Pulse or digital communications – Transceivers – Transmission interface between two stations or terminals
Reexamination Certificate
1999-06-29
2002-05-21
Vo, Don N. (Department: 2631)
Pulse or digital communications
Transceivers
Transmission interface between two stations or terminals
C375S222000, C375S260000, C370S465000
Reexamination Certificate
active
06393051
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a digital subscriber line communicating system and a transceiver in the system which utilize an existing telephone line as a high speed data communication line. More particularly, it relates to an improvement of a modulation/demodulation system in a transmission apparatus used in the above mentioned communication system.
In recent years, multimedia services such as internet and so forth have expanded throughout society and into homes. Accompanied by such development, it has been strongly required to promptly provide an economical and reliable digital subscriber line communicating system for utilizing such services.
2. Description of the Related Art
(1) An Explanation of an ADSL
As a technique to provide a digital subscriber line communicating system which utilizes the existing telephone line as a high speed data communication line, an xDSL (Digital Subscriber Line) is known. xDSL is a communicating system which utilizes a telephone line and a modulation/demodulation technique. xDSLs are generally classified into a symmetric type and an asymmetric type. In the symmetric type, upstream transmission speed from a subscriber home (hereinafter referred to as a remote terminal side or an RT side) to an accommodating central office (hereinafter referred to as a central office side or a CO side) is symmetric with the transmission speed from the central office side to the remote terminal side. In the asymmetric type, the transmission speed from the remote terminal side to the central office side is asymmetric with the transmission speed from the central office side to the remote terminal side.
In the asymmetric xDSLs, there is an Asymmetric DSL (ADSL) modem which is provided with the G.DMT standard having a downstream transmission speed of about 6 Mbit/sec. and the G.lite standard having a downstream transmission speed of about 1.5 bits/sec. Both of the G.DMT and G.lite employ Discrete Multitone (DMT) modulation.
In the prior art, the digital subscriber line communicating system has a problem of long data transmission delay.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a digital sub scriber line transmission system and a transceiver therein in which the data transmission delay amount is suppressed,
To attain the above object, there is provided, according to an aspect of the present invention, a digital subscriber line communicating system for communicating modulated symbols between a transmitting side and a receiving side through a communication line, comprising: a bitmap calculating unit, provided in the receiving side, for calculating a bit map which defines the number of transmissible bits for each carrier signal al of the symbols in each of periodical noise durations, the calculated bitmap being sent to and stored in the transmitting side during an initialization period of the communication; and a rate converter, provided in the transmitting side, for converting a constant rate of an input transmitting data into a rate determined by the bitmap, and for adding, in a predetermined number of the periodical noise durations, dummy bits to the data having the converted rate, the dummy bits corresponding to the difference between the rate determined by the bitmap and the constant rate. The bitmap calculating unit includes a line quality measuring unit for measuring the quality of the communication line in each of the periodical noise durations, a transmission bit number converter for calculating the number of transmissible bits to be allocated to each carrier to form the bitmap, and a bitmap optimizing unit for minimizing the dummy bits by decreasing the number of the transmissible bits allocated to each carrier signal of the symbols. The decreasing is performed in the order from the number of bits allocated to a carrier with a smaller S/N margin to the number of bits allocated to a carrier with a larger S/N margin.
After the initialization period, the transmitting side transmits data according to the bitmap optimized in the receiving side and transmitted from the receiving side to the transmitting side.
The subscriber line communicating system according to above mentioned, further comprises a timing signal generating unit for generating the timing signal synchronized with a periodical noise including the periodical noise durations which interfere with the transmitting side and the receiving side, and a sliding window generating unit for generating sliding windows based on the timing signal. 345 continuous modulated symbols including 5 synchronization symbols constitute a hyperframe including 34 of the sliding windows. According to a single bitmap mode in which the symbols are transmitted and received through only insides of the sliding windows, the number of the dummy bits is expressed as:
(a transmitting capacity of data output from the rate converter)−(a transmitting capacity of data input to the rate converter)=(N_bitmap_inside)*(N_inside)−(N_rate)*(340*8)
where “N_bitmap_inside” is the number of bits transmitted per each symbol in each inside of the sliding windows;
“N_inside” is the number of symbols in the insides of the sliding windows per each hyperframe;
“N_rate” is (N_rate*32 kbps)=user data rate;
340*8 is the number of bits in each hyperframe per 32 kbps
wherein the dummy bits are minimized by replacing
N_rate=int {(Mi*N_inside)/(340*8)} and
N_bitmap_inside=int [{(N_rate*340*8) +N_inside
—
1}/N_inside]
where “int” means to round down to an integer, and “Mi” is number of the transmittable bits calculated by line quality measuring.
According to a dual bitmap mode in which the symbols are transmitted and received through both insides and outsides of the sliding windows, the number of the dummy bits is expressed as:
(a transmitting capacity of data output from the rate converter)−(a transmitting capacity of data input to the rate converter)=(N_bitmap_inside)*(N_inside) +(N_bitmap_outside)*(N_outside)−(N_rate)*(340*8)
where “N_bitmap_inside” is the number of bits transmitted per each symbol in each inside of the sliding windows;
“N_inside” is the number of symbols in the insides of the sliding windows per each hyperframe;
“N_bitmap_outside” is the number of bits transmitted per each symbol in each outside of the sliding windows;
“N_outside” is the number of symbols in the outsides of the sliding windows per each hyperframe;
“N_rate” is (N_rate*32 kbps)=user data rate;
340*8 is the number of bits in each hyperframe per 32 kbps
wherein, for example, the dummy bits are minimized by replacing
N_rate= int{(Mi*N_inside+Mo*N_outside)/(340*8)} and
N_bitmap_outside=Mo
N_bitmap_inside =int[{(N_rate*340*8)−N_bitmap_outside* N_outside +N_inside−1}/N_inside]
where “int” means to round down to an integer;
“Mitt” is number of the transmittable bits per each inside symbol calculated by line quality measuring; and
“Mo” is number of the transmittable bits per each outside symbol calculated by line quality measuring.
According to another aspect of the present invention, there is provided a transceiver having the same features as in the above-mentioned digital subscriber line communicating system.
Specifically, the conversion delay of the rate converter is given as the sum of the delay caused by the addition of dummy bits and the delay caused by the rate conversion of the data stream corresponding to the sliding window. The present invention is intended to suppress the whole data transmission delay by minimizing each of the delays,
REFERENCES:
patent: 5063574 (1991-11-01), Moose
patent: 6266347 (2001-07-01), Amrany et al.
Hasegawa Kazutomo
Koizumi Nobukazu
Miyoshi Seiji
Sasaki Takashi
Rosenman & Colin LLP
Vo Don N.
LandOfFree
Digital subscriber line communicating system and a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Digital subscriber line communicating system and a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Digital subscriber line communicating system and a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2866091