In this paper we present a proxy-level scheduler that can significantly improve QoS in heterogeneous wireless sensor networks while at the same time reducing the overall power consumption. Our scheduler is transparent to both applications and MAC in order to take the advantage of the standard off-the-shelf components. The proposed scheduling reduces collisions through a generalized TDMA implementation, and thus improves throughput and QoS, by activating only a subset of stations at a time. Power savings are achieved by scheduling transfer of larger bursts of IP packets followed by longer idle periods during which node?s radio can either enter sleep or be turned off. Our simulation and measurement results show significant power savings with an improvement in QoS. On average we get 18% of saturation throughput enhancement for real traffic and 79% of power reduction in a highly loaded network.