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The DAS & Small Cells Column

August 15, 2013

Smart DAS, the New Kid on the Block — 

By Ernest Worthman,  Editor,  DAS & Small Cells Magazine

The evolution of distributed antenna system technology is exactly what the doctor ordered for the emerging wireless small cell infrastructure. In fact, going forward, DAS will be a majority player. In that vein, there is a new kid on the block – “smart DAS” – the integration of DAS, small cells and multiple-input multiple-output (MIMO) antennas. Other smart antenna technologies exist, of course, but MIMO is bubbling to the top as the technology of choice for small cells.

Smart DAS is seen as a significant uptick in the development of small cell technology and an ideal platform for MIMO. What makes smart DAS so intriguing is that it utilizes today’s cutting-edge technology in sophisticated digital signal processing equipment. That integration will be the ideal one-two punch needed to develop the next generation of DAS and small-cell-specific antenna systems.

Various schemes of antenna manipulation have been used for some time (more than 45 years in RADAR and some military apps) to add a measure of intelligence to RF transmissions. This runs the gamut from simple sectorized and signal-shifting systems to more sophisticated schemes such as diversity, switched beam and antenna arrays. For antennas themselves, using approaches such as direction of arrival (DOA) and beam forming improves signal recognition and precision. But that isn’t really “smart.” It’s just optimization, and it’s fairly simple to implement.

There are also signal analysis and routing schemes in the processing equipment that identify target signals and attenuate interferers. Again, although this can be considered “smart” by some standards, there really isn’t any deductive reasoning (insofar as a computer can emulate that) to intelligently analyze the signal, especially for emerging DAS and small cell environments.

Such technologies are designed for non-DAS and macro-cell deployments and do not scale well to small cells. Only recently has advanced antenna and signal processing technology trickled down to DAS and small cells. Small cell systems-on-chip (SoC) have not really been designed to support specific DAS design parameters such as long cable run delays and the specific antenna technology involved in small cell MIMO.

Conventional “smart” and antenna systems capture the input/output RF signals just as normal antennas do. In smart antenna systems’ digital receivers RF signals are converted to digital domain by analog-to-digital converters (ADCs). In transmit mode, the process is reversed and the baseband digital signals are converted to RF using digital to analog converters (DACs). The down conversion from RF to baseband or up conversion from baseband to RF is still generally done with IF signals.

The “smart” part comes into play in the digital domain and the latest advancements in wafer geometries, which allow the development of SoCs that address these intelligence shortcomings, and consequently can be scaled to DAS and small cells.

Now we’re moving into the smart part of the system. Once processed, the baseband signals are combined using the “smart” algorithms in a digital signal processing (DSP) section and managed relative to the system’s design and components. New technology small cell SoCs integrate the digital processing section on DSP OR FPGA and integrate platform support for local area base stations (LABS) soft handover (SHO) standards and 3GPP. With today’s SoCs, “smart” algorithm implementation usually is a software code, making them field programmable and upgradeable. In some cases, smart algorithms are implemented in an ASIC or FPGA but these are generally for application-specific systems.

From a technology standpoint, DAS integration with small cell technology is exciting. Going forward, small cell deployments are expected to be 70 percent of all new cell installation. From what I can gather, I expect the small cell stratagem, and DAS support within that, to rival the cellular rollout of the late 20th century. Wow and we get to be part of that!

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Ernest Worthman is the Editor of DAS and Small Cells Magazine, a contributing editor to AGL magazine and the principle of Worthman & Associates, a technical writing and high-tech media/PR firm

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