In this paper we present the design of QOMET, the Wireless LAN (WLAN) emulator that we develop. Our approach to WLAN emulation is a versatile two-stage scenario-driven design. In the first stage a real-world scenario representation provided by the user is converted successively into physical, data link and network layer effects that correspond to the emulated WLAN scenario. The output of the first stage is a description of the network states at successive moments of time, which is used in the second stage to accurately reproduce the wireless environment conditions by means of a wired-network emulator. We give here the details of the overall model that makes it possible to accomplish this conversion in QOMET. We then present our test methodology and illustrate our approach by several experimental results.