U.S. patent application number 10/863246 was filed with the patent office on 2004-11-11 for method and multi-carrier transceiver supporting dynamic switching between active application sets.
This patent application is currently assigned to Aware, Inc.. Invention is credited to Gross, Richard W., Hunter, David C., Padir, Halil, Tzannes, Marcos C., Tzannes, Michael A..
Application Number | 20040223510 10/863246 |
Document ID | / |
Family ID | 32831181 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040223510 |
Kind Code |
A1 |
Tzannes, Marcos C. ; et
al. |
November 11, 2004 |
Method and multi-carrier transceiver supporting dynamic switching
between active application sets
Abstract
A transceiver and method for communicating over a communications
channel having a plurality of subchannels are described. In
particular, the transceiver is capable of dynamically switching
between communicating data for a first active application set and
communicating data for a second different active application set.
An active application set is defined as the set of one or more
active applications for which the transceiver is currently
communicating data. As part of communicating data for the first
active application set, the transceiver allocates the subchannels
to the one or more applications in the first application set. The
transmission requirements of the first active application set
defines a first communication state of the transceiver. When the
transceiver dynamically transitions to communicating data for the
second different application set, the transceiver reallocates the
subchannels to the one or more applications in the second different
application set. The transmission requirements of the second
different active application set defines a second communication
state of the transceiver. In one embodiment the transceiver
modifies the data rates of subchannels in the Bit Allocation Table
according to the transmission requirements of the application whose
data is being transmitted on the particular subchannel. In another
embodiment, the transceiver is capable of dynamically switching
from transmitting data for an Internet access application to
transmitting data for a voice telephony application in addition to
the Internet access application. In a further embodiment, the ABCD
voice telephony signaling bits can be transmitted with either the
data from the Internet access application or the data from the
voice telephony application.
Inventors: |
Tzannes, Marcos C.; (Orinda,
CA) ; Tzannes, Michael A.; (Lexington, MA) ;
Hunter, David C.; (Winchester, MA) ; Gross, Richard
W.; (Acton, MA) ; Padir, Halil; (North
Andover, MA) |
Correspondence
Address: |
MILES & STOCKBRIDGE PC
1751 PINNACLE DRIVE
SUITE 500
MCLEAN
VA
22102-3833
US
|
Assignee: |
Aware, Inc.
Bedford
MA
|
Family ID: |
32831181 |
Appl. No.: |
10/863246 |
Filed: |
June 9, 2004 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10863246 |
Jun 9, 2004 |
|
|
|
09663001 |
Sep 15, 2000 |
|
|
|
6775320 |
|
|
|
|
09663001 |
Sep 15, 2000 |
|
|
|
09522869 |
Mar 10, 2000 |
|
|
|
6498808 |
|
|
|
|
60124222 |
Mar 12, 1999 |
|
|
|
60161115 |
Oct 22, 1999 |
|
|
|
60177081 |
Jan 19, 2000 |
|
|
|
60154116 |
Sep 15, 1999 |
|
|
|
Current U.S.
Class: |
370/464 |
Current CPC
Class: |
H04L 1/0057 20130101;
H04L 5/0087 20130101; H04B 1/38 20130101; H04L 1/0018 20130101;
H04L 1/0025 20130101; H04L 1/0071 20130101; H04L 1/0075 20130101;
H04L 5/0064 20130101; H04L 27/2608 20130101; H04L 1/007 20130101;
H04L 5/0044 20130101; H04L 5/0042 20130101; H04L 5/0053 20130101;
H04L 47/18 20130101; H04L 47/828 20130101; H04M 11/062 20130101;
H04L 25/4915 20130101; H04L 47/263 20130101; H04L 47/803 20130101;
H04L 5/008 20130101; H04L 47/826 20130101; H04L 5/0007 20130101;
H04L 5/0096 20130101; H04L 47/10 20130101 |
Class at
Publication: |
370/464 |
International
Class: |
H04J 015/00 |
Claims
1. In multicarrier communications having a plurality of
subchannels, a system configurable to support at least two
applications comprising: means for associating each application in
a set of currently active applications with a different
Framer/Coder/Interleaver block for processing bits associated with
that application; means for allocating at least one subchannel to
one application in the set of currently active applications for
carrying bits processed by the Frame/Coder/Interleaver block
associated with that application; and means for allocating the at
least one subchannel, in response to a change in the set of
currently active applications, to a second different application in
the changed set of currently active applications, for carrying bits
processed by the Framer/Coder/Interleaver block associated with the
second application.
2. The system according to claim 1, wherein the means for
allocating the at least one subchannel to the second application
includes means for changing the number of bits carried on that
subchannel.
3. The system according to claim 1, wherein the means for
allocating the at least one subchannel to the second application
includes means for allocating a first subset of the bits of the at
least one subchannel to the second application and means for
allocating a second subset of the bits of the at least subchannel
to at least one other application.
4. The system according to claim 1, wherein the first application
is an asynchronous transfer mode data application and the second
application is a voice telephony application.
5. The system according to claim 1, further comprising means for
selecting one or more subchannels that are allocated to one of the
applications, and wherein the means for selecting includes: means
for ordering the subchannels based on the frequency of the
subchannels, and means for and iteratively ascending through the
subchannels starting from the lowest frequency subchannel until a
sufficient number of bits are allocated to that one
application.
6. The system according to claim 1, further comprising means for
selecting one or more subchannels that are allocated to one of the
applications, and wherein the means for selecting includes: means
for ordering the subchannels based on the frequency of the
subchannels, and means for and iteratively descending through the
subchannels starting from the highest frequency subchannel until a
sufficient number of bits are allocated to that one
application.
7. The system according to claim 1, further comprising means for
selecting one or more subchannels that are allocated to one of the
applications, and wherein the means for selecting includes: means
for ordering the subchannels based on the number of bits carried by
the subchannels, and means for iteratively ascending through the
subchannels starting from the subchannel carrying the lowest number
of bits until a sufficient number of bits are allocated to that one
application.
8. The system according to claim 1, further comprising means for
selecting one or more subchannels that are allocated to one of the
applications, and wherein the means for selecting includes: means
for ordering the subchannels based on the number of bits carried by
the subchannels, and means for iteratively descending through the
subchannels starting from the subehannel carrying the highest
number of bits until a sufficient number of bits are allocated to
that one application.
9. The system according to claim 1, wherein one of the applications
in the second active application set is a voice telephony
application having a plurality of bits including a set of ABCD
signaling bits, and the ABCD signaling bits are processed by a
different Framer/Coder/Interleaver block than the other bits of the
voice telephony application.
10. The system according to claim 1, wherein one of the
applications in the second application set is a voice telephony
application having a plurality of bits including a set of ABCD
signaling bits, and the ABCD signaling bits are processed using the
same Framer/Coder/Interleaver block as the other bits of the voice
telephony application.
11. The system according to claim 1, wherein at least one of the
applications in the first active application is not used in the
second different active application set.
12. The system according to claim 1, wherein at least one of the
subchannels is allocated to at least two applications.
13. The system according to claim 1, wherein the changed set of
currently active applications includes an ATM data application and
a voice telephony application.
14. In multicarrier communications having a plurality of
subchannels, a system. that is configurable to supporting at least
two applications comprising: means for associating each application
in a set of currently active applications with a different
Framer/Coder/Interleaver block for processing bits associated with
that application; means for allocating at least one subchannel to
each application in the set of currently active applications for
carrying bits processed by the Framer/Coder/Interleaver block
associated with that application; and means for allocating a
previously unallocated subchannel, in response to a change in the
set of currently active applications, to one application in the
changed set of currently active applications for carrying bits
processed by the Framer/Coder/Interleaver block associated with
that one application in the changed currently active application
set.
15. In multicarrier communications having a plurality of
subchannels, a system that is configurable to support at least two
applications comprising: means for processing bits associated with
one or more applications in a first active application set using a
different latency path for each application in the first active
application set; means for allocating subchannels to the one or
more applications in the first active application set for carrying
bits associated with the one or more applications in the first
active application set; means for transitioning to processing bits
associated with one or more applications in a second different
active application set over a different latency path for each
application in the second different active application set; and
means for changing the allocation of subchannels to the one or more
applications in the second different active application set for
carrying bits associated with the one or more applications in the
second active application set.
16. The system according to claim 15, wherein the means for
changing the allocation of subchannels includes means for
reallocating at least one subchannel from one application to a
second different application.
17. The system according to claim 15, wherein the means for
changing the allocation of subchannels includes means for changing
the number of bits carried on at least one subchannel.
18. The system according to claim 15, wherein the means for
changing the allocation of subchannels includes means for
allocating at least one of the subchannels to at least two of the
applications in the second different application set.
19. The system according to claim 15, wherein the first active
application set includes an asynchronous transfer mode data
application and the second different active application set
includes the asynchronous transfer mode data application and a
voice telephony application.
20. The system according to claim 15, wherein the first active
application set includes an asynchronous transfer mode data
application and a voice telephony application and the second
different active application set includes the asynchronous transfer
mode data application and excludes the voice telephony
application.
21. The system according to claim 15, wherein the means for
changing the allocation includes means for allocating to the second
different active application set a subchannel previously used by
one of the one or more applications in the first active application
set.
22. The system according to claim 15, wherein at least one
subchannel that was used by at least one application in the first
active application set is unused by the applications in the second
different active application set.
Description
FIELD OF THE INVENTION
[0001] This invention relates to transmission systems using
multicarrier modulation. More particularly, the invention relates
to multicarrier transmission systems that support multiple
applications.
BACKGROUND OF THE INVENTION
[0002] Digital Subscriber Line (DSL) technology provides high-speed
transport of digital information over twisted pair phone lines. The
typical DSL system uses a multicarrier modulation format that
employs Fourier Transform as the modulation/demodulation engine.
This transmission scheme is denoted as Discrete Multitone
Modulation (DMT). The DSL system divides the transmission spectrum
into multiple frequency bands called subchannels. Each subchannel
can be modulated with a sinusoidal carrier to transmit information.
A transmitter modulates an output data stream containing
information bits onto one or more subchannels. A receiver
demodulates all the subchannels in order to recover the transmitted
information bits as an input data stream. For simplicity of
reference, the term transceiver refers collectively to transmitters
and receivers.
[0003] DSL systems can be used in an asymmetrical configuration
(ADSL) where the data rate in a given direction, upstream from the
residence to the central office and downstream from the central
office to the residence, is different. DSL Systems can also be used
in a symmetrical configuration where the data rate is equal in both
directions.
[0004] The quality of transmission, in terms of Bit Error Rate
(BER), can also be varied for different subchannels within the
composite data stream. In addition to the high-speed digital
transport over the twisted pair telephony wire, analog telephony,
plain old telephone service (POTS), is also supported. The POTS
signal occupies the low frequency region from 0-4 kHz and the
digital data occupies the higher frequency band from approximately
30 kHz to many hundreds of kilohertz or several megahertz depending
on the application.
[0005] ADSL enables a variety of applications, such as Internet
access, digitized voice calls, video-on-demand, broadcast video,
and video conferencing. Typically transceivers are designed and
optimized for a single application because each application has
different requirements for at least a) data rate, b) bit error
rate, c) latency, d) symmetry/asymmetry of transmission and e)
immunity to impulse noise and other transient phenomena. As a
result, a transceiver that is optimized for one application, such
as video-on-demand, does not work as well if used for a different
application, such as Internet access.
[0006] Classic transceiver architecture includes a
Framer/Coder/Interleave- r (FCI) block, a digital modulation block,
an Analog Front End (AFE) block, and a communications channel. In
most cases, it is the FCI block that is optimized for a specific
application because the FCI block has significant control over
three of the four parameters mentioned above: bit error rate,
latency and immunity to impulse noise. Many transceivers use
forward error correcting (FEC) codes, block and/or convolutional
codes, to improve the bit error rate (BER) performance. Combining
large block FEC codes with interleavers provides immunity to
impulse noise. The disadvantage of large block FEC codes and
interleaving is that they add latency to the system. As an example,
if low BER and immunity to impulse noise are required for a
specified application, the transceiver may include FEC codes and
interleaving. If for another application low latency is important
but a higher BER and/or burst errors resulting from impulse noise
are tolerable, convolutional codes and no interleaving may be
used.
[0007] The Digital Modulation block, the AFE block and the
transmission channel establish the data rate of the transceiver for
a specified BER and margin. Advancements in signal processing
techniques and silicon processes in the digital modulation block
and AFE technology have led to significant improvements in the data
rates achievable on twisted pair phone lines. The result of this
dramatic increase in transmission bandwidth is the ability to
transport multiple applications over a single transceiver
connection. Given the different performance requirements of
different applications, there is a need for a transceiver designed
to transmit and receive for multiple applications. Furthermore,
there is a need for a transceiver designed to dynamically switch
from transmitting and receiving data for a first set of
applications to transmitting and receiving data for a second
different set of applications.
SUMMARY OF THE INVENTION
[0008] One objective is to provide a DMT transceiver that can
support multiple applications and that can dynamically change the
transmission and reception of data as a set of active applications
changes. In one aspect of the invention a multicarrier system has a
communication channel and features a method for supporting at least
two applications.
[0009] Each application in a set of currently active applications
is associated with a different Framer/Coder/Interleaver block for
processing bits associated with that application. One application
in the set of currently active applications is allocated a
subchannel for carrying bits processed by the
Frame/Coder/Interleaver block that is associated with that
application. In response to a change in the set of currently active
applications, the subchannel is allocated to a second different
application for carrying bits processed by the
Framer/Coder/Interleaver block that is associated with that second
application.
[0010] In one embodiment, the number of bits carried on the
subchannel allocated to the second application is changed with
respect to the number of bits that were carried on the subchannel
for the first application. In another embodiment, the subchannel
that is allocated to the second application has a first subset of
the bits allocated to the second application and a second subset of
the bits allocated to at least one other application. In yet
another embodiment the first application is an asynchronous
transfer mode data application and the second application is a
voice telephony application.
[0011] In still another embodiment, the step of allocating the one
subchannel to the second application includes selecting each
subchannel by ordering the subchannels based on the frequency of
the subchannels and iterating through the subchannels from the
lowest frequency subchannel to the highest frequency subchannel. In
another embodiment, the step of allocating the one subchannel to
the second application includes selecting each subchannel by
ordering the subchannels based on the frequency of the subchannels
and iterating through the subchannels from the highest frequency
subchannel. to the lowest frequency subchannel. In another
embodiment, the step of allocating the one subchannel to the second
application includes selecting each subchannel by ordering the
subchannels based on the number of bits carried by the subchannels
and iterating through the subchannels from the subchannel carrying
the lowest number of bits to the subchannel carrying the highest
number of bits. In yet another embodiment, the step of allocating
the one subchannel to the second application includes selecting
each subchannel by ordering the subchannels based on the number of
bits carried by the subchannels and iterating through the
subchannels from the subchannel carrying the highest number of bits
to the subchannel carrying the lowest number of bits.
[0012] In still another embodiment, one of the applications in the
second active application set is a voice telephony application
having a plurality of bits including a set of ABCD signaling bits,
and the ABCD signaling bits are processed by a different
Framer/Coder/Interleaver block than the other bits of the voice
telephony application. In yet another embodiment one of the
applications in the second application set is a voice telephony
application having a plurality of bits including a set of ABCD
signaling bits where the ABCD signaling bits are processed by the
same Framer/Coder/Interleaver block as the other bits of the voice
telephony application.
[0013] In still another embodiment at least one of the applications
in the first active application set is also in the second different
active application set. In another embodiment at least one of the
subchannels is allocated to at least two applications.
[0014] In another aspect of the invention, a multicarrier system
has a communication channel and features a method for supporting at
least two applications. Each application in a set of currently
active applications is associated with a different
Framer/Coder/Interleaver block for processing bits associated with
that application. At least one subchannel is allocated to each
application in the set of currently active applications for
carrying bits processed by the Framer/Coder/Interleaver block
associated with that application. In response to a change in the
set of currently active applications, a previously unallocated
subchannel is allocated to one application in the changed set of
currently active applications for carrying bits processed by the
Framer/Coder/Interleaver block associated with that one application
in the changed currently active application set.
[0015] In another aspect of the invention, a multicarrier system
has a communication channel and features a method for supporting at
least two applications. The system processes bits associated with
the one or more applications in a first active application set
using a different Framer/Coder/Interleaver block for each
application in the first active application set. The system
allocates subchannels to one or more applications in the first
active application set for carrying bits associated with the one or
more applications in the first active application set. The system
transitions and processes bits associated with one or more
applications in a second different active application set over a
different latency path for each application in the second different
active application set. The system changes the allocation of
subchannels to one or more applications in the second different
active application set for carrying bits associated with the one or
more applications in the second active application set.
[0016] In one embodiment of the invention, when the system changes
the allocation of subchannels it changes the number of bits carried
on at least one subchannel. In another embodiment of the invention,
when the system changes the allocation of subchannels it
reallocates at least one subchannel from one application to a
second different application. In yet another embodiment, when the
system changes the allocation of subchannels it allocates at least
one of the subchannels to at least two of the applications in the
second different application set.
[0017] In another embodiment, the first active application set
includes an asynchronous transfer mode data application and the
second different active application set includes the asynchronous
transfer mode data application and a voice telephony application.
In still yet another embodiment the first active application set
includes an asynchronous transfer mode data application: and a
voice telephony application and the second different active
application set includes the asynchronous transfer mode data
application and excludes the voice telephony application.
[0018] In another embodiment when the system changes the allocation
of subchannels, it at least allocates to the second different
active application set a subchannel that was previously unused by
one of the one or more applications in the first active application
set. In yet another embodiment when the system changes the
allocation of sub channels, at least one subchannel that was used
by the applications in the first active application set is unused
by the applications in the second different active application
set.
BRIEF DESCRIPTION OF THE DRAWING
[0019] The invention is pointed out with particularity in the
appended claims. The advantages of the invention described above,
as well as further advantages of the invention, may be better
understood by reference to the following description taken in
conjunction with the accompanying drawings, in which:
[0020] FIG. 1 is a block diagram of an embodiment of a transceiver
having multiple Framer/Coder/Interleaver blocks and a Digital
Modulation block;
[0021] FIG. 2 is a block diagram of an embodiment of the
transceiver showing the details of three Framer/Coder/Interleaver
blocks designed for three applications and the details of the
Digital Modulation block; and
[0022] FIG. 3 is a flow diagram of an embodiment of a process by
which the transceiver changes the allocation of subchannels from
one application to another application.
DETAILED DESCRIPTION OF THE INVENTION
[0023] FIG. 1 shows a block diagram for an exemplary transmitter
100 of a DSL transceiver embodying the principles of the invention.
The transmitter 100 includes multiple FCI blocks 110, 110', 110",
110'" (generally 110), multiple active applications 120, 120',
120", 120'" (generally 120), a digital modulator 130, and an Analog
Front End (AFE) 140. Those skilled in the art will recognize that
although this embodiment describes a transmitter, the inventive
concepts contained herein apply equally to a receiver with the same
functional blocks in reverse order.
[0024] Each of the FCI blocks 110 is in communication with a
respective application 120 and is designed to transmit application
data 115, 115',115", 115'" (generally 115), from that respective
application 120. An FCI block includes any combination framing, and
coding and interleaving for application data. More specifically,
each FCI block 110 includes framing, and possibly coding and/or
interleaving the application data 115 so that an appropriate
combination of BER, latency and impulse noise immunity for the
given application is achieved.
[0025] The digital modulator 130 is also in communication with the
AFE 140, and the AFE 140 is in communication with a communications
channel 150. When modulating data, the digital modulator 130
divides the transmitting and receiving frequency spectrum of the
communications channel 150 into divisions referred to as
subchannels. The digital modulator 130 is also in communication
with a Bit Allocation Table (BAT) 145 that specifies the number of
bits that are to be modulated onto each of the subchannels of the
communications channel 150.
[0026] In operation, the transmitter 100 is capable of
simultaneously supporting multiple applications 120 with different
transmission characteristics and is capable of dynamically
switching between modulating data for a first active set of
applications and modulating data for a second different active set
of applications. An active application set specifies the unique set
of one or more currently active applications of different types
(e.g. a video application, an Internet access application, and a
voice telephony application) for which the transmitter 100 is
transmitting data.
[0027] Each set of applications has a corresponding parameter set
for transmitting (and receiving) signals according to the one or
more applications in the application set. Each parameter set
includes a variety of parameters that characterize the DMT
transmissions of signals associated with the one or more
applications over the communications channel. Such parameters
include:
[0028] the data rate (in bits/second) for transmissions to and from
the transmitter 100;
[0029] the number of tones (i.e., sub-channels) used in the
upstream and downstream transmission paths;
[0030] the minimum and maximum quadrature amplitude modulation
(QAM) constellation size used on each sub-channel;
[0031] the inclusion or exclusion of a trellis code;
[0032] the length of the cyclic prefix;
[0033] the Reed Solomon (R-S) codeword size;
[0034] the interleaver depth, if an interleaver is used;
[0035] the number of latency paths, and the data rate of each
latency path;
[0036] the framing mode (e.g., the ITU ADSL transmission standards
G.922.1 specify four different framing modes);
[0037] the number of bits allocated to each sub-channel or BAT;
[0038] the fine gain adjustments made to each tone, or gain
adjustment table (GAT);
[0039] the performance margin; and
[0040] the allocation of subchannels to applications.
[0041] The collection of the transmission parameters of the set of
currently active applications define the communication state of the
transmitter 100 at a particular point in time.
[0042] FIG. 2 shows an embodiment of transmitter 100 supporting
three active applications. The transmitter 100 includes three
specialized FCI blocks 110, 110', 110", the ADSL Modulator Block
130, the AFE 140, and the communications channel 150. The three FCI
blocks 110, 110', 110" receive input from three respective
applications: e.g., a Video Application 260, a Voice Telephony
Application 270, and an application transmitting ATM (asynchronous
transfer mode) data 280. The output from the specialized FCI blocks
110, 110', 110" is multiplexed together at the ADSL Modulator Block
130. Again, although this embodiment specifies a transmitter, the
inventive concepts contained herein could equally be applied to a
receiver with the same functional blocks in reverse order.
[0043] The FCI block (Video FCI block) 110 is designed to transmit
video and includes a Framer block 211, a R-S Coder block 212, a
Interleaver block 214, and a Trellis Coder block 216. The FCI block
(Voice Telephony FCI block) 110' is designed to transmit voice data
and includes a Multiplexer/Framer block 221, a Cyclic Redundancy
Check (CRC)/Scrambler (SCR) block 222, and a Hamming Coder block
224. The Multiplexer/Framer block 221 receives data from the Voice
Telephony Application 270 and possibly voice telephony signaling
bits (ABCD bits) 295. The FCI block (ATM data FCI block) 110" is
designed to transmit ATM data and includes a Multiplexer/Framer
block 232, a Cyclic Redundancy Check/Scrambler (CRC/SCR) block 234,
a R-S Coder block 236, and an Interleaver block 238. The
Multiplexer/Framer block 232 multiplexes data from the ATM data
Application 280, Embedded Operations Channel/ADSL Overhead Channel
(EOC/AOC) data 285, and the possibly the ABCD bits 295.
[0044] The ADSL Modulator block 130 includes a Quadrature Amplitude
Modulation (QAM) Encoder 242 and an Inverse Fast Fourier Transform
(IFFT) Modulator 244.
[0045] The components of the specialized FCI blocks 110, 110', 110"
depend on the transmission requirements of their respective
applications 260, 270, 280. For example, compressed video data
requires very low BER (<1E-9) and a high immunity to impulse
noise because a single bit error can result in multiple video frame
errors when the video stream is decompressed. The R-S Coder block
212 addresses this need by providing large Forward Error Correction
(FEC) encoding. The Trellis Coder 216 block is included to provide
additional error correction functionality. While data errors are a
significant concern for compressed video data transmission, video
applications can tolerate a large amount of latency (i.e., greater
than approximately 100 ms). This is due to video applications
generally not being interactive. The Interleaver block 214,
therefore, can be configured for large interleaving codeword
depth.
[0046] Unlike video data, the transmission of voice telephony data
has low latency requirements (i.e., less than approximately 1.5 ms)
because it is highly interactive. Accordingly, the Voice Telephony
FCI block 110' does not include an interleaver block. Voice
telephony transmissions, in contrast to video, can tolerate a high
BER (<1E-3) which means that large block FEC codes are
unnecessary. Instead the Voice Telephony FCI block 110' is
configured with the smaller block Hamming Coder 224. In one s
alternative embodiment, the Voice Telephony FCI block does not
include any coding.
[0047] When voice is transmitted over DSL, the Voice Telephony
Application 270 transmits the ABCD bits 295 to provide signaling
information. As shown in FIG. 2, the ABCD bits can be transmitted
either with data from the Voice Telephony Application 270, in-band,
or with data from the ATM data Application 280, out-of-band.
[0048] ATM data transmission is a typical configuration of ABSL
systems that takes raw digital information and formats the data
into ATM cells that comprises the data with ATM overhead
information. ATM cells can be used to transmit a broad range of
data including video and voice telephony data. In this illustrative
example, the ATM data Application 280 is an Internet Access Web
browsing application. Due to the TCP/IP retransmission protocol,
Internet Access Web browsing data transmissions can handle some bit
errors, and, therefore, can operate well at a moderate BER of
<1E-7. However, the TCP/IP retransmission protocol requires
moderate amounts of latency (i.e., less than approximately 20 ms)
which means that very large interleavers are not allowed. Based on
these requirements, the R-S Coder 236 is configured with medium
codeword size, such as 200 bytes. The Interleaver 238 is configured
with a medium interleaving depth, such as 5 codewords. These
specific configurations are illustrative only, and other specific
configurations would also meet the transmission requirements of an
Internet Access Web browsing application.
[0049] The result of the configuration discussed above is that
transmissions from the ATM data FCI block 110" have a high
reliability. ABCD bits are transported at a very low data rate
(<2 kbps) and carry important information that needs to be well
protected. Therefore, it can be advantageous to process the ABCD
bits by the ATM data FCI block 110". If, however, it is important
to transmit the ABCD bits with the same latency as the Voice
Telephony application 270, then it can be advantageous to process
the ABCD bits by the Voice Telephony FCI block 110'.
[0050] In operation, the transmission data rate of the transmitter
100 varies depending on a number of factors. These factors include:
(1) the channel conditions, such as noise, selective fading,
multi-path, and impulse noise; (2) the AFE 140 specifications, such
as sampling rate, filtering, noise, and hybrid; and (3) the Digital
Modulator 130 specifications such as modulation type, constellation
size, equalization, and echo cancellation.
[0051] In FIG. 2, the transmitter 100 is shown to be transmitting
data in one communication state having three active applications
260, 270, 280. According to the principles of the invention, the
transmitter 100 is capable of dynamically switching to transmitting
data according to a second communication state having, for example,
one or two of the applications as active. Specifically, consider
that the transmitter 100 has a total data rate of 2.5 Mbps.
Initially out of this 2.5 Mbps, 1.5 Mbps is allocated to the Video
Application 260. The Voice Telephony Application 270 supports three
channels of 64 kbps, and, therefore, has a total of 192 kbps
allocated to it. The remaining 0.808 Mbps is allocated to the
Internet Access Web Browsing Application 280. When the transmitter
100 dynamically switches to transmitting data according to the
second communication state, the allocation of the 2.5 Mbps of data
throughput is changed to support such applications that remain
active. The process of dynamically changing the allocation of the
subchannels is described below in more detail.
[0052] Changing the Allocation of Subchannels
[0053] In a multicarrier modem, the allocation of subchannels to an
application means that the data bits corresponding to that
application are modulated on that subchannel. When the set of
currently active applications changes, the transmitter 100
dynamically changes the allocation of subchannels to applications
to accommodate the currently active applications. Such a dynamic
change in the allocation of subchannels can include one or more of
the following: (1) a subchannel previously allocated to one
application is reallocated to a second different application; (2) a
subchannel allocated to one application is allocated to two or more
applications, or the reverse in which a subchannel allocated to two
or more applications becomes allocated to one application; (3) the
number of bits on a subchannel is modified; and/or (4) a previously
unused subchannel is allocated to one or more applications, or the
reverse in which a previously allocated subchannel becomes
unused.
[0054] 1) Reallocation of Subchannels
[0055] FIG. 3 shows an exemplary embodiment of a process by which
the subchannels are reallocated from one application to another
application. For purposes of illustration, the active application
set first includes the ATM data Application 280. Subsequently, the
active application set changes to include the Voice Telephony
Application 270 in addition to the original ATM data Application
280.
[0056] The transmitter 100 receives data (step 305) from the ATM
data Application 280. The ATM data is processed by the ATM data FCI
block 110" (step 310). The Digital Modulator 130 allocates
subchannels and modulates the ATM data (step 320). As the ATM data
Application 280 is the one active application, the transmitting
subchannels are used for ATM data. An exemplary allocation of bits
to subchannels is shown in Table 1 below. As indicated by
subchannel 13, some of the subchannels may not be used due to
variations in subchannel quality. The AFE 140 processes the
modulated data and communicates them (step 325) to the
communications channel 150.
1TABLE 1 Number of Bits Modulated onto each Subchannel (1 Active
Application) Subchannel Number Number of Bits (Application) 1 4
(ATM) 2 3 (ATM) 3 2 (ATM) 4 8 (ATM) 5 1 (ATM) 6 2 (ATM) 7 4 (ATM) 8
6 (ATM) 9 5 (ATM) 10 7 (ATM) 11 4 (ATM) 12 2 (ATM) 13 0 (None) 14 4
(ATM) 15 1 (ATM) 16 3 (ATM)
[0057] Next, the current active application set changes (step 330).
Subsequently, the transmitter enters a new communication state
wherein the transmitter begins receiving data (step 335) from the
Voice Telephony Application 270 in addition to the original ATM
data Application. The voice telephony data and the ATM data are
processed (step 340) by the Voice Telephony FCI block 110' and the
ATM data FCI 110" block. The data outputs from the FCI blocks 110',
110" are multiplexed (step 345) together at the Digital Modulator
130. The Digital Modulator 130 reallocates the subchannels between
the currently transmitting applications 270, 280 and modulates each
set of application data (step 350) onto its respective set of
subchannels. An exemplary reallocation of bits to subchannels is
shown below in Table 2.
2TABLE 2 Number of Bits Modulated onto each Subchannel (2 Active
Applications) Subchannel Number Number of Bits per DMT Frame
(Application) 1 4 (ATM) 2 3 (ATM) 3 2 (ATM) 4 8 (Voice) 5 1 (ATM) 6
2 (ATM) 7 4 (ATM) 8 6 (Voice) 9 5 (ATM) 10 7 (ATM) 11 4
(2-ATM/2-Voice) 12 2 (ATM) 13 0 (None) 14 4 (ATM) 15 1 (ATM) 16 3
(ATM)
[0058] As can be seen by a comparison of Tables 1 and 2, the
reallocation of subchannels includes allocating to the newly
activated Voice Telephony Application 270 subchannels that were
previously used for transmissions from the ATM data Application
280. In particular subchannels #4 and #8 are dynamically allocated
to the voice channel when the phone goes off hook. Discussed below
in more detail, subchannel #11 is allocated to both the ATM data
Application 280 and the Voice Telephony Application 270.
[0059] The technique of reallocating subchannels for a single phone
channel can be expanded to support multiple phone channels. Every
time a new voice channel is activated an additional 64 kbps is
allocated to the voice channel path in order to complete the phone
call.
[0060] Various algorithms can be used to select the subchannels
allocated to an application in the active application set. For
example, one technique for selecting the subchannels allocated to
the Voice Telephony Application 270 is to iterate through the
subchannels and select the first two subchannels having 8 bits
assigned. This iteration of. subchannels can use an ordering of the
subchannels based on various factors including the frequency or
constellation size of the subchannels. Another technique is to
iterate through the subchannels and allocate the first 16 bits to
the voice telephony application. Unless exactly 16 bits are
provided by the set of subchannels allocated to the Voice Telephony
Application 270, a subchannel will have some of its bits allocated
to the Voice Telephony Application 270 and some of its bits
allocated to another application. The sharing of subchannels is
discussed below in more detail. Again, the iteration of subchannels
can use an ordering of the subchannels based on various factors
including the frequency or constellation size of the subchannels.
After the Digital Modulator 130 reallocates the subchannels and
modulates the data, the AFE 140 process the modulated signals and
communicates (step 355) them to the communications channel 150.
[0061] The process described above specifies the transition from
the ATM data Application 280 to the combination of the ATM data
Application 280 with the Voice Telephony Application 270. This
represents the situation where a phone is taken off hook. The
reverse process of transitioning from the ATM data Application 280
and the Voice Telephony Application 270 to the ATM data Application
280 is described by the reverse of the steps specified above. In
general this includes transmitting according to Table 2 and then
switching to transmitting according to Table 1. This represents the
situation where the phone is placed back on hook. Although this
embodiment specifies a transmitter, the inventive concepts
contained herein apply equally to a receiver with the same
functional blocks in reverse order.
[0062] 2) Sharing of Subchannels
[0063] As part of the allocation of subchannels to applications, it
is possible for a subchannel to carry data for two different
applications. This means that when the active application set
changes and the allocation of subchannels is modified, a subchannel
allocated to a single application can become allocated to two or
more applications. Conversely, a subchannel allocated to two or
more applications can become allocated to one application.
3TABLE 3 Number of Bits Modulated onto each Subchannel (2 Active
Applications) Subchannel Number Number of Bits per DMT Frame
(Application) 1 4 (Voice) 2 3 (Voice) 3 2 (Voice) 4 8
(7-Voice/1-ATM) 5 1 (ATM) 6 2 (ATM) 7 4 (ATM) 8 6 (ATM) 9 5 (ATM)
10 7 (ATM) 11 4 (ATM) 12 2 (ATM) 13 0 (None) 14 4 (ATM) 15 1 (ATM)
16 3 (ATM)
[0064] The former modification in the allocation of subchannels is
shown with respect to Tables 1 and 3. In Table 1 subchannel #4
carries eight bits of data for the ATM data Application 280. Table
3 shows that as part of the change in the allocation of subchannels
due to the activation of the Voice Telephony Application 270, one
bit of subchannel #4 now carries data for the original ATM data
Application 280 and seven bits now carry data for the Voice
Telephony Application 270. The subchannels allocated to the Voice
Telephony Application shown in Table 3 were selected by iterating
through the subchannels using an ordering of the subchannels based
on starting from the lowest frequency subchannel and ascending in
frequency. The ordering of the subchannels could also have been
done based on starting from the highest frequency subchannel and
descending in frequency. In this event, subchannels #16, #15, #14,
#12, #11, and 2 bits of subchannel #10 would be allocated to the
voice telephony application (assuming subchannel #13 remains
unused). The other bits of subchannel #10 are still allocated to
the ATM data Application 280. Another ordering of the subchannels
could have been based on starting from subchannel with the least
number of bits and ascending through the subchannels based on the
number of bits per subchannel. In this event, subchannels #5, #15,
#3, #6, #12, #2, #16, and 2 bits of subchannel #1 would be
allocated to the voice telephony application (again assuming
subchannel #13 remains unused). The other bits of subchannel #1 are
still allocated to the ATM data Application 280. A further
alternative ordering of the subchannels could have been based on
starting from subchannel with the highest number of bits and
descending through the subchannels based on the number of bits per
subchannel. In this event, subchannels #4, #10, and 1 bit of
subchannel #8 would be allocated to the voice telephony. The other
bits of subchannel #8 are still allocated to the ATM data
Application 280.
[0065] 3) Modification of the Number of Bits Carried by a
Subchannel
[0066] In one embodiment, as part of dynamically changing the
allocation of subchannels, the BAT 145 is modified in accordance
with the set of applications that are presently being transmitted
over the communications channel 150. In particular, a reallocated
subchannel of the BAT 145 may be modified to carry a different
number of bits depending on the transmission characteristics of the
application whose data is presently being transported by that
subchannel. For example, a particular subchannel might be allocated
4 bits per DMT frame when transmitting ATM data and the same
subchannel might be allocated 6 bits per DMT frame when
transmitting voice telephony data.
[0067] The modification is based on the different BER and margin
requirements of the respective applications. The margin is defined
as the amount of increased noise power (in dB) relative to the
noise power that the system is designed to tolerate and still meet
the target BER. For example typically ADSL systems are designed and
deployed with a 6 dB margin relative to a 1E-7 BER. This means that
if the received noise power increases by 6 dB, then the modem would
still achieve the 1E-7 BER requirement. The margin is used to
provide additional immunity to noise, both crosstalk and impulse
noise. Different applications may require different margins as each
may have a different tolerance for bit errors.
[0068] Table 4 shown below is an example of where the allocation of
bits to subchannels, i.e. the BAT, is determined by the margin and
BER requirements of the application data being transmitted. Columns
1 and 2 respectively indicate the subchannels and their measured
Signal-to-Noise (SNR). Columns 3 through 6 specify different BATs
given the subchannel quality and application transmission
requirements. Column 3 is constructed with an equal 6 dB margin and
1E-7 BER across all subchannels and would be appropriate for the
transmission of ATM data. As the bottom of the column 3 indicates,
the specified SNR of the subchannels allows for a total of 52 bits
per DMT frame given the BER and margin requirements. Column 4 is
constructed for a voice only transmission with an equal 4 dB margin
and 1E-3 BER across all subchannels. As the bottom of the column 4
indicates, the specified SNR of the subchannels allows for a total
of 84 bits per given the BER and margin requirements.
[0069] Columns 5 and 6 show how subchannels are reallocated in
accordance with the invention. Column 5 is a BAT where 1 voice
telephony and an Internet access application are running over the
ADSL communication channel 150. The subchannels allocated ATM data
are designated with a (d) and those allocated to voice telephony
are designated with a (v).
4TABLE 4 Modified BATs Supporting Dynamic Switching Example of
Example of Number of bits Number of bits BAT with 1 BAT with 2
Measured with 1E-7 and 6 with 1E-3 and 4 voice channels voice
channels Subchannel SNR per dB margin dB Margin active and active
and # subchannel (data only) (voice only) Internet data Internet
data 1 18 1 3 1 (d) 1 (d) 2 18 1 3 1 (d) 1 (d) 3 28 4 6 4 (d) 6 (v)
4 40 8 10 8 (d) 10 (v) 5 25 3 6 3 (d) 3 (d) 6 25 3 5 3 (d) 3 (d) 7
31 5 7 5 (d) 5 (d) 8 34 6 8 6 (d) 6 (d) 9 21 2 4 4 (v) 4 (v) 10 25
3 5 3 (d) 3 (d) 11 21 2 4 2 (d) 2 (d) 12 34 6 8 8 (v) 8 (v) 13 15 0
2 2 (v) 2 (v) 14 15 0 2 2 (v) 2 (v) 15 25 3 5 3 (d) 3 (d) 16 31 5 7
5 (d) 5 (d) (Total # of bits (Total # of bits (Total # of bits
(Total # of bits per DMT frame) = 52 per DMT frame) = 84 per frame)
= 60 per frame) = 64 (208 kbps) (336 kbps) (240 kbps) (256 kbps) 64
kbps voice 128 kbps voice 176 kbps data 128 kbps data
[0070] One example that illustrates the operation of the invention
is where an Internet access application is running alone and then a
voice telephony application is activated. In this situation, the
transceiver is able to add the voice telephony throughput without
losing the same amount of Internet access throughput. A comparison
of the throughput of columns 3, 4, and 5 demonstrates this aspect
of the invention. First, it reveals that the throughput of column 5
is less than column 4 (voice only) but more than column 3 (Internet
access only). Further, it reveals that the Internet access data
rate decreases only 32 kbps when the 64 kbps voice channel is
activated. This is partially due to two factors. First, the
subchannels #13 and #14 had a SNR of 14 dB which made them unusable
for the Internet application but acceptable for the voice telephony
application. Second, the lower margin and higher BER tolerances for
the voice telephony application means that when the subchannels #9
and #12 are switched from Internet access to voice telephony the
number of bits carried by t he subchannel can be increased. In
particular, subchannel 9 switched from 2 to 4 bits and subchannel
#12 switched from 6 to 8 bits.
[0071] Column 6 shows how the BAT is modified when 2 voice channels
are active. In this case the Internet access data rate decreases
only 48 kbps when two phones (64.times.2=128 kbps) are activated.
When three or more voice channels are activated, the BAT is
modified in a similar manner.
[0072] Columns 3 through 6 indicate different active application
sets and transitions between any of these communication states are
possible as applications are activated and deactivated. In one
embodiment, the method for changing the number of bits carried on a
particular subchannel is to dynamically modify a single BAT. In
another embodiment, the method includes switching between BATs that
represent the different possible communication states of the
transceiver.
[0073] 4) Utilization and Non-Utilization of Subchannels Due to
Subchannel Quality
[0074] Different applications typically have different requirements
for subchannel quality. This means that when an application
requiring lower subchannel quality becomes active, a previously
unused subchannel can become active. It also means that when an
application requiring lower subchannel quality becomes inactive, a
subchannel allocated to that application may become unused if only
applications requiring higher subchannel quality remain active.
[0075] Table 5 shows an embodiment in which only previously unused
subchannels are utilized for the voice channel. This is can occur
when there are several subchannels that have a SNR that is adequate
to support voice, e.g. data at 1E-3 BER and 4 dB margin, but not
Internet access data, e.g. data at 1E-7 BER and 6 dB margin. In
this illustrative example, subchannels #1-8 are capable of
supporting 2 bits for the voice application but 0 bits for the
Internet access data application. Column 5 shows the BAT when 1
voice channel and an Internet access application are supported.
Because the voice channel uses subchannels that were unused in the
data only mode (column 3) there is no decrease in the Internet
access data rate when 1 voice channel is active.
5TABLE 5 BATs Demonstrating Utilization of Previously Unused
Subchannels Example of Number of bits Number of bits BAT with 1
Measured with 1E-7 and 6 with 1E-3 and 4 voice channels Subchannel
SNR per dB margin dB Margin active and # Subchannel (data only)
(voice only) Internet data 1 15 0 2 2 (v) 2 15 0 2 2 (v) 3 15 0 2 2
(v) 4 15 0 2 2 (v) 5 15 0 2 2 (v) 6 15 0 2 2 (v) 7 15 0 2 2 (v) 8
15 0 2 2 (v) 9 31 5 7 5 (d) 10 31 5 7 5 (d) 11 34 6 8 6 (d) 12 34 6
8 6 (d) 13 37 7 9 7 (d) 14 37 7 9 7 (d) 15 40 8 10 8 (d) 16 40 6 6
6 (d) (Total # of bits (Total # of bits (Total # of bits per DMT
frame) = 50 per DMT frame) = 82 per frame) = 66 (200 kbps) (328
kbps) (264 kbps) 64 kbps voice 200 kbps data
[0076] This embodiment provides significant advantage in operation
in that the Internet access data path is not affected when
telephones are activated or de-activated. As more voice channels
are activated, it may be necessary to reallocate some of the
Internet access subchannels to voice telephony and therefore
decrease the Internet access application data rate. This is shown
in the illustrative example in Table 4. Another advantage of this
embodiment of the invention is that the voice channel can be always
connected, even when the telephone is on-hook, because there is no
decrease in the data rate of the Internet access application. This
simplifies the protocols for handling activation and de-activation
of telephone calls because the BAT is not modified dynamically and
the voice channel bandwidth is always allocated.
[0077] The BATs indicated by columns 3, 4 and 5 indicate different
active application sets and transitions between any of these
communication states are possible as applications are activated and
deactivated. Methods for achieving these transitions were discussed
above.
[0078] While the invention has been shown and described with
reference to specific preferred embodiments, it should be
understood by those skilled in the art that various changes in form
and detail may be made therein without departing from the spirit
and scope of the invention as defined by the following claims. For
example, although the invention is described with respect to DMT
modulation, the principles of the invention apply to DWMT (Discrete
Wavelet Multitone) modulation. Also, IP frames instead of ATM
packets can be used to transport data. The principles of the
invention also apply to any DMT communication system that supports
multiple sets of applications, where the applications are activated
and de-activated over time. Further, although the specification
uses ADSL to describe the invention, it is to be understood that
any form of DSL can be used, i.e., VDSL, SDSL, HDSL, HDSL2, or
SHDSL. Although several embodiments described above included
Internet and voice applications, it is also to be understood that
the principles of the invention apply to any combination of
applications transported over DSL systems (e.g., telecommuting,
video conferencing, high speed Internet access, video-on
demand).
* * * * *