Husileng Bao, Microwave Electronics Laboratory

Husileng is a PhD student at the Microwave Electronics Laboratory

Main supervisor: Prof. Christian Fager

Examiner: Prof Magnus Karlsson

Reviewer: Dr. Ulf Gustavsson is a senior specialist in Ericsson Research, Gothenburg, Sweden. Researcher in the research group Communication Systems of E2

Read the thesis here: Research

Abstract: 

There will be more and more users while beyond-5G (B5G) and 6G bring more wireless applications. Current cellular communication networks assign specific serving boundaries for each radio, which becomes a limitation when too many users work with one radio simultaneously. Physically distributed radios can support many users by serving them uniformly.

To have several tens of Gbit/s data rate, we need to apply millimeter-wave (mm-Wave) frequency band in radio-over-fiber (RoF). However, mm-Wave signals have weak penetration and high propagation loss. Hence, beamforming and/or multiple-input-multiple-output (MIMO) technology become necessary for mm-Wave RoF to overcome those drawbacks.

This thesis introduces an automatic distributed MIMO (D-MIMO) testbed with a statistical MIMO capacity analysis for an indoor use case. A raytracing-based simulation also predicts the indoor case to make a comparison. The statistical MIMO capacity analysis shows that D-MIMO has a higher and more uniform capacity than co-located MIMO (C-MIMO) in measurements and simulations.

Next, a mm-Wave sigma-delta-over-fiber (SDoF) link architecture is proposed for MIMO applications. In the implementation of this link, a QSFP28 fiber link connects a central unit with a remote radio unit with four bandpass sigma-delta-modulation (BPSDM) bitstreams. The remote radio unit generates four mm-Wave signals from four BPSDM signals and feeds a linear array antenna. The measurement characterizes the remote radio head at each stage and concludes that this proposed link can reach 800 Msym/s data rate with -0.5 dBm output bandpower.

Furthermore, the proposed link is demonstrated with digital beamforming and multi-user MIMO (MU-MIMO) functionalities. The digital beamforming function reaches 700 Msym/s with -25 dB error vector magnitude (EVM) results by improving the received bandpower in comparison with (single-input-single-output) SISO results. The MU-MIMO function serves two independent users at 500 Msym/s symbol rate and satisfies 3GPP requirements at 1 m over-the-air distance.

In conclusion, this thesis proves that D-MIMO has a higher and more uniform capacity than C-MIMO by statistical analysis from measurements and simulations. The proposed novel mm-Wave SDoF link can pave the way for future D-MIMO applications.

Keywords: Radio-over-Fiber, central unit, remote radio head, multiple-input-multiple-output, millimeter-wave.