Modelling a DS-CDMA fading Channel with Bursty Traffic Arrivals

We propose an analytic model for the performance of a faded DS­CDMA radio channel carrying bursty traffic. For the IP traffic model we propose a two­state Markov Modulated Poisson Process (MMPP) to model slow Poisson arrivals of packets interspersed by bursts of IP traffic with a much higher arrival rate. The channel model is a modified multi­state Gilbert­Elliot model which takes into account both the number of interfering users and whether the channel is in a faded or non­faded state. We analyse both Ricean and Rayleigh distributions for the user signal. For the final result we relied on a discrete event simulation of the same DS­CDMA radio channel data transmission process in order to parameterise the model. Results for metrics such as the slot success rate as a function of the number of interfering users and the packet throughput as a function of the IP traffic arrival rate are derived

Delay Analysis of Downlink IP Traffic on UMTS Mobile Networks

Since wireless networks which can carry high bit rates have become ubiquitous, mobile computing is no longer just spoken about. Mobile computing always implies access through a wireless network to an IP network such as the Internet. In order to understand the performance of such links, we propose an analytic model for the down link delay of IP traffic between the Mobile Gateway Server and the End User in a UMTS mobile network. Traffic arriving at the Gateway Server is considered to be bursty in nature and we use a Batch Markovian Arrival Process (BMAP) to model this arrival process. We model the wireless link itself as a modified multi-state Gilbert–Elliot Markov model which takes into account the number of interfering users and whether the channel experiences Ricean fading or not for what we consider a typical indoor, IP-centric environment. We also account in both the analytical model and the simulation for the Forward Error Correction provided by Turbo coding in UMTS to establish realistic packet retransmission rates. Finally we calibrate and verify the correctness of the model with a discrete event simula

ChattaBox: A Case Study in Using UML and SDL for Engineering Concurrent Communicating Software Systems

This paper describes a case study that was conducted to investigate software engineering of concurrent communicating systems (CCSs). Best practice software engineering methodologies were used to specify and design a Voice over IP (VoIP) system, which was then implemented. The methodologies utilised were the Unified Modelling Language (UML) and the Specification and Description Language (SDL), and the project specifically explored their combined use. The VoIP system implemented, called ChattaBox, allowed users to communicate via voice, as well as several other features. The system requirements and static design for the system were carried out using UML diagrams. Dynamic design was done using UML initially, followed by a conversion to SDL using a tool provided by Telelogic. The resulting SDL design was verified using the tool. The final system was tested for correctness, performance and usability. It met all of the requirements set out at the initial phase of the engineering process, whilst remaining stable and protocol compliant. After evaluating the engineering process itself, it was concluded that the software engineering paradigm is vital to the field of CCS engineering. Furthermore, UML was useful for providing fast high level design capabilities, but was unable to provide adequate verification of the design. The converted SDL diagrams made up for this, although the biggest drawback of the proposed software engineering process was the inefficient and error-prone conversion, which needed much manual correction and intervention

DS-CDMA Fading Channels with Bursty IP Traffic Arrivals

We propose an analytic model for the performance of a faded DS-CDMA radio channel carrying bursty traffic. For the IP traffic model we propose a two-state Markov Modulated Poisson Process (MMPP) to model slow Poisson arrivals of packets interspersed by bursts of IP traffic with a much higher arrival rate. The channel model is a modified multi-state Gilbert-Elliot model which takes into account both the number of interfering users and whether the channel is in a faded or non-faded state. We analyse both Ricean and Rayleigh distributions for the user signal. For the final result we relied on a discrete event simulation of the same DS-CDMA radio channel data transmission process in order to parameterise the model. Results for metrics such as the slot success rate as a function of the number of interfering users and the packet throughput as a function of the IP traffic arrival rate are derived