ThinkSmallCell Interview with Pletronics

Pletronics OeXOThe team at Pletronics have a very up to date view of what's going on today at many small cell vendors. As one of the two leading suppliers of specialist oscillator components to the industry, they have a birds-eye view of the types of products under development and some of the issues arising. While not divulging specific customer details, they shared some great insights into the state of the industry today. Residential femtocells showing steady rather than spectacular growth; LTE small cell designs needing refinement and a new requirement for 3G Metrocells.

I spoke with the team there including K. Claude Lee (President); Johanna (Joey) Warren (Director Global Accounts); Dave Kenny (Vice President Research & Development) and Robert Henry (Vice President Quality Engineering).

Residential Femtocells – steady growth

We've read forecasts of many tens of millions of residential femtocells imminently about to be deployed. Each year, it seems is to be the year where volumes will take off. I asked if there was any evidence of a "hockey stick" growth trend developing soon.

According to Joey Warren, "In Taiwan, the ODMs (Original Device Manufacturers) are not looking optimistic about residential femtocell volumes to be shipped this year and forecast numbers are down. We're still talking about millions of units to be shipped this year, but with a few exceptions there is less confidence about mass market takeup.

Specifically for residential femtocells, the requirements for potentially costly components such as an oscillator remain tight. Some of the competing lower cost alternatives have poorer long term stability, requiring much more frequent sync – as much as 8 times more often. Long term reliability and performance is essential in consumer products to avoid large numbers of returns and/or poor brand perception, leading to ODMs to remain with established and proven suppliers.

The industry has bottomed out the hardware cost of a femtocell unit through extensive value engineering and the only way to reduce further would be through much larger production runs. Volume is key.

For the oscillators themselves, 100ppb (parts per billion) is the standard specification we have seen even though the 3GPP standards have relaxed the tolerance to 250ppb.

There may be several reasons why femtocell numbers have been held back. In North America, the strict E911 emergency call requirement for accurate location has meant units need to be positioned to receive GPS signals at all times. Other regions may have different issues, and there are exceptions (such as Vodafone Group) where numbers are up."

LTE Small Cells – The market is (literally) heating up

"Much of the small cell industry development effort today is focused on LTE. Many ODMs are getting in on the act, with products targeted for public access rather than residential use. While some are suitable for indoor locations, many are for outdoor use and have much wider thermal range.

One of the issues we've seen with the latest LTE designs is that of thermal issues. The huge processing power and RF circuitry generates a lot of heat, and the box gets quite hot – more than 90oC in some cases. To avoid this, it's undesirable to have long runs in the RF sections.

From our perspective, the frequency tolerance requirements for FDD or TDD mode don't differ. However, the need for phase synchronization in TDD mode does leads to different choice of timing source.

Many vendors are working hard to get their initial LTE products into the field – several are having to re-spin and optimize their circuit boards, which is not unexpected at this stage of product development."

3G Public Access Small Cells – Metrocells

At the same time, there continues to be further development of 3G public access small cells, both indoor and outdoor. We've seen requests for an interesting specification here – a "triple dog bone" spec with relaxed tolerances at more extreme temperatures.

This might be 50-100ppb between 10-60oC, a relaxation between -10 to +70oC and a third tolerance of (say) 200ppb between -40 to +85oC. In some ways, you could say the industry is playing games with suppliers to find the sweet spot between acceptable performance and lowest cost.

While there are a few combined 3G/LTE small cell products available today, to our knowledge these are still two separate hardware circuit boards sharing the same enclosure. It may be some time before truly integrated 3G/LTE small cells appear, partly because there are further LTE features (including LTE Advanced) which are still in their early stages of development.

Most of small cell product activity is concentrated in Taiwanese ODMs. Initially, these products will mainly be sold through the large equipment vendors but perhaps later they will develop their own brands and sell direct to network operators.

The dramatic difference in cost

The TCXOs developed for residential femtocells with a 100ppb tolerance over a temperature range of 0-70oC have pushed the technology almost as far as it can go. For indoor use, a part like this could cost as little as $5 (in volume) compared to over $100 for a similar OCXO that could handle -40C through +85C range. Perhaps this is more acceptable in public access small cells located in more hostile environments but which carry higher traffic levels.

For this market need, Pletronics have developed their OeXO range which provides equivalent performance to an OCXO but at reduced cost – the "e" in OeXO stands for equivalent. What differentiates the company is their ability to respond to these often unusual requirements, providing engineering support and customization to match their needs. Pletronics prides itself in listening to customers and continues to grow market share in this specialist area. Claude Lee added, "We've significantly expanded our product line in the last year. We have also expanded our sales channels to include Mouser for off the shelf products and to provide fast access to our newest technology products."

Further reading:

ThinkSmallCell – Timing and Synchronisation requirements for small cells

Pletronics Website

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