Support for Femtocell
Document Number:
IEEE C802.16m-08/642
Date Submitted:
2008-07-07
Source:
Guang Han
Voice:
+1-847-632-5678
Motorola Inc.
E-mail:
guang.han@motorola.com
Venue:
IEEE 802.16m-08/024: Call for Comments and Contributions on Project 802.16m System Description Document (SDD), on the topic of
“Upper MAC Concepts”.
Base Contribution:
Purpose:
For review and adapt.
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 >.
Outline
• Motivation
• Major technical challenges
–
–
–
–
Mobility
Interference
Synchronization
Self-organization
• Conclusions and recommendations
Why Femtocell?
• Problem:
– Poor indoor coverage for high data rate applications due to large
penetration loss.
– Most mobile data usage is from indoors.
• Alternate solution is costly:
– Adding more outdoor base stations is not an economically desirable
solution.
• Femtocell benefits:
– Femtocells will improve indoor coverage for high data rate
applications.
– Femtocells will reduce network infrastructure cost.
– By using existing broadband connection as backhaul, Femtocells will
significantly increase network capacity and reduce network operation
cost.
• Additional notes:
– SPWG is preparing Wimax Femtocell requirements document. (Current
version 0.2.0)
– 3GPP has been discussing Femtocell topics from early 2007.
Major technical challenges I: Mobility
• The density of Femtocells can be significantly larger
than that of macro cells. In urban area, a passenger on
the street may detect hundreds of Femtocells in a
short period of time.
– Handover
• The upper limit of the size of the neighbor list is far below the
number of potential Femtocell neighbors of a macro cell. Thus the
passenger may not be able to perform handover even if an
accessible Femtocell is nearby.
– Control signal pollution
• Assume the neighbor list is properly enhanced to support handover
Since Femtocells can have closed access such that only very few
end users can access a Femtocell, most camping/handover requests
by the passenger will be rejected. Such frequent futile
camping/handover attempts will increase network signaling load
and impact end user mobility performance.
Major technical challenges II: Interference
• Neighboring Femtocells in the same apartment
building will cause large interference to each other.
• When Femtocells use the same frequency as outdoor
cells, they will also cause large interference to nearby
Macro cell users.
– First scenario: Macro users in the close proximity (E.g. in
the same room) of a Femtocell will not be able to detect
MAP headers of the Macro BS , thus they are completed
blocked from the Macro cell.
– Second scenario: Macro users relatively farther away from
a Femtocell will still be able to receive Macro cell service
at the expense of lower data rate and/or more Macro cell
resource.
Major technical challenges III: Synchronization
• GPS receiver may not work well indoors. Also
a GPS receiver can be too expensive for a
Femtocell.
• Using high accuracy crystal oscillator (E.g.
OCXO) for each femtocell is not a
economically viable solution either.
• IEEE 1588 requires symmetric delay and very
small jitter over the backhaul connection.
Existing broadband connection (cable/DSL)
can hardly meet these requirements.
Major technical challenges IV: Self organization
• Similar to WiFi access points, A Femtocell is
supposed to be installed by its owner. Thus
pre-planning is not feasible.
– Self configuration
• A Femtocell needs to automatically acquire its working
parameters (frequency, transmission power, neighbor
list, cell ID, etc) from the network before serving its
users.
– Self optimization
• A Femtocell adaptively adjust its parameters with
respect to external environment (RF, network, etc)
variation in order to optimize its performance.
Conclusions and recommendations
• Conclusions:
– Femtocell will bring significant benefit to the operators,
such as solving indoor coverage problem, increasing
network capacity, reducing network infrastructure and
operation cost, etc.
– But we need to overcome many technical challenges to
enable successful Femtocell deployment. Those technical
challenges need to be addressed in IEEE 802.16m context.
• Recommendations:
– Incorporate Femtocell topics into IEEE 802.16m SDD.
– Either a standalone section is allocated for Femtocell or we
can discuss each topic under existing sections.