Femtocell chip gains channels blurs definitions

A chip designed to act as the heart of 32 or 64 channel public-access femtocells has been launched by picoChip.

The UK company expects the chip to be used to build 'metro femto', rural femto and high-capacity in-building femtocells, marking a shift from the consumer devices, such as Vodafone's SureSignal box, in which picoChip has found its initial sales.

Doug Pulley, CTO of picoChip, said: “With the PC333 we have extended the parameters of femtocell performance to levels that would traditionally have been considered as ‘picocell’ or even ‘microcell’. This high performance coupled with zero-touch provisioning means carriers can routinely deploy femtocells as part of their wide-area network rollouts. We are already seeing the emergence of femtocells in rural and metropolitan-area basestations.”

Peter Jarich, service director with Current Analysis, said: “Until now an HSPA-capable basestation with 32 or 64 channel Release 8 LABS specification would have been called a ‘microcell’ – a market segment that’s largely been ignored by most major 3G basestation vendors. Supporting this type of infrastructure development, picoChip’s PC333 could shake up the 3GPP radio access network space – helping to extend the life of 3G as LTE matures.”

The PC333 supports 32 channels of simultaneous voice and HSPA+ data. Pulley says that some other vendors are specifying their parts as supporting a certain number of users, rather than as supporting a certain number of full voice, data and signalling channels, which is less technically challenging to achieve. The PC333s can also be used in pairs to support 64 channels.

The part supports MIMO antenna arrays, which helps it achieve the signal discrimination necessary to support 32 channels. "It's not a 'nice to have', it is essential," said Pulley. "It is pointless deploying these boxes if you don't have it."

picoChip also claims it is the first to conform to the Local Area Basestation (LABS) standard, a fuller definition of the initial 3GPP femtocell standard that is intended to make designs meeting its requirements more suitable for use in public access situations.

LABS is the 3GPP definition for systems with higher performance than home basestations, allowing higher capacity, 120km/h mobility and +24dBm output power for greater than 2km range.

"Some companies have not designed to the full LABS requirements, for cost reasons," said Pulley, arguing that meeting the full standard makes the resultant cells much more useful and more deployable. "Operators don't want their choices to be constrained [by underspecced kit].' he said. "It's quite a big [design] envelope for a small basestation, but it is unlikely that you will encounter areas in which it is deficient."

The PC333 includes 'SmartSignaling' as a way of keeping network connections alive for what it claims will be 'in excess of 400' smartphones at once. One of the problems that operators have been facing since smartphones became really popular in 2007 is managing the signalling overhead associated with maintaining their connections and dealing with services such as polling for email and synchronising data. The picoChip solution is to include support for part of the 3GPP protocol that enables terminals to maintain shared network connections for small amounts of data without having to set up and tear down a full connection for every scrap of data that needs to be passed.

"This is the light touch in terms of signalling," said Pulley. "Otherwise you hog other parts of the air interface to multiplex the 'keep alive' messages for many users." Pulley added that many macrocell networks don't support the right part of the protocol yet, which may explain the problems some operators have been having.

picoChip sees the PC333 being used to build femtocells that can save operators money by offloading data from their wireless networks onto Internet backhaul connections at low cost. Pulley says some estimates suggest it costs operators $9 to carry one gigabyte of data over a macrocell network, compared with $2 over a femtocell network.  

The chip samples to lead customers this winter.

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