Multiplex communications – Duplex – Time division
Patent
1997-10-21
2000-07-11
Hsu, Alpus H.
Multiplex communications
Duplex
Time division
370347, 455464, 455515, 455560, H04L 514, H04B 7212, H04B 700, H04Q 720
Patent
active
060883383
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a personal telephone system, suitable for the transmission and reception of digital signals between mobile sets, and fixed stations in a cordless system.
In particular the invention finds its preferred but not restrictive application in the DECT system (Digital European Cordless Telecommunications) which constitutes a European standard for radio telecommunication systems of the cordless type which is suitable to offer phone and data services.
Personal telephone systems include a plurality of fixed transceiver radio stations to cover the interested areas and connected to a switching network which may be a public one or a private switching system (PABX), and portable user equipment which establish the connection with fixed base stations via radio. These systems are therefore suitable to communicate with each other and residential users connected to the telephone network. The connections may be of a voice type or can enable the exchange of data occupying the equivalent of one or more voice "channels".
A typical DECT network structure is schematically illustrated, as an example, in FIG. 1 and includes groups of k (in the example of the figure k=4) fixed transceiver radio stations--labelled in the DECT standard Radio Fixed Parts RFP--connected to branches (in the example 3 branches) set up by connecting lines L through drop-insert devices Dl. Each radio fixed part (RFP) can manage, via radio, a predetermined number of users--labelled in the DECT standard Portable Parts (PPs)--which are generally mobile. The branches are connected to a set of transcoders TRAS, and the latter one is connected to the public network PSTN (Public Switching Telephone Network) through a central control fixed part CCFP. In some applications the functions carried out by the CCFP may be inserted in a user card of a switching exchange or of a PABX.
The interface between the CCFP and the DECT network, for what is regarded the voice signal, is typically set up by digital channels of 64 Kbit/s (8000 samples/sec. each one codified through 8 bits). As specified above, to the CCFP unit a set of transcoders TRAS is connected which provides for the conversion of the eight bits PCM coding, used on the PSTN side, in an ADPCM (Adaptive Differential Pulse Code Modulation) four bits coding, used on the DECT side. The line L (bidirectional) at 2.048 Mbit/s which connects the CCFP to the different radio fixed parts RFP supports therefore 48 voice channels plus a prefixed number of synchronism and signalling channels.
The area covered by a fixed radio part, labelled cell, is in general quite reduced, sometimes reaching just a coverage with a radius of tenths or hundreds of meters. Typical applications of personal telephone systems are in industrial plants where they may replace the installation of a cable network, in commercial units or urban centres where they may replace for example, the public telephone boxes, which is an advantage.
The network for said personal telephone systems is a digital type. The radio access being of the category FDMA - TDMA - TDD.
The system is of the TDD type (Time Division Duplex) as the transmission and the reception do not take place at the same time. More precisely, as illustrated with reference to FIG. 2, the basic frame of 10 ms is divided into two halves: usually during the first 5 ms the radio fixed part transmits and the portable parts receive (half frame TX DECT for the radio fixed part and RX DECT for the portable parts), and during the following 5 ms the opposite happens. Each half frame is subdivided in 12 time channels or time slots (and therefore the system is of the TDMA type), each one of which is set up by 420 (or in certain cases 424) bits. The time slots are transmitted or received using 10, or more different frequencies. Therefore the system is of the FDMA type, for a total of 120 (or more) available channels which are allocated in order so as not to create interference problems.
The DECT system foresees logical channels among which a channel labell
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patent: 5371783 (1994-12-01), Rose et al.
patent: 5636243 (1997-06-01), Tanaka
patent: 5870673 (1999-02-01), Haartsen
patent: 5959984 (1999-09-01), Dent
Luca Marnoni
Rossella De Benedittis
Hsu Alpus H.
Italtel SpA
Qureshi Afsar M.
Siemens Information and Communication Networks S.p.A.
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