Telecommunications Industry Association
(TIA)
TR-30.1/99-11-063
Clearwater, 29 November 1999
COMMITTEE CONTRIBUTION
Technical Committee TR-30 Meetings
SOURCE:
Broadcom Corporation
CONTRIBUTOR:
Name:
Phone:
Fax:
E-mail:
Gottfried Ungerboeck
+41-1-713-2408
+41-1-713-2462
gu@broadcom.com
TITLE:
Information-Theoretic Considerations for V.90 Issue 2
DISTRIBUTION:
Members of TR-30.1 and meeting attendees
ABSTRACT
A significant performance gap exists between capacity-achieving modulation and uncoded modulation
for the ideal PCM downstream channel with constrained signal power. This gap could be narrowed with the
application of suitable coding and shaping techniques offering the possibility of approaching true 56 kbit/s
transmission. This paper calls for further study of these techniques for V.90 Issue 2.
Copyright Statement
The contributor grants a free, irrevocable license to the Telecommunications Industry Association (TIA) to incorporate
text contained in this contribution and any modifications thereof in the creation of a TIA standards publication; to
copyright in TIA’s name any TIA standards publication even though it may include portions of this contribution; and at
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Page 1 of 2
1
Introduction
The ideal downstream channel in PCM voiceband modems is analyzed in [1], first in the absence of a
power constraint, and second in the case of signal power being constrained to –12 dBm0. Analysis of the
latter case identifies for a rate of 56 kbit/s an SNR gap of 8.8 dB between capacity-achieving modulation
and uncoded modulation using i.i.d. symbols at a symbol error rate of 10-6. The gap is interpreted as
permitting coding gain up to 7.5 dB and shaping gain up to 1.3 dB. Further, the 8.8 dB SNR gap is
shown to correspond to a rate gap of 6.6 kbit/s.
Proposals to date have focused on increasing the upstream speed of V.90 Issue 2 relative to that
achieved in V.90. We propose the application of coding and shaping techniques in Issue 2 on both the
downstream and upstream channels, and thus open the way to true 56 kbit/s transmission in the downstream
direction while offering a significant improvement in upstream speed.
We recommend that coding and shaping techniques be considered for downstream and upstream
transmission in V.90 Issue 2.
Reference
[1] G. Ungerboeck, "Information-Theoretic Reflections on PCM Voiceband Modems," in Codes, Curves, and Signals –
Common Threads in Communications, edited by A. Vardy, Kluwer Academic Publishers, 1998.
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