Femtocell Silicon Gets Flexible Yet Stays Cost Competitive

Lime Microsystems LMS 6002 is a multi-band multi-standard rf transceiver for femtocells.

The goal of wireless operators is to provide full mobility and seamless roaming to ensure permanent access to broadband connectivity for the end user. Today this is available via the mobile phone network, though coverage is patchy indoors and in remote areas. This means that not all users can get the seamless coverage they desire.

Networks of small cell base stations–“femtocells”–are being deployed to enable better coverage in buildings and high-performance data services on mobile devices. A femtocell is essentially an access point that allows a user to reliably connect from their mobile handset to the mobile phone network via a home DSL or cable broadband connection. For operators, femtocells represent a cost-effective way of increasing in building network coverage and capacity.

Having solved many of the technical challenges, femtocell OEMs have to contend with a market that is constantly evolving with the introduction of new standards and frequency bands. One example of such an emerging standard is Long Term Evolution (LTE), which has been developed to bring true high-speed broadband to consumers. The key features of LTE include data rates that are 5x that of HSPA with reduced data latency for video and TV streaming.

It’s no surprise that there is a lot of interest in LTE from operators. The issue is that with so many wireless standards already out there, LTE is fighting for spectrum. Hence, emerging standards such as LTE are likely to end up in different frequency bands for various countries, similar to the situation with 3G and WiMAX. In the U.S., Verizon and AT&T have announced plans to deploy LTE in the band formerly used by analogue TV at 700MHz. European operators are looking at the 2.6GHz band which is not currently in use in most countries.

WiMAX is another standard that is being adopted in different frequency bands in a number of countries around the world. The WiMAX forum has published three licensed spectrum profiles: 2.3, 2.5 ,and 3.5GHz, each of which has already seen some deployment. For example, 2.5GHz looks to be the most important in the U.S., while Asia will likely adopt the 2.3GHz band. There is still the possibility for other frequencies to open up.

Although there are many arguments in favour of wider adoption of LTE compared with WiMAX, there is nevertheless a battle emerging as the two are directly competing for spectrum in some countries. For example WiMAX has opportunities in emerging markets such as China and India where wireless infrastructure is not already in place.

Going forward, it’s clear that these emerging standards and frequency bands that are on the horizon will require a fresh set of products from wireless system OEMs. A way forward in tackling the complexities associated with these emerging standards and frequency bands is to have fully programmable chip sets that can be configured for a given standard and frequency band of interest.

How Programmable Silicon Can Help

When a country allocates spectrum to a particular operator or standard, femtocell OEMs will typically need to develop a new product for that particular market. This means that they will require a new baseband IC, RF transceiver IC, power amplifier, associated filters, passives, and antenna.

Evidently, in the fast-moving wireless market, femtocell makers need to develop a new product or range of products to stay competitive. The problem here is that developing new ICs for the new standard or frequencies could take several years, typically 2-3 years, from conception to volume production. Deployment of femtocells in various markets is thus limited by the time it takes for the silicon vendors to develop new chipsets.

Programmable silicon designed specifically for femtocells may fill the gap. Baseband ICs are increasingly becoming multi-band or multi-standard, with programmable RF transceivers not far behind.

A programmable RF transceiver can simply be configured to operate in any frequency band. Provided it is sufficiently frequency-agile, it could facilitate fast, reliable, and economical deployment of femtocells. The same transceiver IC can be used in different product ranges and geographical locations without the need for the development of a new chip.

So if a new frequency band emerges, or femtocell OEMs wish to move into a different global market, they can simply reconfigure the RF transceiver accordingly. Design reuse can be maximised across their product range, shortening the production cycle and allowing them to move quickly into new and emerging markets.

There are convincing arguments for how programmable silicon can reduce costs for femtocell OEMs. Using just a single type of RF transceiver and baseband ICs for a whole range of products results in economies of scale by capturing larger volumes. There are also significant cost benefits associated with simplifying manufacturers’ inventory (see the figure).

On the other hand, flexibility is absolutely the key to reducing OEMs’ response time in a market where standards and frequency bands are continuously emerging, evolving, and changing. Programmable silicon can provide this flexibility to give OEMs a head start on designing new femtocell products.

In fact, femtocell silicon is becoming increasingly flexible whilst remaining cost competitive. The ultimate goal is a single bill of materials for a femtocell product that the manufacturer configures to operate in the desired standard and frequency band. Baseband and RF transceiver ICs are already providing this flexibility with power amplifiers and antennas following suit.