In the initial stage of LTE deployment, most of them use a hybrid networking method 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's HRPD (High Speed ​​Packet Network) cannot directly interoperate with LTE for data service switching and needs to be upgraded to eHRPD (Evolved High Speed ​​Packet Network).
3G network eHRPD upgrade
eHRPD is the evolution and enhancement of the original HRPD. eHRPD enhances the 3G network's ability to carry data services, improves network convergence, enables more reasonable use of resources, and makes less changes to the wireless side. The eHRPD network architecture can be divided into three types: non-roaming network architecture, Home Routed scenario and Local Breakout scenario network architecture during roaming. From HRPD to eHRPD, related network elements need to be upgraded, including AN / PCF to eAN / ePCF, PDSN is upgraded to HSGW (HRPD Serving Gateway, HRPD service gateway), base station BTS software is upgraded 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 reduce operating costs. New features of eHRPD include: support for terminal UE to establish multiple PDN connections at the same time, support for network side to initiate QoS, and support for bearer multiplexing; eHRPD is compatible with HRPD and has no effect on original users; new eHRPD users need to update terminals and SIM cards.
Interoperability between eHRPD and LTE data services
QoS requirements for mobile data services
There are many types of mobile data services, and the quality of service QoS required by various services is also different. The quality of service QoS mainly includes: bit error rate, delay, throughput, reliability and security. According to different characteristics of QoS, data services can be divided into conversational, streaming, interactive, and background services.
(1) Conversational business: It is required to ensure the time correlation between the information entities of the traditional model, and strict requirements for low latency, such as IM service interaction delay <200ms, online game delay <20ms.
(2) Streaming media services: to ensure a certain time correlation between the information entities of the media stream, usually requiring a delay within 5s, for example, streaming media playback requires a delay of <1s.
(3) Interactive services: A request-response model is used to ensure the integrity of the data. The total loopback delay should not be too large, usually within 1 to 4s, for example, webpage browsing click delay <1s, microblog interaction delay < 3s.
(4) Background service: It is required to ensure the integrity of the data, and the time for sending and receiving data is relatively low. For example, the time delay of the background email can be more than 10s.
LTE and eHRPD interoperability
Currently, the 3GPP standard defines two-way handover between LTE and eHRPD, including optimized and non-optimized handovers in the active / sleep state. The 3GPP2 standard defines unidirectional handover from LTE to eHRPD (including optimized and non-optimized handover including active / sleep state), and idle non-optimized handover from eHRPD to LTE.
The data services of LTE and eHRPD interoperate, and the impact of handover delay needs to be considered. The optimized switching delay can be less than 1 second, but the implementation is more complicated, and the S101 and S103 interfaces need to be added. The non-optimized handover delay is 6 to 8s. The S101 and S103 interfaces are not used. Tunneled signaling is not used between the target access network and the original service network.
eHRPD's evolution strategy
In the initial stage of LTE network deployment, a hybrid networking with 3G is mainly adopted. To save LTE investment and ensure LTE user perception, the original HRPD network must be upgraded to an eHRPD network to realize the interoperability of LTE and 3G data services. The evolution of the HRPD network to the eHRPD network needs to meet the continuity of data service bearers according to the deployment of LTE. The migration of HRPD users to LTE / eHRPD users has a long process. In order to protect HRPD network investment and not affect the use of existing HRPD services, it is necessary to ensure the smooth evolution of HRPD network to eHRPD. In the 3GPP2 standard, the eHRPD network and the EPC network tend to be unified, and the upgrade deployment of HRPD network elements (such as PDSN / HSGW, HA / PGW) and the introduction of new functions (PCC architecture, QoS control, multiple PDN, etc.) need to be considered Consider the evolution architecture of the next generation mobile network.
In the early stage of LTE deployment, the original HRPD network can be partially upgraded to an eHRPD network, and small-scale LTE and eHRPD core networks are newly built and coexist with the HRPD core network. There are fewer LTE / eHRPD dual-mode end users.
In the mid-term of LTE deployment, with the expansion of the LTE network scale, all the original HRPD networks were upgraded to eHRPD networks to meet the data service interoperability requirements with LTE, and to achieve the integration of some network elements of the HRPD and eHRPD networks. PDSN, vigorously develop LTE / eHRPD dual-mode end users.
In the initial stage of LTE network deployment, a hybrid networking with 3G is mainly adopted. To save LTE investment and ensure LTE user perception, the original HRPD network must be upgraded to an eHRPD network to realize the interoperability of LTE and 3G data services. The eHRPD network evolution needs to comprehensively consider the deployment rhythm of LTE. At present, the handover delay between eHRPD and LTE still needs to be improved.
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