Wireless traffic is growing everywhere, from videos downloaded to your favorite tablet to the sensor networks monitoring the works inside massive industrial facilities. But despite the demands, the technologies responsible for communicating all of this data must continue to do so quickly and reliably. Recent breakthroughs from Freescale and Dust Networks will help ease the information crunch.
Processors Match Heterogeneous Networks
Freescale’s QorIQ Qonverge rolls with the dramatic changes taking place in the wireless infrastructure to form the heterogeneous network, or hetnet. Het networks combine small and large cell sites that cover both long and short distances. This is the industry’s solution to dealing with the explosion of demand for high-speed wireless data access. The QorIQ line of processors covers the entire basestation range from large macrocells to metrocells, picocells, and home/office femtocells.
Thanks to the amazing growth in smart-phone usage, the data demand on wireless operators has continued to rise at a rapid pace, seriously straining the networks. While current macrocells can be updated to full LTE capacity, another solution is also needed. There’s a need for more smaller cells that bring the basestation closer to the user.
This approach provides not only the speed demanded for the growing use of mobile video and other data intensive applications, it also supplies the quality of service (QoS) demanded at the same time. And in addition to meeting the tough LTE standard requirements, basestations must continue to support current 3G technologies like WCDMA, HSPA, cdma2000, EV-DO, and legacy voice technology.
There are two major trends in basestation design. First, there’s a push to make the circuitry smaller and more compact, with significantly greater power efficiency. One popular approach is to put the radio into a compact package called a remote radio head (RRH) that’s mounted with the power amplifiers on the tower along with the antenna. The signals are then sent to the RRH via a fiber optic cable, eliminating the huge coax cable losses and cost.
The second trend involves small packages with lower-power power amplifiers (PAs) that can be mounted on the sides of buildings, on light poles, and in similar locations. The range of coverage is less than a macro basestation, but putting the basestation closer to the subscriber yields better performance. More basestations are needed to cover a given area, but the low cost and smaller power consumption make the solution feasible. Different sizes of these smaller cells are defined for the variety of situations and coverage areas encountered. Smaller cells handle fewer users, so they’re less powerful.
Basestations are designed in three parts. First, the RF section includes up and down conversion and filtering along with the analog-to-digital converters (ADCs) and digital-to-analog converters (DACs) that work for the I and Q inputs and outputs. Second, the critical PA section consumes most of the power. Finally, the baseband section handles all of the modulation/demodulation, coding/decoding, and other physical-layer (PHY) processes in addition to the media access control (MAC), radio link control (RLC), and packet data convergence protocol (PDCP) network layers.
This design requires general-purpose processors and DSPs along with the necessary memory, accelerators, and interfaces. The number of necessary processors varies with the number of expected users, the mix of speeds supported, and the number of antennas in the multiple-input multiple-output (MIMO) versions. One size does not fit all.
Freescale’s baseband chips scale to fit the most popular cell sizes, and that scaling can handle the continued evolution in LTE to LTE-Advanced including both frequency-division duplex (FDD) and time-division duplex (TDD) versions through reprogramming.
The QorIQ chips consist of a mix of Freescale’s general-purpose processors, DSPs, and accelerators for commonly used functions. Freescale’s e6500 Power Architecture 64-bit general-purpose processor provides dual threads and a clustered L2 cache. It runs at 1.8 GHz and has a real 40-bit address space.
The Freescale SC3900 StarCore Flexible Vector Processors are grouped in clusters. These DSPs each deliver 38.5 GMACs per core at a clock speed of 1.2 GHz. Two cores are clustered under a 2-Mbyte multi-banked L2 cache. Multiple MAPLE-B accelerators and interfaces are included. These multiple processors are tied together with a 256-bit side fabric capable of 1.6-Tbit rates.
The flagship QorIQ device is the B4860 for macro basestations (Fig. 1). Marcocells support more than 1000 subscribers in a cell with a radius up to 10 km. The B4860 includes four e6500 general-purpose processors and six SC3900 StarCore DSPs supported by 12 MAPLE accelerators and the related L2 cache. Multiple interfaces including 16 lanes of 10G serializers-deserializers (SERDES) support the chip.
By itself, this chip can implement a 20-MHz bandwidth, three-sector, 24-MIMO antenna LTE basestation with an aggregated throughput of 1.4 Gbits/s. The B4860 also could be used to support an LTE-Advanced macrocell by enabling a 60-MHz, one-sector, 16-antenna solution with up to 1.8-Gbit/s aggregated throughput.
The QorIQ B4420 targets metrocell/microcell basestations. Metrocells and microcells support up to 256 users in a cell with a radius to 2 km. A single metrocell can handle two full-sector LTE as well as four-cell HSPA. The B4420 boasts two e6500s and two SC3900s. The 12 MAPLE accelerators are included along with the L2 cache and eight lanes of 10G SERDES.
The BSC9132 is designed for picocells that can handle up to 100 users over a range of about 200 meters. Also targeting indoor enterprise femtocell applications, it includes two e6500 GPP cores and two SC3850 DSPs plus the MAPLE accelerators and four lanes of 6-Gbyte/s SERDES. Meanwhile, the BSC9131 is designed for residential femtocells. It can support up to 16 subscribers over a range of about 10 meters. It uses one e6500 and one SC3850 DSP and the MAPLE accelerators.
This line of processors covers the full range of forthcoming basestation designs. All of them are software compatible and fully programmable to handle future LTE releases, including LTE-Advanced.
Making Larger Sensor Networks A Snap
Sensors are the eyes and ears of industrial automation and process control. In a large plant or factory, there are hundreds of sensors or more and many actuators like relays, valves, and solenoids that need to be controlled. In the past, each of these devices was hard-wired into the system, which was costly and inflexible.
As wireless technology meets industry’s quality and reliability demands, many companies are replacing their older wired networks and building new wireless networks. The LTC5800 and LTP5900 SmartMesh devices from Dust Networks, a division of Linear Technology, implement self-forming, self-healing mesh networks that can provide 99.999% reliability by using path-diversity, time-synchronized, and channel-hopping methods (Fig. 2).
Every node serves as a router. The LTC5800 and LTP5900 also offer excellent security with FIPS-197-compliant standards including AES 128-bit encryption and low power consumption that lets each node run on batteries for five to 10 years or use energy harvesting methods. They can be used to monitor process controls, tank levels, machine and asset health, emissions and toxins, pipelines, energy and HVAC systems, structural corrosion, steam traps, wellheads, and seismic activity. Control functions include valves, lighting, and a wide range of factory automation.
The devices come in several forms. First, there are chips and complete modules, making application fast and easy. Second, there are two versions of the SmartMesh line, which uses the core mesh technologies of time diversity, frequency diversity, and physical diversity to ensure reliability, resiliency, scalability, power source flexibility, and ease of use.
The SmartMesh WirelessHART version meets the IEC6291 standard. WirelessHART is the cable-free radio version of the widely used wired industrial HART standard. While there are other wireless industrial control standards, WirelessHART dominates with upwards of 80% of the industry market share.
The WirelessHART LTC5800-WHM single-chip radio is based on the IEEE 802.15.4 standard. Complete printed-circuit board (PCB) drop-in modules also are available. The LTP5901-WHM includes an on-board chip antenna, whereas the LTP5902-WHM has an MMCX connector for an external antenna. The WirelessHART LTP5903-WHR, which is an embedded manager and a complete master router for a mesh network, can support up to 500 nodes and provide a link to any external systems via Wi-Fi, machine-to-machine (M2M) cellular, or Ethernet.
The SmartMesh IP line is compatible with the Internet Engineering Task Force’s 6LoWPAN standard protocol, which uses a wrapper approach to provide IPv6 capability in wireless networks. The devices are also compatible with the IEEE’s 802.15.4e version of the standard, which modifies the MAC networking layer to ensure greater energy efficiency and to address the latency issues in real-time applications.
The LTC5800-IPM is the chip version. The LTP5901-IPM PCB module has a chip antenna, and the LTP5902-IPM PCB module has the MMCX connector for an external antenna. The LTC5800-IPR, LTP5901-IPR with on-board antenna, and LTP5902-IPR with MMCX connector embedded managers can support up to 100 nodes.
The LTC5800 system-on-chip comes in a 7- by 7-mm, 72-pin, quad flat no-lead (QFN) package. All circuitry including the impedance matching circuitry, a PA, and an ARM Cortex M3 32-bit processor are on the single chip. It only needs power, ground, and an antenna.
PCB module sizes run 42 by 24 mm with the onboard antenna and 37.5 by 24 mm with the MMCX antenna connector. The LTP5903 WirelessHART network Manager is 102.9 by 55.6 mm with the MMCX connector. It operates from a 5-V source and consumes 150 mA.
All of the LTP5900 series PCB modules have been tested for Federal Communications Commission, CE, and IC modular radio certifications, eliminating one more design step and cost. There are also certifications for China, Japan, and Korea.
The LTC5800 offers a 50-µA average current consumption for a mesh routing node. Receive current consumption for a packet is 4.5 mA. Transmit current consumption is 5.4 mA at 0 dBm. An 8-dBm power level is also available, consuming 9.7 mA. And, the SmartMesh products have UART, I2C, SPI, and an internal ADC for sensor interfacing.