It’s obvious that operators would constantly be on the lookout for ways of increasing the fidelity of their coverage – but it’s equally obvious that the best coverage in the world couldn’t justify an enormous increase in expenditure. So, how to solve this conundrum? DT editor James Barton spoke to Frank Oehler of Ubidyne, who believes that the solution to the dilemma may lie in active antennae.
DT: How does an active antenna differ from a passive antenna?
FO: All antennae contain an amplifier. As the name suggests, the purpose of this is to amplify the signal towards the antenna, which then beams out the signal. The idea behind active antennae is to get this amplifier as close as possible to the radiators of the antenna so as to minimise the losses that naturally occur when using any cables or connectors. This means moving the amplifiers into the antenna housing.
Panel antennae are typically used in telecoms – these take the form of long, flat boxes which contain an array of antenna elements, or radiators. The amplifier is divided into smaller components, and there is a small transceiver included for each radiator. This means that the electronic is close to the radiator, and in turn the cable between the amplifier and the radiator is very short, optimising the losses in the antenna housing.
This creates around 16 small transceivers – one per antenna element. If you can control the phase and the amplitude of each antenna element, this allows for beam-forming, tilting, and many other things.
DT: You have successfully trialled active antennae in the US – was this due to the availability of infrastructure, and if so then could the comparative lack of established infrastructure in many emerging markets act as an impediment to deploying active antennae in these regions?
FO: Yes. Active antennae offer a few features which aren’t possible with current solutions. There are four that I’d like to highlight, and the first is independent uplink-downlink tilting. Normally networks are downlink-optimised, and the uplink has to follow, but there’s always a compromise. If you can optimise an antenna to be independent on the uplink and the downlink, you can gain much more throughput on the cell – there is normally interference at the cell edge.
Site density in emerging markets is likely very thin, so this feature definitely provides the possibility of increasing coverage as well as providing better throughput to subscribers in the cell edge area. Our simulation shows that you can double the coverage area with an active antenna.
DT: So, with half the infrastructure you could provide the same amount of coverage?
FO: Yes, approximately. The second thing is also important for emerging markets: an optimisation of different standards that apply in the same band. If you have a passive antenna in the 1800MHz band – currently a typical GSM frequency, which will be used for LTE in the future – and you have an electrical tilt, you can provide it with one angle of tilt. The GSM signal is normally optimised at somewhere between 0-3 degrees, while for LTE it’s optimised at between 8-12 degrees.
The question therefore is which tilt angle you implement - if the angle is too high, you receive more interference through neighbouring cells, while if it’s too low you lose GSM coverage. With an active antenna, you can implement a different tilt for each standard, meaning that your LTE carrier can run on 10 degrees while your GSM carrier is running on 1 or 2 degrees. That definitely provides better coverage and better throughput, so the end user benefits.
When LTE does come to emerging markets, it will likely launch in more populated urban areas such as capital cities, and obviously there will be neighbouring cells there so that’s where this feature will have the advantage. LTE is less likely to take off immediately in rural areas so active antennae are less likely to be bought exclusively for this particular feature in remote locations.
DT: Which markets are currently showing the most interest in active antennae?
FO: Operators look into active antennae whenever they have a new rollout underway. Their benefits are more apparent in the arena of mobile broadband, so it’s doubtful that GSM operators would purchase active antennae unless they wanted to upgrade their network. There’s currently a lot more traction in developed markets and I think that terminal prices would need to scale before operators in emerging markets would really take interest.
That said, implementation of an active antenna is getting cheaper and the total cost of ownership is essentially lower than any passive solution, including a remote radio head. This commercial benefit should drive interest from all operators and particular those in emerging markets. The savings come largely from maintenance – although this of course hangs on the operator’s strategy – but if you have a conventional system and there’s an outage in a remote radio head or base station, this can result in an outage for the whole cell. Depending on the cell’s importance, there’s an emergency call out to get it back up and running.
With active antennae, as there are 16 transceivers, if one of them fails it’s not a huge problem. Of course with more components it is more likely that one will fail, but in our trial we switched off four of the twelve elements and the MTBF was still stronger than any passive solutions. There was no loss of coverage or uplink – only downlink, and that was because the lacking amplifier power degraded throughput by around 30%. The cell was still completely functional, and that’s a key selling point for emerging markets – we’re not talking about an outage anymore, just a slight degradation in service.
DT: Would the solution therefore be suited to remote areas where infrastructure maintenance is challenging?
FO: Certainly – I believe that particularly in remote areas, people will accept a slight degradation in services if the trade-off is that they don’t have to maintain the infrastructure so stringently. In addition, the installation is easy – normally with a passive antenna, the mechanical pre-tilt recommended by the network planner comes as standard, and this can be optimised with remote electrical tilt.
Active antennae meanwhile are mounted plain to the mast, so there’s no mechanical stuff in between – they’re very easy to install, all that’s needed is a power source and a fibre cable up the mast. No copper cables are required, which is worth considering as they’re both heavy and a target for theft - particularly in emerging markets. There’s a shelter where the base unit is, but it doesn’t need any air conditioning as the amplifiers are at the top of the tower and so are cooled passively. The hugely reduced air conditioning therefore reduces diesel consumption for any generators used. Cutting down on diesel consumption is a major goal for emerging market operators, as it allows them to be more environmentally friendly while saving money.
DT: Which features would be particularly advantageous to operators in emerging markets?
FO: There is one more particularly interesting feature of active antennae: vertical sectorisation. If you consider an antenna as having one beam in its cell, vertical sectorisation allows you to split this into an inner and an outer beam, allowing frequencies to be reused – for LTE, for example. Theoretically you could therefore double capacity; practically, we’ve measured an increase of around 40% in the low band and 60% in the high band.
In the language of emerging markets, it would help operators in more densely populated areas to increase their capacity with the same site. Having fewer sites is in every operator’s interest, but in emerging markets it’s particularly relevant with regard to site security and theft, as well as maintenance. Most of the operators will exhaust their macro sites before investing in small sites, vertical sectorisation allows them to do this.
It’s also of significance for emerging markets that many features of active antennae are automatic, like self-healing: there’s an algorithm in the antenna which automatically runs the healing process and provides information and alerts to the operation centre, allowing the operator to decide when to visit the site. All the tilting and vertical sectorisation is run remotely from an operations centre, so there’s no need for anyone to travel there in order to make mechanical changes on the tilt. There are no mechanical parts used – it’s all fully digital, enabling a new concept of network optimisation.