In an usual approach, ZTE has developed a product that uses existing electricity wiring for Enterprise Small Cell backhaul. We researched how it works, and consider some of the benefits and the limitations.
Powerline data transmission using HomePlug
Transmitting data between electricity power outlets has matured since its launch in 2001, and there are numerous mass market products available primarily for residential use today – I even have one installed in my home myself.
These plug in to existing power outlets and provide a seamless/transparent connection between Ethernet cables at two or more points nearby. Some products also include a Wi-Fi hotspot, extending Wi-Fi service to areas with poor or no service. Many include a power socket so you don't lose one - they effectively operate inline and you could plug in a small femtocell directly.
You can even buy power sockets with the feature integrated, hosting both Ethernet RJ45 and USB alongside the main electricity supply.
The benefit of such products is very quick and simple installation, without the need to lay additional cables. They are also portable and can be quickly moved or installed elsewhere. I’ve seen these being used to connect residential Femtocells in remote parts of a home.
Powerline’s greatest challenge is electrical noise, which is dealt with by transmitting the signal on the neutral conductor and so independent of which phase is connected on the live terminal. Remote units operate best when plugged directly into the power socket rather than using extender cables or shared with distribution blocks.
The family name for power line communication standards is HomePlug, and there is a set of different standards targeted at different applications. No respectable standard would be without a Forum or organisation acting as champion, and the HomePlug Powerline Alliance fulfils that role here.
The key standard is IEEE 1901 comprising three specifications for HomePlug AV, HomePlug Green PHY and HomePlug AV2). AV2 is higher speed while Green PHY is 10Mbps with very low power consumption.
A certification scheme (similar to Wi-Fi Alliance) is in place with a HomePlug logo for products which have proven to comply.
Transmissions are encrypted using 128-bit AES.
Physical transmission uses OFDM (same as LTE) with up to 1155 sub-carriers.
Residential compatibility with Small Cells
When installing a small cell, Powerline can be used for the broadband connection within a home or small office. The small cell would simply see an Internet connection which looks and operates as if directly wired. There would be some additional delay and potential for interference (e.g. dropped packets) but that could occur for many other reasons.
Consumer product vendors such as Askey or Zyxel, who supply both residential small cells and powerline products in large volume, could combine both into a single product if their customers asked for it. Typically, wireline broadband service providers and mobile network operators are different organisations with their own requirements and commercial business models. There are still relatively few quad play service providers who provide an integrated small cell/broadband modem/set-top box solution today (Free France being an exception).
Turkcell had reported using Powerline to connect a small enterprise with two femtocells last year (powerpoint with measurement results).
Enterprise Small Cell with integrated Powerline backhaul
Chinese vendor ZTE has developed a larger distributed radio system targeted at Enterprise buildings. Rather than a traditional standalone small cell with baseband processing at the edge, they have used a centralised baseband controller and Powerline transceivers. The baseband controller scales up to 192 radio heads; the Powerline transceivers scale up to 10 remote radio heads.
The QPower supports LTE over a 20MHz TD-LTE carrier providing up to 60Mbps down and 50Mbps uplink speeds across a radius of up to 30 metres.
The clear benefit is that remote radio heads can be very quickly deployed simply by plugging them in to existing power outlets throughout the building. The downside is that it assumes there are enough spare power outlets available (although they can be shared, it would affect performance), and that they are located in the right places. While installation may be feasible without much technical knowledge, good seamless service and performance is best achieved with some RF planning and verification.
Sceptics may question how effective the solution would work at large scale – sharing the same electricity distribution wiring throughout a building must limit the total bandwidth available. Electrical interference may make this unsuitable for buildings with heavy machinery that generates a lot of electrical noise. The cost and disruption of installing new power sockets in the best locations may exceed that of pulling through single CAT5 Ethernet cables.
However, the use of Powerline may be another useful tool in the toolkit for connecting more remote or harder to reach locations. An example is inside elevators, where a remote radio head or small cell connected via Powerline operating inside the cabins at very low RF power would give excellent connection throughout with minimal interference elsewhere.
I like the innovative idea of adopting technology developed elsewhere and making use of it.
Powerline has been used informally to connect residential small cells already, and will likely continue to be used in this way in the future. Perhaps it may be embedded for use in that market in the future, but this depends more on commercial aspects and partnerships/co-ordination between wireline and wireless service providers.
ZTE’s initiative to adopt this for the Enterprise is a bolder step, partly because they’ve used a distributed radio architecture rather than standalone small cells. Early trials by China Telecom have proven that the system works and can deliver very high speeds in the right circumstances. ZTE wouldn't say how many buildings are being served using this technology, but confirm that trials were successful and it is available as a potential approach.
It's possible that Powerline could find a place for use in the Enterprise sector, especially smaller buildings with few units or to connect a small number of remote units in larger installations. Whether it is mature and resilient enough to scale to handle entire large scale distributed radio systems remains to be seen. We look forward to hearing the results of further trials.