Signal processing and beamforming techniques for cell free mm-wave massive MIMO systems

Date

2023-6-20

Author

Karataş, Metehan

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This thesis presents a hybrid beamforming uplink receiver detector for massive MIMO (mMIMO) cell-free (CF) networks operating in millimeter-wave (mmWave) frequencies. CF networks aim to provide uniform service by jointly serving user equipments (UEs) through multiple access points (APs) connected to a central processing unit (CPU). However, serving all UEs with all APs is impractical and computationally complex. The user-centric (UC) variant was introduced to address this, where each UE is served by a subset of APs based on channel conditions. Additionally, the shift to mmWave frequencies offers increased network capacity by leveraging wider bandwidth and larger antenna arrays. Hybrid beamformers, consisting of analog and digital stages, were proposed to reduce the number of radio frequency (RF) chains. The proposed analog beamformer (AB) in this work is the modified eigen beamformer (MEB). MEB promotes a trend of fairness among served UEs compared to well-known eigen beamformer (EB). The digital stage introduces two detectors, namely the cell-free iterative detector (CFI-D) and the user-centric iterative subset detector (UCIS-D), both employing single carrier frequency domain equalization (SC-FDE) modulation. CFI-D is an unscalable CF implementation of the iterative block-decision feedback equalization (IB-DFE) structure, while UCIS-D offers a scalable UC alternative. UCIS-D incorporates a parallel interference cancellation (PIC) stage before IB-DFE, selectively processing interferers based on their relative strength. The weakest interferers are ignored, while the strongest are processed by IB-DFE, considering residual interference from PIC. Both detectors utilize soft decisions and employ frequency domain decision feedback (FDDF). The performance of these detectors is evaluated using the achievable information rate (AIR) and bit-error-rate (BER). Simulation results demonstrate the proposed receiver's ability to handle ultra-high loads in terms of BER and AIR.

Subject Keywords

Cell-free, User-centric, Hybrid-beamformer, mmWave, Massive MIMO

URI

https://hdl.handle.net/11511/104523

Collections

Graduate School of Natural and Applied Sciences, Thesis