I I
`
`T1E1.4/97-319
`
`Standards Project: T1 E 1 .4 : VDSL
`
`Title: Power Down in Multi-carrier Transmission
`
`Source:
`
`Author:
`
`Thierry Pollet, Peter Reusens
`F. Wellesplein 1
`B-2018 Antwerp, Belgium
`Tel.:
`+32 3 240 8834
`Fax.:
`+ 32 3 240 9932
`E-mail: Pollett@rc.bel.alcatel.be
`
`Date:
`
`September 22-26, 1997 -Minneapolis
`
`Distribution to:
`
`T1 E1.4
`
`ABSTRACT
`
`When during modem operation, data transport over the modem is interrupted for some time, the
`modem can go in a power down operation mode where its power consumption is only a fraction
`as compared to the power consumption in normal operation. In this contribution we consider
`power down mode operation in multi-carrier systems where a fast transition from power down
`mode to normal operation mode (power up) is mandatory.
`
`In the described method, the transmission of all but one carrier is halted. The remaining
`modulated carrier ensures synchronization between transmitter and receiver.
`In addition, it
`provides a data channel enabling a fast power up.
`
`NOTICE
`
`This contribution has been prepared to assist Standards Committee T 1-Telecommunications. This document is
`offered to the Committee as a basis for discussion and is not a binding proposal on Alcatel Telecom. The
`requirements and recommendations are subject to change after further study. Alcatel Telecom specifically
`reserves the right to add to, amend, or withdraw any and all statements contained herein.
`
`Contribution T1 E 1.4/97-319 , September 22-26, 1997 -Minneapolis
`
`p. 1
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`

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`1. INTRODUCTION
`
`\
`
`I
`
`In case the traffic profile of the services supported over an V(A)DSL modem can be characterized
`as the exchange of chunks of data separated by
`long times periods (long as compared to the
`symbol period) where no data is to be transmitted over the copper line, powering down several
`functional blocks of the modem during the non-active time periods can reduce considerably
`power consumption. Especially for VDSL deployment from the ONU, power dissipation is a major
`concern. However, QOS requirements can impose constraints on the transition time from power
`down to normal operation mode.
`
`To illustrate the above imagine the following situations:
`
`-an end-user who has temporarily aborted this tele-working activity and has left the VDSL
`connection to the ONU open. He resumes his activity after several minutes.
`
`-a web browser based application: here periods of user data transfer are interrupted by non(cid:173)
`active periods that can last several seconds ( = thousands of DMT symbol periods).
`
`In the both cases, a modem which was put in power down mode must resume operation within a
`few milliseconds at the moment new date transfer is requested. A complete reinitialisation of the
`modem which can take several tens of seconds is intolerable. A fast transition from power down
`operation mode to normal operation mode is mandatory.
`
`This requirement imposes that during power down-mode the modem maintains
`
`1) synchronization (of the symbol timing, framing, RS coding, interleaving)
`
`2)
`
`the modem measures periodically the channel, and noise environment and takes appropriate
`action in case the modem parameters have to be modified as result of the changing channel
`environment
`
`2. POWER DOWN MODE IN A MULTICARRIER SYSTEM
`
`Power down operation can easily be achieved in a multi-carrier transmission system. When the
`modem detects that no user data traffic has been transmitted in the downstream nor received
`from the upstream for a given time period, it can request a transition from normal operation
`mode to power down mode. The request for power down is initiated provided that period of non(cid:173)
`activity exceeds the transmission delay experienced by the interleaved data path. This ensures that
`no user data is present in the interleaver/de-interleaver memory for the downstream channel. For
`the upstream, a mechanism must be provided to prevent that useful data is still present in the
`interleaver/deinterleaver path.
`
`When no user data is presented to the modem, idle ATM cells are transported over the link.
`Hence, non-activity can easily be detected at the TC layer. Operations software will indicate for
`how long idle cells have to be (continuously) transmitted before the request for power down is
`generated. A power down request must be rejected when on of the following conditions are met:
`
`1) V(A)OC or EOC message exchange is in progress
`2) Actions between the NT and LT are in progress on the physical layer (e.g. bit swap
`action, rate adaptation action, EOC command execution).
`
`Power down will be negotiated between the transmitter and receiver. Power down message
`requests will be transported over an operations channel.
`
`Contribution Tl E1.4/97 -319 , September 22-26, 1997- Minneapolis
`
`p.2
`
`

`
`, .
`
`In a multi-carrier system all but one carrier can halt transmission. The remaining carrier (pilot) [1]
`is required for timing synchronization between transmitter and receiver. This carrier must be
`modulated in order to provide an operations channel. In case case new user data is received at
`either side of the modem, power up can be indicated to the receiver over the operations channel.
`As during power down the modem remains synchronized, fast power up (several tens of DMT
`symbol periods) can be achieved.
`
`In power down only a single carrier is modulated . Therefore, a number of functional bloks in the
`digital part of the modem can be put in non-active mode. In addition, the power consumption of
`the analog part of the modem can be reduced significantly.
`
`3. CONCLUSION
`
`In this contribution we have considered power down in multi-carrier systems. It has been shown
`how the requirement for a fast power up can be met by using a single carrier (pilot) to maintain
`synchronization. The carrier must transport an operations channel in order to negotiate power
`up. During power down, the power consumption of the modem is only a fraction of the power
`consumption during normal mode operation.
`
`4. REFERENCES
`
`[1] Spruyt P.,"Modulation of the pilot tone", ANSI T1 E 1.4 Committee Contribution No. 97-051,
`Clearwater Beach (FL), May'97.
`
`Contribution T1 E 1.4/97-319 , September 22-26, 1997 - Minneapolis
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`p. 3
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