Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
2000-06-09
2004-03-30
Urban, Edward F. (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S439000, C370S331000
Reexamination Certificate
active
06714784
ABSTRACT:
TECHNOLOGICAL FIELD
The invention relates in general to the technological field of packet-switched cellular radio systems. More precisely the invention relates to the cell change procedures, i.e. the procedures for rerouting an active packet-switched communication connection between a mobile station and a fixed packet-switched network through a new base station. An important application framework for the invention is the GPRS or General Packet Radio Service system which is undergoing specification at the priority date of the present patent application. Other at least equally important application frameworks are the UMTS (Universal Mobile Telecommunication System) where the so-called connectionless data services are packet-switched, and the EDGE (Enhanced Data rates for GSM evolution) where also connectionless data services will be implemented.
BACKGROUND OF THE INVENTION
The services that are offered over telecommunication connections may be broadly categorized into real time and non-real time services. The former class covers such services where an essentially continuous or at least piecewise continuous stream of information is carried from the transmitter to the receiver and the intelligibility of the received information depends on the continuity: only relatively small and relatively constant delays are allowed. Typical real time services involve the transmission of speech and (moving) images like in a telephone or videophone connection, where e.g. a voice activity detection system may be used to provide piecewise continuity, i.e. to periodically halt the transmission when there is nothing important to transmit. Non-real time services cover the transmission of information with less critical timing requirements and are typically referred to as transmission of data. Electronic mail and downloading of files from or to a distant location are examples of non-real time service applications.
Packet-switched cellular radio systems have usually been designed to complement the known circuit-switched mobile telephone systems and their future successors so that the division of work would involve the use of circuit-switched systems to provide real time services and packet-switched systems to provide non-real time services. Circuit- and packet-switched transmission may even be implemented as alternative operational modes within the framework of a single telecommunication systems, or in hybrid network arrangements where the same base stations and other radio access hardware are used for both systems but the other fixed network devices and communication connections between them are separate. An arrangement of the last mentioned type is the combination of a GSM mobile telephone network (Global System for Mobile telecommunications) and the GPRS network.
FIG. 1
illustrates a combined GSM/GPRS arrangement where an MS or mobile station
101
may choose one of the BSs or base stations
102
to
107
to communicate with. Base stations
102
and
103
operate under a controlling device
108
where a PCU or packet control unit is combined to a BSC or base station controller. Similarly base stations
104
and
105
operate under controlling device
109
and base stations
106
and
107
operate under controlling device
110
. From this level upwards the GSM arid GPRS networks have different architectures. Each base station controller is coupled to a MSC or a mobile switching centre and these are in turn interconnected through a GSM transmission network
115
. Each packet control unit is coupled to a SGSN or serving GPRS support node and these are in turn interconnected through a GPRS transmission network
116
, where the connections go through GGSNs or gateway GPRS support nodes (not shown). The small number of devices shown in
FIG. 1
is for graphical clarity only: in realistic GSM/GPRS systems there are typically thousands of base stations, hundreds of BSC/PCUs and dozens of MSCs and SGSNs.
It should be noted that the location of a PCU is not defined very strictly in the known GPRS: in addition to the arrangement shown in
FIG. 1
a PCU may be located in a base station or in an SGSN. The present invention does not have any particular biasing towards any most advantageous location of the PCU. The general network architecture and the interconnections of the base stations, PCUs and SGSNs naturally depend on the location of the SGSN.
Around each base station there is a cell or radio coverage area within which a mobile station may communicate with that base station. When a mobile station moves out of one cell and into another, a cell reselection, a handover or a cell change must be performed. Cell reselection takes place when the mobile station is in idle mode and no communication connections are currently active between it and the fixed parts of the network. A handover means that an active circuit-switched communication connection must be rerouted through a new base station. A cell change means that an active packet-switched communication connection must be rerouted through a new base station. Regarding packet-switched (GPRS) communications in an arrangement according to
FIG. 1
the cell reselection or cell change may be intra-PCU (for example from base station
102
to base station
103
), inter-PCU but intra-SGSN (for example from base station
103
to base station
104
) or inter-PCU and inter-SGSN (for example from base station
105
to base station
Although the GPRS system like many other packet-switched cellular radio systems has been designed primarily for providing non-real time services, there is a tendency towards using it also to provide some real time services, of which the Internet calls are a good example. An Internet call is a telephone connection routed through the Internet instead of the common telephone networks. It may be accompanied with a video part. Also other applications requiring real time services through a packets switched cellular radio network are known.
A problem of the known GPRS that also appears in many other packet-switched cellular radio systems is that the cell change procedures have been opimized for simplicity rather than short delay. According to the standardized GPRS procedure the exchange of packet data between a mobile station and the old base station is first terminated, after that a new cell is chosen and only thereafter the transfer of packets is resumed through the base station of the new cell. The procedure works well for non-real time services since the delay between terminating the old connection and establishing the new one does not matter. However, the length of the delay is easily several hundreds of milliseconds or even up to some seconds, which is definitely too much for a real time service where such a long delay is at least annoying and may even cause the call or other connection to be dropped if the delay is interpreted as a severe breakdown in the flow of information. The long delay may also cause frustration to the users of non-real time services even when it does not actually affect the intelligibility of the transmitted information: for example the downloading of web pages is unnecessarily slowed down by the delays.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and an arrangement for performing a cell change in a packet-switched cellular radio network with a delay that is short enough to be acceptable for real time services and to avoid unnecessary retardation for non-real time services.
The objects of the invention are achieved by commencing the cell change before terminating the old connection and preferably also using a countdown timer to trigger the switchover from the old cell to the new cell.
The method of the invention is designed for implementing a cell change for a mobile station in a packet-switched cellular radio system comprising a first base station, a second base station and a controlling unit controlling the operation of at least the first base station. It comprises as its characteristic features the steps of
establishing at the controlling unit the knowledge about the mobile station
Forssell Mika
Hamiti Shkumbin
Parantainen Janne
Nguyen Simon
Nokia Mobile Phones Ltd.
Perman & Green LLP
Urban Edward F.
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