Key points for interoperability of LTE and eHRPD hybrid networks

In the early stage of LTE deployment, most of them adopt the hybrid networking mode with 3G. In the case of imperfect LTE coverage, the interoperability solution of LTE and 3G data services can effectively reduce LTE investment, ensure LTE user data service experience, and protect 3G network investment. At present, 3G HRPD (high speed packet network) cannot directly interoperate with LTE for data services and needs to be upgraded to eHRPD (evolved high speed packet network).

　　3G Network eHRPD Upgrade

　　eHRPD is an evolution and enhancement of the original HRPD. It enhances the ability of 3G networks to carry data services, improves network integration, and makes more rational use of resources, with relatively little change to the wireless side. The eHRPD network architecture can be divided into three types: non-roaming network architecture, roaming Home Routed scenario network architecture, and Local Breakout scenario network architecture. From HRPD to eHRPD, relevant network elements need to be upgraded, including AN/PCF upgrade to eAN/ePCF, PDSN upgrade to HSGW (HRPD Serving Gateway), and base station BTS software upgrade to support eHRPD.

　　The advantages of eHRPD include: support for interoperability with LTE data services, can use the same core network as LTE, easy maintenance and management, and reduced operating costs. The new features of eHRPD include: support for terminal UE to establish multiple PDN connections at the same time, support for network-side initiated QoS, support for bearer multiplexing; eHRPD is compatible with HRPD and has no impact on existing users; new eHRPD users need to update their terminals and SIM cards.

　　eHRPD and LTE data service interoperability

　　QoS requirements for mobile data services

　　There are many types of mobile data services, and the service quality QoS required by various services is also different. Service quality QoS mainly includes indicators such as bit error rate, delay, throughput, reliability and security. According to different QoS characteristics, data services can be divided into conversational, streaming, interactive and background services.

　　(1) Conversational services: They require the time correlation between information entities in the traditional mode to be maintained, and they strictly require low latency. For example, the latency of IM service interaction should be less than 200ms, and the latency of online games should be less than 20ms.

　　(2) Streaming media services: Ensure a certain time correlation between information entities in the media stream. Usually, the delay is required to be within 5 seconds. For example, streaming media playback requires a delay of less than 1 second.

　　(3) Interactive services: The request-response mode is adopted, and the data integrity must be guaranteed. The total round-trip delay cannot be too large, usually between 1 and 4 seconds. For example, the web browsing click delay is less than 1 second, and the Weibo interaction delay is less than 3 seconds.

　　(4) Backend services: require data integrity to be ensured and have lower requirements on data sending and receiving time. For example, the delay of backend email can be >10s.

　　LTE and eHRPD interoperability

　　Currently, the 3GPP standard defines bidirectional handover between LTE and eHRPD, including optimized and non-optimized handover in active/dormant states. The 3GPP2 standard defines unidirectional handover from LTE to eHRPD (including optimized and non-optimized handover in active/dormant states), as well as non-optimized handover from eHRPD to LTE in idle state.

　　The data service interoperability between LTE and eHRPD needs to consider the impact of handover delay. The optimized handover delay can be less than 1 second, but the implementation is more complicated and requires the addition of S101 and S103 interfaces. The non-optimized handover delay is 6 to 8 seconds, the S101 and S103 interfaces are not used, and tunneled signaling is not used between the target access network and the original service network.

　　Evolution strategy of eHRPD

　　In the early stage of LTE network deployment, the hybrid networking with 3G is mainly adopted. In order to save LTE investment and ensure LTE user perception, the original HRPD network needs to be upgraded to the eHRPD network to achieve interoperability between LTE and 3G data services. The evolution of the HRPD network to the eHRPD network needs to meet the continuity of data service bearer according to the deployment of LTE. It takes a long time for HRPD users to migrate to LTE/eHRPD users. In order to protect the investment in HRPD network and not affect the use of existing HRPD services, it is necessary to ensure the smooth evolution of the HRPD network to eHRPD. In the 3GPP2 standard, the eHRPD network and the EPC network are unified. The upgrade deployment of HRPD network elements (such as PDSN/HSGW, HA/PGW) and the introduction of new functions (PCC architecture, QoS control, multi-PDN, etc.) need to take into account the evolution architecture of the next generation mobile network.

　　In the early stage of LTE deployment, part of the original HRPD network can be upgraded to an eHRPD network, and a small-scale LTE and eHRPD core network can be newly built and superimposed and coexist with the HRPD core network. There will be fewer LTE/eHRPD dual-mode terminal users.

　　In the mid-term of LTE deployment, as the scale of LTE network expands, all the original HRPD networks will be upgraded to eHRPD networks to meet the data service interoperability requirements with LTE, realize the integration of some network elements of HRPD and eHRPD networks, such as jointly setting up HSWG/PDSN, and vigorously develop LTE/eHRPD dual-mode terminal users.

　　In the early stage of LTE network deployment, the hybrid networking with 3G is mainly adopted. In order to save LTE investment and ensure LTE user perception, the original HRPD network needs to be upgraded to the eHRPD network to achieve interoperability between LTE and 3G data services. The evolution of the eHRPD network needs to take into account the deployment rhythm of LTE. At present, the switching delay between eHRPD and LTE still needs to be improved.