As the consumer electronics industry is revolutionizing the way people consume content in the home, there is an underlying need for a reliable and capable networking technology to enable this connectivity. Even though a mix of technologies exists – Ethernet and wireless – consumers often desire a connectivity option that blends ease-of-use, reliability and ubiquity. Enter powerline.
Even though powerline technologies have existed since the 1980s, the HomePlug Alliance was established in 2000 to create several standards that support broadband and smart grid applications in the home. Over the last decade, this alliance has published the HomePlug 1.0, HomePlug AV, HomePlug GreenPHY standards and will publish its next generation HomePlug AV2 technology standard later this year. HomePlug technology is also the baseline technology for the newer IEEE 1901 global standard for powerline. With the help of these standards and the wider adoption of the technology by retailers and service providers alike, HomePlug has become the technology of choice for many carrier-grade triple-play (voice, video and data) applications in the home.
Communication signals over powerline face a variety of impairments – high attenuation, dynamic noise, impedance loading – caused by devices (loads) turning on or off. Powerline signals can typically propagate between any two points by several paths, each of varying lengths. As a result, signals get reflected, arrive at the destination out-of-order and possibly with different amplitude levels. This may lead to signal distortion. Further, depending on the location of the impairments, signal-to-noise characteristics and channel rate changes. With the help of advanced MAC/PHY technologies and robust error correction techniques, HomePlug powerline technologies have provided a robust and secure connectivity offering to consumers.
Older powerline technologies, such as X10, operated at lower frequencies and hence did not work across phases or leg wires of transformer. With the advent of HomePlug, carrier frequencies jumped from kHz to MHz and powerline technology was able to couple across phases by overcoming the impedance (in breaker panels) that existed at lower frequencies. Similarly, the ability to deliver performance and coverage in the presence of increased attenuation and dynamically changing noise characteristics in the home was of heavy concern. Unlike wireless, where walking closer to the router may improve your connectivity, electrical outlets in the same room may show differences in performance. Physically closer outlets may be electrically further depending on the wiring (under the electrician’s control) and also exhibit different signal-to-noise characteristics due to potential noise impairments.
HomePlug technology addressed these concerns by techniques that include:
* AC line cycle synchronization to eliminate line-synchronous noise emitted by devices such as dimmers and halogen lamps
* Variable bit loading to take advantage of the best channels by loading the signal bits on alternate carriers thereby ensuring higher modulation
* Turbo codes for better error correction that prevents signal distortion at the destination thereby delivering best-in-class connectivity
Further, operating at higher bandwidths (above 2 MHz) allows HomePlug technologies to bypass increased levels of interference caused by typical home appliances, HVAC compressors and consumer electronics devices with switching power supplies.
All powerline devices that we see in the market today communicate over two of the three wires of an electrical outlet – line and neutral. With the help of the advanced techniques discussed above, these devices were able to provide excellent performance and coverage within the home. However, by taking advantage of the unused third wire in the electrical outlet – protective Earth (commonly known as ground) – there is now an option to further improve the reach and reliability of the powerline link.
Qualcomm Atheros technology uses real-time channel information to communicate over the best powerline path – line-neutral or line-protective Earth. Most power supplies used in modern consumer electronics equipment, such as computers and satellite receivers, typically attenuate communication signals by providing a low impedance path to high frequency signals. In addition, the switching power supply in these devices injects noise on the line-neutral path but the line-protective Earth path does not have the injected noise. In situations like these, an alternate path of transmission, line-protective Earth, would provide higher throughput.
Similarly, devices that perform line conditioning such as UPS or surge suppressors also tend to load the line-neutral line only, thereby providing an opportunity to connect to those devices through line-protective Earth path. Having an additional path is often not enough, as their characteristics change dynamically; hence, there is a need for a smart algorithm to constantly monitor the channel and look at several metrics before deciding to switch paths between the links to deliver seamless connectivity. SmartLink technology is built upon the robust HomePlugAV standard and is fully interoperable with existing HomePlugAV/IEEE 1901 devices. Full performance benefit is obtained with SmartLink devices on both ends. In a legacy environment, SmartLink devices will continue to operate over two wires and deliver greater performance.
Powerline interference characteristics vary dynamically by path. In general, the line-neutral path is highly susceptible to noise and provides lower attenuation while the line-protective earth path has lesser noise but possibly higher attenuation. By understanding these environments dynamically, SmartLink technology allows powerline devices to collectivity provide a robust link between nodes, thereby substantially increasing the coverage, throughput and ability to deliver carrier-grade triple-play applications in the home.
About the Author
Ganesh Swaminathan is senior product marketing manager for the Qualcomm Atheros networking business unit. With more than nine years of experience in networking and connectivity technologies, he manages the company’s powerline product portfolio and related technology advancements.