Interview with Rich Kerr, CEO of Public Wireless, a US based Metro-Femto pioneer

rich-kerrPublic Wireless is a new US company pioneering the use of various femtocells and related small cell technology in public areas – providing unobtrusive coverage and capacity where cell towers wouldn’t otherwise be viable. Rich Kerr, the CEO, explains his approach and how it could be set to radically change the face of mobile cellsite topology.

What exactly does Public Wireless provide?

As a common carrier utility in many US states, we sell a  turnkey service directly to the carriers – the mobile phone networks – in the US. We have access to a huge number of potential sites. There are several hundred thousand miles of telephone, cable and electricity street wiring we can hang our equipment from in conjunction with various incumbent partners. We also have agreements with billboard owners, payphone operators, retail chains, and any owners of real estate traditionally not usable for high impact wireless siting.

We design our own miniature cellsite equipment in partnership with radio OEMs, and adapt it for outdoor use with a commonly addressable management environment designed to minimise truck rolls and maintenance visits. The equipment is housed in a  hardened enclosure with remote management, diagnostics  and control. We facilitate a secure tunnel for remote management and traffic back to the operator network to meet the operator requirements.

The equipment is then installed unobtrusively and quickly on a typically 10 year managed service lease to the network operators. A single site can accommodate multiple networks, supporting technologies such as 3G UMTS, 3G CDMA and Wi-Fi all in the same box.

Such an approach is much more acceptable in communities who might object to a large cell tower yet demand high speed mobile service in their area.

What’s unique about your approach?

We build our own RF front end for our systems, ranging from 1 Watt to 20 Watts. We use a variety of interference mitigation techniques to avoid affecting the existing macro cellular network. Our technology is independent of RF technology, RF boards or backhaul transmission.

We focus on how to minimize the speed of deployment. For example, we reused our design with Ubiquisys to engineer a working prototype in a few weeks for a trial demonstration. Once we have the engineering prototype, then we progress it into our production environment. Additionally, our sites can be shared by multiple operators in the same box and we can add an operator to one of our sites as a fast upgrade.

Do you install indoor sites too?

We don’t do much indoor space today, unless our products add enough value to make that attractive. It isn't really our sweet spot. Many stores need to provide coverage for several networks at the same time and up to now this hasn’t been feasible at a price point suitable for small to medium businesses. The present way to do this is to put in-building DAS systems.

Enterprise [Business] customers tend to be tied to a single network operator in return for lower cost calls and extra indoor coverage/capacity. These would be handled by a single femtocell vendor and operator.

Why did you get involved with femtocells?

There’s a lot of “name pollution” in this market, making it difficult to draw the line between pico, femto and other terms. We’ve been using picocells for some time. Our requirements are for a solution that is a managed Distributed Network Element (DNE) which contains:

  • 8 to 32 voice channels
  • 1 EV-DO or HSPA carrier
  • 1 to 2 km cell radius
  • 10 Mbit/s backhaul using IP

This approach gives us a tele-density which is at least as great as a macrocell, but much cheaper in backhaul terms. This is because it uses virtually any available IP transport layer (DSL/Cable/Fiber/Microwave) over existing fiber, coaxial or copper wires, rather than needing a newly constructed and/or dedicated connection to each and every site, such as with outdoor DAS installations.

We believe that the answer to the current capacity of many carriers’ problems is cell splitting. Although LTE has extra performance and will be used with additional frequencies, it can take 7 to 10 years to take full advantage of a technology in a new spectrum band. New handsets and cellsite equipment needs to be bought and installed across the whole user base before this can be used. For example, the 700MHz spectrum has been out for a few years and is only now coming into use. AWS has been in play for longer than that.

Why did you choose Ubiquisys?

We chose Ubiquisys due to the level of innovation they have achieved. They are unique because they have really spent time on features such as handover calls between femtocells without going through the RAN core and many network IP features. This substantially reduces the load on the network. While the concept of cell splitting can give much greater capacity overall than adding new frequencies, if this burdens the RAN core then it wouldn’t scale.

Although Ubiquisys and other femtocells offer some self-organizing and self-configuring aspects, some radio planning is still required to determine the best locations for new planned cellsites, for example to avoid ping-ponging handovers between cells and assure a contiguous underlay of coverage footprint. The outdoor femto or pico must be planned into the overall carriers network.

Are your sites all used for the same purpose?

There are three classes of these small cellsites which our products address:

  1. Coverage, in areas where it’s not been possible to get zoning permission or planning permission to erect a cell tower from the local authority. We can install a site unobtrusively within a short period of time that doesn’t require the same levels of special permission.
  2. Macro Sector Off-load, in areas where there are hotspots of capacity in a large cell area that adversely affect the rest of the coverage area. An example would be a student dormitory, which can be offloaded to a local hotspot. This allows the students much better throughput and the macro cell users  get better service.
  3. Data Capacity, providing a mesh of small cellsites which give enormous data capacity in urban areas at a higher backhaul density and a higher data throughput.

What about LTE, the new 4G technology?

4G needs a very small cell radius to get the high data rates. For example, we’ve seen WiMAX go down to smaller cell radius than 3G EV-DO. We have an LTE capability in our box on the roadmap for later this year to meet this need. We see LTE as a major driver of this small cell splitting technology.

Won’t the full speed of LTE be limited by using DSL/Cable backhaul?

Our approach on LTE is to get it to market first. Given the reduced coverage area per site, we think 10 Mbit/s may be satisfactory enough at launch, but that is up to the customer. With new variants of xDSL, cable modems and even microwave, we believe we can meet the demand for faster backhaul in the medium term. We have plans to be able to upgrade the backhaul when needed.

What is the power consumption of your boxes?

The RF transmitter sets the power consumption of the box. The linear power amplifiers in cellsites aren’t nearly as efficient for 3G as they are for 2G because of the high modulation techniques used.

A typical 2G/3G combined site could use from 40 to 200 Watts (depending on the configuration) when operating at full power, and may be emitting anywhere from 2 watts to 20 watts of RF power per PA. A simpler 2G GSM only site could be down at 25-50 Watts power consumption for a similar range.

Why is this approach needed now?

Smartphone usage has changed the game. It’s killing the network capacity and grows rapidly over time as applications are used more. There’s an unpredictable demand to satisfy.

Carriers are still in a cycle of macro cellsite rollout and upgrades. While it is what they know well, this just takes too long and the operators will be outrun forever by data demand if they continue on this path without fully embracing the paradigm shift. They need not only faster ways to roll this out, but more flexible ways to roll it out as well.

Many in the siting services industry are tied into a site deployment ecosystem that is rapidly becoming less relevant with its construction oriented cost structure and timelines. Layers, delay and complexity are the enemy of efficiency and have no place in a new siting era focused on optimized OPEX.

There needs to be a different technology and commercial approach. An eco-system is now emerging for developing dense cell siting based on a different scope and cost structure.  The new technologies (Wimax/LTE) are rolling out faster than the siting and deployment can keep up.

Why not just rollout Wi-Fi using the same approach?

We can and do provide Wi-Fi (802.11a/g/n) and other items in the same box as a modular option. Since so many smartphones have this feature why not use it?

However, Wi-Fi networks haven’t proved commercially viable on their own – the economics of hotspots aren’t profitable to the operator as a standalone business. Wi-Fi only has 3 non-overlapping channels and is subject to interference from other usage on the same frequency. This means it may be a nice to have but it’s not so optimal a system design as found in cellular networks. It is also a nomadic service at best, not mobile.

And finally….where’s your most unusual installation to date?

That has to be at the Diamond Head Lighthouse in Hawaii. After years of most operators not being unable to find a suitable site for a cell tower, we were able to install a small cell in a matter of hours which gave full coverage of the area without affecting its natural beauty.


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#1 david Conklin said: 
I have a really dumb question. I am new to the Femto technology but come from the telecom supply world providing long range pair gain technologies and ADSL extension products. My question is this; does a Femto deployment always need a broadband backhaul? Where there is this exceptional creativity in locating Femto's to both expand cell coverage and increase throughput don't you need to connect the Femto product to a broadband connection no matter where the Femto product is installed? Sorry for the dumb question but having gone through the battles of getting telcos to approve range extension devices my understanding is that deployment of Femto sites would be limited by the availability of a broad band connection.

Thank you

0 Quote 2010-04-23 21:25
#2 ThinkFemtocell said: 
@David Conklin: Not a dumb question - although femtocells are simple to use they are quite a complex technology spanning several disciplines. Answer is yes, the formal definition of a femtocell is that is requires an IP broadband backhaul to connect back to the mobile operator's network. This is usually ADSL or Cable modem.

This differentiates femtocells from repeater devices, such as the concept presented by Qualcomm (see separate article on ThinkFemtocell) . For areas without any broadband today, then either some form of repeater could be considered or perhaps the latest/cheapest satellite broadband now coming to market.
0 Quote 2010-04-29 09:19
#3 dorna d said: 
I've been looking for an outdoor setup 2-5k range that i can couple with a solar panel fed by a 5ghz backhaul. google has not been co-operative.
0 Quote 2010-08-18 09:39
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