'Active DAS can address call drop concerns'

BANGALORE, INDIA: Mobile call drops due to weak signals are commonplace today, especially inside a mall or stadium or airport. Although all the five bars on the mobile device will be flashing green, indicating a strong signal strength, people do experience call drops inside such buildings, very often.

“The problem is with the radio frequency (RF) signals transmitted from BTS or base stations of telecom operators, placed outdoors. RF signals give a good coverage when it is in an open area. The moment you come inside a building, these signals get blocked by brick walls or glass doors. Interference due to signals from various BTS sources around also play havoc resulting in calls drop in spite of presence of strong signal,” says Partha Das, business development manager, India, CommScope.

Speaking to Deepa Damodaran of CIOL in an interview, he said it can be solved by adopting the distributed antenna system (DAS).

Excerpts:

CIOL: How can we solve this issue of signal block inside buildings?

Partha Das: We cannot put a base station inside a building. What we can do is artificially propagate RF signals inside a building using a distributed antenna architecture, which has several small antennas along with a tower or base station. These antennas can be fitted into the ceiling or corridor walls of such buildings.

These indoor antennas are connected to through a network of RF cables and Couplers / Splitters, and finally connected to the RF source i.e. a base station or an Off-air Repeater.  RF signals coming from several operators' BTS are combined using a combiner (POI) before being distributed through these indoor antennas.

This technology is called distributed antenna system (DAS). DAS is of two types - passive distributed antenna system (passive DAS) and active distributed antenna system (active DAS).

CIOL: How is active DAS technology different from passive DAS network?

Partha Das: Generally Passive DAS has limitations on coverage with a single RF source (BTS / Repeater) and is meant for smaller areas. Typically RF signals die out when traveling over cable lengths exceeding 200~250m, unless RF signals are boosted again using boosters (not effective as it also increases noise levels in RF signals). Therefore for larger sites, multi-BTS locations are essential if a Passive DAS network is decided to be implemented.

However, telecom operators may have objections to allowing multi-BTS for the same site owing to capacity restraints.

Active DAS solutions greatly help in case of large networks. Keeping a single BTS location, it can extend the RF signals throughout the building / site by converting the RF signals into optical signals, transmitting it up to much longer distances (up to 20Km) and then re-converts the optical signals to RF signals at specific locations of choice.

The system comprises few building blocks:

MASTER UNIT (MU) which collects RF inputs from various operator BTS, mixes the RF signals, processes for noise filtering and converts the RF signal to Optical Signal.

OPTICAL FIBER PATH which is used to transmit the optical signals to various strategic points / places in side the building (at various floor levels / blocks). Optical splitters are used to divert one optical signal to multi-locations.

REMOTE UNITs (RU) which collects optical signals and re-converts to RF signal which is then used to feed the DAS covering smaller locations ensuring adequate transmit levels.  .

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CIOL: How is the India market adopting this technology?

Partha Das: As far as India is concerned, active DAS is limited to a few installations, such as in Mumbai and Delhi airports.

There is a huge difference in price between passive and active DAS solutions. Indian market is very price sensitive. So, despite knowing the limitations of passive DAS, companies are still building passive DAS network and trying to manage with it.

We have found that in some cases, since the existing passive DAS network was unable to cover the required area, companies had to use multiple passive DAS, which is neither the right nor the optimum way of achieving scalability.

The market is right for the DAS adoptions now. However, a lot of convincing and explanations are required. If we are still fine with call drops and weak signals, then progress will be slow.

CIOL: What is i-POI (intelligent-Point of Interface) and how is it different from other POI solutions?

Partha Das: i-POI is a part of active DAS. Inside the Master Unit (MU) of an Active DAS system, typically a mechanical combiner is used to combine the RF signal inputs in various bands from multiple operators. This combiner is also often referred as a Point of Interface (POI).

So, when you are feeding BTS signals from multiple operators, in multiple frequency bands, such as GSM 900 band, 1800 Mhz, or 3G 3100 MHz, you need a POI device to combine them.

The problem with mechanical POIs is that they can only combine a set number of frequency bands and operators,  as they are designed and manufactured as per the configuration set during the first installation.

So, in case you want to change or add or remove operators or frequency bands, they cannot. That is where i-POI or intelligent POI comes in. 

Here, instead of a mechanically designed POIs, we have an electronically designed one, which gives the flexibility to add or remove any frequency band, or operator at any point of time. It is also a scalable architecture and going forward can also support 4G LTE (TDD or FDD).

It also provides remote monitoring facility, wherein if a configuration needs changes, it can be done by an operator remotely, from a network that is connected to its LAN.

CIOL: Whom are you targeting at with this?

Partha Das: Since it is not the prime objective of business for a telecom operator or a builder to set up a network, they will not be interested in this. It is the third party vendors such as, GTL, Viom Network or Bharti group, who will invest and can benefit from it.

However, average revenue per user, ARPU, of telecom operators is very low in the country. This is why operators are not able to share their profit with the vendors who set up such networks.

Telecom operators and vendors appreciate the technology, but unless ARPU improves and the neutral host companies get good returns out of their investment, they will not invest in this technology.