Christine Niyizamwiyitira

Evaluation of Voice-driven Web Application Architecture

This paper quantifies the implications and trade-offs of three different architectures for voice driven web application, architectures are implemented as prototypes. The prototypes differ from each other by either using recording, or Text To Speech (TTS) as server based, or TTS as client based to process output speech. A typical application used in this paper, is the most dynamic weather information source which is presented as web feeds or Really Simple Syndication (RSS) feeds. The evaluated quality attributes are performance, maintainability, and development effort. The empirical results show that, each systems architecture has a different quality profile, for instance, one architecture has the lowest development time but the highest maintainability cost, and another has the lowest bandwidth requirements but the highest development cost. Finally, suggestions about optimal choice of system architecture according to the quality requirements of the final system are drawn.

Utilization-Based Schedulability Test of Real-Time Systems on Virtual Multiprocessors

The number of applications that use virtual systems is growing, and one would like to use this kind of systems also for real-time applications with hard deadlines. Virtual machines with many cores are interesting since the underlying physical infrastructure usually contains many cores. We consider hard real-time tasks that execute on a virtual machine with m cores. Tasks are scheduled globally on the cores using fixed-priority preemptive scheduling. This means that a task can execute on different virtual cores at different instances in time. In order to avoid Dhalls effect, which may cause task sets with even very low utilization to miss deadlines, we classify tasks into two priority classes, namely heavy and light tasks. Heavy tasks have higher priority than light tasks. For light tasks we use rate monotonic priority assignment. In this paper we propose a utilization-based test that shows if a task set is schedulable or not. If the task set is schedulable the test provides the priority for each task. The input to the test is the task set, the number of cores in the virtual machine (m), a period for the virtual machine with m cores, and the blocking time when a virtual machine does not have access to the underlying hardware in each period.

Joint BLAST-STTC for MIMO-OFDM System

This study focuses on improving MIMOOFDM systems by combining a wireless communication architecture known as vertical BLAST(bell laboratories layered space-time) or V-BLAST and STTC(space time trellis coding). In this paper, the combination is done by introducing STTC in each V-BLAST layer. Moreover, this architecture uses multiple antennas that are grouped into small number of antennas which makes it less complex to decode by decoding every group. Whereas, in traditional VBLAST, all the antennas form one group and they are decoded together at the receiver, therefore, this increases the complexity as the number of antennas is getting high. We compare the bit error rate performance of this system with MIMO-OFDM that uses convolutional coding instead of STTC. Under the same spectral efficiency, the simulation results prove that joining V-BLAST with STTC improves MIMO-OFDM systems performance.