Femtocell discovery and access Document Number:

IEEE C80216m-08/1432r1

Date Submitted:2008-10-31

Source:Jin Lee, Inuk Jung, Ronny Yongho Kim, Voice: +82-31-450-1856Kiseon Ryu and Youngsoo Yuk E-mail: {jins978, cooper, ronnykim, ksryu, sixs}@lge.comLG Electronics

Venue: TGm SDD: Femtocells

Base Contribution:None

Purpose:Discuss and adopt by TGm for Femtocell SDD Text

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Number of Femto Cells within a Macro Cell is too large and broadcasting such large information (e.g. Femto neighbor list) incurs too much overhead.

Without a providing neighbor list to an MS, discovery (scanning) of Femto BSs in the vicinity of the MS becomes difficult and requires new procedures for it

The scanning problem is critical for initial network entry and handover cases where neighbor Femto BS lists are required

Scenarios for network entry and handover cases in Femto Cell need to be defined, since the cell has a heterogeneous entity design (Macro, Femto and Relay BS) with possibly complicated provider right issues (Femto accessible rights)

Clear definition of Femto BS types (e.g. open, closed Femto BS, initial accessible BS types) need to be defined

Need to be considered for femtocells

Classification of femtocells Since a large number of femtocells can be installed by subscribers, in certain

scenarios femtocell access shall be restricted to certain subscribers who are authenticated and authorized for exclusive access and related network service.

Additionally, femto BS can provide a mechanism delivering initial access information (e.g. BS ID, frequency, closed group information, NSP, roaming capability) of it’s own and neighboring femto BSs to any MSs in order to facilitate their network discovery/selection and entry procedure to femtocells.

Femto BS can be classified into 4 types:Based on bearer connection capability

Open femto BS : Provides bearer connectivity (full network services) to any MS

Closed femto BS : Only provides bearer connectivity to allowed (identifiable) MSs

Based on initial access information capabilityInitial access able femto BS : Provides initial access information for any MSs

Initial access unable femto BS : Not allow to provide initial access information

Based on the aforementioned clarifications, we propose Femto BS access procedures that allow efficient network entry and handover to Femto BSs with low overhead

Initial network discovery (Accessible Femto BS discovery) There are two cases, where an MS powers on and starts to scan the DL

Finds a femto BS with initial access capability Finds a femto BS with no initial access capability

Handover from Macro BS to Femto BS Serving BS coordinates the handover of MS from Macro BS to a Femto

BS by provisioning information of allowed Femto BSs to scan for populating a Femto BS neighbor list.

Objective and Considered Scenarios

Two initial network access information acquisition procedures(1) If a Femto BS with initial access capability is found, MS requests and obtains initial network

access information through that Femto Cell

(2) Else, if only Femto BSs with no initial access capability are found, MS requests and obtains initial network access information (without registration) through Macro BS

Initial Network Discovery

Initial access information gathering The information gathering procedure for

network entry applies to the aforementioned initial access cases (1) and (2)

During the initial access, MS transmits the information of found Femto BSs to the initially accessed BS entity (e.g. Macro/Femto BS managing entity)

The BS entity populates a list of neighbor Femto cells residing in the vicinity of the MS based on the given extra Femto BS information by the MS

The neighbor list, including the Femto Cells and their system information, is given to MS, who tries initial network entry to one of the provided Femto BS within the given list

Fig 1. Initial Network Entry to Macro BS-case (2)

Femto BS Managing Entity

FAP1

FAP2

FAP5

FAP3

FAP4FAP6

FAP7

Macro Cell

MS

Femto Cells(1) MS connects to Macro BS first

(3) Provide MS with coordination of which Femto BS to connect to (here it would be FAP7)

(2) Populate an Femto NBR list based on the extra

Femto BS information given by MS

Handover

Femtocell entry from connected macro BS An MS performs femtocell search The MS reports initially detected femto BS to

macro BS Macro BS may forward them to a femto BS

managing entity to query a list of allowed Femto BSs residing in the vicinity of the MS based on the given extra Femto BS . If Macro BS has knowledge about femto BSs, macro BS may response immediately

The list, including the Femto BSs of which have permission to connect is given to MS

The MS scans accessible femto BS candidates based on the received list

The MS requests handover to one of femto BS candidates

Femtocell discovery during handover (Macro BS Femtocell)(1) Since MS has been authorized by serving BS, serving BS can provide a list of accessible

(permission to connect) femto BSs based on the initially given Femto BS information by Macro BS

(2) The MS performs channel measurement on the femto BSs included in the list for HO candidate selection

FAP 1

FAP 2

FAP 5

FAP 3

FAP 4FAP 6

FAP 7

Allowed Femto BSs (1) MS sends initially detected Femto BS

(3) Provide MS with coordination of which Femto BS to connect to

Femto BS Managing Entity

Macro Cell

(2) Populate an

list based on the extra Femto BS information given by MS

allowed Femto NBR

(here it might be FAP7)

(here a list might include FAP 7,2,1 under the allowed group)

Non-allowed Femto BSs

Fig 2. Handover

Proposed Text (1/3)

17. Support for femtocells

The Femto BS is classified into two modes in terms of bearer connection capability and initial access capability. Details of initial access information are FFS.

• Open Femto BS: Provides bearer connectivity (full network services)

to any MS• Closed Femto BS: Only provides bearer connectivity to allowed

(identifiable) MSs• Initial access able Femto BS: Provides on demand initial access

information for any MSs. Initial access information can be provided before authentication to expedite network discovery and selection procedure.

• Initial access unable Femto BS: Not allow to provide on demand initial access information.

Proposed Text (2/3)

17.1 Network Discovery/Selection and EntryThe IEEE802.16m system shall support applicable procedures for entering and registering a new MS at a Femto BS. The network facilitates the initial network discovery procedure by providing network information (details are FFS) to the MS prior to full registration including authentication to a BS entity.

An overall procedure of the network entry would be as follows. The MS scans the DL for any neighbor BS entities (Macro/Femto). Among the searched BSs, the MS distinguishes them and prioritizes them in terms of network entry candidates. The MS further prioritizes Femto BSs by their types (Open/Closed and initial access able/unable types). Based on the scan result, the MS makes network entry to the best BS candidate.

Proposed Text (3/3)

17.2 Handover to Femto BS Macro BS facilitates femtocell scanning through the information on allowed

femtocells, e.g., the MS’s CSG femtocells, for MS in order to save MS power and avoid unnecessary scanning. MS provides initially detected femtocell information to macro BS. This is to provide information that the macro BS utilizes for generating a HO candidate list, which includes a list of neighbor Femto BSs that the MS is able to establish connection. The HO candidate list is given to the MS by the macro BS. Upon receiving the list of HO candidate BSs, the MS scans the HO candidate BS list and selects the most preferable BS for HO.