Telecommunications – Transmitter and receiver at separate stations
Patent
1991-06-26
1993-07-20
Eisenzopf, Reinhard J.
Telecommunications
Transmitter and receiver at separate stations
455 541, 455 561, 379 59, H04B 726
Patent
active
052300811
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Technical Field
This invention is applicable to mobile radio communication. This invention relates, more particularly, to a method and apparatus for deciding in which sector of a mobile communication system a mobile station is in, where a radio zone (referred to as a zone herein) covered by one base station is divided into several sectors in operation.
2. Description of the Related Art
In the prior art mobile communication system, a zone is divided into plural sectors and each sector is covered by an antenna having directivity. Such method is advantageous in that interferences between sectors can be reduced by the directivity of the antennas, and the frequency utilization efficiency is improved as the distance between cells which are using the same frequency channels is shortened. In this type of mobile communication system, it is necessary for a mobile station to find out the serial number zone and of the sector in which the station is in at the time to set up a voice channel before the start of communication.
Even in the prior art mobile communication system where a zone is not divided into sectors, a mobile station sometimes must decide in which zone it is in. In the system where different zones are assigned different frequencies respectively, a mobile station scans control channels assigned to the zones, and detects a zone in which the station is in from the frequency (the serial number) of which control channel the station could receive. Similarly, in a different prior art mobile communications system if a zone is divided into sectors, it is possible for a station to discriminate a sector by its frequency. In other words, sectors are assigned with control channels of different frequencies, and a mobile station decides in which sector it is in by detecting the frequency or channel it can receive; or if a plurality of such channels exists, by measuring receiving levels of these frequencies, comparing them and discriminating the one with the maximum reception level.
However, in such a system of locating the sector in which one mobile station is in from the sector frequency, as sectors are assigned with a control channel of different frequencies, the number of frequencies for control channels is much larger than the number required for the system in which control channels are assigned to different zones. For instance, if the zones are assigned with control channels of different frequencies in the unit of nine zones, and the same frequency is repeatedly assigned to the next unit of nine zones or the 10th zone, then the number of necessary frequencies is nine. But if the sectors are assigned with different frequencies, a zone is divided into six sectors, and the zones are grouped in the unit of seven, 42 frequencies (6.times.7=42) will be required for control channels as the same frequency is reassigned only to the 8th zone. Even if the system has a comparatively simple structure as above, the required number of control channels is as much as five times more.
Moreover, the number of control channels which one mobile station receiver must scan for discriminating the sectors is large. Further, as it generally takes a certain amount of time to monitor the receiving level of a channel, the time required from activation of the power switch of a mobile station to when communication is ready with a set up control channel becomes inconveniently long.
In the above conventional system, moreover, when one mobile station moves across the boundary of sectors, the number of frequencies it must scan in order to detect the next control channel is so large that the station takes much time for detection and control of movement between sectors to conduct switching between the control channels smoothly. As the mobile station moves further during the delay in detection and control, the receiving strength becomes lower than the marginal level at which a mobile station could receive control signals. Occasionally, switching of control channels becomes inoperable. Because one control channel can only
REFERENCES:
patent: 4797947 (1989-01-01), Labedz
Onoe Seizo
Umeda Narumi
Utano Takanori
Yamada Tomoyuki
Eisenzopf Reinhard J.
Nippon Telegraph and Telephone Corporation
Pham Chi H.
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