Software-defined radio (SDR) is a technology of widespread interest in wireless communications. With the SDR terminal, packets may be transmitted through multiple wireless communication links. The terminal may recognize the channel conditions and select one of the links. For this purpose, the channel estimation is required. In this paper, the channel estimation for IEEE802.11b WLAN system is investigated through an experiment. In order to estimate the impulse response of the channel, a pseudo-inverse matrix with a threshold is employed. The results indicate that the channel can be estimated precisely with an optimum threshold.