This post is by Brendan Millard, Director-Wireless, Southeast Asia, at CommScope
Wireless operator networks are facing unprecedented demands for more and more capacity every day, driven by the services available on smartphones, tablets and laptops. In order to meet these demands they are looking to newer technologies in both existing and new frequency bands such as refarming 1800MHz GSM spectrum to be used for LTE or implementing new LTE networks in 700MHz. These days, it seems there are two things a wireless operator cannot get enough of: spectrum and tower space to hang the antennas required for these new services.
It is becoming an almost commonplace situation for an operator to be running networks in multiple bands including the 700, 850, 900, 1800, 2300 and 2600MHz bands. The requirements for networks in multiple frequency bands coupled with the difficulty of obtaining new cell towers or space on existing towers has led to the need for base station antennas that take up the same space as an old 900MHZ antenna but covering multiple bands.
Just a couple of years back, wireless operators were installing 2-port (single band), 4-port (dual band) and 6-port (tri-band) antennas whereas today’s operators with one eye on their current requirements and the other eye on the not too distant future are installing 10-port and 12-port antennas to cover combinations of all bands they plan to use over the coming years.
Not only have multi-band antennas become much more widely deployed but the bandwidth of the antennas has become much broader in order to cover more frequency bands in each array. These days, a state-of-the-art base station antenna will cover 698MHz through to 960MHz on the low band arrays and the ultra broad high band of 1710MHz to 2690 MHz on the high band arrays.
In addition to the need to cater for multiple frequency bands, antennas also need to be suitable for use with newer technologies. For instance, to obtain the optimal benefit of 4 x 4 MIMO in an LTE system the antenna arrays should be horizontally spaced. Traditionally tri-band antennas would incorporate a low band and two high band arrays where the high band arrays were spaced vertically, one directly above the other. Leading edge antennas designed with LTE and 4 x 4 MIMO in mind will incorporate horizontal spacing of the two high band arrays.
With networks growing and evolving so quickly, another aspect of antenna selection to keep in mind is electrical tilt. Initially, networks were deployed using fixed electrical tilt antennas with some mechanical tilt being employed to fine tune. However it was soon recognised that using variable electrical tilt was a far more effective method that gave better coverage and less interference. Then as networks evolved to a stage where the electrical tilts on antennas were adjusted more frequently, the need to remotely adjust electrical tilts became apparent. Remote electrical tilt (RET) has now become a common requirement for modern base station antennas with leading edge antennas employing RET actuators that are internal to the antenna and hence protected from the elements.
Whilst in the past operators still employed separate RET cables to the antennas, some operators are now utilising antennas with internal smart bias tees that enable the input of the AISG signal using the antenna RF port. This further minimizes the external components and cables that are required on site.
Another way operators can add capacity to existing cell towers is to convert an existing 3-sector site to a 6-sector site by splitting the cells. This could be done by replacing the existing three 65 degree azimuth antennas with six narrower azimuth beamwidth antennas (38 degree azimuth) and adding three additional radios to the site. However, with many cell towers already so congested, it is difficult to add three additional antennas to the tower. One solution that is becoming more prevalent is for the operator to replace the existing three 65 degree azimuth antennas with three twin beam antennas with each beam covering a 38 degree sector, thus effectively achieving the cell split but maintaining the antenna count on the tower.
Our Vice President of Strategic Marketing, Mr Philip Sorrells will be speaking at the upcoming LTE Asia event in Singapore on 18th and 19th of September about this and other Practical Considerations for Network Modernization and Optimization with LTE.