JPH0537542A - Wavelength split multiplex transmission method and wavelength split multiplex network - Google Patents

Abstract

PURPOSE:To expand the transmission capacity of the entire network by multiplexing information subject to frequency dispersion by a CDM code onto a signal in addition to a frequency component in wavelength split multiplex transmission and sending the resulting signal. CONSTITUTION:A reception node uses a control signal receiver 12 to receive separately only a signal encoded by using a CDM code Cb from a multiplexed signal by a CDM decoder 16 at all times. Since a channel control signal from a node 1 is encoded by using the code Cb, the signal is separated from other signals and the result is inputted to a reception channel control section 17. The control section 17 sends a channel selection signal to a wavelength selection circuit 14 based on node identification information in the received control signal. The circuit 14 converts the signal into a wavelength selection signal and gives it to a local oscillation laser of a wavelength selection receiver 13 so as to allow the receiver 13 to selectively receive only the wavelength data from the node 1. Thus, the receiver 12 receives the control signal addressed to its own node from all nodes.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency division multiplex transmission method and a frequency division multiplex network, more specifically,
The present invention relates to a method of connecting a plurality of nodes to each other via a common transmission medium, frequency-multiplexing and transmitting information and control signals, and a network therefor.

[0002]

2. Description of the Related Art With the progress of the information-oriented society, in networks for transmitting information between information devices, transmission information has been increased in capacity and speed. Networks in this field are shifting from conventional networks using pair cables and coaxial cables as transmission media to optical networks using transmission media such as FDDI. Since the optical fiber has a significantly smaller transmission loss as compared with the coaxial cable, it is suitable for a wide area network such as MAN (metropolitan area network "M etropolitan A rea N etwork" ). The low loss wavelength range of the optical fiber is 1.3 to 1.6 μm, which is 40T when converted to frequency.
It is suitable for large-capacity information transmission networks because it reaches over Hz. However, the current practical speed in a system for transmitting a single wavelength in an optical fiber is 2.4 Gb / s, which is far below 40 THz, which is the transmission line band of the optical fiber. This is because the transmission speed is limited by the operating band of the transmitter / receiver (electronic circuit) at both ends of the transmission line and the received waveform distortion due to the dispersion characteristic of the transmission line.

Wavelength division multiplexing (abbreviated as WDM) transmission is an example of a transmission system that effectively uses the transmission band originally possessed by an optical fiber. In WDM transmission, a plurality of channel information is multiplexed and transmitted by wavelength multiplexing in one optical fiber. Since the transmission rate per wavelength is about the same as that of the conventional system, which is limited by the electronic circuit and the waveform distortion, the transmission capacity can be expanded to the number of multiplexed multiples.

As a typical example of applying WDM transmission to a network, Electronics Letters, 30th and July,
Volume 23, No. 16, 824-826 (Electronics Letters 30
th July 1987 Vol.23 No.16, pp.824-826). In this network, a transmission wavelength unique to each node is allocated, optical signals of these wavelengths transmitted by the node are multiplexed by a star coupler, then demultiplexed and distributed to each node. Since the reception signal distributed to each node is subjected to WDM, a transmission node to be received is selected by selectively receiving a signal of a required wavelength from among these, and connection between the transmission and reception nodes is performed. Since the total capacity of this network is the sum of the transmission speeds of the nodes, the transmission capacity can be expanded as compared with the conventional network. Further, since all the nodes transmit with different wavelengths, there is no collision between the transmitting nodes.

[0005]

However, the above-mentioned conventional WDM star network has the following problems. That is, the number of receivers in the node is increased in order to be able to change the channel assignment appropriately. In a one-to-one connection, that is, in a network that does not perform broadcasting, only one receiver is required for each node.
However, as long as it is received by one receiver, there is no means to know the information from the node other than the node currently receiving it, so the transmission request from other nodes and the channel control information for allocating the channel are known. I can't. In order to dynamically change the channel between all nodes in this type of network, it is necessary to know the channel control information from all nodes. Therefore, the node needs to have a receiver corresponding to the wavelengths transmitted by all the nodes on the network. This is a great waste, while the information received by one node is less than one receiver on average. Further, when the number of nodes is increased and the network is expanded, it is necessary to add receivers to all the nodes. This is a major obstacle to network expansion. A first object of the present invention is to further increase the transmission capacity of a network in which a plurality of nodes are combined. Another object of the present invention is to realize a frequency division multiplex transmission method and a network therefor capable of appropriately changing channel assignment with a minimum number of receivers.

[0006]

In order to achieve the above object, the present invention connects a plurality of nodes to each other through a common transmission medium and frequency-multiplexes information signals (hereinafter, FDM, W).
In a frequency division multiplex network for DM (also referred to as wavelength division multiplexing) transmission, a node-specific transmission frequency and a CDM code are assigned to the plurality of nodes, and the transmission node transmits the information signal to be transmitted, which is unique to the node itself. The frequency and the CDM code unique to the receiving node of the destination are transmitted to the common transmission medium as a transmission signal, and the receiving node receives the information signal modulated at the transmission frequency unique to the transmitting node and the unique CDM of the receiving node. The information signal modulated by the code is received and demodulated.

It is not necessary that all of the plurality of nodes be configured as described above, and only a part of the nodes may be configured as described above. Further, the information signal modulated at the transmission frequency peculiar to the transmission node and the information signal modulated at the peculiar CDM code of the reception node need not be transmitted at the same time, and may be transmitted separately in the time domain. For example, as a preferred embodiment, an information signal modulated with a unique CDM code of a receiving node is a control signal including an identification signal for identifying the transmitting node, and the node to which the CDM code is assigned transmits the identification signal. The control signal including the control signal is received, the unique frequency assigned to the transmitting node detected from the identification signal is obtained, and the information signal modulated from the transmitting node specific transmitting frequency is received from the transmitting node. The common transmission medium may be wired or wireless, but in order to expand the transmission capacity, a bus using an optical fiber and a star coupler are effective from the viewpoint of network configuration.

[0008]

According to the present invention, in addition to the frequency components of the conventional wavelength division multiplex transmission, the information dispersed in frequency by the CDM code can be multiplexed and transmitted, so that the transmission capacity of the entire network is significantly expanded. Furthermore, in the configuration described as the preferred embodiment and described in the following example, each node device of the node has one transmitter and a CD.
With a minimum device provided with a first receiver for receiving a reception signal modulated with an M code and a second receiver for receiving a reception signal modulated with a node-specific transmission frequency, the identification information of the transmission node can be obtained. It is possible to send control signals including the above, and the receiving node can tune the receiving wavelength based on the identification information, so that data signals and control signals can be exchanged between any nodes in the network, and dynamic channel allocation is possible. It will be possible.

[0009]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows a WDM network according to the present invention.
It is a block diagram of an Example. In this embodiment, an optical fiber is used as the transmission medium. n nodes 1-1, 1-2, ... 1
-I ... 1-n are optical star couplers 2 which are common transmission media
Are connected to each other by. Λi is assigned to the node 1-i as a unique transmission wavelength, and Ci is assigned as a unique reception CDM code. The optical output of the transmission wavelength λi from each transmission node is multiplexed by the star coupler 2, and the multiplexed signals {λ1, λ2 ... λi are transmitted to each node.
... λn} is distributed.

FIG. 2 is a block diagram of an embodiment of a node used in the network according to the present invention of FIG. Not all nodes need to have this configuration. at least,
It suffices that a plurality of nodes have the configuration of FIG. In the figure, 1 has a transmitter 3 and a receiver 9, and the transmitter 3 has a CDM code table 5, a channel-code converter 6, a CDM encoder 7, a signal switching selector 8 and a transmitter 4. The receiving unit 9 includes a data receiver 11 that processes one signal branched by the optical branching device 10 and a control signal receiver 12 that processes another one signal, and the data receiver 11 is a wavelength selective receiver. 13 and a wavelength selection circuit 14. The wavelength selection receiver 13 is composed of a heterodyne receiver, and selects the reception wavelength by changing the emission wavelength of a local oscillation laser (abbreviated as local oscillation laser) in the wavelength selection receiver 13. The wavelength selection circuit 14 is a circuit that controls the current injected into the local laser.

The control signal receiver 12 is a wavelength independent optical receiver 15 capable of receiving signals of all wavelengths, and a CDM decoder 1.
6. It has a reception channel controller 17. Since the wavelength-independent optical receiver 15 needs to linearly add the received signals {λi}, it is configured as a direct detection receiver. Since the PIN photodiode and APD used in the optical receiver 15 have sensitivity over a wavelength band of 1.3 to 1.5 μm, they are usually wavelength independent optical receivers. The CDM decoder 16 is composed of a correlator of the received waveform and the CDM code Ci unique to each node. The reception channel control unit 17 uses the signal decoded by the CDM decoder 16 to transmit a request from the transmission node and the transmission node identification signal (address channel,
(Wavelength information, etc.) is detected, and if reception is possible, a channel selection signal corresponding to the wavelength to be received is sent to the wavelength selection circuit 14.

FIG. 3 is a block diagram of another embodiment of the CDM decoder 16 of FIG. 2, and the configuration of the decoder itself is already known. The decoder 16 does not perform correlation processing in the electrical domain, but a plurality of optical delay lines 19, 19 ′, 19 ″ having different optical delay times, a demultiplexer 18 and a multiplexer 20 on the input side of the wavelength-independent optical receiver 15. A despreader composed of and is arranged.

In the above embodiment, the transmitted optical signal is intensity modulated (I
M) signal, but C for a FSK-modulated signal
A DM receiver can be constructed. Figure 4 (a) shows FS
It is a block diagram of one Example of the CDM receiver with respect to a K signal, and the frequency discriminator 21 is a wavelength independent optical receiver 15, C
It is preceded by a CDM receiver for IM signals with a DM decoder 16. FIG. 4B shows the characteristic of the frequency discriminator 21. The function of the frequency discriminator 21 is to IM the FSK signal.
(Intensity) signal, but it is necessary to convert simultaneously to a plurality of different wavelengths. This is achieved by allocating the transmission frequency so that the pass frequency of the optical circuit having the periodic pass characteristic becomes the mark M of the FSK signal and the non-pass frequency becomes the space S of the FSK signal. As the frequency discriminator 21, specifically, a Fabry-Perot etalon or a Mach-Zehnder interferometer can be used. When the CDM code is directly intensity-modulated and transmitted, the frequency discriminator 21 is not necessary.

Next, the operation of the embodiment shown in FIG. 2 will be described by taking the case where the node 1-a transmits a control signal to the node 1-b and sets the channel. Note that FIG. 2 shows the configuration of one node, but for convenience sake, the description will be given using both the transmission unit of the node 1-a and the reception unit of the node 1-b. Node 1
The channel switching request signal is added to the channel-code converter 6 in the transmitting unit 3 of -a. The channel-code converter 6 determines the receiving node 1 based on the node number of the node 1-b.
In order to search the CDM code table 5 for the CDM code Cb of -b, set the code Cb in the CDM encoder 6, and set the signal switching selector 8 to the CDM side,
Generate a switching signal. After the CDM encoder 6 and the signal switching selector 8 are set to a predetermined state, a control signal including the channel information or the transmission wavelength information of the node 1-a is added to the CDM encoder 7, encoded by the code Cb, and the selector 8 Is transmitted to the transmitter 4, is converted into an optical signal, and is transmitted to the optical star coupler 2.

At the receiving node 1-b, the control signal receiver 1
2 is C from the signals multiplexed by the CDM decoder 16
Only the signal encoded by the DM code Cb is always separated and received. Since the channel control signal from the node 1-a is encoded by the CDM code Cb, it is separated from other signals and input to the reception channel control unit 17. When the reception channel control unit 17 can receive the data from the node 1-a, it sends a channel selection signal to the wavelength selection circuit 14 based on the node identification information (wavelength, address, channel, etc.) included in the reception control signal. . In the wavelength selection circuit 14, the channel selection signal is transmitted to the wavelength selection receiver 13.
Is converted to a wavelength selection signal to select the wavelength of the local laser of
It is added to the local laser of the wavelength selective receiver 13. As a result, the wavelength selective receiver 13 switches the reception wavelength to λa and selectively receives only the data of the wavelength λa from the node 1-a. According to this embodiment, the control signal receiver 12 can receive the control signal addressed to the own node from all the nodes without wavelength separation or wavelength selection. Therefore, the number of receivers required in the node can be significantly reduced.

In the present embodiment, a CDM code by intensity modulation is used, but since the intensity modulation signal is a unipolar signal with polarities of 0 and +, a bipolar-based CDM code used in radio cannot be used. Therefore, as an optical CDM code, IEE Transaction of Information Theory, Vol.35, No.3, May1989, p
p.595-604 (IEEE Transaction of Information Theory, V
35, No. 3, May 1989, pp. 595-604).

In this embodiment, another C is used in the CDM reception.
The DM signal does not interfere, but the data modulated with the random data may interfere with the control signal. Data disturbance can be efficiently removed by the following means, for example. That is, the data is 1 bit T
Encode using Manchester code of time width of. On the other hand, the control signal is encoded by a CDM code having a time width T of 1 chip. Here, one chip is a unit bit of a plurality of bits that constitutes a CDM code.

FIG. 5 shows the data of the Manchester code and the spectrum of the control signal of the CDM code.
The data spectrum consists of a DC impulse due to the DC component and a spectrum due to the randomness of the data around 1 / T. This spectral shape depends on the envelope of the Manchester code waveform. The Manchester code is regarded as a modulation waveform with 1 / T as the carrier wave, and the roll-off rate (α in the figure) 0
Considering the% cosine roll-off spectrum, the spectrum of the random component of the data can be concentrated in 1 / 2T to 3 / 2T. On the other hand, the spectrum of the control signal also depends on the waveform of one chip, but this can also be concentrated to 1 / 2T or less by setting the roll-off rate to 0%. Therefore, in the CDM receiver, the interference of the data signal can be removed by using the filter having the cutoff frequency of 1 / 2T. Further, since the DC component of data is equivalent to a constant bias in the time domain, the influence can be neglected by setting the threshold level of the CDM decoder. Note that this multiplexing method is not limited to the CDM code, and two types of data can be multiplexed by modulating normal data with the NRZ code.

In this embodiment, when a plurality of nodes simultaneously make a communication request to the same node, the control signals collide. This can be dealt with by processing by another network control / higher level protocol. For example, when the control signal is correctly received and the channel is receivable, the transmitting node can know that the information to be sent is correctly transmitted by returning the acknowledge signal. As described above, the embodiment is W
Although the case where the DM optical signal is transmitted using the optical transmission path has been described, a frequency multiplexing network can be similarly configured in a network sharing a transmission medium, for example, wireless transmission in space.

[0020]

According to the present invention, the conventional WDM star network can be improved to further increase the communication capacity, and the number of transmitters and receivers per node can be minimized to realize dynamic channel control.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of a WDM network according to the present invention.

FIG. 2 is a diagram showing a configuration of an embodiment of a node used in a WDM network according to the present invention.

FIG. 3 is a diagram showing a configuration of an embodiment of a CDM optical receiver used in a WDM network according to the present invention.

FIG. 4 is a diagram showing a configuration of an embodiment of a CDM optical receiver for an FSK signal used in a WDM network according to the present invention.

FIG. 5 is a diagram showing an example of spectrum in a CDM receiver used in a WDM network according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Node, 2 ... Optical star coupler, 3 ... Transmission part, 4 ... Transmitter, 5 ... CDM code table, 6 ... Channel-code converter, 7
... CDM encoder, 8 ... Signal changeover switch, 9 ... Reception unit, 10
... Optical branching device, 11 ... Data receiver, 12 ... Control signal receiver, 13 ... Wavelength selection receiver, 14
… Wavelength selection circuit, 15… Wavelength independent optical receiver,
16 ... CDM decoder, 17 ... Reception channel control unit,
18 ... Demultiplexer, 19 ... Optical delay element,
20 ... Combiner, 21 ... Frequency discriminator.

Claims (13)

[Claims] 1. A transmission method in which a plurality of nodes are connected to each other via a common transmission medium and an information signal is frequency-multiplexed and transmitted, in which a CDM code is assigned to at least one node of the plurality of nodes, When the destination receiving node is assigned the above CDM code when the transmitting node transmits, the first frequency and the second information signal are respectively assigned to the own frequency and the CDM code assigned to the destination node. The node to which the CDM code is assigned is modulated from the received signal received from the common transmission medium,
A wavelength division multiplexing transmission method, comprising: receiving an information signal of a frequency to be received by the own node and an information signal modulated by a CDM code assigned to the own node. 2. The wavelength division multiplexing transmission method according to claim 1, wherein the second information signal is a control signal including an identification signal for identifying the specific node, and the CDM.
The node to which the code is assigned receives the control signal including the identification signal, obtains the unique frequency assigned to the transmission node detected from the identification signal, and receives the first information signal from the transmission node. A wavelength division multiplexing transmission method, characterized in that the receiving unit is controlled as described above. 3. The wavelength division multiplexing transmission method according to claim 1, wherein the node to which the CDM code is assigned receives a control signal including the identification signal, and when the node can receive the control signal, an acknowledge signal is sent to the identified transmission node. And the identified transmission node receives the acknowledge signal, modulates the transmission data as the first information signal at a specific frequency, and transmits the modulated data. 4. In a frequency division multiplexing network for connecting a plurality of nodes to each other via a common transmission medium and frequency-multiplexing and transmitting information signals, each of the plurality of nodes has a transmission frequency and a CDM code unique to the node. Are allocated, and the transmitter of at least one node modulates the first information signal with the transmission frequency specific to the allocated own node and the second information signal with the CDM code of the destination node. A receiver having at least one other node, and a first receiver for selectively decoding the information signal with a received CDM code specific to the own node; A frequency division multiplexing network comprising a receiving section having a second receiving means for demodulating. 5. The frequency division multiplexing network according to claim 4, wherein said transmitting section has means for switching outputs of said first modulating means and second modulating means, and said first information signal identifies a transmitting node. A control signal including identification information, which is the first signal
The receiving means and the second receiving means are each capable of selectively receiving an arbitrary frequency used on the network, have sensitivity to a data receiver for receiving the first information signal and all frequencies used on the network, and A frequency division multiplexing network comprising a CDM receiver that constantly receives a second information signal. 6. The frequency division multiplexing network according to claim 5, wherein the CDM receiver has means for controlling a reception frequency of the data receiver based on the identification information. 7. The frequency division multiplexing network according to claim 4, 5 or 6, wherein the transmission medium is an optical fiber and is a bus or star type transmission line. 8. The frequency division multiplexing network according to claim 5, wherein C is provided from the transmitting node at the receiving node.
When receiving a control signal modulated with a DM code and receiving data, a means for transmitting an acknowledge signal indicating that data can be received by encoding the CDM code of the transmitting node and transmitting the acknowledge signal, and the transmitting node receiving the acknowledge signal. And a means for initiating data transmission only in case of frequency division multiplexing network. 9. A transmission system, wherein a signal modulated by a Manchester code having a bit time T and a signal modulated by an NRZ code having a bit time T are multiplexed and transmitted. 10. A transmission system, wherein a signal modulated by a Manchester code having a bit time T and a signal modulated by a CDM code having a chip time T are multiplexed and transmitted. 11. A receiver for transmitting a first information signal modulated by a specific frequency and a second information signal modulated by a CDM code, and wavelength selective reception for receiving only a specific frequency component from the received signal. A node device comprising a receiving section having a second receiver for decoding an information signal modulated by a CDM code from a machine-received signal. 12. A C for modulating a control signal with a CDM code.
From the optical transmission line, a transmission unit having a DM encoder, a selector for switching the transmission data and the output of the CDM encoder, and a transmitter for converting the output of the selector into an optical signal of a specific wavelength and transmitting the optical signal to the optical transmission line. Optical branch for branching the received optical signal of, a data receiver for selectively receiving a component of a specific wavelength in the branched one received optical signal, and a control signal by a CDM decoder from the other branched received optical signals And a receiver having a control signal receiver for obtaining the node signal. 13. The node device according to claim 12, wherein the control signal includes identification information of the node device, and the receiving unit uses the identification information received by the control signal receiver to identify the identification of the data receiver. A node device having means for controlling a wavelength.