Mobile Backhaul Revolution

The increasing demand for bandwidth combined with new mobile equipment like smart phones, tablets, and laptops is creating new challenges for mobile operators. As more and more customers are adopting these devices and using them for a growing number of services, we are witnessing an unprecedented growth in the mobile telecommunication market. The smart phone applications market is booming, with hundreds of new apps presented to the market every day creating an explosive demand for bandwidth. According to new figures from Juniper Research, the amount of mobile data traffic generated by smart phones, feature phones and tablets will exceed 14,000 Petabytes by 2015, equivalent to 18 billion movie downloads or 3 trillion music tracks.

But while mobile traffic is going up, revenue is going down. Data now accounts for about 33 percent of the average revenue per user (ARPU) for U.S. operators. To minimize the cost of delivering these services and improve ARPU - while providing the bandwidth scalability to meet future needs - mobile providers must re-evaluate their networks.

The mobile data surge, together with the LTE and LTE-Advance standards, represent many changes both in technology and in the business models and opportunities for operators and providers in this domain. To meet these bandwidth demands, mobile providers have to increase the bandwidth they deliver to every cell tower.

Using legacy backhaul base stations based on PDH, ATM or SONET would require that the number of lines be increased - creating a proportional cost increase thereby reducing the ARPU realized by the mobile operation even further. Packet-based base stations, on the other hand, could handle the increase in traffic, without the need to add costly leased lines.

This may mean that the mobile operator will need to lease dark fiber from the wholesale providers who already have a footprint in the service area, clearly creating a huge opportunity for utilities, wholesale providers and even the incumbent fixed broadband operators to provide the infrastructure that mobile operators will require for mobile backhaul.

The need for higher bandwidth is also driving mobile providers to look at femto and pico cells as part of their backhaul strategy. These are smaller base stations have been designed to support smaller areas, allowing the mobile operator to offload the larger cell traffic and offer higher bandwidth to areas with high density user areas such as shopping malls, convention centers and transportation centers.

Mobile Backhaul Challenges and Solutions

While using Ethernet for mobile backhaul is a cost-effective and scalable solution, it is not without its challenges.

Timing and Synchronization

As a packet-based technology Ethernet was not designed to support the timing requirements of a circuit-based technology like TDM. Therefore clock synchronization poses a major challenge for backhauling cell traffic. To further complicate matters, these radio access networks generally contain multiple generations of cellular technologies from different vendors, each based on a different standard. As a result, one of the most important requirements for backhaul solutions is to be able to interconnect multiple generations of mobile technology within a site and across multiple cell sites, supporting multiple protocols over the same transport infrastructure.

Frequency synchronization is required for all mobile networks for accurate call handoff. LTE, 4G and WiMAX also require phase/time synchronization. There are several ways to maintain base station timing and synchronization using Ethernet. Among the schemes commonly found in this market are the following:

- IEEE 1588v2 (Precision Timing Protocol) is a packet-based protocol and is carried in-band with user traffic. It can support both frequency and phase synchronization. Devices in the path that do not support 1588v2 will transparently pass the protocol, which eliminates the need to replace these devices while allowing sync requirements to be met. However, without strict QoS policies applied to all devices in the path, it is susceptible to network congestion.

- Sync-E (based on ITU.T G.8261) is a physical layer technology and is not affected by network congestion. However it requires that every node in the path have hardware support for Sync-E. However, Sync-E does not support phase synchronization, so in order to support 4G technologies, Synch-E will need to be supplemented by 1588v2 or some other mechanism to provide the phase synchronization requirement.