Technology Insight

Published: 21 February 2014

Today’s solution to mobile coverage inside buildings is still mostly based on distributing RF through feeder cables to the antennas, much as it was 15 years ago. Yet it’s the frequency bands and technologies that have changed.

Add to that the increasing use of mobile devices and operators face the challenge of an increasing demand for services where DAS have not been updated as often as they should.

So we have been faced with old systems that were once designed for nothing more than GSM 900 and 1800 and perhaps upgraded for UMTS with new antennas but not much else. Now we are looking at another two frequency bands in addition to LTE.

The original designs were merely about basic coverage – there were no smart phones back then. As a result, antenna placement only had to consider coverage and these could be far apart because these systems were only installed in buildings with poor macro coverage.

PIM wasn’t an issue back then. However, multiple operators on a single antenna – and each using up to four frequency bands – create a lot of potential intermodulation issues which in turn reduces system performance. These days, tests are performed on the quality of the DAS in order to ensure problem free installations.

It is important to continually invest attention in the technology we use and how we design a DAS. The most important part of our work is to keep up to date with the changes around us and be at the forefront of new technology.

An important part of this work is the use of new software tools to predict coverage and speed up design. Now we are also witnessing a large change in the distribution mobile coverage inside buildings. Although a passive DAS is still the most common solution, we are seeing a shift to alternative solutions that gives greater options for the operators.

Our work with SpiderCloud is one example of this, working with them at the development stage of the product leading to a quicker deployment. SpiderCloud uses a number of hotspots to provide coverage in offices using an IP network that links them together like any IT system. These can replace a conventional DAS in many situations and bring in a number of advantages. These bring new skill requirements to traditional RF engineering.

In large scale systems the most common solution has been to distribute RF over fibre to cover greater distances. When the RF is converted to light, this introduces its own problems and each manufacturer brings their own solution. The best approach is to always work closely with suppliers to maximise system performance.

Keeping up to date is a task in itself and the complexity of large systems with MiMo antennas now places more demand on the quality of the installation work. This is now a determining factor in the end performance of a DAS and this is where CAM has lots of experience.

The knowledge and experience we gain is put into the systems we design to meet the needs of our clients both now and in the future.