# An Improved Radio Resource Management with Carrier Aggregation in LTE Advanced
## 2 Related Work  
Downlink radio resource management has a major impact on the overall performance of the mobile network. Therefore, a wide range of study has been conducted by researchers on various aspects of resource management. A good number of researchers have used PF and modified algorithms for packet scheduling with different approaches of CC selection. Joint scheduling also has been proposed to enhance the QoS. The Circular Selection (CS) scheme is used in [9] where CCs have been assigned circularly to the users. The authors proposed CC coupling method to balance the load. This method first determines whether the particular CC is idle or busy. If any CC is idle, the load from the other CC will be transferred to the idle one until the CC turns into the busy state. This coupling occurs in every TTI. Round Robin packet scheduling algorithm is chosen for allocating the RB. Compared to other schemes, the authors claim that their method provided higher throughput and improved coverage performance due to efficient balance of the load over multiple CCs. However, in the case of different packet size of user, the efficiency can be decreased. Moreover, it significantly increases the power consumption of the users and the signal processing complexity. In [24], CCs have been assigned to a lower frequency at first, then users with higher CQI (Channel Quality Indicator) values move to a higher frequency based on the load of all other CCs. The authors consider two frequencies (2 GHz and 5 GHz) for the proposed method. When a user arrives, the scheduler directly allocates the 2 GHz band, then it checks the load in both bands. If the load is lower in 5 GHz than in 2 GHz, the user with the highest CQI value will be assigned to the 5 GHz band. In case of higher network loads, the users with the lowest CQI value will be moved to the 2 GHz band as propagation loss is typically lower than 5 GHz. Load is calculated based on the availability of the resources for the cell and utilized by the users. Although this approach increases the computational complexity and it does not consider the multi-band approach. In [25], user grouping PF algorithm (UG-PF) is proposed to improve fairness among users. In this model, path-loss with a certain threshold and coverage of each CC is calculated. Then, the users are divided into some specific groups according to the number of available CCs which can be assigned to the users from their location. The cell-edge user groups are also allowed to access the RBs in the CCs of lower frequencies. Moreover, the users with poor CQI value can obtain higher throughput and better fairness among the users by this algorithm compared with the conventional PF algorithm. However, the average cell throughput can go down by allocating a lot of RBs to users with poor CQI. A generalized PF based Cross-CC PF is proposed in [7] to adapt the level of fairness between users with different aggregation capabilities and with different channel conditions. This method selects CC randomly for users and distributes the load across all CCs. It proves that when the CC selection is predetermined for a user, Cross-CC PF is a better scheduler to improve the throughput. The proposed method requires the exchange of data on the previous user throughput for all CCs. Considering that throughput of all CCs makes the scheduling metric of LTE-A users smaller compared with the basic PF. Their results show better fairness to the users and it is also shown that Cross-CC PF boosts the average user throughput and coverage performance without sacrificing the average cell throughput. Absolute and relative policy is proposed in [26] by considering the signal quality of the CC. Their method divided the cell coverage area into two different cells, named 'primary serving cell (PCell)' with designated primary CC and'secondary serving cell (SCell)' with secondary CC. When an LTE-A user arrives, eNB firstly attaches it with a PCell as the authors assumed that PCell has best signal quality.