# An Admission Control Mechanism for 5G LWA
## 3 System Model  
We consider a scenario with eNB and APs, enabling many UEs to fall under the coverage of both LTE and WLAN APs, as shown in Figure 1. An eNB is connected to the MNO-operated \(Q\) APs, usually called wireless terminal (WT)/access controllers (ACs), by a high-speed backhaul link, which is common practice in the present day. \(M\) UEs equipped with both LTE and WLAN transceivers (smartphones) and another set of \(N\) UEs supported with WLAN-only transceivers (laptops/tablets) are uniformly distributed under the coverage of both LTE and a WLAN network. As mentioned in TS Report 36.300 [6], the eNB holds all the necessary statistics of all MNO-operated APs and UEs  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Components** & **LTE-U/LAA** & **LWA** & **LWIP** & **MPTCP** \\ \hline \multirow{2}{*}{Complete name} & LTE in unlicensed/License & \multirow{2}{*}{LTE WLAN Aggregation} & LTE WLAN & \multirow{2}{*}{Multipath TCP} \\  & Assisted Access & & & & IP Tunneling \\ \hline WLAN relation & Coexistence & Aggregation & Aggregation & Aggregation \\ \hline \multirow{2}{*}{RAT \({}^{*}\)} & \(\frac{1.9}{1.9}\) & \(\frac{1.9}{1.9}\) & \(\frac{1.9}{1.9}\) & \(\frac{1.9}{1.9}\) & \(\frac{1.9}{1.9}\) \\  & \(\frac{1.9}{1.9}\) & \(\frac{1.9}{1.9}\) & \(\frac{1.9}{1.9}\) & \(\frac{1.9}{1.9}\) & \(\frac{1.9}{1.9}\) \\ \hline Standardization & LTE-U forum/3 GPP & 3 GPP & 3 GPP & 1 ETF \\ \hline \multirow{2}{*}{Leading work group (WG)} & \multirow{2}{*}{RAN WG1} & \multirow{2}{*}{RAN WG2} & \multirow{2}{*}{RAN WG2} & \multirow{2}{*}{MPTCP WG1} \\  & & & & \\ \hline Release & Release 12/Release 13 & Release 13 & Release 13 & RFC6824, etc. \\ \hline \multirow{2}{*}{Protocol layer} & \multirow{2}{*}{Link layer (MAC layer)} & \multirow{2}{*}{Link layer (PDCP)} & \multirow{2}{*}{IP layer (IP tunnel)} & Network layer \\ \hline \multirow{2}{*}{New device function} & UE and eNB & & & (MPTCP) \\  & (5 GHz LTE) & PDCP & IPsec & \\ \hline \multirow{2}{*}{Network element} & LTE-U/LAA small cell & LWA eNB, WT & \begin{tabular}{c} LWA eNB, \\ LWIP-SeGW \\ \end{tabular} & \begin{tabular}{c} LWA eNB, \\ MPTCP Proxy \\ \end{tabular} \\ \hline Performance gain & High & High & Medium & High \\ \hline Traffic direction & Downlink & Downlink & Uplink + Downlink & Uplink + Downlink \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} Deployment eNB/AP \\ \end{tabular} } & Collocated & Collocated/Non-collocated & Non-collocated \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Access network cost \\ \end{tabular} } & High (new LTE small cell with LTE-U/LAA @ 5 GHz) & Medium (new small cell: LWA & None (uses existing WLAN AP) & None (uses existing WLAN AP) \\  & with LTE-U/LAA @ 5 GHz) & & \\ \hline \hline \end{tabular}  
* Blue: LTE Band, Green: Unlicensed band, Character: MAC/PHY, Space: non-collocated.  
\end{table}
Table 1: Comparison of alternative technologies in 5G.  
under the APs in its database. The \(M\) UEs under the coverage of both standards will have three options: option 1, WLAN-only; option 2, LTE-only; and option 3, LWA. Options 1 and 2 are the default connections available on the market. Option 3 will be added for LWA service. Moreover, each UE is restricted from using more than one communications mode. Whenever the LTE UEs' attachments are modified to accommodate option 3, they will be reported to the eNB. Note that we consider a case where, even if UEs choose option 3 mode, there is no guarantee they will be served by LWA. However, they will be listed as LWA-preferred UEs in the eNB hardware, and later approved in the eNB by our proposed algorithm. Following 3 GPP release 13, LWA supports downlink transmission for WLANs and both uplink and downlink transmission for LTE.