4G/LTE - LWA

LWA

LWA stands for LTE-WLAN Aggregation. It is a kind of technology on the evolution path of LTE Unlicencesed technology. You would get the overview of LWA under the context of LTE Unlicensed technology, refer to LTE-U/LAA/LWA page. I decided to create a separate page for LWA since the technical details will be too long to put in the overview page. I will describe the details of the LWA based on 3GPP documents in this page.  However, it will take very long before I complete this page because this technology is at very early stage as of now (as of Jun 2016) and I haven't seen any real implementation of this technology personally.

Overall Network Architecture for LWA

Following is overal network architecture of LWA. As you see here, there can be two different type of scenario(implmentation) of LWA. One is called 'Colocated scenario' and the other one is called 'Non-Colocated scenario'. Regardless of the scenario, one common thing is that the data is split at PDCP layer of LTE and forwarded to LWAAP (LWA Adaptation Protocol) which in turn forwarded to WLAN MAC layer. The difference between the two scenario is the location of WLAN MAC/PHY. In Colocated scenario, LLAN MAC/PHY reside within the eNB (i.e, in the same location of LTE Radio Stack). So LTE PDCP can directed connected to LWAAP and it does not need any special interface between LTE and WLAN. On the contrary, in non-colocated scenario WLAN MAC/PHY resides out side of eNB, so they need special interface called Xw (Xw-C and Xw-U) to convey the control and user data between LWAAP and WLAN MAC/PHY.

Overall Protocol Sequence for LWA

Following is overall protocol sequence for LWA operation. As you see, there are roughly 3 types of operation as listed below.

1) WT (WLAN Termination) Attach

2) WT Modification : This operation can be devided into two types depending on who (eNB or WT) initiate the modification

3) WT Release  :  This operation can be devided into two types depending on who (eNB or WT) initiate the

At a very high level view, you may notice that the overall procedure is similar to LTE-LTE carrier aggregation process

(Following diagram is based on 36.300 22A.1.7 LTE-WLAN Aggregation Operation)

Reference :

[1] Collaboration on LTE - WLAN Integration - 3GPP

[2] TS 36.300, section 22A.1 : Stage-2 high level description

[3] TS 36.323 : Stage-3 data plane (PDCP)

[4] TS 36.360 : Stage-3 data plane (LWAAP)

[5] TS 36.331 : Stage-3 control plane (RRC)

[6] TS 36.463, TS 36.462, TS 36.461 : Stage-3 control plane network interface (Xw)

[7] TS 36.465. TS 36.464 : Stage-3 data plane network interface (Xw)

[8] TS 33.401 : Stage-3 security aspects – TS 33.401