Pulse or digital communications – Transceivers – Modems
Patent
1994-04-15
1998-09-15
Pham, Chi H.
Pulse or digital communications
Transceivers
Modems
455422, 455557, H04B 138, H04B 166
Patent
active
058090665
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an arrangement for enhancing data transmission in a digital cellular radio network.
BACKGROUND OF THE INVENTION
In the European mobile telephone system GSM, it is possible to establish a circuit switched data transmission connection or traffic channels so as to enable a data terminal connected to the data interface of a mobile radio unit to transfer data to and from a data modem in a mobile exchange and further by means of a modem link to and from another data modem and a data terminal connected to it. The maximum transmission rate of such data transmission is determined by the maximum capacity of the data channel established over the radio path, e.g. 9600 bit/s in the GSM system. In many applications there exists, however, a need for considerably higher transmission rates of user data.
SUMMARY OF THE INVENTION
An object of the present invention is to enhance data transmission in a digital cellular radio network.
According to the invention, an arrangement is provided for enhancing data transmission in a digital cellular radio network. This arrangement includes a radio data terminal; a network terminating unit connected to a mobile exchange and comprising a data modem; a remote data modem; and call control means for establishing a digital transmission connection between the radio data terminal and the data modem and a modem connection between the data modem and the remote data modem. The radio data terminal and the remote data modem comprise means for transmitting data in a compressed form, the digital transmission connection between the mobile radio data terminal and the data modem is a non-transparent asynchronous data connection of a cellular radio system, over which connection the compressed data is transmitted using the error correction of the cellular system, and the data modem of the network terminating unit comprises means for transmitting compressed data over the modem connection by using the error correction protocol of the remote modem and for transmitting compression parameters to the radio data terminal at the beginning of a data session, the parameters being determined on the basis of a handshaking procedure between the data modem and the remote data modem.
According to the invention, user data is transmitted between a radio data terminal and a remote data modem in a compressed form, whereby any possible redundancy has been removed from the data stream, and thus the amount of data to be transmitted over the radio link is reduced. The typical maximum compression ratios obtained by compression algorithms are 2:1 or 4:1, which allows a user data stream of up to 19200/38400 bit/s to be sent along and received from a data channel of 9600 bit/s in a cellular radio system. The actual compression ratios achieved by the compression algorithms are, however, highly dependent on the type of user data.
The transmission of compressed data requires a completely error-free transmission channel, as even a minor transmission error corrupts the decompression algorithm at the reception end. It is therefore necessary to use as efficient error correction as possible over the entire transmission connection in order to prevent transmission errors. An obvious solution is to use, in addition to compression, the same error correction algorithm in the radio data terminal as in the remote data modem of the other end, whereby the intermediate transmission connection would only be a transparent "tube" through the radio path. However, the error correction uses the transmission capacity to some extent, wherefore the maximum capacity of the data channel over the radio path cannot be utilized solely for the transmission of user data.
According to the invention, this is solved so that the digital transmission connection over the radio path between a mobile radio data terminal and a data modem in a network terminating unit is a non-transparent asynchronous transmission connection, where the error correction protocol of the radio system, optimized for correcting errors in the
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Newton, Newton's Telecom Dictionary, pp. 1102-1103, Jul. 1994.
Suomi Arto
Terho Mikko
Luther William
Nokia Telecommunications Oy
Pham Chi H.
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