One of the challenges of 5G network construction is to provide Indoor coverage in large stadiums, where Indoor interference severely affects network coverage and capacity. Which of the following solutions can effectively mitigate the interference caused by Indoor coverage with high-density site deployment?

In a high-density indoor environment like a stadium, deploying many small cells or radio heads leads to significant co-channel interference. Sector splitting, or more accurately, cell splitting in this context, is an effective solution. This technique involves dividing the large coverage area into many smaller, well-defined coverage zones, each served by a low-power, directional antenna or radio head. This reduces the coverage footprint of each cell, minimizes overlap between cells using the same frequency, and thereby mitigates inter-cell interference, allowing for higher capacity and better user experience.

A. High-power RRUs would increase the power of each cell, which would drastically worsen the interference problem in a high-density deployment, not mitigate it.
B. Massive MIMO AAUs are typically large antenna arrays designed for outdoor macro deployments and are not the standard solution for indoor venues due to size and form factor constraints.
C. Multi-sector cell is a result of sector splitting, but "sector splitting" is the name of the technique or solution used to achieve this, making it the more precise answer.

1. Huawei Technologies Co., Ltd. (2021). 5G Indoor Digitalization: From a Connected Society to an Intelligent Society White Paper. This paper discusses solutions for high-density indoor venues, emphasizing the use of digital indoor systems (like LampSite) which enable flexible cell splitting and coordination to manage interference and boost capacity.

2. Zhang, J., et al. (2017). 5G-Oriented Indoor Hotspot Network: A Solution of Digital Indoor System. IEEE Communications Magazine, 55(6), 132-140. https://doi.org/10.1109/MCOM.2017.1600888. This article describes how digital indoor systems facilitate cell splitting to handle high traffic density and interference in indoor hotspots.