Multiplex communications – Duplex – Transmit/receive interaction control
Reexamination Certificate
1999-05-07
2004-03-30
Patel, Ajit (Department: 2664)
Multiplex communications
Duplex
Transmit/receive interaction control
C375S296000
Reexamination Certificate
active
06714520
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a system, an apparatus and a method for multi-carrier transmission which in particular use a bit allocation switching system and a FDM (frequency division multiplexing) system and implements the data transmission using multi-carrier under the noise environment that the changing timing of noise level is known.
DESCRIPTION OF THE RELATED ART
Recently, an xDSL (digital subscriber line) technology has been focused on, by which the high-speed transmission of a few megabits/second becomes possible using a metallic cable, such as a loop. In this, x of the xDSL means any of the various types of DSL and x has an alphabet such as A, S, V and H depending on its technology. In this technology, an ADSL (asymmetric digital subscriber line) technology has been highly focused on. This ADSL has different transmission speeds between upstream and downstream directions and this asymmetrical nature is suitable for the access for Internet.
This ADSI, apparatus uses a named DMT (discrete multi-tone) system as a MODEM (modulator-demodulator), and converts digital signals to analog signals and transmits the converted signals. The DMT system implements the modulation applying a QAM (quadrature amplitude modulation) for 256 carriers and the modulated carriers are multiplexed using an IFFT (inverse fast Fourier transform) and are transmitted. The receiving side extracts each carrier from the multiplexed signals using a FFT (fast Fourier transform) and implements the demodulation to signals modulated QAM, with this, the high-speed transmission becomes possible.
However, more over 4 million loops of an ISDN (integrated services digital network) being a TCM (time compression multiplexing) system have been installed in Japan. At the case that the loop for the ADSL is installed adjacent to the loop for the ISDN, a cross-talk noise making the communication speed of the ADSL loop lessen occurs effected by the ISDN loop. In this case, it is possible that the loop for ASDL is separately installed from the loop for ISDN, not to be installed in the same bundle of cable. However, it is too big for an operator to bear the cost. Therefore, it is desirable to establish a transmission method that can secure the transmission capacity not influenced by the cross-talk noise caused in the same batch of the loops for ISDN and the loops for ASDL.
FIG. 1
is a cross-talk noise diagram showing a cross-talk noise generated in the ADSL apparatus caused by the ISDN line. Referring to
FIG. 1
, the cross-talk noise generated in the ADSL apparatus which used the adjacent line to the ISDN line using the TCM system is explained. In
FIG. 1
, the cross-talk noise generated in an ATU-R (ADSL transceiver unit, remote terminal end) caused by the data transmission of the TCM-ISDN loop is shown, at the time when the downstream data transmission is implemented in the ADSL loop.
In the TCM-ISDN loop, the data transmission of upstream and downstream directions is implemented alternately every 1.25 milliseconds. At the time when the ADSL loop implements downstream data transmission and the TCM-ISDN loop implements upstream data transmission, a high power signal before attenuation of the TCM-ISDN influences an attenuated signal of the ADSL loop and a NEXT (near end cross-talk) is generated at the ATU-R. At the time when the ADSL loop implements downstream data transmission and the TCM-ISDN loop implements downstream data transmission, a signal of the TCM-ISDN influences an attenuated signal of the ADSL loop and a FEXT (far end cross-talk) is generated at the ATU-R. The same kind of influences is generated at an ATU-C (ADSL transceiver unit, central office end).
FIG. 2
is a noise amount diagram showing the amount of the cross-talk noise in FIG.
1
. As shown in
FIG. 2
, the amount of noise generating at the NEXT is larger than that at the FEXT. The reason why this occurs is that the high power signal before attenuation of the TCM-ISDN influences the attenuated signal of the ADSL loop. Focusing on this difference of the amount of noise, a system is proposed, this system transmits data by switching the amount of data to be transmitted between at the time generated NEXT and the FEXT. This system is called a DBM (dual bit-map) and transmits large data at the time generated the FEXT that the amount of noise is small and transmits small data at the time generated the NEXT that the amount of noise is large, as shown in FIG.
2
.
As mentioned above, at the ADSL apparatus whose loop is adjacent to the TCM-ISDN loop, the amount of noise changes cyclically, therefore SNR (signal to noise ratio) of each carrier is measured in each of upstream and downstream directions, and the bit allocation is obtained corresponding to this measured SNR.
FIG. 3
is a block diagram showing the structure of a conventional ADSL apparatus. Referring to
FIG. 3
, the structure of the conventional ADSL apparatus is explained.
The transmitting section of the ATU-C
300
includes a rate converter
301
in which data transmitted in a constant speed from the external equipment are temporarily stored, a mapping section
302
which switches the bit allocation and transmission power allocation of each carrier corresponding to the changing timing of noise level and implements the bit allocation and transmission power allocation to each carrier, an IFFT (inverse fast Fourier transform)
303
which implements the modulating and multiplexing in each carrier for multi-point QAM (quadrature amplitude modulation) signals being the output of this mapping, and a DAC (digital to analog converter)
304
which converts this digital mutiplexed output to a downstream analog signal and transmits the analog signal.
The receiving section of the ATU-C
300
includes an ADC (analog to digital converter)
305
which converts analog signals transmitted from an ATU-R
400
to digital signals, a FFT (fast Fourier transform)
306
which implements the fast Fourier transform for these digital signals, a demapping section
307
which switches the bit allocation and transmission power allocation of each carrier corresponding to the changing timing of noise level and demodulates the transmitted signals, and a rate converter
308
which adjusts the change of the amount of data transmission caused by the change of bit allocation and transfers the data to the external equipment in a constant speed.
The transmitting section of the ATU-R
400
includes a rate converter
401
in which data transmitted in a constant speed from the external equipment are temporarily stored, a mapping section
402
which switches the bit allocation and transmission power allocation of each carrier corresponding to the changing timing of noise level and implements the bit allocation and transmission power allocation to each carrier, an IFFT (inverse fast Fourier transform)
403
which implements the modulating and multiplexing in each carrier for multi-point QAM (quadrature amplitude modulation) signals being the output of this mapping, and a DAC (digital to analog converter)
404
which converts this digital multiplexed output to an upstream analog signal and transmits the analog signal.
The receiving section of the ATU-R
400
includes an ADC (analog to digital converter)
408
which converts analog signals transmitted from the ATU-C
400
to digital signals, a FFT (fast Fourier transform)
407
which implements the fast Fourier transform for these digital signals, a demapping section
406
which switches the bit allocation and transmission power allocation corresponding to the changing timing of noise level and demodulates the transmitted signals, and a rate converter
405
which adjusts the change of the amount of data transmission caused by the change of bit allocation and transfers the data to the external equipment in a constant speed.
The ATU-C
300
further includes a pseudo-random signal generating section
310
and a bit & power allocation calculating section
312
and the ATU-R
400
further includes a pseudo-random signal generating section
409
and a bit & power
NEC Corporation
Patel Ajit
Scully Scott Murphy & Presser
LandOfFree
System, apparatus method for multi-carrier transmission does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System, apparatus method for multi-carrier transmission, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System, apparatus method for multi-carrier transmission will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3282175