Multi-SIM wireless devices have become increasing popular because of the versatility that they provide, particularly in countries where there are many service providers. For example, dual-SIM wireless devices may allow a user to implement two different plans or service providers, with separate numbers and bills, on the same device (e.g., business account and personal account). Also, during travel, users can obtain local subscriber identification module (SIM) cards and pay local call rates in the destination country. By using multiple SIMs, a user may take advantage of different pricing plans and save on mobile data usage.
In various types of multi-SIM wireless communication devices, each modem stack associated with a subscription may store information provisioned by its respective network operator in a SIM, which may allow the SIM to support use of various different communication services. For example, various wireless networks may be configured to handle different types of data, use different communication modes, implement different radio access technologies, etc.
One type of multi-SIM wireless device, referred to as a dual-SIM dual active (DSDA) device, allows simultaneous active connections with the networks corresponding to two SIMs using separate transmit/receive chains associated with each SIM. However, such separate components may provide convenience to a user, but may require high power consumption during operation. Another type of multi-SIM wireless device, referred to as a dual-SIM dual standby (DSDS) device, includes a single radio frequency (RF) resource and typically provides for a “standby” mode (i.e., idle mode) in which services associated with either SIM may originate or terminate a communication (e.g., a voice call or data call), and in which services associated with both SIMs may receive pages using the shared RF resource. By sharing an RF resource between the services enabled by both SIMs, a DSDS device may allow for a longer battery life than that of a DSDA device, as well as other benefits (e.g., lower cost of the device, avoiding receiver desense from co-located radios, etc.).
In a conventional DSDS device, when an out-of-service (OOS) state is detected for at least one SIM, the modem stack associated with each out-of-service SIM typically starts a service recovery process, which may involve using the RF resource for system acquisition and cell selection procedures to camp on a serving cell. Such service recovery process recovery is generally employed independently by each modem stack associated with an out-of-service SIM, which creates conflicting RF resource requests in a DSDS device in which two or more SIMs are in an OOS state. The order in which each modem stack associated with an out-of-service SIM is granted use of the RF resource may be pre-determined based on fixed settings on the wireless device, or may be “first-come first-serve,” without any consideration of other SIM requirements. Further, the amount of time allocated to each SIM to perform OOS recovery processes may be static, restricted only by a time-out after unsuccessful attempts to perform system acquisition and/or to camp on any cell.
If at least one SIM is in the OOS state while at least one other SIM remains in service, in a conventional DSDS device the determination of whether, and how long to attempt service recovery on the out-of-service SIM may be based solely on current conditions associated with the in-service SIM (e.g., currently network state, ongoing activities, etc.). As a result, the DSDS wireless device may experience a long overall delay for all SIMs to successfully recover service and camp on a serving cell.
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