Power-line communications (PLC) is becoming a key communications technology. Thanks to new standards and a flood of new chips and products, PLC is finding a place in home area networks (HANs), the Smart Grid, and in industry.
Sending data over the existing ac power lines is an old and good idea that has been chronically plagued by noise and high attenuation problems. Today, new technology—specifically orthogonal frequency division multiplexing (OFDM)—has made PLC reliable over longer distances and incredibly useful. It is even replacing wireless in some high-speed video applications in consumer electronics equipment.
The PLC marketplace is divided between the broadband (BB) high-speed short-range applications and the narrowband (NB) low-speed longer-range applications. The HomePlug specification and related IEEE P1901.1 standard dominates the BB arena, but the newer ITU standard G.hn is poised for taking market share.
In the NB sector, the G3 standard and its IEEE cousin P.1901.2 are doing well, but multiple other standards are finding their place in the Smart Grid and HANs. With plenty of new silicon now available, it won’t be long before you see some new and interesting PLC products.
Lantiq’s XWAY HNX100 G.hn networking transceiver includes a fully ITU G.9960/G.9961-compliant media access controller (MAC) and physical layer (PHY). It supports transmissions over power line, coax, and twisted pair. Also, its OFDM band plans can support data rates to 1 Gbit/s.
The integrated serializer-deserializer (SERDES) interface lets the device connect to different analog front-ends (AFEs). The transceiver incorporates a MIPS processor for the software and can use a wide range of available operating systems. The HNX156 is designed for cost-effective systems that don’t require external double-data rate (DDR) memory. The HNX176 supports DDR1/2 memory for larger, more sophisticated systems.
Freescale Semiconductor’s 56F8000 DSPs can be used to implement space frequency-shift keying (S-FSK) modems or any flavor of OFDM modem. These devices target smart metering applications. They’re used in the modem back to the utility and in concentrator designs. Freescale recommends its ZigBee wireless solutions for the home-area network (HAN).
Marvell’s ITU-T G.hn-compliant transceiver chipset accommodates all three existing home wiring network media: ac power line, telephone wiring, and cable TV coax. It appears to be an ideal solution for the wired distribution of bandwidth-intensive and real-time applications such as HD Internet Protocol television (IPTV), Voice over Internet Protocol (VoIP), gaming, multi-room DVR, and video surveillance. It has the potential to deliver a theoretical data rate up to 1 Gbit/s with an expected realistic data rate in the 200- to 400-Mbit/s range.
Marvell’s G.hn chipset comprises the 88LX3142 digital baseband processor and the 88LX2718 AFE interface. The 88LX3142 includes a powerful CPU and a full set of serial interfaces, while the 88LX2718 AFE includes two fully programmable receiving and transmitting paths that enable multiple-input multiple-output (MIMO) operation.
While MIMO is generally considered a wireless technology, it nevertheless works well over a wired medium where multiple streams of parallel data boost the data rate while providing a more reliable connection in the presence of noise and interference. The 88LX3142 fully complies with the ITU-T G.hn standards, including G.9960/61/72 on any wire line like coax, twisted pair, or ac power-line (Fig. 1).
The 88LX2718 is all a user needs to accommodate the signal between the 88LX3124 G.hn baseband digital processor and the coax, phone-line, or power-line line transformer. It integrates all circuitry—amplifiers, active filters, line drivers—required for this function.
The AFE is built upon two transmission/reception paths to enable true MIMO operations. Each transmission path integrates a low-pass filter, a programmable gain amplifier (PGA), and a line driver to condition the OFDM signal provided by the 88LX3142 circuit to the coax, phone, or power-line transformer. The output of the transmission path directly drives the line transformer input through an external decoupling capacitor.
Maxim Integrated Products offers a G3-PLC chipset that’s widely used in Europe. It complies with the International Telecommunications Union (ITU) standards. The MAX2992 modem combines the PHY and the MAC layer. It uses OFDM with binary phase-shift keying (BPSK), quadrature phase-shift keying (QPSK), and eight-phase-shift keying (8PSK) modulation. The modulation is fully adaptive to noise and attenuation levels. The maximum data rate is 300 kbits/s.
The modem uses the 6LoPAN ITEF adaption standard to support IPv6. Both dynamic routing and mesh networking are supported. Access is CSMA and ARQ to improve reliability. Forward error correction (FEC) and CRC16 are used to further improve transmission reliability. AES128 provides security. The MAX2992 includes Maxim’s MAXQ 32-bit microcontroller. Interfaces are two standard universal asynchronous receiver-transmitters (UARTs) and two serial peripheral interfaces (SPIs).
The MAX2991 AFE chip interfaces to the ac line. The receive path includes a filter, a variable gain amplifier (VGA), and a 10-bit analog-to-digital converter (ADC). The chip also features a 62-dB dynamic range automatic gain control (AGC) and dc offset cancellation. The transmit path includes a 10-bit digital-to-analog converter (DAC) and a shaping filter. Its programmable filters comply with the CENELEC, Federal Communications Commission (FCC), and Association of Radio Industries and Businesses (ARIB) band limits.
Qualcomm Atheros, which entered the PLC marketplace with its acquisition of PLC pioneer Intellon, makes a full range of HomePlug-related products. For example, its INT6400 is a full MAC and PHY for HomePlug AV capable of the 200-Mbit/s speed defined by the specification. The INT1400 is the matching line driver IC and AFE. It includes an Ethernet Media Independent Interface (MII) and works with external SDRAM.
The company’s AR7400 MAC and PHY chip and the matching AR1500 line driver/AFE fully comply with the HomePlug AV specification and the IEEE P1901 standard. This chipset extends the OFDM band plan from 2 MHz out to 86 MHz, providing data speeds up to 500 Mbits/s. Primary applications include set-top boxes (STBs) and video streaming. The smaller AR7420 offers similar specifications and is available with the AR1540 companion line driver IC.
The Qualcomm Atheros QCA7000 IC is another solution designed for HANs (Fig. 2). Target devices include smart meters, home energy management systems, appliances, and electric vehicle charging stations. The IC is based on the new HomePlug Green PHY standard from the HomePlug Alliance.
The QCA7000 is single-chip device with an integrated power management unit, AFE, and memory in a tiny 8- by 8-mm package. A single 3.3-V rail powers it to allow for reduced system cost and easy integration into customer designs.
To support embedded applications, SPI and UART host interfaces are available on the chip to allow direct connectivity to low-cost, low-power microcontrollers commonly found in the smart energy ecosystem. A general-purpose I/O (GPIO) bus and an optional flash interface are available to support simple applications like smart plugs and sensor monitors.
Sigma Designs offers a variety of chips, but the most flexible is the CG5110. This complete G.hn modem complies to G.9960/8861/9962. It’s also backward compatible with HomePlug AV, P1901.1, and Home PNA standards, providing a way for service providers to transition smoothly from the older legacy solutions to G.hn.
Texas Instruments has directed its PLC efforts to the narrowband (NB) arena for Smart Grid applications. It has products for PRIME, G3, and G.hnem all based on its C2000 microcontroller architecture. The F28PLC83 is designed to be configured for either PRIME or G3 in the CENELEC A band. The AFE031 is a matching AFE.
The F28M35 is designed for higher speeds in the FCC band. The F28PLC Lite incorporates TI’s own OFDM standard, which the company calls FlexOFDM. It lets designers adapt the modulation and other features to better fit the profile of the specific grid topology and other local environmental conditions.
These devices are also capable of S-FSK solutions (IEC61334) to provide backwards compatibility where needed. TI’s focus appears to be on the robustness of the communications link. A good starting place with its products is the TMDSPLCKIT developer’s kit.