Text

theses

In millimeter-wave (mmWave) channels, to overcome the high path loss, beamforming is required. Since beamforming is technically a spatial filtering operation, the spatial representation of the channel is essential. Specifically, for accurate beam alignment and minimizing the outages, inter-beam interferences, etc., cluster-level spatial modeling is necessary. Further, to balance and optimize the hardware complexity at the receiver front-end and the received power, a detailed analysis for the beamforming efficiency at PHY layer is required. In the first part of this study, we first create a ray-tracing based intra-cluster channel model (RT-ICM) for stationary mmWave communications and then using RT-ICM, in the second part, we inquire the optimum beamwidth values that maximizes the received power in the case of both perfect and imperfect alignments. Using the theoretical array antenna gain models for uniform linear array (ULA) and uniform planar array (UPA), we estimate the required number of antennas for the optimum beamwidth; thereby analyzing the cost at the receiver structure and study the trade-off curves for the reasonable optimum hardware complexity. We also show how to realize an adaptive beamwidth structure by means of phase-only beam broadening approach and then implement it into an hybrid beamforming system. In the simulations, we first show that the proposed intra-cluster model, RT-ICM is in a perfect agreement with the full-scan software results and the measurements held in the literature. For the beamwidth analysis, we demonstrate that the optimum beamwidth is a function of standard deviation of the channel power spectrum and the amount of misalignment. For a perfect alignment, we also show that the optimum beamwidth is zero, but to reach 95% of the maximum power for an indoor mmWave cluster, a practical beamwidth of 7◦ − 10◦ is enough, which can be created with 18 − 20 antenna elements for ULA. It is concluded that the antenna gain dominates the received power in the UPA case and intra-cluster power angular spectrum of the channel becomes less critical. Finally, in the third part, we propose two fast beam searching protocols that work at MAC layer to complete the beamforming efficiency analysis at mmWave communications.

ETD_10444

Ph.D.

Includes bibliographical references

doi:10.7282/t3-bk7v-4d59

ETD doctoral

The author owns the copyright to this work.