With the proliferation of wireless and sensor techniques, data can be shared conveniently through the air. However, wireless communication is vulnerable since unauthorized machine may try to intrude a server without being physically connected. In this paper, we wish to control the communication between a wireless client and the infrastructure based on the client location. Our idea is toimplement a digital wall, which is a user-defined boundary so that access is allowed within the boundary and denied outside the boundary. To do this, we need to do accurate location estimation since the decision around the boundary line is critical. Furthermore, computational efficiency is also important since we need to reduce computation cost so as to save power energy. In this paper, we propose k-nearest-neighbor (KNN) based method to determine the location of a mobile client based on received signal strength (RSS) values. We further use information gain as a feature selection criterion to reduce the estimation time. We study how the performance may be affected when the controlled area is confined by physical or virtual walls. Experimental results show that we can well distinguish whether a client device is located within anexpected digital wall.