Mobile networks are evolving with the introduction of newer technologies and generations, opening up possibilities for new speeds and throughputs, as well as applications and services. This has created new requirements for access networks to evolve so as to support the ever-increasing bandwidth demand, as well as delay the variation requirements for traffic flow. In such a ­scenario, fibre-based backhaul can serve as the key medium for mobile backhauling in different types of network architectures including passive optical network (PON), point-to-point (P2P) and ring topologies by providing superior throughputs and speeds, and better maintenance.

Evolution of mobile networks

Mobile networks are changing rapidly owing to 4G and 5G as well as the high demand for bandwidth and changes in consumer behaviour. There is a growing demand for wireless bandwidth due to the emergence of new applications, the increasing use of internet services and the rise in user-generated content.

Mobile networks are evolving in two dimensions.  First, there is the technology evolution towards 4G (long term evolution [LTE] and LTE-Advanced [LTE-A]) and future evolution to 5G networks, and second, mobile networks are becoming heterogeneous networks (HETNETs) with heterogeneous access via different micro, metro and small cells.

Fibre backhaul options

A number of options have evolved to backhaul mobile traffic in HETNET configurations, be it macro, metro or small cells. These options leverage fibre technologies and architectures for catering to the huge throughputs as well as the stringent delay/delay variation requirements for traffic flows. 4G throughputs are now look­ing at sustainable averages of 60 Mbps and peaks reaching more than 100 Mbps. With the implementation of LTE-A, the peak figures are expected to reach 300 Mbps and beyond.

A number of options are being considered for backhauling mobile wireless sites using fibre. Every solution has its advantages, and these depend on the availability of fibre and the topology of transmission facilities. In reality, these solutions can be used to backhaul macro and metro cells, as well as small cells providing fibre-to-cell-site connectivity to connect to the backhaul network, and stream traffic towards the evolved packet core for signalling and switching with greater efficiency, higher throughput and lower maintenance costs.

FTTH as a fibre backhaul option

Gigabit PON and P2P access are already widely deployed for residential and business service delivery in many markets. Fibre-to-the-home (FTTH)  networks offer a viable alternative to address the mobile backhaul challenge. It  is created by expanding FTTH’s footprint to backhaul wireless networks in HETNET configurations. The solution allows operators to capitalise on the running residential FTTH deployment for transforming to an all-packet, high capacity and cost-efficient mobile backhaul network. It should include very high speed non-blocking bandwidths, a large set of quality of service capabilities, and a set of support tools to monitor and troubleshoot the network.

A very challenging dimension in the full packet-based mobile backhaul network is synchronisation. GPON and P2P solutions provide a wide array of options for frequency synchronisation. On the optical line terminal (OLT) side, frequency synchronisation options include building integrated timing source (BITS), SyncE and IEEE1588v2. These functions can work in conjunction with a variety of optical network terminals. FTTH fulfils numerous benefits and capabilities in backhauling mobile networks including service offerings as well as reliability, availability and efficient bandwidth scaling and converged transport, not to mention the quality of service, synchronisation capabilities, and operations, administration and management features.

For FTTH PON and P2P to connect the OLT in the central office to macro sites as well as to metro and Wi-Fi sites, the outside plant can be planned to have a primary concentration point with optical pass through or optical split. This will lead to a subsequent secondary concentration point for second-stage split, or pass-through to connect to the home/building, or a macro, metro or Wi-Fi hotspot. Ring or dual-homed connectivity may be used from the edge across aggregation to the access network, depending on the available transmission and its topology.

Fibre backhaul synchronisation

Synchronisation is important for mobile backhaul as providing an accurate and stable clock is mandatory for mobile networks for cell site synchronisation. There are several synchronisation techniques like PON or P2P that can be used in conjunction with FTTH, for delivering the required clock accuracy. GPON supports physical layer synchronisation that can deliver clock-to-base stations or cell site gateways in mobile sites. The clock can be delivered to OLT via BITS or packet synchronisation like SynchE or 1588v2. Most modern OLT and optical network terminal implementations support the 1588v2 clock. 1588v2 is beco­ming a more prominent synchronisation technique as it supports LTE carrier aggregation and LTE-A through the relay of time of day and phase information.

Based on a white paper, “Mobile Backhauling in Fibre” by the Technology and Training Committee, Fibre-to-the-Home Council, MENA, published in June 2016