Handoff method for cellular digital mobile communication system and mobile station

Abstract

According to a handoff method for a cellular digital mobile communication system, a communication test of a new channel is performed by utilizing a free time of a time-divisionally multiplexed channel. A mobile station of this invention includes a communication circuit for performing communication by using a time-divisionally multiplexed channel, a switching circuit for connecting a new channel during a free time of the time-divisionally multiplexed channel, and a communication test circuit for performing a communication test when the switching circuit is connected to the new channel.

What is claimed is: 
     
       1. A mobile station comprising: communicating means for performing communication using a time-divisionally multiplexed communication channel;   switching means for switching a present channel to a new channel during the free time of the time-divisionally multiplexed communication channel; and   a communication test circuit for performing a communication test of the new channel when said switching means is connected to the new communication channel.   
     
     
       2. A hand off method for a cellular digital mobile communication system comprising the steps of: providing a time-divisionally multiplexed communication channel;   changing a frequency to that of a new communication channel at a time at which communications at time slots of the time-divisionally multiplexed communication channel are completed; and   switching the new communication channel back to the time-divisionally multiplexed communication channel when one of a communication test of the new communication channel is completed and a predetermined period of time has elapsed, thereby performing the communication test of the new communication channel.   
     
     
       3. A mobile station comprising: communication means for performing communication using a time-divisionally multiplexed communication channel;   switching means for switching a frequency or the time-divisionally multiplexed communication channel into a frequency of a second time-divisionally multiplexed communication channel at a time at which communications at time slots of the time-divisionally multiplexed communication channel are completed and for switching from said second time-divisionally multiplexed communication channel to the time-divisionally multiplexed communication channel when one of a communication test of said second time-divisionally multiplexed communication channel is completed and a predetermined period of time has elapsed; and   a communication test circuit for performing the communication test of said second time-divisionally multiplexed communication channel while said switching means switches the frequency of the time-divisionally multiplexed communication channel to that of said second time-divisionally multiplexed communication channel.   
     
     
       4. A handoff method for a cellular digital mobile communication system, said method comprising: providing a plurality of base stations and mobile stations, wherein each base station comprises at least one time-divisional multiplex access radio transmitter/receiver, transmission/reception timings of the time-divisional multiplex access radio transmitter/receiver are identical within a given base station but are differentiated in adjacent base stations by one or more time slots, and   performing a communication test by a mobile station with a base station adjacent to a specific base station during the free time between time slots in the communication channel of said specific base station, while said mobile station is still maintaining communication with said specific base station. .Iadd.5. A mobile assisted handoff method for use in a digital cellular system, comprising the steps of:   a) receiving at a mobile station a communication signal transmitted from a first base station in a first time slot of a first frequency;   b) transmitting from said mobile station to said first base station a communication signal in a second time slot of a second frequency, said second time slot being different in time from said first time slot;   c) detecting at said mobile station a signal transmitted from a second base station in a third time slot of a third frequency, said third time slot being different in time from said first and second time slots; and   d) responsive to the result of said detecting step (c), determining whether said mobile station enters a cell site other than the cell site of said   
     
     
        first base station..Iaddend..Iadd.6.  A method for use in a digital cellular system including a plurality of mobile stations and a plurality of base stations, comprising the steps of: a) receiving at a first one of said plurality of mobile stations a communication signal transmitted from a first one of said plurality of base stations in a first time slot of a first time-divisionally multiplexed frequency;   b) transmitting from said first mobile station to said first base station a communication signal in a second time slot of a second time-divisionally multiplexed frequency, said second time slot being different in time from said first time slot;   c) detecting at said first mobile station a signal transmitted from a second one of said plurality of base stations in a third time slot of a third time-divisionally multiplexed frequency, said third time slot being different in time from said first and second time slots; and   d) responsive to the result of said detecting step (c), determining whether handoff of said mobile station is needed..Iaddend..Iadd.7. A method as claimed in claim 6, wherein said detecting step (c) comprises the steps of:   c1) detecting at said first mobile station the levels of signals transmitted from a plurality of base stations including said second base station;   c2) calculating the mean values of the signal levels detected at step (cl);   c3) producing said mean values calculated at step (c2) as the result of   
     
     
        said detecting step (c)..Iaddend..Iadd.8.  A mobile assisted handoff method for use in a digital cellular system, comprising the steps of: a) receiving at a mobile station a communication signal transmitted from a first base station in a first time slot of a first frequency;   b) transmitting from said mobile station to said first base station a communication signal in a second time slot of a second frequency, said second time slot being different in time from said first time slot;   c) detecting at said mobile station a signal transmitted from a second base station in a third time slot of a third frequency, said third time slot being different in time from said first and second time slots; and   d) responsive to the result of said detecting step (c), determining whether handoff of said mobile station is needed..Iaddend..Iadd.9. A mobile station comprising:   means for receiving a communication signal transmitted from a first base station in a first time slot of a first frequency;   means for transmitting to said first base station a communication signal in a second time slot of a second frequency, said second time slot being different in time from said first time slot; and   means for detecting a signal transmitted from a second base station in a third time slot of a third frequency, said third time slot being different   
     
     
        in time from said first and second time slots..Iaddend..Iadd.10.  A handoff method for a cellular digital mobile communication system comprising the steps of: providing a time-divisionally multiplexed communication channel;   changing a frequency to that of a new communication channel at a time at which communications at time slots of the time-divisionally multiplexed communication channel are completed; and   switching the new communication channel back to the time-divisionally multiplexed communication channel when one of a crossover test is completed and a predetermined period of time has elapsed, thereby performing the crossover test during the change to the new communication   
     
     
        channel..Iaddend..Iadd.11.  A mobile station comprising: communicating means for performing communication using a time-divisionally multiplexed communication channel;   switching means for switching a present channel to a new channel during the free time of the time-divisionally multiplexed communication channel; and   a crossover test circuit for performing a crossover test by receiving a transmission on said new channel when said switching means is connected to the new communication channel..Iaddend..Iadd.12. A handoff method for a cellular digital mobile communication system, said method comprising:   providing a plurality of base stations and mobile stations, wherein each base station comprises at least one time-divisional multiplex access radio transmitter/receiver, transmission/reception timings of the time-divisional multiplex access radio transmitter/receiver are identical within a given base station but are differentiated in adjacent base stations by one or more time slots, and   performing a crossover test by a mobile station with a base station adjacent to a specific base station during the free time between time slots in the communication channel of said specific base station, while said mobile station is still maintaining communication with said specific   
     
     
        base station..Iaddend..Iadd.13.  A mobile station comprising: communication means for performing communication using a time-divisionally multiplexed communication channel;   switching means for switching a frequency of the time-divisionally multiplexed communication channel into a frequency of a second time-divisionally multiplexed communication channel at a time at which communications at time slots of the time-divisionally multiplexed communication channel are completed and for switching from said second time-divisionally multiplexed communication channel to the time-divisionally multiplexed communication channel when one of a crossover test at said second time-divisionally multiplexed communication channel is completed and a predetermined period of time has elapsed; and   a crossover test circuit for performing the crossover test while said switching means switches the frequency of the time-divisionally multiplexed communication channel to that of said second time-divisionally multiplexed communication channel..Iaddend.