1 Introduction
As one of the mainstream technologies of IMT-Advance, TD-LTE will make mobile networks truly enter the era of mobile broadband. Compared with the existing 2G and 3G mobile communication systems, TD-LTE puts forward higher requirements on the backhaul network in terms of high bandwidth, low latency, horizontal forwarding, and time synchronization ground transmission.
â— First, the bandwidth demand has grown from a few megabits in the 2G/3G period to a few tens of megabits to hundreds of megabits in the LTE era.
â— Secondly, LTE needs to provide flexible QoS and stricter end-to-end delay. According to 3GPP regulations, the end-to-end one-way delay from user terminal to server is 50ms for real-time game-class services with the most strict delay requirements. The transmission delay between them needs to be within 10ms.
Third, LTE introduces inter-base station interconnection (X2 interface) and base station multi-homing (S1-Flex) requirements, resulting in a back-to-point convergence network that changes from point-to-point convergence to point-to-multipoint or multipoint Point routing network, the existing 2G/3G backhaul network can not meet this horizontal forwarding needs.
â— Fourth, the TD-LTE air interface requires high-precision time synchronization. It is required that the air interface synchronization deviation between different cells is not more than 3? s, therefore, it is necessary to transmit a high-precision time synchronization signal in the TD-LTE backhaul network.
The Packet Transport Network (PTN) can provide high-efficiency multi-service bearers, powerful protection, OAM and network management functions, flexible statistical multiplexing and QoS capabilities, and meet the requirements of TD-LTE high bandwidth and low latency. The TD-LTE system provides accurate time and frequency synchronization information transmission, so China Mobile has chosen PTN as the main solution for TD-LTE backhaul. On the other hand, during the TD-LTE period, OTN equipment may gradually sink to the metropolitan area aggregation equipment room. It is necessary to further promote OTN to support 1588v2 time synchronization technology and realize time-synchronous ground transmission networking of OTN+PTN.
This paper proposes various key problem solutions for TD-LTE backhaul network requirements:
â— First, in order to meet the high bandwidth requirements, it is proposed to develop PTN to a larger capacity and higher rate interface.
â— Secondly, in order to meet the requirements of horizontal forwarding, PTN provides two solutions: core layer enhanced L3 function and core layer docked CE router.
â— Thirdly, in order to meet the requirements of TD-LTE backhaul networking, it is proposed that PTN fully interoperates in services, OAM, protection, QoS and synchronization.
â— Fourth, in order to meet the requirements of high-precision time synchronization, it is proposed that the OTN and PTN jointly provide a time-synchronous ground transmission solution. China Mobile has carried out a large number of research, testing and pilot work in the above four aspects.
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