A lot of investment has gone into development of specialist silicon for small cells in recent years. In this article, we've taken a step back and reviewed the landscape, talked to many of the major players, and developed our view of what's going on. It might be controversial for some, but should help navigate through the plethora of press releases and announcements.
Before we start
It's no small task to design and develop a proven, efficient and cost effective silicon solution. We're talking tens of millions of dollars here, sometimes more like $100 millions over the lifetime of a product family. Teams of hundreds of designers can be involved across multiple aspects. Proof points publicly confirming this include VC funding in excess of $100million for Picochip and the $86 million that Broadcom paid for Percello. Revenues can also be substantial - TI disclosed annual embedded processing revenues of $1.9 billion in 2012, of which a significant contribution is believed to come from mobile basestation components.
A complete reference design has multiple components. The baseband processing chipset attracts the greatest attention, probably because it's also the most costly. So-called SoC's (Systems on a Chip) may not actually include all of the components required, with different designs requiring any or all of separate RF front end chipset, GPS, Ethernet, memory and timing/sync elements.
Software is also an important part of the solution. While many Layer 2/3 stacks are multi-vendor, the PHY (Physical Layer or Layer 1) needs to be tightly integrated into the specific baseband processing in order to take full advantage of any silicon "accelerator" hardware. Timing/sync software may be a third party solution such as that from Symmetricom or developed internally. Layer 2/3 stacks and application software are available from several mainstream vendors and a few smaller niche players, and can be more independent of the hardware.
The core capabilities of a small cell chipset are baseband processing and signalling, which require DSP and traditional scalar CPUs respectively. Reusing an existing commercial silicon design is quite feasible – for example the DSPs can be adapted from CEVA or similar, while the scalar processors might be sourced from ARM or MIPS. Specific hardware accelerator circuitry may be designed for specific, highly demanding tasks. High speed busses which enable efficient and effective throughput are essential to make the most of the huge processing capacity.
Millions of 3G WCMA residential Femtocells have shipped today, with AT&T the largest with some 1 million in use. The majority are still based on Picochip's PC2xx and PC3xx series chipsets. They dominated the early designs for Femtocells and continue to reap the benefits. Mindspeed, who acquired Picochip in 2012, have stated that they'll continue to manufacture and support this product family as long as there is demand for it. However, we have not seen any major new releases or features on that platform.
Instead, Mindspeed are investing in their Transcede product, and have migrated the Picochip 3G PHY across to that product family. The Transcede also supports LTE and has been demonstrated with multi-mode 3G/LTE operation. It seems likely that customers will be encouraged to migrate to that platform in the medium term, with the original Picochip withdrawn in the longer term.
3G small cells vendors using the Mindspeed design include ip.access, Ubiquisys and Alcatel-Lucent although the latter two also use/support Broadcom. Taiwanese ODMs such as Tecom are understood to use the Broadcom BCM61630 as part of a Ubiquisys reference design.
Broadcom have continued to invest in their Percello acquisition, evolving their 3G solution in two ways. Their latest chipset family now supports LTE and will soon integrate the RF front end, GPS receiver and Wi-Fi driver onboard into the same chip package. This will continue to drive down total femtocell costs because of reduced chip count.
Infonetics estimates today a residential 3G market share split of about 2/3rds Mindspeed and 1/3rd Broadcom, but I could see Broadcom's share growing across a number of categories. Further evidence for that includes Huawei's recently announced selection of Broadcom's BCM61670 chip for their own 3G small cell ePico products.
The only other major player promoting a residential femtocell 3G WCMDA chipset at this stage is Qualcomm with their FSM solution. Perhaps they brought their product to market a little too late for the early residential femtocell designs and to date have not announced any 3G WCMDA design wins. They acquired DesignArts in 2012 to contribute to their solution. I would not rule out their gaining a market share in the future.
Some of the larger 3G enterprise small cells were designed with more powerful chipsets from the outset. TI had several design wins, making it clear that they weren't aiming at the low end residential market and instead targeted the larger enterprise and Metrocell opportunities.
Despite there being a significant volume of 3G CDMA femtocells sold - Sprint alone have installed over 1 million - few chipset vendors have invested to design a dedicated CDMA small cell on a chip. The main vendors of 3G CDMA femtocells - Samsung, Airvana and Airwalk - have had to rely on more expensive FPGA designs which inherently make the unit cost higher than comparable 3G UMTS products. Qualcomm offer a version of their Femtocell Station Modem specifically for CDMA which has been incorporated into Ubee/Airwalk product, and this could quickly capture market share once the cost/performance is validated.
Picochip developed a reference design for this Chinese variant of 3G from an early stage, opening an R&D office in Beijing. Almost all 3G TD-SCDMA femtocells make use of this, and Picochip (now Mindspeed) appear to have little competition in this field.
(Click below to read about 4G/LTE Small Cell Chipset vendor landscape)
Much higher processing power is being demanded for LTE for several reasons:
- 4G technology itself is more demanding than 3G, partly because it uses more spectrum per carrier (10MHz or 20MHz vs 5MHz for 3G)
- The concurrent user capacity of the largest small cells is increasing, with metrocells that can handle 32 or 64 active users now quite common.
- Operators want metrocells to have a long lifetime, and so are keen to have a lot of spare "headroom" available to handle future LTE-Advanced features delivered by subsequent software upgrades
- The nirvana of a combined 3G/LTE small cell driven by a single chip
This has attracted several groups of chipset vendors to the party:
a) Those upsizing from 3G femtocells, such as Picochip, Broadcom etc.
b) Those downsizing from 3G/4G macrocells, such as TI, Freescale
c) New entrants such as Cavium, some bringing a background in WiMax that is relevant for LTE.
The key players (in alphabetical order) in our view are:
- Mindspeed (since acquired by Intel)
- Texas Instruments
There are a few others on the sidelines promoting their solutions at conferences.
Exploiting their growing success in residential Femtocells, Broadcom's latest release spans the range from single mode residential 8 user chip through to the high capacity 3G/LTE multimode capable of 128 LTE users and 32 3G users simultaneously.
A key design benefit for existing customers is that their latest chips continue to support their earlier 3G software interfaces. This will substantially reduce time/cost/risk to migrate to this device and allow a single codebase to be compatible with existing products.
The BCM61630 SoC integrates the RF front end, GPS onboard to reduce cost, with volume production slated for 1H2013. This sits alongside larger capacity chipsets for multimode 3G/LTE - the BCM61730 for residential, BCM61750 targeted at enterprise and BCM61760 for metrocells.
Cavium's OCTEON Fusion chipset support up to 128 concurrent users and has been commercially deployed in Korea by both KT and SK Telecom. The current CN7130 product supports LTE only, but 3G is planned for release during 2013. Today's chips use 64bit MIPS processors, but the company has signed a deal with ARM last year that might see these replaced in the future.
Somewhat unusually, the company has developed its own LTE Layer 2/3 stack as part of its software solution. They offer an end-to-end design "ready to manufacture" which also incorporates Symmetricom timing/sync software, TR.069 client and SON.
The company is aiming at products with capacities for 16 users and above, targeting the enterprise and Metrocell market rather than residential.
Their standard LTE reference design uses the ADI (Analog Devices) RF front end, delivering 100mW RF per antenna which achieves a useful range of up to 250 metres. Higher RF power designs are also offered.
TD-LTE will require software development and is a roadmap item.
With a heritage of supplying chips for both handsets and wireless infrastructure, this former Motorola subsidiary has tailored its QorIQ range of processors to the needs of small cell designs. The chipset family offers capacity ranging from 8/16 concurrent users for small cells up to thousands for macrocells. Freescale offers both baseband and RF chipsets.
Freescale has developed their own Layer 1 PHY for LTE and collaborates with others for the Layer 2/3 software.
Those products relevant to small cell designers will be:
The BSC9131 which supports 8 to 16 users for any of LTE (FDD or TDD) 3G WCDMA or CDMA.
The BSC9132 which supports up to 100 concurrent users also for any of LTE (FDD or TDD) 3G WCDMA or CDMA has been selected by ip.access for their dual mode 3G/LTE E-100 product.
Intel (formerly Mindspeed and Picochip)
Mindspeed already had established several design wins for LTE prior to acquiring Picochip, who had led in 3G. The company has ported the 3G Picochip firmware across to their Transcede chipset, making it dual mode. They demonstrated concurrent 3G and LTE operation, and also showed the LTE-Advanced Carrier Aggregation feature at MWC in February 2013.
Their longer term roadmap includes the T4400 which will offer up to 400 concurrent LTE users and 128 3G sessions simultaneously with products due to sample before end 2013.
CEVA DSP cores and clusters of ARM Cortex A15 scalar processors are embedded to provide high performance. Mindspeed have developed their own PHY Layer 1 for both 3G and LTE, and also partner with Aricent for LTE software.
Commercially deployed in Korea, winning an award for the first commercial LTE small cell deployment.
Intel acquired the wireless assets of Mindspeed in December 2013, and have since stabilised the business.
This company dominates LTE smartphone chipsets. It's done a lot of marketing on Small Cells and HetNets, with advanced research on concepts branded as UltraSON, Neighbourhood Small Cells, HSPA+ Range Extension and seamless 3G/4G/Wi-Fi integration. A quick search of their website didn't uncover specific chipsets that address anything outside the 3G residential femtocell yet, so it remains to be seen exactly what physical products Qualcomm will bring to market in this field.
TI continue to be a mainstream vendor of chipsets for macrocells, as part of a multi-billion dollar business supplying DSPs and other embedded processing chips to the industry. Their Keystone architecture stretches between high end LTE and multi-mode 3G/LTE small cells through to the largest macrocells and allows the same software to be used throughout.
Keystone incorporates multiple ARM Cortex A15 cores and TMS320C66 DSPs together with specialised accelerator hardware. Backhaul functionality for IPSec and Ethernet and their own timing/sync solution are also included.
While this might make their solution somewhat heavyweight for residential femtocells, it should suit mainstream RAN vendors who need to support a mix of macro/micro/metrocell products using the same underlying platform.
Partnerships with software vendors support both 3G and LTE technologies, but the company announced their own in-house LTE PHY layer 1 earlier in 2013.
Product variants include the TMS320C6612 and 6614 for enterprise and smaller metrocells; alongside the 6636 for larger metrocells.
Ubquisys announced selection of TI for their flagship tri-mode product which was demonstrated at MWC 2013.
Purewave also announced TI selection for their LTE small cells in May 2012.
ZTE has also publicly selected TI for their small cell product range.
Although developed primarily by the Chinese wireless industry, this technology has already been adopted and deployed elsewhere (e.g. Softbank, Japan). It is much closer to the FDD LTE standard that was its 3G counterpart and is in a much better position to become popular in other countries. Large scale deployment of TD-LTE is likely in China from 2013, and this could include significant numbers of metrocells and other small cells. It is already being used to backhaul thousands of public access Wi-Fi hotspots.
Mindspeed appears to be the leading reference design for this technology today and have been adopted in most of the publicly visible designs at this stage. They were demonstrating TD-LTE at Mobile World Congress. Some of the other vendors tell me that they could invest in adapting their chipsets to support TDD mode, but most seem reluctant to do so at this early stage – presumably they see greater long term commercial rewards by investing in mainstream FDD mode first. Small cell vendors will be keen to have a choice of competing chipset vendors, and this seems likely once the size and timing of the market opportunity is more concrete.
The residential 3G femtocell market remains dominated today by Mindspeed and Broadcom. The latter seem to be increasing their market share with continued investment that drives down total cost, such as combining baseband and RF into a single chip package.
Now that small cell vendors develop their LTE small cells, they will be keeping an eye on how those designs can evolve to support multi-mode 3G/LTE in the future. Here again, Broadcom has a good story with a platform that can support either 3G or LTE by software configuration. TI is one of the most advanced with a comprehensive, powerful architecture that has expanded to include firmware and related scope. Cavium are one to watch with very high capacity and in-house software solution. Other vendors may be further advanced in their LTE programs and a few have demonstrated concurrent multimode to date.
But with operator looking for long term high performance and capacity that can cope with future LTE-Advanced and other features through software updates, it may be the high end macrocell chip suppliers who can be the most convincing.
Cavium and Mindspeed both have a strong story to tell about how their solutions can deliver the kind of throughput and peak performance demanded, and are up against TI and Freescale who both have a track record and investment funding to match.