Brief Introduction to the development status of LTE access Bearer Network

At present, LTE access bearer network is not widely used, but there are still many problems. So I have studied the development status and problems of the LTE access bearer network. I will share with you here, hoping it will be useful to you. From 2G/3G to LTE access bearer network, more than 90% of wireless site addresses will be reused, and 2G/3G will coexist with the LTE access bearer network for a long time, this determines that the transmission network must meet the differentiated needs of different stages of wireless technology development. However, in the whole wireless network construction investment, the site (data center, rent, etc.) investment accounted for nearly 50%, the wireless base station was about 40%, and the transmission network was less than 10%. Due to the huge investment difference, carriers seldom transform the existing 2G/3G base stations due to the IP address of the transmission network, but in turn require the transmission network to have multi-service transmission capabilities. Currently, there are only two technologies that support multi-service transmission: the traditional MSTP Technology and the PWE3/MPLS-based grouped transmission technology. With the IP transformation of the transmission network, PWE3/MPLS technology has become a key demand in the mobile bearer field.

TD-SCDMA, CDMA, Wi-MAX and LTE (including TD-LTE and FDD-LTE) have requirements for time synchronization, currently only GPS or IEEE1588v2 can meet the requirements. Due to the frequency impact, the coverage capacity of the LTE access bearer network is less than 2G/3G, which means more base stations will be needed to supplement the coverage in the future. Compared with GPS, the full-network use of IEEE1588v2 ground synchronization technology can lower investment, and can be used as a synchronous protection solution when GPS fails, thus ensuring the security of telecom infrastructure.

In addition, another major application scenario of wireless broadband is indoor. Because GPS cannot penetrate the roof, the synchronization requirements of indoor base stations must also be met through the transmission network, in this way, GPON and Ethernet Access Technologies also need to support IEEE1588v2. There are two main interfaces for the LTE access Bearer Network: S1 interface, used for the connection between the base station and the core network gateway; X2 interface, used for the logical connection between the base station and the base station.

The X2 interface is designed to improve the user experience when switching between different base stations. After the switchover is complete, the service still needs to be transmitted through S1. Because the switchover only occurs between adjacent base stations, in the X2 interface design, mainstream operators explicitly require that only logical connections be allowed between adjacent base stations, rather than intercommunication between adjacent base stations. From the perspective of avoiding the spread of one base station to other base stations, it is reasonable to avoid the full MESH communication between all base stations.

Because the base station overwrites the complexity of the adjacent relationship, the connection relationship X2 can only be achieved through static configuration. This means that the interfaces X2 and S1 have been configured (including the connection relationship, protection mode, and QoS characteristics) before the LTE access bearer network goes online ), this connection will not automatically age or change. Therefore, the LTE access bearer network is essentially implemented based on the connection technology. The new logical interface X2 of the LTE access bearer network is mainly used for switching. The emergence of this interface introduces the bearing difficulties of the logical part of Mesh interconnection for the base station, and challenges the traditional point-to-point transmission network architecture. However, the actual X2 interface does not require much bandwidth (up to 3% of the S1 Interface), and the X2 service plane transmission latency requires an end-to-end 50 ~ 100 ms, signaling plane transmission latency Requirement 10 ~ 20 ms. This requirement is much looser than the latency of the S1 user plane (5 ms.

In this way, if the bearer network can meet the S1 latency requirements, it is easy to meet the latency requirements of X2. The implementation of X2 logical exchange is acceptable in the bearer network or AGW aggregation point. It is worth noting that if the bearer network access aggregation layer is required to support X2 logical interconnection, the bearer network will increase investment by more than 30%. Is it worthwhile to increase the investment by 3% for 30% of the traffic and affect the QoS and maintenance quality of 97% of the S1 service? In-depth research is required.

There are two typical ideas for LTE transmission: one is concerned about the new technology-2G/3G is carried by MSTP, and the other is a group transmission network; another idea is to protect future investment. Both 3G and LTE access bearer networks use the grouped transmission network, and the 2G services of the current network are gradually migrated from MSTP to the group transmission network. Either way, you must consider the fact that the space at the end of the base station is usually very small, and the transmission equipment is built in the base station cabinet, with only 2U SPACE ~ 3U, and the base station itself supports the smooth evolution of the 3G to LTE access bearer network, and 2G/3G does not return to the network for a long time. This means that the solution is uniform on the end access point and may be implemented in one box.

Considering that wireless networks often need to adjust the bandwidth, increase the carrier frequency, and migrate sites, it is necessary to maintain a unique maintenance interface between the wireless and transmission networks after the transmission network is segmented, otherwise, a large amount of cross-Department communication costs will increase and fault resolution efficiency will be reduced. Therefore, the unified Maintenance and Management of the grouped transmission network and the existing MSTP network is a key requirement for smooth evolution.