M.Sc. Theses (Supervised by Prof. Kaveh Pahlavan)

Next Generation Wireless Networks - A Case Study of Voice over IP and Vertical Mobility
Mika Ylianttila, University of Oulu, 2001
Advisor: Prof. Kaveh Pahlavan

The evolutionary convergence of the wireless networks has opened the road for many new applications. There is an obvious trend towards interoperability and convergence among various wireless networks, as well as a tendency towards IP based solutions. The most challenging task for the designers of these emerging networks is to provide means to deliver time sensitive information such as voice over the heterogeneous IP-based Internet that is shifting towards a new version (IPv6). An important area for traffic optimization in these next generation wireless networks is to manage the delay and throughput in handoff process in heterogeneous networks. Geolocation information may provide new possibilities to help this process. A comparative evaluation of alternative protocols for an efficient delivery of voice over heterogeneous wireless access to Internet is discussed in this thesis.

This thesis provides a case study of wireless voice over Internet and vertical mobility in the emerging heterogeneous integrated wireless networks. The focus of the thesis is on three areas related to the analysis of the performance of these networks at architectural, protocol and algorithm levels. This thesis identifies the importance of integration between telecommunication and geolocation networks, the complexity of vertical handoff in heterogeneous networks, and impacts of IPv6 on emerging voice over IP applications as three technical issues to be studied in the rest of the thesis. First, an overview of the key concepts in the emergence of the next generation heterogeneous wireless networks is provided. Then, architectural issues related to integration of geolocation with the emerging heterogeneous telecommunication networks is addressed. Next, the efficiency of vertical handoff between 802.11 WLAN and GPRS networks is analyzed. Thesis analyzes the effects of handoff latency, user population, dwell-timer and other important parameters for vertical handoff performance. Handoff smoothing with a dwell-timer is discussed as one potential scheme for optimizing vertical handoff. Lastly, the impact of IPv6 on evolving VoIP applications has been analyzed, by comparing the performance of VoIPv6 and VoIPv4 in a wireless LAN testbed. Comparisons have been made with both varying ICMP payload and with actual VoIP application using three different codecs.

Keywords: IPv6, VoIP,
Wireless LAN, GPRS, Mobility

Block-Oriented Time and Frequency Domain Simulation of the JTC Channel Model for PCS Applications
A. Parker, M.S., 1994
Advisor: Prof. Kaveh Pahlavan

Currently, RF Channel Characterization and System Deployment are major issues in the development of Standards for Personal Communication Systems (PCS). This thesis presents work done to develop a block-oriented software to simulate the air interface recommended by the Joint Technical Committee (JTC). The algorithm, which is based on the JTC recommendation for statistical modelling of the radio channel in the time domain, is presented and discussed. The model gives channel profiles that represent general circumstances for PCS applications. The goal of the channel modelling is to provide an accurate mathematical description of radio propagation to be used in radio link and systems simulation. The thesis also provides an alternate approach to modelling the air-link equivalent to the time-domain model. The model is a frequency auto-regressive (AR) process that requires fewer parameters and exemplifies less computational expense. The accuracy of the frequency domain model is examined by comparing the CDF of the RMS delay spread of simulations in the frequency domain with that of the time domain JTC model. Both models are simulated in Signal Processing WorkSystem (SPW) software. Several applications in the SPW system development software are given that explain the properties of the channel model and provide a visual understanding of the statistical process occurring in the radio channel.

Performance Evaluation of Wireless LANs in the Indoor Environment
G. Bronson, M.S., 1993
Advisor: Prof. Kaveh Pahlavan

This paper presents the results of a performance evaluation of a wireless LAN (WLLAN) in an indoor environment. The LAN operates in the ISM bands using spread spectrum technology. Hardware specific parameters such as bit error rate vs. signal to noise ratio (BER vs. SNR), maximum transmission rate, and platform software overhead are measured experimentally for a single node. This empirical data, in combination with manufacturer specifications, was then used as a basis for deriving a network simulation model. A ray trace algorithm is employed to obtain the indoor channel characteristics for point to point transmissions within a test room. The network simulation employs the measured BER vs. SNR, node and hardware specifications, and the ray trace channel characteristics to model the behavior of a multiple node network in a wireless environment. The network simulation model developed was used as a general purpose tool to predict the performance of CSMA type WLLANs in different working environments.

Development of Custom Coded Blocks in Signal Processing Worksystem (SPW) Software for Indoor Radio Propagation Modeling
J. Meditz, M.S., 1993
Advisor: Prof. Kaveh Pahlavan

This thesis concerns the development of software tools for performance evaluation of wireless communication systems. Two statistical indoor radio propagation models were written in the C programming language and then incorporated into the Comdisco Signal Processing WorkSystem (SPW) software platform as custom coded blocks. Treating the statiscitcal channel model as a single object significantly simplifies communication system simulation. Linked to each block is a parameter screen that pops up when selected by the user. The parameter screen enables easy modification of model parameters. One block is a time domain model whose statistics match those of the measurements taken in office areas and manufacturing floors. The path arrival times form a modified Poisson process; the amplitudes are lognormal, Nakagami, Rayleigh, Suzuki, or Weibull. Items such as areas and pdf are selectable through the parameter screen. The other block is a frequency domain model in which the frequency response of the channel is modeled as a statistical autoregressive (AR) process. The statistics ofthe parameters used in the AR model are taken from the results of local and spatially distributed measurements in the office environment. The time response is generated by taking the invers Fourier transform of the output of the AR model.

A Computer Graphics Package for Indoor Raio Channel Simulation Using a 2D Ray Tracing Algorithm
T. Holt, M.S., 1992
Advisor: Prof. Kaveh Pahlavan

This thesis presents a graphical user interface program that uses a two dimensional ray tracing algorithm to predict the radio propagation in the indoor radio channel from the layout of the floor plan. Modeling the indoor radio channel is extremely difficult due to the effects of multipath propagation. Current statistical models of multipath propagation in the indoor environment cannot take into account the many variations in building layout and materials and only general conclusions about the channel can be made. Another approach to this channel modeling problem is to use deterministic models (ray tracing) which take into account the details of the environment (walls, doors, etc.). The graphical interface program allows the user to interactively specify the location of the walls in the floor plan, the type of material in the construction, and the location of the radio transmitter and receiver. The ray tracing algorithm determines the magnitude, phase, time of arrival, and direction of every signal path between the specified radio transmitter and receiver when an RF pulse is transmitted. The accuracy of the model for a small shielded cage is examined by comparing the results of simulations with those obtained from empirical measurements. Comparisons are also made between the simulation and the results of measurements in a more complex laboratory environment in the Atwater Kent Laboratories at Worcester Polytechnic Institute. This area represents a typical indoor environment for using a wireless LAN since it includes both line-of-sight (LOS) and off-line-of-sight (OLOS) areas. The effects of the various parameters of the ray tracing algorithm on the received power and RMS delay spread are discussed as well.

Multiple Accessing in Local Area ALOHA Networks in the Presence of Capture
R. Ganesh, M.S., 1987
Advisor: Prof. Kaveh Pahlavan

In local area ALOHA systems, the capture effect has been found to greatly improve the system performance. This improvement is shared by all the users in the system, not just the ones with the strongest received signals. However, the retransmission problem, in these multipel access systems having the capture effect, has thus far not been fully investigated. There have been attempts to mathematically relate the retransmission probability to the capture parameter, but the analysis fails to predict accurate results even at the boundaries. This report, shows results which relate the retransmission probability and the effects of capture to the throughput and delay characteristics of a network, suited for wireless local area communications. The optimum retransmission probability for the system is found to vary with the capture parameter at the receiver. To find the performance of a system which has a capture parameter between that of perfect capture and no capture, computer simulations were done and the results are presented in this work.