Packet-Based Backhaul for Small Cells

In the internet era, the wireless and backhaul networks of operators must have large bandwidth, be quickly deployed, be capable of fast service provisioning, and have convenient O&M in order to provide good experience for end users on mobile applications.
Traditional macro eNodeBs have large capacity and wide coverage but are not suitable for deploying LTE services. Especially in populous urban areas, the installation environment is complex, the cost is high and the maintenance is difficult. To address these issues, small cells have been introduced to operators and have developed rapidly in recent years. Statistics from Mobile Experts indicate that the global shipments of small cells are about two million in 2014. It is estimated that this figure will quadruple, reaching eight million by 2019.
Small cells are compact, functional, and cost-effective. They can be easily deployed and maintained. They are classified as microcells, picocells, and femtocells according to their coverage.
Small cells can be used both indoors and outdoors. Indoors, small cells serve households, offices, and enterprises using EPON or GPON (mainstream access technologies) and packet-based backhaul technologies (supplementary technologies). Outdoors, small cells serve populous urban areas by connecting to the backhaul and microwave networks of macro eNodeBs through optical fibers or cables.

 

The large-scale deployment of small cells has created significant challenges to operators in constructing corresponding backhaul networks. Although small cells resemble traditional macro eNodeBs in backhaul requirements, they still bring many new challenges to backhaul networks.
●    Large scale of small cells. Small Cell Forum predicts that a small cell has a four to seven times larger scale than a macro eNodeB. The consequential larger investment on backhaul networks pressurizes operators in the total cost of ownership (TCO).
●    High dependence on environment. Small cells can be used at various application scenarios. Outdoors, they are mostly deployed on streets, light poles, and walls. It is complex to install and maintain the required backhaul devices. Moreover, citizens advocate green life; they are unlikely to accept noise and radiation of nearby telecom devices.
        An outdoor environment is complex and changing. The adaptability of backhaul devices to adverse environments and power shortage affects operation stability and deployment convenience of networks. Therefore, environmental factors, such as the power source, temperature and humidity, must be considered when installing backhaul devices. In addition, small cells deployment is even more difficult and expensive due to issues of site selection and leasing.
●    Diversified access services. Indoor small cells carry frequent services. The service carrying quality affects user satisfaction. A solution will have its hard power tested by deploying backhaul networks outdoors, and likewise, will have its soft power tested by deploying backhaul networks indoors.
       An indoor backhaul solution handles not only small cell services but also internet, video and key account services. Therefore, it demands large bandwidth on the backhaul device interfaces. Diversified interfaces need to carry different services at the same time.
      It is fundamental to prioritize services and ensure key indexes of delay variation.
●    Clock synchronization difficulty. Great challenges will be brought to time signal transmission for small cell services. In indoor scenarios, signals will be interfered by walls, it is impossible to synchronize time signals by GPS. Small cells backhaul solutions need to ensure precise, reliable time signal transmission.
●    Service vulnerability. In most cases, deployed in public environments, such as office buildings, stadiums, shopping malls, airports, and hotels, small cells carry services more vulnerable to be intercepted, wiretapped, and tampered compared with macro eNodeBs. Therefore, backhaul solutions are required to ensure high security and reliability in service transmission.
 
Packet-Based Backhaul Solution for Small Cells

To help operators to overcome the above challenges, ZTE has proposed a packet-based backhaul solution for small cells. This solution interconnects ZTE’s specific small access devices to small cell base stations to meet all requirements of small cells on backhaul networks. In the aggregation and core layers, ZTE’s packet-based devices are used to build integral, capacious, flexible and reliable end-to-end backhaul networks for customers.
ZTE’s packet-based backhaul solution has the following advantages (Fig. 1):

●    Easy installation and maintenance. Small cell base stations do not take up much space and connect to the access devices with width of 320 mm and height of 1 U.
       The devices support IP/MPLS and MPLS-TP carrier technologies. The compact devices with smart configurations are easily installed and minimize space occupation.
       All backhaul devices are managed by ZTE NetNumen U31. This backhaul solution provides graphical end-to-end management over service configurations, alarms, and performance monitoring. It also simplifies service subscription and O&M.
●    High adaptability to environment. Access devices of small cell backhaul networks need to meet all the requirements of indoor and outdoor environments to minimize onsite restrictions.
       In this solution, access devices can be mounted on poles and walls, installed in light boxes and cabinets, or fixed on platforms. IP65 protection adapts the interfaces to all extreme environment conditions. The POE function enables the devices to supply power for small cells if necessary.
●    Multiservice access. Carrying mobile services of small cells, the backhaul networks need to meet the requirements of mobile eNodeB FE/GE interfaces, and may provide E1/STM-N interfaces to meet fixed network access and key account requirements.
      The ZXCTN 6000 provides not only FE/GE and E1 interfaces but also STM-N, microwave, and xDSL interfaces to carry Ethernet, TDM, and ATM services. Moreover, as the first outdoor device that supports 10GE interfaces, the ZXCTN 6000 adapts the packet-based backhaul solution to more scenarios and creates a potential platform for bandwidth upgrades of customer networks.
●    High-precision synchronization. ZXCTN 6000 supports in-band synchronous Ethernet (SyncE) and 1588v2 technologies as well as out-band 2 Mbits/Hz and 1PPS+PoD technologies to synchronize network frequencies and phases for most customers.
       In addition, ZTE developed the SyncE+1588v2 solution with an industry-leading precision of time synchronization. This provides a comprehensive synchronization solution for traversing third-party networks.
●    High reliability and security. The packet-based backhaul solution isolates services using the VPN to guarantee confidentiality for customer services and supports service-based QoS mechanisms, such as traffic classification, priority mapping, congestion control, and access rate control, to ensure QoS for users of different levels.
      The solution provides protection technologies based on services, networks, interfaces, boards, and devices to ensure service stability between small cell base stations and aGWs.
●    Future-oriented smooth evolution. In the future, networks will evolve toward intelligent networking, virtualized network resources, simplified management and maintenance, and open application interfaces.
      SDN technology is the key to achieve the above goals. ZTE has designed the ZXCTN products based on the SDN architecture to build end-to-end SDN standard networks for customers.

 

The packet-based backhaul solution for small cells ensures security and reliability for user services, simplifies implementation, and achieves unified management for end-to-end services to ease network deployment and improve service performance. This solution is compatible with backhaul solutions of macro eNodeBs, and reduces investment and maintenance costs for customers. In addition, the prospective product design based on the SDN architecture builds a future-oriented network platform for customers.