Experience with an implementation of the Idle Sense wireless access method

An overwhelming part of research work on wireless networks validates new concepts or protocols with simulation or analytical modeling. Unlike this approach, we present our experience with implementing the Idle Sense access method on programmable off-the-shelf hardware---the Intel IPW2915/abg chipset. We also present measurements and performance comparisons of Idle Sense with respect to the Intel implementation of the 802.11 DCF (Distributed Coordination Function) standard. Implementing a modified MAC protocol on constrained devices presents several challenges: difficulty of programming without support for multiplication, division, and floating point arithmetic, absence of support for debugging and high precision measurement. To achieve our objectives, we had to overcome the limitations of the hardware platform and solve several issues. In particular, we have implemented the adaptation algorithm with approximate values of control parameters without the division operation and taken advantage of some fields in data frames to trace the execution and test the implemented access method. Finally, we have measured its performance to confirm good properties of Idle Sense: it obtains slightly better throughput, much better fairness, and significantly lower collision rate compared to the Intel implementation of the 802.11 DCF standard.