The main implementation methods for an indoor positioning system are either based on the received signal strength (RSS) or the pseudo-range measurement. The positioning method based on the RSS is to take advantage of the signal propagation model, that is, the signal strength decays as the transmission distance increases, and this signal propagation characteristic can be used to determine the position. On the other hand, measuring the signal time- of-flight to estimate the pseudo-range is another indoor positioning method. However, due to the lack of common protocol for timing standards for indoor communication systems, measuring the signal time-of-flight could be very complicate and challenging, and thus this method is less preferred than the positioning method based on the RSS. With the rapidly gaining popularity of WiFi (IEEE 802.11) enabled devices indoors, the demand of the active management of network resource (i.e., transmission power and data rate) promotes the new IEEE 802.1 lv protocol standard. The two main features of the IEEE 802.1 lv that are attractive to the indoor positioning system are 1) the time stamps in the transmission and reception of specific message frames, and 2) the time synchronization between the connected WiFi nodes. These two features greatly reduce the complexity of measuring the signal time-of- flight to estimate the pseudo-range and thus enable the direct use of the time of arrival (TOA) technique. As a result, a prototype indoor positioning system using WiFi is developed in this work, and the positioning engine is implemented by the Kriging fingerprinting method based on RSS. Accordingly, the Department of Aeronautics and Astronautics building at National Cheng Kung University in Taiwan is used as an example to describe the implementation of a WiFi based indoor positioning system. The development of the Kriging fingerprinting method based on RSS measurement is explained in the paper. Then, the TOA based on IEEE 802.1 lv protocol standard is discussed in the paper as well. A software defined radio (SDR) based user platform is developed as the positioning performance evaluation node. Several experiments are conducted to evaluate the positioning performance under different conditions.