Generalized precoder for the upstream voiceband modem channel
US6434190B1 · kind B1 · utility
Assignee
Inventor
Key dates
| Filing date | May 19, 2000 |
| Grant date | Aug 13, 2002 |
| Priority date | — |
| Expiry date | May 19, 2020 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L25/4927
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
For PCM upstream, the analog modem must transmit a filtered sequence of symbols so that the samples of the signal at the input to the codec at the central office (CO) are at a predetermined set of levels. This requires that the analog modem use an 8 kHz symbol rate synchronized to the CO clock. Typical telephone channels have nulls at DC and at 4 kHz. Therefore, for best performance, the signal transmitted by the analog modem should be spectrally shaped to match the channel. The present invention utilizes a generalized Laroia-Tretter-Farvardin (LTF) precoder similar to the one used in V.34. This precoder structure allows spectral shaping and could also allow for constellation shaping gains. Using this precoder structure with spectral shaping has the potential to improve data rates by 3-3.5 kbps.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.