Proximity-based Service Beyond 4G Network :
Peer-aware discovery and communications using
E-UTRAN and WLAN
Shiann-Tsong Sh...
A. Restricted Discovery
Restricted discovery use case [1] describes a basic scenario
for ProSe discovery. For restricted d...
in RAN (radio access) and SA (network architecture) will start
in 2013 following LTE release 12 schedule.
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WLAN Bearer Service External Bearer Service
Fig. 2. QoS Architecture for WLAN Direct...
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3GPP AAA
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Proximity-based Service Beyond 4G Network: Peer-aware discovery and communications using E-UTRAN and WLAN

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The arising Proximity-based applications and services represent a recent and enormous socio-technological trend that has been generating innovative business models for the mobile networks. This paper proposes a WLAN-based B4G network architecture for Proximity-based Service (ProSe) where WLAN serves as the direct communication path between user equipment. The peer-aware discovery and communication are supported by an integrated E-UTRAN (LTE radio plus core networks) and WLAN. The main advantages are faster time-tomarket and utilizing unlicensed spectrums for Proximity-based Services in beyond 4G network.

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Proximity-based Service Beyond 4G Network: Peer-aware discovery and communications using E-UTRAN and WLAN

  1. 1. Proximity-based Service Beyond 4G Network : Peer-aware discovery and communications using E-UTRAN and WLAN Shiann-Tsong Sheu∗§, Yi-Hsueh Tsai†¶, Yi-Ting Lin†, Kan-Chei Loa†, Tsing-Yu Tsai†‡, Chun-Che Chien†‡, and Dun-Cheih Huang∗ ∗Dept. Communication Engineering, National Central University, Taoyuan, Taiwan †Institute for Information Industry, Taipei, Taiwan ‡Graduate Institute of Communication Engineering, National Taiwan University, Taipei, Taiwan Email: stsheu@ce.ncu.edu.tw§, lucas@iii.org.tw¶ Abstract—The arising Proximity-based applications and ser- vices represent a recent and enormous socio-technological trend that has been generating innovative business models for the mobile networks. This paper proposes a WLAN-based B4G network architecture for Proximity-based Service (ProSe) where WLAN serves as the direct communication path between user equipment. The peer-aware discovery and communication are supported by an integrated E-UTRAN (LTE radio plus core networks) and WLAN. The main advantages are faster time-to- market and utilizing unlicensed spectrums for Proximity-based Services in beyond 4G network. Index Terms—proximity-based service, beyond 4G, device-to- device communication, service discovery, LTE, WLAN I. INTRODUCTION The arising ProSe applications and services represent a recent and enormous socio-technological trend that has been generating innovative business models for the mobile net- works. The purpose of these applications is to discover in- stances of the applications running in devices within proximity of each other, and ultimately exchange application-related information. Currently in 3G/4G networks, ProSe has been realized in a limited scope and functionalities through Over The Top (OTT) applications, e.g. Foursquare, Facebook, and other OTT applications. These applications enable ProSe with centralized servers combining with the location information supplied by Global Positioning System (GPS). However, GPS is not reliable in the indoor environment. Moreover, the OTT approach with centralized servers incurs undesired network overheads and latency for discovery and communication ser- vices. In short, the drawbacks of the OTT approach are un- scalable when the density of user equipment (UE) is high, unreliable when a user is indoor or requires low delay services, and un-sustainable for the operator that cannot control or build a business model to share the revenue from OTT providers. Long-Term Evolution (LTE), specified by 3rd Generation Partnership Project (3GPP) standard organization, has been se- lected as the technology for the 4G networks by vast majority of commercial wide area network (WAN) operators and public safety communities. However, current 3GPP LTE Release 10/11 specifications are only partially suitable for advanced ProSe applications and services for commercial and public safety usages, because all such traffic and signaling would have to be routed through the radio and core networks. Thus it impacts their performance and adds unnecessary load to the network while performing ProSe services. These limitations must be lifted in future LTE releases such that more advanced proximity-based applications could be enabled in beyond 4G (B4G) network. The general approach of resolution is to introduce direct device-to-device (D2D) communication into LTE, where all ProSe traffic would take the shortest path between two users. The existing LTE-based ProSe discovery and communi- cation would require fundamental adaptation of the LTE physical layer and radio. As compared with the LTE-based ProSe, this paper proposes a simpler approach that requires fewer adaptations at higher layers to quickly enable ProSe by using interworking architecture between Wireless Local Area Network (WLAN) and E-UTRAN (LTE radio plus core networks), where the WLAN is served for ProSe discovery and communication. The rest of this paper is organized as follows. First, Section II characterizes ProSe by several use cases, whilst Section III and IV depict current ProSe standard activities and existing technologies. Section V and VI illustrates proposed architecture in details with reference models and sequence charts. Finally, Section VII provides conclusions and potential research directions. II. PROXIMITY-BASED SERVICE USE CASES ProSe discovery and ProSe communication are two key technologies of the proximity-based services. Compared to the existing server-based location positioning on the 3G/4G networks, ProSe discovery directly seeks interesting targets in proximity without any location information. Similarly, ProSe communication provides a new service whose path is established between the UEs or via local routing through the base station without traversing the backhaul link and the core network. In general, ProSe could be best characterized by the following service scenarios and related business models.
  2. 2. A. Restricted Discovery Restricted discovery use case [1] describes a basic scenario for ProSe discovery. For restricted discovery, the ProSe dis- covery only operates with explicit permission from the UEs being discovered. A social networking application subscriber uses a ProSe-enabled UE to find his friends in proximity. For instance, Mary and John are friends, John and Peter are friends, but Mary and Peter are not friends. Mary, John, and Peter subscribe to a given social networking application that has a proximity-based discovery feature. As Mary’s UE comes into proximity of John’s and Peter’s UEs, Mary’s UE and John’s UE mutually detect each other in proximity. However, Mary’s UE and Peter’s UE do not detect each other though in proximity because they do not permit a UE to be discoverable by unrelated subscribers. After the restricted ProSe discovery, Mary could perform regular social-networking activities, e.g. transferring data or sharing photos, with John via the social networking application. Note that in order to allow Mary, John, and Peter directly discovering each other while their network service subscriptions might belong to different operators, a common operating frequency band among different operators for the proximity-based discovery services are required. B. Open Discovery Open discovery use case [1] describes a case in which an UE discovers another UE without permission by the discoverable UE. A local advertisement scenario [6], where a subscriber uses ProSe-enabled UE to find points of interest (POI), is used to illustrate the open discovery. Assume Mary carries her ProSe-enabled UE and stores of 7-Eleven, Starbucks, and McCafe equipped with ProSe- enabled UEs with a local advertisement application, which permits being discovered by any UEs. As Mary walks into the neighbourhood of a 7-Eleven store, Mary’s UE discovers the UE of 7-Eleven. Hence Mary is notified of the proximity of the 7-Eleven. Mary then decides to look for a coffee shop, and thus following interaction with her application, Mary is notified of the proximity of a Starbucks, whose UE was discovered by Mary’s UE. Note that during the discovery process, Mary is not notified of the proximity of other establishments not found of interest to her. Generally, after discovery, Mary’s UE should reveal its identity to the UE of the store in order to establish a ProSe communication session with the UE of the store for retrieving further advertised information (texts, coupons, pictures, video clips, and other information). One way to address this privacy concern of revealing user’s identification is to smartly combine anonymous discovery with the digital signage in the local advertisement setup depicted below. Assume that a digital signage in the neighborhood is used to display advertisements of the 7-Eleven, Starbucks and McCafe and is equipped with a ProSe-enabled UE. As Mary walks into the viewing range of the digital signage, the digital signage is notified of the event that an anonymous user, who had discovered the Starbucks, is within its proximity. The ProSe-enabled UE of the digital signage interactively displays the Starbucks’ related information to Mary without knowing the identity of Mary’s UE. In this case, Mary anonymously found all related information of her preferred coffee shop on the digital signage with only light-weighted ProSe discovery signals without invoking any ProSe communications at all. In practice, the open discovery could create a new business model of value-added services where the operator is able to receive local advertisement revenues from the store owners, who could use these ProSe services for free. A ”free” ProSe service would further motivate more users to use the local advertisement service that in turn generates more revenues for the operator. C. Service Continuity This use case depicts service continuity between the net- work infrastructure and the direct communication path. In this use case, ProSe discovery and communication are used to seamlessly offload traffic from the infrastructure network when two UEs are within proximity. Assume Mary and Peter use ProSe-enabled UEs and they are engaged in a data session that is being routed over the operator’s core network infrastructure. As Peter moves within proximity of Mary, Peter and Mary’s UEs discover each other and the data session is switched to a proximity-based communication path between them. When Peter moves out of the proximity of Mary, the data session is switched back to the infrastructure path. Importantly, the switching of the data session would not perceived by the users at all. III. PROXIMITY-BASED SERVICE IN 3GPP AND IEEE 3GPP and Institute of Electrical and Electronics Engineers (IEEE) are currently in the process of studying Proximity- based Service. A. 3GPP 3G/4G WANs, the 3GPP dominating technologies, have vast opportunity to promote future and more advanced proximity- based applications by becoming the platform to enable proximity-based discovery and communication between de- vices. The feasibility study item of ProSe has been created in 3GPP Technical Specification Group (TSG) Service and System Aspects Working Group 1 (SA1) since 2011, where use cases and service requirements are being studied, includ- ing network operator control, authentication, authorization, accounting, and regulatory aspects [1]. The objectives of this study item are to study use cases and identify potential requirements for an operator network which devices are in proximity under continuous controlled 3GPP networks coverage. The scopes of the study include commercial/social use, network offloading, public safety, and integration of current infrastructure services to assure the consistency of the user experience including reachability and mobility aspects. The ProSe study in SA1 is scheduled to be completed by the end of 2012. It is expected that studies on ProSe solutions
  3. 3. in RAN (radio access) and SA (network architecture) will start in 2013 following LTE release 12 schedule. B. IEEE Infrastructure Service Discovery (ISD) Study Group [7] is created within the IEEE 802.11 working group to address the problem of how a station, e.g., a mobile device, discovers the availability of services within the network from another station, e.g., the associated Access Point (AP). During the meeting held in May 2012, the ISD SG concludes to schedule the PAR for review and vote in July 2012. IV. EXSTING PROXIMITY-BASED SERVICE TECHNOLOGIES A. WLAN The IEEE 802.11 standard supports two operating modes, the infrastructure mode and ad-hoc mode. The former provides users the Internet connections and the latter is a simple method for wireless devices to directly communicate with each other without the assistance from AP. Currently, the Wi-Fi Alliance has developed a new specification, called the Wi-Fi Direct or Wi-Fi Peer-to-Peer (P2P) [8], for directing Wi-Fi connections between client devices which may have associated with AP(s). However, the 802.11 STAs adopting ad-hoc mode and P2P mode still rely on the active scan procedure to retrieve the Layer-2 neighborhood information, including the service set ID (SSID), basic service set capability, security suites, and other information. Lacking the precise ProSe information would force a station to establish Layer-2 connection with every neighbor in order to determine whether there is any desired ProSe service provided in the peer device. How to quickly enable the ProSe service over WiFi P2P networks is still an open and interesting issue. B. Bluetooth A specific service discovery protocol (SDP) is needed in the Bluetooth environment, as the set of available services would change dynamically due to the RF proximity of devices in motion. More specifically, such SDP provides a means for applications to discover which services are available and to determine the characteristics of those available services. The major problem with Bluetooth SDP is that every SDP client must first establish an L2CAP connection and then an SDP connection with SDP server before attempting to discover a designated service. If both SDP client and server are slaves in a piconet, the client has to form a new piconet and act as a master of this piconet for inviting the server to be the slave of this piconet. Such burden procedure definitely impacts the user experience. C. FlashLinQ FlashLinQ [2]-[3] is a proprietary Qualcomm technology using synchronous OFDM-based physical layer for direct D2D communication that supports device discovery over a 1 km range and can discover a few thousands devices within 8 sec- onds. FlashLinQ exploits existing cellular network as a global WLAN 3GPP IP Access 3GPP Home Network WLAN Access Network WLAN UE Ww HSS HLR Offline Charging System OCSWa Wn Wx D' / G r' Wf Wo Wi Intranet / Internet Wm WAG Wp PDG Wg Wu Dw SLF 3GPP AAA Server Wy Wz Fig. 1. 3GPP/WLAN interworking reference model [4]. timing synchronization sources. Each mobile device advertises its presence and discovers other D2D devices autonomously and continuously without any group owner. Single carrier based discovery signal in FlashLinQ prolongs discovery range and standby time. A key feature of the D2D communication in FlashLinQ is the cross-layer PHY/MAC mechanism that utilizes analog signaling to enable distributed channel-aware spatial resource allocation and scheduling through analog signaling. FlashLinQ could coexist and share the resource with an existing cellular network. Therefore, the operation of FlashLinQ requires licensed spectrum allocation by the network operator. V. PEER-AWARE DISCOVERY AND COMMUNICATIONS USING E-UTRAN AND WLAN TECHNOLOGIES Albeit 3GPP ProSe enables LTE subscribers to discover and communicate with other subscribers in proximity under continuous operator network control, there is no restriction on the radio access technology used for the data plane of the direct communication. Therefore, ProSe could conceivably be implemented by integrating WLAN with the 3GPP system, where the 3GPP system is used for network control and the WLAN is used for data exchange. Enabling WLAN for ProSe in 3GPP systems can be achieved by adding ProSe functionalities to existing LTE/WLAN interworking mechanisms (I-WLAN), which have been defined in 3GPP specifications in Release 6. Even though the communication between UEs is traversing through WLAN, the control is not taken away from the operator. Actually this scheme extends the operator’s control by placing the WLAN connections of the UE under the operator’s man- agement for D2D services, which effectively expands the operator’s network and, consequently, improves the operator’s service capabilities and diversity. Access Network Discovery and Selection Function (ANDSF) facilitates a UE to choose the best access network that in turn assists the operator to manage network resources without losing the ability to control and charge for wireless access through WLAN. Proximity- based discovery and direct communication over WLAN is particularly well suited to offload ProSe traffic, since it allows a 3GPP operator to divert traffic and interference from the 3GPP radio access network. The distinct features of using WLAN for direct mode in ProSe are: • utilizing unlicensed spectrum for direct communication,
  4. 4. WLAN UE WLAN AN TE End-to-End Service WLAN Bearer Service External Bearer Service Fig. 2. QoS Architecture for WLAN Direct IP Access [4]. • designating a common WLAN spectrum for UEs camped on different Public Land Mobile Networks (PLMNs). A. Basic interworking reference model and direct IP access In 3GPP TS 23.234 [4], it specifies system description for interworking between 3GPP systems and WLANs. The intent of 3GPP/WLAN interworking is to extend the 3GPP services and functionality to the WLAN access environments. The 3GPP/WLAN interworking System provides bearer services allowing a 3GPP subscriber to access 3GPP packet switch (PS) based services with WLANs. The basic 3GPP and WLAN interworking reference model is shown in Fig. 1. Fig. 2 shows the QoS architecture of WLAN Direct IP Access defined in 3GPP TS 23.234. The End-to-End Service provides transport of the signaling and user data between the WLAN UE and another (external) terminal equipment (TE) or correspondent node passed over different bearer services of the network. B. E-UTRAN/WLAN interworking reference model According to 3GPP TS 22.234 [5], the 3GPP system shall support WLAN UE concurrent connections to both WLAN and 3GPP system. Based on the 3GPP-WLAN interworking reference model in Fig. 1, the proposed reference model for two WLAN UEs simultaneously connecting to both WLAN and E-UTRAN is illustrated in Fig. 3, where the direct communication between two WLAN UEs can be realized by WLAN Direct IP Access, as shown in Fig. 2, through the WLAN access network (i.e., the Ww interface). C. Scenario for E-UTRAN and WLAN interworking A scenario regarding ProSe using E-UTRAN and WLAN interworking demonstrates the operator’s control over E- UTRAN and WLAN interworking is addressed as follows. While walking down the street, Sam’s ProSe-enabled UE is aware of point of interest (POI) in proximity by proactively detecting or being informed by the 3GPP network. Sam has previously specified his preferences in his configuration. Thus, he continuously receives announcements, advertisements and special offers, matching his preference, in various media formats via the E-UTRAN or WLAN. As Sam moves, POIs continuously move in and out of WLAN range of his UE. While being nomadic, Sam’s UE communicates with an enhanced ANDSF to dynamically discover and select an optimized WLAN network for ProSe based on operator policy and his UE profile. As Sam’s POIs move in and out of WLAN range, the operator maintains the continuity and QoS of Sam’s sessions by monitoring the sessions via periodic updates from WLAN access network WLAN UE eNB SG PDG PCRF Operator IP ServicesMME HSS S1u S5 S7 LTE-Ub S1-MME S6a Rx+ SGi S11 LTE-Ub SGi WLAN UE WAG 3GPP AAA Server Wn Sp OCS Intranet / Internet Wy Wo Wg Wm Wa Wx SLF HLR Dw D'/Gr' Offline Charging System Wf Wz Wu WwWw Wu Fig. 3. E-UTRAN/WLAN interworking reference model. the UEs and by moving the sessions back to the E-UTRAN when/if the performance falls below some acceptable level. Since each access network connection, E-UTRAN or WLAN, is authorized by the operator’s evolved packet core (EPC), ProSe via WLAN is charged by the operator accordingly. VI. PROXIMITY-BASED PEER-AWARE DISCOVERY AND COMMUNICATION VIA WLAN Scenario 1: ProSe Discovery via two WLAN APs Based on Figure 3, the reference model for two WLAN UEs perform ProSe via two WLAN APs is shown in Fig. 4. The following procedure is proposed to perform proximity- based discovery piggyback on legacy WLAN registration pro- cedure to the Authorization, Authentication, and Accounting (AAA) server. 1) The ProSe-enabled application registers to the ProSe module of the WLAN UE. 2) The ProSe module of the WLAN UE registers to the ProSe AAA via a WLAN AP. 3) The WLAN AP is notified the ProSe capability infor- mation of the WLAN UE from the ProSe AAA server. 4) The WLAN UE sends the application information of the user to the WLAN AP. 5) The WLAN AP updates the application information of the user to other WLAN AP(s) in proximity via inter-AP protocol (IAPP). 6) The WLAN AP updates the neighbor WLAN UE’s (e.g. matched WLAN UE) application information of the user to the WLAN UE. 7) The WLAN UE notifies the applications the list of users who are in proximity. Moreover, in Fig. 4, GLMC (Gateway Mobile Location Centre) requests routing information from HLR and HSS to support LCS (LoCation Service). LEMF (Law Enforcement Monitoring Facility) and DF2 (Delivery Function 2) support operators to perform lawful interception for WLAN peer-to- peer communication. An example of the sequence chart is shown in Fig. 5 where the detailed descriptions are given as follows.
  5. 5. OCS Wo WAG Wn Internet Wa Offline Charging System Wf Wn Wa WLAN AN 3GPP AAA Server Wg User#1 APP User#2 APP WLAN UE#1 WLAN UE#2 ProSe Module ProSe Module Ww Ww ProSe AAA WLAN AP#2 ProSe FB#2 WLAN AP#1 ProSe FB#1 ProSe CB ProSe Server Wp2p GMLC La LRF ProSe Centre DF2 LEMF Fig. 4. ProSe discovery via WLAN APs. Assume that Mary and Peter have carried ProSe-enabled UEs with WLAN capability and subscribed to the same operator with ProSe. As soon as the WLAN AP connects to the 3GPP network, the ProSe function block (FB) in WLAN AP registers to the ProSe AAA server. When user, e.g., Mary or Peter, starts a proximity-based application, the application first registers to the ProSe module in user’s UE, and then the ProSe module confirms the registration. Upon user’s WLAN UE detecting a WLAN AP, the WLAN UE connects to network via the WLAN AP. Afterward, user’s UE registers to 3GPP AAA server via WLAN AP, and the ProSe module in user’s UE also registers to the ProSe AAA server at the same time. The ProSe AAA server sends back the ProSe capability information of user’s WLAN UE to the ProSe FB in the associated WLAN AP. Furthermore, the ProSe FB in WLAN AP requests the WLAN UE for application information of the user such as user friend list, and then the ProSe module in user’s WLAN UE sends those to the WLAN AP. Afterward, the ProSe FB in WLAN AP updates the application information of the user to other WLAN AP(s) in proximity. As Mary’s and Peter’s ProSe-enabled WLAN UEs have completed the above procedure, the ProSe FBs in the corresponding WLAN APs are aware of that Mary and Peter are associated. Then the ProSe FBs in corresponding WLAN APs send the ProSe information to the Mary’s UE and Peter’s UE, respectively. After receiving the ProSe information, the ProSe module in user’s WLAN UE notifies the user that his/her friend(s) is in proximity. Furthermore, instead of sending the ProSe information to Mary’s and Peter’s UEs directly, the ProSe FBs in corresponding WLAN APs can request those WLAN UEs to scan neighbors directly via WLAN peer-to- peer discovery. The sequence chart of WLAN peer-to-peer discovery is shown in Fig. 6. Scenario 2: ProSe Discovery via WLAN Group Owner In addition to ProSe discovery via WLAN APs, ProSe discovery can be perform through WLAN peer-to-peer dis- covery, where WLAN AP operates as a WLAN peer-to-peer Same procedures between WLAN UE#2, WLAN AP#2 and AAA Server Peter s APP Peter s UE Register to P2P Module turn on Confirm ProSe Module WLAN AP#1 ProSe FB#1 3GPP AAA Server WAG turn on Register to ProSe AAA Confirm Register to 3GPP AAA Server Send information of Mary s UE To ProSe FB#1 Mary s APP Mary s UE Register to P2P Module turn on Confirm ProSe Module Confirm Confirm Connected to WLAN AP WLAN AP Synchronization & Indication Register to ProSe AAA Confirm Mary and Peter are relatedMary s UE is detected Peter s UE is detected Peter s UE is detected Mary s UE is detected ProSe AAA WLAN AP#2 ProSe FB#2 turn on Register to ProSe AAA Confirm Update Mary s Info. to FB#2 Request for Mary s information Mary s information Mary and Peter are related Fig. 5. Sequence chart of WLAN AP-assisted discovery. Peter s APP Peter s UE ProSe Module WLAN AP#1 ProSe FB#1 Mary s APP Mary s UE ProSe Module Request to scan neighbor (search for Mary s UE) Request to scan neighbor (search for Peter s UE) Peter s UE is detected Mary s UE is detected WLAN AP#2 ProSe FB#2 Update Mary s Info. to FB#2 Update Peter s Info. to FB#1 Same procedures for WLAN peer-to-peer discovery Mary and Peter are related Fig. 6. Sequence chart of WLAN peer-to-peer discovery. group owner [8]. The following procedure is proposed to perform proximity-based discovery via WLAN peer-to-peer technology shown in Fig. 7, where the ProSe server provides Proximity-based service and controls the signaling, including ProSe discovery, network communication selection, network security, and other service and controls. 1) The ProSe-enabled application registers to the ProSe module of the WLAN UE. 2) The WLAN UE joins the WLAN peer-to-peer group established by WLAN AP as a WLAN GO (WLAN group owner). 3) WLAN GO exchanges member information to every WLAN UE, and the WLAN UEs detect all together in proximity. 4) The ProSe modules of WLAN UEs register to ProSe AAA server via WLAN GO. 5) The AAA server sends WLAN UEs’ information to ProSe server. 6) ProSe server requests for WLAN UEs’ information from WLAN UEs. An example of the sequence chart is shown in Fig. 8 where the detailed descriptions are given as follows. Assume that Mary and Peter have carried ProSe-enabled UEs with WLAN peer-to-peer capability under a WLAN AP acting as a WLAN peer-to-peer group owner. As soon as the WLAN GO connects to the 3GPP networks, the ProSe FB if
  6. 6. WAG User#1 APP ProSe Module WLAN UE#1 User#2 APP ProSe Module WLAN UE#2 ProSe AAA 3GPPAAA Server OCS Offline Charging System ProSe Server LEMF DF2 Internet Wn Wp2p Wg Wo Wf ProSe Module WLAN GO P2P Module Wp2p Wp2p WLAN AP as WLAN GO Wa Fig. 7. ProSe discovery via WLAN AP as group owner with ProSe server. the WLAN GO registers to the ProSe AAA server. After syn- chronizing with WLAN UEs, users’ UEs join the WLAN GO. Through periodical synchronization, the WLAN GO updates Mary’s and Peter’s member information to Peter and Mary, respectively. After completing the procedure above, Mary’s and Peter’s UEs detect each other in proximity, enabling to perform WLAN peer-to-peer communication. Afterward, users’ UEs register to 3GPP AAA server, and the ProSe modules of UEs register to ProSe AAA server. The ProSe AAA server then sends users’ UEs information to ProSe server. Finally, the ProSe server requests UEs to send APP’s information, and the ProSe modules of UEs response with APP’s information and geometry location information of the UEs to ProSe server. Moreover, the Mary’s and Peter’s UEs can also be detected by other ProSe-enabled UEs via both WLAN peer-to-peer discovery and WLAN AP assisted discovery. VII. CONCLUSIONS The emerging LTE-based proximity-based service (ProSe) discovery and communications would require fundamental adaptation of the LTE physical layer (PHY) and radio. Taking standardized procedure in 3GPP to make major change in PHY and radio will normally take several years to complete. As a consequence, the products will take another several years to be available in the market, and more time on top of that to ensure a large enough device population for any LTE-based ProSe to be viable. Nowadays, WLAN-based offload solutions are already embedded in smart phones and supported by 3G/4G networks. As compared with the LTE-based ProSe, this paper proposes a simpler approach that only requires few adaptations at higher layers to quickly enable ProSe via standardized 3GPP/WLAN interworking solution. The faster time-to-market envisioned solution will provide operators a chance to capture a portion of the Over The Top (OTT) proximity service market much earlier than an LTE-based ProSe solution. The proposed scheme also allows network operators that do not have licensed spectrum allocated for ProSe usage to deploy ProSe. turn on Same procedures between Peter's UE, WLAN GO, AAA Server & ProSe Server Mary's APP Mary's UE ProSe Module Peter's APP Peter's UE ProSe Module WAG 3GPPAAA Server ProSe AAA Register to P2P Module Confirm Register to ProSe AAA Register to 3GPPAAA Server Register to ProSe AAA via WLAN GO Confirm Confirm Mary's & Peter's UE can be detected by other ProSe-enabled UEs WLAN GO ProSe FB P2P Module ProSe Server Register to ProSe Server Confirm Register to P2P Module Confirm Synch. & WLAN GO Info. turn on Synch. & WLAN GO Info.turn on Notify WLAN GO detected Notify WLAN GO detected Join WLAN GO Send Mary's Info. Join WLAN GO Send Peter's Info. Synch. & WLAN GO Info. Synch. & WLAN GO Info. t0 Update Peter's member Info. Update Mary's member Info. Notify Peter's UE & Peter detected Notify Mary's UE & Mary detected Confirm Confirm Send Mary's Info. Request for Mary's Info. Send Mary's Info. to ProSe Server Fig. 8. Sequence chart of ProSe discovery via WLAN GO with ProSe server. Finally, WLAN-based ProSe solution is a fertilized ground for innovations. Challenges for beyond 4G ProSe evolutions might include, but not limited to, low-power-always-on ProSe discovery, WLAN and LTE radio integrations, New Carrier Type (NCT) of LTE for direct communication, and non- orthogonal radio design for high performance ProSe. ACKNOWLEDGEMENT The authors of this paper would like to thanks participants of 3GPP SA1 FS ProSe for their constructive inputs and debates on ProSe use cases and requirements. REFERENCES [1] 3GPP TR 22.803 V0.3.0 “Feasibility Study for Proximity Services (ProSe) (Release 12),” May. 2012. [2] M. S. Corson, J. Li, V. Park, T. Richardson and G. Tsirtsis, “Toward Proximity Aware Internetworking,” IEEE Wireless Communications, pp. 26-33, Dec. 2010. [3] F. Baccelli, N. Khude, R. Laroia, J. Li, T. Ricahrdson, S. Shakkottai, S. Tavildar, X. Wu, “On the design of device-to-device autonomous discovery,” 10.1109/COMSNETS.2012.6151335, pp. 1-9, Dec. 2012. [4] 3GPP TS 23.234 V10.0.0 “3GPP system to Wireless Local Area Network (WLAN) interworking; System description (Release 10),” Mar. 2011. [5] 3GPP TS 22.234 V10.0.0 “Requirements on 3GPP system to Wireless Local Area Network,” Sep. 2012. [6] 3GPP SA1 No.58 S1-121152 “Enhanced Open Discovery Use Case,” Jun. 2012. [7] http://www.ieee802.org/11/Reports/isd update.htm [8] WF-P2P1.1 “Wi-Fi Peer-to-Peer (P2P) Technical Specification Version 1.1,” Mar. 2011.

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