A user equipment, UE, comprising: a wireless transceiver, configured to perform wireless transmission and reception to and from a service network; and a controller, configured to receive minimum system information, SI, from the service network via the wireless transceiver, and initiates a first random access procedure with the service network for requesting on-demand SI, wherein the first random access procedure comprises: transmitting a random access preamble configured for contention-based random access procedures to the service network via the wireless transceiver; receiving a random access response corresponding to the random access preamble configured for contention-based random access procedures from the service network via the wireless transceiver; and transmitting a message for a scheduled transmission, which comprises information requesting the on-demand SI, to the service network via the wireless transceiver, in response to receiving the random access response; characterized in that the controller is further configured to determine whether there is association information corresponding to one or more types of on-demand SI in the minimum SI, and initiates the first random access procedure with the service network for requesting the on-demand SI when the determination result indicates that there is no association information corresponding to the types of on-demand SI; wherein the association information comprises at least one of: an association between a type of the on-demand SI and a random access preamble, and an association between a type of the on-demand SI and a physical random access channel, PRACH, time-frequency resource; and wherein, when the determination result indicates that there is no association information corresponding to the types of on-demand SI, the UE selects the random access preamble configured for contention-based random access procedures randomly from a set of random access preambles configured by the service network for contention-based random access procedures. a wireless transceiver, configured to perform wireless transmission and reception to and from a service network; and a controller, configured to receive minimum system information, SI, from the service network via the wireless transceiver, and initiates a first random access procedure with the service network for requesting on-demand SI, wherein the first random access procedure comprises: transmitting a random access preamble configured for contention-based random access procedures to the service network via the wireless transceiver; receiving a random access response corresponding to the random access preamble configured for contention-based random access procedures from the service network via the wireless transceiver; and transmitting a message for a scheduled transmission, which comprises information requesting the on-demand SI, to the service network via the wireless transceiver, in response to receiving the random access response; transmitting a random access preamble configured for contention-based random access procedures to the service network via the wireless transceiver; receiving a random access response corresponding to the random access preamble configured for contention-based random access procedures from the service network via the wireless transceiver; and transmitting a message for a scheduled transmission, which comprises information requesting the on-demand SI, to the service network via the wireless transceiver, in response to receiving the random access response; characterized in that the controller is further configured to determine whether there is association information corresponding to one or more types of on-demand SI in the minimum SI, and initiates the first random access procedure with the service network for requesting the on-demand SI when the determination result indicates that there is no association information corresponding to the types of on-demand SI; wherein the association information comprises at least one of: an association between a type of the on-demand SI and a random access preamble, and an association between a type of the on-demand SI and a physical random access channel, PRACH, time-frequency resource; and wherein, when the determination result indicates that there is no association information corresponding to the types of on-demand SI, the UE selects the random access preamble configured for contention-based random access procedures randomly from a set of random access preambles configured by the service network for contention-based random access procedures.