Microwave Engineering Europe - March 2009 - (Page 19) WIRELESS INFRASTRUCTURE 19 applications based on these standards will be overlay, or home basestation types. In contrast, newer standards such as China’s TD-SCDMA, and future developments such as LTE, will include femtocells ‘from the ground up’, as an intrinsic part of the operator network. As a result — and because it is a mature standard in high volume deployments around the world — the WCDMA market is furthest down the road towards ‘consumerization’. What this means is that a device such as the PC302 needs to enable OEMs to manufacture a femtocell as a fully-fledged consumer product. The use of advanced fabrication technology is therefore essential — the PC302 uses a 65 nm process — and in addition to the 3GPP NodeB modem itself, the design must include as much support as possible for self-configuration and self-optimization, core network integration, radio network control, and security. The uncomfortable reality for chip makers is that this is not a list of ‘nice-to-have’ add-ons. Because the use of femtocells poses considerable practical difficulties, these features are not optional. Fortunately, 3GPP recognized many of the challenges early on, and has made considerable progress towards defining how they should be solved. These requirements are now included in Release 8. As great as the culture shock of consumerization is the move away from the traditional approach to constructing a network, in which basestations are deployed in a carefully planned, co-ordinated way. Of course this is not the case with femtocells, and is the root of many of the changes and extra features added to the standards. Traditional network architectures were manually planned and configured. For GSM this means complex frequency planning: WCDMA-based systems require the allocation of unique scrambling codes. In a traditional basestation the transmit power also needed to be set at the time the node was added to the network and constantly adjusted. The self-configuring femtocell has to perform all of these tasks for itself automatically; implementing such functions turns out to be a major part of the overall design task. In order to do this, the system designer needs access to information about the surrounding radio environment: it is this requirement that makes it essential that a singlechip femtocell implementation should fully support SON principles. A device such as the PC302 does this by implementing ‘sniffer’ or ‘network listen’ functions. When it is first powered-up, the femtocell configures itself as a terminal (‘user equipment’, or UE, in the 3GPP jargon) in order to discover what other cell sites are surrounding it. It is therefore able not only to choose an appropriate coding scheme and radio power level, it also has the information it needs to facilitate hand-over between itself and adjacent cells. As users move in and out of range in a mixed 2G/3G network, the 3G femtocell can even hand-off to a nearby GSM basestation. In addition to initial configuration (sometimes known as ‘zero-touch provisioning’), sniffer functionality also allows the femtocell to adapt to on-going changes in the radio environment, for instance adjusting its power levels when other femtocells appear in the network. Network architecture implications The advent of the femtocell also has implications for overall network architecture. Traditional WCDMA networks include a basestation (NodeB) that interfaces with a radio network controller (RNC) and then communicates with the core network. The interface between the NodeB and RNC is via the 3GPP Iub standard (TS 25.434), over expensive dedicated leased lines. Incorporating femtocells into such an arrangement presents a number of architectural challenges. RF testing out of control? Only Keithley gives you the RF test tools you need to rein in today’s devices and tame tomorrow’s challenges. MODEL 2920 RF SIGNAL GENERATOR MODEL 2820 RF SIGNAL ANALYZER ■ Test the most complex signal structures, including 802.11n WLAN MIMO and 802.16e Wave 2 WiMAX. Configure a 4x4 MIMO test system costeffectively. Generate and analyze signals up to 6 GHz repeatybly and accurately with our instruments’ software-defined radio architecture. Reduce your time to market and cost of test with MIMO systems optimized for R&D and production test. ■ ■ ■ Go to www.keithley.com/tame and try a demo. www.keithley.com/contact info@keithley.de Microwave Engineering Europe ● March 2009 ● www.mwee.com http://www.keithley.com/tame http://www.keithley.com/tame http://www.keithley.com/contact http://www.mwee.com
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