Small Cell Chipsets

Several key chipset functions are needed to build a small cell. These provide the same capabilities as found in larger macrocells but at a fraction of the cost, consuming little power and taking up minimal space.

Three major elements can be physically integrated or combined into a common solution:

1. An RF Front-End connects to the antenna and converts the digital signals to and from radio transmissions
2. Baseband processing which analyse and decode the complex transmissions into meaningful data
3. 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.

Small cells have achieved tremendous reduction in component count by integrating much of the functionality into a few critical chipsets. Each new revision of vendor chipsets integrates more capability as we move closer to a complete system on a chip (SoC).

There is still a distinction between the baseband processing chipset (which are digital) and the RF front end (which is analog), although recent iterations from some vendors have combined the two especially for lower power (indoor) products.

Baseband Small Cell Chipsets

Separate small cell chipsets have been developed specifically for 3G and LTE technologies, but more recently we have seen powerful products capable of running either (or both) simultaneously.

The 3G residential small cell market was initially dominated by Picochip (since acquired by Mindspeed, then Intel) and later overtaken by Percello (acquired by Broadcom) whose latest hardware can run 3G and/or LTE. Qualcomm who offer both CDMA and UMTS chipset variants, are newer to the market. It's now a two horse race between Broadcom and Qualcomm, especially for emerging new designs for LTE and/or 3G/LTE multimode products. A few older products continue to ship using the picochip design.

Higher capacity Enterprise and Urban small cells have attracted investments and specific product variants from the larger vendors who already supplied macrocell parts: specifically TI (Texas Instruments), Freescale and Cavium.

Intel appear to be refocussing on Cloud RAN solutions where the baseband processing hardware is centralised although do continue to support earlier picochip/Mindspeed customers.

RF Front End Small Cell Chipsets

MAXIM have been the major supplier of RF front end components for 3G residential femtocells, and continue to be a major player. Other vendors including ADI and Lime Microsystems also have market share.

Qualcomm take a slightly different approach and incorporate the RF front end into their solution set, so a separate vendor RF front end chipset isn't required. Broadcom have also integrated the RF in some of their latest products, such as the BCM616x0

For some insights about how these vendors are approaching the market, read our interview with Jerry Wei, Business Manager for Wireless RF transceivers at MAXIM and Dr Busheri, CEO of Lime Microsystems.

The wide range of frequency spectrum options which could potentially be used for LTE brings a requirement for a single but adaptable design. Some RF components can be easily tailored by selecting alternative passive components during the final stages of product assembly.

TDD mode requires a different circuit design but can often use the same standard components.