Apparatus for handover in TDMA communications

Abstract

A mobile communications system including a plurality of base stations includes a plurality of mobile telephones. Each mobile telephone communicates with at least a base station from the plurality of base stations using a timeslot and a frame. The frame has a plurality of timeslots for the base station to use to communicate with various of the plurality of mobile telephones in a cell covered by the base station. Each mobile telephone has a single radio capable of communication on various frequencies. The radio is not capable of communicating on different frequencies on adjacent timeslots in a frame. A mobile telephone may establish communication with a first base station on a particular timeslot in a frame. If another timeslot is available in the frame in a second base station, communication may be established with the second base station on another timestot in the frame. The another timeslot is not next to the particular timeslot if the frequency used on the particular timeslot and the another timeslot are different. If the frequencies used on the particular timeslot and the another timeslot are the same, communication may be established with the second base station on the another timeslot in the frame where the another timeslot is next to the particular timeslot or not next to the particular timeslot.

1 . A mobile communications system comprising: 
 a plurality of base stations;    a plurality of mobile telephones, each mobile telephone communicating with at least a base station from the plurality of base stations using a times lot of a frame, the    frame having a plurality of timeslots for the base station to use to communicate with various of the plurality of mobile telephones in a cell covered by the base station, each mobile telephone having a single radio capable of communication on various frequencies, the radio not capable of communicating on different frequencies on adjacent timeslots of a frame; and    circuitry that, when a mobile telephone has established communication with a first base station on a particular times lot in a frame, if another timeslot is available in the frame in a second base station, (a) causes communication to be established with the second base station on the another timeslot in the frame, the another times lot not next to the particular timeslot if the frequencies used on the particular timeslot and the another timeslot are different and (b) if the frequencies used on the particular timeslot and the another timeslot are the same, causes communication to be established with the second base station on the another timeslot in the frame, the another timeslot being next to the particular timeslot or not next to the particular timeslot.    
     
     
         2 . The system of  claim 1 , the circuitry being comprised by the mobile telephone.  
     
     
         3 . The system of  claim 1 , the circuitry being comprised by equipment coupled to the base stations.  
     
     
         4 . The system of  claim 1 , wherein communication established on a particular timeslot includes use of the timeslot for down link communication one frame and for uplink communication on the next frame.  
     
     
         5 . The system of  claim 1 , wherein the circuitry attempts to establish communication with the second base station if signal quality of communication with the first base station is below a particular level.  
     
     
         6 . The system of  claim 1 , wherein the circuitry drops communication with a base station if signal quality of communication with the base station is below a particular level.  
     
     
         7 . The system of  claim 1 , wherein system capacity is controlled by adjusting a combination of ( a) a particular level of signal quality of communication with the first base station below which the circuitry attempts to establish communication with the second base station and (b) a particular level of signal quality of communication with a base station below which the circuitry drops communication with the base station.  
     
     
         8 . The system of  claim 7  in which the combination is adjusted automatically based on measured utilization of system resources and desired communications link reliability.  
     
     
         9 . The system of  claim 1 , wherein the circuitry selects the second base station from among a set of base stations based on signal quality between the base stations and the mobile telephone.  
     
     
         10 . The system of  claim 1 , wherein the circuitry selects as the second base station a base station having the best signal quality between the base station and the mobile telephone, from among base stations other than the first base station.  
     
     
         11 . The system of  claim 1 , the mobile telephone having a list of base stations ordered based on signal quality between the base stations and the mobile telephone, and the mobile telephone including circuitry that selects the second base station as the first available base station on the list.  
     
     
         12 . The system of  claim 11 , wherein the list is ordered based on RSSI.  
     
     
         13 . The system of  claim 11 , wherein the list is ordered based on FER.  
     
     
         14 . The system of  claim 1 , including circuitry that reallocates another mobile telephone to another times lot in the second base station to allow the reallocated timeslot to be used by the mobile telephone.  
     
     
         15 . The system of  claim 14 , wherein the second base station includes circuitry that provides the mobile telephone an estimate of time to prepare the another times lot for communication with the second base station.  
     
     
         16 . The system of  claim 1 , including circuitry that selects between a signal from the first base station and a signal from the second base station based on a frame error rate in the respective signals.  
     
     
         17 . The system of  claim 1 , wherein the mobile telephone occasionally uses the particular timeslot for exchange of control information.  
     
     
         18 . The system of  claim 1 , wherein a frame comprises two half frames, and a half frame includes no more than six timeslots.  
     
     
         19 . A mobile telephone comprising: 
 a single radio not capable of communicating on different frequencies on adjacent timeslots of a frame;    circuitry that monitors signal quality with various base stations;    circuitry that, when the mobile telephone is in communication with a base station using a particular timeslot of a frame, wherein the frame has a plurality of times lots for the base station to use to communicate with various of a plurality of mobile telephones in a cell covered by the base station, causes the mobile telephone to request communication with a second base station based on the measured signal quality of the respective base stations, wherein a timeslot used to communicate with the second base station is not next to the particular timeslot of the frame if the frequencies used on the particular times lot and the another timeslot are different, and a timeslot used to communicate with the second base station is next to the particular timeslot or not next to the particular times lot if the frequencies used on the particular timeslot and the another timeslot are the same.    
     
     
         20 . The mobile telephone of  claim 19  including circuitry that causes the mobile telephone to make the request of communication with the second base station if signal quality of communication with the first base station is below a particular level.  
     
     
         21 . The mobile telephone of  claim 19  including circuitry that drops communication with a base station if signal quality of communication with the base station is below a particular level.  
     
     
         22 . The mobile telephone of  claim 19 , including circuitry that maintains a list of base stations ordered based on the measured signal quality, and wherein the second base station is selected based on the list.  
     
     
         23 . The mobile telephone of  claim 22 , wherein the list is ordered based on RSSI.  
     
     
         24 . The mobile telephone of  claim 22 , wherein the list is ordered based on FER.  
     
     
         25 . The mobile telephone of  claim 19  including circuitry that receives a message from the second base station indicating that communication cannot take place with the second base station and circuitry that in response requests communication with a third base station.  
     
     
         26 . The mobile telephone of  claim 19  including circuitry that receives a message from the second base station including an estimate of time to prepare the another timeslot for communication with the second base station.  
     
     
         27 . The mobile telephone of  claim 19  including circuitry that selects between a signal from the first base station and a signal from the second base station based on a frame error rate in the respective signals.  
     
     
         28 . The mobile telephone of  claim 19  including circuitry that occasionally uses the particular times lot for exchange of control information.  
     
     
         29 . The mobile telephone of  claim 19  wherein the frame comprises two half frames, and a half frame includes no more than six timeslots.  
     
     
         30 . A mobile communications system comprising: 
 a plurality of base stations;    a plurality of mobile telephones, each mobile telephone communicating with at least a base station from the plurality of base stations using a times lot of a frame, the    frame having a plurality of timeslots for the base station to use to communicate with various of the plurality of mobile telephones in a cell covered by the base station, each mobile telephone having a single radio capable of communication on various frequencies, the radio not capable of communicating on different frequencies on adjacent timeslots of a frame; and    circuitry that, when a mobile telephone has established communication with a first base station on a particular timeslot in a frame, if another timeslot is available in the frame in a second base station (a) causes communication to be established with the second base station on the another timeslot in the frame, the another times lot not next to the particular timeslot if the frequencies used on the particular timeslot and the another timeslot are different and (b) if the frequencies used on the particular timeslot and the another timeslot are the same, causes communication to be established with the second base station on the another timeslot in the frame, the another timeslot being next to the particular timeslot or not next to the particular timeslot, wherein the circuitry attempts to establish communication with the second base station if signal quality of communication with the first base station is below a particular level and the circuitry drops communication with a base station if signal quality of communication with the base station is below a particular level, where in the frame comprises two half frames neither comprising more than six timeslots;    circuitry in the mobile telephone that monitors signal quality with various base stations;    circuitry in the mobile telephone that selects the second base station based on the measured signal quality of the various base stations.    
     
     
         31 . The system of  claim 30 , wherein system capacity is controlled by adjusting a combination of (a) a particular level of signal quality of communication with the first base station below which the circuitry attempts to establish communication with the second base station and (b) a particular level of signal quality of communication with a base station below which the circuitry drops communication with the base station.  
     
     
         32 . The system of  claim 31  in which the combination is adjusted automatically based on measured utilization of system resources.  
     
     
         33 . The system of  claim 30 , wherein the signal quality is determined based on RSSI.  
     
     
         34 . The system of  claim 30 , wherein the signal quality is determined based on FER.  
     
     
         35 . The system of  claim 30 , including circuitry that reallocates a timeslot in the second base station to allow the reallocated timeslot to be used by the mobile telephone.  
     
     
         36 . The system of  claim 30 , including circuitry that selects between a signal from the first base station and a signal from the second base station based on a frame error rate in the respective signals.