This presentation gives an overview of the ongoing 3GPP Study Item on LTE-WiFi interworking.
One of the 3GPP Rel-12 Study Items focuses on Small Cell Enhancements.from the perspective of higher layers. There are 3 scenarios under consideration:
Scenario 1: Macro and small cells on the same carrier frequency, connected via non-ideal backhaul.
Scenario 2: Macro and small cells on different carrier frequencies, connected via non-ideal backhaul.
Scenario 3: Only small cells on one or more carrier frequencies, connected via non-ideal backhaul.
The challenges posed by these scenarios are summarized in the table below.
To address these challenges, 3GPP’s RAN Working Group 2, is currently working towards a set of solutions, with the following design goals in mind:
The idea of ‘dual connectivity’ has more or less been accepted as the way forward. This term refers to operation where a given UE consumes radio resources provided by at least two different network points connected with non-ideal backhaul. Each eNB involved in dual connectivity for a UE may assume different roles and these roles do not necessarily depend on the eNB’s power class and can vary among UEs.
Within the dual-connectivity framework, there are two potential solutions being discussed:
Inter-node radio resource aggregation: This solution is aimed at improving per-user throughput by aggregating radio resources in more than one eNB for user plane data transmission.RRC Diversity: This solution is targeted at improving mobility robustness by transmitting handover related RRC signalling could from/to a potential target cell. The RRC diversity scheme could also be applied for handovers from the macro to pico cells, between macro or between pico cells.
Further details of these solutions can be found in TR36.842.
While current LTE deployments are mostly based on Rel. 8/9, work is ongoing in 3GPP on Release 12. The July issue of IEEE Communications Magazine has a nice article which provides an overview of the key features being developed in Release 12. It can be viewed online via the IEEE Digital Library at http://digital.comsoc.org/publication/ieee-communications-magazine.
At the recent RAN2 meeting (May 20-24, 2013), the discussions focused mainly on access network selection and traffic steering in 3GPP-WLAN interworking scenarios. The proposed solutions addressed the following cases:
UE is within UTRAN/E-UTRAN coverage, is using 3GPP and goes into WLAN AP coverage
B. UE is within UTRAN/E-UTRAN and WLAN coverage, is using WLAN and goes out of WLAN AP coverage
C. UE is within the coverage area of both, UE using WLAN, all or a subset of the UE’s traffic should be routed via UTRAN/E-UTRAN instead
D. UE is within the coverage area of both, UE using UTRAN/E-UTRAN, all or a subset of the UE’s traffic should be routed via WLAN instead
E. UE using both accesses and should be connected to only one (WLAN or UTRAN/E-UTRAN) or some traffic should be moved to the other access
In broad terms, there are 3 solutions currently being discussed in RAN2:
Solution 1: 3GPP RAN provides UE with information that assists in network selection and traffic steering. This information may be combined with ANDSF rules and/or UE configuration to decide whether to connect to a WLAN, if one is available, and to steer one or more flows to the WiFi link.
Solution 2: 3GPP RAN provides the access network selection parameters, based on which the UE decides when to connect to a WLAN. These parameters may includes thresholds, priorities, rules etc.
Solution 3: UE reports available WLAN(s) based on measurements configured by 3GPP RAN and the decisions related to WLAN selection as well as traffic steering are taken by the network.
In the next post, I will discuss each of these solutions in more detail.
3GPP-WLAN interworking support at Core Network level is already specified in the standard. As part of Release 12, a study on ‘WLAN/3GPP Radio Interworking’ is in progress to find solutions for RAN-level interworking between 3GPP and WLAN. The aim and scop of this study are defined in document no RP-122038. The following issues are being addressed during the study:
1. Under-utilization of operator-deployed WLAN
2. Sub-optimal user experience when UE connects to an overloaded WLAN
3. Unnecessary WLAN scanning leading to draining of UE battery resources
The first phase of this study identified the requirements for RAN level interworking and defined the scenarios to be considered in the study. The outcomes are captured in the 3GPP Technical Report TR 37.834.
In the current phase of this study, the focus is on identifying solutions addressing the requirements identified in the first phase and evaluation of the benefits and impacts of identified mechanisms over existing functionality, including core network based WLAN interworking mechanisms (e.g. ANDSF).
This TR is updated after every RAN2 meeting to capture the results of this study. I will summarise the key points in the coming days.