A method comprising: creating a list of preferred navigation models for a mobile receiver by - identifying a plurality of navigation model types supported at the mobile receiver; - identifying one or more suitable navigation models for each of the plurality of navigation model types, wherein identifying one or more suitable navigation models for each of the plurality of navigation model types comprises identifying a plurality of suitable navigation models for at least one of the plurality of navigation model types; - determining for each of the plurality of navigation model types an order for the one or more suitable navigation models for assistance data based on preferences for said navigation model type; and - creating an ordered data structure (400a; 400b) comprising identifiers for each of the suitable navigation models for each navigation model type, wherein the data structure (400a; 400b) is ordered based on preferences for each of the navigation model types; transmitting the list of preferred navigation models; transmitting an assistance data request; and receiving a response to said assistance data request, said response comprising assistance data associated with a satellite data signal, wherein said assistance data is formatted in accordance with at least one of the list of preferred navigation models. creating a list of preferred navigation models for a mobile receiver by - identifying a plurality of navigation model types supported at the mobile receiver; - identifying one or more suitable navigation models for each of the plurality of navigation model types, wherein identifying one or more suitable navigation models for each of the plurality of navigation model types comprises identifying a plurality of suitable navigation models for at least one of the plurality of navigation model types; - determining for each of the plurality of navigation model types an order for the one or more suitable navigation models for assistance data based on preferences for said navigation model type; and - creating an ordered data structure (400a; 400b) comprising identifiers for each of the suitable navigation models for each navigation model type, wherein the data structure (400a; 400b) is ordered based on preferences for each of the navigation model types; - identifying a plurality of navigation model types supported at the mobile receiver; - identifying one or more suitable navigation models for each of the plurality of navigation model types, wherein identifying one or more suitable navigation models for each of the plurality of navigation model types comprises identifying a plurality of suitable navigation models for at least one of the plurality of navigation model types; - determining for each of the plurality of navigation model types an order for the one or more suitable navigation models for assistance data based on preferences for said navigation model type; and - creating an ordered data structure (400a; 400b) comprising identifiers for each of the suitable navigation models for each navigation model type, wherein the data structure (400a; 400b) is ordered based on preferences for each of the navigation model types; transmitting the list of preferred navigation models; transmitting an assistance data request; and receiving a response to said assistance data request, said response comprising assistance data associated with a satellite data signal, wherein said assistance data is formatted in accordance with at least one of the list of preferred navigation models.