The present invention concerns a process for recovering lower carbon olefins from MTO or DTO product gas. Respective time periods for sounding a channel between the multiple subscriber stations and the serving base station are then set based on the respective geometries of the multiple subscriber stations. A partition holder mounted on a frame holds the partition parallel to the left and right side walls. The Si1-xGex layer forms a first junction with the unstrained silicon active layer and has a graded concentration of Ge therein that decreases monotonically in a first direction extending from a peak level towards the surface of the unstrained silicon active layer.