# An Optimal Resource Allocation Scheme with Carrier Aggregation in 5G Network under Unlicensed Band
## 1 Introduction  
To accommodate the quality-of-service (QoS) requirement diversity including high throughput, low latency of proliferation of data-hungry devices and applications in recent years, new advanced features have been added to the Fifth-Generation (5G) technology. Meanwhile, 5G has been proposed as the key technology to unlock the potential in realizing the Industry 4.0 communication goals [1]. In 5G network, one main challenge is to support 10 Gbps data rate of transmission for low-mobility users at the same time as 1 Gbps for high-mobility users, which requires a hundreds of MHz carrier bandwidth. Nevertheless, it is impossible to achieve a contiguous spectrum band with such a wide bandwidth on the licensed spectrum [2, 3]. Then, the scarcity of licensed spectra for cellular network forces wireless industries to utilize the unlicensed bands, such as 5G in unlicensed band (5G-U) [4, 5]. As the most important candidates of 5G-U, industrial, scientific and medical (ISM) radio bands such as 6 GHz bands for wireless fields (Wi-Fi) 6 have been considered [6]. It is well known that the utilization of Wi-Fi systems for offloading data traffic from macrocell BSs has achieved a remarkable performance gain [7]. Furthermore, the main challenge to utilize 5G-U is that the cellular service users can be allocated to an unlicensed spectrum and force the unlicensed band users to silent mode due to the carrier sense multiple access with collisionavoidance (CSMA/CA) mechanism utilized by the traditional unlicensed system, while there is no carrier sensing before cellular services on unlicensed band transmission [8; 9]. Meanwhile, Ref. [10] shows that the introduction of cellular services in unlicensed bands can significantly degrade the unlicensed band users due to the interference, while the cellular service performance is nearly unchanged, which makes the cooperative operation for 5G-U system a challenge but essential and necessary [5]. On the other hand, the 3 rd Generation Partnership Project (3 GPP) introduces carrier aggregation (CA) as one of the most important features in Rel-10, and subsequently enhances in Rel-11 and Rel-12. CA technology enables the aggregation of multiple resource blocks (RBs) from different component carriers (CCs) into a virtual carrier with larger bandwidth to achieve higher throughput and lower latency [11; 12]. Without a doubt, as a remedy with the understanding that it cannot be used to achieve the needed bandwidth for the currently allocated licensed frequency spectrum, CA is introduced as one of the most momentous features in 5G networks [13; 14]. However, it is advantageous while challenging to consider the 5G-U network with the CA feature, which requires elaborately designed system operation. In [15], the authors proposed optimum joint CC selection and RB allocation schemes to maximize the average throughput of users and satisfy the delay constraint of users. However, as one of the main characters of the 5G network, the diversity of QoS requirement is not considered in this paper. Then, in [16], the authors proposed the first joint CC selection and RB allocation scheme while optimizing user equipment (UE)'s power and rate and simultaneously taking delay constraint into consideration. However, multiple types of services in the 5G-U need to be analyzed based on their own characteristics and variable QoS requirements. As one of the most important performance metrics to evaluate the coexistence performance of multiple radio access technologies, outage probability in coexisting subnetworks is derived based on the primary and secondary cell association metric in this paper. Also, to meet the QoS requirements of various services for network performance at the system level, system satisfaction of QoS should be taken into account. In [17], the authors compared throughput fairness among UEs in the cell, although without considering the variable QoS requirements.