## 4 Simulation Environment
### Scheduling of Radio Resources, Precoding, and Power Allocation
Firstly, in step 10 the spatial correlation between all users within the _allocatedUEs_ set is calculated, with the spatial correlation coefficient between the \(i\)-th and \(k\)-th UE at RB \(r\) defined as:  
\[\Theta_{r,j,k}=\Bigg{|}\frac{\sum_{l=1}^{N_{\text{RU}}}\mathbf{h}_{i,l,r}\mathbf{ D}_{i,l}\cdot\mathbf{D}_{k,l}\mathbf{h}_{k,l,r}^{H}}{\sqrt{\sum_{l=1}^{N_{ \text{RU}}}\|\mathbf{h}_{i,l,r}\|^{2}\cdot\sum_{l=1}^{N_{\text{RU}}}\|\mathbf{ h}_{k,l,r}\|^{2}}}\Bigg{|}. \tag{11}\]  
```
0: past rate of each UE, inter-cluster interference calculated from the total past interference by each UE, radio channel coefficients, channel correlation threshold \(\Delta\)
1:for\(r\) in 1 to \(N_{\text{rb}}\)do
2: compute the maximum wanted power for each UE using the _Desired Signal_ term from (3), assuming that a single UE is scheduled, MRT precoder, and \(p_{i,l,r}=\frac{p_{i}}{N_{\text{rb}}}\)
3: compute the maximum expected UE throughput for RB \(r\) using the Shannon formula, with the SINR of each UE being the ratio of its maximum wanted power computed in step 2 and reported inter-cluster interference
4: compute the PF metric for each UE, being the ratio of its past rate and the current maximum expected throughput for RB \(r\)
5: create a sequence \(\mathcal{K}\) containing the indices of UEs, sorted according to their PF metrics in descending order
6:\(sumRate\gets 0\)
7:\(allocatedUEs\leftarrow\varnothing\)
8:for\(k\) in \(\mathcal{K}\)do
9: add \(k\) to set of \(allocatedUEs\)
10: compute channel correlation coefficients between UEs being within the set of \(allocatedUEs\) using (11)
11:if any correlation coefficient exceeds \(\Delta\)then
12: remove \(k\) from set of \(allocatedUEs\)
13:else
14: set \(\mathbf{D}_{k,l}=\mathbf{0}_{M_{l}}\) for all RUs that reached the maximum number of \(N_{\text{L}}\) spatial layers
15: compute precoding ZF vectors for \(allocatedUEs\)
16: allocate power equally between the \(allocatedUEs\)
17: compute the expected SINR\({}_{i,r}\) of \(allocatedUEs\) using (4) and reported inter-cluster interference
18: compute \(newSumRate\) of \(allocatedUEs\) using the Shannon formula and expected SINR computed in the previous step
19:if\(sumRate>newSumRate\)then
20: remove \(k\) from set of \(allocatedUEs\)
21:break
22:else
23:\(sumRate\gets newSumRate\)
24:\(\delta_{k,r}\gets 1\)
25:endif
26:endif
27:endfor
28:endfor
```  
**Algorithm 1** Radio resource scheduling in a UCCF M-MIMO network  
If any of the computed channel correlation coefficients exceeds the threshold \(\Delta\), the last added user is removed from the set of \(allocatedUEs\). This is because the spatial correlation is directly mapped to the interference, e.g., with the Maximum Ratio Transmission (MRT) precoder, the power of the inter-user interference (between the \(i\)-th and \(k\)-th user) rises proportionally to \(\Theta_{r,j,k}^{2}\). The next condition that the \(k\)-th user must meet is to increase the \(sumRate\) within RB \(r\). This is performed in steps 14-18 of the algorithm. For scalability purposes, each RU has a limit of \(N_{\text{L}}\) spatial layers; if this limit is reached, the RU is no longer considered for serving users by setting \(\mathbf{D}_{i,l}=\mathbf{0}_{M_{l}}\) for this RU. Next, the Zero-Forcing (ZF) precoder is calculated for each RU in step 15. Note that the precoding weights are normalized to ensure \(\|\mathbf{w}_{i,l,r}\|^{2}=1\). Although the ZF precoder has higher computational complexity than the MRT precoder, it has an important ability to suppress interference between users. This was shown in initial studies to be very beneficial for the considered UCCF M-MIMO network. It should be noted that we assume an architecture where precoding is performed independently for each RU. Moreover, we place a limitation on the number of spatial layers that the scheduler can create. As a result, the radio channel matrix, which is subject to ZF precoding, has a maximum size of \(M_{l}\times N_{\text{L}}\).