Localization and Mobility Management for Heterogeneous
Wireless Networks based on ANDSF
Nam Hoai Nguyen, Takuro Sato, Hidetoshi Yokota, Dae Sun Kim
Graduate School of Global Information and Telecommunication Studies, Waseda University
KDDI R&D laboratories
1Introduction

Wireless communication technology is evolving to realize aubiquitous network in which multiple wireless access such as
3GPP (GSM, EDGE, UMTS, LTE), IEEE (802.11, 802.16,802.3...) and 3GPP2 (CDMA 2000, EVDO) coexist. It allows
realizing a vision of a human centric network in which theuser’s devices can automatically select an optimum wirelessnetwork corresponded to user’s demands such as transmissionrate, quality of service (QoS), communication charges, policy,etc. In this network, the users can smoothly and seamlessly
handoff between available access networks without
experiencing any service disruption. This trend of network
evolution is becoming more and more apparent today with theexponential growth of smartphones, tablets or other gadgets
which are equipped with multiple interfaces such as 3G, Wi-Fi,
WIMAX and LTE. On top of that operators are craving fortaking advantage of Wi-Fi, Pico-cell or other low cost wirelessnetworks to offload for their overloaded cellular network due tothe surging demand for data traffic and mobile internet.
The integration of non-3GPP access technologies and legacy
3GPP networks into the Evolved Packet Core (EPC) which isthe core network designed for 3GPP’s next generation mobile
network poses both new opportunities and challenges relating tointer-system handover and mobility management. Therefore,
3GPP currently proposes a new optional entity for EPC socalled Access Network Discovery and Selection Function(ANDSF). The ANDSF designed to provide policy andinformation for detecting and selecting the most suitable target
network based on user reference and operator handoff (HO)policies to minimize the latency incurred by the intersystem
handover. One of use cases of ANDSF is to provide alwaysbest-connected service for the mobile station (MS). As
aforementioned, in heterogeneous networks, the MS will be
encompassed by various access networks with different data rateplan, QoS and communication costs at a particular location. The
MS must automatically detect and select the optimal network at
its location. However, as far as I concerned, the current
immature ANDSF has not supported such scenario due to somedeficiencies such as MS localization and Mobility management
issues when MS moves around different access networks are notconsidered in this standard. Therefore, in this paper, we propose
two enhancements for current ANDSF standard to support
above use case. Our first proposal is an additional procedure tomanage UE’s mobility across multiple access networks and thesecond one is a method to Localize MS based on available WiFi’s APs information (SSID, BSSID, and RSSI). We also
implement our proposed extensions to ANDSF server and client
in a real working system at KDDI R&D laboratories.
22.1

BackgroundAccess Network Discovery and Selection Function
ANDSF is a new entity proposed by 3GPP to resolve thecomplexity in handover across multiple access technologies ofnext generation mobile network. The ANDSF was introduced as
an optional component for Evolved Packet Core (EPC) in the

S14

H-ANDSF

HPLMN
VPLMN
UE

3GPP IP Access orTrusted/Untrusted
Non-3GPP IPAccess

S14
V-ANDSF

Fig. 1. ANDSF Architecture (Src TS 23.402)
3GPP standard TS 23.402[1], TS 24.312[2] to exchange
discovery information and network selection policies with theUser Equipment (UE) to facilitate HO in heterogeneous networkand meet operator requirements. The ANDSF is accessible forUEs either through any 3GPP or non-3GPP access technologies
that are interconnected through the EPC and IP connection. TheANDSF can provide three types of information:•Intersystem mobility policy (ISMP).
•Access network discovery information.
•Inter system routing policy (ISRP).
The architecture of ANDSF is shown in Fig 1, ANDSF
integrated with the EPC which can be accessible by the UE
through S14 interface. S14 is an IP-based interface which isindependent to access technology. OMA DM (DeviceManagement) is used to manage to manage Inter-System
Mobility Policy (ISMP) and Inter-System Routing Policy(ISRP) as well as access network discovery information storedin UE. If the UE has access network discovery information,inter-system mobility policies or inter-system routing policies
valid at its current location indicating that there is an accessnetwork in its vicinity with higher priority than the currently
associated access network(s), the UE should perform HO
procedures to switch to the higher priority access network.
However, the ANDSF is still in the initial state of its
standardization process. There are still several issues need to beaddressed before it can be deployed in the real network. One ofthe major issues is how to detect MS’s location. Identifying MS
location is very important to provide corresponded ISMP andISRP policies. Another issue is mobility management when MS
moves from one access network to the others. In this paper wetry to resolve these two issues.
2.2
Localizing Mobile Station based on Wi-Fi accesspoints and macro cells
As we mentioned above, identifying MS location is crucialfor ANDSF system since all of its provisioned ISMP, ISRP
policies and discovery function are based on MS specificlocation. In order to identify MS location, the most typical andeasiest way is to use GPS (Global Positioning System).
However, GPS may not suitable for this kind of situation. As thematter of fact, not all of mobile device are equipped with GPS
receiver. In addition, GPS cannot work in indoor environment.
Furthermore, ANDSF does not need very high accuracy toprovide information of Wi-Fi APs. Therefore, we propose analternative method to identify MS’s location in which we takeadvantage of the cell IDs of cellular network along with Wi-Fi

(a)Fig. 2. Identifying location based on Wi-Fi APs
APs information such as SSID, BSSID, and RSSI. As shown on
Fig 2, we propose an additional procedure (in red color) when
UE retrieves information from ANDSF server. The MS can turnon its Wi-Fi interface to collect information of Wi-Fi APs in its
vicinity and turn off again to save power. The Wi-Fi information
includes SSID and BSSID which can identify a unique AP. The
more number of APs can collect the higher accuracy we canachieve. Subsequently, the information can be forwarded toANDSF server to calculate MS’ location based on the precoordinated survey database.
2.3
Additional primitives for mobility management
The ANDSF server has to keep track of the associatednetwork to which the MS is associated. According to latest
release of TS 23.402[1] the ANDSF server does not have any
interface or connection to other nodes in EPC. It relies on theprovisioned policies and information to operate, therefore its
functionality is very limited and cannot be used for loadbalancing or preventing congestion between different accessnetworks. In this paper, we propose an extended procedure forANDSF in which the MS is required to update its associatedaccess network to the ANDSF whenever it switches to otheraccess network or cells. As shown in Fig 2, after retrieving new
policy from ANDSF server, in case that a new access network
available with higher priority, the MS will attempt to handoff tothat network. When the HO process completes successfully, theMS will send information of its current associated network toANDSF. Therefore, the ANDSF can keep track of mobile
associated network. Thank to this new procedure, the ANDSF
server can monitor the payload of the network, if it detects that
one Cell or Wi-Fi AP of the network is overloaded, it willchange the policy to instruct the MS to switch to another accessnetwork or cell. This extension has two advantages. One
advantage is that it does not require any modification fromexisting network infrastructure or adding new interfaces. The
second is that it is independent of access network technology aslong as the MS can connect to ANDSF server through the accessnetwork.
3 Implementation and result
We have implemented our proposed enhancements as well as
ANDSF server and client into a real working system at KDDI’slaborites using an open source code [3]. This open source codeis originally developed for synchronizing Personal Informationsuch as contact, calendar, email. etc. from the mobile handset toa centralized server. We have developed the ANDSF
Management Object (MO) according to TS 24.312 [2]specifically for intelligent detecting and selecting Wi- Fi,
WiMAX PoSs when they are available at MS location. We also
implemented our proposals into this demo system.

(b)(c)
Fig. 3. The ANDSF server and client
As shown in Fig 3, figure 3(a) is the GUI of Our ANDSF
server running on a server powered by Ubuntu 10.4 OS. Figure3(b), (c) are our client running on a mobile handset (HTC EVO)
powered by Android 2.3 OS which supports WiMAX, Wi-Fi,
3G. the mobile can turn on its Wi-Fi interface to collect nearby
Wi-Fi APs and turn off again. It will send this information toANDSF server to identify its location. The figure 2.(b) describes
the MS retrieves new policy corresponded to MS location fromANDSF server. Afterward, MS can automatically turn on Wi-Fi
interface and tries to connect to available Wi-Fi access point or
WiMAX using the information retrieved from the server. Figure2.(c) illustrates that after successfully handoff to Wi-Fi, the MS
updates the ANDSF to report its new associated network.
4Conclusion

In this paper, we proposed two enhancements for current
ANDSF standard. The first proposal is MS localization based on
Wi-Fi and Cell-ID information. This method can achieve theaccuracy good enough for detecting Wi-Fi access point which isbest suitable for our experience scenario. We also proposed any
additional primitive for ANDSF system to help the ANDSF
server to keep track of associated point of server without any
modification to the existing network’s infrastructure andindependent to the access network technology. Your future
research is to evaluate our proposal and implementation inbigger scale in which we deploy multiple Wi-Fi access pointsand WiMAX. We want to evaluate the effectiveness of ourproposal in term of power saving for mobile device and loadbalancing and preventing congestion in heterogeneous networks.
References[1] Architecture enhancements for non-3GPP accesses,
3GPP TS 23.402, V11.0.0 Release 11, Sep 2011.
[2] Access Network Discovery and Selection Function,
3GPP TS 24.312, V11.0.0 Release 11, Sep 2011.
[3] “Funambol”, Funambol, Inc, http://www.funambol.com/