INTER-COUNTRY PLMN RESELECTION FOR A VEHICLE TELEMATICS UNIT
A system and method for making vehicle originated calls to a telematics service provider or other call center. The method includes identifying a call type associated with a desired wireless communication of speech or data to the call center, and then carrying out one of a number of different call connection processes depending on the call type. For voice channel cellular connections, an in-band modem cellular connection is preferably established in most instances using a connection retry strategy that includes primary, secondary, and possibly tertiary connection attempts. Cell selection can be carried out using an acquisition task, background scan and inter-country PLMN reselection process that are used to select among available PLMNs and base stations. The system and method can be carried out in connection with various cellular system technologies, but is especially suited for use with GSM systems.
1 . An inter-country PLMN reselection method for use with a vehicle telematics unit, comprising the steps of:
(a) carrying out a cellular network reselection process in an attempt to attach to a base station on a cellular network that is more preferred than a current cellular network to which the telematics unit is attached;
(b) maintaining the registration of the telematics unit on the current cellular network if no more preferred cellular network was found in step (a); and
(c) if there is an available cellular network that is more preferred than the current cellular network, then attaching to a base station of the more preferred cellular network.
2 . An inter-country PLMN reselection method as defined in claim 1 , wherein step (a) further comprises identifying the more preferred cellular network using a preferred network list.
3 . An inter-country PLMN reselection method as defined in claim 2 , wherein the step of identifying the more preferred cellular network further comprises using at least a user controlled selector list and an operator controlled selector list.
4 . An inter-country PLMN reselection method as defined in claim 2 , wherein the step of identifying the more preferred cellular network further comprises using a list of cellular networks to which the vehicle telematics unit has previously connected.
5 . An inter-country PLMN reselection method as defined in claim 2 , wherein the list of cellular networks comprises a list of recently attached cellular networks, and wherein step (c) further comprises updating the list to include the more preferred cellular network.
6 . An inter-country PLMN reselection method as defined in claim 1 , wherein step (c) further comprises carrying out an idle mode process using the more preferred cellular network.
7 . An inter-country PLMN reselection method as defined in claim 1 , wherein step (c) further comprises updating a list of recently attached cellular networks to include the more preferred cellular network.
8 . An inter-country PLMN reselection method as defined in claim 1 , wherein step (a) further comprises determining whether a downlink signaling failure has occurred and, if so, performing the cellular network reselection process that includes cellular networks having a different mobile country code than the current cellular network and, if not, then carrying out the cellular network reselection process for cellular networks that have the same mobile country code as the current cellular network.
9 . An inter-country PLMN reselection method as defined in claim 8 , wherein, following determination that the downlink signaling failure has occurred, the method further comprises determining that a new base station is available for which reselection is desired, and thereafter carrying out the cellular network reselection process that includes cellular networks having a different mobile country code than the current cellular network.
10 . An inter-country PLMN reselection method as defined in claim 9 , wherein the step of determining that a new base station is available further comprises detecting an available basis station that meets reselection criteria based on C1, C2 parameters.
11 . An inter-country PLMN reselection method as defined in claim 10 , wherein, following the determination that the downlink signaling failure has occurred, the method further comprising the step of detecting an available base station that does not meet the reselection criteria and thereafter carrying out the cellular network reselection process for cellular networks that have the same mobile country code as the current cellular network.
12 . An inter-country PLMN reselection method as defined in claim 8 , wherein, following determination that no downlink signaling failure has occurred, the method further comprises determining if a new base station is found having a different mobile country code that that of the current cellular network.
13 . An inter-country PLMN reselection method as defined in claim 1 , wherein the cellular network reselection process of step (a) comprises a background scanning process.
14 . An inter-country PLMN reselection method for use with a vehicle telematics unit, comprising the steps of:
(a) providing a first cellular network reselection process that attempts to find a cellular network that is more preferred than a current cellular network on which the telematics unit is registered, and that has a mobile country code that is the same as the current cellular network;
(b) providing a second cellular network reselection process that attempts to find a cellular network that is more preferred than the current cellular network regardless of the mobile country code associated with the more preferred cellular network; and
(c) carrying out either the first or second network reselection process based at least in part on whether there is an available base station in the current cellular network.