Stalkers: A Physical-Layer Solution Towards Co-Existence With Wifi

We present a prototype implementation of Stalkers; a physical layer solution that lets a pair of opportunistic secondary nodes to co-exist with a primary IEEE 802.11-type transmitter-receiver pair using simultaneous in-band transmissions. For this co-existence, the secondary system first stalks the primary system, following which it shapes its own transmissions so as to cause no degradation in the primary network's performance while at the same time not necessitating any change in the primary nodes' physical layer. Drawing inspiration from existing information theoretic literature, the secondary transmissions of the implemented solution rely on (a) forwarding of the primary system's signal by the secondary system to compensate for the interference caused by the latter at the former, and (b) Tomlinson-Harashima precoding to mitigate the primary interference seen by the secondary network. The solution prototype is built with software- defined radios, using which we experimentally demonstrate that the performance of the primary 802.11-type system remains unaffected with the introduction of the secondary system, thereby acquiring throughput for the in-band co-existing solution.