Telecommunications – Transmitter and receiver at separate stations
Patent
1993-08-27
1996-02-13
Urban, Edward F.
Telecommunications
Transmitter and receiver at separate stations
455 561, 379 60, H04Q 722
Patent
active
054918340
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to handover determination between cells in a cellular radio system handling communications to and from a mobile unit.
2. Related Art
It is important that handover between cells in a cellular radio network is conducted appropriatley and reliably. In mixed cell environments comprising macrocells and overlying microcells, the usability of an established communication channel with a base station could be both noise and interference limited. As far as maintaining signal quality and the limitation of the effects of interference are concerned, it is Possible to use dynamic channel assignment in all cells. However, to afford an appropriate level of reliability for a mobile unit on the move it is necessary to be able to perform intercell handover both reliably and at the appropriate time.
In a cellular radio system comprising both macrocells and overlaying smaller microcells, a call to or from a mobile unit within the operating area of the system is handled by a base station for each cell. Whereas, a macrocell may be of a size covering a number of streets and extending for 1 or 2 kilometers in all directions, a microcell will often be about 200 to 500 meters long and may only extend linearly along a street, within the coverage area of a macrocell.
The handover between a microcell and a macrocell is subject to special considerations. It is important for the system to be able to determine whether it is worthwhile effecting a handover of a mobile unit from a macrocell to a microcell as the latter is approached or between adjacent microcells. It may be that the mobile unit is going to enter the candidate microcell for a significant period, in which case a handover is beneficial, or relatively momentarily as the candidate microcell is crossed.
SUMMARY OF THE INVENTION
According to the present invention there is provided a handover determination system for a mobile radio network comprising a plurality of cells, each having associated with it a base station for supporting communications with a mobile unit, the system comprising: between each of a plurality of candidate base stations and the mobile unit; quality; and supporting communications with the mobile unit to another base station, on the basis of the rise/fall in the said quality of the signals associated with the plurality of candidate base stations being monitored.
Preferably, the mobile unit comprises the monitoring means and the producing means, the mobile unit further comprising signalling means for addressing the serving base station with an indication of the need for a handover to be initiated. The signalling means may be arranged to address the serving base station with an indication of the level of priority of a handover and/or with an indication of the possibility of a handover contingent upon the proceeding results of monitoring the quality of the transmitted signal. Advantageously, the monitored signal is transmitted from each mobile unit to the base station.
The monitored signal may be the received signal power. However, in digital communications systems the bit error ratio can be used.
Preferably, the control means are arranged to instruct the monitoring means to monitor a set of signals, each signal being distinctive of one of the corresponding set of base stations, the composition of the set being defined in accordance with the identity of the serving base station. In particular, each signal in the set of signals may distinguish a respective base station by the frequency of the signal.
In one particular form of the invention, the indication producing means include a quality decrement/increment estimator which is arranged to determine the rise or fall in the quality from the calculation of the running average of the indications. There may also be provided means for storing templates of changes in signal quality and/or rates of change thereof, the control means are arranged to initiate a handover based at least partially on the recognition of a substantial match betw
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38th IEEE Vehicular Technology Conference, Jun. 1988, pp. 340-343.
40th IEEE Vehicular Technology Conference, pp. 276-281, (Jun. 1988).
British Telecommunications public limited company
Soburka Philip J.
Urban Edward F.
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