Abstract—Because the global positioning system (GPS) consumes a large amount of power and does not work indoors, many virtual-coordinate-based routing protocols are proposed for wireless sensor networks in which geographic location information is unavailable. Each of them, however, cannot guarantee packet delivery or constructs a virtual coordinate system with a complex structure. In this paper, we propose a method capable of augmenting virtual-coordinate-based routing protocols to guarantee packet delivery. Firstly, we introduce the virtual face construction protocol and the virtual face naming protocol to construct and name virtual faces, respectively. Subsequently, the VirtualFace algorithm is presented to route a packet from a dead-end node to a progress node by traversing the boundaries of the virtual faces from face to face. Simulations show that virtualcoordinate-based routing protocols including GLIDER, Hop ID, GLDR, and VCap augmented with the VirtualFace algorithm guarantee...