Patent ID: 6067455
Filing Date: 2000-05-23
Classification: H04W

Abstract:
A digital mobile telephone system connected to a public telephone line, comprising:a switching station connected to the public telephone line;at least one base station connected to said switching station, including a corresponding base station for each sector covered by said digital mobile telephone system, transmitting a first radio signal having a first frequency different from one sector to another, the field strength of said first radio signal exceeding a predetermined level in each sector, the corresponding base station for each sector receiving a second radio signal having a second frequency different from said first frequency and different from one sector to another, each base station transmitting a third radio signal having a third frequency different from said first and second frequencies to cover an overlay region and having a field strength and a range smaller than said first radio signal;a mobile terminal, connected to the public telephone line by said switching station, receiving, in each sector, said first radio signal having said first frequency, monitoring, in each sector, the field strength of said first radio signal transmitted from the corresponding base station, and transmitting said second radio signal having said second frequency and a control signal indicative of the result of the monitoring to the corresponding base station; anda control apparatus provided in said switching station to control transmission of said first and second radio signals by said at least one base station and said mobile terminal, respectively, the corresponding base station forwarding the control signal transmitted from said mobile terminal to said control apparatus and in response said control apparatus switches transmission by the corresponding base station from said first frequency to said third frequency, when the field strength of said first radio signal transmitted from the corresponding base station and monitored by said mobile terminal exceeds a predetermined threshold level, while, at the same time, switching reception by the corresponding base station from said second frequency to a fourth frequency, switching reception by said mobile terminal from said first frequency to said third frequency; and switching transmission by said mobile terminal from said second frequency to said fourth frequency.