JPH04347945A - Cdma optical receiver - Google Patents

Abstract

PURPOSE:To realize a CDMA(code division multiple access) receiver which correctly inversely diffuses even coherent light of high coherence and is correctly operated. CONSTITUTION:A power divider 1 which branches a received optical signal subjected to code division multiplexing into plural optical signals, plural optical delay elements 2a, 2b...2n which delay plural optical signals by prescribed delay times to inversely diffuse the light correspondingly to a code assigned to a receiver, photodetectors 3a, 3b...3n which photoelectrically convert respective output light of plural optical delay elements, and a circuit 4 which connects photodetectors in parallel to amplify the sum of currents flowing to photodetectors by preamplification are provided to constitute the CDMA optical receiver. Consequently, delay for correlation is performed in the optical area and addition is performed by currents, and beat and output stop due to light interference are prevented.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a CDMA optical receiver, and more specifically, to a CDMA optical receiver. Access (Code Division Multiple A
The present invention relates to an optical receiver that regenerates a received signal using CDMA (hereinafter abbreviated as CDMA), and particularly relates to a CDMA optical receiver that optically receives a signal spread with a specific code or an arbitrary code.

0002

[Prior art] Optical fiber transmission has large capacity, low loss,
Due to its ability to transmit over long distances and the recent increase in communication traffic, it is rapidly replacing traditional coaxial cable or wireless transmission systems. Conventional optical fiber transmission mainly connected only one pair of nodes to a single fiber, but multiple optical signals can be multiplexed onto a single fiber by taking advantage of optical fiber's broadband and low loss characteristics. Application as a network for transmission is being considered. CDMA, which is one type of spread spectrum, is being considered as an access method for multiplexed optical signals.

[0003] Optical communication systems using CDMA are described, for example, in Document 1, ``I.C.C.'87 Minutes, pp. 1601-16.
09 page (ICC'87 Proc., pp.1,601
-1,609). The specific configuration of the optical correlation circuit used in CDMA described therein is described in, for example, Document 2, “IEE Transactions on Microwave Theory and
Technic Volume 33 1985 Number 3
March issue, pages 193 to 208 (IEEE Transa
tions on Microwave Theor
y and Techniques, VOL. MTT-
33, No. 3, March 1985, pp. 193
-208)", or a signal branched with a predetermined delay time as described in Document 3, "1988 Institute of Electronics, Information and Communication Engineers Autumn National Conference B-407". After passing through an optical fiber with an optical fiber, a power combiner is used to combine the signals in the optical region. In either case, the received optical signal at the receiver is delayed in accordance with the received spreading code, and the delayed signals are combined in the optical signal state.

0003

However, the optical correlation circuit of the conventional CDMA optical receiver described above has the following problems. In other words, currently, single-mode light emitting elements and optical fibers are normally used for high-speed communication due to the dispersion characteristics of optical fibers, but the light output from light emitting elements oscillating in a single longitudinal mode is coherent. Highly sexual. In conventional optical receivers, it is necessary to combine the lights that are branched and delayed during despreading, but with highly coherent lights, the lights interfere, creating beats, and may not be output to the port. Therefore, a highly coherent light source cannot perform correct despreading. Furthermore, since the receiver requires an optical correlation circuit that corresponds one-to-one to each spreading code, it is not possible to receive optical signals spread with other spreading codes. The purpose of the present invention is to create a CD that can correctly despread even highly coherent light and receive it accurately.
The objective is to realize an MA optical receiver. Another object of the present invention is to configure a CDMA optical receiver capable of switching spreading codes.

0004

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a power divider that branches a received code division multiplexed optical signal into a plurality of optical signals, and a power divider that supports codes assigned to a receiver. a plurality of optical delay elements that delay the plurality of optical signals by a predetermined delay time so as to despread them, a light receiving element that photoelectrically converts each output light of the plurality of optical delay elements, and each of the above light receiving elements in parallel. A CDMA optical receiver was constructed by providing a circuit for amplifying the sum of currents connected to each light receiving element using a preamplifier. In addition, in order to configure a CDMA optical receiver capable of switching spreading codes, a current switch is installed in each of the above-mentioned light-receiving elements in order to turn on/off the current flowing through each of the light-receiving elements connected in parallel in accordance with the spreading code. are connected in series, or an optical switch is provided between the input and output of the optical delay element, and a channel control circuit is added that controls the current switch or optical switch on and off in accordance with the despreading code of the specified channel. It was configured as follows.

[0005]

[Operation] Signals delayed by a plurality of optical delay elements are converted into electric current by each light receiving element and then added, so that generation of beats and loss of pulses due to optical interference are prevented. Furthermore, since the channel control circuit can perform current addition in accordance with the received spreading code, it is possible to selectively receive a channel with an arbitrary spreading code. In particular, since division and delay are performed in the optical domain and then photoelectrically converted to obtain the sum of currents, compared to other conceivable cases where multiple front ends perform photoelectric conversion and then division, delay, etc. are performed in electrical circuits. , the S/N ratio is significantly improved.

[0006]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a configuration block diagram of one embodiment of a CDMA optical receiver according to the present invention. A plurality of optical signals code division multiplexed at the transmitter side (not shown) are transmitted through a single mode optical fiber 0 to C
transmitted to a DMA receiver. The received optical signal is branched into n pieces by an optical power divider 1, and each of them is divided into n pieces of optical delay elements 2a, 2b . ．． ．． 2n. The number n of optical delay elements required here corresponds to the number of bits on which light is emitted during diffusion. Optical delay elements 2a, 2b. ．． ．． As 2n, for example, an optical fiber whose length is adjusted can be used. The output lights of the optical delay elements 2a to 2n are independently converted into currents by the light receiving elements 3a to 3n, and then the currents are added together. The electrical signal with the added currents is amplified by a preamplifier 4, and the received data is reproduced by a threshold detector 5.

[0007] The elements constituting the CDMA optical receiver are:
In both cases, well-known elements can be used, so a detailed explanation thereof will be omitted. Optical delay elements 2a, 2b. ．． ．． 2n
If the bit period of the spreading code is about 100 p seconds, it is constructed of optical fibers with a length difference of about 2 cm. A PIN photodiode or APD is used as the light receiving element. According to this embodiment, the optical signals delayed according to the spreading code are converted into currents and then added, so that no interference occurs due to multiplexing of the optical signals as they are. Since it is amplified by a single preamplifier, the S/N ratio of the current sum is high, and the sensitivity of the receiver is also increased. These advantages also apply to other embodiments described below.

FIG. 2 shows a block diagram of a second embodiment of a CDMA optical receiver according to the present invention. This embodiment is a CDMA optical receiver that can receive channels corresponding to arbitrary spreading codes having the same spreading code length. As in the embodiment of FIG. 1, the received optical signal is branched into n optical signals by an optical power divider 1, and n optical delay elements 2a, 2b, . ．． ．． 2n. Optical delay elements 2a, 2b. ．． ．． The number 2n is the number of spreading code bits n
The delay time differences based on the optical delay element 2a are each mT (where m=1 to n-1, T is the time and pulse width of one bit of the spreading code). Optical delay elements 2a, 2b. ．．
．． The output lights of 2n are respectively transmitted to the light receiving elements 3a. ．． ．． 3n independently converted into current. Each light receiving element 3a. ．． ．． 3n
respectively have current switches 6a. ．． ．． 6n are connected in series. The series circuit of the light receiving element and the current switch is connected in parallel. Current switch 6a. ．． ．． 6n is
The on/off state is controlled by a bit signal of a despreading code corresponding to the channel to be received from the channel control circuit 7, respectively. Therefore, the series-parallel circuit of the light receiving element and the current switch has a current of 6a. ．． ．． Of the 6n, only those that are conductive are added and amplified by the preamplifier 4, and the data is reproduced by the threshold detector 5. On the transmitter side, one bit of information data is spread with an n-bit spreading code, but according to the configuration of the CDMA receiver of this embodiment,
The spreading code for despreading is the current switch 6a. ．． ．． 6n
Therefore, if the number of bits of the spreading code is n or less and the bit times of the spreading codes are equal, it is possible to receive and reproduce the signal of the channel corresponding to the spreading code of any number of bits.

FIG. 3 shows a block diagram of a third embodiment of a CDMA optical receiver according to the present invention. In this embodiment, the current switch 6a for switching the spreading code in the embodiment of FIG. ．． ．． 6n is composed of an optical switch, and optical delay elements 2a, 2b . ．． ．． This configuration is provided on the output side of the 2n. As in the embodiment of FIG. 1, the received optical signal is branched into n optical signals by an optical power divider 1, and n optical delay elements 2a, 2b, . ．． ．． 2n. Optical delay elements 2a, 2b. ．． ．． Optical switches 9a, 9b . ．． ．． 9n are generated, and are controlled to be on (transparent) or off (non-transparent) by the bit signal of the spreading code corresponding to the channel to be received from the channel control circuit 8, respectively. Optical switch 9a, 9
b. ．． ．． On (transparent)/off (non-transparent) depending on 9n
The controlled light is transmitted to the light receiving elements 3a, 3b, . ．． ．．
Added to 3n. Light receiving elements 3a, 3b. ．． ．． The electrical signals subjected to 3n photoelectric conversion are added in parallel, amplified by a preamplifier 4, and data is reproduced by a threshold detector 5. The numbers of optical delay elements, optical switches, and light receiving elements are each equal to the number n of spreading code bits. The current input to the preamplifier 4 is the same as in the second embodiment, and the sign for despreading can be switched by an optical switch. Therefore, signals spread by different spreading codes can be selectively received.

FIG. 4 shows a frequency deviation keying modulated FS.
FIG. 2 is a configuration diagram of a CDMA optical receiver compatible with K signals. 1
0 is an optical frequency discriminator, 11 is Fig. 1, Fig. 2, or Fig. 3.
This is the optical receiver shown in the figure. The optical frequency discriminator 10 is composed of an etalon resonator. Since the FSK signal is converted into an intensity signal by the optical frequency discriminator 10, FIGS.
Alternatively, CDMA reception becomes possible with the optical receiver shown in FIG. As the constituent elements of each of the above embodiments, such as the power divider, optical delay element, and photoreceiver, are conventionally well-known components, and detailed explanations thereof will be omitted.

0012

[Effects of the Invention] As described above, according to the present invention, since the delay for correlation is performed in the optical domain and the addition is performed in the electric current, it is possible to despread even highly coherent light, making CDMA reception possible. Become. Further, by switching the current to be added using a current switch, it is possible to despread an arbitrary spreading code whose bit time is equal and the length is n bits or less.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a first embodiment of a CDMA optical receiver according to the present invention.

FIG. 2 is a configuration block diagram of a second embodiment of a CDMA optical receiver according to the present invention.

FIG. 3 is a block diagram of a third embodiment of a CDMA optical receiver according to the present invention.

FIG. 4 is a configuration block diagram of a fourth embodiment of a CDMA optical receiver according to the present invention.

FIG. 5 is a configuration diagram of a conventional CDMA optical receiver.

[Explanation of symbols]

1... Optical power divider, 2a-2n... Optical delay element, 3a-
3n...Photodetector, 4...Preamplifier, 5...Threshold detector, 6a to 6n...Current switch, 7...Channel control circuit, 10...Optical frequency discriminator, 11...Optical receiver consisting of Figure 1 or Figure 2 vessel.

Claims (4)

[Claims] Claim 1: In a CDMA optical receiver that selectively receives an optical signal corresponding to a spreading code assigned to the receiver from a plurality of optical signals subjected to code division multiplexing, the received optical signal is branched into a plurality of optical signals. a plurality of optical delay elements that delay the plurality of optical signals by a predetermined delay time so as to despread them in accordance with codes assigned to the receiver; and each output light of the plurality of optical delay elements. and a circuit that connects each of the above-mentioned light-receiving elements in parallel and amplifies the sum of the current flowing through each light-receiving element using a preamplifier.
DMA optical receiver. [Claim 2] A plurality of optical signals code-division multiplexed using a spreading code with a 1-bit time width of T and a code length of n bits are transmitted through an optical fiber, and the corresponding optical signals are extracted from the output light of the optical fiber. CDM to selectively receive
In the A optical receiver, a power divider that branches the output light of the optical fiber into n branch paths;
an optical delay element, n light receiving elements that photoelectrically convert the output of each of the optical delay elements, a current switch that turns on/off a current flowing through the light receiving elements connected in series to each of the light receiving elements, and A front end section in which a circuit consisting of an element and a current switch is connected in parallel and the sum of the currents flowing through each current switch is amplified by a preamplifier, and the current switch is turned on and off in accordance with the despreading code of the specified channel. A CDMA optical receiver comprising a channel control circuit for controlling a CDMA optical receiver. 3. A method for selectively receiving an optical signal corresponding to a spreading code with a 1-bit time width of T and a code length of n bits from a plurality of optical signals subjected to code division multiplexing.
In a DMA optical receiver, a power divider that branches a received optical signal into n signals, n optical delay elements connected to each optical output of the power divider and having a time difference of T, and connected to each of the optical delay elements. n optical switches, n photodetectors that photoelectrically convert the output of each of the optical switches, a preamplifier that amplifies the sum of the current flowing through each photodetector, and a A CDMA optical receiver characterized by having a channel control circuit that performs on/off control in accordance with a spreading code. 4. A CDMA optical receiver for receiving an optical signal subjected to code division multiplexing and frequency shift keying modulation, comprising: an optical frequency discriminator; and an optical frequency discriminator connected thereto. CDM
A CD characterized in that it is constituted by an optical receiver.
MA optical receiver.