Method and Apparatus for Determining Coverage and Switching Between Overlay Communication Systems

Abstract

Techniques to determine whether or not a terminal is under the coverage of a current wireless communication system (e.g., a packet data system) and to switch from the current system to another wireless communication system (e.g., a voice/data system). In one method, at least one measurement of at least one parameter for at least one base station in the current system is initially obtained. The measurement(s) may be SNR measurements. A metric is derived based on the measurement(s) and used (typically along with a metric threshold and a timer) to determine whether or not the terminal is within the coverage of the current system. A switch to another system is initiated if the terminal is deemed to be outside the coverage of the current system. The two systems provide at least one common service (e.g., packet data service).

1 . A method of switching a terminal from a first wireless communication system to a second wireless communication system, comprising:
 obtaining at least one measurement of at least one parameter for at least one base station in the first communication system;   deriving a metric based on the at least one measurement;   determining whether or not the terminal is within coverage of the first communication system based on the metric; and   initiating a switch to the second communication system if the terminal is deemed to be outside the coverage of the first communication system.   
   
   
       2 . The method of  claim 1 , wherein the switch to the second communication system is initiated only if at least one signal of sufficient signal quality is received from the second communication system. 
   
   
       3 . The method of  claim 1 , wherein the metric is derived based on quality of signals received by the terminal from base stations in the first communication system. 
   
   
       4 . The method of  claim 1 , wherein the metric is derived based on quality of signals received by the terminal from base stations in one or more sets selected from an active set, a candidate set, and a neighbor set. 
   
   
       5 . The method of  claim 1 , wherein the determining is further based on a metric threshold. 
   
   
       6 . The method of  claim 5 , wherein the metric threshold is a fixed value. 
   
   
       7 . The method of  claim 5 , wherein the metric threshold is an adaptive value. 
   
   
       8 . The method of  claim 5 , wherein the metric threshold is determined based on one or more measurements obtained for the second communication system. 
   
   
       9 . The method of  claim 5 , wherein the determining is further based on a timer. 
   
   
       10 . The method of  claim 9 , wherein the terminal is deemed to be outside the coverage of the first communication system if the metric is below the metric threshold for the duration of the timer. 
   
   
       11 . The method of  claim 10 , wherein the timer duration is an adaptive value. 
   
   
       12 . The method of  claim 11 , wherein the timer duration is determined based on one or more measurements obtained for the first communication system. 
   
   
       13 . The method of  claim 1 , wherein the switch is initiated only if at least one base station in the second communication system is received by the terminal with sufficient signal quality. 
   
   
       14 . The method of  claim 1 , wherein the first and second communication systems provide at least one common service. 
   
   
       15 . The method of  claim 1 , wherein the at least one common service includes packet data service. 
   
   
       16 . The method of  claim 1 , wherein the first communication system is an IS-856 system and the second communication system is a cdma2000 system. 
   
   
       17 . A terminal comprising:
 a metric computation unit operative to receive at least one measurement of at least one parameter for at least one base station in a first wireless communication system and to derive a metric based on the at least one measurement;   a coverage determination unit operative to determine whether or not the terminal is within coverage of the first communication system based on the metric; and   a controller operative to initiate a switch to a second wireless communication system if the terminal is deemed to be outside the coverage of the first communication system.   
   
   
       18 . The terminal of  claim 17 , wherein the metric relates to an active set that includes base stations in the first communication system received by the terminal with sufficient signal quality. 
   
   
       19 . The terminal of  claim 17 , wherein the metric is derived based on quality of signals received by the terminal from base stations in one or more sets selected from an active set, a candidate set, and a neighbor set. 
   
   
       20 . An apparatus comprising:
 means for obtaining at least one measurement of at least one parameter for at least one base station in a first wireless communication system;   means for deriving a metric based on the at least one measurement;   means for determining whether or not the terminal is within coverage of the first communication system based on the metric; and   means for initiating a switch to a second wireless communication system if the terminal is deemed to be outside the coverage of the first communication system.   
   
   
       21 . A memory communicatively coupled to a digital signal processing device (DSPD) capable of interpreting digital information to:
 receive at least one measurement of at least one parameter for at least one base station in a first wireless communication system;   derive a metric based on the at least one measurement;   determine whether or not a terminal is within coverage of the first communication system based on the metric; and   initiate a switch to a second wireless communication system if the terminal is deemed to be outside the coverage of the first communication system   
   
   
       22 . A method of determining coverage for a terminal in a wireless communication system, comprising:
 obtaining at least one signal quality measurement for at least one base station in the wireless communication system;   deriving a metric based on the at least one signal quality measurement; and   determining whether or not the terminal is within coverage of the wireless communication system based on the metric.   
   
   
       23 . The method of  claim 22 , wherein the metric is derived based on signal quality measurements for base stations in one or more sets selected from an active set, a candidate set, and a neighbor set. 
   
   
       24 . The method of  claim 22 , wherein the metric is derived based on a sum of the at least one signal quality measurement. 
   
   
       25 . The method of  claim 22 , wherein the metric is derived based on the maximum of the at least one signal quality measurement. 
   
   
       26 . The method of  claim 22 , wherein the terminal is deemed to be outside the coverage of the wireless communication system if the metric is below a metric threshold for the duration of a timer. 
   
   
       27 . A method of switching a terminal between a plurality of communication systems, comprising:
 identifying a preferred system for the terminal;   determining an operating state of the terminal;   determining coverage obtained by the terminal;   determining current data requirements of the terminal; and   switching the terminal among the plurality of communication systems based on the preferred system for the terminal, the operating state of the terminal, the coverage obtained by the terminal, and the current data requirements of the terminal.   
   
   
       28 . The method of  claim 27 , wherein the terminal is switched to the preferred system if it is under the coverage of the preferred system. 
   
   
       29 . The method of  claim 27 , wherein the terminal is switched to the preferred system if it is in an idle operating state and not currently receiving service. 
   
   
       30 . The method of  claim 27 , wherein the preferred system is a packet data system, and wherein the terminal switches to the preferred system if there is data to send. 
   
   
       31 . An apparatus comprising:
 means for identifying a preferred system for a terminal;   means for determining an operating state of the terminal;   means for determining coverage obtained by the terminal;   means for determining current data requirements of the terminal; and   means for switching the terminal among a plurality of communication systems based on the preferred system for the terminal, the operating state of the terminal, the coverage obtained by the terminal, and the current data requirements of the terminal.   
   
   
       32 . A program recorded on a computer readable medium and executable by a computer, comprising the steps of:
 obtaining at least one signal quality measurement for at least one base station in the wireless communication system;   deriving a metric based on the at least one signal quality measurement; and   determining whether or not the terminal is within coverage of the wireless communication system based on the metric.   
   
   
       33 . A program recorded on a computer readable medium and executable by a computer, comprising the steps of:
 identifying a preferred system for the terminal;   determining an operating state of the terminal;   determining coverage obtained by the terminal;   determining current data requirements of the terminal; and   switching the terminal among the plurality of communication systems based on the preferred system for the terminal, the operating state of the terminal, the coverage obtained by the terminal, and the current data requirements of the terminal.