Multiplex communications – Communication over free space – Combining or distributing information via time channels
Patent
1998-08-10
2000-12-19
Patel, Ajit
Multiplex communications
Communication over free space
Combining or distributing information via time channels
455441, H04B 7212
Patent
active
061635340
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for determining the speed of a terminal equipment in a radio system using a time division multiple access method, which method comprises measuring the mean strength of the envelope of a received sampled signal within a given time window.
BACKGROUND OF THE INVENTION
The present invention is suitable for use especially in cellular radio systems and also in other digital radio systems where terminal equipments communicating with base stations move beyond cell boundaries. Information on the moving speed of the terminal equipment will make it essentially easier to manage resources of the radio system, such as handover anticipation and power control optimization.
For example, in a system using small microcells and bigger, so-called umbrella cells overlapping microcells, it is advantageous that fast moving terminal equipments are connected to umbrella cells and slowly moving or stationary terminal equipments to smaller microcells. In this way it is possible to diminish significantly the number of required handovers and thus signalling loading in the network.
One known solution for determining the speed of a mobile terminal equipment is to monitor Doppler shift of carrier frequency. This method is, however, impractical as it requires a stable frequency reference source which is expensive.
Another known method has been described in Doumi T., Gardiner J. G., Use of base station diversity for mobile speed estimation, Electronic Letters, Vol. 30, No. 22, pp. 1835-1836. The method of the reference cited utilizes base station antenna diversity. The antenna providing the strongest signal level is always selected for diversity. The frequency shift of the antenna is proportional to Doppler shift on the basis of which the speed of the equipment can be deduced.
U.S. Pat. No. 5,396,645 describes a method for measuring the speed of an equipment. In the method of the reference cited, variations of the strength of a received signal are measured during a predetermined time interval and the speed of the equipment is deduced on the basis of this variation.
None of the known methods is, however, suitable in a TDMA radio system where frequency hopping is used, that is, where the carrier frequency used by the user of the equipments varies by time slots in accordance with some given variance pattern.
CHARACTERISTICS OF THE INVENTION
The object of the present invention is to implement a determination method of the speed of an equipment which is suitable to be used in TDMA systems and in connection with frequency hopping as well as without frequency hopping.
This will be attained by a method shown in the preamble which is characterized in that the given time window is at most half a time slot in length, that a parameter proportional to the mean strength of the signal envelope is formed during each time window, that in each received time slot the parameter is measured by using at least two time windows, and that the variation of the envelope is calculated by time slots on the basis of the parameter, that the derived variation value is averaged over several time slots, and that the averaged variation value is compared with the calculated reference value, which comparison indicates the speed of the equipment.
The invention also relates to a receiver in a radio system using a time division multiple access method, which receiver comprises means for sampling the received signal. The receiver of the invention is characterized in that the receiver comprises means for forming a parameter proportional to the mean strength of the signal envelope during a time window at most half a time slot in length, in each received time slot by using at least two time windows, and means for calculating the variation of the envelope by time slots on the basis of the parameter, and for averaging the derived variation value over several time slots, and means for comparing the averaged variation value with the calculated reference value, and for indicating the speed of the equipment.
The method
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IEEE Transaction on Vehicular Technology, vol. 43, No. 3, Aug. 1994,Mark d.Austin et al, "Velocity Adaptive Handoff Algorithms for Microcellular Systems".
Electronics Letters, Oct. 27, 1994 vol. 30, No. 22, pp. 1835, 1836.
Nguyen Brian
Nokia Telecommunications Oy
Patel Ajit
LandOfFree
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