Wireless device, base station, random access method for wireless device and preamble configuration method for base station

A random access method for a wireless device, the wireless device being used for a mobile communication system, the mobile communication system defining a plurality of preambles, N number of low priority preamble sets and a high priority preamble set, N being a positive integer, each of the N number of low priority preamble sets having a part of the preambles, an ith low priority preamble set including an (i−1)th low priority preamble set, i being a positive integer and ranging from 2 to N, the high priority preamble set having a part of the preambles, a Nth low priority preamble set being independent of the high priority preamble set, a union of the Nth low priority preamble set and the high priority preamble set including the preambles, the wireless device comprising a transceiver, a storage and a processor, the storage being configured to store the preambles, the N number of low priority preamble sets, the high priority preamble set and a priority value, the priority value representing a high priority or a low priority, the random access method being executed by the processor and comprising:

• determining whether the priority value represents the high priority or the low priority;
• when the priority value represents the low priority, further comprising:
• (a) randomly selecting a preamble from the jth low priority preamble set, j having an initial value of 1;
• (b) generating a random access request message according to the selected preamble;
• (c) transmitting the random access request message to a base station via the transceiver;
• (d) when a random access response message is not received from the base station via the transceiver within a preset time, determining whether j is equal to N, and setting j=j+1 if j is not equal to N;
• (e) after the step (d), repeatedly executing the above steps (a) to (d) until the random access response message is received from the base station or a number of transmissions of the random access request message reaches a threshold;
• and
• (f) transmitting data through a radio resource indicated in the random access response message if the random access response message is received from the base station;
• when the priority value represents the high priority, further comprising:
• (g) randomly select a preamble from the Nth low priority preamble set;
• (h) generating the random access request message according to the selected preamble;
• (i) transmitting the random access request message to the base station via the transceiver;
• (j) when the random access response message is not received from the base station via the transceiver within the preset time, randomly selecting a preamble from the high priority preamble set, generating the random access request message according to the selected preamble, and transmitting the random access request message to the base station via the transceiver;
• (k) after the step (j), repeatedly executing the above step (j) until the random access response message is received from the base station or the number of transmissions of the random access request message reaches the threshold;
• and
• (l) transmitting the data through the radio resource indicated in the random access response message if the random access response message is received from the base station.