Public mobile radio spectrum is a scarce resource while wide spectral ranges are only rarely used. Here, we consider a new strategy called Spectrum Pooling enabling public access to these new spectral ranges without sacrificing the transmission quality of the actual license owners. By temporarily leasing their spectrum during idle periods the license owners could tap new sources of revenue. We favor a modified wireless LAN as rental system. Especially OFDM based WLANs like IEEE802.11a and HIPERLAN/2 are suitable for an overlay system like spectrum pooling as they allow a very flexible frequency management on a carrier-by-carrier basis. The modifications of these standards comprise many areas of the physical and MAC layer. Idle frequency subbands can be detected by spectral power measurements conducted in each single participating mobile terminal. Hence, the volume of measurement data can become very high.