# Resource Allocation for GBR Services in D2D-Enabled Communication
## 4 Numerical Results
We also investigated the case, denoted Pre-assigned, where each CU was pre-assigned a channel. The remaining channel assignment problem was to find the best matches between CU and DU, which is simply a 2-D channel assignment problem. The proposed 3-D assignment algorithm outperformed the pre-assigned case, and the performance gain was higher with a larger \(D_{max}\) and more CUs. For example, with \(D_{max}\) = 50 m and 32 CUs, a 33% wider channel bandwidth was required for the pre-assigned case than the optimal one. As the cell radius increases, the interference between the matched CU-DU pair tend to decrease and the effectiveness of the resource allocation may diminish. We additionally simulated the proposed scheme for R = 200 m. Unlike the case with R = 100 m, the proposed scheme  
Figure 4: Average channel bandwidth vs. the number of CUs, \(N\). reduces the average channel bandwidth only by 4% with R = 200 m. We can say that the proposed resource allocation scheme is more effective for a dense small cell deployment of 5G networks. Figure 5 compares the cumulative distribution function (CDF) of the data rate when \(N=32\) by varying \(D_{max}\). As expected, the proposed resource allocation scheme guarantees the target data rate. As \(D_{max}\) increases, the DTs tend to transmit with a higher power, which results in higher interfence in a shared mode. Then, the required channel bandwidth is increased, and higher data rates than \(R_{T}\) are observed with a higher probability as \(D_{max}\) increases. When \(D_{max}\) = 50 m in the sum rate-maximization scheme with SINR guarantee, approximately 20% of users could not meet the target rate. These users suffered from severe co-channel interference in a shared mode. Consequently, they were forced to be in a dedicated mode to guarantee the target SINR but the target data rate is not guaranteed with a fixed channel bandwidth, as seen in Figure 3. It is interesting to note that only 7% of the channels are in a dedicated mode in the proposed scheme, since the channel bandwidth is adaptively adjusted according to the SINR. Table 2 shows the average bandwidth per user when the number of CUs \(N\) is 16 with varying numbers of DUs \(M\), from 0 to 16. The average bandwidth per user is calculated by dividing the total bandwidth by the total number of users, i.e., \(N+M\). This is a measure of how many users can be serviced with a given bandwidth. When there are only 16 CUs, i.e., \(M=0\), there is no co-channel interference. Since SNR based power control is applied, the received SINR always meets the target SNR of 15 dB and the channel bandwidth of 0.2 MHz suffices for the target data rate. When DUs emerges, the DUs tries to find a best match with a CU. As a special case of \(M=1\), if a DU is too close to the BS, severe interference is induced in the BS. Then, this DU is forced to operate in a dedicated mode. Assuming a uniform distribution, a user falls into this situation with a probabiity of 12%, which corresponds to a sharing rate of 0.88. Note that since fading varies over channels, this best match may differ for different channels. So the resource allocation becomes a 3-D matching problem of CU, DU, and channels. When a channel is in a dedicated mode, the channel bandwidth becomes 0.4 MHz, where each user (CU or DU) is allocated half of the bandwidth. When a channel is in a shared mode, this implies that the required channel bandwidth is smaller than 0.4 MHz. So, as more channels are operated in a shared mode, the average bandwidth per user can be decreased. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Number of DUs, \(M\)** & **0** & **1** & **4** & **8** & **12** & **16** \\ \hline Average bandwidth per user (Hz) & 0.2 & 0.19 & 0.17 & 0.15 & 0.14 & 0.13 \\ Number of CHs in a shared mode & 0 & 0.88 & 3.51 & 6.97 & 10.33 & 13.45 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Average bandwidth per user with various numbers of DUs, \(M\) (\(N=16\)).