Advanced cognitive radio algorithms involve different technical fields like signal processing, wired network communication, computing, etc. Prototyping such systems raise new issues when one wants to find `off the shelf' bricks, ready for experiments: the integration step is time consuming, is not free of risks of non-compatibility and most of the time does not fall in the scope of a PhD work. For these reasons, many research groups have invested in building a testing platform for their cognitive radio activities. Because the Alcatel Lucent Chair on Flexible Radio is engaged in research covering a wide field of topics, the need for a fully customizable experimental test bed rose and was initiated with SDR4ALL on the radio side, and continued with the FlexiCells project for the infrastructure. This paper presents the platform we are designing at Supélec.