Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-11-08
2002-09-03
Urban, Edward F. (Department: 2685)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S442000, C455S453000
Reexamination Certificate
active
06445924
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to reduction of the traffic load from a congested cell in a mobile communications system.
BACKGROUND OF THE INVENTION
In mobile communications systems mobile stations and base transceiver stations may set up connections through the channels of a so-called radio interface. A certain frequency range is always allocated for use by the system. To obtain sufficient capacity in the mobile communications system on this limited frequency band, the channels in use must be used several times. For this reason, the coverage area of the system is divided into cells formed by the radio coverage areas of individual base transceiver stations BTS, for which reason the systems are also often called cellular radio systems.
FIG. 1
shows the network elements and the relations between them in a known mobile communications system. The network shown is accordant with a GSM system, which is used as an example in the present application. The solid lines in the figure depict connections including both signalling and call connections while the dashed lines show connections including signalling only. The network includes base transceiver stations BTS which via a radio path may set up connections with the mobile stations MS of mobile station subscribers, base station controllers BSC controlling the base transceiver stations, and mobile services switching centres MSC. Hierarchically below the MSC there are several base station controllers BSC and below these there are several base transceiver stations BTS. The interface between MSC and BSC is called interface A while the interface between BSC and BTS is called interface A-bis.
Call connections which have been set up pass from base transceiver station BTS through base station controller BSC to mobile services switching centre MSC. MSC connects calls to its subordinated base station controllers, to other MSC centres or to a public switched telephone network PSTN or to an integrated services digital network ISDN. The network also includes a network management system NMS, which may be used for collecting information on the condition of the network and for supplying information and programmes to other network elements.
In the idle state, mobile stations measure the signals sent by base transceiver stations and when required they will request a connection setup from the base transceiver station which is serving best at each time. During the connection the network may move the mobile station to another cell through handover between cells whenever required and without disconnecting.
In an active call state, mobile station MS sends measuring results regularly as a report message through the serving base transceiver station BTS to base station controller BSC. The report message includes the measuring results of signal strengths of the serving base transceiver station and of no more than six adjacent base transceiver stations providing the best signal. Besides the mobile station, the base transceiver station BTS also performs measurements of the connection quality. The results of measurements performed by mobile stations and base transceiver stations are analysed in the base station controller BSC. The base station controller also maintains information on free channels in base transceiver stations of its subordinated cells. In a GSM system, the management of radio resources is almost entirely the responsibility of the base station controller BSC.
A mobile station is moved through handover from the serving cell to some adjacent cell e.g. when
The measuring results of a mobile station/base transceiver station indicate a low signal level and/or quality of the present serving cell and a better signal level can be obtained from an ambient cell,
some ambient cell allows communications at lower transmission power levels,
when a mobile station MS has moved too far from the serving base transceiver station BTS, or when
there is too much load in the serving cell.
Handover may also be done for some other reason, e.g. due to trouble in a base transceiver station. Factors affecting the choice of target cell in handover are e.g. the signal level and/or load of the target cell. To ensure stability of the mobile communications network, the measuring results and parameters used in handover are averaged over a certain time slot. In this way, handover is made less susceptible to distorted measuring results that may be caused by temporary interference or fading.
Handovers may be done
Inside a cell (intra-cell handover),
between two cells subordinated to the same base station controller (handover between base transceiver stations),
between cells subordinated to two base station controllers subordinated to the same mobile services switching centre MSC (handover between base station controllers), or
between cells subordinated to two different mobile services switching centres MSC (handover between mobile services switching centres).
Handovers are almost solely the responsibility of the base station controller BSC. The mobile services switching centre MSC participates only in such handovers between base station controllers which are due to loading of the cell.
This invention relates to such a handover due to excessive cell loading the basic principle of which is illustrated in FIG.
2
. The figure shows seven cells, cells A-G, wherein the load situations are different. Cell A is loaded to the extreme limits of its capacity. Cell C is loaded a little more lightly than cell A. The loading of cells B and E is normal in view of their capacity, while cells D, F and G are lightly loaded. The load situation is proportionate to the thickness of oblique lines in the cells shown in the figure. From the viewpoint of the whole, the optimum network operation is achieved when the loads of all cells are on the same level, or when at least all cells have resources for setting up new connections. To achieve this situation, the load of cell A is discharged through handovers indicated by arrows and due to the loading of the cell into cells D, F and G which are lightly loaded.
With the aid of handover due to excessive cell loading, room for a new connection can be made in a cell. If there is no room for a connection, the connection is handed over to another channel through directed retry already in the call setup phase. However, directed retry in the call setup phase must be made only on the basis of a few measuring reports. The handover target cell must hereby be chosen on a basis of very deficient measurements. On the other hand, at least some mobile stations having a connection with a base transceiver station of the cell would typically achieve a similar connection quality also with some other base transceiver station. From the viewpoint of the whole it is hereby most advantageous to move from the cell one or several mobile stations in an active state to adjacent cells and to set up the new connection without any handover in the call setup phase.
Another example of the advantages of handover due to excessive cell loading is a situation where there is one free channel both in cell S
1
and in cell S
2
, and an attempt is made in cell S
1
to set up a high-speed connection requiring the use of two channels. It is hereby possible with handover to move one of the connections in cell S
1
to cell S
2
, whereby two free channels are obtained in cell S
1
for use by the new connection.
The following is an examination of a state-of-the-art handover due to excessive cell loading as described in the GSM 08.08 (version 4.7.1) specification published by the European Telecommunications Standards Institute ETSI, the required signalling for which is shown in FIG.
3
.
MSC inquires of base station controller BSC about the congestion situation of an individual cell by sending to the base station controller a RESOURCE REQUEST message
301
, wherein the cell, the type of reporting and the reporting period, if any, are identified.
Base station controller BSC begins reporting on the utilisation rate of the cell's capacity with the type of reporting stated by MSC. The base stat
Altera Law Group LLC
Gesesse Tilahun
Nokia Networks Oy
Urban Edward F.
LandOfFree
Method and apparatus for implementing handover in a mobile... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for implementing handover in a mobile..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for implementing handover in a mobile... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2832586