OTN Deployment in the Convergence and Access Layers

Mobile internet is developing fast and is changing the way people work. HD videos and other services that require large bandwidth are pushing mobile networks to evolve to LTE. Limited capacity of the metro bearer network is a challenge for LTE development. OTN is a large-capacity, multi-service bearer platform that has been widely deployed in metro core networks and is used in the convergence layer of MANs. We discuss the bandwidth requirements of LTE services propose deploying OTNs in the convergence and access layers so that LTE services can be efficiently carried.

LTE Bandwidth Requirement of a Metro Transport Network

In a 3G network, base stations and bearer network equipment in the access layer mainly connect through FE/E1 ports. In an LTE network, GE optical ports are used for connection (Fig. 1). The typical bandwidth requirement of a single base station in an LTE network is about 100 Mbps, and the peak bandwidth is 300 Mbps. The number of GE optical ports is greatly increased in an LTE network. A PTN/IP-RAN network, which is the access layer of an LTE backhaul network, usually has 10GE networking. In a typical wireless backhaul network, an access loop has about six to eight access nodes, a convergence loop has about four to six convergence nodes, and each convergence node has two access loops. The bandwidth of a single convergence layer is about 20–30 Gbps. In a moderately developed city, there are multiple convergence planes, so the total bandwidth of the convergence layers is multiplied. The bandwidth of the current 10GE PTN/IP-RAN networks cannot meet the LTE requirements, and network upgrades are required.

Bearing PTN/IP-RAN Traffic by Deploying OTN in the Convergence Layer

OTN leverages the bandwidth of optical fibers through WDM and transparently carries 10GE PTN/IP-RAN traffic from 3G networks. OTN also carries PTN/IP-RAN traffic of services that require a higher rate. OTN is an important bearer technology for the convergence layer of LTE networks.  

An alternative solution to bearing RTN/IP-RAN traffic is 40G PTN/IP-RAN. The two solutions have their own advantages and can be selected as required.

OTN in the Convergence Layer: A PIC Solution

OTN equipment with integrated PIC modules has large bandwidth and is easy to maintain. A single PIC module can bear 80–120G traffic and is suitable for converged loops in LTE networks.

The PIC solution supports 8/10/12 EA modulated lasers and optical receivers (Fig. 2). This greatly reduces the size and power consumption of optical components. EA modulated lasers are sensitive and OSNR tolerant. When applied in the MAN convergence layer of LTE networks, the PIC solution has the following advantages:

●    The number of fiber pigtails and ODFs are reduced, and this is helpful in maintenance.

●    Lower network investment is required, and carbon emissions are reduced because the PIC modules consume little power.

●    PIC modules are well designed and can be easily replaced and maintained.

C-RAN in the Access Layer

A C-RAN is a centralized/collaborative/cloud radio-access network. In a cutting-edge architecture oriented towards 4G, C-RAN can reduce system capex and opex. In C-RAN, centralized BBUs are separated from multiple RRUs. The volume of IQ data transmitted between BBUs and RRUs is a multiple of that transferred between BBUs and RRUs in traditional macro base stations. Because of IQ latency and clock synchronization requirements, a packet solution is not feasible. Current bearer solutions use fiber connection. As more and more BBUs are deployed, each RRU has to use a pair of optical fibers, and many optical fiber resources need to be used. Moreover, fiber-connected link security cannot be ensured, and it is difficult to maintain fiber jumpers at BBUs. With the OTN WDM solution, additional optical fibers are not required. Security is guaranteed, and C-RAN maintenance is simplified.

The flat transport structure is suitable for future LTE requirements, and the super baseband pool is connected directly to the convergence layer (Fig. 3). This reduces the number of router hops. The access layer uses compact OTN equipment to provide a multiservice bearer platform that can bear the traffic of CPRI services, big customer services, and even future services.

Conclusion