JP2010093717A - Optical access system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To separate upward signals by a blind sound source separation technology in an optical access system. <P>SOLUTION: A sound and light modulating portion 23 of a subscriber device modulates the upward signals having different types of wavelengths of more than 2 by audio signals. A signal processing portion 34 of an intra-office device separates into a signal for each subscriber device the upward signals having different types of the wavelengths of more than 2 which are mixed by a power splitter 14 and modulated by the audio signals of a plurality of subscriber devices by means of blind sound source separation. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical access system.

  Blind signal separation that separates and extracts sound source signals before mixing without using sound source signals and mixing process information as a technique for separating and extracting sound source signals before mixing from a mixed signal in which multiple sound source signals are mixed Techniques are conventionally known.

  FIG. 22 is a diagram showing the concept of this blind sound source separation technique.

As shown in FIG. 22, in the blind signal separation technique, a plurality (N in this example) of sound generators 201-1 to 201-N (hereinafter, if there is no need to distinguish each of the sound generators, simply the sound generators). 201 referred to as. the same applies in other cases) audio signals emitted from the _{S i (i = 1, ···} , N) are mixed, the sound collection unit of the plurality (M number in this example) 20 2 Under the condition observed at 1 to 202-M, the signal separation unit 203 uses the observation signal x _j (j = 1,..., M) alone as the separation signal y _k estimated as the original speech signal. (K = 1,..., N) is taken out.

  As a signal separation method when the number N of the sound generation units 201 and the number M of the sound collection units 202 are in a relationship of M ≦ N, there is a method using a time frequency mask.

  In this method, the N sound generators 201 are statistically independent from each other, and each signal is assumed to be sufficiently sparse. “Sparse” means that the signal is 0 at almost all times, and this sparsity is confirmed by, for example, an audio signal in the time-frequency domain.

  When mutual independence and signal sparsity can be assumed in this way, even if a plurality of signals are present at the same time, it is considered that the probability that they will be observed at each time frequency point is low. Therefore, it can be assumed that the observation signal x in the sound collection unit 202 at each time frequency point is composed of only one signal active at that time frequency point.

  Therefore, each signal can be separated by clustering the observation signal x with an appropriate feature amount and estimating a time frequency mask for extracting the observation signal x corresponding to the time frequency of the observation signal x in each cluster. Details of this method are described in Patent Document 1 and Non-Patent Document 2.

  In the methods described in Patent Document 1 and Non-Patent Document 2, a delay difference between signals that is caused by a difference in distance between each sound source and a plurality of sound collection devices is used as a feature amount.

In this case, the observation signal x _j is expressed by Expression (1).

In Expression (1), a _ij and τ _ij are attenuation and delay in the sound collection unit 202-j of the sound generation unit 201-i in the example of FIG. 22, and the sound source depends on the distance between the sound source and the sound collection device. Only one value is assumed.

For example, when there are two sound collection units 202 (M = 2) and the delay difference between the signals is a feature amount, the feature amount represented by Expression (2) is calculated at all the time frequencies f and t ( Here, x _j (f, t) is obtained by subjecting the observation signal x _j (t) to a short-time Fourier transform), and this feature quantity is then clustered.

Each cluster C _i corresponds to a respective audio signal S _i . Based on the clustering result, the time-frequency mask is calculated by Expression (3), and a separation signal in the time-frequency domain is obtained by Expression (4) using this time-frequency mask, for example.

  The separated signal in the time frequency domain is converted into a signal in the time domain by inverse short-time Fourier transform, and a final separated signal y is obtained.

  This technique is suitable for voice communication applications such as telephones that have a large number of users and cannot allow delays because they do not need to learn individual voices for separation and are excellent in real-time characteristics.

  By the way, in a communication network, an optical access system having a topology called PON (Passive Optical Network) is becoming widespread.

  FIG. 23 is a diagram illustrating a configuration example of a PON system. In the PON system, a plurality of subscriber devices 212 are connected to one intra-station device 211 via an optical fiber 213 and a power splitter 214.

  As described above, since a plurality of subscriber devices 212 are connected to one intra-station device 211, the cost of service can be distributed to a plurality of subscribers, and the service provision price can be reduced. However, since the subscriber device 212 itself needs to be owned by each user, there is no such distributed effect of costs, and it is desired to reduce the cost, for example, by reducing the number of members. Therefore, application of the above-described blind sound source separation technique is expected.

  For example, if the audio signal can be separated by applying the blind sound source separation technique as the uplink voice signal separation technique, the subscriber apparatus 212 does not need a function for realizing user multiplexing. The offered price can be reduced.

WO2006 / 085537 S. Araki, H. Sawada, R.D. Mukai, S. Makino, “UnderdeterminedBlind Sparse Source Separation for Arbitrarily Arranged Multiple Sensors”, Signal Processing, 87pp. 1833-1847, EIsevier, 1March 2007.

  However, the methods described in Patent Document 1 and Non-Patent Document 1 are based on the premise that a plurality of sound sources and a plurality of sound collection devices are in the same space, and thus light beams that are installed in different spaces. Application to access systems is difficult.

  Furthermore, in the methods described in Patent Document 1 and Non-Patent Document 1, in order to separate the sound band signal (about 300 to 4 kHz) as a sound source, the sound collecting devices are spatially separated, so However, in the optical access system, even when the maximum distance of 20 km is considered, the time for propagation of the optical signal is only about 100 μsec. It is extremely difficult to create a delay difference. Therefore, the methods described in Patent Document 1 and Non-Patent Document 1 cannot be applied to an optical access system as they are.

  In view of the above points, the present invention provides an optical access system capable of separating an upstream signal by a blind sound source separation technique.

  The optical access system of the present invention is an optical access system comprising an intra-station device and a subscriber device connected via an optical transmission line and a power splitter, and the subscriber device has two or more different wavelengths. Modulation means for modulating a signal with an audio signal, the in-station device has separation means for performing blind sound source separation for signal separation, and the separation means modulates a plurality of subscriber devices mixed by a power splitter. The upstream signal having two or more different wavelengths modulated by the audio signal by the means is separated into signals for each subscriber unit by blind sound source separation.

  A delay line may be installed between the subscriber unit and the power splitter.

  The subscriber unit further includes a generating unit that generates an upstream signal having two or more different wavelengths, and the modulating unit of the subscriber unit generates the upstream signal having two or more different wavelengths generated by the generating unit. It can be modulated with an audio signal.

  The intra-station device further has a generating means for generating an upstream signal having two or more different wavelengths, and the upstream signal having two or more different wavelengths generated by the generating means is transmitted to the subscriber device, The modulation means of the user apparatus can modulate the uplink signal having two or more different wavelengths transmitted from the in-station apparatus with the audio signal.

  The subscriber unit further includes high frequency modulation means for performing high frequency modulation on an upstream signal having two or more different wavelengths modulated by the audio signal, and the two modulated by the audio signal modulated by the high frequency modulation means. The uplink signals having the different wavelengths are transmitted to the intra-station apparatus, and the separation unit of the intra-station apparatus has two or more different wavelengths modulated by the high-frequency modulated voice signal transmitted from the subscriber apparatus. The upstream signal can be separated into signals for each subscriber apparatus by blind sound source separation.

  The intra-station device further includes a high-frequency modulation means for performing high-frequency modulation on an upstream signal having two or more different wavelengths modulated by the audio signal, and the separation means of the intra-station device is an audio signal that is high-frequency modulated by the high-frequency modulation means Uplink signals having two or more different wavelengths modulated by the above can be separated into signals for each subscriber unit by blind sound source separation.

  The intra-station device further includes high-frequency modulation means for high-frequency modulating upstream signals having two or more different wavelengths, and the upstream signals having two or more different wavelengths modulated by the high-frequency modulation means are transmitted to the subscriber device. The separating means of the in-station device transmitted transmits the upstream signal having two or more different wavelengths, which are modulated by the high frequency modulation means modulated by the voice signal and transmitted from the subscriber device, by blind source separation. Can be separated into signals for each person device.

  The in-station device may further include a demodulating unit that demodulates a signal for each subscriber unit separated by the blind sound source separation by the separating unit and extracts a voice signal.

  The frequency at which the high frequency modulation is performed can be ½ or less of the reciprocal of the difference in the amount of time delay caused by the difference in the amount of chromatic dispersion generated between the upstream signal lights from the plurality of subscriber apparatuses.

  According to the present invention, an upstream signal can be separated by a blind sound source separation technique in an optical access system.

Hereinafter, an optical access system according to an embodiment of the present invention will be described with reference to the drawings. This optical access system is, for example, PON (Passive
Configure the Optical Network system.

[First Embodiment]
FIG. 1 is a block diagram showing a configuration example of an optical access system according to an embodiment of the present invention.

  In this optical access system, N subscriber units 12-1 to 12-N (hereinafter referred to simply as subscriber units 12 if they do not need to be individually distinguished) are the same in other cases. An intra-station device 15 is connected via an optical fiber 13 and a power splitter 14.

Each of the N subscriber apparatuses 12-1 to 12- _N is supplied with subscriber's voice signals S _{1 to} S _N provided via the voice generators 11-1 to 11-N. The subscriber unit 12-1 includes M (integer of 2 or more) laser transmission units 21-1 to 21-M, a multiplexing unit 22, and an audio / optical modulation unit 23. Here, only the configuration necessary for uplink communication from the subscriber unit 12 to the intra-station device 15 is shown.

Laser transmitting unit 21 - 1 to 21-M of the M sends the optical signals of different wavelengths lambda ₁ to [lambda] _M, respectively. The optical signal transmitted by the laser transmission unit 21 is input to the multiplexing unit 22. The number M of types of wavelengths λ used can be any number greater than or equal to 2, but in order to reduce the cost of providing the laser transmitter 21, the relationship with the number N of subscriber devices 12 In this case, it is desirable that M ≦ N.

  The multiplexing unit 22 multiplexes the input optical signals from the laser transmission units 21-1 to 21 -M and outputs the multiplexed optical signal to the audio / optical modulation unit 23.

In addition to the optical signal from the multiplexing unit 22, the audio / light modulation unit 23 also receives the audio signal S ₁ supplied from the audio generation unit 11-1 to the subscriber device 12-1. The audio / light modulator 23 modulates the intensity of the input optical signal based on the change in the amplitude of the input audio signal S ₁ .

Optical signal modulated by audio signals S ₁ by the audio / optical modulation section 23 is transmitted to the optical fiber 13 as an upstream signal light.

That is, in the subscriber unit 12-1, the upstream signal light having M types of wavelengths is modulated by the voice signal S ₁ supplied from the voice generation unit 11-1 to the subscriber unit 12-1, and is transmitted to the optical fiber 13. Sent out.

Other subscriber units 12-2 (not shown) to 12-N are configured in the same manner as the subscriber unit 12-1. That is, in the subscriber devices 12-2 to 12-N, the upstream signal light having M kinds of wavelengths is transmitted from the sound generators 11-2 (not shown) to 11-N to the subscriber devices 12-2 to 12-N. Are modulated by the audio signals S ₂ (not shown) to S _N supplied to the optical fiber 13 and transmitted to the optical fiber 13.

  In FIG. 1 and the drawings to be described later, only the configurations of the subscriber devices 12-1 and 12-N are illustrated. The components of the subscriber device 12-N include the components of the corresponding subscriber device 12-1. The same reference numerals are given.

  The power splitter 14 mixes the upstream signal light transmitted from the subscriber units 12-1 to 12-N to the optical fiber 13. The upstream signal light from the subscriber devices 12-1 to 12 -N mixed by the power splitter 14 reaches the in-station device 15.

  The in-station device 15 includes a demultiplexing unit 31, M receiving units 32-1 to 32-M, M AD converting units 33-1 to 33-M, and a signal processing unit 34. Here, only the configuration necessary for uplink communication is shown.

The demultiplexing unit 31 demultiplexes the upstream signal light from each of the subscriber devices 12 that has been mixed by the power splitter 14 and has reached the intra-station device 15 for each of the wavelengths λ ₁ to λ _M, and the upstream signal of each wavelength λ. It outputs to the receiving units 32-1 to 32-M that receive light. Each of the reception units 32-1 to 32-M converts the received upstream signal light into an electrical signal and outputs the electrical signal to the corresponding AD conversion units 33-1 to 33-M. The AD conversion units 33-1 to 33-M convert the analog electric signal input from the receiving unit 32 into a digital electric signal and output the digital electric signal to the signal processing unit 34.

The signal processing unit 34 performs processing based on blind sound source separation technology (hereinafter referred to as blind sound source separation processing) based on the electrical signals input from the AD conversion units 33-1 to 33-M, and the audio signal S as ₁ to S _N, separates the separated signals y ₁ ~y _N.

That is, in the intra-station device 15, the upstream signal light from each of the subscriber devices 12 that has been mixed by the power splitter 14 and has reached the intra-station device 15 is demultiplexed for each of the wavelengths λ _{1 to} λ _M and converted into a digital signal. in the processing unit 34, a blind source separation process, as an audio signal S ₁ to S _N, the separation signals y ₁ ~y _N are separated.

For example, when the distance between a certain subscriber device 12 and the power splitter 14 and the distance between another certain subscriber device 12 and the power splitter 14 are different, the amount of chromatic dispersion generated between those subscriber devices 12 and the power splitter 14 is Each takes a different value. Further, a delay occurs in the time until the intra-station device 15 receives the signal depending on the amount of chromatic dispersion. Therefore, between the received signals of the same wavelength (for example, λ 1) transmitted from the subscriber devices 12 (for example, the subscriber devices 12-1 and 12 -M) having different distances between the power splitters 14, A delay difference corresponding to the difference in the amount of chromatic dispersion of each signal according to the distance is generated. Therefore, the delay difference between the signals for each wavelength caused by the difference in the chromatic dispersion amount is equivalent to the delay difference in the example of FIG. 22 as the feature amount in the blind sound source separation technique. Therefore, the signal processing unit 34 performs blind sound source separation processing using a delay difference due to a difference in chromatic dispersion amount as a feature amount. For example, in the case of description corresponding to the configuration of FIG. 22, each audio signal S _{1 to} S _N corresponds to a situation in which each of the M wavelengths λ is observed. Thus, the blind sound source separation technique can be applied.

That is, a _ij and τ _ij of the observation signal x _j represented by the expression (1) are the delay difference due to the attenuation of the audio signal S _{i at} the receiving unit 32-j and the difference of the chromatic dispersion amount.

In addition, for example, the feature amount (that is, the difference in chromatic dispersion amount) expressed by the equation (2) when the wavelength λ is two types is calculated at all the time frequencies f and t (where x _j ( f, t) is obtained by subjecting the observation signal x _j (t) to a short-time Fourier transform), and this feature quantity is then clustered.

Each cluster C _i corresponds to a respective audio signal S _i . Based on the clustering result, a time-frequency mask is calculated by the equation (3), and using the time-frequency mask, a separated signal in the time-frequency domain is obtained by the equation (4), for example.

  The separated signal in the time frequency domain is converted into a signal in the time domain by inverse short-time Fourier transform, and a final separated signal y is obtained.

  In the case of this example, the relationship of M ≦ N is established in the number N of subscriber devices 12 and the number M of types of wavelengths λ. The N sound generators 11 are statistically independent from each other, and each signal is assumed to be sufficiently sparse. In other words, the preconditions necessary for using the blind sound source separation technology are established.

  As described above, each subscriber unit 12 modulates an upstream signal having two or more different wavelengths with an audio signal and transmits it to the optical fiber 13, and the in-station unit 15 is mixed by the power splitter 14. The upstream signals having two or more different wavelengths modulated by the voice signals by the plurality of subscriber devices 12 are demultiplexed for each wavelength, and the blind sound source separation process is performed using the delay difference due to the difference in the chromatic dispersion amount as the feature amount. Therefore, the voice signal from the voice generator 11 (ie, the sound source) in a different space can be separated from the voice signal of the subscriber device 12 by, for example, blind sound source separation processing.

  In the above description, the upstream signal light is modulated by the audio / light modulation unit 23 (that is, the external modulator), but each laser transmission unit 21 may be directly modulated (direct light modulation method).

Further, in order to suppress beat noise generated in the upstream signal, a laser transmitter 21 having a line width of about several nm can be used. For example, ASE (Amplified Spontaneous Emission) light source and SLD (Super
Luminescent Diode) can be used.

  FIG. 2 is a block diagram illustrating a configuration example of the subscriber device 12 when the laser transmission unit 21 is configured by an ASE light source or an SLD.

  If the laser transmitter 21 is composed of an ASE light source or an SLD, a broadband optical signal can be oscillated, so that the laser transmitter 21 can be integrated as shown in FIG. In this case, the demultiplexing unit 41 is provided between the multiplexing unit 22 and the audio / optical modulation unit 23, and the demultiplexing unit 41 generates two or more different wavelengths λ having a line width of about several nm. It is taken out.

  It is preferable that a large amount of chromatic dispersion can be obtained due to the relationship between the difference in chromatic dispersion and the bit resolution necessary for detecting the amount of time delay. In order to obtain a large amount of chromatic dispersion, a wider wavelength interval is better. For example, light of around 1300 nm and 1580 nm needs two waves with a width of about 3 nm. However, an actual wide wavelength band light source cannot cover all of these wavelengths. For example, the width is several tens of nm at the center of 1300 nm, 1550 nm, or 1575 nm, or about 100 nm width even if another light source is used. Therefore, as shown in FIG. 3, the wavelength interval can be widened by preparing two (or more) laser transmitters 21 including ASE light sources and SLDs.

  Further, as shown in FIG. 4, the multiplexing unit 22 and the demultiplexing unit 41 in the example of FIG. 2 can be omitted. By not providing the multiplexing unit 22 and the demultiplexing unit 41, the members of the user device 21 can be further reduced.

  In addition, although only the configuration necessary for the uplink communication is shown in the subscriber device 12 and the intra-station device 15 in FIGS. 1 to 4 and the drawings to be described later, actually, the configuration necessary for the downlink communication is also provided. It has been. For example, as in a general optical access system, a laser transmission unit for downlink communication is provided on the in-station device 15 side, and a receiving unit is provided on the subscriber device 12 side, and both the in-station device 15 and the subscriber device 12 are provided. In addition, a multiplexing / demultiplexing unit for multiplexing / demultiplexing the upstream signal light and the downstream signal light is provided.

[Second Embodiment]
FIG. 5 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention. Again, only the configuration necessary for uplink communication is shown. Note that in the figure showing another configuration example of the optical access system described later, only the configuration necessary for uplink communication is shown.

  In this optical access system, delay lines 51-1 to 51-N are provided between each subscriber unit 12 and the power splitter 14 shown in FIG. Other configurations are the same as those in the example of FIG.

  In the example of FIG. 1 (that is, the first embodiment), the delay difference depends only on the distance between each subscriber device 12 and the power splitter 14, but in this way, between the subscriber device 12 and the power splitter 14. Different delay lines 51 may be provided depending on the subscribers to increase the delay difference.

  Even in the case where the distance difference between each subscriber unit 12 and the power splitter 14 is small and a minute delay can be taken, it is possible to have a large delay difference by arranging the delay line 51 in this way.

  In addition, even when the distance between the subscriber unit 12 and the power split 14 is exactly the same, it becomes possible to use the delay line 51 to have different delay differences.

  The delay line 51 can also be installed in the subscriber unit 12.

[Third Embodiment]
FIG. 6 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the laser transmission unit 21 and the multiplexing unit 22 are deleted from the subscriber unit 12 shown in FIG. 1, and the M laser transmission units 61 and the multiplexing unit 62 and the directionality are added to the in-station device 15. A demultiplexing unit 63 is provided. Other configurations are the same as those in FIG.

  In the example of FIGS. 1 and 2 (first embodiment) and the example of FIG. 5 (second embodiment), the upstream signal light is generated by the subscriber unit 12, but in this embodiment, The upstream signal is generated by the M laser transmitting units 61 and the multiplexing unit 62 in the in-station device 15, and the upstream signal light (unmodulated signal light) is transmitted to each subscriber via the directional demultiplexing unit 63. A loop-back configuration is adopted in which the subscriber device 12 transmits the signal to the device 12 and modulates the uplink signal with an audio signal and returns it to the in-station device 15.

  Specifically, the upstream signal light transmitted from the intra-station device 15 reaches each subscriber device 12 via the power splitter 14. The upstream signal light reaching each subscriber device 12 is modulated by the audio signal S in the audio / light modulation unit 23 of each subscriber device 12. By making the audio / light modulator 23 in this case a reflective structure, the modulated upstream signal light is transmitted to the in-station device 15 side via the power splitter 14. The upstream signal light reaching the in-station device 15 is received by the receiving unit 32 via the directional demultiplexing unit 63 and the demultiplexing unit 31.

  Since the laser transmitter 61 and the like are placed in the intra-station device 15 in this way, the members (the laser transmitter 21 and the multiplexer 22) of the subscriber device 12 can be reduced, and the cost of the subscriber device 12 can be reduced. Can be achieved.

  Here, the audio / light modulation unit 23 of the subscriber unit 12 has a reflection type structure, but it can also have a loop type structure using a directional branching unit 71 as shown in FIG.

  Further, in order to suppress beat noise generated in the upstream signal, a laser transmitter 61 of the in-station device 15 having a line width of about several nm can be used. For example, an ASE light source or SLD can be used.

  FIG. 8 is a block diagram illustrating a configuration example of the in-station device 15 when the laser transmission unit 61 is configured by an ASE light source or SLD.

  If the laser transmission unit 61 is composed of an ASE light source or an SLD, a broadband optical signal can be oscillated, so that the number of laser transmission units 61 can be one as in the case of FIG. In this case, a demultiplexing unit 81 is provided between the laser transmission unit 61 and the multiplexing unit 62, and two or more different wavelengths λ having a line width of about several nm are extracted by the demultiplexing unit 81.

  Similarly to the case shown in FIGS. 3 and 4, as shown in FIGS. 9 and 10, two (or more) laser transmitters 21 including an ASE light source and an SLD can be provided. The multiplexing unit 22 and the demultiplexing unit 41 in the example of 8 can be omitted. By not providing the multiplexing unit 22 and the demultiplexing unit 41, the members of the user device 21 can be further reduced.

[Fourth Embodiment]
FIG. 11 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, a modulation signal generator 91 is provided in each subscriber device 12 shown in FIG. 1, and M demodulation units 101-1 to 101-M are provided in the in-station device 15. Other configurations are the same as those in the example of FIG.

  In the example of FIG. 5 (second embodiment), the delay line 51 is installed to increase the delay difference and the blind sound source separation technique is applied. However, in this embodiment, high-frequency modulation is performed. The audio signal is separated so that a minute delay difference can be directly observed.

  On the subscriber device 12 side, the upstream signal light is intensity-modulated with the audio signal S and then further intensity-modulated with a high-frequency signal. Alternatively, intensity modulation is performed in the reverse order. As a result, the upstream signal light is intensity-modulated with the product signal of the audio signal and the high frequency signal.

  In the example of FIG. 11, a signal having a frequency higher than that of the audio signal is supplied from the modulation signal generation unit 91 to the audio / light modulation unit 23. That is, the upstream signal light having M types of wavelengths modulated by the voice signal S supplied from the voice generation unit 11 to the subscriber device 12 is further modulated to a high frequency.

  The upstream signal light of each subscriber device 12 generated in this way is mixed by the power splitter 14 and reaches the in-station device 15. The upstream signal light reaching the in-station device 15 is demultiplexed by the demultiplexing unit 31 for each wavelength λ, received by the receiving unit 32, converted into a digital signal by the AD conversion unit 33, and sent to the signal processing unit 34.

In the signal processing unit 34, the audio signal is separated into audio signals modulated in high frequency by blind sound source separation processing, demodulated by the demodulation unit 101, and audio signals y _{1 to} y _N as audio signals S _{1 to SN.} Is extracted.

Here, the effect of high frequency modulation will be described. For example, assuming that two signals having the same frequency and shifted in time are sin (2πft) and sin {2πf (t + Δt)}, the amplitude difference between the two signals is expressed by Expression (5).
f (t) = sin (2πft) −sin {2πf (t + Δt)} (5)

The maximum value of Equation (5) is as shown in Equation (6).

Therefore, if the time difference Δt is constant, the maximum value of the amplitude difference between the two signals increases as the frequency f increases, and the number of AD conversion quantization bits for discriminating the difference between the two signals can be reduced. When the minimum number of quantization bits necessary for obtaining the phase difference between two signals in AD conversion is n, the relationship shown in Expression (7) is established.

  Therefore, by modulating the audio signal at high frequency and converting the signal frequency to high frequency, the value on the left side of the equation (7) can be increased, and the number of quantization bits n can be reduced to a small delay difference. Can be directly observed by AD conversion with a small number of quantization bits.

  FIG. 12 is a diagram showing the relationship between the distance resolution and the bit resolution required for AD conversion. The horizontal axis represents the distance resolution converted from the delay time, and the vertical axis represents the bit resolution required for AD conversion. FIG. 12 also shows the capacities LL1 and LL2 of a commercially available AD converter having a sampling rate of 10 kHz and a sampling rate of 10 MHz.

  The line L1 shows the relationship between the distance resolution and the bit resolution required for AD conversion when the high frequency modulation is not applied, and the line L2 is the high frequency modulation (4 MHz high frequency modulation in this example).

  In the optical access service using the PON system, it is assumed that the subscriber's house is adjacent, so the distance resolution is required to be in the meter order. From FIG. 12, according to the line L1, when high frequency modulation is not applied, the bit resolution required to obtain the distance resolution of the meter order is about 26 bits. However, for AD conversion at a sampling rate of 10 kHz, since only an AD converter of about 24 bits is currently available (LL1), a commercially available AD converter cannot be used when high frequency modulation is not performed. On the other hand, according to the line L2, when high frequency modulation is applied, the bit resolution required to obtain a distance resolution on the order of meters is about 14 bits, and the required bit resolution is reduced by about 12 bits compared to the case where high frequency modulation is not performed. As for AD conversion at a sampling rate of 10 MHz, a 16-bit AD converter is currently available on the market (LL2). By applying high-frequency modulation, a meter-order resolution can be realized using a commercially available AD converter. Is possible.

  If the frequency for high-frequency modulation is set to a frequency equal to or less than 1/2 of the reciprocal difference in the amount of time delay caused by the difference in chromatic dispersion generated between two different upstream signal lights, a spatial aliasing phenomenon occurs. In addition, the blind sound source separation technique can be accurately applied even at the maximum distance of the optical access system. The spatial aliasing phenomenon is described in “acoustic system and digital processing” (p. 180 of Toshiro Oga, Yoshio Yamazaki, Yutaka Kaneda, The Institute of Electronics, Information and Communication Engineers, 1995).

  By performing high frequency modulation, the above effects can be obtained.

  In the above description, the audio / optical modulation unit 23 (that is, the external modulator) performs audio modulation and high-frequency modulation, but each laser transmission unit 21 may be directly modulated (direct optical modulation method).

[Fifth Embodiment]
FIG. 13 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the modulation signal generator 91 connected to the audio / optical modulator 23 of the subscriber device 12 shown in FIG. 11 is connected to the preceding stage of each laser transmitter 21. Other configurations are the same as those in the example of FIG.

  In the example of FIG. 11 (ie, the fourth embodiment), high-frequency modulation is performed at the optical stage, but in this embodiment, high-frequency modulation is performed at the electrical stage before the laser transmitter 21.

[Sixth Embodiment]
FIG. 14 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the modulation signal generation unit 91 provided in the subscriber device 12 of FIGS. 11 and 13 is provided as the modulation signal generation unit 111 in the in-station device 15. In the intra-station device 15, M modulation units 112-1 to 112-M are also provided. Other configurations are the same as those in the example of FIGS.

  In the example of FIG. 11 (ie, the fourth embodiment) and the example of FIG. 13 (ie, the fifth embodiment), high-frequency modulation is performed on the subscriber unit 12 side. High frequency modulation is performed on the 15 side.

  Since the modulation signal generator 111 and the like are provided in the in-station device 15 in this way, the members of the subscriber device 12 can be reduced, and the cost can be reduced.

[Seventh Embodiment]
FIG. 15 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the modulation signal generation unit 111 and the modulation unit 112 that are installed in the previous stage of the reception unit 32 of the intra-station device 15 illustrated in FIG. 14 are provided in the subsequent stage of the reception unit 32. Other configurations are the same as those in the example of FIG.

  In the example of FIG. 14 (ie, the sixth embodiment), high-frequency modulation is performed in the optical stage upstream of the receiving unit 32. In this embodiment, high-frequency modulation is performed in the electrical stage subsequent to the receiving unit 32. Has been done.

[Eighth Embodiment]
FIG. 16 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, M laser transmitters 21 and multiplexers 22 are deleted from the subscriber unit 12 shown in FIG. 11, and the M laser transmitters 61 and multiplexers 62 are added to the in-station device 15. In addition, a directional branching unit 63 is provided.

  In the example of FIG. 11 (that is, the fourth embodiment), the upstream signal light is generated in the subscriber unit 12, but in this embodiment, the upstream signal is transmitted to the M laser transmitting units in the in-station device 15. 61 and the multiplexing unit 62, the upstream signal light (unmodulated signal light) is transmitted to the subscriber device 12 via the directional demultiplexing unit 63, and the subscriber device 12 converts the upstream signal into voice. A loopback configuration in which the signal is modulated by the signal and returned to the in-station device 15 is employed.

[Ninth Embodiment]
FIG. 17 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the modulation signal generator 91 connected to the audio / optical modulator 23 of the subscriber device 12 shown in FIG. 16 is provided in front of the audio / optical modulator 23 together with the modulator 112. ing. Other configurations are the same as those in the example of FIG.

  In the example of FIG. 16 (that is, the eighth embodiment), the modulation signal generator 91 is connected to the audio / light modulator 23 and high frequency modulation is performed at the optical stage. However, in this embodiment, the audio / light High frequency modulation is performed in an electrical stage preceding the modulation unit 23.

[Tenth embodiment]
FIG. 18 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the modulation signal generator 91 is deleted from the subscriber device 12 shown in FIG. 16, or the modulation signal generator 91 and the modulator 112 are deleted from the subscriber device 12 shown in FIG. 16 and the intra-station device 15 of FIG. 17 are provided with M modulation signal generators 111 and M modulation units 112.

  In the example of FIG. 16 (that is, the eighth embodiment) and the example of FIG. 17 (that is, the ninth embodiment), high-frequency modulation is performed on the subscriber unit 12 side. High frequency modulation is performed on the side.

  Since the modulation signal generator 111 and the like are provided in the in-station device 15 in this way, the members of the subscriber device 12 can be reduced, and the cost can be reduced.

[Eleventh embodiment]
FIG. 19 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the modulation signal generation unit 111 and the modulation unit 112 that are installed in the previous stage of the reception unit 32 of the intra-station device 15 illustrated in FIG. 18 are provided in the subsequent stage of the reception unit 32. Other configurations are the same as those in the example of FIG.

  In the example of FIG. 18 (that is, the tenth embodiment), the modulation signal generation unit 111 and the modulation unit 112 are installed in the front stage of the reception unit 32 of the in-station device 15 and high frequency modulation is performed in the optical stage. In this form, high frequency modulation is performed in the electrical stage subsequent to the receiving unit 32.

[Twelfth embodiment]
FIG. 20 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the modulation signal generation unit 111 and the modulation unit 112 installed in the previous stage of the reception unit 32 of the intra-station device 15 shown in FIG. 18 or the rear stage of the reception unit 32 of the intra-station device 15 shown in FIG. The modulation signal generation unit 111 and the modulation unit 112 that have been provided are installed in the preceding stage of the laser transmission unit 61, and high-frequency modulation is performed during transmission. Other configurations are the same as those in the example of FIGS.

  In the example of FIG. 18 (the tenth embodiment) and the example of FIG. 19 (the eleventh embodiment), high frequency modulation is performed on the receiving side of the intra-station device 15, but in this embodiment, when transmitting an uplink signal High frequency modulation is performed.

[Thirteenth embodiment]
FIG. 21 is a block diagram showing another configuration example of the optical access system according to the embodiment of the present invention.

  In this optical access system, the modulation signal generation unit 111 installed in the subsequent stage of the laser transmission unit 61 of the in-station device 15 shown in FIG. 20 is provided in the previous stage of the laser transmission unit 61, and the modulation unit 112 is deleted. . Other configurations are the same as those in the example of FIG.

  In the example of FIG. 20 (that is, the twelfth embodiment), high-frequency modulation is performed by the modulation signal generation unit 111 and the modulation unit 112 installed at the subsequent stage of the laser transmission unit 61 (that is, at the optical stage). In this embodiment, high-frequency modulation is performed by the modulation signal generation unit 111 installed in the previous stage of the laser transmission unit 61 (that is, in the electrical stage).

  11 and 13 to 21 are provided with the demodulator 101, but without the demodulator 101, an audio signal modulated by a high frequency is output as it is. The in-station device 15 can also be configured.

1 is a block diagram showing a configuration example of a first embodiment of an optical access system to which the present invention is applied. FIG. It is a block diagram which shows the other structural example of 1st Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the other structural example of 1st Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the other structural example of 1st Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 2nd Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 3rd Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the other structural example of 3rd Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the other structural example of 3rd Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the other structural example of 3rd Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the other structural example of 3rd Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 4th Embodiment of the optical access system to which this invention is applied. It is a figure which shows the relationship between distance resolution and the bit resolution calculated | required by AD conversion. It is a block diagram which shows the structural example of 5th Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 6th Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 7th Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 8th Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 9th Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 10th Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 11th Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 12th Embodiment of the optical access system to which this invention is applied. It is a block diagram which shows the structural example of 13th Embodiment of the optical access system to which this invention is applied. It is a figure which shows a blind sound source separation technique notionally. It is a figure which shows the structural example of a PON system.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 Audio | voice generating part, 12 Subscriber apparatus, 13 Optical fiber, 14 Power splitter, 15 In-station apparatus, 21 Laser transmission part, 22 Multiplexing part, 23 Voice / light modulation part, 31 Demultiplexing part, 32 Receiving part, 33 AD Conversion unit, 34 signal processing unit, 41 demultiplexing unit, 51 delay line, 61 laser transmission unit, 62 multiplexing unit, 63 directional demultiplexing unit, 71 directional demultiplexing unit, 81 demultiplexing unit, 91 modulation signal generation , 101 demodulator, 111 modulation signal generator, 112 modulator, 121 modulator

Claims (9)

In an optical access system comprising an intra-station device and a subscriber unit connected via an optical transmission line and a power splitter,
The subscriber device is
Modulation means for modulating an upstream signal having two or more different wavelengths with an audio signal;
The intra-station device has a separating means for performing blind sound source separation for signal separation,
The separating means converts the upstream signals having two or more different wavelengths, which are mixed by the power splitter and modulated by the sound signals by the modulating means of the plurality of subscriber devices, into the subscribers by the blind sound source separation. An optical access system characterized in that it is separated into signals for each device. The optical access system according to claim 1, wherein a delay line is installed between the subscriber unit and the power splitter. The subscriber unit further includes generating means for generating an upstream signal having the two or more different wavelengths,
3. The optical access according to claim 1, wherein the modulation unit of the subscriber unit modulates the upstream signal having the two or more different wavelengths generated by the generation unit with the voice signal. 4. system. The intra-station device further includes generating means for generating an upstream signal having the two or more different wavelengths,
The upstream signal having the two or more different wavelengths generated by the generating means is transmitted to the subscriber unit,
3. The light according to claim 1, wherein the modulation unit of the subscriber unit modulates the upstream signal having the two or more different wavelengths transmitted from the intra-station device with the audio signal. 4. Access system. The subscriber unit further includes high-frequency modulation means for performing high-frequency modulation on upstream signals having two or more different wavelengths modulated by the audio signal,
Upstream signals having two or more different wavelengths modulated by the audio signal modulated at high frequency by the high frequency modulation means are transmitted to the intra-station device,
The separation means of the intra-station device transmits the uplink signal having two or more different wavelengths modulated by the high-frequency modulated voice signal transmitted from the subscriber device by the blind sound source separation. The optical access system according to claim 3 or 4, wherein the optical access system is separated into signals for each user device. The intra-station apparatus further includes a high-frequency modulation means for performing high-frequency modulation on an upstream signal having two or more different wavelengths modulated by the audio signal,
The separation unit of the intra-station device converts an upstream signal having two or more different wavelengths modulated by the voice signal modulated by the high frequency modulation unit into a signal for each subscriber unit by the blind sound source separation. The optical access system according to claim 3 or 4, wherein the optical access system is separated. The intra-station device further includes high-frequency modulation means for performing high-frequency modulation on upstream signals having two or more different wavelengths,
The upstream signal having the two or more different wavelengths modulated by the high frequency modulation means is transmitted to the subscriber unit,
The separation unit of the intra-station device transmits an upstream signal having two or more different wavelengths, which are modulated by the high frequency modulation unit modulated by the audio signal, transmitted from the subscriber unit, and having two or more different wavelengths. The optical access system according to claim 4, wherein the signal is separated into signals for each subscriber device by separation. 8. The intra-station device further comprises demodulation means for demodulating a signal for each of the subscriber devices separated by the blind sound source separation by the separation means, and extracting the voice signal. Optical access system as described in. The frequency at which the high-frequency modulation is performed is ½ or less of the reciprocal of the difference in the amount of time delay caused by the difference in the amount of chromatic dispersion generated between the upstream signal lights from the plurality of subscriber devices. The optical access system according to 5 to 8.

Images