# An Improved Radio Resource Management with Carrier Aggregation in LTE Advanced
## 1 Introduction  
LTE is introduced as the fourth generation (4G) mobile communication by 3 GPP in Release-8 (Rel-8) which is based on the Orthogonal Frequency Division Multiple Access (OFDMA) technology. With some modification in Release-9 (Rel-9), LTE has set a benchmark in achieving peak downlink data rate of 300 Mbps and better (QoS) than the 3G network. However, the current forecast of future demand indicates that the immense challenge is far beyond the initial establishment of 4G. Due to both the explosion of mobile data traffic along with new services and applications, it is necessary to upgrade the LTE system. 3 GPP initiated LTE-A in Release-10 (Rel-10), which fulfilled the requirements of International Mobile Telecommunication-Advanced (IMT-Advanced) with a major enhancement that included a peak data rate of 1 Gbps in downlink and 500 Mbps in uplink [1]. To reach out with the future demands and to implement the IMT-Advanced requirements, LTE-A introduced some new technologies along with the enhancement of previous technologies. In Rel-10, LTE-A proposed CA for supporting wider bandwidth up to 100 MHz [2]. This technology is also known as channel aggregation, which uses multiple (maximum five) CCs of different frequencies joined together to form a higher overall transmission bandwidth and is used to provide an improved throughput as required for LTE-A system. Each CC may appear as LTE carrier to the legacy userswhile LTE-A users are able to transmit and receive on several CCs simultaneously. CA is designed to be backward compatible which means that legacy Rel-8 and Rel-9 users can co-exist with LTE-A users on part of the total bandwidth. Moreover, CA supports the frequencies previously occupied by other systems, such as UMTS and GSM for possible CC aggregation [3]. Therefore, the scheduler can allocate resources on any one of the available CCs with a different bandwidth (maximum 20 MHz) to Rel-8 and Rel-9 users. CA will allow the operator to provide additional capacity without causing any unfavorable impact on the legacy LTE (Rel-8 and Rel-9) users. LTE-A supports three types of CA, namely intra-band contiguous, intra-band non-contiguous and inter-band contiguous or non-contiguous. Intra-band contiguous is the simplest CA deployment, which aggregates multiple adjacent CCs in the same operating band. It requires less power and lower costs than the other two types. It can be implemented without making much change to the LTE physical layer structure [4]. Moreover, it is possible to use a single transceiver to utilize the continuous CCs for an LTE-A user. Intra-band non-contiguous CA combines multiple non-adjacent CCs in the same operating band. The multicarrier component is no longer considered as a single signal and therefore, it requires more transceivers which adds more complexity and cost. Inter-band CA aggregates multiple CCs in separate operating bands. These CCs in different bands can be contiguous or non-contiguous. More advanced multiple transceivers are required, which increases the complexity, cost, and power requirement. This paper considers intra-band contiguous CA technique for simplicity. Multiple CC assignment to a user introduces some new challenges related to the functionalities of radio resource management (RRM). Figure 1 shows the RRM framework of multiple CCs aggregated in LTE-A system. The admission control which is executed by Evolved NodeB (eNB) determines whether to accept or reject the incoming connection. Thereafter, it allocates multiple CCs to the incoming user based on different criteria, such as QoS requirements and the terminal capability of different users. Moreover, each of the users will experience various channel conditions affected by geographical location and various types of noise and interference. Each CC operates independently in separate RRM blocks.