A pedestrian-located UE monitors selected subframes of a sidelink resource to detect periodic transmissions from other mobile devices to assist it in selecting a free resource for its own sidelink transmissions. The subframe selection is based on a cost metric which takes into account a probability of missing detection of a transmission with periodicity p from another mobile device, an average number of transmissions with periodicity p that are expected from another mobile device within a predefined transmission period of the mobile device, and a number of transmission cycles of the mobile device that need to occur in order to have a single potential collision with each periodic transmission from said at least one other wireless communication. The method provides a trade-off between avoiding future collisions and battery life.