Small Cell Backhaul

Wireless Small Cell Backhaul – Speed vs flexibility

FlexibilityWhile take-up is slower than originally forecast, the cellular industry is beginning to show signs of densification through urban small cells. One of the constraints has been suitable backhaul, with fibre being strongly preferred but not universally available.  Several wireless backhaul vendors have recently launched higher speed products. We ask if throughput is the most critical factor for adaptable and rapid urban small cell roll out, or more relevant for adjacent markets.

 

 

Macrocell backhaul has dramatically increased

Mobile data traffic growth takes its toll on all parts of the network, not just the smartphones and basestations but backhaul, core network and interconnect. Limited capacity in any of these areas throttles speeds and wastes investment elsewhere.

Macrocell backhaul has dramatically increased through widespread adoption of Gigabit Ethernet, most commonly delivered by fibre. Some service companies have even built their business on that, such as Towerstream in the US. Cable MSOs quietly provide extensive fibre Ethernet backhaul to almost every mobile network operator in the US and Europe.

It’s mostly Gigabit Ethernet usually as a managed service. In many countries there are regulatory hurdles limiting dark fibre provision, but this is slowly being relaxed. Here in the UK, the regulator has recently announced a decision to mandate BT (the incumbent fixed operator) to offer dark fibre nationwide (excluding Central London) from 2017.

But fibre isn’t available everywhere – even in the cities – and wireless backhaul vendors have upgraded the capacity and performance of their products to match.

Techniques such as 2048 QAM and 4x4 MIMO enable point-to-point microwave links to achieve data rates of several Gigabits per second.

Urban Small Cell Wireless backhaul has different requirements

The traditional methods that have worked well for macrocell deployment don’t apply to urban small cells because:

  • -       There will be many more sites;
  • -       They need to be deployed and commissioned rapidly and at low cost;
  • -       They need to be compact to comply with planning/zoning regulations

Small Cell Wireless Backhaul Vendors increase their speeds

I’ve seen several small cell wireless backhaul companies expand their market scope because frankly urban small cell backhaul isn’t yet mature enough to be profitable and remains a medium to longer-term play. Typical adjacent markets include interconnecting campus buildings, temporary sites (festivals etc.), wireline broadband extension (reaching sites where cables/fibre doesn’t yet cover) and even some macrocell wireless backhaul.

This has driven demand for higher throughput speeds than perhaps might be required for individual urban small cells.

Recent examples of adjacent market deployment include CCS in London, where Luminet are deploying a common wireless infrastructure capable of serving both Enterprise and Urban Small Cells from any of their 1900 sites. Their wireless mesh topology supports up to 1Gbps speeds.

Another is Fastback Networks, who now claim up to 2Gbps (1Gbps in each direction) for point-to-point Non-Line-of-Sight links. These have been deployed to serve urban macrocells in otherwise difficult to reach areas.

eBlink have targeted very high speeds from the outset, aiming to satisfy the more demanding RRH (Remote Radio Head) solutions connected by CPRI. These need up to 2Gbps per link. The company illustrates a range of case studies serving unusual and awkward locations – one even beaming through an office window to an adjacent building to avoid installing any external antennas.

Mimosa, addressing Wi-Fi backhaul rather than small cells, make use of advanced techniques to serve residential or rural village environments with an alternative to wired broadband.

These and other new entrants are maturing their solutions and capturing revenues from adjacent markets while they continue to conduct trials with mobile network operators. Revenues from small cell wireless backhaul today are just too thin to operate profitably on that market alone.

Intracom, Siklu and numerous wireless startups are at different stages of technical and commercial evolution ready to address the market as it matures. Larger players such as Ceragon and Dragonwave also have products targeted at this niche, with too many other potential vendors and players to list here.

What will network operators be looking for in urban wireless?

While throughput speeds are important, I’d suggest that individual LTE small cells would typically only need around 100Mbps today. One very senior operator executive told me he had instructed his backhaul planning team to aim to satisfy 5G backhaul requirements when installing any new small cell sites. That’s a tough challenge, given that we don’t really know what 5G is supposed to be, and may encourage cautious designers to focus on costly dark fibre for Cloud RAN.

I’d be concerned if we restrict urban small cell to fibre backhaul – these sites need to be very easily and quickly deployed to meet rapidly changing and growing data demand. A more likely scenario is to distribute backhaul from a number of fibre-connected hubs. These might be existing macrocell sites or any convenient wireless backhaul node, and further capacity can be added by connecting fibre to a greater proportion of small cells as traffic increases and fibre connection costs permit.

I believe several factors more important than speed include the flexibility and ease of deployment. There should be little need for specialist technical skills or technicians to visit both ends of every new link. It must be very simple and straightforward to add or move sites.

This tends to favour the technologies which are Non-Line-of-Sight or Point-to-Multipoint. Higher speed point-to-point links (say at 60GHz) can be used to connect from rooftop to street level, allowing a mix of both to prevail.

Summary

Many startup Wireless Small Cell vendors are surviving on revenues from adjacent markets today. Few, if any, are yet profitable from urban small cell backhaul alone.

Urban small cell backhaul has a different set of requirements than for macrocells – peak speeds are perhaps less important than simplicity of deployment, resilience to network outages/growth, physical format and size. Central management and performance reporting are important throughout.

Extensive trials with many network operators worldwide over several years have matured and refined these products. Several vendors now have solutions that are more than fit for purpose.

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