herein n1 identifies the time positions of the discovery resource elements in the preceding discovery resource period of the current discovery resource period; n2 and k2 identify the time positions and the frequency positions of the discovery resource elements in the current discovery resource period, respectively; N represents the number of the discovery resource elements in the time direction; K represents the number of the discovery resource elements in the frequency direction; and the value of L is an integer; or

interleave the frequency positions of the discovery resource elements in the preceding discovery resource period of the current discovery resource period using the interleaver, establish a mapping relationship between the frequency positions of the discovery resource elements in the preceding discovery resource period of the current discovery resource period and the frequency positions of the discovery resource elements in the current discovery resource period according to the result of the interleaving;

determine the frequency positions of the discovery resource elements for sending the device discovery signals in the current discovery resource period according to the frequency positions of the discovery resource elements which send the device discovery signals in the preceding discovery resource period of the current discovery resource period and one of the established mapping relationships; and

determine the discovery resource elements corresponding to the selected time positions and the determined frequency positions as the discovery resource elements for sending the device discovery signals.

The first UE 4 is further arranged to determine the positions of the discovery resource elements for sending the device discovery signals for the first time by any one of: