Patent Publication Number: US-2015071251-A1

Title: L2 tunneling based low latency single radio handoffs

Description:
BACKGROUND OF THE INVENTION 
     Mobile service providers already possess and operate several heterogeneous access technologies and networks. The mixed network environments are expected to become more prevalent as different radio technologies best serve different deployment types and environments. For example, Wi-Fi™ has shown to be a great technology for indoor operation, whereas cellular technologies such as 2G/3G (2 nd  Generation/3 rd  Generation) and WiMAX (Worldwide Interoperability for Microwave Access) operate best in licensed spectrum covering large outdoor environments. It is also expected that multi-mode wireless devices shall become widespread. Hence, it is of great interest to the mobile operators, technology users, and vendors to provide seamless mobility between these heterogeneous access technologies with uninterrupted service continuity. 
     The current technologies have focused on pure layer 3 (L3) mobility solutions such as Mobile IP (Internet Protocol). Although, these technologies support an inter-access mobility solution, the handoff delay could be extremely high. Furthermore, such L3 mobility procedures rely completely on the mobile device to make a handoff decision. These solutions rely on dual radio operation, i.e., both the radios involved in handover would be transmitting at the same time. However, this may not always be possible, because due to interference, platform noise and/or co-existence issues, it might only be possible to have a single radio operating at any point in time. 
     This disclosure proposes an alternative architecture to support a Single Radio Handover solution leading to tighter handover control and synchronization and overall lower latency of handovers and packet loss. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example of architecture for optimized single radio handover using L2 tunneling between WiMAX and 3GPP networks, utilized in an embodiment of this invention. 
         FIG. 2  shows a high level flow of Control Plane and Data Path setup Signaling between 3GPP and WiMAX networks, utilized by an embodiment of this invention. 
         FIG. 3(   a ) and (b) show the detailed low latency handover flow from E-UTRAN to WiMAX networks, based on L2 tunneling between WiMAX and 3GPP, utilized by an embodiment of this invention. 
         FIG. 4  shows an example of architecture for optimized single radio handover using L2 tunneling between WiMAX and legacy 2G/3G networks (via 3GPP), utilized in an embodiment of this invention. 
         FIG. 5  shows the low latency handover flow from WiMAX to legacy 2G/3G networks based on L2 tunneling between WiMAX and 3GPP, utilized by an embodiment of this invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of this invention uses an alternative architecture to for single radio handover between two wireless networks such as WiMAX and 2G/3G/4G. This embodiment uses a Data Link Layer (L2) tunneling between the source/target and core (e.g., evolved packet core) networks to achieve a tighter handover control and synchronization, support for network initiated handoffs based on operator policy and Radio resource management (RRM), and overall lower latency of handovers and packet loss. In one embodiment, the actual path between the two entities is still IP based, but the tunnel carries L2 messages, as opposed to L3 messages. 
     In an embodiment of this invention, (referring to  FIG. 1 ), a user equipment (UE) ( 110 ), which is connected to a source wireless network such as an E-UTRAN (evolved-universal mobile telecommunication system (UMTS) terrestrial radio access network) ( 150 ) via an evolved-node B (eNB) ( 152 ), is handed over to a target wireless network, such as WiMAX ( 120 ). At the completion of the handover, UE will be able to communicate with an operator&#39;s IP services ( 140 ) (such as IP Multimedia Subsystem (IMS) and Packet Switch Service (PSS)) through a WiMAX Access Service Network (ASN) ( 122 ) and a Packet Data Network (PDN) gateway ( 136 ) (such as one in a 3 rd  Generation Partnership Project (3GPP) network ( 130 )). In this example, prior to handover, UE ( 110 ) communicates with the operator&#39;s IP services ( 140 ) though eNB ( 152 ), a Serving Gateway (S-GW) ( 134 ) in 3GPP ( 130 ) network, and the PDN Gateway ( 136 ). 
     To achieve this handover, in an embodiment, the WiMAX ASN ( 122 ) and a Mobility Management Entity (MME) ( 132 ) in the 3GPP core network ( 130 ) establish an L2 tunnel ( 124 ) to exchange control signals, such as pre-registration, pre-authentication, context transfer, and handover command, while UE ( 110 ) is still connected to the E-UTRAN ( 150 ). In an embodiment of this invention, a bearer path ( 126 ) is also set up between the WiMAX ASN ( 122 ) and the Serving Gateway ( 134 ) to use for data packet forwarding between the 3GPP and WiMAX networks. In one embodiment, the forwarded packets sent via this bearer path ( 126 ), e.g., from/to 3GPP network to/from WiMAX network, reduces the amount of re-transmission of the data packets, while UE ( 110 ) hands over the connection from the source to target network. 
     In an embodiment of this invention, the handover latency between the source and target networks is reduced by establishing the required control signaling before the actual handover of the data connection through the L2 tunnel connection. 
     A high level flow ( FIG. 2 ) used in an embodiment of this invention demonstrates the examples of one or more control signaling, such as Pre-Registration, Pre-Authentication, Context Transfer, and Handover Command, that are transmitted through L2 tunnel between a core network and a target network (or a source network), such as 3GPP and WiMAX networks, through networks elements, such as a 3GPP MME in 3GPP network and a WiMAX ASN Authenticator in WiMAX network. In one embodiment, one or more of such control signals are associated with the Control Plane. 
     An embodiment of this invention uses packet forwarding between a core network and a target network, such as 3GPP and WiMAX networks (e.g., see the packet forwarding flow illustrated in  FIG. 2 ). In an embodiment, the data packets are forwarded between network elements, such as a 3GPP Serving Gateway and WiMAX ASN Data Packet Forwarding (DPF), after a handover event occurs (e.g., when WiMAX ASN sends a Handover Command (response)). In one embodiment, the packet forwarding occurs through a bearer path setup during the control signaling. 
       FIG. 3(   a ) and ( b ) illustrate an example of a handover flow used in an embodiment of this invention using a Long-Term Evolution (LTE) access network, e.g., E-UTRAN, as the source network and WiMAX as the target network through 3GPP System Architecture Evolution (SAE) network. Prior to the handover, UE communicates to an IP cloud (IP services) via PDN Gateway/Home Agent (GW/HA). The user data flow between UE and PDN GW/HA through eNB (in E-UTRAN) and Serving Gateway (in 3GPP). 
     In one embodiment, one or more WiMAX system information elements are broadcast to UE from eNB or MME ( FIG. 3(   a )). In an alternate embodiment, UE obtains target network information (e.g., for WiMAX neighboring cells) in one or more ways, such as cached information, pulled or pushed information from services such as network access provider, network service provider operator, an operator&#39;s IP service, or any other service, from target network directly, or directly or indirectly from a “peer” UE. In one embodiment, the examples of one or more types of information obtained about a target network such as WiMAX are shown in Table 1. 
     In one embodiment, UE measures the radio parameter in a source network (e.g., E-UTRAN), and provides the source network (e.g., eNB) such measurement. 
     In one embodiment, UE starts measuring target network radio parameters, e.g., when the source network (e.g., E-UTRAN) parameter values fall below threshold, or alternatively, when UE receives a message from source network (e.g., eNB) to start radio measurement in target network. For example, in one embodiment, UE uses short occasional gaps in communications in E-UTRAN to temporarily turn off 3GPP radio (e.g., ˜10 msec) and perform measurement in WiMAX network with WiMAX ASN. In one embodiment, parameters such as Received Signal Strength Indication (RSSI), Carrier to Interference-plus-Noise Ratio (CINR), Cell Type, Quality of Service (QoS) Parameters are examined and a selection criteria is checked. 
     In one embodiment, the decision to handover to target network (e.g., WiMAX) is network initiated, e.g., based on operator policy, or Radio Resource Management (RRM). In an alternate embodiment, the decision to handover is determined by UE. In one embodiment, a source network element, e.g., eNB (in source network such as E-UTRAN), sends a handover preparation message to UE. In an alternate embodiment, such message is initiated by MME or other network elements. In an alternate embodiment, handover preparation is self-initiated by UE. 
     In one embodiment, an L2 tunnel is established between the core and the target (or source) network elements, e.g., between MME in 3GPP and WiMAX ASN, and UE communicates with one or more target network elements through this L2 tunnel. In one embodiment, this L2 tunnel is reused by the source/target networks for multiple handover events. In one embodiment, communication between UE and the target network element such as WiMAX ASN, is supported via tunneling in source network (e.g., via a E-UTRAN radio tunnel between UE and eNB, and a tunnel between eNB and MME), in addition to L2 tunnel between core network and target network (e.g., MME in 3GPP and WiMAX ASN). 
     In an embodiment, UE performs registration with target network through L2 tunnel, e.g., in one embodiment, UE performs WiMAX Registration with WiMAX ASN. In one embodiment, UE and the target network element (e.g., WiMAX ASN) communicate messages (e.g., Handover request/response) through L2 tunnel. 
     In one embodiment, UE and an authentication/authorization service such as HSS/AAA (Home Subscriber Server/Authentication, Authorization and Accounting AAA) perform a security action, such as pre-authentication, through L2 tunnel. 
     In one embodiment, context information is passed to target network, e.g., WiMAX ASN, to support handover. Examples of context information include: information to establish types of connection (e.g., voice, bursty), security attributes, MAC context, Proxy Mobile IP (PMIP) context, and other context information communicated via Feature Profile Types (FPTs). 
     In one embodiment, target network, e.g., WiMAX ASN, performs resource allocation/reservation for UE to support the UE handover. 
     In one embodiment, a target network element (e.g., WiMAX ASN) and source network element (e.g., Serving Gateway in 3GPP) setup a bearer path to forward packets to/from UE. 
     In one embodiment, target network, e.g., WiMAX ASN, sends Handover Command (or a Handover response) to UE, through L2 tunnel. In one embodiment, target network (e.g., WiMAX ASN) notifies core network (e.g., MME) of Handover command through L2 tunnel. Alternatively, UE notifies core network of Handover completion. 
     In one embodiment, a core network element (e.g., MME in 3GPP) sends a message to a core network gateway (e.g., Serving Gateway in 3GPP) to start forwarding data packets to target network through a bearer path. In one embodiment, after establishing the bearer path, Serving Gateway determines when UE has moved to target Radio Access Technology (RAT) based on HARQ/ARQ retransmissions (e.g., within 50 msec), in order to commence forwarding packets to target network through the bearer path. 
     In one embodiment, having received the handover command (response), UE switches its radio to target network, and completes network entry to target network. 
     Handover latency is the duration between UE receiving Handover command and UE completing target network entry. 
     In one embodiment, UE receives forwarded user data sent to target network via the bearer path. 
     In one embodiment, target network (e.g., WiMAX ASN) sends PMI Binding Update message to PDN Gateway/HA to receive the data for UE. At the completion of the handover, UE user data flows through target network (e.g., WiMAX ASN) and PDN Gateway. 
     In one embodiment of this invention (referring to  FIG. 4 ), a user equipment (UE) ( 410 ), which is connected to a source wireless network such as an WiMAX ( 420 ) via WiMAX ASN ( 422 ), is handed over to a target wireless network, such as UTRAN ( 460 ) (or GERAN ( 470 )). At the completion of the handover, UE will be able to communicate with an operator&#39;s IP services ( 440 ) through a 2G/3G network access, e.g., Serving GPRS Support Node (SGSN) ( 466 ), Serving Gateway ( 434 ), and a PDN gateway ( 436 ). 
     One embodiment uses a virtual eNB ( 438 ) in 3GPP network. In one embodiment, the virtual eNB has a Radio Network Controller (RNC) like functionality to allow UTRAN ( 460 ) (or GERAN ( 470 )) to take advantage of low latency L2 handoffs with little impact to legacy 2G/3G networks, SGSN or MME. 
     In one embodiment, the control signaling to handover from source network (e.g., WiMAX) to target network (e.g., UTRAN or GERAN) is performed through an L2 tunnel ( 424 ) between source network (e.g., WiMAX ASN ( 422 )) and 3GPP MME ( 432 ). In one embodiment, a bearer data path ( 426 ) is established for data packet forwarding between source network, e.g., WiMAX, and Serving Gateway ( 434 ) to pass the data packet during the handover. 
     In one embodiment, UE performs an attach procedure with MME in 3GPP through L2 tunnel from source network (e.g., WiMAX), without leaving source network. In one embodiment, the resources in target network are setup through SGSN ( 466 ). 
       FIG. 5  illustrate an example of a handover flow (e.g., through SAE network) used in an embodiment of this invention using WiMAX as the source network and UTRAN as the target network. Prior to the handover, UE communicates to an IP cloud via PDN Gateway and WiMAX ASN. 
     In one embodiment, the decision to handover from source network (e.g., WiMAX) to target network (e.g., UTRAN ( 460 ) or GERAN ( 470 )) is network initiated (e.g., based on network RRM and measurement of radio parameters in source and/or target network). 
     In one embodiment, source network (e.g., WiMAX ASN) sends UE a message to prepare for handover. In an alternate embodiment, UE initiates the handover process. 
     In an embodiment, UE performs an attach procedure (e.g., UTRAN attach procedure) with MME, Serving Gateway, and PDN gateway in 3GPP via an L2 tunnel established between source network (e.g., WiMAX ASN) and 3GPP MME and a tunnel within source network (e.g., WiMAX radio tunnel). 
     In one embodiment, MME sends resource setup request to the target access network (e.g., SGSN) to allocate resource for UE handover. 
     In one embodiment, MME sends an update message to Serving Gateway to update the location of UE. 
     In one embodiment, MME sends a Handover command to a virtual eNB which sends the Handover to UTRAN to UE via L2 tunnel to source network. 
     In one embodiment, source network (e.g., WiMAX ASN) and core network (e.g., Serving Gateway in 3GPP) elements establish a bearer path to forward packets to/from UE during handover. 
     In one embodiment, UE switches its radio to target network (e.g., UTRAN), and completes handover with target network access (e.g., SGSN), e.g., via Radio Resource Control (RRC) response message. In one embodiment, SGSN sends PMIP Proxy Binding Update to PDN Gateway. At this point, user data flows from UE through target network (e.g., in case of UTRAN ( 460 ), through NodeB ( 464 ) and RNC ( 462 ); or in case of GERAN ( 470 ), through Base Station Subsystem (BSS), including Base Transceiver System (BTS) ( 474 ) and Packet Control Unit/Base Station Controller (PCU/BSC) ( 472 )), 2G/3G network access (e.g., SGSN), 3GPP Serving Gateway, and PDN Gateway. 
     In one embodiment of this invention, UE is handed over from WiMAX network to E-UTRAN, through similar steps as shown in  FIG. 5 , and in similar architecture as shown in  FIG. 4 . However, the E-UTRAN resource allocation message is sent from MME to an eNB in E-UTRAN network, and UE upon receiving handover command, switches radio to E-UTRAN with Serving Gateway performing PMIP Binding Update with PDN Gateway for user data flow commence between UE and PDN Gateway through eNB (in E-UTRAN) and 3GPP Serving Gateway. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Examples of WiMAX System Information  
               
               
                 obtained by a UE (e.g., via broadcast 
               
               
                 at source network(s) such as E-URAN/UTRAN) 
               
            
           
           
               
               
               
            
               
                   
                 Type 
                 Description 
               
               
                   
                   
               
               
                   
                 Downlink 
                 Identifies the DL center carrier frequency of  
               
               
                   
                 (DL) center 
                 WiMAX neighboring cells. 
               
               
                   
                 carrier 
                 In one example, DL center carrier frequency  
               
               
                   
                 frequency 
                 is a multiple of 250 kHz. 
               
               
                   
                 Cell 
                 Identifies the size of cell bandwidth. 
               
               
                   
                 bandwidth 
                   
               
               
                   
                 Preamble 
                 Identifies the PHY-specific preamble for the  
               
               
                   
                 index 
                 WiMAX neighboring based station (BS). 
               
               
                   
                 BS ID 
                 Base Station ID is a global unique identifier  
               
               
                   
                   
                 for a WiMAX base 
               
               
                   
                   
                 station, as defined in the IEEE Std  
               
               
                   
                   
                 802.16-2004 and IEEE Std 
               
               
                   
                   
                 802.16e-2005 standard. The BS ID  
               
               
                   
                   
                 represents a logical instance of a 
               
               
                   
                   
                 PHY and MAC function providing  
               
               
                   
                   
                 802.16 radio connectivity services 
               
               
                   
                   
                 to an mobile station (MS)/subscriber  
               
               
                   
                   
                 station (SS) (equivalent to a 
               
               
                   
                   
                 single frequency sector of a physical base station). 
               
               
                   
                 NAP ID 
                 NAP (Network Access Provider)  
               
               
                   
                   
                 is a business entity that provides 
               
               
                   
                   
                 WiMAX radio access infrastructure  
               
               
                   
                   
                 to one or more WiMAX 
               
               
                   
                   
                 Network Service Providers (NSPs).  
               
               
                   
                   
                 A NAP implements this 
               
               
                   
                   
                 infrastructure using one or more  
               
               
                   
                   
                 Access Service Networks (ASNs). 
               
               
                   
                   
                 NAP ID is contained in the upper 24 bits of BS ID. 
               
               
                   
                 NSP ID 
                 NSP (Network Service Provider) is a business  
               
               
                   
                   
                 entity that provides 
               
               
                   
                   
                 IP connectivity and WiMAX  
               
               
                   
                   
                 services to WiMAX subscribers 
               
               
                   
                   
                 compliant with the Service Level Agreement  
               
               
                   
                   
                 it establishes with WiMAX subscribers. 
               
               
                   
                   
                 To provide these services, an NSP  
               
               
                   
                   
                 establishes contractual agreements with one 
               
               
                   
                   
                 or more NAPs. Additionally, an NSP may 
               
               
                   
                   
                 also establish roaming 
               
               
                   
                   
                 agreements with other NSPs and 
               
               
                   
                   
                 contractual agreements with third-party  
               
               
                   
                   
                 application providers (e.g. 
               
               
                   
                   
                 ASP or ISPs) for providing WiMAX  
               
               
                   
                   
                 services to subscribers. 
               
               
                   
                 MAC 
                 MAC Version specifies the version of. 
               
               
                   
                 Version 
                 IEEE 802.16 for BS/MS. 
               
               
                   
                 System 
                 This indicates the Mobile WiMAX  
               
               
                   
                 Version 
                 release as specified by the WiMAX Forum 
               
               
                   
                   
                 Mobile Air Interface System Profile. 
               
               
                   
                 Available 
                 This indicates the average ratio of 
               
               
                   
                 downlink 
                 non-assigned DL radio resources to 
               
               
                   
                 (DL) Radio 
                 the total usable DL radio resources. The average  
               
               
                   
                 Resources 
                 ratio shall be calculated over  
               
               
                   
                   
                 a time interval defined by the 
               
               
                   
                   
                 DL_radio_resources_window_size 
               
               
                   
                   
                 parameter. The reported average 
               
               
                   
                   
                 ratio will serve as a relative load indicator. 
               
               
                   
                 Available 
                 This indicates the average ratio of non-assigned  
               
               
                   
                 uplink (UL) 
                 UL radio resources to the total usable UL radio 
               
               
                   
                 Radio 
                 resources. The average ratio shall be 
               
               
                   
                 Resources 
                 calculated over a time 
               
               
                   
                   
                 interval defined by the 
               
               
                   
                   
                 UL_radio_resources_window_size  
               
               
                   
                   
                 parameter. The reported average 
               
               
                   
                   
                 ratio will serve as a relative load indicator. 
               
               
                   
                 Cell Type 
                 This specifies the cell size for  
               
               
                   
                   
                 hierarchical cell architecture. A lower 
               
               
                   
                   
                 value of “Cell Type” can represent a  
               
               
                   
                   
                 smaller value for cell size and a 
               
               
                   
                   
                 higher value of “Cell Type” can  
               
               
                   
                   
                 represent larger cell size. Based on 
               
               
                   
                   
                 the frequency of handovers, decision can  
               
               
                   
                   
                 be made to move to a larger 
               
               
                   
                   
                 cell (in case of high handover frequency)  
               
               
                   
                   
                 or to a smaller cell (in case 
               
               
                   
                   
                 of low handover frequency). 
               
               
                   
                 Optimized 
                 This flag specifies if optimized handover is  
               
               
                   
                 Handover 
                 supported by the 3GPP system. 
               
               
                   
                 Support 
                   
               
               
                   
                 Address of 
                 This specifies the address  
               
               
                   
                 Interworking 
                 of the inter-working function entity that 
               
               
                   
                 Function 
                 may be used in optimized handovers. 
               
               
                   
                 (IWF) 
               
               
                   
                   
               
            
           
         
       
     
     In one embodiment, target network (e.g., WiMAX) system information is broadcast in source access network e.g., 2G/3G/4G networks or Wi-Fi™ network, to facilitate network discovery and selection. 
     One embodiment of this invention achieves low latency handoffs between access networks with no need for simultaneous radio operation to reduce or eliminate issues related to co-existence and/or platform interference. 
     In one embodiment, a low latency L2 tunnel is established between core network and target (or source) access network, e.g., between 3GPP MME and WiMAX ASN, for control plane signaling. 
     One embodiment of this invention reduces inter-RAT handoff delays as the context and security parameters are transferred through networks in the preparation phase. In one embodiment, pre-registration, pre-authentication and context transfer to the target network is performed while UE is connected to source access network and maintains connections over the source access network. 
     In one embodiment, a bearer path is setup between core network and target (or source) network, e.g., between 3GPP Serving Gateway and WiMAX ASN data packet forwarding function. In one embodiment, once the handover command is sent, packet forwarding happens with lower latency leading to a much smoother handoff than with an L3 tunnel. In this embodiment, through L2 tunneling, the source is informed of final tunneled message (e.g., Handover Command) that the UE is moving to target RAT and/or the core network determines UE leaving the source network based on HARQ/ARQ retransmissions, e.g., within about 50 msec. Thus, in one embodiment, packet forwarding to target network commences within about 50 msec, whereas for L3 tunnel this could take about 1 second to detect. 
     In an embodiment of this invention, a virtual eNB (equivalent to RNC like functionality) allows UTRAN/GERAN networks to take advantage of low latency L2 handoffs with minimum impact to legacy 2G/3G networks (with minimal impact to SGSN and MME). 
     An embodiment of this invention uses low latency handovers between Mobile WiMAX and 2G/3G/LTE with a single radio transmitting at UE at any given point of time. One embodiment of this invention uses access independent network interfaces with L2 tunneling and single radio handover. 
     In an embodiment of this invention, UE is implemented in a (embedded or not-embedded) mobile device, e.g., a communication processor. In an embodiment of this invention, UE is implemented in products such as multi-mode radio product, laptop, mobile intelligent device, personal digital assistant, or mobile phone. 
     The embodiments above are provided to illustrate the invention. Other radio access networks, as source or target, are considered part of this invention. Examples of such radio networks include WiMAX, 2G/3G/LTE, GERAN, UTRAN, E-UTRAN, and Wi-Fi. 
     Any variations of the above teachings are also intended to be covered by this patent application.