The IEEE 802.15.4 standard has no provisions for rate sensitive applications because of its ability to operate in pure CSMA/CA or TDMA modes. Some operating scenarios for rate-sensitive applications arise when one considers wireless video surveillance and target detection applications for wireless sensor networks. To support such rate-sensitive applications in wireless sensor networks, we present a multirate-based service differentiation (MRSD) based on unslotted CSMA/CA. Unlike existing priority-based service differentiation models, the MRSD defines independent virtual MACs, each of which consists of Adaptive Backoff Window Control (ABWC) and Virtual Collision Avoidance (VCA) algorithms. The ABWC dynamically adjusts the backoff window to reflect the local network state in the local collision domain. The VCA prevents virtual collisions and preempts packets with the minimal utility in the virtual collision domain. By analyzing these algorithms, we prove that the ABWC enables the achieved transmission rate to converge to the rate requirement and the VCA produces a virtual collision-free schedule to avoid degradation of the achieved transmission rate. Through the simulation, we validate our analysis and show the MRSD outperforms existing algorithms in terms of convergence to the rate requirement.

We consider garbage collection (GC) in dynamic, multiprocessor real-time systems. We consider the time-based, concurrent GC approach and focus on real-time scheduling to obtain mutator timing assurances, despite memory allocation and garbage collection. We present a scheduling algorithm called GCMUA. The algorithm considers mutator activities that are subject to time/utility function time constraints, stochastic execution-time and memory demands, and overloads. We establish that GCMUA probabilistically lower bounds each mutator activity's accrued utility, lower bounds the system-wide total accrued utility, and upper bounds the timing assurances' sensitivity to variations in mutator execution-time and memory demand estimates. Our simulation experiments validate our analytical results and confirm GCMUA's effectiveness.

We consider garbage collection (GC) in dynamic realtime systems. We consider the time-based GC approach of running the collector as a separate, concurrent thread, and focus on real-time scheduling to obtain assurances on mutator timing behavior, while ensuring that memory is never exhausted. We present a scheduling algorithm called GCUA. The algorithm considers mutator activities that are subject to time/utility function time constraints, variable execution time demands, the unimodal arbitrary arrival model that allows a strong adversary, and resource overloads. We establish several properties of GCUA including probabilistically-satisfied utility lower bounds for each mutator activity, a lower bound on the system-wide total accrued utility, bounded sensitivity for the assurances to variations in mutator execution time demand estimates, and no memory exhaustion at all times. Our simulation experiments validate our analytical results and confirm the algorithm's effectiveness and superiority.

We present a garbage collector scheduling algorithm for dynamic multiprocessor real-time systems called GCMUA. The algorithm considers mutator activities that are subject to time/utility function time constraints, stochastic execution-time and memory demands, and overloads. We prove that GCMUA probabilistically lower bounds each mutator's accrued utility, lower bounds the total accrued utility, and upper bounds the assurances' sensitivity to variations in execution-time and memory demand estimates. Our simulation results confirm our analytical results