Pulse or digital communications – Systems using alternating or pulsating current – Antinoise or distortion
Reexamination Certificate
2000-10-23
2002-09-10
Le, Amanda T. (Department: 2634)
Pulse or digital communications
Systems using alternating or pulsating current
Antinoise or distortion
C375S349000, C375S354000, C370S201000, C370S507000, C370S517000, C370S521000
Reexamination Certificate
active
06449316
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a communication device for performing data communication by means of a DMT (discrete multi tone) data set method between communication devices. In particular, this invention relates to a communication device that performs interference rejection between TCM (Time Compression Multiplexing: time-shared transmission method)—ISDN and ADSL, or between ADSL and ADSL, relative to each other, and also relates to interference rejection method thereof.
BACKGROUND ART
A conventional communication device will first be described. At first, in a conventional communication device for performing data communication by means of a DMT (Discrete Multi Tone) data set method, the operation of a transmission system will be described briefly. For example, when data communication is to be performed with the DMT data set method, using an existing transmission line such as a telephone line or the like, in the transmission system, there is performed a tone ordering processing (thereby, the transmission rate is determined), that is, a processing for allocating transmission data having number of bits that can be transmitted, respectively, to a plurality of tones (multi carrier) of a frequency band set in advance based on a S/N ratio (signal-to-noise ratio). Specifically, for example, transmission data having number of bits corresponding to the respective S/N ratio are allocated to tones of from tone 0 to tone X (X is an integer showing the number of tones) in each frequency.
The transmission data are then multiplexed for each frame, by performing the tone ordering processing corresponding to the S/N ratio and a coding processing. Moreover, in the transmission system, inverse fast Fourier transform (IFFT) is performed with respect to the multiplexed transmission data, to convert parallel data after the inverse fast Fourier transform to serial data, and thereafter, the digital waveform is converted to the analog waveform through a D/A converter, which is finally subjected to a low-pass filter, and the transmission data is transmitted on the telephone line.
Operation of a reception system in a conventional communication device that performs data communication by means of a DMT data set method will now be described briefly. Similarly to the above case, when data communication is to be performed with the DMT data set method, using an existing transmission line such as a telephone line or the like, in the reception system, the received data (the above-described transmission data) is subjected to a low-pass filter, and thereafter, the analog waveform is converted to the digital waveform through an A/D converter, and an adaptive equalization processing of time domain is performed by a time domain equalizer.
The data subjected to the time domain adaptive equalization processing is converted from serial data to parallel data, which is then subjected to the fast Fourier transform. Thereafter, an adaptive equalization processing of frequency domain is performed by a frequency domain equalizer.
The data subjected to the frequency domain adaptive equalization processing is converted to serial data through a complex processing (complex method of maximum likelihood) and the tone ordering processing, and thereafter, processing such as rate convert processing, FEC (forward error correction), de-scramble processing, CRC (cyclic redundancy check) or the like is performed, to finally reproduce the transmission data.
As a wire system digital communication method that performs data communication using the above-described DMT data set method, there can be mentioned an XDSL communication method such as an ADSL (Asymmetric Digital Subscriber Line) communication method that performs high speed digital communication at several megabits per second, using an existing telephone line. This method is standardized in ANSI, T1.413 or the like. With this digital communication method, in particular, the ADSL transmission line and the ISDN transmission line in the ISDN communication system of a half duplex communication method are tied up at an aggregate line on the way and adjacent to each other. The ISDN communication system referred herein is a method heretofore adopted in NTT, for example, the TCM-ISDN service, which service is generally referred to as a ping-pong method.
FIG. 9
shows a signal flow in the TCM-ISDN service heretofore serviced by NTT. With this service, for example as shown in
FIG. 9
, ISDN-DS (Downstream) is transmitted from OCU (Office Channel Unit), that is, a base station, and the ISDN-DS is received by DSU (Digital Service Unit), that is, by a reception device side. Then, on the reception device side, after 7 UI (1 UI: 3.125 &mgr;s) since having completed reception, ISDN-US (Upstream) is transmitted, and the ISDN-US is received by the base station side.
Specifically, with the above DSU, for example as shown in
FIG. 9
, a delay corresponding to the distance with OCU exists in the ISDN service. For example, if the distance between OCU and DSU is a short distance (here, a distance 0 is shown), there is no delay, and upon transmission of ISDN-DS by the OCU, the DSU receives the ISDN-DS. Moreover, ISDN-US transmitted from the DSU after 7 UI is transmitted to the OCU without any delay. On the other hand, if the distance between the OCU and the DSU is a long distance (here, a long distance limit is shown), when the OCU transmits ISDN-DS, the DSU receives the ISDN-DS after a predetermined delay time has passed. Moreover, ISDN-US transmitted from the DSU after 7 UI is transmitted to the OCU after a predetermined delay time has passed. Here, TTR (TCM-ISDN Timing Reference) shown in the figure is a signal serving as a reference for synchronization in the downstream and upstream on the network, and in the TCM-ISDN, this timing may be known only in the base station. Furthermore, one cycle of TTR is designated herein as, for example, 2.5 ms.
On the other hand, the ADSL transmission line is tied up with and adjacent to the above-described TCM-ISDN transmission line of the half duplex communication method at an aggregate line on the way. Hence, without timing adjustment between the ADSL and the TCM-ISDN, the TCM-ISDN signal becomes interference signal, thereby causing deterioration in the communication characteristic in the ADSL. That is to say, as shown in
FIG. 10
, NEXT (Near End Cross Talk) noise and FEXT (Far End Cross Talk) noise occur, causing deterioration in the communication characteristic in the ADSL.
Accordingly, in the ADSL service, as shown in FIG.
11
and
FIG. 12
, a boundary (dotted line shown in the figure) is provided, taking the delay into consideration, so as to be downstream at the time of DS of the TCM-ISDN, and to be upstream at the time of US of the TCM-ISDN. Here, FIG.
11
and
FIG. 12
show a hyper-frame symbol form in the ADSL, respectively, and constitutes one hyper frame with, for example, 345 symbols. One hyper frame is designated herein as 85 ms, and this value is a multiple of TTR (2.5 ms) described above. Also, in FIG.
11
and
FIG. 12
, an example of a hyper frame including a cyclic prefix is shown, but similar operation is possible even in a hyper frame including no cyclic prefix. In this case, however, one hyper frame (345 symbols) becomes 80 ms.
Furthermore, a netted portion in
FIG. 11
is referred to as FEXT
R
data symbol (indicating the time when the reception device side is in the FEXT period), and other data is referred to as NEXT
R
data symbol (indicating the time when the reception device side is in the NEXT period). Also, a netted portion in
FIG. 12
is referred to as FEXT
c
data symbol (indicating the time when the base station side is in the FEXT period), and other data is referred to as NEXT
c
data symbol (indicating the time when the base station side is in the NEXT period).
Specifically, FEXT-DS transmission is performed by the ATU-C at the time of ISDN-DS transmission by means of the OCU, and FEXT-US transmission is performed by the ATU-R at the time of ISDN-US transmission by means of the DSU.
As a result, a conventional ADS
Matsumoto Wataru
Narikawa Masafumi
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