Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Patent
1997-04-03
1999-11-09
Urban, Edward F.
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
455444, 455504, H04Q 720
Patent
active
059831049
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a device at telecommunication system, for instance DECT which comprises mobile units which are moving within or between the cells of the system.
STATE OF THE TECHNOLOGY
It is in itself known to perform determinations of speed based on the Doppler effect or on a longer time of measuring of the passage of the mobile through several cells. The Doppler effect is proportional to the quotient speed of vehicle/speed of light, which at the speed of 10 ms would imply a doppler shift of 60 Hz, which is quite negligible compared with bandwidth, operating frequency and normal frequency change caused by for instance heat release in the equipment. Measuring of the passage of the mobile through several cells is a blunt instrument if there is no indication whether the portable passes the cell diametrically or peripherally. Even a comparatively slow portable can peripherally pass many cells rapidly. The method also assumes that connection is established and is by that not good to use to deny connection.
DESCRIPTION OF THE INVENTION
Technical Problem
DECT (Digital European Cordless Telecommunications) is a pronounced small cell system, with typical cell radius of 100-500 meters at mobile applications i open environment. A user who is travelling "rapidly" through a region which is covered by several linked up DECT-cells will therefore cause many handovers (shifting of existing call from one cell to another; there are both intercell handovers and intracell handovers; it is the former which is related to here). If the number of intercell handovers becomes very large, this will load down the underlying network and cause increased signalling (to the central unit existing behind, and/or to VLR, etc).
Even if high handover frequency is accepted, problems remain with keeping a high transmission quality at higher speeds. The problem is caused by the fact that the gain with antenna diversity is reduced at higher speeds for DECT, because diversity algorithms where only one unit has antenna diversity must perform some form of prediction with speed depending validity--at higher speeds the mobile gets time to travel as far during a time frame that the level of the Rayleigh fading will get time to change several dB. This means that one for higher speeds either must increase the fading margin, which implies a reduced cell size, or resort to coding and/or interleaving as for instance for GSM.
For this reason all public operators of DECT have an interest in sorting out those DECT portables which are moving "too rapidly" for making it possible/profitable to deal with the calls.
For an operator who operates both mobile networks and DECT-networks it is even more interesting to be able to distinguish those portables which are moving "too rapidly". If dual-mode hand units (for instance DECT+GSM) are used, the operator has a very great interest in that rapid portables are using the mobile telephone system, so that motorized mobiles which are moving rapidly do not "flow over" to DECT. The operator will of course see to it that each network is used optimally, and also that the combination of these becomes optimal.
In this connection it can be worth explaining what is meant by "rapid movement". Tests have shown that DECT-systems manage dealing with portables which are moving with speeds up to 70 km/h (in these tests there were probably not time to reach higher vehicle speeds within a DECT-covered area). It is reasonable to assume that the tests were performed so that the portable passed on the whole diametrically through the cells, in order to cause as few handovers as possible. With the assumption that the cell passages on the average are considerably more peripheral, it is reasonable to use speed limits in the range 20-40 km/h (i.e. about 10 m/s; 5-10 times walking speed). The operator shall of course have possibility to decide which limit that should be used.
As a conclusion the technical problem is that DECT-portables which are moving "too rapidly" causes a too high handover frequency wit
REFERENCES:
patent: 5239667 (1993-08-01), Kanai
patent: 5265263 (1993-11-01), Ramsdale
patent: 5396645 (1995-03-01), Huff
patent: 5513380 (1996-04-01), Ivanov et al.
patent: 5548806 (1996-08-01), Yamagushi et al.
patent: 5574971 (1996-11-01), Aihara
Olanders Peter
Wickman Johan
Telia AB
Urban Edward F.
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