JP3773504B2 - Optical code division multiplexing communication system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical code division multiplexing communication system and can be applied to, for example, an optical subscriber transmission system.
[0002]
[Prior art]
[0003]
[Non-Patent Document 1]
P. C. Tea et al., “A 4-channel WDA / OCDMA system incorporating 255-chip, 320 Gchip / s quaternary phase coding and decoding gratings”, OFC2001, PD37 (2001)
Conventionally, as an optical code division multiplexing / demultiplexing system in the optical code division multiplexing (OCDM) system, a phase encoding system as described in Non-Patent Document 1 has been proposed.
[0004]
The phase encoding method is a matched filtering method in which a high correlation peak appears in the received signal only when the transmission and reception codes match. Ideally, a desired received signal and an undesired received signal are selected by threshold determination. It is said that signals on the same wavelength can be multiplexed by codes.
[0005]
FIG. 2 shows a multiplex conceptual diagram based on the conventional OCDM. Transmission signals (electrical signals) of the respective channels having the same period Tdata are optical signals of the same wavelength (FIG. 3A) by the electric / optical converters (O / E) 1-1 to 1-N for each channel. ) Is encoded (time-spread) by an encoding pattern unique to the channel by the encoders 2-1 to 2-N for each channel (FIG. 3B), and then by the coupler 3 Are multiplexed and sent to the transmission line 4 to reach the decoder 5 (5-1) for each channel. FIG. 2 shows only the reception configuration for channel CH1. The decoder 5-1 for channel CH1 performs temporal despreading according to the decoding pattern according to the coding pattern for channel CH1 so that the transmission signal to itself emerges, and threshold decision circuit 6 -1 selects a desired received signal and an undesired received signal, converts the signal into an electrical signal by an optical / electrical converter (O / E) 7-1, and sends it to a data processing circuit (not shown) side. give. 3C1 shows a signal after decoding processing in the case where only the encoded optical signal for channel CH1 is given instead of the multiplexed optical signal, and FIG. 3C2 and FIG. CN) respectively indicate signals after decoding processing when it is assumed that only encoded optical signals for channel CH2 and channel CHN are given, not multiplexed optical signals.
[0006]
[Problems to be solved by the invention]
As described above, in the OCDM system, it is ideally possible to multiplex signals of the same wavelength, and by applying OCDM on one wavelength, the number of channels can be expanded.
[0007]
However, since all the channels are multiplexed within the same time slot (period Tdata), the undesired signal level in the optical signal after decoding increases as the number of simultaneously connected channels increases. Further, the undesired signal is mixed at the same timing as the desired signal peak (main peak). Here, ideally, the undesired signal level is simply an addition of light intensity, but in an actual multiplexing system, a coherent light source such as a DFB laser is used as an optical signal source (E / O). Therefore, if signals having the same wavelength component exist within the same timing, optical interference noise caused by the phase noise of the laser occurs and channel identification becomes impossible.
[0008]
Therefore, an optical code division multiplexing communication system that can correctly perform channel identification even when the number of channels is large is desired.
[0009]
[Means for Solving the Problems]
In order to solve such a problem, the optical code division multiplexing communication system of the present invention is (1) a code pattern in which an optical transmission signal in which a chip period in which a signal pulse is appropriately inserted appears for each data period is assigned to itself. N-channel encoding means for time-spreading and outputting an encoded optical signal in accordance with (2) optical signal multiplexing means for multiplexing N-channel encoded optical signals, and (3) multiplexed encoding Optical signal demultiplexing means for demultiplexing the optical signal into N channels, and (4) decoding having an autocorrelation peak by time despreading the demultiplexed encoded optical signal according to a decoding pattern assigned to itself. N channel decoding means for outputting an optical signal, and (5) adding a phase difference to the signal of each channel at the optical signal stage or electrical signal stage of each channel before reaching the optical signal multiplexing means. Yes and the phase difference providing means that (6) The phase difference providing means is a phase difference between the two channels with the smallest phase difference, and the other channel at the timing of the autocorrelation peak in the decoded optical signal from the decoding means related to one channel. Signal components are not generated, and a phase difference in which the side ropes of the decoded optical signals of these two channels overlap is given. It is characterized by that.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
(A) First embodiment
Hereinafter, a first embodiment of an optical code division multiplexing communication system according to the present invention will be described in detail with reference to the drawings.
[0011]
(A-1) Configuration of the first embodiment
FIG. 1 is a block diagram illustrating a basic configuration example of an optical code division multiplexing communication system according to the first embodiment. In FIG. 1, only one channel (for channel CH1) is shown for the reception configuration. In FIG. 1, the same and corresponding parts as those in FIG. 2 described above are denoted by the same reference numerals.
[0012]
In FIG. 1, also in the optical code division multiplexing communication system of the first embodiment, the reception configuration is the same as in the prior art, with the decoder 5 (5-1) and the threshold determination circuit 6 (6-1) for each channel. ) And an optical / electrical converter 7 (7-1).
[0013]
On the other hand, the transmission configuration in the optical code division multiplex communication system of the first embodiment includes electrical / optical converters 1-1 to 1-N and encoders 2-1 to 2-N for each channel, and multiplexing In addition to the coupler 3, each channel includes optical delay devices 8-1 to 8-N.
[0014]
In the case of the first embodiment, the optical delay units 8-1 to 8-N are interposed between the corresponding encoders 2-1 to 2-N and the multiplexing coupler 3. The delay time by each of the optical delay devices 8-1 to 8-N will be clarified in the description of the operation.
[0015]
(A-2) Operation of the first embodiment
Next, the operation of the optical code division multiplexing communication system of the first embodiment will be described in detail with reference to the timing charts of the respective parts in FIG.
[0016]
The transmission signal formation output unit (not shown) of each channel incorporates a clock synchronized with the clock of the entire system, for example, so that the transmission signal of each channel is transmitted to the electrical / optical converters 1-1 to 1-1. -N is input synchronously, Respectively It is converted into an optical signal having the same wavelength. As the electrical / optical converters 1-1 to 1-N, a coherent light source such as a DFB laser can be applied.
[0017]
FIG. 4A shows a transmission signal converted into an optical signal (the same applies to an electrical signal). As the transmission signal, an effective signal (signal pulse) appears in one chip period Tchip for each data cycle Tdata. Is. FIG. 4A shows the case where data “1” is continuous, but if the data is “0”, no signal pulse is generated in the chip period Tchip.
[0018]
The encoders 2-1 to 2-N are, for example, phase modulation type fiber Bragg grating encoders or tap delay type encoders, and the encoders 2-1 to 2-N of each channel are configured to input optical signals. Then, temporal spreading processing is performed according to the coding pattern (for example, M sequence) assigned to itself.
[0019]
FIG. 4B shows an optical signal after encoding processing (temporal spreading processing) of a certain channel. Data (FIG. 4A) that appeared in one chip period Tchip for each data cycle Tdata is converted into an optical signal over the code period Tcode by the encoding process. Naturally, the code period Tcode is shorter than the data period Tdata.
[0020]
The optical delay units 8-1 to 8 -N of each channel add a delay to the encoded optical signal by the delay time assigned to it, and supply the delayed signal to the multiplexing coupler 3.
[0021]
The encoded optical signals of the respective channels given to the coupler 3 have different phases depending on the functions of the optical delay groups 8-1 to 8-N. In the following description, it is assumed that the delay time of the optical delay device 8-1 for the channel CH1 is the shortest (may be 0), and that the delay time increases as the channel number increases.
[0022]
The encoded optical signals of the respective channels input to the coupler 3 are multiplexed and sent to the transmission line 4.
[0023]
The multiplexed encoded optical signal transmitted through the transmission path 4 is branched into N channels by an optical branching device (not shown) and then input to the decoder 5 (5-1) of each channel. As the decoder 5, for example, a phase modulation type fiber Bragg grating encoder (decoder) or a tap delay type encoder (decoder) can be applied in the same manner as the encoder.
[0024]
Decoder 5-1 for channel CH1 performs temporal despreading (decoding) in accordance with a decoding pattern according to the coding pattern for channel CH1, and causes a transmission signal to self to emerge, thereby determining a threshold value. A desired reception signal and an undesired reception signal are selected by threshold determination by the circuit 6-1, converted into an electric signal by an optical / electrical converter (O / E) 7-1, and a data processing circuit (not shown). Give to the side.
[0025]
Note that the despreading process performed by the decoder 5 focuses on a certain chip period, and in the same way as the spreading process performed by the encoders 2-1 to 2-N, spreads the signal pulses of that chip period into the code period Tcode. As a result, the decoded optical signal has a time spread of 2 × Tcode-Tchip per bit of the signal.
[0026]
The reception configurations of the other channels CH2 to CHN perform the same operation as the reception configuration of the channel CH1.
[0027]
4 (C1) to 4 (CN) are output from the optical delay units 8-1,..., 8-N to the decoder 5-1 for the channel CH1, instead of the multiplexed encoded optical signal. The optical signal after decoding when it is assumed that the encoded optical signal of each channel is input alone and the decoder 5-1 decodes it.
[0028]
It should be noted that the N-decoded optical signal shown in FIGS. 4C1 to 4CN is superimposed on the decoded optical signal when the multiplexed encoded optical signal is input to the channel CH1 decoder 5-1. It is a signal.
[0029]
From the start time t0 of the reception period of the signal including the side rope of the decoded optical signal (FIG. 4 (C1)) obtained by inputting the encoded optical signal for channel CH1 to the decoder 5-1 for channel CH1. As seen, the start time of the decoded optical signal (FIG. 4 (C2)) obtained by inputting the encoded optical signal for channel CH2 to the decoder 5-1 for channel CH1 is the optical delay unit 8 for both channels. -1 and 8-2 delay time difference Tdelay (1-2), the decoded optical signal obtained by inputting the channel CH3 encoded optical signal to the channel CH1 decoder 5-1 (FIG. 4 ( The start time of C3)) is delayed by the delay time difference Tdelay (1-3) between the optical delayers 8-1 and 8-3 of both channels, and similarly, the channel CHn (n) is connected to the decoder 5-1 for the channel CH1. 2 to N) are input as encoded optical signals. Beginning of the resulting decoded optical signal Te is delayed by the delay time difference Tdelay of optical delay 8-1 and 8-n of both channels (1-n).
[0030]
Here, by selecting a delay time difference between two adjacent channel numbers (for example, delay time difference Tdelay (1-2)), as shown in FIGS. During the main peak period, no decoded optical signals of other channels are generated at all, and during the side rope period, only the decoded optical signals of other one channel are generated.
[0031]
In the following, conditions for the delay time for forming such a decoded optical signal for each channel will be described in detail.
[0032]
Even in the multiplexing by the multiplexing coupler 3, Tcode ≦ Tdata / N is set so that the timings of the encoded optical signals of the respective channels do not overlap.
[0033]
Further, as described above, the decoded optical signal has a spread of 2 × Tcode-Tchip per bit of the signal, and the decoded optical signal based on the normal decoding pattern has a center chip period as a main peak period. Become. Therefore, if the delay time difference ΔT between adjacent channels is set to be longer than the code period Tcode, the decoded optical signals of other channels are not generated in the main peak chip period.
[0034]
For example, when the delay time Tdelay1 of the channel CH1 is 0, if the delay time Tdelay2 of the channel CH2 is Tdelay2 ≧ Tcode (in other words, if Tdelay2-Tdelay1 = ΔT ≧ Tcode), the main peak of the channel CH1 In this chip period, the decoded optical signal of channel CH2 is not generated. That is, the delay time Tdelay2 of the channel CH2 may be set to = ΔT + Tdelay1 (where ΔT ≧ Tcode).
[0035]
If the difference between the delay times Tdelay2 and Tdelay3 between the channels CH2 and CH3 satisfies the condition Tdelay3-Tdelay2 = ΔT ≧ Tcode, a decoded optical signal of the channel CH3 is generated in the chip period of the main peak of the channel CH2. In addition, as is clear from the above-described relationship, the decoded optical signal of channel CH1 does not occur. Such a delay time Tdelay3 of the channel CH3 is equal to the delay time Tdelay of the channel CH1. 1 and In this relationship, Tdelay3 = Tdelay1 + 2 · ΔT may be selected.
[0036]
Similarly, if the delay time Tdelay of the channel CHn (n is 2 to N) is selected as Tdelay = Tdelay1 + (n−1) · ΔT, the channel CH (n−1) in the chip period of the main peak of the channel CHn. Neither the decoded optical signal nor the decoded optical signal of channel CH (n + 1) is generated.
[0037]
Note that the delay time TdelayN of the channel CHN having the maximum delay time is set to be within Tdata-Tcode, so that the decoded optical signal of the channel CHN can be prevented from being generated during the main peak chip period of the channel CH1.
[0038]
By selecting the delay times Tdelay1 to TdelayN as described above, as shown in FIGS. 4C1 to 4CN related to the channel CH1, in the main peak period of the decoded optical signal of each channel, the decoded light of other channels No signal is generated, and only the decoded optical signal of the other one channel is generated even in the side rope period.
[0039]
According to the first embodiment, each channel can be distinguished by encoding, but the encoded optical signals of each channel are multiplexed with different phases (in other words, the data period ( Since time division multiplexing is performed during the time slot period), the overlap of the desired signal and the undesired signal in the decoded optical signal can be suppressed as much as possible, and the desired signal (signal of the corresponding channel) can be more accurately discriminated. .
[0040]
As a result, even if the number of channels N increases, the desired signal of each channel can be accurately extracted with the receiving configuration.
[0041]
Even when a large number of channels are connected simultaneously, the interference component is for one channel in the vicinity of the main peak, so that the requirement for setting accuracy of the determination threshold level does not become severe. Further, it is not necessary to change the determination threshold level according to the change in the number of connections.
[0042]
FIG. 5 is an explanatory diagram showing the waveform (simulation result) of the decoded optical signal in the first embodiment (FIG. 5B) and the conventional technique (FIG. 5A), and the time axis of the signal pulse portion is shown. It is an eye-pattern-like drawing that is displayed together. Note that the multiplexing number is 2 channels, and is an output waveform of the decoder 5-1 of the channel CH1.
[0043]
Conventionally, as shown in FIG. 5A, the period of channel CH1 and the period of channel CH2 completely overlap. In other words, there is a possibility that the reception eye is not open and the signal cannot be identified. On the other hand, in the first embodiment, as shown in FIG. 5B, the period of the channel CH2 starts immediately after the main peak of the channel CH1, and the time difference (phase difference) is The delay time difference ΔT between the optical delay devices 8-1 and 8-2 of CH1 and channel CH2. In other words, the on / off level of the main peak of the desired signal is constant, and no signal quality degradation due to channel multiplexing is observed.
[0044]
That is, even in the simulation result, the decoded optical signal of the other channel is not generated at all in the main peak period of the decoded optical signal of each channel, and the decoded light of the other one channel is also generated in the side rope period. It can be seen that only the signal is generated.
[0045]
(B) Second embodiment
Next, a second embodiment of the optical code division multiplexing communication system according to the present invention will be described with reference to the drawings.
[0046]
The optical code division multiplexing communication system of the second embodiment is characterized by the reception configuration side, and the transmission configuration is the same as that of the first embodiment. FIG. 6 is a block diagram showing a reception configuration of a certain channel (here, channel CH1). The same reference numerals are given to the same and corresponding parts as in FIG.
[0047]
In FIG. 6, in the case of the second embodiment, a gate circuit 9-1 is interposed between the decoder 5-1 and the threshold determination circuit 6-1, and the gate circuit 9-1 is transmitted and blocked. For this purpose, a time gate signal forming circuit 10-1 for forming a time gate signal is provided.
[0048]
The time gate signal forming circuit 10-1 receives the decoded optical signal and forms a time gate signal indicating a short period centered on the main peak. The gate circuit 9-1 The decoded optical signal output from the decoder 5-1 is transmitted and given to the threshold determination circuit 6-1 only for a short period of time.
[0049]
The specific configurations of the gate circuit 9-1 and the time gate signal forming circuit 10-1 are arbitrary, but for example, those described in the following references can be applied.
[0050]
Reference: K.K. Kitayama et. al. , “Optical Code Division Multiplexing (OCDM) and Its Applications to Photonic Networks,” IEICE Trans. Fundamentals, vol. E82-A, no. 12, pp. 2616-2625, Dec. 1999
In the case of the second embodiment, the influence of interference components (undesired signals) can be eliminated by the time gate. Here, if the decoded optical signal itself from the decoder 5-1 has the same components of all channels as in the conventional case, the time gate signal may not be properly formed. In the case of the mode, the decoded optical signal of the other channel is not generated at all during the main peak period of the decoded optical signal, and only the decoded optical signal of the other channel is generated even during the side rope period. In other periods, the other two channels of decoded optical signals are superimposed, so that the time gate signal can be appropriately formed and the time gate can function effectively.
[0051]
(C) Third embodiment
Next, a third embodiment in which the optical code division multiplexing communication system according to the present invention is applied to an optical subscriber transmission system will be described with reference to the drawings. The optical subscriber transmission system of the third embodiment is a combination of a wavelength division multiplexing communication system (CWDM) and an optical code division multiplexing communication system (OCDM).
[0052]
FIG. 7 is a block diagram showing the configuration of the optical subscriber transmission system according to the third embodiment. Corresponding parts to those in FIG. In FIG. 7, the threshold determination circuit is provided as a processing circuit for the electrical signal stage, and is therefore omitted in FIG. 7, which describes the optical signal stage.
[0053]
The optical subscriber transmission system according to the third embodiment includes an optical line terminal (OLT) 100 and a number of optical node units (ONUs) 200. In the following description, the transmission direction from the optical node device 200 to the optical line terminal 100 is referred to as an uplink direction, and the transmission direction from the optical line terminal 100 to the optical node device is referred to as a downlink direction.
[0054]
The wavelength channels used in the entire system are X channels (λ1 to λX), and the code channels used in the entire system are N channels (C1 to CN). In the third embodiment, all N channels of code channels are used for a certain wavelength channel.
[0055]
In FIG. 7, in the reference sign “ABC” that defines the component, “A” represents the type of the component, and “B” represents the transmission wavelength channel λB in the case of a transmission system element and the reception system. If it is an element, it represents the reception wavelength channel λB, and “C” represents the code channel CC. “B” and “C” of 0 indicate that they are common elements regardless of wavelength channels or code channels. In addition, “B” in which “B1 · B2” represents a transmission / reception common element in which the upstream wavelength channel is the λB1 channel and the downstream wavelength channel is the λB2 channel.
[0056]
In the following, as shown in FIG. 8A, in the X channel of the wavelength channel, the half wavelength channel on the short wavelength side is used for uplink transmission, and the half wavelength channel on the long wavelength side is in the uplink direction. Suppose that it is used for transmission. In addition, as shown in FIG. 8B, the wavelength channel can be assigned by alternately assigning an upstream wavelength channel and a downstream wavelength channel.
[0057]
In the optical line terminal (OLT) 100, transmission / reception configurations 201-1 to 201- (M-1) are divided for each group of optical node devices 200 having the same upstream and downstream wavelength channels. The configurations 201-1 to 201- (M-1) are connected to the transmission line 4 via a wavelength multiplexing / demultiplexing coupler (WDM coupler) 202.
[0058]
The transmission / reception configurations 201-1 to 201- (M-1) of each group are the same as those in the first embodiment. Although omitted in FIG. 1 described above, a coupler 12-1-0 for N-branching the received optical signal is also provided on the reception configuration side.
[0059]
Each optical node device 200 is provided with a transmission / reception configuration for each one of the code channels, and the transmission / reception configuration is the same as that of the first embodiment. In addition, wavelength multiplexing / demultiplexing couplers 13-1 and M-1 for separating the transmission and reception directions are provided.
[0060]
The wavelength multiplexing / demultiplexing couplers 13-1, M-1 to 13-1, MN of each optical node device 200 are connected to the transmission line 4 via the couplers 14-1, M-0.
[0061]
Needless to say, the arrangement positions of couplers for multiplexing and demultiplexing and wavelength multiplexing / demultiplexing couplers are not limited to those shown in FIG.
[0062]
Further, wavelength allocation other than the wavelength allocation shown in FIG. 8 may be applied. For example, a configuration in which signals in the vertical direction in the optical node device 200 are assigned to the same wavelength is possible. In this case, a configuration in which a branch coupler is used instead of the WDM coupler in the optical node device 200 is also possible. Similarly, when an encoder having a wavelength filter function such as a fiber Bragg grating is used, a configuration using a branch coupler instead of a WDM coupler is possible.
[0063]
In the case of the third embodiment, the N optical node devices 200 that transmit the encoded optical signal to the optical line terminal 100 using the same wavelength are distributedly arranged. 8 is selected so that the delay time satisfies the relationship described in the first embodiment.
[0064]
In the following, a communication operation between the optical line terminal 100 and the optical node devices 200-1, M-1 to 200-1, MN having the upstream wavelength channel of λ1 and the downstream wavelength channel of λM will be described. .
[0065]
In each of the optical node devices 200-1, M-1 to 200-1, MN, a transmission signal (electrical signal) is transmitted through the electrical / optical converters 1-1-1 to 1-1-N as light having a wavelength λ1. After being converted into a signal, the signals are encoded by the encoding patterns of the code channels C1 to CN assigned thereto by the encoders 2-1-1 to 2-1 -N, and the optical delay units 8-1-1 to 8-1. 8-N gives a delay time determined by the code channels C1 to CN, and then passes through the wavelength multiplexing / demultiplexing couplers 13-1, M-1 to 13-1, MN, and then the coupler 14 N-1 multiplexed by −1 · M-0 and sent to the transmission line 4.
[0066]
The component light of wavelength λ1 of the optical multiplexed signal that has reached the optical line terminal 100 from the transmission line 4 is emitted toward the coupler 12-1-0 by the wavelength multiplexing / demultiplexing coupler 202, and the coupler 12-1-0 is The input optical signal is branched into N and supplied to N decoders 5-1-1 to 5-1 -N. Each of the decoders 5-1-1 to 5-1 -N decodes the input encoded optical signal of the wavelength λ 1 with the decoding pattern relating to the code channels C 1 to CN allocated to itself. The decoded optical signals are supplied to the optical / electrical converters 7-1-1 to 7-1 -N, and the optical / electrical converters 7-1-1 to 7-1 -N convert the decoded optical signals into electrical signals. To a received data processing circuit (not shown).
[0067]
In the optical line terminal 100, transmission signals (electrical signals) addressed to the optical node devices 200-1, M-1 to 200-1, MN are transmitted from the electrical / optical converters 1-M-1 to 1-M. -N is converted into an optical signal of wavelength λM by the encoder 2-M-1 to 2-MN, and is encoded with the encoding pattern of the code channels C1 to CN allocated to the optical signal by the encoder 2-M-1 to 2-MN. The delay times determined by the code channels C1 to CN are given by the devices 8-M-1 to 8-MN, and then N-multiplexed by the coupler 13-M-0, and then the wavelength multiplexing / demultiplexing coupler 202. Wavelength multiplexed and sent to the transmission line 4.
[0068]
The component light of the wavelength λM of the optical multiplexed signal that has reached the coupler 14-1 · M-0 from the transmission line 4 is branched into N, and each of the optical node devices 200-1, M-1 to 200-1, MN Is incident on.
[0069]
In each of the optical node devices 200-1, M-1 to 200-1, MN, the multiplexed optical signal of wavelength λM is transmitted as a component wavelength multiplexing / demultiplexing coupler 13-1, M-1 to 13-1. Provided to decoders 5-M-1 to 5-MN by MN. Each of the decoders 5-M-1 to 5-MN decodes an input multiplexed encoded optical signal having a wavelength λM with a decoding pattern related to the code channels C1 to CN allocated to the decoder 5-M-1 to 5-MN. The decoded optical signals are supplied to the optical / electrical converters 7-M-1 to 7-MN, and the optical / electrical converters 7-M-1 to 7-MN convert the decoded optical signals into electrical signals. The data is converted and given to a received data processing circuit (not shown).
[0070]
According to the third embodiment, code multiplexing can be realized on each wavelength channel, and the technical idea described in the first embodiment is applied to the code channel for each wavelength channel. Thus, it is possible to accurately identify each user channel determined by the combination of the wavelength channel and the code channel.
[0071]
As a result, it is possible to increase the number of users without expanding the use wavelength band.
[0072]
(D) Other embodiments
In each of the above embodiments, the optical delay device is provided on the rear stage side of the encoder. However, the optical delay device may be provided on the front stage side of the encoder. Further, a delay time difference (phase difference) corresponding to the code channel may be given at the transmission signal stage that is an electric signal input to the electric / optical converter.
[0073]
In consideration of setting of a new code channel or the like, it is preferable that an optical delay device or the like be variably settable.
[0074]
In the first embodiment, the wavelength of the encoded optical signal is the same even if the code channel is different. However, even if the wavelength differs depending on the code channel, a phase difference is given to each code channel. Anyway. Even in this case, it is possible to expect an improvement in reception accuracy due to a timing shift of interference waves. Furthermore, even when each code channel employs wavelength hopping, a phase difference may be given to each code channel.
[0075]
In the description of the first embodiment, the main peak of the decoded optical signal of a certain channel has been shown in the case where other signal components are not completely generated. However, only a part of the signal components of other channels are generated. It may be a difference in delay time. Conventionally, all other channels have become interference components, but even in this case, the interference components can be reduced as compared with that.
[0076]
In the first embodiment, the receiving side has been described as having one channel, but it may have N channels, and there may be a plurality of receiving configurations related to the same code channel. . In addition, a code channel to be received may be selected by switching the decoding pattern in the decoder. The expression of the claims is an expression that cannot be read directly in this case, but includes such a modified example.
[0077]
【The invention's effect】
As described above, according to the present invention, it is possible to realize an optical code division multiplexing communication system capable of correctly performing channel identification even when the number of channels is large.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a first embodiment.
FIG. 2 is a block diagram showing a conventional configuration.
FIG. 3 is a waveform diagram of each part in the related art.
FIG. 4 is a waveform diagram of each part of the first embodiment.
FIG. 5 is an explanatory diagram of an effect of the first embodiment.
FIG. 6 is a block diagram showing a main configuration of the second embodiment.
FIG. 7 is a block diagram illustrating a configuration of a third embodiment.
FIG. 8 is an explanatory diagram of channel assignment according to the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1-1 to 1-N ... Electric / optical converter, 2-1 to 2-N ... Encoder, 3 ... Coupler, 4 ... Transmission path, 5-1 ... Decoder, 6-1 ... Threshold determination circuit, 7 -1 ... optical / electrical converter, 8-1 to 8-N ... optical delay device.

Claims (4)

Code means for N channels, which time-spreads an optical transmission signal in which a chip period in which signal pulses are appropriately inserted appears for each data period in accordance with a code pattern assigned to itself, and outputs an encoded optical signal;
Optical signal multiplexing means for multiplexing encoded optical signals for N channels;
Optical signal demultiplexing means for demultiplexing the multiplexed encoded optical signal into N channels,
Decoding means for N channels, which outputs a decoded optical signal having an autocorrelation peak by time despreading the demultiplexed encoded optical signal according to a decoding pattern assigned to itself;
In the optical signal stage or electrical signal stage of each channel before reaching the optical signal multiplexing means, it has a phase difference providing means for giving a phase difference to the signal of each channel ,
The phase difference providing means generates the signal component of the other channel at the autocorrelation peak timing in the decoded optical signal from the decoding means related to one channel as the phase difference between the two channels with the smallest phase difference. not, and these two channels optical code division multiple access communication system that is characterized in that the grant phase difference side lobe overlap of the decoded optical signal. The phase difference providing means makes the phase difference between the two channels with the maximum phase difference smaller than the period obtained by subtracting the spread time width of the encoded optical signal from the encoding means from the data period. The optical code division multiplexing communication system according to claim 1 . The phase difference providing means, N channels or (N-1) with respect to encoded optical signal channels, according to claim 1 or 2, characterized in that to impart different delay times for each channel An optical code division multiplexing communication system. The optical code division multiplexing communication system according to any one of claims 1 to 3 , wherein encoded optical signals of all channels have the same wavelength.

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