In this second of two articles, Andy Sutton, Principal Network Architect at EE, walked around central London with me. He pointed out the practicalities of Small Cell backhaul for our urban streets. As the network densifies, more street-level small cell sites will be needed. Andy explains how these will be connected back into the network, and clarifies the technical requirements for this rollout.

What bandwidth should operators allocate for a typical urban small cell? Too little, and they may throttle the capabilities that 3G and LTE can provide both now and in the future. Too much, and it could impact the cost significantly.

Several small cell backhaul vendors have told me in the past that 100 Mbps is perfectly adequate for individual urban small cells, even including the latest multi-mode 3G/4G/Wi-Fi products. While macrocell backhaul links are increasing to 1Gbps or more, this has been seen as overkill for individual on-street units. But is this the right choice when equipment lifetimes are budgeted for 5 years or more? A few backhaul vendors are offering higher speed products that may satisfy both bandwidth and budget.

Wi-Fi is growing in popularity despite (or because) it operates in unlicenced spectrum. LTE-U (using LTE technology in the Wi-Fi spectrum bands) has become another recent hot topic.

Taking things a step further, several backhaul vendors are proposing use of unlicensed (Wi-Fi) spectrum to connect Urban Small Cells or remote radio heads back into the network. Is this a sensible fit with delivery of consistent and high quality cellular service?

One of the critical factors for the success of outdoor/urban small cells is low cost wireless backhaul. Various technologies at different frequency bands are being actively proposed, with the lightly licenced 60GHz V-Band being a popular early choice. One way of assessing whether the industry is on-track to achieve that lower price point is to examine investments and progress being made today by RF silicon vendors.

Here, we can clearly see a couple of associated applications that should accelerate development of this specific technology generally, enabling lower costs in the longer term.

There are many technologies contending for use in outdoor Small Cell Backhaul today, and one thing is certain – none of them is suitable for all scenarios and the industry consensus is that a mix of different technologies will be needed. We've seen free space optics (using infra-red beams) being proposed before, but it's often dismissed out of hand. A Norwegian company is setting out to change that perception, with a novel approach to reduce cost and improve effectiveness.

Backhaul connections for small cells are seen to be a costly component, especially for outdoor/public access where dedicated wireless equipment is required. The higher bandwidth demands from LTE and Wi-Fi place ever greater loads driving further investment. Data caching, storing frequently accessed data within each small cell, could significantly reduce backhaul bandwidth required and also improve the quality of service to customers. We look at two small cell vendors who champion this approach.

Metrocells will need wireless backhaul with sufficient data throughput to deliver the high speeds which 3.5G and LTE are capable of. It's also important that the total capacity of that wireless backhaul within a geographic area matches or exceeds that of the metrocells themselves.

The key tradeoffs are the cost (and availability) of suitable spectrum, the cost of the equipment itself and the ease of deployment and maintenance. The relatively unused 42GHz sits between the licence free 60GHz and the more heavily utilized 28GHz bands, attracting some spectrum licence fees while offering lower costs by using a Point-to-Multipoint topology.

London was again home to the 15th annual Transport Networks for Mobile Operators (TNMO) conference. As with quite a few events these days, there was a strong theme of small cells which were mentioned in the majority of talks. Also in common with other conferences, I found a wide range of quality of content – from the outstanding to the truly banal. New takeaways for me related to small cells included the work being done by the MEF to determine the characteristics of Ethernet required for LTE small cell backhaul, various offers of Small Cell Hosting and the (mostly private) comments from operators about the reality of Metrocell rollouts.

We've also recorded a short (3 minute) vox-pop style video from the chairmen and several speakers during the event to give you a sample of the atmosphere.

Alongside a strong interest in public access small cell products themselves, we've also seen plenty of attention for wireless backhaul solutions. But who's going to provide the specialist expertise to glue this together on the gorund - designing and choosing the best sites, the most appropriate backhaul option, then install and maintain them? We asked Peter Jennings, CTO at MLL Telecom, one of the UK's largest backhaul network providers, to share his view of where these skills will fit – a range of services that may soon be needed from others by network operators worldwide.