## 3 Challenges in Resource Allocation of Sharing Network  
After achieving deep co-construction and sharing between operators, in addition to sharing infrastructure at the base station hardware level, the spectrum resources available to operators become more abundant. For instance, before co-construction and sharing, Operator A possesses a 100 MHz bandwidth spectrum around the 3.5 GHz band, and Operator B also has another 100 MHz bandwidth spectrum around the 3.5 GHz band. After the co-construction and sharing, users of both Operator A and Operator B can access a combined 3.5 GHz spectrum with a total bandwidth of 2 \(\times\) 100 MHz. With the increase in spectrum resources following co-construction and sharing, the network scenarios and systems become more intricate, effectively leveraging the advantages of increased spectrum resources, achieving globally optimal resource allocation across multiple frequency bands, maximizing spectrum efficiency, and enhancing user experience. However, despite these improvements, they still face numerous challenges. In this section, we will elaborate on the challenges faced in resource allocation after co-construction and sharing across three dimensions: time domain, frequency domain, and spatial domain. Time Domain Challenges: One of the challenges in the time domain is the uneven distribution of scheduled users per Transport Time Interval (TTI) across different operator frequency bands, leading to higher communication delays for different users. How to organize the users and allocate the time-domain resources can significantly impact the user experience. As shown in Figure 1, in the cell of Operator B, multiple User Equipment (UE) have different scheduling priorities. Due to limited scheduling resources, the network prioritizes high-priority users, resulting in delayed scheduling for some low-priority users and consequently affecting their user experience. However, Operator A's resources remain idle. In this scenario, it becomes necessary to leverage the idle resources of Operator A to alleviate congestion in the time-domain resources of Operator B's users. Therefore, it is essential to coherently allocate time-domain resources among different operators. This involves scheduling users with varying priorities on different carriers simultaneously, reducing scheduling delays for low-priority users. Frequency Domain Challenges: The challenges in the frequency domain arise due to the differences in frequency ranges and duplexing modes between Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) frequency bands among different operators. This leads to varying user experiences when users are located in different coverage areas of the cell or reside in FDD/TDD frequency bands. As shown in Figure 2, the green lines represent TDD, while the blue lines represent FDD. In Area 1 of the TDD cell, the close-coverage point, TDD provides advantages such as larger bandwidth and precise channel estimation based on Sounding Reference Signal (SRS), resulting in better user experiences for both uplink and downlink compared to FDD. In Area 2 of the TDD cell, the mid-coverage point, TDD enhances coverage by multi-antenna beamforming and benefits from the large bandwidth, leading to superior downlink user experiences compared to FDD. However, TDD uplink coverage is constrained by the lower transmit power of the terminal, resulting in weaker uplink user experiences compared to FDD. In Area 3 of the TDD cell, the far-coverage point, TDD uses the Precoding Matrix Indicator (PMI) for data channel precoding. As TDD frequencies are generally higher than FDD, signal attenuation increases with the increase of distance, leading to worse uplink and downlink user experiences compared to FDD. Hence, when a sharing network is made up of both TDD frequency bands and FDD frequency bands in the frequency domain, it is crucial to select appropriate resident frequency bands for users in different areas based on coverage and bandwidth considerations.