High speed data modem using multilevel encoding
US4646305A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Sep 26, 1983 |
| Grant date | Feb 24, 1987 |
| Priority date | — |
| Expiry date | Sep 26, 2003 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04L27/3494
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
A 14.4 kilobit/second modem uses an encoding scheme in which groups of five bits are encoded as one of thirty-two (2.sup.5) possible code groups. This is done by using quadrature amplitude modulation and a 6 by 6 space-state constellation which allows a maximum of thirty-six different points to be encoded. Since only thirty-two points are needed the four outer corner points of the constellation are not used. In order to achieve the desired 14.4 KBPS data rate the baud clock must run at 2880 Hz. However, this bandwidth is very close to the maximum bandwidth available on voice-grade telephone lines. Accordingly, data encoding and data recovery techniques must be used which maximize the probabilities of correctly receiving the encoded data signals. These techniques include (1) data scrambling/descrambling; (2) assigning groups of five bits to constellation points, including performing rotational and Gray encoding; (3) a baud clock recovery scheme at the receiver which is performed prior to partial response encoding; and (4) a start-up technique using a three-level partial response ideal reference sequence during initial training at the receiver. In addition, the invention uses passban…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.