JP2002538669A - Apparatus and method for tone allocation in digital subscriber line system - Google Patents

Abstract

(57) Abstract A method and apparatus are provided for reducing the strength of interference (eg, crosstalk noise and / or echo interference) in multicarrier communications. A carrier sub-channel is selected from a plurality of carriers having a frequency domain. The selection of the carrier sub-channel is performed by first selecting a first subset over a frequency domain consisting of a plurality of carriers and having a highest frequency end and a lowest frequency end. Each sub-channel of the subset can carry at least one bit of signal. At least one of the subset of carrier subchannels is assigned to one of the edges of the frequency domain for transmission of one or more bits of the digital signal. The input digital signal is modulated and transmitted on a carrier sub-channel and received and demodulated as an output digital signal. The carrier subchannel is used to reduce or minimize the intensity of interference phenomena such as near-end crosstalk, far-end crosstalk, echo, and noise when transmitting digital signals.

Description

DETAILED DESCRIPTION OF THE INVENTION

CROSS REFERENCE TO RELATED APPLICATIONS This application is a US provisional application, application no.
March 23 Priority is claimed for the name "Tone assignment method in digital subscriber line system". The entire provisional application is hereby incorporated by reference.

FIELD OF THE INVENTION [0002] The present invention relates to communication systems, and more particularly, to information transmission using multi-carrier transmission technology.

[0003] A brief discussion of background information [0003] Telephone company research has shown that twisted pair wires currently used for analog telephone services can also be used for high-speed digital signal transmission.
Digital signals enable the provision of data services, including high-speed Internet access, television programming and traditional telephone services.

[0004] Digital signal transmission technology using twisted pair wires includes ADSL (Asymmetric Digit).
tal Subscriber Line), HDSL (High-bit rate Digital Subscriber Line), RA
DSL (Rate Adaptive Digital Subscriber Line) and VDSL (Very high sp
eed Digital Subscriber Line). These techniques are generally xDSL or DS
This is called L transmission technology.

[0005] Until now, modems using xDSL transmission technology have been developed.
Information is transmitted over a plurality of subdivided frequency channels called tones or carrier subchannels. The carrier subchannels are separated from each other by ± 50 ppm in relatively narrow frequency intervals (for example, 4.3125 kHz for tone). The collection of carrier sub-channels forms a practical broadband communication channel. Advantages of a multi-carrier system include the ability to vary the amount of information transmitted for each tone and the SNR (si
gnal-to-noise ratio (signal-to-noise ratio) can be set for each tone.

[0006] Single carrier systems have also been used to provide data communication over twisted pair wires. Single carrier systems are distinguished from multicarrier systems in that they do not use narrowband tones for data transmission, but many single carrier systems are either downlink (central office to subscriber) or uplink (
Utilize one or more carriers in both directions from the subscriber to the central office). As used herein, the term tone (or carrier subchannel) refers to both wideband tones formed from a single modulated carrier and narrowband tones in a multicarrier system.

[0007] Current multi-carrier systems, ie, systems that utilize multiple carrier sub-channels, use as many tones as possible and transmit each tone / carrier sub-channel at the maximum allowable power, so that each tone / SNR margin of carrier subchannel is maximized. As a result, when the information quantification is small, a large amount of tones will be used at higher powers than required to transmit the information quantification with acceptable quality. This results in excessive output to the twisted pair line group, which ultimately reduces the total transmission capacity of the twisted pair line group.

[0008] The maximum amount of information that can be encoded on a particular carrier subchannel depends on the SNR of the communication channel for that carrier subchannel. Communication channel SN
Since R changes with frequency, the maximum amount of information that can be encoded on a carrier subchannel has frequency dependence.

One of the problems in the xDSL system is crosstalk, that is, electromagnetic interference generated between twisted pair wires when transmitting a signal. Crosstalk occurs when signals are coupled from one twisted pair line along the transmission path into another twisted pair line. This is indicated by the fact that another modem receives a signal intended to be transmitted to one modem. And the interference limits the performance of the xDSL system, and in some situations, the twisted pair lines cannot be used for any type of xDSL service.

In addition to the problem of using more than the number of tones / carrier sub-channels required to transmit a certain amount of information and the problem of crosstalk, xDSL systems also have a “near-far problem”. The problem is that signals are transmitted over a relatively long distance from one modem in the central office to one home in the service area, while at the same time a second modem in the same group of twisted pair lines from a second modem close to the home. Occurs when a signal is transmitted on a twisted pair wire. If both modems output at the maximum allowable output level (e.g., in the range of -38 to -40 dBm / Hz) in the allowable frequency band, the signals of the second modem may require a practical SNR margin to ensure a satisfactory SNR margin. Requires higher output than is required for This excess power can cause significant crosstalk problems with the first twisted pair wire or other twisted pair wires in the same twisted pair wire group.

Echo and noise are other types of twisted pair cable that may cause a decrease in service quality. An echo is a reflection of a signal transmitted along a twisted pair line, and occurs when a signal is transmitted with impedance mismatch or when a transmission line is not properly terminated. In particular, the echo has a root cause when a signal is transmitted from a transmitter of a transmitter and a receiver of the transmitter receives a spurious signal. Noise is an apparently random signal and is caused by natural phenomena such as lightning or by artificial phenomena such as switching the power supply on or off.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to reduce or minimize interference in a multi-carrier communication system.

It is another object of the present invention to provide a method for allocating tone / carrier sub-channels for transmitting digital signals at a frequency and power such that the overall transmission capability of the twisted pair of wires is maximized. .

In one aspect, the invention features a multi-carrier data modulation method that reduces the effects of interference phenomena in a communication system that includes a plurality of transceivers. A plurality of carrier sub-channels are provided for use in modulating a digital signal of the input data stream. For the carrier sub-channel, a subset over the frequency domain having the highest frequency edge and the lowest frequency edge is defined. Each carrier subchannel of the subset is capable of carrying at least one bit of the digital signal. At least one of the subset of carrier subchannels
One is assigned to the transmission of one or more bits of said digital signal. All the assigned carrier sub-channels of the subset are at one of the ends of the frequency domain such that the effects of interference phenomena are reduced.

In one embodiment, at least one carrier subchannel of the subset carries fewer bits than the carrier subchannel can carry. In another embodiment of the present invention, the assignment of the carrier sub-channel uses a part of the carrier sub-channel included in the subset. In yet another embodiment, the frequency domain of the subset of carrier sub-channels includes at least one carrier sub-channel that cannot carry at least one bit. In yet another embodiment, a digital signal communicated from a first transceiver to a second transceiver is modulated using a first frequency domain allocated from a first subset of a plurality of carrier sub-channels, A digital signal communicated from the second transceiver to the first transceiver comprises a plurality of carrier subchannels and a second signal allocated from a second subset different from the first subset.
Is modulated using the frequency domain of

In another embodiment, the gain of at least one carrier sub-channel of the subset is adjusted such that the number of bits that the carrier sub-channel can carry carries information contained in the digital signal from the maximum number of bits. Reduced to a smaller number of bits sufficient to In some embodiments, the interference phenomenon is at least one of near-end crosstalk, far-end crosstalk, noise, and echo.

In another embodiment, the maximum number of bits of a digital signal that can be carried by each carrier subchannel of the subset is determined to provide a predetermined quality service.
In yet another embodiment, the predetermined quality service is determined based on at least one of a bit transmission rate, a bit error rate, a signal to noise ratio margin, and power.

In these embodiments, the higher frequency tone / carrier subchannel is
Selected for short loop. In the short loop, such tones and carrier subchannels provide sufficient SNR. Low frequency tone / carrier subchannels become available for long loops. In the long loop, the SNR of the higher frequency tone / carrier subchannel is not enough to maintain an acceptable bit error rate.

One advantage of these embodiments is that far-end crosstalk is reduced in one or both directions. Another advantage of these embodiments is that the maximum spectral separation between the downstream and upstream bands is maintained. An advantage of these embodiments is that near-end crosstalk is reduced in one or both directions. Near-end crosstalk is caused by the upstream signal interfering with the downstream signal and the downstream signal interfering with the upstream signal within the binder, so increasing the frequency spacing between the upstream and downstream bands results in near-end crosstalk. The effect of edge crosstalk is reduced.

Yet another advantage of these embodiments is that echo interference is reduced. By maximizing the separation of the upstream band from the downstream band, the echo effects inside the transceiver, where the transceiver's transmitted signal is received by its own receiver, are reduced. The receiver does not detect this even when an echo is present. This is because the receiver is not sensitive to the frequency corresponding to the transmitted signal returning as an echo. This is achieved by the fact that the expanded frequency separation between the transmitted and received signals results in more effective filtering of the reflected signal.

Another feature of the present invention is the ability to control tone power to prevent over-utilization of power. Excessive power utilization has the additional consequence of reducing the overall capability of the twisted pair. This feature is achieved by defining the SNR of each tone to ensure that the payload increases until the SNR has an acceptable but not excessive margin. In this way, each tone carries a power level that supports the maximum data rate with an acceptable margin. For data rates where it is not necessary to use all the tone / carrier sub-channels, by leaving the lower tone / carrier sub-channels unused,
Reduces overall output power and interference caused by the modem.

An advantage of the present invention is to provide a system that can allocate tone / carrier subchannels and reduce crosstalk within binders.

In another aspect of the invention, a multicarrier data modulator reduces the effects of interference phenomena in a communication system including a plurality of transceivers communicating with each other.
The module modulates a digital signal of the input data stream on a plurality of carrier sub-channels. The sub-channel selection module selects a subset of the plurality of carrier sub-channels. The subset spans a frequency region having a highest frequency edge and a lowest frequency edge. Each carrier sub-channel of the subset can carry at least one bit of the digital signal. The carrier subchannel allocation module allocates at least one carrier subchannel in the subset for transmission of one or more bits of the digital signal. All assigned carrier sub-channels of the subset are at one of the edges of the frequency domain so that the effects of interference phenomena are reduced.

In one embodiment, the digital signal modulation module uses a part of the carrier sub-channel included in the subset. In other embodiments, a subset of the carrier sub-channels spans the frequency domain that includes at least one carrier sub-channel where at least one bit cannot be carried. In yet another embodiment, the apparatus further comprises a module for receiving a digital signal modulated and transmitted on one or more carrier subchannels. In one embodiment, the transmitted digital signal is modulated using a first frequency domain assigned from a first subset of a plurality of carrier sub-channels, and the received digital signal is transmitted to a plurality of carrier sub-channels. Modulated using a second frequency domain consisting of sub-channels and assigned from a second subset different from the first subset.

In another embodiment, the apparatus adjusts a gain of at least one carrier sub-channel of the subset, wherein the number of bits that the carrier sub-channel can carry is included in the digital signal from the maximum number of bits. There is further provided a gain control module for reducing the number of bits to a smaller number sufficient to carry information. In another embodiment, the gain control module controls the gain such that the reduced number of bits is the minimum number of bits required to carry the information contained in the digital signal.

In yet another embodiment, the apparatus further comprises an interference detection module for determining a maximum number of bits of a digital signal that can be carried by each carrier subchannel of the subset to provide a predetermined quality service. In another embodiment, the interference detection module determines a parameter selected from a parameter group consisting of a bit transmission rate, a bit error rate, a signal-to-noise ratio, power, near-end crosstalk, far-end crosstalk, noise level, and echo. To detect.

In another aspect, the invention relates to a multi-carrier data modulator for reducing the effects of interference phenomena in a communication system using multiple transceivers communicating with each other. The apparatus comprises a module for receiving a transmitted digital signal modulated on one or more carrier sub-channels, the one or more carrier sub-channels being assigned from a plurality of carrier sub-channels,
A carrier sub-channel subset, wherein the subset spans a frequency domain having a highest frequency end and a lowest frequency end, wherein each carrier sub-channel of the subset is capable of carrying at least one bit of the digital signal; All assigned carrier sub-channels of the subset are at one of the ends of the frequency domain such that the effects of interference phenomena are reduced. The apparatus also includes a demodulation module that demodulates the transmitted digital signal modulated on one or more carrier subchannels and generates an output data stream from the demodulated transmission signal.

In another aspect, the invention features a computer program recorded on a readable medium. When the computer program is executed on a computer, the computer program determines a subset of a plurality of carrier sub-channels, wherein the subset spans a frequency domain having a highest frequency end and a lowest frequency end, and each carrier sub-channel of the subset Can carry at least one bit of a digital signal. Also, when the computer program is executed on a computer, assigning at least one carrier sub-channel of the subset to transmission of one or more bits of the digital signal, and assigning all assigned carriers of the subset. A sub-channel is at one of the ends of the frequency domain so that the effects of interference phenomena are reduced.

In one embodiment, the computer program, when executed on a computer, further performs the step of determining a maximum number of bits of a digital signal that a carrier subchannel can carry to provide a predetermined quality service. . In another embodiment, the computer program, when executed on a computer, converts the digital signal on a first carrier sub-channel having a first frequency, the maximum number of bits that the first carrier sub-channel can carry. A step of modulating with a number and then modulating the digital signal with a second carrier sub-channel having a second frequency is performed. In yet another embodiment, the computer program, when executed on a computer, includes a reduced number of bits carried by a carrier subchannel from a maximum number of bits that the carrier subchannel can carry in a digital signal. Calculating the number of bits down to a number of bits sufficient to carry the encoded information, and modulating the digital signal on the carrier subchannel using the fewer bits instead of the maximum number of bits. Is executed.

The present invention is applicable in situations where a single network operator controls the binder group, or where multiple network operators are using twisted wire pairs inside the binder. In the case of multiple operators utilizing twisted wire pairs inside the binder, use of the present invention allows any one of the network operators to reduce the signal to noise margin in order to use as many tone / carrier subchannels as possible. The overall throughput of the binder can be improved over using a maximized payload / power allocation scheme.

The present invention is also applicable in situations where the subscriber is located at various distances from the source of the ADSL signal. The present invention describes the "near-far problem",
That is, the use of excessively high power signals for subscribers close to the transmitter can alleviate the problem of causing high levels of crosstalk on lines connecting subscribers far away from the signal source. Help.

According to the present invention, there is provided a multi-carrier communication scheme in which bit loading is performed to reduce or minimize the intensity of interference phenomena (eg, crosstalk, echo, noise interference).

[0033] These and other features and advantages of the present invention will become apparent with reference to the following description and drawings, wherein like numerals represent like parts.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1A shows an embodiment of a system for service transmission using an xDSL modem. The first modem channel bank 100 includes a first exchange-side xDSL modem (here, ATU-C1) 110. The xDSL modem 110 has a first
Is connected to the twisted pair wire 140 of FIG. The first twisted pair wire 140 is part of a binder group 130. The first exchange side xDSL modem 110 transmits the xDSL signal to the first subscriber side xDSL modem (here, ATU-R1) 160. The first subscriber xDSL modem 160 is connected to the first residence 1
Exists within 50.

As shown in FIG. 1A, the second exchange-side xDSL modem (ATU-C2)
And transmits signals over twisted pair lines 142. The twisted pair wire 142 is a part of the binder group 130. ATU
-C2 115 transmits the xDSL signal to the second subscriber modem (ATU-R2) 165. A second subscriber modem 165 resides in the second residence 152.
ATU-R1 160 or ATU-R2 165 may be in a business or apartment building or other subscriber location. FIG. 1A shows a first switching xDSL modem 110 and a second switching xDSL modem 115 located in a single channel bank, with subscribers located at various distances from the switching office. It shows the configuration. As an example, first residence 150 is only a few hundred feet away from the exchange, while second residence 152 is 20,000 from the exchange.
In some cases, the feet are far away.

As shown in FIG. 1A, a computer 120 is used to monitor the first modem channel bank 100. In some embodiments, the tone or carrier subchannel allocation system
Resides in the computer 120. In another embodiment, the tone / carrier subchannel allocation system resides on a microprocessor that is part of an xDSL modem or on an ASIC (Application Specific Integrated Circuit).
The tone / carrier sub-channel allocation system can be implemented on a single processor, either in the computer 120 or in an xDSL modem, and uses multiple computers for tone / carrier sub-channel payload allocation and tone / carrier sub-channel. This can be realized even in a distributed configuration in which the above power control is executed. The module including the tone / carrier sub-channel allocation system can be realized by hardware or a combination of hardware and software.

FIG. 1B shows that the second modem channel bank 105 is present and the second exchange side xD
2 shows a configuration in which a second modem channel bank 105 is used to accommodate an SL modem (ATU-C2) 115. This configuration is based on CLEC (Competitive Local
Exchange Carrier) is second from ILEC (Incumbent Local Exchange Carrier)
Is typical when gaining access to a group of twisted pair wires, including the twisted pair wire 142 of FIG. First twisted pair wire 140 and second twisted pair wire 142 together form part of binder group 130. As shown in FIG. 1B,
A second computer 122 for controlling the second modem channel bank 105
Can be used. The tone / carrier sub-channel allocation system may reside on the second computer 122, in a modem in the second channel bank 105, or distributed among various processors in the system. The module including both tone / carrier subchannel allocation systems can be implemented in hardware or a combination of hardware and software.

FIG. 1C illustrates an arrangement for transmitting signals using optical fiber to a remote location in an access area where an xDSL modem is used for data transmission and reception over a connection to a home over a twisted pair wire. Show. As shown in FIG. 1C, the host digital terminal (HDT) 101 includes a first exchange-side modem 110. First exchange-side modem 110 is connected to first subscriber-side modem 160 in first residence 150 via first twisted pair line 140. HDT 101 also includes a first optical fiber transceiver 118. The first optical fiber transceiver 118 is connected to the first optical fiber 125 and further to the cabinet 135. Cabinet 135 includes a first remotely located xDSL modem 115. First remote configuration xD
The SL modem 115 is connected to the second subscriber xDSL modem 16 in the second residence 152.
5 is connected. The HDT 101 includes a second optical fiber transceiver 121. The second optical fiber transceiver 121 is connected to the node 138 via the second optical fiber 127. Node 138 includes a second remotely located xDSL modem 122. The second remotely located xDSL modem 122 is connected via a twisted pair line 143 to a third subscriber xDSL modem 167 in the third residence 155.

As shown in FIG. 1C, the twisted pair wires 140, 142, 143 form part of the binder group 130. FIG. 1C illustrates a situation where optical fiber is used to support remotely located equipment, resulting in various variations in the length of the twisted pair wire connecting the xDSL modem. Any of the modules including the tone / carrier sub-channel assignment system can be implemented in hardware or a combination of hardware and software.

FIG. 1D shows a configuration of another example. Although only one twisted pair line 171 is shown here, the telephone exchange 170 is connected to a plurality of subscribers by a number of twisted pair lines at the same time. System 185 includes a central office 170 and a subscriber home 190. The telephone exchange 170 is connected to a remote subscriber by a twisted pair subscriber line 171. The exchange also sends and receives digital data,
SLAM (Digital Subscriber Line Access Multiplexer) or, alternatively, a data enabled switch line card
) Is connected to the digital data network 180. The exchange 170 is connected to a public switched telephone network (PSTN) via a local switch bank 172 for transmitting and receiving voice and other low frequency communications. The DSLAM 178 is connected to the PDSL via the ADSL transceiver unit 176.
It is connected to an OTS (plain old telephone service) splitter 174. AD
The SL transceiver unit 176 can be a line card. Local switch 172 is also connected to splitter 174. The splitter 174 separates a data signal and an audio signal received from the twisted pair line 171.

At the subscriber's house 190 which is one end of the twisted pair wire 171, the splitter 19
2 transmits a POTS signal from the twisted pair line 171 to devices such as telephones 188 and 189 and uses a personal computer 196 that uses digital data.
Pass digital data signals to the subscriber ADSL transceiver unit 194 for use in such devices. ADSL transceiver unit 194
Can be incorporated into the personal computer 196 as a card, or attached to a computer port or connector of the personal computer 196 as a stand-alone device.

FIG. 2A is a diagram showing a crosstalk phenomenon between the first twisted pair wire 140 and the second twisted pair wire 142. The first signal transmitted from the ATU-C1 110 and propagating on the first twisted pair line 140 is a second signal transmitted from the second twisted pair line 14.
2 may be electromagnetically coupled. Similarly, a second signal propagating on the second twisted pair line 142 may be electromagnetically coupled to the first twisted pair line 140. Either situation can result in crosstalk. As shown in FIG. 2A, a near-end (Near-End) crosstalk (NEXT) 210 and a far-end (Far-En)
d) Two types of crosstalk of crosstalk (FEXT) 220 can result.

Considering the connection mediated by twisted pair wire 140, NEXT 210
Is the first twisted pair 14 of the signal transmitted on the second twisted pair 142
Binding to zero. This coupling occurs at the transmission end of the system. FEXT220 is
It can be viewed as a coupling from the second twisted pair wire 142 to the first twisted pair wire 140. This coupling occurs along the transmission path.

[0044] NEXT 210 and FEXT 220 have different characteristics as a function of frequency. FEXT 220 typically increases faster than NEXT 210 as a function of frequency. However, FEXT 220 does not support first and second twisted pair wires 140,1.
Attenuated by 42 channel transmission functions. As a result, NEXT 210 tends to be more harmful than FEXT 220 in many xDSL systems. FIG.
As shown in A, NEXT 210 and FEXT 220 can occur in both directions (upstream and downstream) of an xDSL system. It mentions the interaction of simply twisted two twisted pair wires, but NEXT and FEXT
Interaction of crosstalk, as well as other forms of interaction, can occur in principle between any two twisted pair wires, and that one particular twisted pair wire is actually more than one other twisted pair wire It is to be understood that it is assumed that they can be interfered simultaneously from

FIG. 2B illustrates one embodiment of a binder group 130 that includes multiple twisted pair wires. In FIG. 2B, each of the multiple twisted pair wires is represented by a number that can identify itself. The invention described here is applicable to any group of twisted pair wires transmitting xDSL signals. The binder group typically contains 20 to 100 twisted pair wires, but the present invention is applicable to groups containing more or less twisted pair wires.

The present invention is applicable to ADSL with evolving standards, as in VDSL or other DSL systems. In one embodiment, an ADSL transmission system according to the International Telecommunication Union Standard is used for ATU-C and ATU-R. These modems are available from ITU G. Recommendation 992.1 or ITU
G. FIG. Follow any of the 992.2 draft recommendations.

FIG. 3 shows a diagram of a tone / carrier subchannel allocation system 300 used to implement the present invention. Tone / carrier sub-channel allocation system 300 achieves measurement of SNR on each tone / carrier sub-channel using a signal-to-noise (ie, S / N) estimation entity. Tone / carrier sub-channel allocation system 300 transmits a tone / carrier sub-channel signal, indicated by reference numeral 335, to S / N evaluation entity 330;
An S / N measurement 338 for the tone signal is received. G. FIG. 922.1 or G.92. A system according to any of the 922.2 standards can evaluate SNR using a C-MEDLY wideband pseudo-random signal. The SNR for each tone / carrier subchannel can be determined using other mechanisms, but these are techniques known to those skilled in the art.

The tone assignment system 300 also has access to a service description record 320. The service description record 320 contains the service level request signal 32
9 can be received and the guaranteed bit rate 327 and the peak bit rate 325 can be returned. Guaranteed bit rate 327 and peak bit rate 325 indicate several levels contracted by the subscriber and indicate the modem (ATU) used by the subscriber.
-C110 and ATU-R160).

As shown in FIG. 3, tone / carrier sub-channel assignment system 300 communicates with tone / carrier sub-channel and power control entity 310. Tone / carrier sub-channel allocation system 300 calculates the payload to be allocated and the power to be assigned to each tone / carrier sub-channel, and for that tone / carrier sub-channel, tone / carrier sub-channel 335, tone / carrier sub-channel. Report channel rate 318 and tone / carrier sub-channel power 318. The tone / carrier sub-channel rate 318 is the number of bits transmitted by the tone / carrier sub-channel and corresponds to the payload transmitted by the tone / carrier sub-channel 335. In one embodiment, the tone / carrier subchannel rate 318 is between 1 and 15
Change up to a bit.

FIG. 4 shows a block diagram of one embodiment of a computer system that can provide a twisted pair line spectrum management system. The system bus 422 is a CPU
203, RAM 204, ROM-BIOS (Read Only Memory-Basic Input Out)
put System) 406 and other components. The CPU 203 accesses the hard drive 400 via the disk controller 402.
The standard input / output device is connected to the system bus 422 via the I / O controller 201.
It is connected to the. The keyboard is connected to the I / O controller 201 via a keyboard port 416, and the monitor is connected to the I / O controller 201 via a monitor port 418. The serial port device uses the serial port 420 to control the I / O controller 201.
Communicate with Expansion slots and connectors, such as an ISA (Industry Standard Architecture) expansion slot 408 and a PCI (Peripheral Component Interconnect) expansion slot 410, allow the card to be further mounted and connected to a computer. As an example, a network card may be used to interface with a local area network, a wide area network, or other networks.

FIGS. 5A and 5B show the tone distribution used in current standard ADSL systems. As shown in FIG. 5A, the downlink signal (ATU-
The direction from C1 110 to ATU-R1 160) is a low frequency (f _dl ) 5 for downlink.
The signal is transmitted over a frequency range defined from 00 to a high frequency for downlink (f _dh ) 510. ITU G. In order to perform transmission conforming to the 922.1 specification,
Two spectral masks have been defined. That is, an overlapping spectrum and a non-overlapping spectrum. In the former case, (f _dl ) 500 is equal to 25.875 kHz and (f _dh ) 510 is 1.1
Equal to 04 MHz. In the non-overlapping spectrum, the uplink spectrum and the downlink spectrum are separated, and the downlink spectrum is 138 kHz ((
f _dl ) 500) to 1.104 MHz ((f _dh ) 510). In contrast, ITU G. According to the 922.2 specification, in the overlap spectrum mask, (f _dl ) 500 is 25.875 kHz and (f _dh ) 510 is 5
It is set to 52 kHz. In non-overlap mode, (f _dl ) 500 is 13
At 8 kHz, (f _dh ) 510 is equal to 552 kHz.

With reference to FIG. 5A, current compliant devices allocate tone or carrier subchannels initially from a lower frequency and reduce the number and power level of tone / carrier subchannels used. Try to maximize margins by maximizing. This results in the worst crosstalk environment.

Although power levels and corresponding spectral masks can be obtained from ITU standards, spectral masks can be obtained from the Federal Communications Commiss
ion) or other government agency specifications. These masks may be pre-programmed in the tone / carrier sub-channel management system or may be dynamically accessible by the tone / carrier sub-channel management system from a server or other storage device. This way,
The tone / carrier subchannel management system allows the spectral mask to be changed dynamically.

As shown in FIG. 5B, uplink transmission (ATU-R1 160 to ATU-R1
The direction to C1 110) is the low frequency f _ul 520 for upstream and the high frequency f _uh 5 for upstream.
30. ITU G. According to one example adapted to 922.1, f _ul 520 is equal to 25.875 kHz and f _uh 530 is equal to 138 kHz. Peak power spectrum distribution (PSD)
option) is -36.5 dBm / Hz for the downlink and -34.5 for the uplink.
It is specified as dBm / Hz.

Although an ADSL system having a particular tone / carrier subchannel spacing has been described herein, the present invention is not limited to RADSL and VDSL systems, but applies to various standard and non-standard xDSL systems, including these. Can be applied. In a VDSL system, the proposed mask has a minimum frequency of 120 kHz or 1.104 MHz and a maximum frequency between 10 and 30 MHz.

FIGS. 6A and 6B show representative examples of tone / carrier subchannel arrangements in accordance with the principles of the present invention. Although the frequency spacing between tones is 4.3125 kHz, tolerance +/- 50 ppm, the invention is not tied to any particular tone / carrier subchannel spacing or width. Rather than assigning a payload to all tones / carrier sub-channels in the uplink and downlink frequency ranges, f _dh 510 is initially assigned to the tones / carrier sub-channels for downlink transmission, as shown in FIG. 6A. Selected. In the upstream direction, the tone / carrier subchannel constellation starts at f _uh 530, as shown in FIG. 6B. As described below, only the tone / carrier sub-channels needed to satisfy the request to transfer the payload are selected. Maximizing the signal-to-noise ratio margin in each tone / carrier sub-channel and using more tone / carrier sub-channels than actually needed to maintain an acceptable signal-to-noise ratio margin Unlike current systems that can, depending on the payload that needs to be transferred, the lower frequency f _dl 500 for downstream and the lower frequency f _ul 520 for upstream may or may not be reached.

In general, the frequencies of the individual carrier sub-channels that make up the subset are selected in consideration of the relationship between the highest frequency end and the lowest frequency end of the subset of carrier sub-channels. You. A subset of carrier subchannels is defined by a plurality of carrier subchannels. At least one carrier subchannel of the subset may carry at least one bit of the digital signal.

In situations where there is a first frequency range that uses a higher frequency than the frequency used in the second frequency range, four combinations of carrier subchannels within the usable frequency range are possible. In one embodiment, the first transceiver uses the carrier subchannel at the high frequency end in the first, higher frequency range, and the second transceiver uses the carrier frequency in the second, lower frequency range. , The carrier subchannel at the high frequency end is used. According to this embodiment, in both directions:
It has the advantage of reducing far end crosstalk and echo. This is illustrated in FIGS. 6A and 6B.

In another embodiment, shown later in FIGS. 6C and 6D, the first transceiver uses the first, higher frequency end carrier subchannel in the higher frequency range and the second
Use the carrier subchannel at the low frequency end in the second, lower frequency range. According to this embodiment, the separation of carrier sub-channels can be maximized. This embodiment has the advantage of reducing near end crosstalk and echo in both directions and reducing the far end crosstalk of the transceiver transmitting at the lower frequency end in the lower frequency range. There is.

In yet another embodiment, not shown, the first transceiver uses the first, lower frequency end carrier subchannel in the higher frequency range, and the second transceiver A second, lower frequency end carrier subchannel in the lower frequency range is used. According to this embodiment, there is an advantage that near-end crosstalk in transmission from the second transceiver to the first transceiver is suppressed, and echo in both directions is suppressed.

In yet another embodiment, not shown, the first transceiver uses the first, lower frequency end carrier subchannel in the higher frequency range, and the second transceiver A second, higher frequency end carrier subchannel in the lower frequency range is used. According to this embodiment, there is an advantage that far-end crosstalk in transmission from the second transceiver to the second transceiver is suppressed.

As one embodiment, the bit error rate (BER) is defined such that the number of error bits is 1 or less per 10 ⁷ bits transmitted. This is also expressed as a rate of 10 ^-7 . An S / N margin of 4 to 6 dB is used, which includes approximately 3 dB of coding gain. As an example, 16 QAM (Quadrature Amplitude Modulatio
n) The SNR required to make the BER 10 ^{−7 for the} signal is 21.3 dB, assuming uncoded data. Since the coding gain is 3 dB, 22
. An SNR in the range of 3 to 24.3 dB can be considered sufficient.

FIGS. 6C and 6D show one embodiment of the present invention. As shown in FIG. 6C, f _dh 510 is initially selected for the tone / carrier sub-channel for the downlink, and as shown in FIG. 6D, the tone / carrier sub-channel for the frequency range for the uplink is f _ul 520 is selected first. An advantage of this embodiment is that it maximizes the frequency separation between the upstream and downstream signals while allowing the downstream band to be assigned a higher frequency tone / carrier subchannel. It is possible.

FIGS. 7A and 7B illustrate another feature of the present invention. Here, the power of each tone / carrier subchannel is limited to the power that keeps a minimum SNR margin. FIG. 7A shows the results of the arrangement of the tone / carrier subchannels and the power control according to this method. Higher frequency tone / carrier subchannels that experience greater losses have more power to maintain minimal SNR, while lower frequency tone / carrier subchannels have less power. I have. As shown in FIG. 7B, the power of the tone / carrier subchannel is similarly controlled in the uplink direction, and higher power is allocated to the tone of the higher frequency. If there is significant interference at a particular tone, that tone / carrier subchannel may require more power than other tones / carrier subchannels. If there is a very high level of interference, the tone / carrier subchannel may not be available at all.

FIGS. 7C and 7D show one embodiment of the present invention. As shown in FIG. 7C, tones of various power levels for the downlink are initially selected at f _dh 510 and, as shown in FIG. 7D, of various power levels in the frequency range for the uplink. For tone, f _ul 520 is selected first. As described with respect to FIGS. 6C and 6D, an advantage of this embodiment is that it allows for the assignment of high frequency tone / carrier subchannels to the downlink band while at the same time combining the uplink and downlink signals. The point is that the frequency separation between them can be maximized.

According to the present invention, the power of the tone / carrier sub-channels whose signal-to-noise ratio margin is much larger than required to keep an acceptable BER with sufficient margin can be reduced. . A signal-to-noise ratio margin in excess of 6 dB is referred to as “excess” in the sense that excess power causes interference with other signals.
Can be considered as If the power is suppressed to keep the signal-to-noise ratio margin in the range of 4 to 6 dB, the problem of interference can be suppressed.

In some embodiments, the power may be reduced by 1-3 dB. The power fine adjustment may be performed after the power rough adjustment. A typical initial power for ATU-R1 160 would be -38 dBm / Hz and a typical initial power for ATU-C1 110 would be -40 dBm / Hz. The power can be reduced to obtain a sufficient and not excessive signal-to-noise margin.

In addition to the problems associated with crosstalk in a system where all of the central office modems are co-located, a second modem channel bank 105 is located very close to a group of subscribers and One modem channel bank 100
When the binder group 130 is shared with the twisted wire pair used by the, a specific problem called “near-far problem” occurs. This near-far problem is caused by the fact that a modem close to the subscriber may transmit at a higher power given the really required power to send the signal to the intended recipient. Current ADSL standards allow modems to operate at the maximum allowable power, and excess power only guarantees a higher SNR margin to the receiver. Such transmissions, while ensuring a high SNR margin for the corresponding receiver, also have a significant effect on twisted wire pairs carrying signals from a central office located far away from the subscriber.

The present invention provides that a modem utilizes only the necessary tone / carrier subchannels, starts with a particular high frequency tone / carrier subchannel, and does not transmit more power than required to maintain an acceptable SNR margin. This solves the above-mentioned perspective problem.

In some embodiments, the power of the carrier subchannel varies depending on its position in the subset's frequency spectrum, with lower frequency carrier subchannels operating at lower power. This is because, for example, a signal of a lower frequency generally has a smaller attenuation per unit length than a signal of a higher frequency.

Combining the features of large frequency separation between uplink and downlink communication channels, and also taking into account the general tendency that lower frequency signals lose less power in radiation than higher frequency signals. In another embodiment, the separation of the carrier sub-channels in the frequency spectrum reduces the power control (gain) in each carrier sub-channel such that excess power and crosstalk are reduced in conventional systems. Control).

Further, it will be appreciated that any carrier sub-channel that does not need to transmit as many bits as the maximum number of bits capable of transmitting can reduce the gain. If a carrier sub-channel does not require transmission of bits for data transmission, the transmission gain of such unused carrier sub-channel is set to zero.

FIGS. 8A and 8B show a flowchart for tone allocation according to the present invention, which assumes the use of a tone / carrier subchannel allocation system 300. Although the principles of the present invention may be implemented in an object-oriented programming language, the flowcharts shown in FIGS. 8A and 8B will be used to better understand the methods and steps applied to tone / carrier subchannel assignment. Things.

Referring to FIG. 8A, starting at a start step 810, the system determines a guaranteed bit rate 820. This step may be performed using a service description record 702 that returns a guaranteed bit rate 327. The power spectrum distribution (PSD) mask to be used on the xDSL line is indexed in a PSD mask indexing step 825. The PSD mask may be any standardized, non-standardized, or agency-specified PSD mask.

Under certain conditions, it may be advantageous to use a PSD mask that sets the rated power to tone at a level substantially below an acceptable level. For example, -50 dB
It is possible to use a rated (coarse) power mask of m / Hz. Power mask is -40
Although more tones can be utilized when set to dBm / Hz, the reduced power results in a 10 dB reduction in the modem contribution to NEXT 110 and FEXT 220.

According to another example, the PSD mask is determined based on measurements made by tone / carrier sub-channel allocation system 300. By integrating the distance estimate between ATU-C and ATU-R determined from the SNR measurement, the value of the rated power mask is determined from the result. This power mask may be uniform throughout the downlink or uplink channels, or may vary from one tone / carrier subchannel to another.

The next step is to determine the highest frequency tone / carrier subchannel that provides an acceptable SNR, under the constraints of the PSD mask. This is called a maximum operating frequency (MUF), and MUF (N _max ) in step 830 for determining MUF (N _max )
Used to determine UF (N _max ). The MUF measures the SNR in each tone / carrier sub-channel and determines the minimum payload, ie, at least one bit to be conveyed with an acceptable S / N margin (typically measured in bits / tone). Can be determined by determining which tone / carrier sub-channel has an SNR that allows The highest frequency tone / carrier sub-channel carrying the smallest payload with the smallest SNR is MUF (N _max )
It is. Here, _Nmax is the number of carrier subchannels counted from the lower frequency end of the frequency range.

Once the highest available tone / carrier subchannel is determined, the tone / carrier
In the step of assigning payload to carrier subchannel N 840, a payload is assigned to the tone / carrier subchannel. The number N of tone / carrier sub-channels is decremented in step 850, which decrements N by 1, and a test is performed to determine whether the payload corresponding to the guaranteed bit rate has already been allocated. This test is performed in the payload allocation test 860. If the payload has not been fully allocated, the system returns to the allocate payload to tone / carrier subchannel N step 840 and continues to allocate the payload to tone / carrier subchannels. If it is determined in the payload allocation determination step 860 that the payload has already been fully allocated, the payload of the final tone / carrier subchannel is determined.

As shown in FIG. 8B, in a “whether the final tone / carrier subchannel payload is too low” decision step 865, the payload assigned to the final tone / carrier subchannel has been determined by the system. The system determines if it is below the limit and if so, the system proceeds to the next step. If the number of bits allocated to the tone / carrier subchannel is acceptable, the process ends at end step 870.

The number of bits allocated to the last tone / carrier sub-channel may be such that transmission of that tone / carrier sub-channel results in under-utilization of bandwidth. This determination is made in a step 875 of determining the reallocation of the payload to the last tone / carrier subchannel. In this step, the system may maintain the relationship between the final tone / carrier sub-channel and its payload, resulting in lower transmission power for that tone / carrier sub-channel. This option ends the process at end step 870. If the determination of the payload reassignment to last tone / carrier subchannel determination step 875 is YES, the payload reassignment step 880
Proceed to. In this step, the number of bits allocated to the last tone / carrier subchannel is redistributed among the already filled tone / carrier subchannels. This redistribution may be done randomly and in a more structured manner, starting with the most recent tone / carrier subchannel above the last tone / carrier subchannel and working towards higher tone / carrier subchannels. May be performed. Redistribution of these bits may require a small increase in the power level of the tone / carrier subchannel.

In another embodiment, redistribution may be made downward from the tone / carrier subchannel N _max . In the reallocation convergence step 885, a test is performed on the payload reallocation process performed in step 880. Step 84
If the payload allocation performed at 0 is such that the payload of the tone cannot be increased, the payload reallocation process diverges, in which case the steps 840, 850 and 860 comprise The system retains the first payload map obtained at the output of the performed loop, and ends the processing in an end step 870.

If the reallocation process converges, the original payload map is replaced with the new payload map obtained from the payload reallocation step 880, and the process ends at end step 870.

FIG. 9 shows a flowchart for tone assignment and power control. In this process, an initial tone is selected at the maximum allowable power level in the same steps as described with respect to FIG. 8A. The maximum allowed power may be determined from the spectrum mask or from calculations used to determine the rated power mask for that tone / carrier sub-channel or set of tones / carrier sub-channels. Processing proceeds to SNR margin excess test 900, where SNR
A determination is made as to whether the NR margin is excessive, and if so, the power in that tone / carrier subchannel may be reduced. The power in the tone / carrier subchannel is reduced in a power reduction step 910. The SNR margin excess test 900 is performed again to determine whether the power on the tone / carrier subchannel is acceptable. Through a cycle through the SNR margin excess test 900 and the power reduction step 910, the power can be repeatedly reduced until the appropriate level of power is reached. After the power level is acceptable, the counter N is decremented in a decrement N step 850 and the payload allocation test 8
60 is performed. If there are remaining payloads to be assigned to the tone, the system returns to assigning payload to tone / carrier subchannel N step 840. When the allocation of the payload for the tone is completed, the process proceeds to end step 870.

As described above, according to the present invention, it is clear that a multi-carrier communication technique that sufficiently satisfies the objects and goals thereof and achieves the above-described effects is provided.

Although the invention has been described with reference to specific embodiments, it will be apparent to those skilled in the art that various modifications and variations can be made that fall within the scope of the invention. Accordingly, the present invention is subject to substitutions, substitutions, and variations within the spirit of the appended claims.
It should be interpreted very broadly to include all modifications and variations.

[Brief description of the drawings]

FIG. 1A is a diagram showing a configuration example of a digital subscriber line system.

FIG. 1B is a diagram showing a configuration example of a digital subscriber line system.

FIG. 1C is a diagram showing a configuration example of a digital subscriber line system.

FIG. 1D is a diagram showing a configuration example of a digital subscriber line system.

FIG. 2A illustrates the problem of crosstalk in an xDSL system.

FIG. 2B is a diagram showing an example of a binder group.

FIG. 3 is a diagram illustrating an example of a spectrum management system.

FIG. 4 is a diagram illustrating a computer to which an embodiment of the present invention is applied;

FIG. 5A is a diagram illustrating an example of tone / carrier subchannel allocation in a conventional multicarrier DSL system.

FIG. 5B is a diagram showing an example of tone / carrier subchannel allocation in a conventional multicarrier DSL system.

FIG. 6A illustrates tone / carrier subchannel allocation according to the principles of the present invention.

FIG. 6B illustrates tone / carrier subchannel allocation according to the principles of the present invention.

FIG. 6C illustrates tone / carrier subchannel allocation according to the principles of the present invention.

FIG. 6D illustrates tone / carrier subchannel allocation according to the principles of the present invention.

FIG. 7A illustrates tone / carrier sub-channel power control in accordance with the principles of the present invention.

FIG. 7B illustrates tone / carrier sub-channel power control in accordance with the principles of the present invention.

FIG. 7C illustrates tone / carrier sub-channel power control in accordance with the principles of the present invention.

FIG. 7D illustrates tone / carrier sub-channel power control in accordance with the principles of the present invention.

FIG. 8A is a flowchart of an example of tone / carrier subchannel allocation according to the present invention.

FIG. 8B is a flowchart of an example of tone / carrier subchannel allocation according to the present invention.

FIG. 9 is a flowchart of an example of tone / carrier subchannel allocation and power control according to the present invention.

──────────────────────────────────────────────────続 き Continuation of front page (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE ), OA (BF, BJ, CF, CG, CI, CM, GA, GN, GW, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, LS, MW, SD, SL, SZ, TZ, UG, ZW), EA (AM, AZ, BY, KG, KZ, MD, RU, TJ, TM), AE, AL, AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CR, CU, CZ, DE, DK, DM, EE, ES, FI, GB, GD, GE, GH, GM, HR, HU, ID , IL, IN, IS, JP, KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MA, MD, MG, MK, MN, MW, MX, NO, (72) Invention NZ, PL, PT, RO, RU, SD, SE, SG, SI, SK, SL, TJ, TM, TR, TT, TZ, UA, UG, UZ, VN, YU, ZA, ZW Marcos Shi. Tzanes USA 94563, California, Olinda La Spiral 121 (72) Inventor Gregory Wellan, Massachusetts 01950, Newburyport Rayleigh Avenue 5 (72) Inventor Stewart Sandberg United States Massachusetts 02174, Arlington Pine Ridge Road 22F Term ( Reference) 5K022 DD01 DD13 DD19 DD22 5K051 AA02 BB01 BB02 DD07 DD13 GG15 HH01

Claims (24)

[Claims] A multi-carrier data modulation method for reducing the effects of interference phenomena in a communication system including a plurality of transceivers communicating with each other, comprising: a plurality of carriers for use in modulating a digital signal of an input data stream. Providing a sub-channel, defining a subset of the plurality of carrier sub-channels, wherein the subset spans a frequency domain having a highest frequency end and a lowest frequency end, wherein each carrier sub-channel of the subset includes at least one of the digital signals. At least one carrier sub-channel of the subset for transmission of one or more bits of the digital signal, wherein all assigned carrier sub-channels of the subset are The effect of the phenomenon will be reduced A multi-carrier data modulation method as described above, wherein the multi-carrier data modulation method is present at one of the ends of the frequency domain. 2. The multicarrier data modulation method according to claim 1, wherein the allocation of the carrier subchannels uses a part of the carrier subchannels included in the subset. 3. The method according to claim 1, wherein at least one carrier subchannel included in the subset includes:
A multicarrier data modulation method, wherein the carrier subchannel carries fewer bits than can be carried. 4. The multi-carrier data modulation of claim 1, wherein the frequency domain of the subset of carrier sub-channels includes at least one carrier sub-channel that cannot carry at least one bit. Method. 5. The method of claim 1, wherein a digital signal communicated from the first transceiver to the second transceiver is transmitted using a first frequency domain allocated from a first subset of a plurality of carrier subchannels. Modulating a digital signal communicated from the second transceiver to the first transceiver, the second signal comprising a plurality of carrier sub-channels and assigned from a second subset different from the first subset. A multicarrier data modulation method, wherein modulation is performed using a frequency domain. 6. The method according to claim 1, further comprising: adjusting a gain of at least one carrier sub-channel of the subset to determine a number of bits that the carrier sub-channel can carry from a maximum number of bits to information included in the digital signal. A multicarrier data modulation method characterized in that the number of bits is reduced to a smaller number of bits sufficient to carry. 7. The multicarrier data modulation method according to claim 1, wherein the interference phenomenon is at least one of near-end crosstalk, far-end crosstalk, noise, and echo. 8. The multi-carrier data modulation method of claim 1, comprising the step of determining a maximum number of bits of a digital signal that each carrier sub-channel of the subset can carry to provide a predetermined quality of service. A multicarrier data modulation method. 9. The multi-carrier according to claim 8, wherein the predetermined quality service is determined based on at least one of a bit transmission rate, a bit error rate, a signal-to-noise ratio margin, and power. Data modulation method. 10. A multi-carrier data modulator for reducing the effect of an interference phenomenon in a communication system including a plurality of transceivers communicating with each other, wherein a digital signal of an input data stream can be modulated on a plurality of carrier sub-channels. And selecting a subset of the plurality of carrier sub-channels, wherein the subset comprises:
A sub-channel selection module spanning a frequency domain having a highest frequency end and a lowest frequency end, wherein each carrier sub-channel of the subset is capable of carrying at least one bit of the digital signal; and at least one of the subsets. One carrier sub-channel is allocated for transmission of one or more bits of the digital signal, and all the allocated carrier sub-channels of the subset are allocated in the frequency domain so that the effects of interference phenomena are reduced. And a carrier sub-channel allocation module, which is present at one of the ends. 11. The multicarrier data modulation device according to claim 10, wherein the digital signal modulation module uses a part of carrier subchannels included in the subset. 12. The multi-channel system according to claim 10, wherein the subset of carrier sub-channels spans a frequency domain including at least one carrier sub-channel that cannot carry at least one bit. Carrier data modulator. 13. The multicarrier data modulator according to claim 10, further comprising a module for receiving a digital signal modulated and transmitted in one or more carrier subchannels. 14. The digital signal as claimed in claim 13, wherein the digital signal to be transmitted is modulated and received using a first frequency domain allocated from a first subset of a plurality of carrier sub-channels. Is composed of a plurality of carrier sub-channels, using a second frequency domain allocated from a second subset different from the first subset,
A multi-carrier data modulation device characterized by being modulated. 15. The method according to claim 10, wherein the gain of at least one carrier sub-channel of the subset is adjusted, and the number of bits that the carrier sub-channel can carry is determined from the maximum number of bits by using information included in the digital signal. A multi-carrier data modulator comprising a gain control module that reduces the number of bits to a number that is small enough to carry. 16. The gain control module according to claim 15, wherein the gain control module controls the gain so that the reduced number of bits is a minimum number of bits necessary to carry information included in the digital signal. A multicarrier data modulation device characterized by the above-mentioned. 17. The apparatus of claim 10, further comprising: an interference detection module that determines a maximum number of bits of a digital signal that can be carried by each carrier subchannel of the subset to provide a predetermined quality of service. Multi-carrier data modulation device. 18. The method of claim 17, wherein the interference detection module comprises at least one of a bit transmission rate, a bit error rate, a signal-to-noise ratio margin, power, near-end crosstalk, far-end crosstalk, noise level, and echo. A multi-carrier data modulation device for detecting one of them. 19. A multi-carrier data modulator for reducing the effects of interference phenomena in a communication system including a plurality of transceivers communicating with each other, wherein the digital data is modulated and transmitted on one or more carrier sub-channels. Receiving the signal, wherein the one or more carrier subchannels include:
A carrier sub-channel subset allocated from a plurality of carrier sub-channels, the subset spanning a frequency domain having a highest frequency end and a lowest frequency end, wherein each carrier sub-channel of the subset includes at least one of the digital signals. A module capable of carrying one bit, wherein all assigned carrier sub-channels of the subset are present at one of the ends of the frequency domain such that the effects of interference phenomena are reduced; A demodulation module for demodulating the transmitted digital signal modulated in one or a plurality of carrier sub-channels and generating an output data stream from the demodulated transmission signal. . 20. A computer program recorded on a readable medium, when executed on a computer, determining a subset of a plurality of carrier sub-channels, the subset identifying a highest frequency end and a lowest frequency end. And wherein each carrier sub-channel of the subset is capable of carrying at least one bit of a digital signal, wherein at least one carrier sub-channel of the subset is associated with one or more of the digital signals. Computer wherein all carrier sub-channels assigned to the transmission of a plurality of bits and assigned to said subset are present at one of said ends of said frequency domain such that the effects of interference phenomena are reduced. program. 21. The computer-implemented method of claim 20, wherein the step of determining the maximum number of bits of the digital signal that the carrier subchannel can carry to provide a predetermined quality service is performed. Characteristic computer program. 22. The computer-readable medium of claim 21, wherein when executed on a computer, the digital signal is transmitted on a first carrier sub-channel having a first frequency,
Modulating using the maximum number of bits that the first carrier sub-channel can carry, and then modulating the digital signal with a second carrier sub-channel having a second frequency. And a computer program. 23. The digital signal according to claim 21, wherein when executed by a computer, the reduced number of bits carried by the carrier subchannel is included in the digital signal from the maximum number of bits that the carrier subchannel can carry. Computer program characterized in that the step of calculating is performed to a smaller number of bits sufficient to carry information. 24. The computer readable medium of claim 23, wherein, when performed by a computer, modulating the digital signal on the carrier subchannel using the smaller number of bits instead of the maximum number of bits. A computer program characterized by the following.