A clear sign that the small cell is poised for volume adoption, and for a strategic role with carriers, is the increased enthusiasm of major chip suppliers. The start-ups which pioneered femtocell system-on-chip platforms for the residential space set many new norms in base station silicon, particularly in terms of the three essentials of the model – cost, power and integration. But those firms have now been acquired (Picochip by Mindspeed, DesignArt by Qualcomm and Percello by Broadcom) and the baton passed to the big names, whose challenge is to translate those three essentials into carrier-class platforms for the enterprise and outdoor segments, and achieve the dream of the fully integrated SoC metrocell.
The Small Cell World Summit saw Texas Instruments proclaiming a ‘game changer’, and the most important chip it has produced in this sector; while Qualcomm and Cavium also unveiled new offerings. These join other developments announced over the past year, such as Freescale’s conversion to ARM-based processors, rather than its usual PowerPC preference in base stations, for low power small cell products.
Such moves are creating a strong market with plenty of choices of approach in SoC design, with the various vendors pushing the particular advantages of their heritage. In the case of TI (and Freescale) that means common software platforms and interfaces between their well entrenched macrocell chips and the small cells; while Qualcomm touts the low power and tight integration credentials of its roots in device chips and (via Atheros) Wi-Fi. Mindspeed and Cavium are smaller names, of course, but are keen to talk about how their small cell platforms fit into their broader position across the range of carrier network processors, a line that is also pushed by Intel.
Intel, of course, does not have a small cell SoC, but is keen to harness the convergence of IT and networking approaches, to insert x86 processors at every point in the carrier infrastructure, from its switch-chips to its Cloud-RAN servers to the ‘Smart Cell’ it has designed with Ubiquisys (now part of Cisco).
Texas Instruments claims its latest offering addresses the critical criteria for small cells ‘ low power consumption, high levels of integration, and mass market options for backhaul and powering. The last two remain challenging in the outdoor space, and that is one reason why TI is focusing mainly on the enterprise, where Ethernet is ubiquitous. Its new platform supports Power over Ethernet (PoE) as well as Ethernet backhaul, and consists of a digital SoC (TCI6630K2L ) paired with a new small cell analog front end (the AFE7500), plus LTE and W-CDMA Base Station SoftwarePac and support chips for clocking, PA and so on (and optional Wi-Fi). Due to sample in the fourth quarter, the chipset claims a power budget well below the PoE standard limit of 25W.
As usual with TI platforms, there is an intense focus on offloading tasks (such as packet processing or security) from the DSP and ARM cores to accelerators. TI also claims a key differentiator in its particular approach to DPD (digital pre-distortion), a technique rarely used in small cells because of the extra processing and power consumption involved. But according to Tom Flanagan, technology strategy director at the firm’s wireless infrastructure business, even at 100mW TI can still reduce the overall power in the system with DPD because of the high level of integration. He said between 2W and almost 4W per antenna is saved by TI’s architecture (depending on the power levels of the system), enabling it to stay well within PoE limits indoors.
The SoC is based on TI’s KeyStone architecture, which underpins all its base station designs and is taking its ARM-based platform out to adjacent markets such as network processors and cloud servers. Although the main focus is on the indoor space for now, the new product will be adaptable for outdoor use cases.
The TCI6630K2L enables cells supporting up to 128 users. It combines L1/L2/L3 baseband with a fully integrated digital radio front end (DRFE), and can support single- or dual-band, simultaneous dual-mode and carrier aggregation scenarios all within a PoE+ power budget. It is based on dual ARM Cortex-15 processors and four TI DSP cores. It also includes a network coprocessor supporting transport capacities of up to 3mpps, enabling traffic aggregation and shaping of 3G, 4G and Wi-Fi combined transport.
Meanwhile, Qualcomm introduced a multimode platform for metrocells, picocells and enterprise access points, combining 3G, LTE and Wi-Fi. It is taking a clear stand in a controversial aspect of small cells ‘ whether Wi-Fi needs to be integrated at chip level. Most operators are keen to have seamless interworking between cellular and Wi-Fi access points, and eventually to house both in one box, but there are varying views on whether that convergence needs to be right down to the silicon, where additional cost and complexity could be incurred.
Texas Instruments believes Wi-Fi should be separate (and optional) because its upgrade cycle is different to that of 3G/4G, and it is not (yet) software updateable like cellular standards. NEC perceives challenges in chip level integration in terms of heat dissipation. But Qualcomm, always the king of integrated SoC designs, believes operators will want Wi-Fi on the chip and its latest small cell range, the FSM99xx family, includes the new high speed Wi-Fi standard, 802.11ac, as well as 802.11n and cellular technologies ‘ concurrent 3G and 4G, or dual-carrier LTE with carrier aggregation.
Manufactured using 26nm process technology, the FSM99xx showcases new developments in power efficiency, says Qualcomm, as well as compliance with power over Ethernet for enterprise deployments. The systems are based on the quad-core Krait mobile processors, which achieve low power consumption as they are more commonly used in smartphones, drawing on the firm’s user device heritage (though the DesignArt architecture provides a route into higher end infrastructure, going up to a four-sector base station if required, and implemented in carrier-grade metrocells by Airspan).
The small cell offerings also feature RF linearization techniques to reduce power amplifier power consumption by up to half ‘ Qualcomm points out this is important since amplifiers can consume more than 50% of a cell’s power budget. Also supported are self-organizing network (SON) techniques, including Qualcomm’s own UltraSON suite. The chips will sample in the second half of this year.
Over at Cavium, the company introduced a small cell reference design based on its Octeon Fusion processor at the Computex show in Taiwan, with support for dual-radio access. It supports over 128 active users and concurrent LTE/W-CDMA technologies.
The design is targeted at carrier and enterprise cells and is production ready, and Cavium will also demonstrate a tri-mode platform which also includes Wi-Fi. The Dual-RAT solution extends the capabilities of Cavium’s existing LTE-only enterprise small cell SoC. The reference design includes manufacturing files as well as LTE and WCDMA L1 ‘ L3 software stacks, application layer APIs and a software development kit.