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- Published on Sunday, 29 March 2009
- Written by David Chambers
Femtocell Hardware ComponentsSeveral chips are needed to build a femtocell.
- An RF Front-End connects to the antenna and converts the digital signals to and from radio transmissions
- Baseband processing which analyse and decode the complex transmissions into meaningful data
- Control processing which runs the software to communicate with handsets and the femtocell gateway.
These chips would be supported by separate memory chips, typically a read/write chip for transient data (called RAM) and a read only chip which holds the program (called ROM). These are standard components used in many electronic devices.
A critical component is the crystal frequency oscillator which provides a very accurate clock, important for synchronising the timing of signals to handsets. Rakon are leading the supply of low cost oscillators for femtocells.
There is a tradeoff for femtocell designers between availability and flexibility of the hardware chips used and their cost. Some femtocells have been developed using standard DSP chips which are immediately available in quantity, but at a price. Other manufacturers have developed femtocell specific "System on a Chip" devices which are much cheaper when bought in large volumes, and also use much lower power in operation.
The main suppliers of these chipsets include:
- picoChip where their PC2xx range was used for many early HSPA, LTE or TD-SCDMA designs. Their more recent PC3xx range has been optimised for HSPA femtocells. They have dominated the initial market for femtocell designs.
- Texas Instruments (TI) who have supplied their DSP solution without any modification. This leads to a higher power design than those with dedicated chips. These are targetted at enterprise and outdoor systems.
- Percello (now Broadcom) who have developed high performance chipsets only for the femtocell market, capable of up to 21 Mbit/s data or 16 voice calls.
- Qualcomm who offer both CDMA and UMTS chipset variants, and are newer to the market.
The RF front end is also integrated into a single chip. The main suppliers being:
MiddlewareFemtocells must comply with the 3GPP standards, including communicating with handsets and femtocell gateways using pre-defined protocol messages. This common set of software programs is closely linked to the hardware used. Femtocell vendors either develop this themselves, or buy it in from a software house. Continuous Computing, Aricent and Node-H (who specialise in the femtocell stack) are well known names in the supply of this type of software, and would also supply services (and experienced people) to adapt and tailor it to match the specific needs of the femtocell vendor. Middleware must be designed to match the industry standards and enable interoperability with other devices including femtocell gateways, management servers and handoff to external cells.
Application SoftwareThis is one area where the individual femtocell vendors differentiate themselves significantly. The so-called "secret sauce" or expert knowledge is added into how the femtocell operates by incorporating specific smart algorithms into the software which controls the overall operation of the femtocell. This would include:
- what the femtocell does on startup and how quickly it is ready to make/receive a call
- how it searches out and determines the correct frequency/scrambling codes to transmit on
- how quickly it responds to a changing environment (e.g. someone opening a window)
- What handover options are available when entering/leaving the home
- what features are provided specifically for enterprise/business users
- what self-service management features are included, such as setting up a list of barred/enabled phones
- what diagnostic features are incorporated to reduce the cost of remote diagnostic/maintenance and customer care
To a large extent, this application software creates the USPs (Unique Selling Points) of the individual femtocell solution and so is very much proprietary to individual femtocell vendors.
Read on to find out who makes femtocells
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