# An Improved Radio Resource Management with Carrier Aggregation in LTE Advanced
## 2 Related Work
According to their absolute policy, when the signal quality of a CC is higher or lower than a predefined absolute threshold, the CC is added or removed to the user respectively. On the other hand, based on the relative policy, if the signal quality of a CC is offset higher or lower than the corresponding CC of PCell, the CC is added or removed respectively. However, it is a challenge to determine the threshold or offset value. In [27], the authors proposed a greedy method to maximize the throughput with PF packet scheduling algorithm. Their method considered link adaptation jointly with CC assignment and RB allocation. After calculating the gain of all possible combinations, CCs have been assigned to users which have the highest gain. Regarding RB allocation, the method checked that whether or not the weighted transmission rate of user with maximum gain is higher than currently assigned RB. However, the authors considered that all CCs have an equal number of RB and all users have similar capabilities which are currently unrealistic assumptions compared to the real world. The results are compared with the Least Lord (LL) and Random Carrier (RC) methods, and a modified algorithm named SS. Table 1 shows the summary of previous studies regarding carrier aggregation methods with different CC selection approaches and packet schedulers. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**CC Selection Method** & **Packet Scheduler** & **Characteristics** & **Reference** \\ \hline Random selection with & & & Select CC randomly for users. & \\ load balancing & Cross-CC PF & & Allows load balancing across CCs over the long-term, but not short-term. & [7] \\ \hline Circular selection & RR & & Select CC randomly without considering any channel condition. & [9] \\ \hline Inter-band carrier switch & PF & & Less complex than others and used as a reference method. & [9] \\ \hline \multirow{3}{*}{Lowest path loss} & & & Assign CC at a lower frequency, then according to the load of all CCs, users with & \\  & & & higher CQI move to a higher frequency. & [24] \\  & & & It increases the complexity and it does not support the multi-band approach. & [24] \\ \hline \multirow{3}{*}{Lowest path loss} & & & Assign a CC to the user with lowest path loss. & [25] \\  & & & Support user grouping based on the number of CCs that the users can be assigned. & [25] \\  & & & Consider cell-edge user by introducing a weighting factor. & \\ \hline \multirow{3}{*}{Absolute and Relative policy} & & & Add or remove a CC depending on the signal quality of a CC is higher/lower to a & \\  & & & threshold/offset value. & [26] \\  & & & It is difficult to determine the threshold/offset value of a CC. & \\ \hline \multirow{3}{*}{Largest gain} & & & Calculate largest gain to assign CC with MCS. & \\  & & & Check whether the weighted transmission rate of maximum gain with user \(i\) is & [27] \\ \hline \multirow{3}{*}{Least load} & & & \(\bullet\) Selects CC with lowest traffic loads. & \\  & & & Ensures better performance than other methods, but does not provide good & [28] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of related work regarding CC assignment and RB allocation.