# Resource Management in Cloud Radio Access Network: Conventional and New Approaches
## 3 Resource Management Techniques in C-RAN
### Computational Resource Management Based on RRH Clustering Techniques  
In conventional RAN architectures, a one-to-one logical mapping exists between RRHs. This implies that one BBU is assigned to one RRH. However, in a C-RAN architecture, it is feasible to establish a one-to-many mapping by assigning one BBU to many RRHs. The former results in the deployment of small cells wherein a user connects to one BBU through one RRH. In this mapping, the BBUs in the BBU pool are not utilized efficiently because all the RRHs do not have equal traffic load perpetually. In a one-to-many mapping, a user can connect to the same BBU through multiple RRHs because multiple RRHs are assigned to the same BBU. This is similar to a distributed antenna system (DAS). The mappings are depicted in Figure 5. The computational resource usage of the BBUs in a C-RAN is minimized via assigning multiple RRHs to one BBU by clustering RRHs according to the user rate requirements. Limiting the number of active BBUs decreases the power consumption  
\begin{table}
\begin{tabular}{c p{142.3 pt} p{142.3 pt}} \hline
**Ref.** & **Evaluation Technique** & **Performance Metrics** \\ \hline
[39] & Performance comparison with Single BS association and Full coordinated association & Total power consumption and user demand \\ \hline
[40] & Comparison with No RRH selection and greedy-based RRH selection & Power consumption with different numbers of RRHs, TDAs and spectral efficiency \\ \hline
[41] & Comparison with SINR-based scheme, cell range expansion, and the Min-power scheme & Number of satisfied users and active RRH, outage probability \\ \hline
[42] & Comparison with BFD and traditional networks & Number of active BBUs and power consumption \\ \hline
[43] & Simulation of the theoretical analysis & Optimal traffic threshold, total power consumption \\ \hline
[44] & Performance comparison with QP-FCRA, Iterative GSB algorithm and Semi-static, adaptive switching & Throughput satisfaction rate, spectrum spatial reuse, transmitted power, number of BBUs and RRHs required \\ \hline
[45] & Simulation and performance comparison with SDPRA and FGA & Number of admitted user, total transmission power, number of BBUs \\ \hline
[46] & Simulation and performance comparison with separate energy minimization solution & Total energy consumption \\ \hline
[47] & Simulation showing the impact of changing computing resources & User–RRH association strategy, achievable sum rate \\ \hline \end{tabular}
\end{table}
Table 3: Performance evaluation techniques and performance metrics used in radio resource management.  
and increases the radio resource utilization because commonly grouped RRHs share the same BBU resource. Deciding which RRHs must be grouped together by forming a cluster to reduce the number of active BBUs is known as an RRH clustering problem. Many techniques have been proposed for formulating and solving the RRH clustering problem in C-RANs. In [48], the authors formulated the RRH clustering problem as a modified bin packing problem to reduce the number of active BBUs while maintaining the QoS.