Channel selection control in a selective call receiver

Details Channel selection control in a selective call receiver Channel selection control in a selective call receiver

1998-01-27

2001-07-17

Hunter, Daniel (Department: 2684)

Telecommunications

Receiver or analog modulated signal frequency converter

Signal selection based on frequency

C455S161200, C455S161300, C455S249100

Reexamination Certificate

active

06263196

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radio selective call receiver and, more specifically, to a channel selection control method in the radio selective call receiver.
2. Description of the Related Art
There has been proposed a receiver having a channel selection function of selecting a receiving channel by scanning a frequency channel scan list (for example, Japanese Patent Unexamined Publication No. 6-315001).
Further, a cordless telephone having an available-channel determination function has been disclosed in Japanese Patent Unexamined Publication No. 1-202939. The cordless telephone is provided with an attenuator at the previous stage of a high-frequency amplifier. Since the attenuator attenuates the level of radio received signal, the effect of strong interference waves can be reduced.
In the conventional receivers as described above, however, the receiving sensitivity is set to a maximum level to increase the probability of detection of a calling area. Therefore, in cases where a plurality of calling areas are overlapped, an optimal calling channel is not always detected. There is a possibility that a receiving channel with lower signal level is selected.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a channel selection control method which can increase the reliability of receiving channel.
Another object of the present invention is to provide a radio selective call receiver and a channel selection control method which are capable of establishing synchronization with reliability in the case of two or more radio selective calling signals being overlapped.
According to an aspect of the invention, the sensitivity of a radio receiver is set to a first sensitivity level which is lower than a second sensitivity level of the radio receiver. In the first sensitivity level, the predetermined channels are searched for a receiving channel while receiving a radio signal before searching in the second sensitivity level.
Since the radio signal is received and a receiving channel is searched for in the state that the sensitivity of the radio receiver is lowered, receiving channel with higher signal level can be selected and the synchronization can be established.
According to another aspect of the present invention, in a radio selective call receiver having a channel scan function of scanning a plurality of predetermined channels in a predetermined order to search for a receiving channel, after a radio received signal is attenuated by a predetermined amount to produce a first radio received signal, the first radio received signal is demodulated to a first baseband received signal and it is determined whether a predetermined signal format is detected from the first baseband received signal. When the predetermined signal format is not detected, the predetermined channels are scanned according to the predetermined order in the attenuation state that the radio received signal is attenuated.
Further, when the predetermined signal format is not detected from the first baseband received signal, the radio received signal which is not attenuated is demodulated to a second baseband received signal, and it is determined whether the predetermined signal format is detected from the second baseband received signal. When the predetermined signal format is not detected from the second baseband received signal, the predetermined channels are scanned according to the predetermined order a first predetermined number of times in the normal state that the radio received signal is not attenuated.
Since the channel scan is performed in the normal state after the receiving channel has not been found in the attenuation state, a receiving channel with higher signal level can be selected with reliability.


REFERENCES:
patent: 4166927 (1979-09-01), Hamaoki
patent: 4620147 (1986-10-01), Niki
patent: 5369799 (1994-11-01), Tsunoda
patent: 5448774 (1995-09-01), Yokozaki et al.
patent: 2 285 327 (1995-07-01), None
patent: 2 296 633 (1996-07-01), None
patent: 1-202939 (1989-09-01), None
patent: 222732 (1994-04-01), None
patent: 6-315001 (1994-11-01), None
patent: 253088 (1995-08-01), None
patent: 260853 (1995-10-01), None
patent: 268173 (1996-01-01), None

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