User equipment and circuit switched fallback switching method

User equipment, comprising:

• a transmitting circuit configured to transmit outgoing wireless signals;
• a receiving circuit configured to receive incoming wireless signals;
• a memory configured to store software instructions;
• and
• a processor that is respectively connected to the transmitting circuit, the receiving circuit, and the memory, wherein the processor is configured to execute the software instructions to cause the user equipment to perform following operations:
• when the user equipment is in an idle mode, acquiring a 2nd/3rd generation mobile phone communications technology (2G/3G) base station candidate set, the 2G/3G base station candidate set including
• one or more 2G/3G base stations belonging to a 2G/3G network, and
• standard information and frequency information respectively corresponding to the one or more 2G/3G base stations;
• when the user equipment initiates, in a Long Term Evolution (LTE) network, a voice service, sending, by the user equipment, a CSFB request message to an LTE base station in the LTE network;
• receiving, by the user equipment, a standard and a frequency of a target 2G/3G base station that are sent by the LTE base station;
• determining, by the user equipment according to the standard and the frequency of the target 2G/3G base station, whether the 2G/3G base station candidate set includes the target 2G/3G base station;
• when the 2G/3G base station candidate set includes the target 2G/3G base station, switching the user equipment from the LTE base station to the target 2G/3G base station according to the standard and the frequency of the target 2G/3G base station;
• when the 2G/3G base station candidate set does not include the target 2G/3G base station, sending a resending request message to the LTE base station, wherein the resending request message is used to indicate to the LTE base station that the 2G/3G base station candidate set does not include the target 2G/3G base station;
• and
• after the LTE base station re-determines another target 2G/3G base station, and sends a standard and a frequency of the another target 2G/3G base station to the user equipment, determining, by the user equipment, whether the 2G/3G base station candidate set includes the another target 2G/3G base station, and when the 2G/3G base station candidate set does not include the another target 2G/3G base station, sending another resending request message to the LTE base station.