The Research of Frequency Synchronization in Carrier Ethernet Backhaul with SyncE Technology

There are major changes undergoing in mobile carrier networks. The introduction of mobile broadband services is the main driving force. The deployments of Long Term Evolution (LTE) will significantly increase the ratio of packet data traffic to TDM traffic in the backhaul [1]. LTE can support a theoretical peak downlink data rate of 330 Mb/s (4x4 MIMO) [2]. Legacy backhaul networks are optimized for circuit switched voice traffic in which the transmission from Base Transceiver Station (BTS) to a base station controller (BSC) is realized using static time division multiplexing (TDM) circuits. TDM networks are inefficient for packet transfer. Therefore it is not possible to deliver LTE service through TDM backhaul and maintain profitability [1]. The LTE standard, finalized in early 2009, defines major architectural changes such as System Architecture Evolution (SAE). It is important to note that LTE focuses on all-IP approach. Current mobile standards use a mix of circuit-switched and IP technologies to support legacy services. Both the data and control planes are based on IP protocol in LTE standard. This delivers a simplified operational model in combination with flatter network approach. Multiprotocol Label Switching Transport Profile (MPLS-TP) is a scalable packet forwarding technology, which enables traffic engineering, Quality of Service (QoS) and fast recovery from node and link failures. The stack of IP/MPLS allows wire emulation (pseudo wire) for TDM, ATM, SDH/SONET and Ethernet services over packet switched networks. E-LAN and E-Line services for Ethernet are provided by the virtual private LAN service (VPLS) and virtual private wire service (VPWS). During our experiment we will investigate the carrier backhaul network based on MPLS-TP technology. Basically there are three possible backhaul migrations from legacy TDM networks to packet networks scenarios [3]. The first scenario is to adapt the operators legacy TDM backhaul to support both TDM and packet data traffic. Second scenario is where two separate data traffic networks are build, TDM and packet based. In these two scenarios BS are synchronized from legacy TDM backhaul network. In the third scenario the backhaul network is fully packet based, for carriers which are new to the market. In second and third scenario we need have possibility to deliver synchronization through packet network. The main goal of this paper is the research of Synchronous Ethernet (SyncE) ITU-T G.8261, G.8264, G.8262 possibilities to deliver BS frequency synchronization. For the transfer of frequency synchronization, SyncE is the ideal solution. It combines the cost effectiveness of the Ethernet with synchronization transfer capabilities of SDH. The alternative to Synchronous Ethernet would be to install GNSS receivers and antennas in all base station sites.


Introduction
There are major changes undergoing in mobile carrier networks.The introduction of mobile broadband services is the main driving force.The deployments of Long Term Evolution (LTE) will significantly increase the ratio of packet data traffic to TDM traffic in the backhaul [1].LTE can support a theoretical peak downlink data rate of 330 Mb/s (4x4 MIMO) [2].Legacy backhaul networks are optimized for circuit switched voice traffic in which the transmission from Base Transceiver Station (BTS) to a base station controller (BSC) is realized using static time division multiplexing (TDM) circuits.TDM networks are inefficient for packet transfer.Therefore it is not possible to deliver LTE service through TDM backhaul and maintain profitability [1].
The LTE standard, finalized in early 2009, defines major architectural changes such as System Architecture Evolution (SAE).It is important to note that LTE focuses on all-IP approach.Current mobile standards use a mix of circuit-switched and IP technologies to support legacy services.Both the data and control planes are based on IP protocol in LTE standard.This delivers a simplified operational model in combination with flatter network approach.
Multiprotocol Label Switching Transport Profile (MPLS-TP) is a scalable packet forwarding technology, which enables traffic engineering, Quality of Service (QoS) and fast recovery from node and link failures.The stack of IP/MPLS allows wire emulation (pseudo wire) for TDM, ATM, SDH/SONET and Ethernet services over packet switched networks.E-LAN and E-Line services for Ethernet are provided by the virtual private LAN service (VPLS) and virtual private wire service (VPWS).During our experiment we will investigate the carrier backhaul network based on MPLS-TP technology.
Basically there are three possible backhaul migrations from legacy TDM networks to packet networks scenarios [3].The first scenario is to adapt the operators legacy TDM backhaul to support both TDM and packet data traffic.
Second scenario is where two separate data traffic networks are build, TDM and packet based.In these two scenarios BS are synchronized from legacy TDM backhaul network.In the third scenario the backhaul network is fully packet based, for carriers which are new to the market.In second and third scenario we need have possibility to deliver synchronization through packet network.The main goal of this paper is the research of Synchronous Ethernet (SyncE) ITU-T G.8261, G.8264, G.8262 possibilities to deliver BS frequency synchronization.
For the transfer of frequency synchronization, SyncE is the ideal solution.It combines the cost effectiveness of the Ethernet with synchronization transfer capabilities of SDH.The alternative to Synchronous Ethernet would be to install GNSS receivers and antennas in all base station sites.

The physical layer
As defined in ITU-T G.8261, Synchronous Ethernet is using physical layer for node synchronization to the same frequency.Mobile Carrier Ethernet realizations are usually deployed as a high-speed point-to-point connection where physical layer (ETY) works great in asynchronous mode as packets get buffered at each node.In Synchronous Ethernet, the link frequency is linked to a traceable primary reference source.The clock is recovered at PHY of incoming interface, on all the nodes along the path, and than it is locked to the phase-locked loop (PLL) (Fig. 1) [4].The process is similar to SDH/SONET which provides highly precise frequency synchronization.However SyncE does not support the distribution of time of the day information, due to that reporting functions in mobile networks are limited as stated in ITU-T G.8264.
In SyncE networks the control of the level of jitter and wander is very important.In ITU recommendations, the so called Network Limits are specified -the maximum acceptable wander and jitter for different classes of interfaces in the network.

Table 1 .Synchr Wireless techn
Data Fig. 1.Clock an Ethernet allow such modernization.SyncE is fully compatible with legacy synchronization networks.This Ethernet solution provides considerable flexibility for mobile operators.