6 Powerline-Based Home Networks In this chapter... I Introduction to Powerline Communications 88 I Powerline Modem Technology 89 I Technical Obstacles of In-Home Powerline Networks 91 I The Criteria for Testing Powerline Solutions 96 I Remote Management Features 98 I In-Field Product Testing 99 I Enikia Incorporated 100 I X-10 107 I Intellon CEBus 108 I Inari Powerline Networking Technology 109 I Summary 114 87 88 6 I Powerline-Based Home Networks Powerline-based home networking is an emerging technology that allows consum- ers to use their existing electrical wiring system to link appliances to each other and to the Internet. Home networks that use high-speed powerline technology can control anything that plugs into an outlet, including lights, televisions, thermostats, and alarms. The most popular powerline technologies are explained in this chapter. INTRODUCTION TO POWERLINE COMMUNICATIONS ............................................... For several decades, researchers have attempted to use AC powerlines to create a com- munications network. Since almost all electronic devices already connect to AC pow- erlines for the electricity they need to operate, it seems only logical to develop a technology that would send data signals over the same wires. Considering that a vast majority of people in the world, even in developing areas, already live in homes with pervasive access to electrical outlets, such a technology would provide a quantum leap forward in the mass-market proliferation of IT and communications products. Using electrical wires seems logical and efficient. Traditional communications networks, such as phone lines, cable television, and computer data networks, use dedicated wir- ing designed specifically for communicating information. Powerline networks, on the other hand, were designed to deliver electricity, not data signals. This difference is not trivial. The highly variable and unpredictable levels of impedance, signal attenuation, and noise combine to create an extremely harsh environment that make high-speed data transmissions over powerlines very challenging. The following sections provide an overview of these technical obstacles and present some of the strategies that different developers are using to overcome them. But first, we will define the powerline network and present a background of how this industry has developed. Industry Background The powerline is not an ideal environment for data communications. Historically, it has proven much easier to modify the existing phone-line and cable networks for the modern needs of a digital economy. By upgrading portions of those networks with new digital communications equipment, the same copper phone lines and coaxial ca- ble lines can be used for transmitting high-speed data traffic. Although it is easier for companies to upgrade existing wiring, phone and cable wiring is not as widespread as electrical networks, especially outside of the United States. And while phone and ca- ble networks might be effective at bringing Internet access to the home, they do not provide networks within the home. In the near future, having ubiquitous access points Powerline Modem Technology 89 within the home will be increasingly important, especially with the proliferation of non-PC devices, or information appliances. And although wireless technology will be needed for battery-powered mobile devices, the majority of devices in the home re- main stationary and connected to the AC powerline network. It is for these reasons that high-speed powerline technology represents one of the most important hurdles in the world of communications and computing. But why weren’t powerline technolo- gies available earlier? The next sections explore the powerline network and the inher- ent obstacles that the medium presents. Defining the Powerline Data Network In conventional terms, the powerline connects the home to the electric utility company in order to supply power to the building. But powerline communications falls into two distinct categories: access and in-home. Access powerline technologies send data over the low-voltage electric networks that connect the home to the electric utility provider. The powerline access technologies enable a “last mile” local loop solution that pro- vides individual homes with broadband connectivity to the Internet. In-home power- line technology communicates data exclusively within the consumer’s premises and extends to all of the electrical outlets within the home. The same electric outlets that provide power will also serve as access points for the network devices. Although the access and in-home solutions both send data signals over the powerlines, they are fun- damentally different technologies. Whereas the access technologies discussed in Chapter 3 focus on delivering a long-distance solution, competing with xDSL and broadband cable technologies, the in-home powerline technologies focus on deliver- ing a short-distance high-bandwidth solution (10 Mbps) that would compete against other in-home LAN technologies, such as phone line and wireless. We will limit the discussion of powerline technology to the following definition of the in-home powerline network. The in-home powerline network, shown in Figure 6.1, consists of everything interconnecting through power outlets, including: • House wiring inside of the building • Appliance wiring (power cords) • The appliances themselves (load devices) • The circuit breaker POWERLINE MODEM TECHNOLOGY....................... Communicating data over the powerline, just like in any other analog medium, re- quires some type of modulation device, or modem, that can transmit and receive data 90 6 I Powerline-Based Home Networks Medium Low voltage voltage Electric Local distribution utility transmitter Access network In-home network e AC powe m r li o ne -h s In breakers Meter Circuit Appliance (load device) Line of demarcation Figure 6.1 In-home powerline network signals. In order to turn a powerline electric network into a data communications net- work, a transceiver must be used to transmit the data from the device across the pow- erline medium. Thus the transceiver sends and receives digital data in analog form using the electrical outlets that it is connected to. Similar to other home network technologies, such as phone line and wireless, these transceiver nodes will take the form of microchips that will be embedded direct- ly into next-generation computers and smart devices. But first generation powerline network products will have to provide backward compatibility for devices that were not originally designed for powerline communications. Wall modules containing powerline transceivers will likely be the first products on the market. These small devices could plug into an electrical outlet and replicate the sockets, similar to a power strip, but with an embedded powerline transceiver. The wall modules couple the device to the electrical network using a standardized commu- Technical Obstacles of In-Home Powerline Networks 91 nications input interface, like a USB or Ethernet port. This way even traditional devic- es, like desktop PCs with Ethernet cards, will communicate with one another over the powerline.1 In such a configuration, different network devices could share data, con- trol one another, and access each other’s resources. But to facilitate these applications, the network’s communication throughput must be high enough to reduce noticeable time delays, especially when the network environment is noisy. The following section addresses some of the key technical obstacles that have made powerline communica- tions so difficult. TECHNICAL OBSTACLES OF IN-HOME POWERLINE NETWORKS ........................................ Typical data and communications networks (like corporate LANs) use dedicated wiring to interconnect devices. But powerline networks, from their inception, were never in- tended for transmitting data. Instead the networks were optimized to efficiently distrib- ute power to all the electrical outlets throughout a building at frequencies typically between 50 to 60 Hz. Thus, the original designs of electrical networks never considered using the powerline medium for communicating data signals at other frequencies. For this reason, the powerline is a more difficult communications medium than other types of isolated wiring like the Category 5 cabling used in Ethernet data networks. The physical topology of the electrical network, the physical properties of the electrical cabling, the appliances connected, and the behavioral characteristics of the electric current itself all combine to create technical obstacles. Signal Attenuation, Impedance, and Appliance Loading Attenuation describes how the signal strength decreases and loses energy as it trans- mits across a medium. In the powerline environment, the amount of attenuation that a signal experiences is primarily a function of the signal frequency and the distance it must travel on the wire. However, recent field studies show that attenuation is also af- fected by other factors, including appliance loading and impedance discontinuities. 1. In this case, two computers in a home could be networked together connecting their RJ45 cables from the Ethernet card into two wall modules that would then stream the Ethernet data across the powerline. Later versions would most likely involve embedding the powerline transceiver directly onto the motherboard of the PC, effectively eliminating the need for an Ethernet card and Cat5 cabling altogether. Instead the data would stream over