Abstract: This paper investigates the indoor ranging capability of ultra-wideband signals under the IEEE 802.15.4 protocol. The traditional schemes usually cannot meet the low-power, high real-time and high-precision requirements in the practical applications. To this end, an enhanced asymmetric double side two-way ranging algorithm is proposed. We first analyze the validity of the algorithm through mathematical models, and then discuss ranging errors due to time and frequency shifting. Finally, the UWB module is implemented in the ranging experiment to test the performance of the improved algorithm. The experimental results show that the ranging accuracy can be further improved by the data fitting calibration algorithm. It is also shown that the overall ranging accuracy of the system can be improved around 88%.