IEEE 802.16ppc-10/0066
Project
IEEE 802.16 Broadband Wireless Access Working Group <http://ieee802.org/16>
Title
Coordinated AP for tightly coupled BS-AP interworking for Multi-RAT devices
Date
Submitted
2010-11-02
Source(s)
Youngsoo Yuk, Eunjong Lee, Heejeong Cho and
Inuk Jung
LG Electronics
E-mail: youngsoo.yuk@lge.com,
eungong.lee@lge.com,
heejeong.cho@lge.com,
inuk.jung@lge.com
Re:
Abstract
Introduction of Coordinated AP for tightly coupled BS-AP interworking scenarios
Purpose
To introduce the possible gain of enhanced AP in HN Multi0RAT scenarios
Notice
Release
Patent
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IEEE 802.16ppc-10/0066
Coordinated AP for tightly coupled BS-AP interworking for MultiRAT devices
Youngsoo Yuk, Eunjong Lee, Heejeong Cho and Inuk Jung
LG Electronics Inc.
1 Introduction
The multi-RAT supporting device is being a key trend with the boom of smart phones. Especially cellular
and WLAN interworking/switching can provide cheaper and more efficient wireless connection to the smart
phone users. Even though SDR-based mobile terminal is one of the candidates for the next generation mobile
terminal, dual-RAT devices becomes a dominant trend of wireless device for long time enough.
In order to provide higher-level of experience to the customers with the dual-RAT devices, various
interworking/co-operation models have been proposed. On the track of such an evolution, we are proposing a
tightly coupled network model for dual-RAT operation.
2 WLAN and Cellular interworking
Table 1 shows the comparisons of Pros/Cons of WLAN and cellular networks. The interworking may be going
through the way choosing advantages relative to each other and making up the drawbacks with the modified
operations.
Table 1. Pros/Cons of WLAN and Cellular systems
WLAN
Cellular
Pros
Higher BW
Mobility Management
Low cost for deployment
Guaranteed QoS support
Low overhead for maintaining
Secure transmission
connections
Low access delay for random
access with small MSs
Cons Uncontrolled Mobility
Higher access delay for
No connection management
scheduled access
Limited QoS support
Large control overhead for data
High power consumption for
transmission
network discovery
Hard to managing interference
Note
WLAN provides Higher BW/Low
latency
Cellular provides QoS support
Cellular provides
mobility/connection management
Cellular co-ordinates the devices
to connect WLAN
The basic approaches for enhancement are as follows:
 In order to provide optimal data connection to the device under certain condition and service.
i. More cost-effective, power-efficient RAT should be used for connections.
ii. Ex) VoIP via cellular, Web via WLAN
 Unified mobility/connection control via cellular network.
i. Unified security association
ii. WLAN mobility support
iii. Unified QoS Management
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Various levels of inter-working architectures we can consider. In the current interworking architecture in
WiMAX forum [2] and 3GPP [3], two independent networks are inter-connected via AAA proxy and/or various
network layer functions. However only network layer interworking functions are considered in those
architectures. If we consider the roaming between different networks, the model can be used as an efficient
model. However many operators have both cellular and WLAN infra-structures and can provide both
connectivity with a single subscription. Higher layer interworking has several limitations such as
 The high power consumption for detecting WLAN AP without co-ordination
 Higher signaling overhead comes from tunneling-based inter-working.
 Large delays comes from higher layer interworking
 Hard to support seamless mobility when the device is connected to WLAN.
 In-device interferences between cellular and WLAN modules and loss from Co-Located Coexistence.
If cellular BS can directly communicate with WLAN AP under its coverage, above challengeable issues can be
resolved.
Various enhanced equipments for wireless network can be considered for providing higher level of co-operation.
Because the enhanced terminals have been proposed and discussed in various usage scenarios, and we focused
on enhanced WLAN AP which provides higher level of interworking function to the mobile users.
A. Enhanced Terminal :
 Terminal which has multi-access capability
 It can connect to both BS and other WLAN devices
 Scenarios : WLAN/Cellular Tethering (Relaying), Multi-RAT Client Co-operation
B. Enhanced AP
 AP which has both WLAN/Cellular/Wired connecting capability
 It is AP but has link to/from BS for control or data connection
 Scenarios : WLAN router with Cellular Backhaul, integrated AP, Coordinated AP
with interworking connection with Cellular BS)
(WLAN AP
3 Enhanced AP
Wireless hotspots show the possible enhancements of scenarios how WLAN and cellular systems can help each
other. In these scenarios, WLAN provides abundant connectivity from various wireless devices with higher BW
while cellular system gives mobility to the devices.
Figure 1 shows the logical structure of Enhanced AP, and it can operate with 3 different modes and provides
connectivity to/from devices with three different ways;
 Wireless Backhaul mode: WLAN connectivity to devices and cellular connection as a wireless
backhaul
 Converged gateway mode: Both WLAN and cellular connectivity to user devices, and wired IP
backhaul
 Coordinated AP mode: WLAN to user devices, cellular connection to/from BS for BS-AP
coordination and wired IP backhaul.
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IEEE 802.16ppc-10/0066
Enhanced AP
WLAN GW
Core Standard Focus of
multi-RAT
802.1X
IEEE802.16 ABS
Data
Plane
802.11
Coordination
Function
GLL Control
Plane
PDN
802.11
PHY/MAC
802.11
Control/
RRM
802.16
PHY/
MAC
802.16
PHY/
MAC
AAA/
HA
CS
/IP
Figure 1. Structure of Enhanced AP
Enhanced AP: Wireless Backhaul
802.1X
Core Standard Focus of
multi-RAT
IEEE802.16 ABS
Data
Plane
802.11
PHY/MAC
GLL Control
Plane
802.11
Coordination
Function
AAA/
HA
PDN
802.11
Control/
RRM
802.16
PHY/
MAC
802.16
PHY/
MAC
CS
/IP
Enhanced AP : Converged Gateway
802.11
PHY/MAC
802.1X
GLL
Femto/WLAN
GW
802.16
PHY/
MAC
4
PDN
AAA/
HA
IEEE 802.16ppc-10/0066
Enhanced AP : Coordinated AP
WLAN GW
802.1X
Core Standard Focus of
multi-RAT
IEEE802.16 ABS
Data
Plane
802.11
PHY/MAC
802.11
Control/
RRM
GLL Control
Plane
802.16
PHY/
MAC
802.11
Coordination
Function
802.16
PHY/
MAC
PDN
AAA/
HA
CS
/IP
Figure 2. Various operational modes of Enhanced AP
In this contribution, we focused on the last mode, “coordinated AP” and its possible gains.
4 The coordinated AP (C-AP)
Enhanced AP (E-AP) in the coordinated AP mode (call it as “C-AP” hereafter) which is for virtual carrier
application can support various useful operations. In coordinated AP mode, a BS has controllability on the CAPs under its coverage.
Even though the wired connection between BS and AP can be helpful to support a certain level of interworking,
wireless link between BS and AP is able to provide more abundant functions for cooperation.
The BS and C-APs may have communication channel to talk to each other.
 The BS and C-APs can communicate for interworking.
 The C-APs can communicate with each other via BS’s relaying and/or moderation.
The following co-operation scenarios we can expect with this system.
A. Sharing Access information
C-AP may be possible to make a relation to its overlaid BS via IEEE802.16 wireless link.
After turning on C-AP, it may start finding BS which it can communicate with, and register itself to the overlaid
BS. From this interaction, BS can make a list of C-APs under its coverage without help of network operator.
C-AP may be also provided the location information, neighbor information, radio configuration parameters and
so on from the BS, and BS-assisted/controlled WLAN mobility can be implemented.
From the information, BS can provide access information on WLAN AP to the dual-mode devices connected
the BS. It can help reducing the device’s the power consumption for detecting WLAN APs.
In addition, AP also can provide access information of cellular BS to the devices.
- BS’s Providing access information on C-APs to the devices
 Low power consumption to detecting WLAN APs
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IEEE 802.16ppc-10/0066
- C-AP’s providing access information on BS to the devices
 Fast BS-AP handover
B. Frame alignment for easy inter-working
Wireless connection between BS and AP also make it possible to align their frame timing to mitigate self
interference. If beacon signals broadcast by C-APs are aligned to BS’s DL subframe, no CLC mode is required
for beacon reception in the devices.
And, distributed beacon timing between C-APs can help detecting beacons with small searching duration for the
devices.
- Frame timing alignment/coordinating
 Beacon signal can be aligned to the BS’s frame timing
 Beacon signal can be distributed over multiple APs for co-ordination
 Easy to scanning without CLC and scanning interval/unified timing reference
 Easy to control the interworking based on timing relation
C. Inter-AP coordination
Inter-AP Protocol (IAPP) and management function for multiple-AP environment can be supported by
IEEE802.11f/v standard. Because that’s a semi-distributed protocol, the coordination may be partially optimized
for not enough information on hidden nodes.
In addition, neighbor AP may use different frequency channel, it’s hard to communicate with each other.
A BS can be a hub for the communication, and it can be a centralized controller to coordinate all APs.
With these communication links, BS can provide following flexibility to WLAN network.
- Coordinated Dynamic Channel Switching
- Coordinated Dynamic Adjustment of Transmission Power
- Coordinated Dynamic Timing Adjustment
- Coordinated Capacity Sharing among APs
The coordinated managements may provide higher integrated network throughput [5].
In addition, with combining cellular off-loading, more optimized load balancing is possible and it yields more
network throughput.
D. Integrated QoS/Connection management
Even though the integrated security and IP flow mobility are already discussed and being standards, the level of
cooperation is limited. Cellular and WLAN can share its security and context of an AMS, and it provides more
easy way of interworking for QoS and connection management.
- QoS/Connection Management
 Prioritized AMS scheduling
 QoS provisioning for off-loading
 Integrated Security Association
 IP Flow mobility support
5 Conclusion
Multi-tier network with cellular and WLAN is considered as an important solution for enhancing network
capacity of wireless network. Interworking via radio interface between cellular BS and C-APs can provide
abundant extension of management function to both the network service provider and the users.
We proposed that IEEE802.16 WG should study of possible gains and feasibility of the introduction of C-AP.
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6 References
[1] C802.16ppc-10/008r1, Study Report on Hierarchical Networks (Working document), Sept. 2010
[2] WiMAX Forum NWG, “Architecture, detailed Protocols and Procedures, WiFi – WiMAX
Interworking,” , June, 2010
[3] TS23.234 V9.0.0 “3GPP system to Wireless Local Area Network (WLAN) interworking”, Sept. 2009.
[4] Ramon Ferrus et al, “Interworking in Heterogeneous Wireless Networks: Comprehensive Framework
and Future Trends,” IEEE Wireless Communication, April, 2010
[5] M.Abusuhaih et al, “AN Inter-Access Point Coordination Protocol for Dynamic Channel Selection in
IEEE802.11 Wireless LANs,”pp17-24, ACNM’07, May, 2007
========== Proposed Text ================================================
[remedy 1: Add following scenario as a section 2.2.6 in page 13]
2.2.6 BS-AP interworking by coordinated AP (C-AP)
In order to provide higher level of interworking function, cellular BS and WLAN AP may help each other
through the wired and wireless connection.
Hierarchical relations based on the coverage are defined between cellular BS and WLAN APs, and BS may
provide configuration/co-ordination information to the WLAN APs in order to increase the interworking
benefits.
Coordinated AP (C-AP) is a WLAN AP which has wireless connectivity to BS
A BS has controllability on the C-APs under its coverage.
The BS and C-APs may have communication channel to talk to each other.
 The BS and C-APs can communicate for interworking.
 The C-APs can communicate with each other via BS’s relaying and/or moderation.
The following co-operation scenarios may be implemented with C-AP and BS interworking.
A. Sharing Access information
In this scenario, C-AP can make a relation with its overlaid BS by itself.
After turning on C-AP, it may start finding BS which it can communicate with, and register itself to the overlaid
BS. From this interaction, BS can make a list of C-APs under its coverage without manual install/configuration.
E-AP may be also provided the location information, neighbor information, radio configuration parameters and
so on from BS, and BS-assisted/controlled WLAN mobility can be implemented.
From the information, BS can provide access information on WLAN AP to the dual-mode devices connected
the BS. It can help reducing the device’s the power consumption for detecting WLAN APs.
In addition, AP also can provide access information of cellular BS to the devices.
- BS’s Providing access information on C-AP to the devices
 Low power consumption to detecting WLAN C-APs
- C-AP’s providing access information on BS to the devices
 Fast BS-AP handover
B. Frame alignment for easy inter-working
Wireless connection between BS and C-AP also make it possible to align their frame timing to mitigate self
interference. If beacon signals broadcast by C-APs are aligned to BS’s DL subframe, no CLC mode is required
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IEEE 802.16ppc-10/0066
for beacon reception in the devices.
And, distributed beacon timing between C-APs can help detecting beacons with small searching duration for the
devices.
- Frame timing Alignment/coordinating
 Beacon signal can be aligned to the BS’s frame timing
 Beacon signal can be distributed over multiple C-APs for co-ordination
 Easy to scanning without CLC and scanning interval/unified timing reference
C. Inter-AP coordination
Inter-AP Protocol (IAPP) and management function for multiple C-AP environment can be supported by
IEEE802.11f/v standard. Because that’s a semi-distributed protocol, the coordination may be partially optimized
for not enough information on hidden nodes.
In addition, neighbor AP may use different frequency channel, it’s hard to communicate with each other.
A BS can be a hub for the communication, and it can be a centralized controller to coordinate all APs.
With these communication links, BS can provide following flexibility to WLAN network.
- Coordinated Dynamic Channel Switching
- Coordinated Dynamic Adjustment of Transmission Power
- Coordinated Dynamic Timing Adjustment
- Coordinated Capacity Sharing among APs
The coordinated managements may provide higher integrated network throughput[]
In addition, with combining cellular off-loading, more optimized load balancing is possible and it yields more
network throughput.
D. Integrated QoS/Connection management
Even though the integrated security and IP flow mobility are already discussed and being standards, the level of
cooperation is limited. Cellular and WLAN can share its security and context of an AMS, and it provides more
easy way of interworking for QoS and connection management.
- QoS/connection management
 Prioritized AMS scheduling
 QoS provisioning for off-loading
 Integrated Security Association
 IP Flow mobility support
Figure X, wireless connection between BS and C-APs for coordinated operation.
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[remedy 2: Add following scenario as a section 2.2.6 in page 13]
4.2 Multi Radio Access Technology
[R-X] IEEE 802.16 BS shall be able to communicate with IEEE 802.11 AP under its coverage via wired and/or
wireless connection for interworking operation. IEEE802.16 BS should be able to configure and control
the operation and configuration of the IEEE802.11 APs under its coverage.
======================== End of proposed text ==============================
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