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Best solutions to improve coverage in elevators

Proving coverage in elevators is always a challenge even to the experienced RF designer. There are various solutions to this problem and they can vary according to the country’s regulation and coverage requirements.

Elevators tend to have a high path loss (15 to 40 dBs), almost behaving like a Faraday cage and are in constant motion. Things can get tricky when it’s a building with a high number of floors. There are some solutions to help to achieve a good coverage in these metal cages.

1-Elevator hall antenna

It’s the most used solution. It’s effective and simple to install since there are no special requirements  An omni antenna placed near the elevator’s entrance can provide coverage when a user passes through that floor. One approach is to place an antenna on each floor, if the elevator path loss is high. A more cost efficient solution is to place an antenna on even floors. The appropriated solution can be validated by running some simulations using a transmitter. It’s also a good idea to keep the elevator antennas of the same sector. This way we can avoid unnecessary handovers when the subscribers are moving.

2-Directional antenna in the elevator shaft

This solution requires special permission of the authorities, but it is very effective when combined with solution 3 – see below. An antenna is placed on the top of the elevator shaft (yagi or panel). The shaft behaves like a waveguide bringing sufficient RF levels inside the elevator. Placing an antenna on the top of the shaft can lead to spending a lot of coaxial cable if the technical room is on the ground floor. It’s a good idea to spend some time doing some math and verify the cost of this solution.

3-Antenna in the elevator

This solution requires to install a passive repeater in the elevator. One example is to install two panel antennas (one outside the elevator and another inside). Remember to use this solution combined with solution 2, so that it can be possible to have enough signal to repeat. Most of the times this installation requires special permission from the authorities.

4-Radiating cable in the elevator shaft

Due to its high cost, installing radiating cable can have a big impact on the project budget. But can be a good solution since obtaining a special permit from the local authorities can be easier. It’s also a requirement to have an adequate link budget for this solution.

As a rule of thumb consider to do some real world simulations, since the path loss can vary, depending on the type of materials the lift car is made. If only the elevator manufacturers could do some tests in most common frequencies, it would be possible to see the pathloss in their product datasheets.

The increasing demand for indoor wireless systems

Imagine you move to brand new luxury apartment in tall building. After unpacking you think on making a call with your mobile phone to your parents or friends to catch up. The voice quality is low and you can’t understand anything the other party is saying. You move to the window to see if the reception becomes better. As you approach the window the quality gets even worst and the call abruptly drops. This is what happens with millions of mobile users all over the world.

This is a well known problem in tall buildings where interference is a major headache for radio planning engineers. New York Times reports that consumers are becoming more demanding, and most of the times an indoor distributed antenna system must be deployed.

(…) Eric Brunnett, the director of information technology for Trump SoHo, said that complaints about cellphone reception from guests at Trump and other companies’ properties had been increasing over the past few years. “They don’t like it when their cell signal doesn’t work,” he said, “and it’s becoming a big part of their decision on where they’re going to stay(…)

According to a recent survey by Parks Associates/FemtoForum, 41% of the users (US) report slow access to mobile internet and 26% complaint about dropped calls at home. This scope of this survey was to evaluate consumer needs in terms of the femtocell market.

Are we seeing a shift in the inbuilding wireless ecosystem where landlords actually install and accomodate mobile operators needs in order to maintain their tenants? Is indoor wireless becoming an utility just like water, gas or electricity?  Time will tell, but things are definitely changing.

2011 Predictions for the in-building wireless industry

graphRecently, Mario Bouchard (for those who don’t know is the CEO of IBwave) asked the LinkedIn Ibwave user group, what were the group’s predictions for 2011. The timming of this question couldn’t be better. The indoor wireless industry is been gaining momento, due to the growing traffic demands and user neeeds. We can expect to see a growing interest in the industry at the eyes of operators and building owners. The DAS will start to be a very valuable asset and become a standard in all major buldings.

Here’s Mobile Grid predicitions and wishes for 2011 for the inbuilding ecosystem:

  • Mobile Applications are created that can take advantage of the existence of a indoor DAS (LBS, venue web portals, etc)
  • Multi-Band Repeaters gain market. – they are more adaptable to future frequencies and technologies (such as LTE). Node-A from Andrew is an example.
  • Repeaters get even more intelligence – allow accurate traffic estimates and adapt to macro-network changes easier
  • change in the building’s owners-mobile operators relationship. No more renting.
  • buildings owner participation on the DAS CAPEX gets higher.
  • Telecom Regulators start having more interest on the indoor DAS regulation.
  • LTE frequency auctions: we will see indoor project demands by the telecom entities.