Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Patent
1996-10-15
2000-03-21
Chin, Wellington
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
455438, 455525, H04Q 722
Patent
active
060412356
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a handover method comprising the steps of: quality of a signal of a serving cell, adjacent to the serving cell, candidate cell for handover.
BACKGROUND OF THE INVENTION
It is characteristic of a modern mobile communication system that it is possible to switch a call from one base station to another while a mobile station is moving from one cell to another within a mobile communication system. This is called handover. So that the need for handover could be detected and a suitable target cell for handover could be selected in a mobile communication system, various measurements of the quality of the connection and field strength in adjacent cells are required. For example, in the pan-European mobile communication system known as GSM (Global System for Mobile Communications), a mobile station (MS) monitors the level and the quality of the signal (downlink signal) received from the base station of the serving cell, as well as the reception level of the downlink signal from the base stations in cells adjacent to the serving cell. Furthermore, the base transceiver station (BTS) of the cell monitors the level and the quality of the signal (uplink signal) received to the base station from every mobile station (MS) that is served by the base station. Handover from the serving cell to an adjacent cell takes place either when (1) the measurement results of the mobile station/base station indicate that the signal level and/or quality in the currently serving cell is low, and a better signal level can be obtained from an adjacent cell, or (2) an adjacent cell allows communication with lower transmission power levels. The latter situation may arise when the mobile station is located in the boundary area of the cells.
The weakness of the decision procedure for handover described above is that the quality of the signals in adjacent cells is a completely unknown factor. The measurements carried out for handover decision described above may indicate that the signal level received from an adjacent cell is sufficient for handover, although the quality of the signal in the adjacent cell is not acceptable for transmission due to co-channel or adjacent-channel interference. Let us assume, for instance, that a call may be handed over from base station BTS1 in a serving cell to that BTS2 in an adjacent cell at two locations; location A and location B. At location A, the transmission of the new base station BTS2 is interfered by the transmission of base station BTS3 belonging to a third cell, as a result the quality of the signal becomes poorer subsequent to the handover. At location B instead, the signal of the interfering base station is weak (due to, e.g., shelter provided by buildings), in which case the quality of the signal will still be sufficient subsequent to the handover if the call is handed over to base station BTS2 at location B.
SUMMARY OF THE INVENTION
The object of the invention is to estimate potential interference in the cells adjacent to the currently serving cell in which the signal level of the adjacent cells is sufficient for handover, and use this estimated information on interference in the selection procedure of the target cell for handover for directing the mobile station to the cell with the best signal quality.
This is achieved with a handover method of the invention which is characterized by at least one candidate cell if said at least one other cell is a potential source of interference in the candidate cell, the selection of the target cell for handover so that the possibility of handover to a cell with a high interference level is diminished.
The invention further relates to a handover arrangement in a mobile communication system in which a mobile station measures the reception level, and preferably also the quality, of the signal at the base station of the serving cell, as well as the level of the signals of adjacent cells, and transmits the measurement results to a fixed network, which determines the need for handover, and selects, with the aid
REFERENCES:
patent: 5239676 (1993-08-01), Strawczynski et al.
patent: 5239682 (1993-08-01), Strawczynski et al.
patent: 5285447 (1994-02-01), Hulsebosch
patent: 5594949 (1997-01-01), Andersson et al.
Chin Wellington
Nokia Telecommunications Oy
Sobutka Philip J.
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