Communication system and communication method

Details Communication system and communication method Communication system and communication method

2000-05-10

2004-08-24

Sam, Phirin (Department: 2662)

Multiplex communications

Communication techniques for information carried in plural...

Adaptive

C370S473000, C370S493000, C370S494000, C370S495000, C370S498000

Reexamination Certificate

active

06782005

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a communication system and a communication method for performing data communication of discrete multi-tone modem type between a plurality of data communication units through a telephone line.
BACKGROUND ART
In recent years, the xDSL communication system including the ADSL (Asymmetric Digital Subscriber Line) communication system, the HDSL (High-bit-rate Digital Subscriber Line) communication system and the SDSL communication system for performing a high-speed digital communication of several mega bits per second using the existing telephone copper cable have been closely watched. The xDSL communication system is called the DMT (Discrete Multi-Tone) modem system. This system is standardized in T1.413, etc. of ANSI.
This digital communication system, especially in the case where the xDSL transmission path and the ISDN transmission path of the half-duplex ISDN communication system are bound together as an aggregated line or otherwise placed adjacently to each other, poses the problem that the XDSL communication through the xDSL transmission path is affected by interference noises from the ISDN transmission path or other lines and decreases in speed. For solving this problem, various techniques are used.
FIG. 12
shows the interference noises of an ISDN transmission path
2
from a central office (CO)
1
, which affect an ADSL transmission path
3
constituting a xDSL transmission path bound with the ISDN transmission path
2
midway as an aggregated line.
When viewed from the ADSL terminal equipment (ATU-R; ADSL transceiver unit, remote terminal end)
4
constituting a communication unit at a terminal of the ADSL communication system, the interference noise transmitted through the ADSL transmission path
3
by the office equipment (ISDN LT)
7
of the ISDN transmission system is called the FEXT (Far-End crossTalk) noise, while the interference noise transmitted through the ADSL transmission path
3
by the terminal equipment (ISDN NT1)
6
of the ISDN transmission system is called the NEXT (Near-End crossTalk) noise. Especially, these noises are transmitted to the ADSL terminal equipment (ATU-R)
4
through the ADSL transmission path
3
which is coupled with the ISDN transmission path
2
midway as an aggregated line.
When viewed from the ADSL office equipment (ATU-C: ADSL transceiver unit, central office end)
5
constituting the office equipment of the ADSL communication system, on the other hand, the result is opposite from the case viewed from the ADSL terminal equipment (ATU-R)
4
. In such a case, the interference noise transmitted by the office equipment (ISDN LT)
7
of the ISDN transmission system constitutes the NEXT noise, while the interference noise transmitted by the terminal equipment (ISDN NT1)
6
of the ISDN transmission system makes up the FEXT noise.
In overseas ISDN communication system which is full-duplexed, the up and down transmissions are performed at the same time. When viewed from the ADSL terminal equipment (ATU-R)
4
, therefore, the NEXT noise generated by the terminal equipment (ISDN NT1)
6
of the ISDN transmission system nearer to the ADSL terminal equipment (ATU-R)
4
is controlling, i.e. has a larger effect.
For this reason, during the training period of the ADSL modem (not shown) installed at the ADSL terminal equipment
4
, the characteristic of the NEXT noise components having a large effect is measured, and the number of transmission bits and the gain of each channel meeting the noise characteristic are determined by bit mapping. Further, in order to improve the transmission characteristics, the coefficients of the time domain equalizer (TEQ) for adaptive equalization in time domain and the frequency domain equalizer (FEQ) for adaptive equalization in frequency domain are converged and determined, so that a set of coefficient tables for NEXT noises are provided for each of TEQ and FEQ.
Although this measure eliminates the problem in the overseas digital communication systems, the half-duplex communication system TCM-ISDN employed in Japan as an existing ISDN communication system, in which the up and down data transmission are switched by time division like Ping-Pong poses a problem. Namely, in the case where the half-duplex transmission path and other transmission path are adjacently placed to each other as an aggregated line or the like, the NEXT noises and the FEXT noises from the half-duplex transmission path have an effect alternately on the communication terminals connected to the other transmission paths adjacent to the half-duplex transmission path.
In the Japanese ADSL system, therefore, a method is proposed in which the bit map is switched in accordance with the FEXT and NEXT sections of the TCM-ISDN interference noises (“G.lite: Proposal for draft of Annex of G.lite”, ITU-T, SG-15, Waikiki, Hawaii Jun. 29,-Jul. 3, 1998, Temporary Document WH-047).
FIG. 13
shows an outline of a digital communication system using the digital communication equipment employing the method described in the above literature. In
FIG. 13
, numeral
11
designates a central office (CO) for controlling the TCM-ISDN communication and the ADSL communication, numeral
12
designates a TCM-ISDN transmission path for the TCM-ISDN communication, numeral
13
designates an ADSL transmission path for the ADSL communication, numeral
14
designates an ADSL terminal equipment (ATU-R; ADSL transceiver unit, remote terminal end) such as a communication modem for performing the ADSL communication with other ADSL communication terminal equipment (not shown) through the ADSL transmission path
13
, numeral
15
designates an ADSL office equipment (ATU-C; ADSL transceiver unit, central office end) for controlling the ADSL communication within the central office
11
, numeral
16
designates a TCM-ISDN terminal equipment (TCM-ISDN NT1) such as a communication modem for performing the TCM-ISDN communication with other TCM-ISDN terminal equipment (not shown) through the TCM-ISDN transmission path
12
, numeral
17
designates a TCM-ISDN office equipment (TCM-ISDN LT) for controlling the TCM-ISDN communication in the central office
11
, and numeral
18
designates a sync controller for synchronizing the communication between the TCM-ISDN office equipment (TCM-ISDN LT)
17
and the ADSL office equipment (ATU-C)
15
. The sync controller
18
may alternatively be installed in the TCM-ISDN office equipment (TCM-ISDN LT)
17
or in the ADSL office equipment (ATU-C)
15
.
As described above, the interference noise transmitted, through the TCM-ISDN transmission path
12
and the ADSL transmission path
13
adjacently placed to each other as an aggregated line, by the TCM-ISDN office equipment (TCM-ISDN LT)
17
providing a far half-duplex communication system when viewed from the ADSL terminal equipment (ATU-R)
14
, as shown in Fig.
13
, is called the “FEXT noise”. On the other hand, the interference noise transmitted, through the TCM-ISDN transmission path
12
and the ADSL transmission path
13
adjacently placed to each other as an aggregated line, by the TCM-ISDN terminal equipment (TCM-ISDN NT1)
16
constituting a near half-duplex communication system is called the “NEXT noise”.
When viewed from the ADSL office equipment (ATU-C)
15
, on the other hand, the case is opposite to that viewed from the ADSL terminal equipment (ATU-R)
14
, and the interference noise transmitted by the office equipment (ISDN LT)
17
of the ISDN transmission system constituting the near half-duplex communication system is the NEXT noise, while the interference noise transmitted by the terminal equipment (ISDN NT1)
16
of the ISDN transmission system making up a far half-duplex communication system constitutes the FEXT noise.
FIG. 14
shows a functional configuration of a transmission unit or a dedicated transmitter (hereinafter collectively referred to as the transmission system) such as a communication modem of the ADSL office equipment (ATU-C; ADSL transceiver unit, central office end)
15
of the digital communication system. On the other

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