Transcript Femtocell Base Station Deployment in Commercial Buildings

A New Handover Mechanism for
Femtocell-to-Femtocell
Adviser: Frank , Yeong - Sung Lin
Presented by Li Wen Fang
Agenda
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Introduction
The Hidden FAP Scenario
Proposed Handover Mechanism
Performance Analysis
Conclusion
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Agenda
•
•
•
•
•
Introduction
The Hidden FAP Scenario
Proposed Handover Mechanism
Performance Analysis
Conclusion
3
Introduction
• It is estimated that nearly 23% of calls and over 90%
of data services occur indoors.
• A poor coverage problem
• The femtocell networks which use FAP and existing
networks as backhaul connectivity can both fulfill the
upcoming demand of high data rate for wireless
communication system and extend the coverage area.
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Introduction
• Femtocell is so important for the following reasons :
1. Femtocell can provide indoor coverage for
places where macrocells cannot.
2. Femtocell will significantly improve the total
network capacity by reusing radio spectrum
indoors.
3. Femtocell is a good solution for FMC (Fixed
Mobile Convergence).
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Introduction
• Femtocell is so important for the following reasons :
4. Femtocell can offload traffic from the
macrocell and improve macrocell capacity.
5. Femtocell can provide significant power saving.
6. Users will pay to install femtocells.
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Introduction
• Three access modes for FAP:
– CSG (Closed Subscriber Group) mode
– OSG (Open Subscriber Group) mode
– Hybrid access mode
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Introduction
• CSG (Closed Subscriber Group) mode
– only for CSG users
– The membership of the CSG can be modified by the
service level agreement between the subscriber and
the access provider.
• OSG (Open subscriber Group) mode
– open to any user
• Hybrid access mode
– non-CSG users can only get limited services
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Introduction
• Three types of handovers in femtocell networks:
– femtocell-to-macrocell handover
– macrocell-to-femtocell handover
– femtocell-to-femtocell handover
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Introduction
• In [7], a new handover algorithm based on the MS’s
speed and Quality of Service (QoS) is proposed.
– better performance than traditional handover
algorithm
• Dense femtocells deployment is the ultimate goal of
the femtocell networks.
– So handover between femtocells is also very
important.
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Introduction
• In this paper, we try to build a neighbor femtocell list
which considers several factors such as received signal
level, the hidden FAP problem and the access mode
of FAP.
• And then we propose a new handover mechanism for
femtocell-to-femtocell.
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Agenda
•
•
•
•
•
Introduction
The Hidden FAP Scenario
Proposed Handover Mechanism
Performance Analysis
Conclusion
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The Hidden FAP Scenario
A. Basic concepts of femtocell
B. Hidden FAP Scenario
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Basic concepts of femtocell
• Femtocell is a low-power and small-capacity base
station which can provide high quality and high speed
transmission of wireless communication services to
balance the loading of macrocell.
• It also contains RNC (Radio Network Controller)
and all the core network elements.
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Basic concepts of femtocell
Figure 1. The basic structure of femtocell access
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Hidden FAP Scenario
• Whenever a mobile station realizes that the received
signal strength from the serving FAP is going down, it
will receive many signals from several neighbor FAPs
for handover.
• neighbor femtocell list
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Hidden FAP Scenario
• The hidden FAP problem is the case when a
neighbor FAP is very close to the MS but the MS
cannot receive a strong enough signal level from
the hidden FAP because of some barriers between
them.
• The hidden FAP will not be included in the neighbor
femtocell list if the neighbor femtocell list is based
on RSSI (received signal strength indicator) only.
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Hidden FAP Scenario
Figure 2. The hidden FAP scenario
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Agenda
•
•
•
•
•
Introduction
The Hidden FAP Scenario
Proposed Handover Mechanism
Performance Analysis
Conclusion
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Proposed Handover Mechanism
• The handover from femtocell to femtocell is
demanding and complicated since there are hundreds
of possible target FAPs when MS moves out of its
serving FAP’s coverage.
• In traditional scheme for femtocell-to-femtocell
handover, handover decision is made according to
received signal level only.
– It is not enough to consider RSSI level only
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Proposed Handover Mechanism
• The access mode of FAP may bring a result that MS may not
be permitted to get access to the target FAP which is selected
by the serving FAP and it will lead to a handover failure.
• The lack of radio resources in the selected FAP will also
cause a handover failure.
• Hidden FAPs in the neighbor femtocell list will cause a
handover failure.
– We take received signal strength level, the access mode
and location of neighbor femtocells into consideration.
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Proposed Handover Mechanism
• When the serving FAP coordinate with the neighbor
FAPs, it will acquire those FAPs’ access mode and
current load.
• A priority setting
– CSG mode femtocell who’s allowed CSG list includes
MS’s ID.
– Hybrid mode femtocell who’s allowed CSG list
includes MS’s ID.
– OSG mode femtocell.
– Hybrid mode femtocell who’s allowed CSG list dose
not include MS’s ID.
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Proposed Handover Mechanism
• Once FAP receives the handover requests containing
the RSSI information of a neighbor FAP whose
RSSI level is stronger than a threshold 𝑆𝑇1 , it will
set a priority to this neighbor FAP.
• The neighbor FAP within a range of distance whose
RSSI level is less than 𝑆𝑇1 , but stronger than 𝑆𝑇0 is
regarded as hidden FAP and it will also get a certain
level of priority.
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Proposed Handover Mechanism
• “If at least one highest priority FAP has spare
bandwidth resource, it will be put into the neighbor
femtocell list.”
• We may face a problem that multiple FAPs with the
same priority exist in the neighbor femtocell list.
– comparing their RSSI level and current load
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Proposed Handover Mechanism
• Our proposed scheme considers initially the received
RSSI level, and then the hidden FAP problem.
Finally, we set priority to certain FAPs and make a
neighbor femtocell list according to the rule.
• The serving FAP can choose a appropriate neighbor
FAP from the list. If there is no FAP meet the
requirements, the MS keeps detecting signals from
neighbor femtocells.
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Proposed Handover Mechanism
Figure 3. Flow chart of the proposed mechanism
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Agenda
•
•
•
•
•
Introduction
The Hidden FAP Scenario
Proposed Handover Mechanism
Performance Analysis
Conclusion
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Performance Analysis
• We randomly distribute femtocells. The MS is assumed
to be at the edge of the reference femtocell.
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Performance Analysis
Figure 4. A comparison of handover failure rate
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Performance Analysis
• The result shows that our scheme has a lower
handover failure possibility than the traditional scheme.
• It is possible that the target femtocell is not
included in the neighbor femtocell list.
– cause a handover failure to the target femtocell
• The increasing number of deployed femtocells
increases the possibility that neighbor FAPs
coordinate with the reference FAP and keep informed
about the location of the hidden FAPs.
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Performance Analysis
Figure 5. A comparison of the number of femtocells in neighbor femtocell
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Performance Analysis
• The result shows that the neighbor femtocell list of
our proposed scheme contains a smaller number of
femtocells than the traditional scheme.
• However, the reduced number of neighbor femtocells in
the neighbor femtocell list does not make the handover
failure probability rise.
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Performance Analysis
•
Our proposed scheme has some other benefits:
– Some unnecessary handovers can be avoided and
the QoS can be ensured through setting priority
of FAPs.
– It could keep a load balance in some extent.
– It can lighten the burden of the resources of
open mode femtocell.
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Agenda
•
•
•
•
•
Introduction
The Hidden FAP Scenario
Proposed Handover Mechanism
Performance Analysis
Conclusion
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Conclusion
• The dense femtocell scenario is the ultimate goal
of the femtocell networks.
• We propose a new handover mechanism which
considers many factors such as access mode, hidden
femtocell and signal strength.
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Thanks for listening !
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