Research on WDM-PON bearer for 5G application scenario and technology

Infiberone managerGVIP2018/3/23 14:04:39

Research on WDM-PON bearer for 5G application scenario and technology

The 5G market is the biggest hot spot in 2017, and all the layers of the industrial chain have high expectations for 5G.In the age of 5G, the bearer has become the consensus of the industry, which has been given high hopes for the fronthaul of 5G network. Since 2017, international operators have studied the WDM-PON as the key program of the 5G fronthaul. Then how will WDM-PON be applied in the 5G scenario? this article analyzes the application scenarios and the latest technology research of WDM-PON bearer in the 5G market through the 5G fronthaul plan, the 5G bearer network architecture and the operators’ requirements for the bearer network.

1.WDM-PON bearer of 5G application scenario 
1.1 Definition of fronthaul network architecture
Along with the rapid development of a variety of new applications of mobile Internet and Internet, the fifth generation of mobile telecommunications technology (5g) emerges at the historic moment in response to the explosive growth in mobile data traffic and massive device connections.

In 2015, ITU-R formally defined three types of typical application scenarios of 5G: eMBB, mMTC and URLLC.EMBB corresponds to large volume mobile broadband services like 3D/high-definition video, mMTC is corresponding to the large-scale Internet business, and URLLC corresponds to business with low latency, high reliability and connectivity, such as driverless and industrial automation. November 28, 2016 China Mobile released 5G C-RAN demand, architecture and the white paper of challenge.

Fig.1 BBU framework: from 4G to 5G single node CU/DU two level architecture

The 5G BBU function will be reconstructed into CU and DU two functional entities (see Figure 1), the CU includes non real-time wireless protocol stack functions, and  supports sinking part of the core network function and edge application deployment of the business at the same time. DU equipment mainly deals with the physical layer function and real-time function layer 2, the fronthaul can be divided into two levels, one is level one fronthaul and the other is level two fronthaul. CU has realized some functions of the original concentration of BBU, which is compatible with the centralized deployment completely,and also supports distributed DU deployment.

Two layers fronthaul C-RAN architecture provides network support for DU pooling or CU pooling. One of them is called Fronthaul, which can support fronthaul agreements such as eCPRI;The secondary prequels are called Midhaul. Fronthaul and Midhaul have different latency and bandwidth requirements for different 5G businesses. 

The large bandwidth demand of 5G fronthaul and backhaul is driving the large interface demand of transmission network, mainly including high-speed Ethernet interface or OTN/DWDM transmission interface. At the same time, with the new fronthaul interface definition of eCPRI, the network architecture has evolved into a new architecture supporting DU and CU pool. It brings new opportunities and challenges to wireless access and 5G bearer.

1.2 WDM-PON bearer of 5G application scenarios


Fig.2 5G new scenario or hot spot scenario

When operators have selection pressure of base station location , or it needs to release the BBU machine room, or the dense urban area needs to deploy DU pool . Under these scenarios, DU location can be moved up and deployed centrally. In particular, the new scenario for the operators of both wired and wireless services is very suitable for using WDM-PON to carry the fronthaul interface. OLT can centralize to deploy DU, DU pool and OLT site by using the advantages of accessing the machine room, For 5G URLLC business, it is suggested that CU also has the site address with OLT and DU.DU pool co-station will make the data transmission path of the user interface of the cooperative demand (such as CoMP) closer to DU.When DU and CU stand together, the Midhaul will disappear, and the transmission delay of 5G RAN users will be lower.

2.The realization of WDM-PON technology and the significance of its 5G bearer


Fig.3  WDM-PON Architecture

The key technology of WDM-PON is currently focused on: colorless ONU technology, namely itu-t g. 989.2 and CCSA WDM-PON standard, which can be used to realize colorless ONU.The other is the auxiliary management channel (AMCC) technology, which is the RF Pilot-tone and Baseband Overmodulation. 

In WDM-PON scheme, the development of key technologies such as optical module technology, OAM management, and protection of reverse transfer plays an important role in the use of WDM-PON.Relevant agreements are being discussed and formulated in standard organizations.

2.1 Fronthaul bearer scheme


Fig.4 WDM-PON fronthaul networking scheme based on OLT unified optical access platform

WDM-PON OLT device unified optical access platform is used for 5G mobile fronthaul while supporting cable optical access business.5G DU or BBU pool and RRU are connected by WDM-PON passive optical network to realize the fronthaul of mobile business. 

WDM-PON has the following technical features as a 5G fronthaul scheme:

a.WDM-PON technology has a low delay, which can provide independent networking and business performance guarantee for 5G and government enterprises and other businesses; 

b.Large bandwidth, supporting 10G and 25G per channel, which can meet the bandwidth requirement of 25G eCPRI fronthaul signal; 

c.High transmission efficiency.It is reflected in two aspects, one is that the exclusive bandwidth does not have DBA scheduling, and the logical point to point.The other is management, with AMCC signal tuning technology, management channel superposition at each wavelength, no OMCC reserved, no waste from GEMPORT resource reservation. 

WDM-PON will also reflect the value in engineering application as a 5G fronthaul scheme:

a.WDM-PON program is suitable for urban residential areas with dense population because of "natural tree line topology", "solid move fusion business", "intensive coverage". 

b.It can share existing fiber base settings.The deployment of 5G network requires a large amount of optical fiber resources. The network architecture is based on the multi-point tree topology based on passive optical network points, which can save a lot of fiber routing resources. At present, FTTx optical fiber network has wide coverage, rich resources of lines and ports, and full utilization. It can reduce the deployment cost of 5G network, reduce duplication of investment, improve the utilization rate of current network resources, and quickly improve 5G network intensive coverage.  

c.Multiple wavelengths are transferred to the branch optical fiber after the AWG gathering, saving a lot of backbone fiber resources. 

d.AWG has smaller losses than POWER SPLITER.In the case of the equivalent ODN network, the replacement of SPLITER with AWG means further transmission distance. 

e.5G and wired access can share computer room resources, such as Local PoP access point. Especially based on AO reconfiguration, the machine room can play a comprehensive construction network, the advantage of amortized investment. 

f.It can share to realize the integration of home users, government and enterprise users and 5G base stations, further improving equipment utilization, saving network equipment deployment cost and reducing resource demand. 

g.After DU pooling, the resources of wireless and wired access can be realized to jointly build and share, so as to build a future solid migration and fusion network,including the consolidation of the solid shift control, the realization of authentication, billing and user information unification, etc.;The UPF solid removal common platform equipment is realized by the solid transfer.It can also realize the integration of solid storage resources, such as CDN and MEC resources. 

2.2 WDM-PON standard progress and operators' demands

At present, the WDM-PON standard mainly studies the WDM-PON system with a single wavelength of less than the 10G rate (1.25G/2.5G/10G). When the single wave rate is up to 10G, the mainstream technology of WDM-PON colorless ONU is adjustable technology. Standard organizations begin to pay attention to the application of WDM-PON in the 5G fronthaul, especially the single wave 25G rate WDM-PON system. The ITU-T g. up.5GP discussion group is advancing and discussing 25G WDM-PON.

WDM-PON has been studied by international operators as the key plan of 5G since 2017.Electric Orange from France, the current network is mostly D-RAN, C-RAN, 5G C-RAN, and they consider to put CU in NG-POP. They also pay attention to 5G fronthaul and  WDM-PON. Electric DT from German, considers to separate C-RAN from CU/DU and CU focused on the convergence layer. They are interested in WDM-PON fronthaul. Australia Telstra compares active DWDM and WDM-PON scheme based on C-RAN fronthaul. The three major domestic operators, the China telecom research institute actively promoted the testing and trial commercial of WDM-PON; China unicom (China unicom) is similar to that of 5G host (G.metro) and WDM-PON, which can be used as a simplified version of G.metro.China mobile has been able to integrate 5G with FlexE and WDM-PON. 

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