Designed to serve as home basestations, femtocells promise to deliver improved coverage and data services to cell-phone subscribers in fringe areas. Most of the large carriers already offer femtocells in selected areas, and that trend is expanding.
But perhaps more importantly, femtocells and their picocell and microcell cousins are going to be used as part of the cell-phone infrastructure as new Long-Term Evolution (LTE) services come online.
These smaller basestations can bring wide-ranging coverage to areas at a fraction of the cost of a standard macrocell basestation. Leading the pack, the PC333 from picoChip is making this femtocell and picocell infrastructure happen.
The picoChip Architecture
The company’s products are based on a multicore processor design that uses an array of hundreds of tiled processors connected using the 32-bit switching picoBus deterministic interconnect system (Fig. 1).
Operating like a blocking double-entry first-in first-out (FIFO), the picoBus is used for synchronization and communication between the processors and memory. The processors themselves are 16-bit very long-instruction-word (VLIW) Harvard architecture devices with local memory.
The typical picoChip IC has more than 300 of these processors accompanied by special co-processor accelerators for various functions. There are three variants of the processors, including some for data, some for control, and some for memory access. With such significant parallel processing power, it is possible to implement even the most complex processes such as modulation/demodulation and protocol schemes.
The picoArray architecture overcomes the limitations of existing single-processor RISC designs. Even with a superscalar architecture that uses instruction parallelism, 45- and 65-nm processes, and up to 3-GHz clock speeds, these legacy processors just cannot meet the needs of some applications. Furthermore, the high power consumption, with up to 40% going to leakage, precludes their use in many products.
Multicore design has been steadily replacing traditional single-processor designs as improved ways have been developed for multiple processors to communicate and share memory. Another key multicore issue is programming, as partitioning and programming the application requires special software.
The company has provided for that with its products. In general, each processor is programmed in ANSI C (or assembler). Then, special software tools are applied to assign the functions to the processors and generate the interconnects necessary to make the processors work together as defined by the design.
The PC333 Femtocell
The PC333 system-on-a-chip (SoC) is the first chip specifically designed to extend the femtocell into the public access infrastructure rather than a home or office product. It makes special basestations like metro femtos or rural femtos a reality.
Also, the PC333 supports 32 channels (scalable to 64) for simultaneous voice and HSPA+ data. It’s the first chip to support multiple-input multiple-output (MIMO), the first to support soft handover, and the first to conform to the Local Area Basestation (LABS) standard as well.
Furthermore, the PC333 enables small basestations for urban hotspots, city centers, or public access to be built and deployed at a cost far lower than traditional approaches, radically changing the economics of network infrastructure.
The PC333 integrates most of a complete 3GPP Release 8 Local Area 42-Mbit/s HSPA+ basestation onto a single chip. The RF transceiver is a separate chip (Fig. 2). LABS is the 3GPP definition for systems with higher performance than home basestations, allowing higher capacity, 120-km/h mobility, and +24-dBm output power for greater than 2 km.
The SoC extends the parameters of femtocell performance to levels that would traditionally have been considered picocell or even microcell. Coupled with zero-touch provisioning, this high performance enables carriers to routinely deploy femtocells as part of their wide-area network rollouts.
Femtocells are now in rural and metropolitan-area basestations as the PC333 redefines the way they’re used and networks themselves are designed. While residential femtocell applications have been the initial focus of the market, the PC333 will have a major impact on the way carriers and vendors operate.
Until now, an HSPA-capable basestation with a 32- or 64-channel Release 8 LABS specification would have been called a microcell—a market segment that’s been ignored by most major 3G basestation vendors. Supporting this type of development, the PC333 could shake up the 3GPP radio access network (RAN), extending the life of 3G as LTE matures.
The PC333 manages 32 channels and two devices can be cascaded to make a 64-channel system, while smartSignaling technology allows the PC333 to support a dramatically larger number of connected smart phones. The product runs on a 700-MHz ARM chip with TrustZone and a variety of specialized hardware features for security. And in addition to LABS conformance and release 8 HSPA+ (42-Mbit/s downlink, 11-Mbit/s uplink), the PC333 supports receive diversity.
The PC333 is part of picoChip’s range of devices for femtocell access points, including the low-cost PC302 for residential systems, the PC312 and PC313 for small and medium enterprises (SMEs) and high-end consumers, and the enterprise-grade PC323.
Also, picoChip recently launched the PC7300, a complete femtocell hardware reference design that combines low system costs and power consumption with the fastest possible time-to-market. Based on the field-proven PC3xx picoXcell family of femtocell devices, the PC7300 cuts bill of materials (BOM) costs to under $50 and requires less than 5-W total power, making it the only femtocell solution on the market today capable of being integrated into gateway devices. The PC7300 is optimized for high-volume ODM production as well.
The PC7300 also integrates all of the hardware required to implement a four-user or eight-user residential femtocell, from antenna to backhaul. It includes the printed circuit board (PCB) and associated schematics and layout, populated with a picoXcell programmable baseband processor, memory, RF circuitry, and passive components. The board includes an external media independent interface (MII)/Ethernet interface and optionally features software GPS, integrated Network Time Protocol (NTP), and a software user services identity module (USIM).
More Basestations on a Chip to Come
A new member of picoChip’s line of small cell systems, the PC500 is a highly integrated, cost-effective baseband processor that’s code-compatible with the company’s PC960x µTCA-based development system, which runs the PC860x software-defined LTE modem. The PC500 provides a low-risk platform for carrier-class enterprise and metro femtocell products. All of picoChip’s LTE solutions support both frequency division duplex (FDD) and time division duplex (TDD) modes of operation and a wide range of industry-standard frequency bands.
The PC500 uses picoChip’s multicore picoArray signal processing technology to deliver the physical layer (PHY), lower media access controller (MAC), and cryptographic features required for LTE. In terms of sheer processing power, it is one of the highest-performing DSP devices on the market, delivering 105 gigabit MACs (GMACs) and nearly 800 GIPS. The programmable system is upgradable to support interoperability, changes in standards, or manufacturer-specific features.
The Femto Phenomenon
Virtually all market analysts say the global femtocell market is growing rapidly and predict this growth to continue. Dell’Oro expects revenues from femtocell deployments worldwide to generate $4 billion by 2014. Shipments should reach 62 million in 2014, the firm said, and more than 80% of the femtocells shipped will be WCDMA. According to the Femto Forum, 17 operators have deployed femtocells, with a further five committed to future launches, bringing the total to 22.
“Operators around the world are facing the challenge of rising network traffic and are turning to femtocells to solve the problems of capacity and offload. Given the importance of data and given the sophistication of the wireless market it is no surprise that Korean operators are taking advantage of the technology and developing innovative approaches,” said Rupert Baines, vice president of marketing at picoChip, about South Korea Telecom’s first 3G femto deployment using South Korean OEM Contela’s femtocell units.
“Based around the latest standards from 3GPP and the Femto Forum, Contela has developed an end-to-end solution which dramatically improves network capacity, solving the ‘data deluge’ that operators are now facing,” Baines continued.
On the LTE front, recent research by the Yankee Group indicates that 65% of carriers expect to build at least some of their LTE coverage using femtocells “from the bottom up.” Applications will include both zones of outdoor femtocells and building out macro and femto basestations in parallel to achieve the most flexible and optimized coverage.
Finally, Informa says that femtocells now outnumber macrocells in the U.S. Conservative estimates suggest there are currently 350,000 femtocells and around 256,000 macrocells. Informa’s report marks a milestone in the evolution of cellular networks and highlights how femtocells are changing the architecture of mobile networks.
Subscribers with poor or unreliable cellular service or slow 3G data services are finding that a femtocell really solves the problem. The new chip and reference design from picoChip promises to make femtocells even better, cheaper, and more widely deployed.