飞思卡尔无线基站SoC参与角逐小型蜂窝基站

Freescale joins small-cell basestation race

Junko Yoshida

While cellular operators conducting a series of 4G trials in the United States and elsewhere in the world, Freescale has begun sampling new wireless basestation SoCs designed for picocells and femto cells.

By using the company’s QorIQ Qonverge family of processors, Freescale developed the new SoCs – dubbed as QorIQ Qonverge PSC9130/31 and PSC9132 – to be used for high-bandwidth and low-power baseband applications in LTE (FDD/TDD), WCDMA (HSPA+) and WiMAX basestations.

How big a market global demand for small-cell basestations may create remains unclear. But the competition among chip suppliers is already heating up. Freescale’s move closely follows Texas Instruments, which announced just two months earlier its own small-cell basestation SoCs designed for metro, pico and enterprise basestations.

Freescale’s new SoCs, which share a common architecture with those used in metro and macro basestations, are based on Freescale’s proven multi-core communication processor, multi-core DSPs and baseband accelerators. The QorIQ Qonverge PSC9130/31 SoCs are for femto cells, supporting performance and cost requirements for 8 – 16 simultaneous users. Freescale’s QorIQ Qonverge PSC913, meanwhile, is designed for multi-mode picocell basestations, supporting up to 64 simultaneous users.

Cellular operators today, in the current 3G network infrastructure, are using small-cell basestations sparingly, “mainly to improve Quality of Service,” said Scott Aylor, director and general manager of Freescale’s wireless access division. But once operators upgrade their network to LTE, “small-cell basestations won’t be an afterthought,” he added. “In 4G networks, small cells will become a key part of their network architecture design.”

What operators expect in small cell basestations

However, Joseph Byrne, a senior analyst at The Linley Group, remained cautious. “I know the operators are looking at small basestations for LTE, but it is unclear how committed they are, and whether deployments would extend to residential femto cells.”

As they build their own LTE network infrastructure, wireless operators are grappling with the right mix of small cells, their features, throughput and the number of users each small cell basestation SoC should support.

If there is one thing SoC vendors could do to cope with this array of variables, it would be keeping their products flexible and scalable.

The Linley Group’s Bryne stressed: “A key requirement for the basestations is cost, which directly impacts the chip suppliers. The ones that can reduce system cost (e.g., through integration) will be in a better position.”

Meanwhile, Abhi Dugar, research manager at IDC, noted, “Operators will be stuck with supporting multi-mode networks for a while so small basestations will be part of their network architecture for LTE and 3G networks.” Asked about key requirements operators are imposing upon small cells, he explained, “They are around multi-mode support, more integration to reduce BoM cost, lower power consumption, ability to source from multiple ODMs/OEMs, ease of installation/use at customer premise, minimal field support.”

When asked to compare small-cell basestation SoCs from TI and Freescale, the Linley Group’s Byrne noted, “TI is targeting small-cell stations for the enterprise and larger.” Meanwhile, “Freescale targets these with the PSC9132 but also targets residential femto with the PSC9130 and PSC9131.”

In Byrne’s opinion, “The closest comparison is between Freescale’s PSC9132 and the TI’s TCI6612. An important difference is that the Freescale part requires 40% less power. Freescale’s chip (PSC9132), however, supports only LTE Category 4 (150Mbps/75Mbps), compared with LTE Category 5 (300Mbps/150Mbps) supported by the TI chip.”

Many variables make the network architecture debate more complex. One of the issues is how to strike a balance between a throughput and a number of users supported by a small-cell basestation. “It’s because it all depends on the use case scenarios,” said Scott Aylor, director and general manager of Freescale’s wireless access division.

How many users can you support?

One of TI’s small cell basestation SoCs,TCI6614, for example, features quad C66x DSP cores and ARM Cortex-A8 and offers simultaneous dual mode, meaning that it can run two standards at the same time – LTE and WCDMA. That chip can support 128 users, according to TI.

Compared to that, Freescale’s PSC9132 supports only 64 users. Asked about that difference, Freescale’s Aylor noted: “We can absolutely support 128 users in our picocell SoC. But it all depends on the specific traffic patterns and the use case.” He added, “We are quoting more realistic numbers based on a typical use case scenario.”

It turns out that a YouTube download, the sort of activity often blamed for congestion on the wireless network, doesn’t necessarily restrict the number of users a small-cell basestation can support. Aylor explained, “Bigger packet applications like YouTube video are actually easy to deal with. Sure, big packets require a lot of data, but it is a simpler operation. It’s not signaling intensive.”

In contrast, GPS/Google Map search on a smart phone does not require a lot of data, but it creates heavy signaling stress on a basestation, said Freescale’s Aylor. “Functions like ‘scheduling’ can be better handled by a processor core in our SoC, rather than a DSP,” he added.

Freescale has made the most of its knowledge of the wireless market and extensive IP portfolio to develop the new SoCs. The QorIQ Qonverge processors are built on market-tested Power Architecture cores, programmable StarCore DSP technology and baseband hardware acceleration engines already deployed in multiple LTE macrocell basestations around the world.

Leveraging StarCore SC3850 DSP and Power Architecture e500 MPU cores, “the new QorIQ Qonverge SoCs are distinguished by offloading Layer 2 processing and above to MPU cores instead of DSP cores, delivering significant efficiency advantages,” according to Freescale.