SHREWD is a real-time emulator for studying the performance of current and next generation wireless data systems. SHREWD currently supports HSDPA (high-speed downlink packet access) downlink channels and UMTS Release 99 uplink channels. The emulator implements the entire UMTS traffic plane from the MAC layer up to the PDCP (header compression) layer. Additionally, we have integrated SHREWD into the Plan 9 operating system, which enables us to use existing IP stacks and applications for experiments. Moreover, since SHREWD runs in real time, IP applications experience the same network behavior as when they are using the real wireless network. SHREWD can, in fact, be configured to run on an actual hardware wireless platform which gives us an opportunity to calibrate the air model.
SHREWD features fast and accurate simulation of an air model to support a large number of mobiles, just-in-time creation of packets for over-the-air transmission, and a file-system interface for dynamic modification of system parameters. We have also extended SHREWD to support other, experimental wireless data air interfaces.
Components of SHREWD for emulating the HSDPA stack
To demonstrate SHREWD's usefulness, we have conducted a series of experiments to measure the effects of cross-layer interactions on the performance of TCP-based applications over HSDPA. We are particularly interested in the interactions between the reliable transmission mechanisms for the MACHS, RLC and TCP layers in the presence of unreliable uplink and downlink channels.
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