# An Admission Control Mechanism for 5G LWA
## 2 Related Work  
An extensive array of research effort exists in the academic and industrial domains over cellular operators utilizing the unlicensed band [12] owing to free and abundant bands. Most of the effort on opportunistically using WLAN APs for delay-tolerant applications has been done in WLAN offloading [13]. To provide unified LTE/WLAN access, there are three main levels of integration between the two technologies: Loose integration, tight integration, and very tight integration. In loose integration [14], WLAN and LTE networks are physically independent, but they are connected to the same internet protocol (IP) network. Some of the examples of loose integration proposed by 3 GPP release 8 are the access network discovery and selection function (ANDSF) [15] and radio access network (RAN)-assisted/controlled LTE WLAN radio interworking (RALWI/RCLWI) [6][16]. In the tight integration standardized by the 3 GPP in release 10 [17], WLAN APs are directly connected to the LTE evolved packet core network. However, UEs still need to use WLAN security mechanisms, which are time consuming. Recently, in releases 12 and 13, the 3 GPP standardized very tight integration [18] in order to overcome the inefficiency that existed in Release 10. That includes LAA [7], LTE-WLAN radio level integration with IPsec tunnel (LWIP) [6], and LWA [6]. Here, WLAN APs under the coverage of LTE eNB are connected to the eNB. The data traffic is offloaded to the WLAN, while the control functions (such as security and mobility) are kept in the LTE network. The main difference between LTE-U/LAA and LWIP/LWA is that LAA uses LTE radio access technology to operate in the unlicensed spectrum, while LWIP and LWA access it through IEEE 802.11 standards, thus allowing them to use the incumbent WLAN deployments. Other remarkable examples to aggregate LTE and WLANs, rather than opportunistically using one of them, include multipath transmission control protocol (MPTCP) at the transport layer by the internet engineering task force (IETF) [19]. MPTCP provides a method of joining independent TCP sub-streams to provide a reliable connection between client and server applications, but it lacks provision of intra-cell fairness between UEs [20]. Table 1 shows the differences between the four main technologies proposed for tighter integration in 5G.  
Regarding LWA, there has not been much research. However, some of the studies relate to TCP delay minimization [21] and traffic steering [22]. Some papers worked on maximizing LWA network throughput based on mathematical optimization [23], which is NP hard, in general. Additionally, most of the research only considered increasing LTE throughput, but failed to consider the ability of AP terminals to aggregate LWA traffic [24]. The AP's capability to hold LWA service is a very important factor for alleviating congestion and enhancing performance under both standards. Therefore, inspired by the above work, the contributions of our paper are as follows.  
* We propose an algorithm to activate the optimal number of LWA UEs, accounting for the accommodating capacity of the WLAN network, as well as guaranteeing QoS for LWA UEs.
* We prove with numerical results that our proposed algorithm achieves better system throughput gain, compared with a random mechanism and an LTE-W mechanism.
* The complexity of our proposed algorithm holds to only \(O(QM^{2})\) for worst-case time complexity, whereas eNB can hold \(Q\) APs, comprised of \(M\) UEs, and \(M\)_logM_ is the complexity in sorting.
* We present a detailed procedure for LWA activation and deactivation.