Cognitive radio systems have gathered a lot of research interest during the last decade. Accuracy of spectrum sensing and efficiency of free spectrum utilization are considered as the primary objectives in this emerging technology, which promises a boost in wireless network performance, through exploitation of underutilized licensed frequency bands. As the focus of researchers is usually on these two major challenges, other aspects have been in part underestimated. In this work, we consider two factors that are rather important for evaluation of cognitive platforms, namely sensing delay and energy efficiency. The first is related to the latency induced by the spectrum sensing process and its impact on sensing efficiency, which is tightly connected to both the QoS performance of secondary users and the protection of primary users. On the other hand, energy consumption is considered as a crucial issue in all types of wireless communications, due to restricted battery autonomy of mobile devices, as well as for moving towards "greener" solutions in telecommunications. Therefore, it is important to extend existing testbed experimentation tools and develop new ones, in order to equip cognitive testbeds with such advanced monitoring capabilities. In this work, we present a monitoring procedure that has been directly integrated in the experimentation tools of the CREW testbed federation and demonstrate how it aids in the online evaluation of four different cognitive platforms in terms of the aforementioned metrics.

Today's handheld devices become more and more multimedia capable. One subsystem of a multimedia terminal that accounts for a considerable amount of the total power consumption is the display unit. The backlight is the major culprit there. As new display units without backlights emerge, the data transfers required to put data on the screen start using up an increasingly important part of the platform's power. We have examined a novel system view that allows for power savings by decreasing the required number of memory accesses to put a frame on the screen. A two-step optimization method for existing platforms is presented. Measurements on a multimedia application show that, on average, power savings of 72% can be obtained on the display related memory accesses. For the proposed optimizations methods to work, it is important that both hardware and software designers become aware of the impact their design-time decisions have on the final power consumption of a system.