ThinkSmallCell interview with George Lamb, VP Operations, Nextivity Cel-Fi

George Lamb, NextivityNextivity have developed the Cel-Fi Booster, a simple to install device which improves indoor coverage. Unlike unmanaged repeaters, it is tied to a single network and can be remotely controlled by the host network operator. Here George Lamb, VP Operations at Nextivity, lifts the covers on the product, and forecasts strong market potential – especially in areas without wireline broadband where traditional small cells could not be used.

What is Cel-Fi?

"We've developed a self-installed signal booster which is physically two separate small units. One is placed near to a window where there is adequate reception and the other further away where signal levels are poor. The system can be up and running in a few minutes, it doesn't require any warm up period or authentication.

Where can I buy one?

"In most cases, the unit would be provided via an operator – often given away free in order to prevent customer churn – and would be locked to that network.

"Alternatively, they are also available from retail outlets and can come with multiple SD-Cards that are used to select the network. The full retail price for a one-off/unlocked device is typically around $600.

"The product is commercially operating today in almost 70 network operators worldwide, with stronger takeup demand in both the newest 3G networks and those which are most mature. Operators are typically targeting small businesses, high spenders/VIPs and residential customers (in that order)."

Cel-Fi Product Range

What technologies/radio bands are supported?

"The product supports 3G UMTS/HSPA+ networks today. Our first model, the RS1 (the two black boxes on the right hand side picture), handles a single 5 MHz carrier frequency. This operates at the most common 2100MHz frequency and was later extended to handle the AWS spectrum in North America.

"We then expanded the system to handle 3x 5MHz carriers in the RS2 model (the two white boxes on the right hand side picture). If the network is configured to always select the best signal, then the RS1 works well. However, if a network radio plan dedicates a specific carrier for voice or assigns a random one, then the RS2 is needed. There is a small price differential between the two models.

"Frequency bands 1,2,4,5 and 8 are all catered for although some frequencies may require an alternative set of passive components to be factory fitted."

How does Cel-Fi differ from a broadband repeater?

"(Unmanaged) repeaters often have a very poor reputation with network planners because they can create havoc and often reduce system performance. For example, they don't have any uplink power control and/or set a fixed gain level.

"Cel-Fi actively decodes the overhead message from the macrocell and executes a real-time pathloss calculation every 3.1 milliseconds. This means it will never overdrive the front end of the macrocell and adapts to external changes such as electrical tilt antenna or additional small cell deployments.

"The overhead message is also used to remotely control the device. By setting specific parameters on the macrocell, Cel-Fi can be turned off (and on again) in any individual macrocell sector. For our UK models, we've extended that feature to target any individual Cel-Fi unit using its serial number. This means the operator doesn't have to install any extra management equipment – they can just use their existing macrocell network management system to configure these specific parameters when needed.

"The main receiver unit has four built-in 5dB antennas – one at each side. The signal to noise ratio is compared from each and the best selected. This means that the unit can't be positioned in the wrong orientation, and if it is inadvertently turned around (for example after dusting or room-cleaning) it will automatically detect and adapt to the situation.

"Finally, we've developed our own custom ASIC chip specifically for this application. This allows us to modify and customize the system for specific operator or national requirements and achieve high performance. With virtually the same component set in both units, it also helps control costs."

What is the range and capacity of the system?

"The capacity of a UMTS sector is primarily determined by the total uplink power. Worst case would be at full HSPA+ data rates. For our single carrier unit, this peaks at 6 concurrent/active data sessions or around 30 active voice sessions depending pn how far away from the base station you are. For our three carrier unit, 18 data and 90 voice respectively. However, there is no hard cutoff, so data rates would be reduced should more users attempt concurrent use.

"The footprint of the booster is determined by the path loss between the two units. If these are placed further apart (for example in a large country house), then the power and range of the transmitter is increased. For small apartments where the units are more closely positioned, then the lower path loss translates to a lower power/shorter range.

"Network capacity is slightly improved overall because the link budget for each mobile connected through Cel-Fi is about 2-3dB better. This reduced power translates to more capacity in the cell. Perhaps surprisingly, the more Cel-Fi deployed the greater the cell capacity. However, this small increase must be matched by the macrocell backhaul and doesn't compare with the large capacity gains possible through traditional small cells."

Can you share some details of your next products?

"We're currently working on the 3rd generation of our chipset which will support HSPA+ or LTE or a combination of both. These units can either be locked to a specific network operator or configured using micro SD cards or micro USB cable.

Any plans for a multi-operator product?

"Not at present. The FCC has been very active in the US to set clearly defined rules for boosters. While not yet completed, it looks like these will disallow broadspectrum devices in favour of carrier specific ones. There should be no problem installing multiple devices in properties which require multiple network coverage, such as guest houses/hostels in remote areas."

What is the strongest market?

"The product works where no wireline broadband is available. Looking across the globe, 51% of the population today have no residential broadband and may never have access to Wi-Fi, cable TV or femtocells but could use Cel-Fi.

"There are also some of the smaller operators for whom the initial cost of a femtocell gateway and integration aren't easily justified. By comparison, the launch cost of the first Cel-Fi deployment is only around $500 (the cost of the unit itself).

"We have seen several networks which offer both residential femtocells and Cel-Fi, choosing our product in locations without adequate broadband or where the customer can't easily self install.

"In fact, the ease of installation has been a strong point – over 95% of installations don't result in a call to the call centre, and of those who do call, the first call resolves the majority of issues. One of our customers claims a 97% success rate to stop churn due to poor coverage."

ThinkSmallCell's take on this product

Nextivity do seem to have addressed the majority of issues associated with repeaters with this innovatively designed cell booster. While today's unit price is comparatively high compared to a femtocell and it doesn't match the total network capacity benefits, it certainly has a place in the market.

I could see this being very popular in regions without any wireline broadband, and will also complement residential femtocells in more mature markets. Today's product is very much targeted at the small business/residential customer and unlikely to be applied in public access areas where metrocells would be more prevalent.

Nextivity Website

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