Multipoint to point radiocommunications network

• US 5,953,371 A
• Filed: 07/21/1997
• Issued: 09/14/1999
• Est. Priority Date: 06/22/1993
• Status: Expired due to Term

• Current Assignee: Schlumberger Industries Ltd (Thales SA)
• Original Assignee: Schlumberger Industries Ltd (Thales SA)
• Inventors: Rowsell, Francis John, Meek, Thomas Robert
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): JIANG, LENNY R
• Application Number:
  US08/897,588
• Time in Patent Office: 785 Days
• Field of Search: 375/201, 375/220, 375/260, 370/344, 370/468, 370/480, 370/515, 340/870.02, 340/870.03, 455/103
• US Class Current: 375/220
• CPC Class Codes: H04B 1/667 using a division in frequency subbands for TV signals H04N19/63
• CPC Class Codes: H04L 2001/0093 Point-to-multipoint

Abstract

A data collection system in which a number of remote terminals (RT) transmit data packets for reception by one or more fixed data collectors (FDC) or a portable data collector (PDC). Each remote terminal (RT) transmits data in two frequency sub-bands to which the fixed and portable data collectors are respectively tuned. Channel capacity is improved in at least the fixed data collector (FDC) sub-band by the use in the remote terminal of minimum shift keying (MSK) encoding and pseudo-random variation of a frequency error applied to the packet transmission frequency for successive packets. In the fixed data collectors dual fast-Fourier transform signal processing enables the interpretation of simultaneous packets with different error frequencies. The use of a single design of remote terminal (RT) in conjunction with portable data collectors (PDC) simplifies system set-up, with the portable collectors providing coverage for those areas where a fixed data collector (FDC) network has yet to be established. The system has particular application to the monitoring of devices such as gas and electricity meters and security systems.

Claims

1. Remote terminal apparatus for use in a multipoint to point data network, the apparatus comprising:

a data encoder operable

to receive a stream of data for radio frequency transmission within a given frequency channel, and

to encode the said data into packets, and

to divide said frequency channel into upper and lower frequency sub-bands and to select a frequency sub-band within the frequency channel, and

a variable frequency transmitter operable

to periodically transmit the data packets and

to apply a pseudo-random frequency error to the packet transmission frequency within said frequency sub-band, in which the transmitter is operable to vary the pseudo-random frequency applied for each successive data packet such that the variation in pseudo-random frequency being chosen ensures that substantially all frequencies within said frequency sub-band are equally likely and so as to maximize channel capacity where the remote terminal apparatus is capable of two different transmissions, one via fixed data collectors and another via portable data collectors.

2. Remote terminal apparatus as claimed in claim 1 in which the variation in the pseudo-random frequency is chosen taking into account natural randomizing factors such as aging and temperature variations.