Method for controlling a modem connection in the event of distur

Details Method for controlling a modem connection in the event of distur Method for controlling a modem connection in the event of distur

1996-05-23

1999-05-11

Bocure, Tesfaldet

Pulse or digital communications

Transceivers

Modems

375 9301, H04L5/16

Patent

active

059036028

DESCRIPTION:

BRIEF SUMMARY
This application claims benefit of international application PCT/F194/00375 filed Aug. 26, 1994.


BACKGROUND OF THE INVENTION

The invention relates to a method for controlling a connection, especially a wireless connection, between two modems in the event of disturbance, this method comprising initiating a so-called retrain procedure in the event of disturbance when either one of the modems receives a signal of unsatisfactory quality, in which retrain procedure the modems transmit predetermined retrain signals to each other in order to achieve synchronism between them. The term wireless connection is used herein to refer to a connection implemented in such a manner that it is at least partly wireless.
A wireless radio network is originally intended for transmission of speech but it is also suitable for transmission of data. Data transmission in a radio network is carried out by means of a modem in a terminal and a mobile phone, e.g. a cellular phone. It is possible to use, for example, a modem positioned in a portable computer or a modem designed for a conventional telephone network. The modem is connected, for example, to a cellular phone by a separate adapter, which, for instance, adjusts the transmission level.
FIG. 1 of the attached drawings is a block diagram of equipment, known per se, for transmitting data between a computer 11 (typically a portable computer) or a terminal with a similar function and another terminal (not shown) connected to it through a radio network RN. The equipment comprises a modem 12, which is connected to the computer 11 and, via the above-mentioned adaptor 19, to a mobile phone 13. The modem 12 comprises an interface unit 14 (e.g. conventional RS-232 serial interface), to which the terminal 11 is connected, an error correction unit 16 connected to the interface unit, a data pump 17 connected to the error correction unit, a line interface unit 18 connected to the data pump 17, and a control processor 15 for controlling the operation of the modem. The actual modem part consists of the data pump 17, which modulates digital signals supplied from the terminal 11 to a form suitable for an analog telephone network and demodulates signals supplied from the telephone network to a form suitable for the terminal equipment. The data pump 17 is connected to the telephone network (adapter) through the analog line interface unit 18. The control processor 15 of the modem controls the data pump and performs error correction and all other functions of the modem, such as communication with the computer through the interface unit 14. The error correction unit 16 receives data transmitted through the interface unit, packs the data in frames of a fixed size, and transmits the frame through the data pump. At the reception end, the data pump 17 converts the received analog signal into digital form, whereafter the receiving error correction unit examines the received frame and detects any possible errors, which are corrected by means of retransmission.
In view of data transmission in a mobile telephone network, the most significant component of the modem is the data pump 17. The CCITT (at present the ITU-T) has defined a number of modulation standards of different rates for use in a general switched telephone network. These standards are illustrated in the following table.


______________________________________ Modula- Carrier Symbol Recom- Rate tion frequencies rate mendation (bit/s) method (Hz) (1/s) ______________________________________ V.21 0-300 FSK 1080/1750 300 V.23 1200/75 FSK 1700/420 1200/75 V.22 600 QAM 1200/2400 600 1200 V.22 bis 1200 QAM 1200/2400 600 2400 V.32 4800 QAM and 1800 2400 9600 TCM V.32 bis 4800 QAM and 1800 2400 7200 TCM 9600 12000 14400 ______________________________________
The abbreviations used in the third column of the table above have the following meanings: FSK=Frequency Shift Keying, QAM=Quadrature Amplitude Modulation, and TCM=Trellis Code Modulation.
As appears from the table, the modems according to recommendation V.32 bis offer a high

REFERENCES:
patent: 4613979 (1986-09-01), Kent
patent: 5202905 (1993-04-01), Sakamoto et al.
patent: 5241565 (1993-08-01), Kloc et al.
patent: 5317594 (1994-05-01), Goldstein

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