111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111
`us 20050190826Al
`US 20050190826A1
`
`(19) United States
`(19) United States
`(12) Patent Application Publication
`(10) Pub. No.: US 2005/0190826 Al
`(12) Patent Application Publication (10) Pub. No.: US 2005/0190826 A1
`Sep. 1, 2005
`(43) Pub. Date:
`Sep. 1, 2005
`Van Bruyssel et ai.
`(43) Pub. Date:
`Van Bruyssel et al.
`
`(54) DIGITAL SUBSCRIBER LINE MODEM WITH
`(54) DIGITAL SUBSCRIBER LINE MODEM WITH
`BITLOADING USING CHANNEL
`BITLOADING USING CHANNEL
`CONDITION MODEL
`CONDITION MODEL
`
`(75) Inventors: Danny Edgard Josephine Van
`Inventors: Danny Edgard Josephine Van
`(75)
`Bruyssel, Temse (BE); Sigurd Jan
`Bruyssel, Temse (BE); Sigurd Jan
`Maria Schelstraete, Mountain View,
`Maria Schelstraete, Mountain View,
`CA (US)
`CA(US)
`
`Correspondence Address:
`Correspondence Address:
`SUGHRUE MION, PLLC
`SUGHRUE MION, PLLC
`2100 PENNSYLVANIA AVENUE, N.W.
`2100 PENNSYLVANIA AVENUE, N.W.
`SUITE 800
`SUITE 800
`WASHINGTON, DC 20037 (US)
`WASHINGTON, DC 20037 (US)
`
`(73) Assignee: ALCATEL
`(73) Assignee: ALCATEL
`
`(21) Appl. No.:
`(21) Appl. No.:
`
`11/064,017
`11/064,017
`
`(22) Filed:
`(22) Filed:
`
`Feb. 24, 2005
`Feb. 24, 2005
`
`(30)
`(30)
`
`Foreign Application Priority Data
`Foreign Application Priority Data
`
`Feb. 26, 2004
`(EP) ........................................ 04290523.2
`Feb. 26, 2004 (EP) ...................................... .. 042905232
`
`Publication Classification
`Publication Classi?cation
`
`Int. CI? ....................................................... H04B 1/38
`(51)
`(51) Int. Cl.7 ..................................................... .. H04B 1/38
`(52) U.S. CI.
`.............................................................. 375/222
`(52) US. Cl. ............................................................ .. 375/222
`
`(57)
`(57)
`
`ABSTRACT
`ABSTRACT
`
`A telecommunication arrangement With modems (MCO;
`A telecommunication arrangement with modems (MCO;
`MCPE) having a receiving module (URX; DRX) able to
`MCPE) having a receiving module (URx; DRx) able to
`receive channels of signals via a communication line (LN).
`receive channels of signals via a communication line (LN).
`The arrangement preferably operates according to the XDSL
`The arrangement preferably operates according to the xDSL
`protocol. The receiving module of each modem is associated
`protocol. The receiving module of each modem is associated
`to storage means (USN, DSN; LDN) storing a "channel
`to storage means (USN, DSN; LDN) storing a “channel
`condition model” corresponding to operational conditions of
`condition model" corresponding to operational conditions of
`the channel, preferably to the "worst case". The channel
`the channel, preferably to the “Worst case”. The channel
`condition model is determined by previously measured
`condition model is determined by previously measured
`operational conditions of this channel and/or by a channel
`operational conditions of this channel and/or by a channel
`condition model managed externally to the modem, and
`condition model managed externally to the modem, and
`which is stored in the storage means before the initialization
`Which is stored in the storage means before the initialization
`of the modem. In different variants, the channel condition
`of the modem. In different variants, the channel condition
`model is a model of the noise level, the signal·to·noise ratio,
`model is a model of the noise level, the signal-to-noise ratio,
`the actual or the maximum bitloading (bJ per carrier of the
`the actual or the maximum bitloading
`per carrier of the
`channel and/or mathematical operations on these. The chan
`channel and/or mathematical operations on these. The chan·
`nel condition model is further updated at regular time
`nel condition model is further updated at regular time
`intervals during initialization or showtime. The modem may
`intervals during initialization or shoWtime. The modem may
`be located at the Central Ollice (CO) or at the Customer
`be located at the Central Office (CO) or at the Customer
`Premises Equipment (CPE). The receiving module (URX) of
`Premises Equipment (CPE). The receiving module (URx) of
`the CO modem (MCO) may receive the channel condition
`the CO modem (MCO) may receive the channel condition
`model from the central office management device via a
`model from the central office management device via a
`management interface. The channel condition model may
`management interface. The channel condition model may
`also be transmitted from the central office management
`also be transmitted from the central office management
`device to the receiving module (DRx) of the CPE modem
`device to the receiving module (DRX) of the CPE modem
`(MCPE), and channel condition measurement information
`(MCPE), and channel condition measurement information
`may even be fed back.
`may even be fed back.
`
`---.---.----------------.-~?--------------.----------
`....................... -20“
`
`_______________ . ______ .. _~~l!: _______ ._. _______ . ______ ._
`
`MCO
`MCO
`
`CCO
`CCO
`VMS
`BCCMCO
`,/BCCMCO"",
`/ 1 UMGCCMl 1\:
`@
`\1 UMCCM 1,/
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`USN
`
`DSN
`
`cePE
`DMS
`• __ -- __ .•
`DMS __ ---
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`BCCMCPE
`
`/1 DMGCCM 1\
`:\1 DMCCM
`I)
`
`"""""
`
`...... '
`
`LN
`
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`
`DMGCCMCPE
`
`'~"~
`
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`US 2005/0190826 A1
`
`Fig 1
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`

`

`US 2005/0190826 A1
`US 2005/0190826 A1
`
`Sep. 1, 2005
`Sep.1,2005
`
`1
`
`DIGITAL SUBSCRIBER LINE MODEM WITH
`DIGITAL SUBSCRIBER LINE MODEM WITH
`BITLOADING USING CHANNEL CONDITION
`BITLOADING USING CHANNEL CONDITION
`MODEL
`MODEL
`
`[0001] The present invention relates to a telecommunica(cid:173)
`[0001] The present invention relates to a telecommunica
`tion arrangement with a modem having a receiving module
`tion arrangement With a modem having a receiving module
`coupled to a controlling module, said receiving module is
`coupled to a controlling module, said receiving module is
`adapted to receive at least one channel via a communication
`adapted to receive at least one channel via a communication
`line, said channel being adapted to transport data by means
`line, said channel being adapted to transport data by means
`of signals With modulation having a bitload Which is modi
`of signals with modulation having a bitload which is modi(cid:173)
`?able, said controlling module is adapted to modify the
`fiable, said controlling module is adapted to modify the
`bitload used by said receiving module as a function of
`bitload used by said receiving module as a function of
`current measurements performed by the modem immedi
`current measurements performed by the modem immedi(cid:173)
`ately prior to a current bitloading.
`ately prior to a current bitloading.
`
`[0002] Such a telecommunication arrangement with a
`[0002] Such a telecommunication arrangement With a
`modem capable of operating at different bitloads/datarates is
`modem capable of operating at different bitloads/datarates is
`generally known in the art. Therein, the bitload/datarate used
`generally knoWn in the art. Therein, the bitload/datarate used
`by the receiving module is based on current channel condi(cid:173)
`by the receiving module is based on current channel condi
`tions measurements, being measurements at one particular
`tions measurements, being measurements at one particular
`point in time, generally immediately prior to the current
`point in time, generally immediately prior to the current
`bitloading.
`bitloading.
`[0003] The "bitload" is defined as following. If the modu(cid:173)
`[0003] The “bitload” is de?ned as folloWing. If the modu
`lation is BaseBand Modulation (BBM) or Single Carrier
`lation is BaseBand Modulation (BBM) or Single Carrier
`Modulation (SCM), the bitload corresponds to the number
`Modulation (SCM), the bitload corresponds to the number
`of information bits per modulation symbol, also called
`of information bits per modulation symbol, also called
`modulation or signaling time slot. If the modulation is Multi
`modulation or signaling time slot. If the modulation is Multi
`Carrier Modulation (MCM), the bitload corresponds to the
`Carrier Modulation (MCM), the bitload corresponds to the
`set of numbers describing the number of information bits per
`set of numbers describing the number of information bits per
`modulation symbol for each carrier, e.g. corresponds to the
`modulation symbol for each carrier, e.g. corresponds to the
`array of bi as defined in ITU-T G.992.3 Section 8.5.
`array of bi as de?ned in ITU-T G.992.3 Section 8.5.
`
`[0004] BaseBand Modulation (BBM) is a modulation type
`[0004] BaseBand Modulation (BBM) is a modulation type
`without first modulating the signal onto a carrier, e.g. Pulse
`Without ?rst modulating the signal onto a carrier, e.g. Pulse
`Amplitude Modulation (PAM); Single Carrier Modulation
`Amplitude Modulation (PAM); Single Carrier Modulation
`(SCM) is a modulation type in which the signal is modulated
`(SCM) is a modulation type in Which the signal is modulated
`onto a single carrier, e.g. Quadrature Amplitude Modulation
`onto a single carrier, e.g. Quadrature Amplitude Modulation
`(QAM), Carrierless AM-PM (CAP); and Multi Carrier
`(QAM), Carrierless AM-PM (CAP); and Multi Carrier
`Modulation (MCM) is a modulation type in which multiple
`Modulation (MCM) is a modulation type in Which multiple
`carriers are used, e.g. Discrete MultiTone modulation
`carriers are used, eg Discrete MultiTone modulation
`(DMT). These modulation types are generally known in the
`(DMT). These modulation types are generally knoWn in the
`art.
`art.
`
`[0005] The process of determining a bitload is called
`[0005] The process of determining a bitload is called
`"bitloading". This can be a determination of the complete
`“bitloading”. This can be a determination of the complete
`bitload as in initialization, a determination of a part of the
`bitload as in initialiZation, a determination of a part of the
`bitload as in "showtime" BitSwapping, e.g. as defined in
`bitload as in “shoWtime” BitSWapping, eg as de?ned in
`ITV-T G.992.1, or a determination of a part of the bitload or
`ITU-T G.992.1, or a determination of a part of the bitload or
`of the complete bitload, as in "Showtime" On Line Recon(cid:173)
`of the complete bitload, as in “Showtime” On Line Recon
`figuration (OLR), e.g. as defined in ITU-T G.992.3.
`?guration (OLR), eg as de?ned in ITU-T G.992.3.
`
`[0006]
`"Initialization" (a.k.a. Training) is the state or time
`[0006] “Initialization” (a.k.a. Training) is the state or time
`period immediately preceding “Showtime”, during Which
`period immediately preceding "Showtime", during which
`signals are exchanged between the modems in order to
`signals are eXchanged betWeen the modems in order to
`prepare showtime, but in which no user data are being
`prepare shoWtime, but in Which no user data are being
`communicated. Showtime (a.k.a. Data Transmission State or
`communicated. ShoWtime (a.k.a. Data Transmission State or
`Steady State) is the state during which user data are being
`Steady State) is the state during Which user data are being
`communicated by the modems.
`communicated by the modems.
`
`[0007] A channel condition is any characteristics of the
`[0007] A channel condition is any characteristics of the
`channel. The channel being defined as starting at the inter(cid:173)
`channel. The channel being de?ned as starting at the inter
`face where the to be transmitted user data is given as input
`face Where the to be transmitted user data is given as input
`to the modem, and ending at the interface where the received
`to the modem, and ending at the interface Where the received
`user data is given as output by the modem connected to the
`user data is given as output by the modem connected to the
`other end of the communication line. Therefore, the channel
`other end of the communication line. Therefore, the channel
`includes, on top of the communication line, following
`includes, on top of the communication line, folloWing
`modem functional blocks, well known in the art: line inter-
`modem functional blocks, Well knoWn in the art: line inter
`
`face, analog front end, analog-to-digital convertors, digital
`face, analog front end, analog-to-digital convertors, digital(cid:173)
`to-analog convertors, transmit and receive ?lters, gain scal
`to-analog convertors, transmit and receive filters, gain scal(cid:173)
`ers, modulation/demodulation, constellation encoding/
`ers, modulation/demodulation, constellation encoding/
`decoding,
`channel coding/decoding, forWard error
`decoding,
`channel
`coding/decoding,
`forward
`error
`correcting coding/decoding, scramblers, CRC generation
`correcting coding/decoding, scramblers, CRC generation
`and verification, ... As such any parameter which can be
`and veri?cation, .
`.
`. As such any parameter Which can be
`measured in any of the functional blocks of the channel
`measured in any of the functional blocks of the channel
`constitutes a channel condition. The channel condition mea(cid:173)
`constitutes a channel condition. The channel condition mea
`surement predominantly used in the prior art is the Signal
`surement predominantly used in the prior art is the Signal(cid:173)
`to-Noise Ratio (SNR) measured at the receiver, for MCM
`to-Noise Ratio (SNR) measured at the receiver, for MCM
`typically on each of the carriers.
`typically on each of the carriers.
`
`[0008]
`In known
`telecommunication arrangements, a
`[0008] In knoWn telecommunication arrangements, a
`problem occurs in the modem on channels with fast chang(cid:173)
`problem occurs in the modem on channels With fast chang
`ing noise conditions. If the noise environment changes
`ing noise conditions. If the noise environment changes
`drastically after startup, i.e. during the shoWtime, due for
`drastically after startup, i.e. during the showtime, due for
`instance to crosstalk caused by a neighboring modem start(cid:173)
`instance to crosstalk caused by a neighboring modem start
`ing up, the bitload may need to be modified in order to adapt
`ing up, the bitload may need to be modi?ed in order to adapt
`to the new conditions. In some cases, such processes (like
`to the neW conditions. In some cases, such processes (like
`BitSWapping or OLR) that adapt the bitload during shoW
`BitSwapping or OLR) that adapt the bitload during show(cid:173)
`time are not sufficient and a re-initialization may be needed.
`time are not suf?cient and a re-initialiZation may be needed.
`This interrupts the service and is disturbing to the customer.
`This interrupts the service and is disturbing to the customer.
`
`[0009] In other Words, the “traditional” bitloading cannot
`[0009]
`In other words, the "traditional" bitloading cannot
`take into account sudden changes in noise environment.
`take into account sudden changes in noise environment.
`When changes are too high, on-line recon?guration cannot
`When changes are too high, on-line reconfiguration cannot
`cope and the only option is to shut down the connection en
`cope and the only option is to shut doWn the connection en
`do a re-initialiZation. Are-initialization Will alWays interrupt
`do a re-initialization. Are-initialization will always interrupt
`the service, even if it can be shorter than a full initialization.
`the service, even if it can be shorter than a full initialiZation.
`[0010] To solve this problem, different solutions exist in
`[0010] To solve this problem, different solutions exist in
`the art.
`the art.
`
`[0011]
`It is first to be noted that, in a preferred embodi(cid:173)
`[0011] It is ?rst to be noted that, in a preferred embodi
`ment of the present invention, the modem is an adaptive
`ment of the present invention, the modem is an adaptive
`xDSL modem.
`XDSL modem.
`
`[0012] Such a modem is a modem which is part of a
`[0012] Such a modem is a modem Which is part of a
`Digital Subscriber Line (DSL) capable of operating at
`Digital Subscriber Line (DSL) capable of operating at
`different bitloads/datarates. An Asymmetric Digital Sub
`different bitloads/datarates. An Asymmetric Digital Sub(cid:173)
`scriber Line (ADSL) modem or a Very high speed Digital
`scriber Line (ADSL) modem or a Very high speed Digital
`Subscriber Line (VDSL) modem for instance belong to the
`Subscriber Line (VDSL) modem for instance belong to the
`adaptive XDSL modem type.
`adaptive xDSL modem type.
`
`[0013] Most, but not all, of known solutions to the above
`[0013] Most, but not all, of knoWn solutions to the above
`problem are applicable to an adaptive xDSL modem.
`problem are applicable to an adaptive XDSL modem.
`
`[0014] A first known solution to limit the vulnerability of
`[0014] A ?rst knoWn solution to limit the vulnerability of
`modems to fast increasing noise levels that could be absent
`modems to fast increasing noise levels that could be absent
`at the time of initialization, is the adapt the bit allocation
`at the time of initialiZation, is the adapt the bit allocation
`and/or datarates during operation (i.e. in shoWtime). In
`and/or datarates during operation (i.e. in showtime). In
`current multi -carrier modems the initial datarate and the
`current multi-carrier modems the initial datarate and the
`initial bitload is determined based on the Channel SNR-per(cid:173)
`initial bitload is determined based on the Channel SNR-per
`carrier measured during initialization, which is only a snap(cid:173)
`carrier measured during initialiZation, Which is only a snap
`shot in time corresponding to the current noise conditions.
`shot in time corresponding to the current noise conditions.
`However, over the course of time (during showtime) the
`HoWever, over the course of time (during shoWtime) the
`noise conditions on the loop can vary, requiring a different
`noise conditions on the loop can vary, requiring a different
`shape of bitload for the same datarate (with decreased SNR
`shape of bitload for the same datarate (With decreased SNR
`margin) or could even require a decrease of the datarate. For
`margin) or could even require a decrease of the datarate. For
`slow variation in the noise conditions, methods have been
`sloW variation in the noise conditions, methods have been
`defined in ADSL and VDSL standards to adapt the bitload in
`de?ned in ADSL and VDSL standards to adapt the bitload in
`both ways: bit swap, i.e. change of bitload without change
`both Ways: bit sWap, i.e. change of bitload Without change
`in datarate, as for instance mentioned in ADSL lTV G.992.1,
`in datarate, as for instance mentioned in ADSL ITU G.992.1,
`ADSL2 ITU G.992.3 and ANSI Tl.424 MCM VDSL, and
`ADSL2 ITU G.992.3 and ANSI T1.424 MCM VDSL, and
`respectively Seamless Rate Adaptation (SRA), i.e. change of
`respectively Seamless Rate Adaptation (SRA), i.e. change of
`bitload with change in datarate, as for instance mentioned in
`bitload With change in datarate, as for instance mentioned in
`ADSL2 lTV G.992.3. Both these methods are also called
`ADSL2 ITU G.992.3. Both these methods are also called
`“On Line Recon?guration” (OLR).
`"On Line Reconfiguration" (OLR).
`
`3
`
`

`

`US 2005/0190826 A1
`US 2005/0190826 A1
`
`Sep. 1, 2005
`Sep.1,2005
`
`2
`
`[0015] This ?rst solution is good for slowly changing
`[0015] This first solution is good for slowly changing
`noise conditions. However, in some crosstalk scenarios, the
`noise conditions. However, in some crosstalk scenarios, the
`noise condition varies fast, and the proposed solution is too
`noise condition varies fast, and the proposed solution is too
`slow to react in time to avoid bit errors and/or to avoid a
`sloW to react in time to avoid bit errors and/or to avoid a
`re-initialization. The reason therefore is that crosstalk noise
`re-initialiZation. The reason therefore is that crosstalk noise
`from a newly switched-on xDSL modem increases instan(cid:173)
`from a neWly sWitched-on xDSL modem increases instan
`taneous.
`taneous.
`
`[0016] A second knoWn solution to limit the vulnerability
`[0016] A second known solution to limit the vulnerability
`of modems to fast increasing noise levels that could be
`of modems to fast increasing noise levels that could be
`absent at the time of initialization, is the use of an a -priori
`absent at the time of initialiZation, is the use of an a-priori
`determined limitation to a certain maximum datarate. The
`determined limitation to a certain maximum datarate. The
`level of limitation is determined by means outside the
`level of limitation is determined by means outside the
`modem, but is communicated to the modem via a manage(cid:173)
`modem, but is communicated to the modem via a manage
`ment interface before bitloading in initialiZation.
`ment interface before bitloading in initialization.
`
`[0017] In modems using BaseBand Modulation (BBM) or
`[0017]
`In modems using BaseBand Modulation (BBM) or
`Single Carrier Modulation (SCM) this second solution gives
`Single Carrier Modulation (SCM) this second solution gives
`sufficient control. Indeed, in the case that the modems use a
`sufficient control. Indeed, in the case that the modems use a
`?xed bandWidth and an adaptive constellation siZe, the
`fixed bandwidth and an adaptive constellation size, the
`limitation to a maximum datarate will result in a limitation
`limitation to a maximum datarate Will result in a limitation
`to a maximum number of bits per symbol (i.e. the PAM or
`to a maximum number of bits per symbol (i.e. the PAM or
`QAM constellation size). Therefore, to an upper limit on the
`QAM constellation siZe). Therefore, to an upper limit on the
`minimum required SNR (eg to sustain a desired Bit Error
`minimum required SNR (e.g. to sustain a desired Bit Error
`Rate (BER) of e.g. 1E-7 with a desired SNR margin of e.g.
`Rate (BER) of eg 1E-7 With a desired SNR margin of eg
`6 dB). The limitation is chosen such that the minimum
`6 dB). The limitation is chosen such that the minimum
`required SNR is loWer than or equal to the expected “Worst
`required SNR is lower than or equal to the expected "worst
`case” (i.e. loWest) SNR, occurring during “Worst case” noise
`case" (i.e. lowest) SNR, occurring during "worst case" noise
`conditions. Modems implementing the ITU-T V.32-bis voi
`conditions. Modems implementing the ITV-T y'32-bis voi(cid:173)
`ceband modem standard are examples of this case.
`ceband modem standard are examples of this case.
`
`[0018]
`In the case that the modems use a fixed constella(cid:173)
`[0018] In the case that the modems use a ?xed constella
`tion size and an adaptive bandwidth (given a fixed transmit
`tion siZe and an adaptive bandWidth (given a ?xed transmit
`power), the limitation of the datarate will result in a limi(cid:173)
`poWer), the limitation of the datarate Will result in a limi
`tation of the bandwidth, and therefore to an increase in
`tation of the bandWidth, and therefore to an increase in
`transmit PSD level. The limitation is chosen such that the
`transmit PSD level. The limitation is chosen such that the
`required transmit PSD level minus the ?xed required SNR is
`required transmit PSD level minus the fixed required SNR is
`higher than or equal to the expected “Worst case” noise level,
`higher than or equal to the expected "worst case" noise level,
`occurring during “Worst case” noise conditions. Modems
`occurring during "worst case" noise conditions. Modems
`implementing the ITU SHDSL G.991.2 Recommendation
`implementing the lTV SHDSL G.991.2 Recommendation
`are examples of this case.
`are examples of this case.
`
`It is further to be noted that modems implementing
`[0019]
`[0019] It is further to be noted that modems implementing
`the ANSI T1.424 SCM VDSL standard are not rate-adaptive
`the ANSI T1.424 SCM VDSL standard are not rate-adaptive
`and are therefore having the concept of maximum datarate.
`and are therefore having the concept of maximum datarate.
`[0020] Moreover, in modems using Multi-Carrier Modu
`[0020] Moreover, in modems using Multi-Carrier Modu(cid:173)
`lation (MCM), this second solution does not give sufficient
`lation (MCM), this second solution does not give suf?cient
`control. Indeed, the a-priori limitation to a maximum dat(cid:173)
`control. Indeed, the a-priori limitation to a maximum dat
`arate will result only in a limitation to a maximum the
`arate Will result only in a limitation to a maximum the
`number of bits per MCM symbol, which is a limitation only
`number of bits per MCM symbol, Which is a limitation only
`on the SVM OF the number bi of bits per carrier, summed
`on the SUM OF the number bi of bits per carrier, summed
`over all carriers used (i.e.
`over all carriers used (i.e.
`
`~b;:;; limit
`2 b; 5 limit
`
`). As it does not provide a limitation of the number
`[0021]
`As it does not provide a limitation of the number
`[0021]
`of bits for each speci?c carrier (bi), it is possible that during
`of bits for each specific carrier (b), it is possible that during
`initialization with low noise conditions, the modem deter(cid:173)
`initialiZation With loW noise conditions, the modem deter
`mines a bitload which allocates a bi on some carriers which
`mines a bitload Which allocates a bi on some carriers Which
`is too high, needing a required SNR higher than the “Worst
`is too high, needing a required SNR higher than the "worst
`case" SNR on those carriers during fast increasing noise
`case” SNR on those carriers during fast increasing noise
`condition. The more the shape of the noise spectrum during
`condition. The more the shape of the noise spectrum during
`initialiZation is differing from the shape of the fast increasing
`initialization is differing from the shape of the fast increasing
`
`noise during operation, the higher the vulnerability, and the
`noise during operation, the higher the vulnerability, and the
`higher the likelihood of excessive BER or re-initialization.
`higher the likelihood of excessive BER or re-initialiZation.
`Modems implementing any of the knoWn (up-to-date) ITU
`Modems implementing any of the known (up-to-date) lTV
`Recommendations ADSL ITU G.992.1, G.992.2, G.992.3,
`Recommendations ADSL lTV G.992.1, G.992.2, G.992.3,
`G.992.4, G.992.5 or VDSLANSI T1.424 MCM standard are
`G.992.4, G.992.5 or VDSLANSI T1.424 MCM standard are
`examples of this case.
`examples of this case.
`
`It is to be noted that this second known solutions is
`[0022]
`[0022] It is to be noted that this second knoWn solutions is
`available in almost all types of modems: baseband, single
`available in almost all types of modems: baseband, single
`carrier, multi-carrier, ...
`carrier, multi-carrier, .
`.
`.
`[0023] Athird knoWn solution to limit the vulnerability of
`[0023] A third known solution to limit the vulnerability of
`modems to fast increasing noise levels that could be absent
`modems to fast increasing noise levels that could be absent
`at the time of initialization, is the use of an a-priori deter(cid:173)
`at the time of initialiZation, is the use of an a-priori deter
`mined (single number) limitation of the maximum constel
`mined (single number) limitation of the maximum constel(cid:173)
`lation size to a certain maximum number of bits per con(cid:173)
`lation siZe to a certain maximum number of bits per con
`stellation, i.e. PAM or QAM constellation size. The level of
`stellation, i.e. PAM or QAM constellation siZe. The level of
`limitation is determined by means outside the modem, but is
`limitation is determined by means outside the modem, but is
`communicated to the modem via a management interface
`communicated to the modem via a management interface
`before bitloading in initialiZation.
`before bitloading in initialization.
`
`[0024] This third solution is identical to the above second
`[0024] This third solution is identical to the above second
`solution and gives suf?cient control in modems using Base
`solution and gives sufficient control in modems using Base(cid:173)
`Band Modulation (BBM) or Single Carrier Modulation
`Band Modulation (BBM) or Single Carrier Modulation
`(SCM).
`(SCM).
`[0025] HoWever, in modems using Multi-carrier Modula
`[0025] However, in modems using Multi-carrier Modula(cid:173)
`tion (MCM) this third solution does not give suf?cient
`tion (MCM) this third solution does not give sufficient
`control. Indeed, the a-priori limitation to a single number
`control. Indeed, the a-priori limitation to a single number
`maximum number of bits per constellation (i.e. max bi limit),
`maximum number of bits per constellation (i.e. max bi limit),
`e.g. the G.992.1 limit that is called BIMAX, does not
`eg the G.992.1 limit that is called BIMAX, does not
`provide a sufficient limitation of the number of bits for each
`provide a sufficient limitation of the number of bits for each
`specific carrier (bJ It only limits the bi on the carriers with
`speci?c carrier
`It only limits the bi on the carriers With
`the largest constellations, and these carriers are not neces(cid:173)
`the largest constellations, and these carriers are not neces
`sarily the carriers that are vulnerable to fast changing noise
`sarily the carriers that are vulnerable to fast changing noise
`levels. Also carriers with smaller constellations could be
`levels. Also carriers With smaller constellations could be
`affected by fast changing noise levels. In other words, a max
`affected by fast changing noise levels. In other Words, a max
`bi acts on carriers With large SNR values during initialiZa
`bi acts on carriers with large SNR values during initializa(cid:173)
`tion, which do not coincide with carriers with large SNR
`tion, Which do not coincide With carriers With large SNR
`variation during shoWtime.
`variation during showtime.
`[0026] Modems implementing any of the knoWn (up-to
`[0026] Modems implementing any of the known (up-to(cid:173)
`date) lTV Recommendations ADSL lTV G.992.1, G.992.2,
`date) ITU Recommendations ADSL ITU G.992.1, G.992.2,
`G.992.3, G.992.4, G.992.5 and VDSL ANSI Tl.424 MCM
`G.992.3, G.992.4, G.992.5 and VDSL ANSI T1424 MCM
`standard are non-perfect examples of this case. The BIMAX
`standard are non-perfect examples of this case. The BIMAX
`is ?xed during the design phase of the modem transmitter,
`is fixed during the design phase of the modem transmitter,
`and not controllable over a management interface.
`and not controllable over a management interface.
`
`It is to be noted that this third known solutions is
`[0027]
`[0027] It is to be noted that this third knoWn solutions is
`available in almost all types of modems: baseband, single
`available in almost all types of modems: baseband, single
`carrier, multi-carrier, ...
`carrier, multi-carrier, .
`.
`.
`
`[0028] A fourth known solution to limit the vulnerability
`[0028] A fourth knoWn solution to limit the vulnerability
`of modems to fast increasing noise levels that could be
`of modems to fast increasing noise levels that could be
`absent at the time of initialization, is the use of an a -priori
`absent at the time of initialiZation, is the use of an a-priori
`determined (single number) Target SNR margin. In this
`determined (single number) Target SNR margin. In this
`solution, the noise level assumed during initialiZation for
`solution, the noise level assumed during initialization for
`determining the datarate, equals the noise level measured
`determining the datarate, equals the noise level measured
`during the current conditions of initialization but increased
`during the current conditions of initialiZation but increased
`with a certain factor called "Target SNR margin". The level
`With a certain factor called “Target SNR margin”. The level
`of the target SNR margin is determined by means outside the
`of the target SNR margin is determined by means outside the
`modem, but is communicated to the modem via a manage(cid:173)
`modem, but is communicated to the modem via a manage
`ment interface before bitloading in initiali