Modelling 3D blockage effects for millimetre-wave communication systems
Alsaleem, Fahd Nasser Mohammed
The millimetre wave (mmWave) band, which has a frequency range of 30-300 GHz, can provide the desired requirements for future communication systems, such as wide bandwidth and high data-rate with very low latency. However, these advantages entail several consequences and challenges: compared with the microwave band, below 6 GHz, the mmWave band not only suffers from increased path loss but also higher sensitivity to blockage effects due to very short wavelengths. Considering the mmWave band, a human blockage, for example, could severely affect the transmitted signal by causing attenuation of 20 dB or more. With motion, the attenuation problem becomes even more serious. The rapid changes of dynamic blockages surrounding a moving transceiver can cause a significant and sudden impact on channel attenuation, which affects the overall quality of service for mmWave systems. The main scope of this thesis is to develop new mathematical models that accurately capture the dynamics of blockers affecting a moving transceiver in order to compute the resulting channel attenuation accurately. The first Markov chain model studied in this work follows a simple approach by assigning a fixed-attenuation value to each blocker and using a geometric model to generate the transition probability matrices. The transition probabilities are calculated both analytically and via a geometric simulation, where the results are found to match well. The proposed model successfully captures the dynamics of the channel caused by blockers surrounding a moving transceiver. The model works well for stationary scenarios, and the proposed technique of switching between several Markov chains makes the model applicable to a non-stationary average number of blockers as well. The adaptive sum of Markov chains (sum of MC) is another proposed model, which can model the dynamics of blockage effects more accurately than the simpler Markov Chain model. It is adaptive to non-stationary scenarios in any given environment, and it efficiently captures the dynamics of blockages arising from a moving transceiver. The sum of Markov chains model can integrate any desired attenuation function, including the third-generation partnership project (3GPP) blockage model and any lab measurement attenuation profile. The sum of MC model could be a very useful tool for communication engineers, allowing them to perform an initial mmWave coverage analysis for a given environment in the presence of time-varying blockage effects. Unlike human blockage, which has been widely studied in the literature, the impact of other small objects on signal strength, such as metal road signs, is not so well understood. This thesis has carried out a measurement campaign for these small blockers, which induce measured loss in the range of 15- 30 dB, depending on the type and size of the blocker. The thesis also compares those results with existing simulation blockage models for these small objects. These blockage models include the 3GPP model, the multiple knife-edge (MKE) model, and the mmMAGIC model, where the latter two models show a better fit to the measured attenuation of relatively small blockers than the 3GPP model. Finally, the thesis evaluates the impact of blockers on the overall performance of mmWave multiple-input multiple-output (MIMO) wireless systems, where a ray-tracing tool is used to establish all possible propagation paths for a moving transceiver in an outdoor scenario. The performance impact of the measured attenuation profiles for road signs are evaluated for an outdoor scenario using the sum of MC model.