Telecommunications – Transmitter and receiver at same station – Radiotelephone equipment detail
Reexamination Certificate
2000-06-13
2003-10-07
Trost, William (Department: 2683)
Telecommunications
Transmitter and receiver at same station
Radiotelephone equipment detail
C455S433000, C455S517000
Reexamination Certificate
active
06631275
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to a call establishment in a radio communication system comprising subscriber terminals, at least one base station, and at least one telephone exchange, whereupon a part of the subscriber connection is formed by a radio path between the terminal and the base station.
BACKGROUND OF THE INVENTION
When building a telephone network, the installation of subscriber lines between the exchange and the subscriber terminals is not only expensive but also takes a considerable amount of time. One solution for saving costs is to replace the fixed subscriber loop between the exchange and a subscriber device with a radio connection. In this case the subscriber device for a fixed network is connected to a terminal which includes a radio transceiver. It converts an audio frequency signal into a radio frequency signal and sends it via a radio path to the base station, and correspondingly, converts a received radio frequency signal into an audio frequency signal.
This kind of solution can be based on a platform system which can be a cellular system as such or a modified cellular system. Together these solutions are referred to in this application as a WLL system (Wireless Local Loop System).
The principle of a WLL system based on a modified cellular system is illustrated in
FIG. 1. A
wireless fixed terminal T comprises a radio part equipped with an antenna and a telephone adapter
4
, which connects a standard subscriber device
5
to the terminal. The user can use the subscriber device
5
just as it would be used in a normal fixed network, even though the main part of the subscriber line connection is formed by using a radio connection between the terminal device T and the base transceiver station (BTS)
2
. The subscriber device can also be a normal mobile station
6
of the system to which the WLL has been adapted. Each base station can serve several subscriber devices. The, base stations are connected to a special network element
1
called an access node, which in turn is connected to a standard telephone exchange.
The access node
1
can be connected to the local exchange with an open V2 or V5.1 multiplexer connection, which uses a 2 Mb/s PCM system. If the local exchange only supports a 2-wire interface, the access node is connected to the switch with a multiplexer with the purpose of converting the V2 signaling into an analog 2-wire subscriber interface. The signaling between the access node and the base stations is the signaling of an applied mobile phone network, but it has been modified in such a manner that the functions typical of a cellular network, such as cell handover and roaming, are not possible. This means that the subscriber must stay within the assigned coverage area. The routing of incoming and outgoing calls is based on the subscriber file of the network element.
The WLL system adapted from a cellular system can be built by using the structural parts of an existing cellular system. A mobile phone system can be an analog or a digital system. In this case the signaling in the WLL system conforms; to the signaling in the cellular system, the base stations are the standard base stations of the cellular system, and the radio unit of a terminal is similar to the radio part of a mobile station, or the terminal device may be a mobile station of the mobile phone system as such. In the latter case, the terminal device and the subscriber device (phone) have been combined into one physical device.
An important network element of the WLL system is the access node. In a pure cellular system this element is a mobile services switching centre, and in an applied system it is a network element described previously in this application. The access node converts the signaling of the WLL system into signaling suitable for a fixed network and correspondingly adapts the signaling of the fixed network for the interface of the WLL network.
FIG. 2
depicts the main elements in a cellular network. It comprises a plurality of mobile services switching centres MSC. Each MSC can establish connections both to other centers and to other telecommunications networks. Several base station controllers BSC are connected to the MSC. One BSC controls a plurality of base stations BTS. A network management system collects information on the network and configures the network elements. The cellular network also includes databases. A home location register HLR stores permanent subscriber data such as subscriber service data and routing information in a visitor location register VLR. The VLR receives subscriber data from the HLR and stores it for the time when the subscriber is visiting in that VLR area.
A cellular network is well suited for a WLL network. The subscriber data in the HLR includes the information that the subscriber is a WLL subscriber. Further, information about the cell or cells where the subscriber is allowed to reside is also included in the subscriber data. These cells are called the home cell and only in these cell areas the subscribers have the right to make and receive calls. In
FIG. 2
, WLL terminal
21
can operate in cell A only.
It was mentioned previously in this application that signaling in the WLL system conforms to the signaling in the cellular system. Accordingly, the call establishment procedure in the WLL system follows that of the cellular system.
The line adapter in the terminal generates a dial tone when the receiver of the telephone connected to the terminal has been taken off the hook. If there is no service available, a busy tone is generated. When service is available, the dial tone is generated, and the user can start dialing. During the dialing the dialed digits, either in DTMF (Dual Tone Multifrequency) format or in pulse code format, are converted into digital format and stored in a buffer. When it is ascertained that the dialing has been completed, the contents of the buffer are sent to the transceiver. After this, a special SEND signal is given to the transceiver of the terminal to send the first message to the network. This triggers a normal call initiation procedure according to the mobile phone network used.
If the WLL system is based on the GSM system, the messages exchanged between the terminal and the network are the same as in GSM.
FIG. 3
depicts messages between the terminal and the network. As the first step, the terminal requests a signaling channel by sending the message “Channel Request”. Then the network searches for a free channel, and when one is located it sends the information about it to the terminal in the message “Immediate Assignment”. After that the network authenticates the terminal by receiving the right response to the message “Authentication Request”. Then the network commands the terminal to cipher the signaling and the subsequent speech information, and the terminal gives notice of compliance in the message “Cipher Mode Complete”. In the ciphered mode the network sends a temporary number called TMSI (Temporary Mobile Subscriber Identity) to the terminal, which acknowledges this in the return message “TMSI Reallocation Complete”.
It is only now that the terminal sends the dialed phone number in the message “Setup”. In response to that message, the network sends to the calling terminal the message “Call Proceeding”, which indicates that the requested access connection establishment has been initiated. After a traffic channel has been allocated, the network sends the message “Assignment Command”, which informs the terminal of the traffic channel to be used. The channel assignment is acknowledged in the message “Assignment Complete”. After these messages, the mobile switching centre starts the connection establishment to the called subscriber, and when the connection is ready, the “Alert” message is sent to the terminal. The user can now hear an alerting tone. If the called subscriber answers, the message “Connect” informs the terminal that the call has been accepted by the called subscriber. The last message “Connect Acknowledge” indicates that the connection between the term
Martin Markus
Tuunanen Heikki
Nokia Corporation
Sobutka Philip J.
Squire Sanders & Dempsey LLP
Trost William
LandOfFree
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