurality of specific signal sequences arranged at a specific cycle in the time direction, and a component amount of an autocorrelation coefficient between the specific signal sequences for each cycle. The autocorrelation acquisition unit to be acquired, the specific period component acquisition unit for acquiring the component amount of the autocorrelation coefficient in the specific cycle from the component amounts of the autocorrelation coefficient for each cycle, and the known signal sequence. It is an optical receiver including an autocorrelation position detection unit which detects a position where the component amount of the autocorrelation coefficient of the specific period becomes maximum in the frame including.

One aspect of the present invention is the optical receiver, wherein the known signal sequence includes the specific signal sequence of a different pattern.

One aspect of the present invention is the above-mentioned optical receiver, further including an averaging unit for averaging the component amounts of the autocorrelation coefficients in the specific period for a plurality of the frames, and the autocorrelation position detection unit. Detects the position where the component amount of the autocorrelation coefficient of the averaged specific period is maximized in the frame including the known signal sequence.

One aspect of the present invention is the above-mentioned optical receiver, and for the adjacent blocks in the frame, the component amount of the cross-correlation coefficient between the predetermined standby signal and the known signal sequence is acquired for each cycle. The cross-correlation acquisition unit is further provided, and a cross-correlation position detection unit that detects the position where the component amount of the cross-correlation coefficient in the specific period is maximized in the frame including the known signal sequence.

One aspect of the present invention is a known signal detection method executed by an optical receiver, which includes a step of acquiring a known signal sequence including a plurality of specific signal sequences arranged at a specific cycle in the time direction, and the specific signal sequence. A step of acquiring the component amount of the autocorrelation coefficient between each other for each cycle and a step of acquiring the component amount of the autocorrelation coefficient of the specific cycle from the component amount of the autocorrelation coefficient for each cycle. This is a known signal detection method including a step of detecting a position where the component amount of the autocorrelation coefficient of the specific period becomes maximum in a frame including the known signal sequence.

According to the present invention, it is possible to reduce the deterioration of the synchronization characteristics of the received signal.

It is a figure which shows the example of the structure of the optical communication system in 1st Embodiment. It is a figure which shows the example of the structure of the frame in 1st Embodiment. It is a figure which shows the example of the structure of the known signal sequence in 1st Embodiment. It is a figure which shows the example of the structure of the block in 1st Embodiment. It is a figure which shows the example of the sample addition processing in 1st Embodiment. It is a figure which shows the example of the output of the autocorrelation of the known signal sequence which has a specific pattern in 1st Embodiment. It is a flowchart which shows the example of the operation of the optical receiver in 1st Embodiment. It is a figure which shows the example of the structure of the optical communication system in 2nd Embodiment. It is a figure which shows the 1st example of the structure of the frame in 2nd Embodiment. It is a figure which shows the 2nd example of the structure of the frame in 2nd Embodiment. FIG. 5 is a diagram showing an example of differential processing between a symbol 0 points ahead of a selected symbol in a known signal sequence and the selected symbol in the second embodiment. It is a figure which shows the example of the differential processing between the symbol one step ahead from the selected symbol in the known signal sequence, and the selected symbol in 2nd Embodiment. It is a figure which shows the example of the differential processing between the symbol 2 ahead from the selected symbol in a known signal sequence, and the selected symbol in 2nd Embodiment. It is a figure which shows the example of the result which the differential component addition circuit generated the differential component of a plurality of symbols at once in 2nd Embodiment. It is a figure which shows the example of the addition result by the adjacent sample addition circuit in 2nd Embodiment. It is a figure which shows the 1st example of the positional relationship between a detection block and a known signal sequence in 2nd Embodiment. It is a figure which shows the 2nd example of the positional relationship between a detection block and a known signal sequence in 2nd Embodiment. It is a figure which shows the example of the addition 1st time of sample synchronization in 2nd Embodiment. It is a figure which shows the example of the additional addition 2nd time of sample synchronization in 2nd Embodiment. It is a flowchart which shows the example of the operation of the optical receiver in 2nd Embodiment.

Embodiments of the present invention will be described in detail with reference to the drawings.
(First Embodiment)
FIG. 1 is a diagram showing an example of the configuration of the optical communication system 1a. The optical communication system 1a includes an optical transmitter 2, a transmission line 3, and an optical receiver 4a. The optical transmitter 2 converts a frame containing data into an optical signal. The optical transmitter 2 transmits an optical signal to the optical receiver 4a via the transmission line 3.

FIG. 2 is a diagram showing an example of a frame configuration. A frame consists of a known signal sequence and a payload that stores data. In FIG. 2, the frame 10 is composed of a known signal sequence 11 and a payload 12. The optical transmitter 2 adds the known signal sequence 11 to an arbitrary position on the frame 10.

FIG. 3 is a diagram showing an example of the configuration of the known signal sequence 11. The known signal sequence 11 is a signal sequence having a specific pattern in which N samples including a specific signal sequence composed of M samples arranged at predetermined intervals are repeated a plurality of times. The known signal sequence 11 is composed of, for example, 300 samples. The specific signal sequence is detected for each specific period (hereinafter referred to as "specific period") "N sample" in the period of each sample (hereinafter referred to as "sample period"). In the known signal sequence, the specific signal sequence may be one type or two or more types. In FIG. 3, the specific pattern 110 includes one type of specific signal sequence detected every specific cycle “10 samples”. The specific pattern 111 includes two types of specific signal sequences detected every specific period "65 samples".

The transmission line 3 shown in FIG. 1 is, for example, an optical fiber. The transmission line 3 may further include, for example, an optical splitter. The transmission line 3 transmits the optical signal transmitted from the optical transmitter 2 to the optical receiver 4a.

The optical receiver 4a includes an optical signal processing unit 40 and a block synchronization circuit 41. The optical signal processing unit 40 acquires the optical signal transmitted from the optical transmitter 2 via the transmission line 3. The optical signal processing unit 40 converts an optical signal into a received signal which is an electric signal according to the data.

FIG. 4 is a diagram showing an example of a block configuration. The block synchronization circuit 41 divides the frame of the received signal into a plurality of blocks. The block synchronization circuit 41 executes autocorrelation processing for each block. The block synchronization circuit 41 extracts the components of the specific period "N sample" from the specific pattern by autocorrelation processing. That is, the block synchronization circuit 41 outputs the component of the autocorrelation coefficient of the specific cycle as the output of the autocorrelation for each cycle.

The block synchronization circuit 41 detects a position (time) in the time direction of a known signal sequence in a frame in a process (internal loop process) performed on a single frame. Here, the block synchronization circuit 41 identifies a block having a large amount of components (power) of the autocorrelation coefficient of a specific period in a single frame. The block synchronization circuit 41 determines that the identified block includes the known signal sequence 11. In FIG. 4, among the blocks 50, the known signal sequence 11 is included in the block 50-2 at time t1 in which the component amount of the autocorrelation coefficient of the specific cycle is large in the output of the autocorrelation for each cycle.

Each frame arrives at the block synchronization circuit 41 in the same positional relationship in the time direction so that the block synchronization circuit 41 can average the component amount of the autocorrelation coefficient of the specific period for each block. The block synchronization circuit 41 averages the component amounts of the autocorrelation coefficients of a specific period for each block in the processing (external loop processing) performed on a plurality of frames adjacent in time. That is, the block synchronization circuit 41 averages the component amount of the autocorrelation coefficient of the specific period for each block for a plurality of frames stored in the buffer.

The block synchronization circuit 41 executes signal processing in the block synchronization circuit 41 based on at least one of an even-numbered block in the time direction and an odd-numbered block in the time direction in a single frame. When the block synchronization circuit 41 executes signal processing based on one of an even-numbered block in the time direction and an odd-numbered block in the time direction, the block synchronization circuit 41 sets the evenness and oddness of the block to be signal processed frame by frame. Swap. When the block synchronization circuit 41 performs signal processing based on either the even-numbered block or the odd-numbered block, the circuit scale of the block synchronization circuit 41 is as follows: the even-numbered block and the odd-numbered block. The block synchronization circuit 41 may be smaller than the case where the signal processing is performed based on both of the above.

The block synchronization circuit 41 executes signal processing in the block synchronization circuit 41 based on at least one of the X polarization and the Y polarization of the received signal. The block synchronization circuit 41 may execute signal processing in the block synchronization circuit 41 based on the result of adding the X polarization and the Y polarization of the received signal. As a result, the block synchronization circuit 41 can synchronize the received signal in sample units at the timing of signal processing even when the polarization of the received signal is rotating.

The block synchronization circuit 41 includes a sample addition circuit 410, an autocorrelation circuit 411, a specific period component acquisition circuit 412, a buffer 413, a frame averaging circuit 414, and a maximum position detection circuit 415. Part or all of each functional unit is, for example, a hardware functional unit such as an LSI (Large Scale Integration) or an ASIC (Application Specific Integrated Circuit). Further, a part of each functional unit may be a software functional unit that functions by, for example, a processor such as a CPU (Central Processing Unit) executing a program stored in a memory.

FIG. 5 is a diagram showing an example of sample addition processing. The sample addition circuit 410 (acquisition unit) divides the frame of the received signal into a plurality of blocks. The sample addition circuit 410 applies a process of adding samples (hereinafter, referred to as “sample addition process”) to each frame 10. As a result, the sample addition circuit 410 can reduce the number of samples of the received signal to which the autocorrelation circuit 411 performs autocorrelation processing. The sample addition circuit 410 determines the number of samples to be added according to the number of oversamplings of the transmission signal. In FIG. 5, the number of oversamplings is 2. When the number of oversamplings is 2, the number of samples of frame 10 at the output of the sample addition process is (1/2) the number of samples of frame 10 at the input of the sample addition process.

The autocorrelation circuit 411 detects the periodicity of the known signal sequence 11 in the frame subjected to the sample addition processing based on the autocorrelation. That is, the autocorrelation circuit 411 acquires the periodicity of the known signal sequence 11 in the frame subjected to the sample addition processing as the output of the autocorrelation. The autocorrelation circuit 411 detects the periodicity of the known signal sequence 11 based on the autocorrelation between the known signal sequences 11. The autocorrelation circuit 411 detects the periodicity of the known signal sequence 11 based on the equation (1), which is an autocorrelation function including operations on the time axis. R _ff (t) represents the autocorrelation coefficient (autocorrelation output). f (τ) and f (t−τ) represent received signals.

The autocorrelation circuit 411 is a known signal based on the equation (2) as an autocorrelation function including an operation using an inverse Fast Fourier Transform (IFFT) and an Fast Fourier Transform (FFT). The periodicity of the sequence 11 may be detected. R _ff (t) represents the autocorrelation coefficient (autocorrelation output). ifft represents the inverse fast Fourier transform. fft represents the Fast Fourier Transform. f (t) represents a received signal.

The autocorrelation circuit 411 multiplies the frequency component of the received signal by the complex conjugate (conj) component of the frequency component, as represented by equations (1) and (2). As a result, the autocorrelation circuit 411 can cancel the linear distortion component generated in the optical signal in the transmission line 3. Therefore, the autocorrelation coefficient is not easily affected by the linear distortion component generated in the optical signal in the transmission line 3.

FIG. 6 is a diagram showing an example of autocorrelation output of a known signal sequence having a specific pattern. The horizontal axis represents the index (i) of the sample period. The vertical axis represents the component amount (power of the received signal) of the autocorrelation coefficient of a specific period. If the known signal sequence 11 does not have a specific pattern, the peak value of the component amount of the autocorrelation coefficient of the specific period appears at the position of the index "0th" sample period. As for the known signal sequence 11, since the known signal sequence 11 has a specific pattern, the peak value of the component amount of the autocorrelation coefficient of the specific cycle appears at the position of the sample cycle corresponding to the specific pattern. When the known signal sequence 11 is the specific pattern 111, peak values appear at the position of the 10th sample cycle and the position of the 65th sample cycle as an example.

The appearance of a peak value at the position of the index "0th" sample period means that the specific patterns in a single block match perfectly with respect to autocorrelation. In the known signal sequence 11, since the specific signal sequence is arranged at equal intervals for each of N samples, the period in which the peak value of the component amount of the autocorrelation coefficient of the specific cycle appears by the block synchronization processing is at equal intervals. In FIG. 6, since the known signal sequence 11 is a specific pattern 111 having two types of specific signal sequences, the self-phase relationship of the specific period is such that the position of the 10th sample period and the position of the 65th sample period. The cycles at which the peak values of the number components appear are not evenly spaced.

In the autocorrelation circuit 411, when the known signal sequence 11 has a plurality of types of specific signal sequences, even if the synchronization characteristics using some types of specific signal sequences deteriorate, the synchronization characteristics can be changed by other types of specific signal sequences. It is possible to maintain.

The specific period component acquisition circuit 412 outputs the result of adding the peak value of the component amount of the autocorrelation coefficient of the specific period and the component amount of the autocorrelation coefficient of the power return period of the received signal. For example, the specific period component acquisition circuit 412 sets the autocorrelation coefficients R _{ff to} each other with respect to the peak value of the component amount of the autocorrelation coefficient of the specific period and the component amount of the autocorrelation coefficient of the power return period of the received signal. to add. The specific period component acquisition circuit 412 adds the autocorrelation coefficients R _{ff to} each other in consideration of the complex number of the peak value of the component amount of the specific period and the component amount of the autocorrelation coefficient of the power return period of the received signal. You may. For example, in the specific period component acquisition circuit 412, as represented by the equation (3), the peak value of the component amount of the autocorrelation coefficient of the specific period and the component amount of the autocorrelation coefficient of the power return period of the received signal. And add. The specific period component acquisition circuit 412 records the addition result in the buffer 413 for a plurality of frames.

Here, P _peak represents the component amount (electric power) of the autocorrelation coefficient of a specific period at the position of the sample period indicated by the index (i). R _ff represents the autocorrelation coefficient. i- _peak represents the index of the sample period indicating the peak value of the component amount (electric power) of the autocorrelation coefficient of the specific period. i _flap represents the index of the sample period of the folding period.

The buffer 413 has a volatile storage medium such as a RAM (Random Access Memory) or a register. The buffer 413 may have a storage device having a non-volatile storage medium (non-temporary recording medium) such as a magnetic hard disk device or a semiconductor storage device. The buffer 413 stores the addition result by the specific period component acquisition circuit 412 for a plurality of frames.

The frame averaging circuit 414 (averaging unit) is a component amount (autocorrelation) of the autocorrelation coefficient of a specific period for each block in the processing (external loop processing) performed on a plurality of frames adjacent in time. Output) is averaged. That is, the frame averaging circuit 414 averages the component amount of the autocorrelation coefficient of the specific period for each block for a plurality of frames stored in the buffer. For example, the frame averaging circuit 414 adds the component amounts of the autocorrelation coefficient of the specific period for each block for a plurality of frames and divides the result by the number of frames to divide the autocorrelation coefficient of the specific period for each block. Average the amount of ingredients in. For example, the frame averaging circuit 414 may use the forgetting coefficient to average the component amounts of the autocorrelation coefficient of a specific period for each block.

The maximum position detection circuit 415 (maximum position detection unit) receives the time at which the component amount of the autocorrelation coefficient of the specific cycle indicates the maximum value based on the addition result by the specific cycle component acquisition circuit 412 in the known signal sequence 11. Detect as time t1. That is, the maximum position detection circuit 415 detects the position where the component amount of the averaged autocorrelation coefficient of the specific period is maximum in the frame including the known signal sequence. The maximum position detection circuit 415 synchronizes the received signal with the signal processing of the block synchronization circuit 41 in sample units.

Next, an example of the operation of the optical receiver 4a will be described.
FIG. 7 is a flowchart showing an example of the operation of the optical receiver 4a. The external loop processing from S101 to S108 is a processing for averaging the component amounts of the autocorrelation coefficient of a specific period for a plurality of frames. The internal loop processing from S102 to S106 is a processing for searching the position of the known signal sequence 11 in a single frame.

The block synchronization circuit 41 initializes the variable (JJ) indicating the frame number on which the component amounts of the autocorrelation coefficients of the specific period are averaged to 1 (S101). The block synchronization circuit 41 initializes the variable (ii) indicating the block number in which the component amount of the autocorrelation coefficient of the specific period is detected to 1 (S102). The sample addition circuit 410 executes the sample addition process (S103). The autocorrelation circuit 411 detects the periodicity of the known signal sequence 11 in the frame subjected to the sample addition processing based on the autocorrelation (S104). The specific cycle component acquisition circuit 412 outputs the result of adding the peak value of the component amount of the autocorrelation coefficient of the specific cycle and the component amount of the autocorrelation coefficient of the power return cycle of the received signal (S105). The block synchronization circuit 41 repeats the internal loop processing from S102 to S106 until the condition regarding the variable (ii) is satisfied (S106).

The frame averaging circuit 414 averages the component amount of the autocorrelation coefficient of a specific period for each block for a plurality of frames stored in the buffer (S107). The block synchronization circuit 41 repeats the external loop processing from S101 to S107 until the condition regarding the variable (JJ) is satisfied (S108). The maximum position detection circuit 415 detects the time at which the component amount of the autocorrelation coefficient of the specific cycle shows the maximum value as the reception time t1 of the known signal sequence 11 based on the addition result by the specific cycle component acquisition circuit 412 ( S109).

As described above, the optical receiver 4a of the first embodiment includes a sample addition circuit 410 as an acquisition unit, an autocorrelation circuit 411 as an autocorrelation acquisition unit, and a specific cycle component acquisition circuit as a specific cycle component acquisition unit. It includes a 412 and a maximum position detection circuit 415 as an autocorrelation position detection unit. The sample addition circuit 410 acquires a known signal sequence including a plurality of specific signal sequences arranged at a specific cycle in the time direction. The autocorrelation circuit 411 acquires the component amount of the autocorrelation coefficient between the specific signal sequences for each cycle. The specific cycle component acquisition circuit 412 acquires the component amount of the autocorrelation coefficient of the specific cycle from the component amount of the autocorrelation coefficient for each cycle. The maximum position detection circuit 415 detects the position where the component amount of the autocorrelation coefficient of the specific period is maximum in the frame including the known signal sequence.

As a result, the optical receiver 4a of the first embodiment can reduce the deterioration of the synchronization characteristics of the received signal.

Autocorrelation is resistant to distortion during optical fiber transmission. Since the optical receiver 4a of the first embodiment calculates the autocorrelation between the distorted waveforms, it is possible to reduce the deterioration of the synchronization characteristics of the received signal.

(Second Embodiment)
The second embodiment differs from the first embodiment in that block synchronization and sample synchronization are combined. In the second embodiment, only the differences from the first embodiment will be described.

FIG. 8 is a diagram showing an example of the configuration of the optical communication system 1b. The optical communication system 1b includes an optical transmitter 2, a transmission line 3, and an optical receiver 4b. The optical receiver 4b includes an optical signal processing unit 40, a block synchronization circuit 41, and a sample synchronization circuit 42.

The sample synchronization circuit 42 acquires the block detected by the block synchronization circuit 41 (hereinafter referred to as “detection block”) from the block synchronization circuit 41. The sample synchronization circuit 42 acquires the cross-correlation coefficient (cross-correlation output) between the known signal sequence in the detection block and the signal sequence of the standby signal. The sample synchronization circuit 42 averages the mutual correlation coefficient for each block for a plurality of frames stored in the buffer. The sample synchronization circuit 42 synchronizes the received signal with the signal processing of the sample synchronization circuit 42 in sample units.

The sample synchronization circuit 42 averages the component amounts of the autocorrelation coefficients of a specific period for each block in the processing (external loop processing) performed on a plurality of frames adjacent in time. The sample synchronization circuit 42 may use other types of known signal sequences in addition to the known signal sequence 11 in order to improve the synchronization characteristics. When the frame has at least one of the known signal sequence 11 and the known signal sequence 13 and 14, the sample synchronization circuit 42 occurs in the optical signal even if the synchronization characteristic using some kinds of known signal sequences deteriorates. Linear distortion components can be compensated for using other types of known signal sequences.

FIG. 9 is a diagram showing a first example of a frame configuration. In FIG. 9, frame 10-1 is composed of a known signal sequence 11 and a payload 12-1. Frame 10-2 is composed of the known signal sequence 13 and the payload 12-2. Frame 10-3 is composed of the known signal sequence 11 and the payload 12-3. The optical transmitter 2 adds a known signal sequence 11 or 13 at an arbitrary position in the frame 10. The sample synchronization circuit 42 synchronizes the received signal with the timing of the signal processing in the sample synchronization circuit 42 based on the result of differential processing or the like being applied to the known signal sequences 11 and 13. The known signal sequence 11 may be used for both block synchronization and sample synchronization.

FIG. 10 is a diagram showing a second example of the frame configuration. In FIG. 10, frame 10-1 is composed of a known signal sequence 11 and a payload 12-1. Frame 10-2 is composed of a known signal sequence 14 and a payload 12-2. Frame 10-3 is composed of the known signal sequence 11 and the payload 12-3. The optical transmitter 2 adds a known signal sequence 11 or 14 at an arbitrary position in the frame 10. The sample synchronization circuit 42 synchronizes the received signal with the timing of the signal processing in the sample synchronization circuit 42 based on the result of performing differential processing or the like on the known signal sequences 11 and 14.

The optical transmitter 2 adds a known signal sequence 11, 13 or 14 at an arbitrary position in the frame 10. The known signal sequences 13 and 14 may or may not have a specific pattern as in the known signal sequence 11. For example, the known signal sequences 13 and 14 may have a PRBS (Pseudo Random Bit Sequence). The known signal sequences 13 and 14 may have any pattern. For example, the known signal sequences 13 and 14 may have a random pattern. The average power of the known signal sequences 11, 13 and 14 is equivalent to the power of the payload 12.

The sample synchronization circuit 42 includes a sample addition circuit 420, a differential processing circuit 421, a differential component addition circuit 422, an interpolar component addition circuit 423, a standby signal unit 424, a cross-correlation acquisition circuit 425, and a buffer. It includes a 426, a frame averaging circuit 427, an adjacent sample addition circuit 428, and a maximum position detection circuit 429. The sample synchronization circuit 42 does not have to include the adjacent sample addition circuit 428.

The sample adder circuit 420 acquires the detection block from the block synchronization circuit 41. The sample addition circuit 420 performs sample addition processing on the detection block. The sample addition circuit 420 determines the number of samples to be added regardless of the number of oversamplings of the transmission signal. According to the determined number of samples, the sample addition circuit 420 holds the standby signal unit 424 so that the known signal sequence subjected to the sample addition process and the standby signal become signals of the same sequence. Sample addition processing is also applied to the series of received issues.

The differential processing circuit 421 acquires the block subjected to the sample addition processing from the sample addition circuit 420. The differential processing circuit 421 multiplies the symbol 0 or more ahead of the selected symbol (own symbol) with the selected symbol.

FIG. 11 is a diagram showing an example of differential processing between the symbol 100 0 points ahead of the selected symbol 100 in the known signal sequence and the selected symbol 100. The differential processing circuit 421 multiplies each sample of the received signal by the complex conjugate of the sample 0 ahead of the selected sample and the selected sample.

FIG. 12 is a diagram showing an example of differential processing between the symbol 101 one step ahead of the selected symbol 100 in the known signal sequence and the selected symbol 100. Since one symbol represents one sample when the number of oversamples is 1, the differential processing circuit 421 has, for each sample of the received signal, the complex conjugate of the sample one sample ahead of the selected sample. Multiply the conj) by the selected sample.

FIG. 13 is a diagram showing an example of differential processing between the symbol 102, which is two symbols ahead of the selected symbol 100 in the known signal sequence, and the selected symbol 100. Since one symbol represents two samples when the number of oversamples is 2, the differential processing circuit 421 has, for each sample of the received signal, the complex conjugate of the sample two samples ahead of the selected sample. Multiply the conj) by the selected sample.

FIG. 14 is a diagram showing an example of the result of the differential component addition circuit 422 generating the differential components of a plurality of symbols at once. The differential processing circuit 421 may multiply each sample of the received signal by the complex conjugate (conj) of the sample 0 or more ahead of the selected sample and the selected sample.

The differential component addition circuit 422 shown in FIG. 1 adds the differential components generated for a plurality of symbols by the differential component addition circuit 422. The differential component addition circuit 422 may add the differential components generated at once for a plurality of symbols by the differential component addition circuit 422.

The interpolarization component addition circuit 423 adds the X polarization and the Y polarization of the signal. As a result, the sample synchronization circuit 42 can synchronize the received signal in sample units at the timing of signal processing even when the polarization of the received signal is rotating.
The standby signal unit 424 outputs the standby signal to the cross-correlation acquisition circuit 425. The standby signal (standby pattern) is a sequence of signals obtained by applying sample addition to interpolar component addition to a known signal sequence.

The autocorrelation circuit 411 detects the periodicity of the known signal sequence 11 based on the autocorrelation between the known signal sequences 11, and blocks-synchronizes the received signal based on the detected periodicity. On the other hand, the cross-correlation acquisition circuit 425 detects the match between the known signal sequence 11 and the received signal based on the cross-correlation between the known signal sequence such as the known signal sequences 11, 13 and 14 and the standby signal. Sample sync the received signal based on the detected match. When the cross-correlation acquisition circuit 425 acquires synchronization based on the equation (2), one of the signal sequences of (fft) in the equation (2) is used as the received signal. When the cross-correlation acquisition circuit 425 acquires synchronization based on the equation (2), the other of the signal sequences of (fft) in the equation (2) is used as the standby signal.

The cross-correlation acquisition circuit 425 records the output of the cross-correlation between the known signal sequence and the standby signal in the buffer 426. The cross-correlation acquisition circuit 425 acquires the cross-correlation coefficient for each sample as the output of the cross-correlation based on the equation (2) as a cross-correlation function including the operation using the inverse fast Fourier transform and the fast Fourier transform.

The buffer 426 has a volatile storage medium such as a RAM or a register. The buffer 426 may have a storage device having a non-volatile storage medium (non-temporary recording medium) such as a magnetic hard disk device or a semiconductor storage device. The buffer 426 stores the cross-correlation coefficient as the output of the cross-correlation for each sample.
The frame averaging circuit 427 averages the output of the cross-correlation for each sample in the process (external loop process) applied to a plurality of frames adjacent in time.

FIG. 15 is a diagram showing an example of the addition result by the adjacent sample addition circuit 428. The adjacent sample addition circuit 428 adds the output of the averaged cross-correlation for each sample between arbitrary adjacent samples. As a result, the adjacent sample addition circuit 428 can increase the maximum value of the cross-correlation output.

The maximum position detection circuit 429 sets the time at which the output of the cross-correlation for each sample shows the maximum value based on the output of the cross-correlation for each sample averaged by the frame averaging circuit 427, and the reception time of the known signal sequence 11. Detected as t1. That is, the maximum position detection circuit 429 synchronizes the received signal in sample units with the signal processing of the sample synchronization circuit 42.

In the acquisition of the cross-correlation using the inverse fast Fourier transform and the fast Fourier transform as in Eq. (2), the first candidate and the first synchronous position are based on the position of the sample period in which the peak value of the output of the cross-correlation appears. Two candidates may be obtained.

FIG. 16 is a diagram showing a first example of the positional relationship between the detection block 51 and the known signal sequence. In FIG. 16, as an example, the head position of a known signal sequence composed of 300 samples is located later in time than the head position of the block. When the index of the true synchronization position in the block detected by the block synchronization circuit 41 is "+64th", the peak value of the cross-correlation output appears at the position of the sample period of the index "+64th", so that the index of the synchronization position Is determined as "+64th".

FIG. 17 is a diagram showing a first example of the positional relationship between the detection block 51 and the known signal sequence. The sample synchronization circuit 42 expresses an index indicating the synchronization position as a positive value. If the index of the true synchronization position in the block detected by the block synchronization circuit 41 is a negative value such as "-64th", the peak value of the cross-correlation output is the index "+236 (= 300-64)". Since it appears at the position of the sample period of, it is uncertain whether the index of the true synchronization position is "-64th" or "+236th".

In order to eliminate this uncertainty, the sample synchronization circuit 42 changes the detection position and executes the cross-correlation process (sample synchronization) twice more. That is, the sample synchronization circuit 42 executes cross-correlation processing (sample synchronization) on the sample of the block that is temporally adjacent to the detection block and the sample of the block that is temporally adjacent to the detection block.

FIG. 18 is a diagram showing an example of the first addition of sample synchronization. In FIG. 18, one block length is equal to the length of the known signal sequence. If the peak value appears at the position of the index "0th" sample period when the detection block 51 is shifted by 64 samples later in time, the sample synchronization circuit 42 performs only 64 samples after the detection block 51 in time. The output of the cross-correlation is acquired for the block 52, which is a sample group having a length of one block adjacent to each other in time after the shifted position. The sample synchronization circuit 42 acquires the output of the cross-correlation for the block 53, which is a sample group having a length of one block adjacent to the block 52 detected in the first addition of the sample synchronization in time. As a result of the output of the cross-correlation of the first addition and the second addition, the sample synchronization circuit 42 can synchronize based on the block 52 detected in the first addition of the sample synchronization.

FIG. 19 is a diagram showing an example of the second addition of sample synchronization. In FIG. 19, one block length is equal to the length of the known signal sequence. If a peak value appears at the position of the index "0th" sample period when the detection block 51 is shifted forward by 64 samples in time, the sample synchronization circuit 42 moves the detection block 51 after 236 in time ( = 300-64) The output of the cross-correlation is acquired for the block 52, which is a sample group having a length of one block, from the position shifted by the sample. The sample synchronization circuit 42 acquires the output of the cross-correlation for the block 53, which is a sample group having a length of one block adjacent to the block 52 detected in the first addition of the sample synchronization in time. As a result of the output of the cross-correlation of the first addition and the second addition, the sample synchronization circuit 42 can synchronize based on the block 52 detected in the second addition of the sample synchronization.

Next, an example of the operation of the optical receiver 4b will be described.
FIG. 20 is a flowchart showing an example of the operation of the optical receiver 4b. The external loop processing from S201 to S208 is a processing for averaging the cross-correlation outputs for a plurality of frames.

The sample synchronization circuit 42 initializes the variable (JJ) indicating the frame number on which the cross-correlation output is averaged to 1 (S201). The sample addition circuit 420 executes the sample addition process (S202). The differential processing circuit 421 multiplies the symbol 0 or more ahead of the selected symbol (own symbol) with the selected symbol. The differential component addition circuit 422 adds the differential components generated for a plurality of symbols by the differential component addition circuit 422 (S203). The interpolarization component addition circuit 423 adds the X polarization and the Y polarization of the signal (S204). The standby signal unit 424 outputs the standby signal to the cross-correlation acquisition circuit 425 (S205).

The cross-correlation acquisition circuit 425 detects the periodicity of the known signal sequence 11 based on the cross-correlation between the known signal sequence such as the known signal sequences 11, 13 and 14 and the standby signal (S206). The frame averaging circuit 427 averages the output of the cross-correlation for each sample in the process (external loop process) applied to a plurality of frames adjacent in time (S207). The sample synchronization circuit 42 repeats the external loop processing from S202 to S207 until the condition regarding the variable (JJ) is satisfied (S208).

The adjacent sample addition circuit 428 adds the output of the averaged cross-correlation for each sample between arbitrary adjacent samples (S209). The maximum position detection circuit 429 detects the time when the cross-correlation output shows the maximum value as the reception time t1 of the known signal sequence 11 based on the addition result by the adjacent sample addition circuit 428 (S109).

As described above, the optical receiver 4b of the second embodiment further includes the sample synchronization circuit 42 as compared with the optical receiver 4a of the first embodiment. The sample synchronization circuit 42 includes a cross-correlation acquisition circuit 425 as a cross-correlation acquisition unit and a maximum position detection circuit 429 as a cross-correlation position detection unit. The cross-correlation acquisition circuit 425 acquires the component amount of the cross-correlation coefficient between the standby signal and the known signal sequence for each cycle for adjacent blocks in the frame. The maximum position detection circuit 429 detects the position where the component amount of the mutual correlation coefficient of the specific period is maximum in the frame including the known signal sequence.

As a result, the optical receiver 4b of the second embodiment can improve the accuracy of the synchronization characteristics as compared with the first embodiment and reduce the deterioration of the synchronization characteristics of the received signal.

At least a part of the optical receiver and the optical communication system in the above-described embodiment may be realized by a computer. In that case, a program for realizing this function may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read by a computer system and executed. The term "computer system" as used herein includes hardware such as an OS and peripheral devices. Further, the "computer-readable recording medium" refers to a portable medium such as a flexible disk, a magneto-optical disk, a ROM, or a CD-ROM, or a storage device such as a hard disk built in a computer system. Further, a "computer-readable recording medium" is a communication line for transmitting a program via a network such as the Internet or a communication line such as a telephone line, and dynamically holds the program for a short period of time. It may also include a program that holds a program for a certain period of time, such as a volatile memory inside a computer system that serves as a server or a client in that case. Further, the above program may be for realizing a part of the above-mentioned functions, and may be further realized for realizing the above-mentioned functions in combination with a program already recorded in the computer system. It may be realized by using a programmable logic device such as FPGA (Field Programmable Gate Array).

Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and the design and the like within a range not deviating from the gist of the present invention are also included.

The present invention is applicable to optical receivers and optical communication systems.

1a, 1b ... optical communication system, 2 ... optical transmitter, 3 ... transmission path, 4a, 4b ... optical receiver, 10 ... frame, 11 ... known signal sequence, 12 ... payload, 13 ... known signal sequence, 14 ... known Signal sequence, 40 ... Optical signal processing unit, 41 ... Block synchronization circuit, 50 ... Block, 51 ... Detection block, 52 ... Block, 53 ... Block, 100 ... Symbol, 101 ... Symbol, 102 ... Symbol, 110 ... Specific pattern, 111 ... specific pattern, 410 ... sample addition circuit, 411 ... autocorrelation circuit, 412 ... specific period component acquisition circuit, 413 ... buffer, 414 ... frame averaging circuit, 415 ... maximum position detection circuit, 420 ... sample addition circuit, 421. ... differential processing circuit, 422 ... differential component addition circuit, 423 ... interpolar component addition circuit, 424 ... standby signal unit, 425 ... mutual correlation acquisition circuit, 426 ... buffer, 427 ... frame averaging circuit, 428 ... adjacent Sample addition circuit, 429 ... Maximum position detection circuit

Claims (5)

An acquisition unit that acquires a known signal sequence including a plurality of specific signal sequences arranged at a specific cycle in the time direction in the cycle of the known signal sequence, and an acquisition unit.
An autocorrelation calculation unit that calculates the component amount of the autocorrelation coefficient between the specific signal series for each period of the known signal series, and
A specific period component acquisition unit that acquires the component amount of the autocorrelation coefficient of the specific period from the component amounts of the autocorrelation coefficient for each period of the known signal series .
It is provided with an autocorrelation position detection unit that detects a position where the component amount of the autocorrelation coefficient of the specific period is maximized in the frame including the known signal sequence .
The acquisition unit performs a process of adding samples included in the known signal sequence to the frame.
Optical receiver. The optical receiver according to claim 1, wherein the known signal sequence includes the specific signal sequence having a different pattern. Further provided with an averaging unit for averaging the component amounts of the autocorrelation coefficient of the specific period for the plurality of frames
The autocorrelation position detection unit detects the position where the component amount of the autocorrelation coefficient of the specific period averaged is maximized in the frame including the known signal sequence, according to claim 1 or 2. The optical receiver described. For adjacent blocks in the frame, a component amount of a cross-correlation coefficient between a standby signal predetermined to be a signal of the same sequence as the known signal sequence including the plurality of specific signal sequences and the known signal sequence. With a cross-correlation acquisition unit that acquires the above for each period of the sample unit ,
Claims 1 to 3 further include a cross-correlation position detection unit that detects a position where the component amount of the cross-correlation coefficient of the specific period is maximum in the frame including the known signal sequence in the sample unit. The optical receiver according to any one of the above. A known signal detection method performed by an optical receiver
A step of acquiring a known signal sequence including a plurality of specific signal sequences arranged at a specific cycle in the time direction in the cycle of the known signal sequence, and
A step of calculating the component amount of the autocorrelation coefficient between the specific signal series for each period of the known signal series, and
A step of acquiring the component amount of the autocorrelation coefficient of the specific period from the component amounts of the autocorrelation coefficient for each period of the known signal series, and
It has a step of detecting a position where the component amount of the autocorrelation coefficient of the specific period is maximized in the frame including the known signal sequence.
In the acquisition step, the frame is subjected to a process of adding the samples included in the known signal sequence.
Known signal detection method.

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