Niklas Jaldén defended his Doctoral Thesis in Telecommunications

Respondent: Niklas Jaldén
Opponent: Professor Pertti Vainikainen, Aalto University, Finland
Date: 2010-03-09, 13:15
Place: Hörsal F3, Lindstedsv. 26, Stockholm

Future wireless communication systems will utilize the spatial properties of the wireless channel to improve the spectral efficiency and thus increase capacity. This is realized by deploying multiple antennas at both the transmitter and receiver. Development and analysis of communication systems utilizing the spatial properties of the channel requires channel models that properly reflect these characteristics.

Due to the unpredictable nature of the wireless channel, a common approach is to model its effects statistically. A few large world-wide cooperations, like the third generation partnership project (3GPP) or wireless world initiative new radio (WINNER) project, have developed channel models intended for reference and standardization use. These models are partly based on some bulk parameters that describe the characteristics of the channel over larger areas of several wavelengths. Such parameters include shadow fading, angle spread, and delay spread, among others, and are within the WINNER project called large-scale (LS) parameters. In the spatial channel model (SCM) and the WINNER model, these large-scale parameters are, however, assumed independent between separate links, i.e., between channels modelling the propagation between one mobile and several base stations, or between one base station and several mobiles. Such assumptions may be valid for single-link, singe-cell systems, where each communication link is sufficiently separated in either time or frequency. In practice, dependencies between parameters describing separate wireless channels is expected. Future systems will allow a dense frequency reuse, and results from system evaluations based on models with independent links may be inaccurate. Examples of this may be in systems that exploit the spatial nature of the channel, like multi-user scheduling using a single carrier, or macro-diversity systems deploying several base stations. Therefore, it is important to analyze multi-node measurements in order to extract and characterize this channel dependence.

This thesis focuses on representing the wireless channel statistically. Through unique multi-site channel measurements and analysis, key parameters describing the channel namely shadow fading, delay spread and angle spread at both the base station and the mobile station are extracted. For these parameters, the first and the second order statistics are derived, and plausible distributions and models are proposed. Further, the spatial and correlation properties of these parameters are analyzed. Moreover, a study highlighting the effect of the independent channel assumption is given, showing the importance of modelling the spatial dependence between the LS parameters when analyzing systems that utilize the channel's spatial properties. Incorporating the models and correlation properties found herein for the LS parameters results in channel models appropriate for multi-node communication analysis and evaluation.