Protocol for packet data communication system
US5668803A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Nov 23, 1994 |
| Grant date | Sep 16, 1997 |
| Priority date | — |
| Expiry date | Nov 23, 2014 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04W84/047
- WIPO fieldDigital communication
- WIPO sectorElectrical engineering
Abstract
A packet data transmission system is used to link a number of remote hand-held data-gathering units such as bar code readers to a central computer. Data packets are sent from the remote units by an RF link to intermediate base stations, then sent by the base stations to the central computer by a serial link. Direct sequence spread spectrum modulation is used for the RF link. The remote hand-held units initiate an exchange using RF transmission to and from the base stations, receiving only during a rigid time window following a transmission from the remote unit. The base stations cannot initiate an exchange with the remote units, but instead send data to the remote units only as part of the exchange. To alert a remote unit when a message is waiting at a base station to be sent to a particular unit, some of the acknowledge (base-to-remote) packets sent by the base station may contain an identification such as a list of all remote units (identified by ID number) which have messages waiting. Alternatively, a bit map can be used to identify these remotes. These base-to-remote packets with the identification of remotes with messages waiting are called "announcements." Each remote unit (i…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.