JP5700562B2 - Optical transmission system - Google Patents

Description

  The present invention relates to an optical transmission system that transmits and receives an OFDM signal.

  Research and development for transmitting and receiving OFDM (Orthogonal Frequency Division Multiplexing) signals on an optical transmission system typified by a PON (Passive Optical Network) system has been actively conducted. The OFDM signal can be generated by IFFT (Inverse Fast Fourier Transform) operation, and the signal can be decoded by FFT (Fast Fourier Transform) operation. With the improvement of signal processing technology and integrated circuit technology, OFDM was used. Expectations for optical transmission systems are increasing.

  The PON system is an optical transmission system including one OLT (Optical Line Terminal), a plurality of ONUs (Optical Network Units), and an optical transmission cable connecting these. The distance from the OLT to the ONU and the transmission loss in the optical transmission path vary depending on the ONU. For this reason, when transmitting an OFDM signal in a PON system, it is necessary to design so that the signal can be correctly received by an ONU having the largest transmission path loss.

  When an OFDM signal is used as a downstream signal of a PON system, that is, an OLT-to-ONU signal, an OLT that is an OFDM optical signal transmitter generates an OFDM signal, and an ONU that is an OFDM optical signal receiver is a signal processor that decodes the OFDM signal Realized by technology.

  An increase in power consumption is a problem in a PON system using an OFDM signal. Depending on the number of carriers used, the circuit scale of IFFT / FFT operation in the OFDM optical signal transmitter / receiver increases, and the power consumption increases. So far, the power consumption of the OFDM optical signal transmitter / receiver has been reduced by simplifying the IFFT / FFT arithmetic unit and improving the integrated circuit technology.

  So far, OFDM has been actively researched in the field of wireless communication. It is known that the OFDM signal is related to the calculation accuracy of IFFT / FFT operation, transmission loss, and OFDM signal transmission bit error rate. As shown in FIG. 11, the signal generated by the OFDM signal transmitting apparatus reaches the OFDM signal receiving apparatus via the transmission path. At this time, the IFFT arithmetic unit 102 of the OFDM signal transmitting apparatus 10 has an arithmetic error corresponding to the arithmetic precision of the IFFT calculation, a transmission error due to transmission loss in the transmission path, and the FFT arithmetic units 112 to 122 of the OFDM signal receiving apparatuses 11 to 12. However, if the sum of these errors is less than a certain value, the OFDM signal receiving device 12 can correctly demodulate the signal, resulting in an OFDM signal transmission bit error. The rate does not increase.

  For example, as a value corresponding to √2, consider 1.41 with a small effective digit number and 1.4142 with a large effective digit number. These values are given as input data for IFFT calculation, and a signal is transmitted via the transmission path. The OFDM signal receiving apparatus receives a signal that has deteriorated according to the transmission loss of the transmission path. In the example of FIG. 11, an error of 0.001 is applied to the signal after the FFT calculation in the OFDM signal receiving apparatus 11 with a small transmission loss, and an error of 0.1 is applied to the signal after the FFT calculation in the OFDM signal receiving apparatus 12 with a large transmission loss. It is assumed that no error occurs in the FFT operation. Whether or not demodulation is possible depends on whether or not the total value of errors resulting from IFFT calculation, transmission loss, and FFT calculation is equal to or less than a certain value. In the example of FIG. 11, if it is assumed that a signal in the range of 1.3142 to 1.5142 can be demodulated correctly, an OFDM signal received in an environment with a small number of effective bits and a large transmission loss cannot be demodulated correctly.

  From the background as described above, it has been found that it is possible to control the OFDM signal transmission bit error rate by adjusting the calculation accuracy by controlling the number of effective bit digits of IFFT / FFT calculation.

  Non-Patent Document 1 proposes a method of controlling the signal transmission bit error rate and the power consumption by controlling the calculation accuracy for each calculation stage of a two-input butterfly calculator used for IFFT / FFT calculation. FIG. 12 shows a variable precision IFFT calculator 20 shown in Non-Patent Document 1. The number of significant bits of the input signal given to the butterfly calculator is controlled by the calculation precision converter to change the calculation precision. By reducing the number of effective bits, it is not necessary to perform calculations related to the lower bits of the butterfly calculator, and power consumption can be expected to be reduced.

  In Non-Patent Document 1, the number of effective bit digits of butterfly computation is controlled for each computation stage. Therefore, the valid bit digits of the input data in the butterfly calculators 221 and 222 are X bits, and the valid bit digits of the input data in the butterfly calculators 241 and 242 are valid of the input data to be given to the butterfly calculator. The number of bit digits is not necessarily the same for all butterfly computing units. Non-Patent Document 1 shows that the OFDM signal transmission error rate depends on the number of effective bit digits of the butterfly operation stage.

  Non-Patent Document 1 is directed to a wireless mobile transmission system. In the field of wireless communication where research related to OFDM has been actively conducted so far, the transmission loss of the transmission path always changes because the terminal moves with time. Therefore, the IFFT arithmetic unit in the OFDM signal transmitting apparatus and the FFT arithmetic unit in the OFDM signal receiving apparatus need to set the calculation accuracy assuming the worst value of allowable transmission loss. In order to follow the change in transmission loss and perform communication with the lowest calculation accuracy without increasing the transmission bit error rate, the OFDM signal receiver measures the transmission loss during operation and transmits the transmission loss to the OFDM signal transmitter. Therefore, it is necessary to perform feedback control such that the OFDM signal transmission apparatus determines the number of effective bit digits of the IFFT calculation based on the transmission loss information. For this reason, a transmission loss measuring device is required during operation, and a transmission band for transmitting the transmission loss is also required.

  In Non-Patent Document 1, as shown in the calculation accuracy converter 25 of FIG. 12, the number of effective bit digits is determined by a bit mask to control the calculation accuracy. The arithmetic precision converter 25 calculates the bit logical product of the input data 251 and the bit mask 252 and sets the value of the lower bit of the data to be supplied to the arithmetic unit to 0. This eliminates the need for the arithmetic unit to perform the lower bit operation. In the method of Non-Patent Document 1, although the operation of the lower bits is made unnecessary by the bit mask, energization to the arithmetic circuit that handles the lower bits is continued. For this reason, dynamic power consumption due to transistor switching can be reduced, but static power consumption due to leakage current (leakage current) when the transistor is not operating cannot be reduced. With the miniaturization of integrated circuits, the proportion of static power consumption due to leakage current is increasing, and a significant reduction in power consumption cannot be expected only by controlling the number of effective bits using a bit mask.

  In the method of Non-Patent Document 1, the calculation accuracy is controlled for each calculation stage of the two-input butterfly calculation circuit, and the number of effective bit digits is changed for each calculation stage. In the N-point IFFT / FFT operation composed of the M input butterfly operation circuit, the number of effective bit digits must be changed N * logMN times, and many operation accuracy converters and control signals for controlling this are required.

  Furthermore, Non-Patent Document 1 is intended for an environment where only one OFDM signal transmission device and one OFDM signal reception device exist, and for an environment where a plurality of OFDM signal reception devices represented by OFDM-PON exist. Power consumption could not be reduced by calculation accuracy control. Further, when signals are simultaneously transmitted to a plurality of OFDM receivers, for example, even when signals for different OFDM signal receivers are assigned to a plurality of carriers, the calculation accuracy cannot be controlled.

Masayuki Tokunaga et al. “Study of Low Energy Consumption Method by Bit Width Control of FFT Circuit for Digital Wireless Communication”, IEICE Technical Report, SDM2005-129, ICD2005-68, pp. 7-12, August, 2005

  In order to solve the above-described problems, an object of the present invention is to reduce power consumption by designing and operating an optical transmission system according to transmission loss characteristics of an optical transmission line.

  In order to achieve the above object, an optical transmission system according to the present invention is an optical transmission system for transmitting an optical signal from an OFDM optical signal transmitting apparatus through an optical transmission line and receiving the optical signal by the OFDM optical signal receiving apparatus. An optical signal transmitting apparatus performs a subcarrier modulator that subcarrier modulates a transmission signal, and performs an IFFT operation on the data signal modulated by the subcarrier modulator with the number of bit digits determined by the transmission loss of the optical transmission path An optical signal transmitter that modulates an optical signal with an IFFT arithmetic signal of the fixed precision IFFT arithmetic unit, and transmits the modulated optical signal to the OFDM optical signal receiving device. The signal receiving apparatus includes: an optical signal receiver that receives an optical signal from the OFDM optical signal transmitting apparatus; and a signal received by the optical signal receiver in the optical transmission path. Comprising a fixed FFT processor for performing FFT operation on bit digits defined by the transmission loss, and a subcarrier demodulator for subcarrier demodulating operation signal of the FFT processor.

  In an optical transmission system typified by a PON system, unlike a wireless communication system, the apparatus does not move after the system is constructed, so that the change in transmission loss with time is small. For this reason, during operation, the transmission loss of the optical transmission line is measured in the OFDM optical signal receiver, and IFFT calculation is performed without performing feedback control for sharing information on the transmission loss between the OFDM optical signal transmitter and the OFDM optical signal receiver. The number of significant bits can be determined.

  In the present invention, it is possible to omit unnecessary calculations by determining the number of bit digits of the IFFT calculator of the OFDM optical signal transmitter and the FFT calculator of the OFDM optical signal receiver. If sleep control is performed to stop power supply at this time, dynamic power consumption due to transistor switching and static power consumption due to leakage current when the transistor is not operating can be reduced.

  In addition, when the butterfly operation is used for the IFFT arithmetic unit of the OFDM optical signal transmission device and the FFT arithmetic unit of the OFDM optical signal reception device, the control stage of the butterfly operation is not performed without performing the effective bit digit control for each operation stage of the butterfly operation. It is also possible to perform calculation accuracy conversion only on the first stage input signal. As a result, the number of effective bit digits in the N-point IFFT / FFT operation is changed to N times, so that the number of operation accuracy converters can be reduced and the control signal for the butterfly operation circuit can be simplified.

In order to achieve the above object, an optical transmission system according to the present invention transmits an optical signal from one variable precision OFDM optical signal transmission device through an optical transmission line and branches the optical signal from the spectroscope. Is transmitted by a plurality of OFDM optical signal receivers, wherein the variable precision OFDM optical signal transmitter includes a subcarrier modulator that subcarrier modulates a transmission signal, and data modulated by the subcarrier modulator. A variable precision IFFT computing unit that performs an IFFT computation with a number of bits determined by the transmission loss of the optical transmission path to the transmission destination OFDM optical signal receiving device, and an IFFT computed signal of the variable precision IFFT computing unit An optical signal transmitter for modulating an optical signal and transmitting the modulated optical signal to any one of the OFDM optical signal receivers, and receiving the plurality of OFDM optical signals The optical signal receiver that receives the optical signal from the variable precision OFDM optical signal transmitter, and the signal received by the optical signal receiver, the optical signal from the variable precision OFDM optical signal transmitter to the own apparatus. A fixed precision FFT computing unit that performs an FFT computation with the number of bits determined by the transmission loss of the transmission path, and a subcarrier demodulator that subcarrier demodulates a signal computed by the fixed precision FFT computing unit , wherein the variable precision The IFFT calculator has a transmission loss information table in which the number of bit digits determined by the transmission loss of the optical transmission path from the variable precision OFDM optical signal transmitter to the OFDM optical signal receiver is represented for each OFDM optical signal receiver. The calculation precision is determined to determine the number of bit digits corresponding to the OFDM optical signal receiving device having the minimum number of effective bits among the OFDM optical signal receiving devices of the transmission destination. It comprises a determination unit, a bit number of digits and the determination of the operation accuracy determination unit, and a variable effective bit digits IFFT calculation unit for performing IFFT operation for modulated data signals of the subcarrier modulation unit.

  In the present invention, it is possible to omit unnecessary calculations by determining the number of bit digits of the IFFT calculator of the OFDM optical signal transmitter and the FFT calculator of the OFDM optical signal receiver. If sleep control is performed to stop power supply at this time, dynamic power consumption due to transistor switching and static power consumption due to leakage current when the transistor is not operating can be reduced.

  In addition, when the butterfly operation is used for the IFFT arithmetic unit of the OFDM optical signal transmission device and the FFT arithmetic unit of the OFDM optical signal reception device, the control stage of the butterfly operation is not performed without performing the effective bit digit control for each operation stage of the butterfly operation. It is also possible to perform calculation accuracy conversion only on the first stage input signal. As a result, the number of effective bit digits in the N-point IFFT / FFT operation is changed to N times, so that the number of operation accuracy converters can be reduced and the control signal for the butterfly operation circuit can be simplified.

  Further, the optical power transmission apparatus determines the number of effective bit digits by referring to transmission loss information managed for each OFDM optical signal receiver, so that power consumption is also achieved in an optical transmission system including a plurality of OFDM signal receivers. To reduce.

  In the optical transmission system according to the present invention, the variable precision IFFT computing unit reduces the number of bit digits as the transmission loss to the transmission destination OFDM optical signal reception device decreases, and the transmission loss to the transmission destination OFDM optical signal reception device. As the value of becomes larger, the number of bit digits may be increased.

  In the optical transmission system of the present invention, the calculation accuracy determination unit outputs a sleep control signal to the variable effective bit number IFFT calculation unit having a bit number that does not correspond to a transmission destination OFDM optical signal receiver, and the sleep control The variable effective bit digit number IFFT calculation unit to which the signal is input may stop supplying power.

  In the optical transmission system according to the present invention, the subcarrier modulator includes a subcarrier modulation according to a transmission loss of the optical transmission path from the variable precision OFDM optical signal transmitting apparatus to the OFDM optical signal receiving apparatus and a required transmission rate. A subcarrier modulation scheme selection unit that selects a scheme, and a subcarrier modulation unit that subcarrier modulates a transmission signal in accordance with the subcarrier modulation scheme selected by the subcarrier modulation scheme selection unit, and the calculation accuracy determination unit includes: Determine the number of bit digits based on the transmission loss of the optical transmission path from the variable precision OFDM optical signal transmitter to the OFDM optical signal receiver and the subcarrier modulation scheme selected by the subcarrier modulation scheme selector. The data signal modulated by the subcarrier modulation unit is input to the variable effective bit digit number IFFT operation unit having the number of bit digits. It may be.

  The above inventions can be combined as much as possible.

  According to the present invention, power consumption can be reduced by designing and operating an optical transmission system according to the transmission loss characteristics of the optical transmission line.

It is a figure which shows the 1st example of the 1st optical transmission system of this invention. It is a figure which shows the 2nd example of the 1st optical transmission system of this invention. It is a figure which shows the 2nd optical transmission system of this invention which implement | achieves reduction of power consumption according to the transmission-line characteristic which consists of one OFDM optical signal transmitter and N OFDM optical signal receivers. It is a figure which shows the optical transmission system which implement | achieves reduction of power consumption according to the transmission-line characteristic which consists of N OFDM optical signal transmitters and one OFDM optical signal receiver. It is a figure which shows the variable precision IFFT calculator which has several IFFT calculators from which the number of effective bit digits differs used in the 2nd optical transmission system of this invention. It is a figure which shows the butterfly arithmetic circuit used with a variable precision IFFT arithmetic unit. It is a figure which shows the variable precision IFFT arithmetic unit which has an IFFT arithmetic unit which can be used for the 2nd optical transmission system of this invention and can control electric power supply by a calculation bit unit separately. It is a figure which shows the 3rd optical transmission system of this invention which implement | achieves reduction of a power consumption, and improvement of a transmission rate according to the transmission-line characteristic which consists of one OFDM optical signal transmitter and N OFDM optical signal receivers. . It is a figure which shows the variable precision IFFT calculator which has several IFFT calculators in which the number of effective bit digits differs from the variable subcarrier modulator used in the 3rd optical transmission system of this invention. It is a figure which shows the OFDM optical signal transmission apparatus which has an IFFT arithmetic unit which can be used for the 3rd optical transmission system of this invention and which can control an electric power supply separately for every calculation bit unit. It is a figure which shows the propriety of the calculation precision control and communication of an OFDM signal transmitter and an OFDM signal receiver. It is a figure which shows the existing method which changes the number of effective bit digits for every calculation stage of a butterfly calculation.

  Embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments described below are examples of the present invention, and the present invention is not limited to the following embodiments. In the present specification and drawings, the same reference numerals denote the same components.

(Embodiment 1)
1 and 2 show a first example and a second example of the first optical transmission system of the present invention. The first optical transmission system of the present invention is an optical transmission system in which one OFDM optical signal transmitting device and one OFDM optical signal receiving device are connected by an optical transmission cable, and the transmission path characteristics of the optical transmission cable. Reduce power consumption according to

  The present invention achieves a reduction in power consumption by controlling the calculation accuracy of the OFDM optical signal transmission device and the OFDM optical signal reception device, but in a transmission system comprising devices other than the OFDM optical signal transmission device / reception device, Power consumption can be reduced by controlling the operation mode in accordance with the transmission path characteristics.

  In a transmission system that converts a digital signal to an analog signal by a signal transmission device, transmits the analog signal via a transmission line, and demodulates the analog signal to a digital signal by a signal reception device, digital at the time of digital / analog conversion and analog / digital conversion An error occurs when the fraction processing is performed in accordance with the limit on the number of significant bits of the signal. By changing the digital signal processing method of the signal transmitting device and the signal receiving device so that the sum of the error due to this signal conversion and the error due to the transmission loss of the transmission line is below a certain value, the transmission bit error rate is reduced. It is possible to transmit a signal with minimum power consumption without increasing it.

  As shown in FIG. 1, the first example of the first optical transmission system of the present invention includes one low-precision OFDM optical signal transmission device 30, one low-precision OFDM optical signal reception device 31, and a small transmission loss. It consists of an optical transmission cable 32. The low-accuracy OFDM optical signal transmission apparatus 30 includes a series-parallel converter 301, a subcarrier modulator 302, a low-precision IFFT calculator 303, a GI (guard interval) adder 304, a D / A converter 305, and an optical signal transmitter 306. Composed.

  The subcarrier modulator 302 performs subcarrier modulation on the transmission signal from the serial / parallel converter 301. Here, the subcarrier modulation uses modulation schemes such as BPSK (Binary Phase Shift Keying), QPSK (Quadrature Phase Shift Keying), 16QAM (Quadrature Amplitude Modulation), and 64QAM. A low precision IFFT computing unit 303 as a fixed precision IFFT computing unit performs an IFFT computation on the data signal modulated by the subcarrier modulator 302 with the number of bit digits determined by the transmission loss of the optical transmission cable 32.

  The low-accuracy OFDM optical signal receiver 31 includes a parallel-serial converter 311, a subcarrier demodulator 312, a low-accuracy FFT calculator 313, a GI remover 314, an A / D converter 315, and an optical signal receiver 316. The optical signal receiver 316 receives the optical signal from the low-accuracy OFDM optical signal transmitter 30. The low-precision FFT calculator 313 as a fixed FFT calculator performs an FFT calculation on the signal received by the optical signal receiver 316 with the number of bit digits determined by the transmission loss of the optical transmission cable 32.

  As shown in FIG. 2, the second example of the first optical transmission system of the present invention includes one high-precision OFDM optical signal transmitter 33, one high-precision OFDM optical signal receiver 34, and a large transmission loss. It consists of an optical transmission cable 35. The high-precision OFDM optical signal transmission device 33 includes a serial-parallel converter 331, a subcarrier modulator 332, a high-precision IFFT calculator 333, a GI adder 334, a D / A converter 335, and an optical signal transmitter 336. The high-accuracy OFDM optical signal receiver 34 includes a parallel-serial converter 341, a subcarrier demodulator 342, a high-precision FFT calculator 343, a GI remover 344, an A / D converter 345, and an optical signal receiver 346.

  OFDM optical signal transmission bit error by selecting and installing a low-precision OFDM optical signal transmission / reception device or high-precision OFDM optical signal transmission / reception device according to the transmission loss of the optical transmission cable measured when designing the optical transmission system An optical transmission system having a function of reducing power consumption of an optical transmission system while maintaining a rate below a certain value.

  Here, a feature of the present invention is that the number of effective bit digits of input data given to the IFFT / FFT calculator of the OFDM optical signal transmitter / receiver is statically determined according to the transmission loss of the optical transmission cable. Thus, a signal that can be correctly received by the OFDM optical signal receiving apparatus is generated and transmitted with minimum power consumption without performing dynamic control during operation.

  In the OFDM optical signal transmission apparatus, a signal is generated by IFFT calculation using a finite number of bits. This finite number of bit digits limits the calculation accuracy of IFFT, and an error occurs due to fraction processing. The OFDM optical signal receiving apparatus receives a signal including an error caused by the number of effective bits of IFFT operation and an error caused by transmission loss of the optical transmission cable, and further, an error caused by the number of effective bit digits of FFT operation at the time of demodulation. Occurs. However, if the sum of these is below a certain value, the OFDM optical signal receiving apparatus can correctly demodulate the signal, and the OFDM optical signal transmission bit error rate does not increase.

  In an optical transmission system in which position information does not change, a change in transmission loss with time is small. In an optical transmission system composed of one OFDM optical signal transmitter and one OFDM optical signal receiver, the OFDM optical signal transmitter / receiver can be uniquely identified, so that IFFT / FFT operations in the OFDM optical signal transmitter / receiver Can be determined statically. This eliminates the need for switching the number of effective bit digits of IFFT / FFT operations and transmitting control information regarding the number of effective bit digits using an optical transmission cable during operation. That is, the power consumption of the optical transmission system can be reduced with only static settings without performing dynamic control during operation.

(Embodiment 2)
As shown in FIG. 3, the second optical transmission system of the present invention includes one variable precision OFDM optical signal transmitter 40, N OFDM optical signal receivers 41 to 4N, optical transmission cables 417 to 4N7, and a spectroscopic unit. It consists of a container 43.

  The signal transmitted from the variable precision OFDM optical signal transmitter 40 reaches the OFDM optical signal receivers 41 to 4N via the spectroscope 43 and optical transmission cables 417 to 4N7 having different transmission losses depending on the distance and installation environment. The spectroscope 43 branches an optical signal from one variable precision OFDM optical signal transmitter to a plurality of OFDM optical signal receivers.

  The variable precision OFDM optical signal transmission apparatus 40 includes a serial / parallel converter 401, a subcarrier modulator 402, a variable precision IFFT calculator 403, a GI adder 404, a D / A converter 405, an optical signal transmitter 406, a transmission loss information table. 407. Subcarrier modulator 402 subcarrier modulates the transmission signal. The variable precision IFFT calculator 403 determines the data signal modulated by the subcarrier modulator 402 by the transmission loss of the optical transmission path from the variable precision OFDM optical signal transmitter 40 to the destination OFDM optical signal receivers 41 to 4N. IFFT operation is performed with the number of bit digits. The optical signal transmitter 406 modulates the optical signal with the signal subjected to the IFFT calculation by the variable precision IFFT calculator 403, and transmits the modulated optical signal to any one of the OFDM optical signal receivers 41 to 4N.

  Each OFDM optical signal receiver includes an optical signal receiver, a fixed precision FFT calculator, and a subcarrier demodulator. For example, the low-accuracy OFDM optical signal receiver 41 connected via an optical transmission cable 417 with a small transmission loss includes a parallel-serial converter 411, a subcarrier demodulator 412, and a low-accuracy FFT calculator 413 as a fixed-precision FFT calculator. , A GI remover 414, an A / D converter 415, and an optical signal receiver 416. The optical signal receiver 416 receives the optical signal from the variable precision OFDM optical signal transmitter 40. The low-accuracy FFT calculator 413 determines the signal received by the optical signal receiver 416 by the transmission loss of the optical transmission path from the variable-precision OFDM optical signal transmitter 40 to the low-precision OFDM optical signal receiver 41 at the transmission destination. Performs FFT operation with the number of bits. The subcarrier demodulator 412 demodulates the signal calculated by the low precision FFT calculator 413.

  A high-precision OFDM optical signal receiving apparatus 4N connected via an optical transmission cable 4N7 having a large transmission loss includes a parallel-serial converter 4N1, a subcarrier demodulator 4N2, a high-precision FFT calculator 4N3 as a fixed-precision FFT calculator, GI It comprises a remover 4N4, an A / D converter 4N5, and an optical signal receiver 4N6. The optical signal receiver 4N6 receives the optical signal from the variable precision OFDM optical signal transmitter 40. The high-precision FFT calculator 4N3 determines the signal received by the optical signal receiver 4N6 by the transmission loss of the optical transmission path from the variable-precision OFDM optical signal transmitter 40 to the destination high-precision OFDM optical signal receiver 4N. Performs FFT operation with the number of bits. The subcarrier demodulator 4N2 demodulates the signal calculated by the high-precision FFT calculator 4N3.

  Select and install low-accuracy OFDM optical signal receiver and high-accuracy OFDM optical signal receiver according to optical transmission cable loss measured at the time of designing optical transmission system, and variable accuracy according to OFDM optical signal destination during operation A function of reducing the power consumption of the optical transmission system while maintaining the OFDM optical signal transmission bit error rate below a certain value by dynamically controlling the calculation accuracy of the variable precision IFFT calculator 403 in the OFDM optical signal transmitter 40 It comprises.

  Here, the present invention is characterized in that the number of effective bit digits of the OFDM optical signal receiver is statically determined according to the transmission loss of the optical transmission cable when designing the optical transmission system, and the OFDM optical signal transmitter is in operation. By dynamically controlling the number of significant bits of input data given to the IFFT calculator, a signal that can be correctly received by the OFDM optical signal receiver is generated, transmitted, and decoded with minimum power consumption. . The variable precision IFFT calculator 403 decreases the number of bit digits as the transmission loss to the transmission destination OFDM optical signal reception device decreases, and increases the number of bit digits as the transmission loss to the transmission destination OFDM optical signal reception device increases. To do.

  In an optical transmission system comprising one variable precision OFDM optical signal transmission device 40 represented by PON and N arbitrary precision OFDM optical signal reception devices 41 to 4N, the variable precision OFDM optical signal transmission device 40 performs variable precision IFFT computation. And a transmission loss information table 407 storing transmission loss for the OFDM optical signal receiving apparatus connected to the device 403 via the optical transmission cable. Transmission loss measurement for the OFDM optical signal receivers 41 to 4N is performed only once at the time of designing the optical transmission system, and the transmission loss information is stored in the transmission loss information table 407.

  The variable precision OFDM optical signal transmission device 40 refers to the transmission loss information table 407 at the time of data transmission, and executes IFFT calculation with the minimum number of effective bit digits that can be restored by the OFDM optical signal reception devices 41 to 4N. It is not necessary to measure the transmission loss in the OFDM optical signal receiving apparatus during operation, and it is not necessary to transmit information on the transmission loss from the OFDM optical signal receiving apparatus to the OFDM optical signal transmitting apparatus. The OFDM optical signal transmission apparatus obtains the minimum number of effective bit digits necessary for the IFFT calculation by referring to the transmission loss information table, and determines the number of effective bit digits to be given to the input of the variable precision IFFT calculator 403. The calculation accuracy of the IFFT calculator is dynamically controlled according to the OFDM optical signal transmission destination, and the power consumption required for generating the OFDM optical signal for the OFDM optical signal receiving apparatus that does not require high calculation accuracy is reduced.

  In an optical transmission system in which position information does not change, a change in transmission loss with time is small. In an optical transmission system consisting of one OFDM optical signal transmitter and N OFDM optical signal receivers, the OFDM optical signal transmitter is uniquely identified, so that the calculation accuracy of the FFT operation in the OFDM optical signal receiver is static. Can be determined. As a result, the OFDM optical signal receiving apparatus does not require switching of the effective bit digit number of the FFT operation or transmission of control information regarding the effective bit digit number using the optical transmission cable during operation. That is, the OFDM optical signal receiving apparatus does not perform dynamic control and can reduce power consumption only by static setting.

  In an environment consisting of a downstream signal of a PON system, that is, one OFDM optical signal transmitter and N optical signal receivers, the transmission loss information table of the transmission destination is referred to in the OFDM optical signal transmitter as described above. The calculation accuracy can be determined. On the other hand, the upstream signal of the PON system, that is, as shown in FIG. 4, optical transmission by arithmetic accuracy control in an environment comprising one variable precision OFDM optical signal receiver 50 and N OFDM optical signal transmitters 51 to 5N. In order to realize a reduction in power consumption of the system, restrictions are necessary.

In FIG. 4, there are two implementation methods for the FFT calculator 503 of the variable precision OFDM optical signal receiver 50.
The first is a method in which the FFT calculation accuracy of the variable accuracy OFDM optical signal receiving device 50 is set to the highest accuracy allowed in the optical transmission system. When a signal having a small effective bit number is modulated by IFFT operation and demodulated by an FFT operation having a large effective bit number, an error due to the transmission path is included in the lower bits of the demodulated signal, but an optical OFDM signal transmission device is expected. The number of valid bit digits to be guaranteed is guaranteed. Although it is the simplest implementation method, it is necessary to perform bit operations with a larger number of digits than necessary, which requires large power consumption.
The second is a method of changing the number of effective bit digits according to the time. Limit the number of OFDM optical signal transmitters that can transmit signals by time division multiplexing. For example, only a signal from the low-precision OFDM optical signal transmitter 51 is allowed at time T1, and a signal from the high-precision OFDM optical signal device 5N is allowed at time TN. As a result, the OFDM optical signal transmitter that transmitted the signal can be uniquely identified, and the number of effective bit digits of the FFT operation can be determined by referring to the transmission loss information table 507, with minimum power consumption. It becomes possible to correctly receive the OFDM optical signal.

  FIG. 5 shows a variable precision IFFT calculator 60 having a plurality of IFFT calculators having different effective bit digits numbers used in the second optical transmission system of the present invention. The variable precision IFFT calculator 60 includes a calculation precision determining unit 601, a low precision IFFT calculator 602, a high precision IFFT calculator 603, and a calculation result selector 604 that convert the calculation precision with reference to the transmission loss information table 61. .

  The low-precision IFFT calculation unit 602 and the high-precision IFFT calculation unit 603 have a function of individually stopping power supply by receiving a sleep control signal transmitted from the calculation accuracy determination unit 601. The difference between the low-precision IFFT calculation unit 602 and the high-precision IFFT calculation unit 603 is the number of effective bit digits of input data used in the butterfly calculation performed by each IFFT calculation unit. Although the error of IFFT calculation increases by reducing the number of effective bit digits, the circuit scale of the butterfly calculation constituting the IFFT calculator can be reduced, and the power consumption required for the calculation can be reduced.

  The calculation accuracy determination unit 601 receives the data signal modulated by the subcarrier modulator, refers to the transmission loss information table 61, and inputs it to the IFFT calculation unit having the number of bit digits corresponding to the transmission destination OFDM optical signal reception device. Output the data signal. In the transmission loss information table 61, the number of bit digits is determined by the transmission loss of the optical transmission cable to each OFDM optical signal receiver.

FIG. 6 shows processing performed at each calculation stage of the butterfly calculation performed by the IFFT calculator. In the case of a two-input butterfly operation in which data x (k) and data x (k + N / 2) are input, one input data x (k + N / 2) is multiplied by a twiddle factor W ^k using a multiplier 702. , X (k) + x (k + N / 2) ^* W ^k _N and x (k) −x (k + N / 2) ^* W ^k _N by performing addition / subtraction twice using the adder 703 and the subtractor 704. Are obtained.

When an OFDM signal is generated by IFFT calculation with low calculation accuracy, the number of effective bit digits given to each input of the butterfly calculation is reduced. In addition, reduces the effective bit digits twiddle factor W ^k in accordance with the input data, the calculation amount required for generating the rotation factor W ^k, the memory capacity required to store twiddle factors W ^k, and also the power consumption required for these reduced To do. In the butterfly operation circuit, addition, subtraction, and multiplication with a small number of effective bits are performed, and the operation can be executed with less power consumption by stopping the power supply to the operation circuit that handles the lower bits.

  The low-precision IFFT calculation unit 602 shown in FIG. 5 has a butterfly calculation circuit with a reduced number of effective bits, and generates an OFDM optical signal with less power consumption than when the high-precision IFFT calculation unit 603 is used. be able to.

  The number of effective bit digits of the IFFT calculation is determined by referring to the transmission loss information table 61 using the transmission destination information of the data signal subjected to subcarrier modulation, and the calculation accuracy determining unit 601 converts the number of effective bit digits of the data signal. To do. The number of effective bit digits is limited by the IFFT calculation unit existing in the variable precision IFFT calculator 60, and when generating an OFDM optical signal including data for a plurality of OFDM optical signal receivers, the OFDM optical signal with the largest transmission loss is generated. Transmission loss information for the receiving device is used.

A data signal converted from the number of valid bit digits is transmitted to an IFFT computing unit having the same number of valid bit digits, and a sleep control signal is transmitted to an unused IFFT computing unit to stop power supply. A plurality of IFFT calculators possessed by the variable precision IFFT calculator are exclusively used. Power is supplied only to the IFFT calculator that operates with the minimum calculation accuracy necessary to generate a signal that can be correctly received by the OFDM optical signal receiver, and the power supply to the other IFFT calculators is stopped. By selecting an IFFT calculator with different calculation accuracy and power consumption according to the transmission partner, a signal that can be correctly received by the OFDM optical signal receiving apparatus is generated with a minimum power consumption. Unlike changing the calculation accuracy by bit mask, multiple IFFT calculators with different power consumption are used exclusively, reducing the dynamic power consumption due to transistor switching and static due to leakage current when the transistor is not operating. Power consumption can also be reduced.
The calculation result selection unit 604 receives data from either the low precision IFFT calculation unit 602 or the high precision IFFT calculation unit 603. The received data is sent to the GI adder as it is.

  FIG. 5 shows a variable precision IFFT computing unit 60 that allows two types of effective bit digits, low precision IFFT computing unit 602 and high precision IFFT computing unit 603, as input data. By mounting the IFFT calculator and the calculation accuracy determination unit, it is possible to flexibly control the power consumption according to the transmission loss between the OFDM optical signal transmitter / receiver.

  FIG. 7 shows a variable precision IFFT arithmetic unit 80 having a butterfly arithmetic circuit that can control power supply individually in units of arithmetic bits used in the second optical transmission system of the present invention. The variable precision IFFT computing unit 80 includes a computation precision determining unit 801 that converts computation precision with reference to the transmission loss information table 81, and a variable bit digit number IFFT computing unit 802 having a function of individually controlling power supply in units of computation bits. Composed.

  By referring to the transmission loss information table 81 using the destination information of the subcarrier-modulated data signal, the number of effective bit digits of the IFFT calculation is determined, and the calculation accuracy determining unit 801 converts the number of effective bit digits of the data signal. To do. When generating an OFDM optical signal including data for a plurality of OFDM optical signal receiving apparatuses, transmission loss information of the OFDM optical signal receiving apparatus having the largest transmission loss is used.

  A data signal obtained by converting the number of effective bit digits is transmitted to the variable bit digit number IFFT calculation unit 802, and a sleep control signal is transmitted to each butterfly calculation circuit constituting the variable bit digit number IFFT calculation unit 802. The power supply to the arithmetic circuit that handles the lower bits of the arithmetic circuit is stopped. By stopping the power supply of the arithmetic circuit, dynamic power consumption caused by transistor switching is reduced, and static power consumption caused by leakage current when the transistor is not operating is also reduced. In the butterfly operation circuit constituting the variable bit number IFFT operation unit 802, the number of effective bit digits of the butterfly operation is controlled by cutting off the power supply sequentially from the circuit that handles the lower bits of the input data and the twiddle factor. By cutting off the power supply in order from the circuit that handles the lower bits, the influence of calculation errors due to the reduction in the number of effective bits is minimized.

In the N-point IFFT / FFT operation including the M input butterfly operation circuit, the number of effective bit digits needs to be changed N ^* log _M N times. When the number of carrier waves used for transmission is large, that is, when the number of input data points N for IFFT computation is large, it is necessary to transmit sleep control signals to a large number of butterfly computation circuits. When the number of individual effective bit digits is set for each butterfly operation circuit, the control signal becomes complicated. In addition, it is necessary to add information on the number of carriers and the operation stage to the transmission loss information table indicating the correspondence between the transmission loss and the number of effective bits, and the transmission loss information table is enlarged. In the present invention, the control signal is complicated and the transmission loss information table is enlarged by setting a uniform number of effective bits for all butterfly operation circuits.

  The signal generated by the variable precision IFFT calculator 80 is sent to the GI adder.

  The variable precision IFFT calculator 60 shown in FIG. 5 has a plurality of IFFT calculators having different effective bit digits and is used exclusively. For this reason, the circuit scale of the variable precision IFFT arithmetic unit 60 increases depending on the type of effective bit digits to be handled. On the other hand, the variable precision IFFT calculator 80 shown in FIG. 7 controls power supply to the butterfly calculation circuit in units of calculation bits. For this reason, the circuit scale per bit tends to increase, and the circuit scale of the variable precision IFFT calculator 80 is proportional to the maximum number of significant bit digits handled.

  Depending on the number of OFDM optical signal receivers existing in the optical transmission system and the transmission loss of the optical transmission cable, the types of required effective bit digits and the maximum effective bit digits are different. The optical transmission system is designed using the variable precision IFFT calculators 60 and 80 properly.

(Embodiment 3)
As shown in FIG. 8, the third optical transmission system of the present invention includes one variable precision OFDM optical signal transmitter 90, N variable precision OFDM optical signal receivers 91 to 9N, optical transmission cables 917 to 9N7, And a spectroscope 93.

  The signal transmitted from the variable precision OFDM optical signal transmitter 90 reaches the variable precision OFDM optical signal receivers 91 to 9N via the spectroscope 93 and optical transmission cables 917 to 9N7 having different transmission losses depending on the distance and installation environment. To do.

  The variable precision OFDM optical signal transmission apparatus 90 includes a serial-parallel converter 901, a variable subcarrier modulator 902, a variable precision IFFT calculator 903, a GI adder 904, a D / A converter 905, an optical signal transmitter 906, and transmission loss information. The table 907 is configured.

  Variable precision OFDM optical signal receivers 91 to 9N connected via optical transmission cables 917 to 9N7 are parallel-serial converters 911 to 9N1, variable subcarrier demodulators 912 to 9N2, variable precision FFT calculators 913 to 9N3, GI. It consists of removers 914 to 9N4, A / D converters 915 to 9N5, and optical signal receivers 916 to 9N6.

  In accordance with the transmission loss and transmission rate requirement of the optical transmission cable measured at the time of designing the optical transmission system, the variable precision OFDM optical signal transmission device 90 operates in accordance with the modulation scheme of the variable subcarrier modulator 902 and the variable precision IFFT calculator 903 during operation. The variable precision OFDM optical signal receiving apparatus controls the demodulation accuracy of the variable subcarrier demodulators 912 to 9N2 and the calculation precision of the variable precision FFT calculators 913 to 9N3 to A function of reducing the power consumption of the optical transmission system and improving the transmission rate while maintaining the signal transmission bit error rate below a certain value is provided.

  In addition to the second optical transmission system of the present invention shown in FIG. 3, the third optical transmission system of the present invention shown in FIG. 8 changes the subcarrier modulation system according to the transmission rate requirement given and changed from the outside. The transmission rate is improved by using a subcarrier modulation scheme with a large number of transmission bits per symbol. On the other hand, in an environment where transmission loss in an optical transmission cable is large, it is difficult to demodulate an OFDM optical signal having a large number of transmission bits per symbol, that is, a small distance between symbols. The available subcarrier modulation schemes are limited according to the transmission loss, and the maximum transmittable rate is determined.

  The variable precision OFDM optical signal transmission apparatus 90 determines the subcarrier modulation scheme using the maximum transmission possible rate calculated from the transmission rate request changing with time and the transmission loss information measured at the time of designing the optical transmission system. A subcarrier modulation scheme that satisfies a given transmission rate requirement and has the largest intersymbol distance is selected. By selecting a subcarrier modulation method with a large inter-symbol distance, the total value of IFFT calculation errors and transmission errors caused by transmission loss included in signals received by the variable precision OFDM optical signal receivers 91 to 9N is large. Even if it is, the possibility of correct demodulation increases. If the error due to transmission loss is constant, the calculation error of IFFT calculation can be increased, that is, the calculation bit number can be reduced, and a signal satisfying the transmission rate requirement can be generated with less power consumption. Means that you can.

  After determining the subcarrier modulation method, the number of effective bit digits of IFFT calculation is determined. The number of effective bit digits of the IFFT calculation is determined according to the transmission loss and the subcarrier modulation scheme. When a subcarrier modulation method with a small inter-symbol distance is selected, the total value of the IFFT calculation error and the transmission error in the transmission path is reduced to prevent an increase in the OFDM optical signal transmission bit error rate due to interference with other symbols. There must be. Therefore, in order to obtain high calculation accuracy in IFFT calculation, it is necessary to increase the number of effective bit digits of IFFT calculation. On the other hand, when a subcarrier modulation method with a large inter-symbol distance is used, even a signal including a certain error generated by an operation with a small number of effective bits can be correctly demodulated without interfering with other symbols.

  The number of effective bit digits of the IFFT calculation is controlled so that the total value of the calculation error and the transmission error falls within the allowable error range defined by the inter-symbol distance depending on the subcarrier modulation method. This makes it possible to generate an OFDM optical signal with minimum power consumption while following a dynamically changing transmission rate request given from the outside.

  In the third optical transmission system of the present invention, a method of referring to the transmission loss information table 907 is conceivable as a method of selecting the subcarrier modulation method and the number of effective bit digits of IFFT calculation. Variable subcarrier modulator 902 determines a subcarrier modulation scheme from transmission rate request and transmission loss information table 907. Further, the variable precision IFFT calculator 903 refers to the selected subcarrier modulation scheme and transmission loss information to the OFDM optical signal receiving apparatus, and determines the number of effective bit digits. This value is specified at the time of design, and this value does not change during operation.

  When changing the subcarrier modulation scheme according to the transmission rate request, unlike the second optical transmission system of the present invention shown in FIG. 3, information on the subcarrier modulation scheme is shared between the OFDM optical signal transmitter / receiver. There is a need to. In the third optical transmission system of the present invention, it is not necessary to measure the transmission loss during operation and share it between the OFDM optical signal transmitter / receiver, but the subcarrier modulation method is transmitted using a transmission cable, and the OFDM optical signal is transmitted. It is necessary to share between the transmitting device / receiving device.

  Also, it is necessary to dynamically control the number of effective bit digits of the FFT operation according to the subcarrier modulation method used in the OFDM optical signal receiving apparatus. This is because the required number of effective bit digits differs according to the inter-symbol distance of the subcarrier modulation scheme to be used. Although the transmission loss does not change between the OFDM optical signal transmitter / receiver, it is necessary to change the number of effective bit digits according to the subcarrier modulation scheme.

  Furthermore, even in an optical transmission system composed of one OFDM optical signal transmitter and one OFDM optical receiver, when changing the subcarrier modulation method according to the transmission rate requirement, the subcarrier modulation method and the FFT computing unit The number of valid bits also needs to be changed during operation. Unlike the first optical transmission system of the present invention shown in FIG. 1, the number of effective bit digits of the IFFT arithmetic unit in the OFDM optical signal transmitting apparatus and the FFT arithmetic unit in the OFDM optical signal receiving apparatus is fixed at the time of system design. I can't.

  FIG. 9 shows a variable subcarrier modulator a0 having a plurality of subcarrier modulators and a variable precision IFFT calculator a1 having a plurality of IFFT calculators having different effective bit digits used in the third optical transmission system of the present invention. Indicates. The variable subcarrier modulator a0 includes a subcarrier modulation scheme selection unit a01 and a plurality of subcarrier modulation units a02 and a03, and the variable precision IFFT calculator a1 includes the subcarrier modulation scheme selected by the subcarrier modulation scheme selection unit a01. It comprises an operation accuracy determination unit a11 that determines operation accuracy using the transmission loss information table a2, a low accuracy IFFT operation unit a12, a high accuracy IFFT operation unit a13, and an operation result selection unit a14. The low-precision IFFT calculation unit a12 and the high-precision IFFT calculation unit a13 have a function of individually stopping power supply by receiving a sleep control signal transmitted from the calculation accuracy determination unit a11.

  The difference between the variable precision IFFT calculator 60 shown in FIG. 5 and the variable precision IFFT calculator a1 shown in FIG. 9 is that information related to the change of the subcarrier modulation scheme is acquired. The variable subcarrier modulator a0 selects a subcarrier modulator to be used based on the transmission rate request given from the outside and the maximum transmittable rate provided by the transmission loss information table a2. A data signal is transmitted to a subcarrier modulator to be used, and a sleep control signal is transmitted to a subcarrier modulator that is not used to stop supplying power.

In FIG. 9, a variable subcarrier modulator a0 having two types of subcarrier modulators a02 and a03 is shown. However, by using different types of subcarrier modulators, a large number of transmission rate requirements can be met.
The subcarrier-modulated data signal is transmitted to the variable precision IFFT calculator a1. The calculation accuracy determination unit a11 determines the number of significant bits from the subcarrier modulation scheme and the transmission loss information table. A data signal is transmitted to the IFFT arithmetic unit according to the number of effective bits, and a sleep control signal is transmitted to an unused IFFT arithmetic unit to stop power supply. Thereby, the power consumption required for the IFFT calculation is reduced while satisfying the transmission rate requirement.

  FIG. 10 shows a variable subcarrier modulator b0 having a plurality of subcarrier modulators used in the third optical transmission system of the present invention and a butterfly arithmetic circuit capable of individually controlling power supply in units of arithmetic bits. 1 shows a variable precision IFFT calculator b1 having The variable subcarrier modulator b0 has a subcarrier modulation scheme selection unit b01 and a plurality of subcarrier modulation units b02 and b03, and the variable precision IFFT calculator b1 selects the transmission result and transmission loss information table of the subcarrier modulation scheme selection unit b01. The calculation accuracy determination unit b11 that determines the calculation accuracy using b2 and the variable effective bit digit number IFFT calculation unit b12 having a function of individually controlling power supply in units of calculation bits.

  The difference between the variable precision IFFT computing unit 80 shown in FIG. 7 and the variable precision IFFT computing unit b1 shown in FIG. 10 is that information relating to the change of the subcarrier modulation scheme is acquired. The variable subcarrier modulator b0 selects a subcarrier modulation unit to be used based on a transmission rate request and a transmission loss information table b2 given from the outside. A data signal is transmitted to a subcarrier modulation unit to be used, and a sleep control signal is transmitted to a subcarrier modulation unit that is not used to stop power supply.

  The subcarrier-modulated data signal is transmitted to the variable precision IFFT calculator b1. The calculation accuracy determination unit b11 determines the number of significant bits from the subcarrier modulation scheme and the transmission loss information table. A sleep control signal is transmitted to the butterfly arithmetic circuit according to the number of effective bit digits, and the power supply of the arithmetic circuit that handles the lower bits is stopped. Thereby, the power consumption required for the IFFT calculation is reduced while satisfying the transmission rate requirement.

  The present invention can be applied to the information communication industry.

10: OFDM signal transmitter 101: subcarrier modulator 102: IFFT calculator 103: transmitter 11: OFDM signal receiver 111: subcarrier demodulator 112: FFT calculator 113: receiver 12: OFDM signal receiver 121: Subcarrier demodulator 122: FFT calculator 123: Receiver 20: Variable precision IFFT calculator 211: Calculation accuracy determination unit 212: Calculation accuracy determination unit 213: Calculation accuracy determination unit 214: Calculation accuracy determination unit 221: Butterfly calculation circuit 222 : Butterfly operation circuit 231: operation accuracy converter 232: operation accuracy converter 233: operation accuracy converter 234: operation accuracy converter 241: butterfly operation circuit 242: butterfly operation circuit 25: operation accuracy calculator 251: input data 252: Bit mask 253: Output data 26: Variable precision IFFT Calculator 261: Input data 262: Input data 263: Output data 30: Low precision OFDM optical signal transmitter 301: Series-parallel converter 302: Subcarrier modulator 303: Low precision IFFT calculator 304: GI adder 305: D / A converter 306: optical signal transmitter 31: low precision OFDM optical signal receiver 311: parallel-serial converter 312: subcarrier demodulator 313: low precision FFT calculator 314: GI remover 315: A / D converter 316: Optical signal receiver 32: Optical transmission cable (Transmission loss: small)
33: High-precision OFDM optical signal transmitter 331: Series-parallel converter 332: Subcarrier modulator 333: High-precision IFFT calculator 334: GI adder 335: D / A converter 336: Optical signal transmitter 34: High-precision OFDM optical signal receiver 341: parallel-serial converter 342: subcarrier demodulator 343: high-precision FFT calculator 344: GI remover 345: A / D converter 346: optical signal receiver 35: optical transmission cable (transmission loss) :Big)
40: Variable precision OFDM optical signal transmitter 401: Series-parallel converter 402: Subcarrier modulator 403: Variable precision IFFT calculator 404: GI adder 405: D / A converter 406: Optical signal transmitter 407: Transmission loss Information table 41: Low-precision OFDM optical signal receiver 411: Parallel / serial converter 412: Subcarrier demodulator 413: Low-precision FFT calculator 414: GI remover 415: A / D converter 416: Optical signal receiver 417: Optical transmission cable (Transmission loss: small)
4N: High precision OFDM optical signal receiver 4N1: Parallel / serial converter 4N2: Subcarrier demodulator 4N3: High precision FFT calculator 4N4: GI remover 4N5: A / D converter 4N6: Optical signal receiver 4N7: Optical transmission Cable (Transmission loss: Large)
43: Spectrometer 50: Variable precision OFDM optical signal receiver 501: Parallel / serial converter 502: Subcarrier demodulator 503: FFT calculator 504: GI remover 505: A / D converter 506: Optical signal receiver 507: Transmission loss information table 51: Low-precision OFDM optical signal transmitter 511: Series-parallel converter 512: Subcarrier modulator 513: Low-precision IFFT calculator 514: GI adder 515: D / A converter 516: Optical signal transmitter 517: Optical transmission cable (Transmission loss: small)
5N: High-precision OFDM optical signal transmitter 5N1: Series-parallel converter 5N2: Subcarrier modulator 5N3: High-precision IFFT calculator 5N4: GI adder 5N5: D / A converter 5N6: Optical signal transmitter 5N7: Optical transmission Cable (Transmission loss: Large)
53: Spectrometer 60: Variable precision IFFT calculator 601: Calculation precision determination unit 602: Low precision IFFT calculation unit 603: High precision IFFT calculation unit 604: Calculation result selection unit 61: Transmission loss information table 70: Butterfly calculation stage 701: Rotation factor table 702: Multiplier 703: Adder 704: Subtractor 80: Variable precision IFFT calculator 801: Calculation precision converter 802: Variable bit digit number IFFT calculator 81: Transmission loss information table 90: Variable precision OFDM optical signal Transmitter 901: Series-parallel converter 902: Variable subcarrier modulator 903: Variable precision IFFT calculator 904: GI adder 905: D / A converter 906: Optical signal transmitter 907: Transmission loss information table 91: Variable precision OFDM optical signal receiving device 911: parallel to serial converter 912: variable subcarrier demodulator 913 Variable precision FFT processor 914: GI remover 915: A / D converter 916: an optical signal receiver 917: optical cable (transmission loss: small)
9N: Variable precision OFDM optical signal receiver 9N1: Parallel / serial converter 9N2: Variable subcarrier demodulator 9N3: Variable precision FFT calculator 9N4: GI remover 9N5: A / D converter 9N6: Optical signal receiver 9N7: Optical Transmission cable (Transmission loss: Large)
93: Spectrometer a0: Variable subcarrier modulator a01: Subcarrier modulation scheme selection unit a02: Subcarrier modulation unit a03: Subcarrier modulation unit a1: Variable accuracy IFFT calculator a11: Calculation accuracy determination unit a12: Low accuracy IFFT calculation Unit a13: high-precision IFFFT calculation unit a14: calculation result selection unit a2: transmission loss information table b0: variable subcarrier modulator b01: subcarrier modulation scheme selection unit b02: subcarrier modulation unit b03: subcarrier modulation unit b1: variable Accuracy IFFT calculator b11: Calculation accuracy determination unit b12: Variable effective bit digit number IFFT calculation unit b2: Transmission loss information table

Claims (4)

An optical transmission system in which an optical signal from one variable precision OFDM optical signal transmitter is transmitted through an optical transmission line, branched by a spectrometer, and received by a plurality of OFDM optical signal receivers. And
The variable precision OFDM optical signal transmitter is
A subcarrier modulator for subcarrier modulating the transmission signal;
A variable precision IFFT calculator that performs IFFT calculation on the data signal modulated by the subcarrier modulator with the number of bit digits determined by the transmission loss of the optical transmission path to the destination OFDM optical signal receiver;
An optical signal transmitter that modulates an optical signal with an IFFT-calculated signal of the variable precision IFFT calculator, and transmits the modulated optical signal to any of the OFDM optical signal receivers;
The plurality of OFDM optical signal receivers are:
An optical signal receiver for receiving an optical signal from the variable precision OFDM optical signal transmitter; and
A fixed-accuracy FFT calculator that performs an FFT operation on the signal received by the optical signal receiver with the number of bits determined by the transmission loss of the optical transmission path from the variable-precision OFDM optical signal transmitter to the own apparatus;
A subcarrier demodulator that subcarrier demodulates the signal computed by the fixed precision FFT computing unit;
Equipped with a,
The variable precision IFFT calculator is
Refer to the transmission loss information table in which the number of bit digits determined by the transmission loss of the optical transmission path from the variable precision OFDM optical signal transmitter to the OFDM optical signal receiver is represented for each OFDM optical signal receiver. A calculation accuracy determining unit that determines the number of bit digits corresponding to the OFDM optical signal receiver with the minimum number of effective bits among the OFDM optical signal receivers of
A variable effective bit digit number IFFT calculation unit for performing an IFFT calculation of the data signal modulated by the subcarrier modulation unit with the number of bit digits determined by the calculation accuracy determination unit;
An optical transmission system comprising: The variable precision IFFT calculator is
Decrease the number of bit digits as the transmission loss to the destination OFDM optical signal receiver decreases,
2. The optical transmission system according to claim 1 , wherein the number of bit digits is increased as the transmission loss to the transmission destination OFDM optical signal receiver increases. The calculation accuracy determination unit outputs a sleep control signal to the variable effective bit number IFFT calculation unit of the number of bit digits not corresponding to the transmission destination OFDM optical signal receiving device,
3. The optical transmission system according to claim 1, wherein the variable effective bit digit number IFFT calculation unit to which the sleep control signal is input stops power supply. 4. The subcarrier modulator is
A subcarrier modulation scheme selection unit that selects a subcarrier modulation scheme according to a transmission loss of the optical transmission path from the variable precision OFDM optical signal transmitter to the OFDM optical signal receiver and a required transmission rate;
A subcarrier modulation unit that subcarrier modulates a transmission signal by the subcarrier modulation method selected by the subcarrier modulation method selection unit;
With
The calculation accuracy determination unit is configured to determine a bit based on a transmission loss of an optical transmission path from the variable accuracy OFDM optical signal transmission device to the OFDM optical signal reception device and a subcarrier modulation method selected by the subcarrier modulation method selection unit. determining the number of digits, to the variable effective bit digits IFFT calculation unit of the determined bit digits, to any one of claims 1 to 3, characterized in that inputting the modulated data signal of the subcarrier modulation unit The optical transmission system described.

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