Is Sector Sculpting the Answer?

The search for a stronger signal on our phones to ensure optimal voice and data services has become routine in our lives. Whether we are on the move or at home, we are always expecting fast and steady connections.

The networks today are facing a massive capacity crunch. With a data hungry mobile society and its love for bandwidth-hungry applications, networks are constantly under pressure and struggling to keep pace, especially in LTE environments.

An effective way to solve the capacity problem is through sector sculpting. It is an ingenious approach to antenna pattern shaping that enables operators to carve out more capacity, improve coverage and limit interference.

Sector sculpting deals with all these issues and boosts network performance by controlling interference between sectors. It also helps in increasing the number of accessible subscriber channels.

Antennas-A Critical Part

The antenna is an important and critical part of the wireless system. It is also the most visible component of the wireless network. These come in various shapes and sizes and are built for specific purposes. The functional distance around an antenna is called the cell and multiple cells like these make up the cellular network.

These cells can also be reused to increase network capacity by reassigning individual frequencies within a particular cell. Typically, cells are represented as interlocking hexagons.

The hexagons can be miles across or cover just a few hundred feet depending on the density of the area served.

Sector Sculpting

Channel sensitivity is limited by external interference instead of noise issues, like older radio communications have traditionally been. Sector sculpting allows precise coverage with minimal interference with neighboring cells, through its specialized pattern shaping made possible with directional antennas, both in azimuth (horizontal direction) and elevation (vertical space).

A critical performance metric is the overlap of energy between neighbouring cells and sectors. The sector power ratio is a comparison of signal power registered outside and inside a desired receiving area as a consequence of an antenna's radiation pattern. The lower the ratio, the better the antenna's performance.

In cellular network applications, higher sector power ratios represent higher interference between antennas in adjacent coverage areas. Interference can increase due to overlapping competing signals and eventually reduce performance.

This causes performance issues, like dropped calls, and precise sectorized planning is required to prevent such interference.

To support the enormous amount of voice and data traffic, cellular networks re-use either frequencies or codes repeatedly throughout the network.

Usually, cells operating on similar frequencies or codes face high interference which can be minimized through sector sculpting techniques.

With sector sculpting and the resulting improved containment of interference, the same frequencies or codes can be reused in cells that are closer to each other while also increasing spectrum efficiency, capacity and network performance.

With the increasing density of cell sites, the coverage of individual cell sites is often reduced in order to reduce cell to cell interference. One can reduce the coverage from a cell site by lowering the antenna radiation center but this is usually not advisable as it will increase the chances of placing the antenna below many surrounding obstacles like buildings or foliage.

Another way to decrease coverage area is through beam tilting with sector antennas.

Beam Tilting

Beam tilting refers to the vertical pattern tilting of the antenna. Doing this reduces the coverage on the horizon-where interference to neighbouring cell sites takes place.

This is most easily achieved by mechanically tilting the entire sector antenna using adjustable brackets that most antenna suppliers supply. But coverage will be reduced more in the boresite direction and less at other angles away from the boresite.

This is also known as 'pattern blooming.' Advanced networks take advantage of electrical downtilt to elegantly tilt the sector antenna's vertical pattern. The antenna remains upright and beam tilting is achieved through changing the electrical phase delivered to each element. This helps in yielding a consistent reduction of the cell coverage. The tilt can be increased without increasing pattern blooming.

Electrical downtilt can also be achieved remotely with advanced antenna systems which will become more important with the migration to more sophisticated technologies like LTE.

Augmenting Capacity

As cellular antennas are directional, usually covering 120 degrees, three sets of these can cover all directions if mounted together on a triangular tower. In densely populated areas, additional traffic can be handled with narrower focus antennas (called a six-sector scheme).

This scheme is a proven and effective way to increase capacity but faces a limitation in terms of practical implementation because it requires replacing one antenna face with two. This causes weight and wind loading issues.

This can be overcome with multi-beam antennas which for example, produce two separate 38-degree beams with centers separated by 60 degrees.

This dual-lobe approach provides excellent coverage and only requires three antennas instead of six separate one-beam antennas. For higher capacity needs in high density capacity areas, antennas with narrower beams can provide capacity for even the most demanding areas.

Alternatives like 3-beam, 5-beam and even 18-beam antennas come with shapes that can significantly add capacity and also improve data throughput by increasing the gain of the antenna and containing the interference to other sectors for improved signal-to-noise ratio.

The Next Step

New technologies are being developed and the most-talked about cutting-edge networks today is collectively known as LTE, which has the potential to completely reshape how networks can perform.

It incorporates a concept called multiple input, multiple output (MIMO), which splits data transmission into multiple streams and sends them simultaneously on the same frequency using multiple antennas.

The fact that makes this development so exceptional is that MIMO takes care of a classic limiting factor of RF communications known as Shannon's Law.

The law dictates the amount of throughput delivered down a given amount of bandwidth. You can only expect to get within 3 dB of a bandwidth's theoretical maximum in practical applications but with 2x2 MIMO, you can potentially achieve double the capacity of a traditional 3G network which is bound by this law.

Sector sculpting becomes even more important for 4G/LTE networks since interference needs to be minimized if one desires to maximize the potential of MIMO. An increasing demand for faster speeds and seamless services means selecting the right antennas and using sector sculpting techniques will become important considerations for all operators.