CommScope has recently undertaken successful field trials of a 700 MHz LTE active antenna system with a leading US mobile operator. The technology turns the passive antenna into an active one by installing remote radio heads at the top of the tower, which can provide a number of benefits for mobile operators.
Active antenna systems are created by integrating the functionality of a traditional remote radio head (RRH) and a dual-polarized antenna into a single housing that can now be deployed at the top of the tower. The active antenna electronics are distributed within the antenna, such that each radiating element will now have its own dedicated transmit and receive paths.
This distributed architecture now provides operators with the ability to control the amplitude and phase of each radiating element. This is one of the key considerations that enable the feature set of active antenna systems. CommScope has worked with chip set and board partner Ubidyne to develop the active antenna.
Philip Sorrells, VP Site Solutions at CommScope, told Wireless: ‘The traditional system is a base station at the bottom with the radio and a coaxial cable going up the tower building over to the antenna. The trend now is to take the radio and break the digital part away from the RF part and move the RF part (the radio head) near the antenna. You feed it with a fibre optic cable and the RF comes out of the radio head into the antenna.
‘The active antenna takes it a step further: it takes the functionality of the remote radio head and integrates it into the antenna. It distributes those features or functionalities across each of the elements of the antenna. So, a base station antenna is now made up of a lot of little antennas wired in parallel. With the active antenna, instead of 60W RF amplifier radio, you put a little radio behind every small antenna element, maybe 5W, almost like a cell phone,’ explained Sorrells.
This provides a number of benefits that should appeal greatly to mobile operators, according to CommScope. The integration of the RRH and the antenna provides a more attractive operating cost and aesthetic quality for operators. As it looks very similar to existing antennas there is unlikely to be any impact on leasing costs.
Reliability is another key benefit. If a standard radio head fails the whole sector goes dead, customers cannot make calls, the operator loses revenue and it has to send a truck and maintenance team out to the base station. But if one of the transceivers in an active antenna fails, the other elements remain live and are still able to propagate radio signals. The service might not be quite as good, but it means there is just a minor disruption. This is referred to as ‘graceful degradation’. The added advantage is that the operator does not have to send out a maintenance team immediately. Instead, it can just wait until the next scheduled maintenance.
Self-healing is another benefit. If one element fails, there is intelligence in that antenna that will sense that that element is out and redistribute the power to the remaining elements to fix the radio beam. It also helps to make the degradation more graceful.
But perhaps the most revolutionary aspect of the active antenna is its ability to split the beam vertically.
Kevin Linehan, VP, CTO, Antenna Systems, explained: ‘The active antenna provides a completely different capability for sector splitting that has never really been available before, which is vertical sectorisation. Most sectorisation is done in the coverage area in the horizontal plane, but this opens up another avenue for capacity efficiency. If you have a sector at maximum capacity the only option is to split that sector or build another cell site which is costly and has a lot of obstacles, such as zoning approvals. With active antenna technology you can take that sector and split it vertically and come close to doubling the capacity of that sector. The sector is split into an inner ring and an outer ring.
‘When the operators start to see the impact this has on the capacity efficiency of their radio system the value proposition will really start to stand out in a way that has a lot more to do with whole life costs than just the price of the antenna. The most expensive investment operators make is spectrum – it’s a very valuable commodity, so this technology allows them to use that spectrum more efficiently,’ pointed out Linehan.
He added that another thing that cannot be done with a standard antenna is that the active antenna can have different beams and point them in different directions for transmit and receive. That way it can collect energy on the uplink from the edge of the cell, while transmitting less energy into the adjacent cell by adjusting where those beams are, so the system gets a lot more uplink throughput that way.
On the downside, active antennas are 60%-80% heavier thanks to all the radios packed in there, but generally installing any macro antenna is a two man job, so it does not take any more manpower to install.
And naturally, active antennas will not be cheap. ‘Everybody would like to say it will cost less, but in reality there is additional cost with all the radios, but you need to look at it in terms of total cost of ownership,’ said Phil Sorsky, VP Europe. ‘In the cost benefit analysis with vertical sectorisation you are almost doubling your capacity, but at nowhere near the same expense as doubling the number of cell sites would cost.’
Sorrells added: ‘We think the total cost will be lower overall – there will be less boxes on the tower. The benefit for operators is that they will understand the powerful impact this antenna has because it can do vertical sectorisation – capacity is the big issue for them. The primary method of improving capacity of the wireless network is to break the cells into smaller cells and break sectors into more precise sectors. If you split the sector vertically and double the number of subscribers think of the additional revenue the operator will get without any real additional expense in infrastructure investment.’
CommScope is talking to European operators here about some trials, although nothing is agreed yet. There will be further trials in 2012, followed by some production in 2013 with a mass roll out probably taking off in the following years.