Femtocell discovery and access
Document Number:
IEEE C80216m-08/1432
Date Submitted:
2008-10-31
Source:
Jin Lee, Inuk Jung, Ronny Yongho Kim,
Kiseon Ryu and Youngsoo Yuk
LG Electronics
Voice:
E-mail:
+82-31-450-1856
{jins978, cooper, ronnykim, ksryu, sixs}@lge.com
Venue:
TGm SDD: Femtocells
Base Contribution:
None
Purpose:
Discuss and adopt by TGm for Femtocell SDD Text
Notice:
This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in
the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material
contained herein.
Release:
The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an
IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the
IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that
this contribution may be made public by IEEE 802.16.
Patent Policy:
The contributor is familiar with the IEEE-SA Patent Policy and Procedures:
<http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and <http://standards.ieee.org/guides/opman/sect6.html#6.3>.
Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >.
Need to be considered for femtocells





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
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, in cases where only closed femto BSs are scanned, where closed
Femto BSs only provide service to a closed subscriber group, shall provide a
mechanism delivering initial access information (e.g. frequency, BS ID, closed
group information) to MSs in order to facilitate their network 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 capability
 Initial access able femto BS : Provides initial access information for any MSs
(allowed or not before authentication). Some suggested information are system
information of neighboring Femto BSs or CSG ID etc.
 Initial access unable femto BS : Not allow to provide initial access information for
unauthenticated MSs
Objective and Considered Scenarios

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 mixture of Macro and Femto BSs
 Finds only Femto BSs
 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 (assuming that
mostly closed femto BSs are residing in) to scan for populating a Femto
BS neighbor list.
Initial Network Discovery

Two initial access entry procedures
(1) If a Femto BS with initial access capability is found, MS makes initial network access to that
Femto Cell
(2) Else, if only closed Femto BSs with no initial access capability are found, MS makes initial
network access (without registration) to Macro BS

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
Macro Cell
(1) MS connects
to Macro BS first
Femto Cells
MS
FAP2
Femto BS
Managing Entity
FAP7
(3) Provide MS with
coordination of which
Femto BS to connect to
(here it would be FAP 7)
(2) Populate an
accessible Femto NBR
list based on the extra
Femto BS information
given by MS
FAP3
FAP1
FAP6
FAP4
FAP5
Fig 1. Initial Network Entry to Macro BS-case (2)
Handover

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
 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
Allowed Femto BSs
(1) MS sends initially detected Femto BS
(here it might be FAP7)
Macro Cell
FAP 2
Femto BS
Managing Entity
(3) Provide MS with coordination of
which Femto BS to connect to
(here a list might include FAP
7,2,1 under the allowed group)
FAP 7
FAP 3
FAP 1
FAP 6
FAP 4
FAP 5
(2) Populate an
allowed Femto NBR
list based on the extra
Femto BS information
given by MS
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.
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 initial access information for any MSs (allowed or
not before authentication). Some suggested information are system information of
neighboring Femto BSs or CSG ID etc.
Initial access unable Femto BS: Not allow to provide initial access information for
unauthenticated MSs
Proposed Text (2/3)
17.1 Network Entry
The 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/Relay/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 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 (BSs with the same CSG ID). 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.