JP4367489B2 - Multi-carrier transmission system, transmission apparatus and transmission method - Google Patents

Description

  The present invention relates to a multicarrier transmission system, a transmission apparatus, and a transmission method, and more particularly to a multicarrier transmission system, a transmission apparatus, and a transmission method known as a DMT (Discrete Multi-Tone) modulation method.

  As an example of this type of conventional DMT multicarrier transmission system, there is a technique disclosed in US Pat. No. 5,479,447. In such a multi-carrier transmission system, the SNR (Signal to Noise Ratio) of each carrier is measured for bit allocation to each of a plurality of carriers, and the bit allocation is obtained according to the measured SNR. It has become.

  The problem with this prior art is that the amount of transmission is reduced. The reason is that, when periodically changing noise occurs, if communication is performed at a certain error rate, bit distribution and power distribution are performed based on the average value of SNR of each carrier. Therefore, this bit distribution and power distribution are limited to only one kind of average value of SNR, so that the data transmission amount is reduced.

  Therefore, the present invention has been made to eliminate the drawbacks of the prior art, and an object of the present invention is to provide a multi-transmission capable of efficiently performing data transmission in a state where noise is periodically generated. A carrier transmission system, a transmission apparatus, and a transmission method are provided.

  Another multi-carrier transmission system according to the present invention calculates at least one of bit distribution and transmission power distribution of each carrier of the multi-carrier according to a periodically changing noise period, and based on the calculated distribution, A multi-carrier transmission system that performs data transmission between a first device and a second device, wherein the first device receives a pseudo-random signal having all components of each carrier, and the noise First measurement means for measuring a signal-to-noise ratio of the pseudo-random signal based on a period of the first and second calculation means for calculating the distribution based on the signal-to-noise ratio, and the second device A second receiving means for receiving a pseudo-random signal having all components of each carrier, and a second receiving means for measuring a signal-to-noise ratio of the pseudo-random signal based on a period of the noise. And measuring means, and having a second calculating means for calculating the distribution based on the signal-to-noise ratio. In addition, it is desirable that the first device receives a clock synchronized with the period of the noise from the outside. Further, it is desirable that the first device transmits a tone whose state changes in synchronization with the clock cycle to the second device. Moreover, it is desirable that the state is level. Further, it is desirable that the period of the noise is known.

  A multi-carrier transmission apparatus according to the present invention is a multi-carrier transmission apparatus that performs data transmission with another apparatus, and receives a first pseudo-random signal transmitted from the other apparatus in a first direction. Receiving means; measuring means for measuring a signal-to-noise ratio of the first pseudo-random signal based on a periodically changing noise period; and data transmission in the first direction based on the signal-to-noise ratio. Calculating means for calculating at least one of bit distribution and transmission power distribution of each carrier to be used; transmitting means for transmitting a second pseudo-random signal in a second direction to the other apparatus; and the second Second receiving means for receiving at least one of bit distribution and transmission power distribution of each carrier used for data transmission in the second direction calculated based on a pseudo-random signal; Characterized in that it.

  The multi-carrier transmission method according to the present invention is a multi-carrier transmission method for transmitting data between a first device and a second device, wherein the first device is transmitted from the second device in a first direction. Receiving a first pseudo-random signal; measuring a first signal-to-noise ratio of the first pseudo-random signal based on a period of periodically changing noise; and Calculating at least one of bit distribution and transmission power distribution of each carrier used for data transmission in the first direction based on a noise ratio; and transmitting a second pseudo-random signal in the second direction. And the second device receives the second pseudo-random signal, and measures a second signal-to-noise ratio of the second pseudo-random signal based on the period of the noise. And calculating at least one of bit distribution and transmission power distribution of each carrier used for data transmission in the second direction based on the second signal-to-noise ratio. .

  The operation of the present invention will be described. Both the central office and the terminals that constitute the transmission system have a transceiver function for mutual transmission. In the initial operation when the terminal is connected to the transmission line and started up, the power distribution and the bit distribution of each carrier are calculated according to the noise that changes at a constant cycle (assumed to be known). Therefore, it is necessary to inform the period of the noise from the central station side, which is the upper station, to the terminal side, which is the lower station, so that the central level is controlled by changing the tone level with a clock synchronized with the noise period. Send from terminal to terminal.

  On the terminal side, a clock synchronized with noise is generated based on the level of this tone, and the SNR of a pseudo random signal including all carriers transmitted from the central office side is measured for each noise period, and according to the SNR The power distribution and bit distribution of each carrier for each noise period are calculated and transmitted to the central station.

  On the central office side, transmission (downlink) to the terminal is performed according to the power distribution and bit distribution calculation of each carrier for each noise period. As for the uplink, the central station side and the terminal side perform the same procedure so that the functions are reversed.

  In this way, by performing power distribution and bit distribution of each carrier according to the period of noise, bit distribution suitable for noise becomes possible, and efficient transmission can be realized.

  By the way, when measuring the SNR and determining the power distribution and bit distribution of each carrier, it is necessary to consider crosstalk noise. In general, crosstalk includes far-end crosstalk and near-end crosstalk. These will be described with reference to FIG. In the figure, the far-end crosstalk FEXT is a signal having a signal line 61 in which a signal flows in the same direction as the signal line 60 of interest as a measurement target. Since the signal to be transmitted is attenuated along with the transmission distance, the amount of the far-end crosstalk FEXT is also relatively attenuated according to the transmission distance. Therefore, when this far-end crosstalk FEXT occurs, the SNR shows a high value regardless of the transmission distance.

  On the other hand, near-end crosstalk NEXT is a signal having a signal line 62 in which a signal flows in a direction opposite to the signal line 60 of interest as a measurement target. The signal to be originally transmitted is attenuated with the transmission distance, whereas the near-end crosstalk NEXT has a large amount of crosstalk at the transmission destination of the signal to be originally transmitted, and thus the SNR shows a low value.

  Therefore, it is appropriate to increase the power allocation and bit allocation of each carrier when a far-end crosstalk with a high SNR occurs, and reduce the power allocation and bit allocation of each carrier when a near-end crosstalk with a low SNR occurs. It is.

  As described above, according to the present invention, the amount of transmission can be increased when the noise is relatively low by controlling the bit distribution and the power distribution in accordance with the noise period. There is an effect that improvement is possible.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a diagram showing a schematic system configuration of the present invention. An XTU-C1 is provided as a central office and an XTU-R2 is provided as a terminal, and transmission between the two is performed by a digital subscriber line. XTU-C is an XDSL Termination Unit-Center side, and XTU-R is an XDSL Termination Unit-Remote side. Here, XDSL means X Digital Subscriber Line, and X is a generic term for A, V, H, and the like.

  As shown in the figure, both XTU-C1 and XTU-R2 have transmitters 3 and 6 and receivers 5 and 4 as large functions. Details of these transmission / reception functions are shown in the block diagram of FIG.

  Referring to FIG. 2, the downstream function of XTU-C1 (transmitting unit 3) performs buffer 11 for temporarily storing input data and power distribution and bit distribution for each carrier according to the period of noise (for details, see FIG. 2). A mapping unit 12, an IFFT (Inverse First Fourier Transform) unit 13 that modulates and multiplexes a multilevel QAM (Quadrature Amplitude Modulation) signal, which is the mapping output, on each carrier, and an analog signal of the multiplexed output to obtain a downstream signal And a DAC (Digital to Analog Converter) unit 14 for transmitting as

  The upstream function (reception unit 5) of the XTU-C1 includes an ADC (Analog to Digital Converter) unit 15 that converts a transmitted signal into a digital signal, and an FFT (Fast Fourier Transform) that demodulates the digital signal. ) Unit 16, a demapping unit 17 that switches and receives the bit distribution of the signal transmitted according to the period of noise, and a buffer 18 for adjusting a change in the amount of data transmission due to the bit distribution. Yes. The EC unit 19 is a block having an echo canceller function.

  Further, in order to realize the present invention, the XTU-C1 includes a pseudo random signal generation unit 20, a tone generation unit 21, an SNR measurement unit 22, and a power / bit allocation calculation unit 23. The pseudo random signal generator 20 generates a pseudo random signal including all carriers and outputs the pseudo random signal to the IFFT unit 13, and the tone generator 21 generates a tone and outputs the tone to the IFFT unit 13. The SNR measurement unit 22 has a function of calculating the SNR of the pseudorandom signal transmitted from the XTU-R2 for each noise period, and the power / bit allocation calculation unit 23 performs each noise period for each noise period according to the measured SNR. The carrier power distribution and bit distribution are calculated and output to the IFFT unit 13 and the demapping unit 17.

  The XTU-R2 downstream function (reception unit 4) includes an ADC unit 24 that converts a transmitted signal into a digital signal, an FFT unit 25 that demodulates the digital signal, and a period of noise. It has a demapping unit 26 that switches and receives bit distribution of a transmitted signal, and a buffer 27 for adjusting a change in data transmission amount due to bit distribution.

  The XTU-R2 upstream function (transmission unit 6) includes a buffer 28 for temporarily storing input data, a power distribution and bit distribution for each carrier according to the period of noise (details will be described later), and The IFFT unit 30 modulates and multiplexes the multilevel QAM signal, which is the mapping output, with each carrier, and the DAC unit 31 converts the multiplexed output into an analog signal and transmits it as an upstream signal.

  Furthermore, in order to realize the present invention, the XTU-R2 includes a pseudo random signal generation unit 36, an SNR measurement unit 34, and a power / bit allocation calculation unit 35. The pseudo random signal generation unit 36 generates a pseudo random signal including all carriers and outputs the pseudo random signal to the FFT unit 30, and the SNR measurement unit 34 calculates the SNR of the pseudo random signal transmitted from the XTU-C1 for each noise period. The power / bit allocation calculation unit 35 calculates the power distribution and bit allocation of each carrier for each noise period in accordance with the measured SNR, and outputs the calculated power distribution and bit allocation to the IFFT unit 30 and the demapping unit 26.

  The clock on the XTU-C1 side is a clock synchronized with the noise period, and in this case, the noise period is known. For example, in the case where the noise is crosstalk from a TCM (Time Compression Multiplexing) ISDN, as shown in FIG. 3, near-end crosstalk and far-end crosstalk occur every 800 Hz. It will change every 800 Hz. Therefore, it is necessary for the transmission unit 3 of the XTU-C1 to receive an 800 Hz clock and send the clock to the reception unit 4 of the XTU-R2.

  That is, it is necessary for the receiving unit 4 to calculate the reception SNR of each carrier for each cycle. Therefore, as a means for knowing the cycle, the tone from the tone generating unit 21 is used in the transmitting unit of the XTU-C1. The level is controlled in synchronization with the clock and sent to the XTU-R2. This clock cycle, that is, the noise cycle can be detected by the clock detection unit 33, and this detection cycle is output to the mapping unit 29 and the demapping unit 26.

  A tone generation unit 37 is also provided in the transmission unit of XTU-R2, and the level of the tone from this tone generation unit 37 is controlled in synchronization with the clock and transmitted to XTU-C1. The XTU-C1 is also provided with a clock detection unit 38 so that the clock cycle can be detected.

  Note that these clocks may be input from the outside of the apparatus, or those synchronized with the clock may be generated inside the apparatus. A command serving as a trigger for starting transmission may be generated by the central station itself or may be generated by a terminal station which is another device.

  Incidentally, in the configuration of FIG. 1, dedicated tone generators 21 and 37 are provided in XTU-C1 and XTU-R2. Instead of providing this dedicated tone generator, a known pilot tone used in ISDN can be used instead. By doing so, it is not necessary to provide a dedicated tone generator, and the amount of hardware can be reduced.

  FIG. 4 is a flowchart showing the operation of the embodiment of the present invention. In the figure, arrows from the top to the bottom indicate the flow of operations within the same device, and the left or right arrows indicate the flow of communication between the devices.

  Referring to the figure, in order to detect the period of noise changing in the receiving unit 4 of the XTU-R2 in FIG. 1 (see FIG. 3), the transmitting unit 3 of the XTU-C1 is synchronized with the periodically changing noise. The tone level from the tone generator 21 is changed in accordance with the received clock (synchronously) and transmitted (step A1). In the reception unit 4 of the XTU-R2, the clock detection unit 33 detects the noise period based on the tone level change (step B1).

  In order to obtain the power distribution and bit distribution of each DMT carrier in the downlink direction, a pseudo random signal is transmitted from the pseudo random signal generation unit 20 in the transmission unit 3 of XTU-C1 (step A2). This pseudo-random signal has components of all DMT carriers, and is 256 carriers in ANSI (American National Standards Institute) standard.

  This pseudo-random signal is received by the receiving unit 4 of the XTU-R2, and the SNR is measured by the SNR measuring unit 34 for each period detected in step B1 (step B2). Based on the measured SNR, the number of bits and the transmission power of each carrier are calculated by the power / bit number distribution calculation unit 35, and the calculated information is stored in the demapping unit 26 and also via the IFFT unit 30. It is transmitted to C1 (step B3). In XTU-C1, the transmitted bit distribution and transmission power distribution are stored in the mapping unit 12 as downlink carrier information (step A3).

  The above is the processing flow for calculating the downlink carrier bit distribution and the transmission power distribution. Next, the processing for calculating the uplink carrier distribution and the transmission power distribution will be described. The pseudo random signal (32 carriers in the ANSI standard) from the pseudo random signal generator 36 in the transmitter 6 of XTU-R2 is transmitted to XTU-C1 (step B4). The receiving unit 5 of the XTU-C1 measures the SNR from the pseudo random signal transmitted from the SNR measuring unit 22 for each clock period synchronized with noise (step A4).

  Based on the measured SNR, the number of bits and the transmission power of each carrier are calculated by the power / bit number distribution calculating unit 23, and the information is stored in the demapping unit 17, and also the XTU is transmitted via the IFFT unit 13. -It is transmitted to R2 (step A5). In XTU-R2, the transmitted bit distribution and transmission power distribution are stored in the mapping unit 29 as uplink carrier information (step B5).

  Simultaneously with the start of communication, in downlink transmission, in the transmission unit 3 of the XTU-C1, the mapping unit 12 stores two types of bit distributions (in the example of FIG. 3) stored for each period of changing noise. Data transmission is performed by switching the transmission power distribution (step A6). Then, the receiving unit 4 of the XTU-R 2 extracts the transmitted DMT data based on the number of bits stored in the demapping unit 26. Since the bit distribution changes periodically, the transmission amount also changes, and the buffer 27 adjusts this.

  Further, in uplink transmission, the XTU-R2 transmitting unit 6 stores two types of bit distribution and transmission power distribution stored in the mapping unit 29 in accordance with the changing noise cycle (in the example of FIG. 3). Is switched to perform data transmission (step B6). Then, the receiving unit 5 of the XTU-C 1 extracts the transmitted DMT data based on the number of bits stored in the demapping unit 17. The buffer 18 adjusts the transmission amount by periodically changing the bit distribution.

  Next, an example of the calculation method of the transmission power and the number of bits of each carrier in steps A5 and B3 in FIG. 4 will be briefly described with reference to FIG. Normalized SNR (i) is obtained with the transmission power of each carrier i as E (i) (step S1). Then, SNR (i) / Γ (i) is calculated (step S2). Here, Γ (i) is called “SNRgap” and is as follows.

  Γ (i) = [Q−1 (Pe / ne)] 2 + γmargin−γeff−4.77 (dB) where γmargin is a performance margin of the apparatus and γeff is a coding gain in error correction.

  Next, the values of SNR (i) / Γ (i) are sorted in descending order (step S3). Here, the correspondence between the original carrier number (i) and the sorted carrier number (i) is recorded. Then, k = 1, bmax = 0, and {b∧j} = 0 are set (step S4). Here, k is a count value, {b∧j} is the number of bits for each carrier, and bmax is a total transmission amount.

  Then, btarget (k) is calculated by the equation btarget (k) = Σbj (step S5). Here, Σ indicates the total sum of j = 1 to k. Here, btarget (k) is the total transmission amount when k carriers are used, and bj is round [log 2 {1+ (EtargetSNR (j) / k) / Γ (i)}] or , Floor [log 2 {1+ (Emax SNR (j)) / Γ (i)}] takes a smaller value. Note that round indicates rounding and floor indicates truncation.

  If btarget (k)> bmax, bmax = btarget (k) is set (steps S6 and S7). The bit distribution bj of each carrier at this time is stored as b∧j. If k is not equal to N, k = k + 1 is set (step S9), and the process returns to step S5. If k = N (step S8), the process proceeds to step S10. At this time, bmax is the maximum transmission amount, and B∧j is the bit distribution of each carrier at that time. The transmission power E∧i of each carrier is obtained from b∧i obtained by rearranging b∧j (step S10).

  Then, Etotal = ΣE∧i is calculated as the total power Etotal (step S11). In this case, Σ represents the sum of i = 0 to N-1. The final Ei is determined as a smaller value of EtargetE∧i / Etotal or Emax, i (step S12). Here, Etarget is given in advance as the maximum value of the total power. Emax is an allowable limit value for each carrier.

  In the above embodiment, as shown in FIG. 3, the period of noise is 200 Hz, and there are two types of noise. However, this is merely an example, and three or more types of noise and their periods are also included. Although various values can be taken, these are assumed to be known. The details of the calculation method shown in FIG. 5 are disclosed in the above-mentioned USP 5,479,447, but are not limited to this method.

1 is a schematic system configuration diagram to which the present invention is applied. It is a block diagram of the Example of this invention. It is a figure which shows the example of the kind and period of noise. It is a float which shows operation | movement of the Example of this invention. It is a flowchart which shows the outline of the example of calculation of the power allocation and bit allocation in the Example of this invention. It is a figure which shows a far end crosstalk and a near end crosstalk.

Explanation of symbols

1 XTU-C
2 XTU-R
3, 6 Transmitter 4, 5 Receiver 11, 18, 28, 27 Buffer 12, 29 Mapping unit 13, 30 IFFT unit 14, 31 DAC unit 15, 24 ADC unit 16, 25 FFT unit 17, 26 Demapping unit 19 EC unit 20, 36 Pseudo random signal generation unit 21 Tone generation unit 22, 34 SNR measurement unit 23, 35 Power / bit calculation unit

Claims (7)

At least one of bit distribution and transmission power distribution of each carrier of the multicarrier is calculated according to a periodically changing noise period, and data transmission is performed between the first and second devices based on the calculated distribution. A multi-carrier transmission system,
The first device comprises:
First receiving means for receiving a pseudo-random signal having all components of each carrier;
First measuring means for measuring a signal-to-noise ratio of the pseudo-random signal based on the period of the noise;
First calculating means for calculating the distribution based on the signal-to-noise ratio;
The second device comprises:
Second receiving means for receiving a pseudo-random signal having all components of each carrier;
Second measuring means for measuring a signal-to-noise ratio of the pseudo-random signal based on the period of the noise;
And a second calculating means for calculating the distribution based on the signal-to-noise ratio. Said first device, a multicarrier transmission system according to claim 1, wherein the receiving a clock synchronized to the period of the noise from the outside. 3. The multicarrier transmission system according to claim 2, wherein the first device transmits a tone whose state changes in synchronization with a cycle of the clock to the second device. 4. The multicarrier transmission system according to claim 3 , wherein the state is level. Multi-carrier transmission system according to any of claims 1 to 4, characterized in that the period of the noise is known. A multi-carrier transmission device that performs data transmission with other devices,
First receiving means for receiving a first pseudo-random signal transmitted in a first direction from the other device;
Measuring means for measuring a signal-to-noise ratio of the first pseudo-random signal based on a period of periodically changing noise;
Calculating means for calculating at least one of bit distribution and transmission power distribution of each carrier used for data transmission in the first direction based on the signal-to-noise ratio;
Transmitting means for transmitting a second pseudorandom signal in a second direction to the other device;
And second receiving means for receiving at least one of bit distribution and transmission power distribution of each carrier used for data transmission in the second direction calculated based on the second pseudo-random signal. A multi-carrier transmission apparatus. A multicarrier transmission method for performing data transmission between a first device and a second device, wherein the first device comprises:
Receiving a first pseudo-random signal transmitted in a first direction from the second device;
Measuring a first signal-to-noise ratio of the first pseudo-random signal based on a period of periodically changing noise;
Calculating at least one of bit distribution and transmission power distribution of each carrier used for data transmission in the first direction based on the first signal-to-noise ratio;
Transmitting a second pseudo-random signal in the second direction,
The second device comprises:
Receiving the second pseudo-random signal;
Measuring a second signal-to-noise ratio of the second pseudorandom signal based on the period of the noise;
And calculating at least one of bit distribution and transmission power distribution of each carrier used for data transmission in the second direction based on the second signal-to-noise ratio. .

Images