Cross-layer designs in wireless network systems have been an active research area. Numerous cross-layer schemes are proposed to improve overall system performance by allowing information to be shared and controlled across protocol layers. However, much of the previous research work in this area is simulation-based. The main obstacle which hinders researchers from real implementation is the complexity involved in lower-level driver modification and kernel programming. Moreover, common pitfalls of cross-layer scheme implementation can lead to unexpected system performance degradation. In this work we propose unified cross-layer framework (UCF), a generic mechanism for OS to support cross-layer schemes. Through this mechanism protocol components export protocol-specific information through parameters and events to protocol components at other layers. Cross-layer extensions are activated only at necessary times according to their assigned priorities so that they can react to events and make decisions at different time scales with minimal overhead. We implement and evaluate UCF on embedded systems running NetBSD to demonstrate the modularity, ease of programming, and utility of UCF.
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