Home Networking Basis: Transmission Environments and Wired/Wireless Protocols

The current electrical power distribution system is based on the invention of Alternating Current (AC) power generation and high voltage power transmission systems in the 1880s and 1890s. Electricity is generated in power plants by three-phase AC generators driven by hydraulic, thermal, or nuclear resources. The voltage of the electricity is then increased many times to tens of thousands of volts through transformers before being connected to the power distribution grid for better transmission efficiency. Depending on the state or local regulation, utility companies can own either or both power-generating plants and/or power distribution grids. Distribution grids of different regions can be interconnected to buy and sell electrical power on demand. These electrical power distribution grids cover almost 100% of all communities. Electricity has become essential to modern life and it is usually more economical to buy electricity from the distribution grid than to generate it locally for each individual community. The utility company converts the electricity to a lower level of about 120 volts (V) for each residential community again through transformers connected to the distribution grid. Two opposite phases of AC power are available to each residence. They can be used individually as 120-V electrical power supplies or combined for a 240-V supply to drive some heavy-duty appliances such as an electrical dryer.

Because of its broad coverage every household and every room of a residence the use of the electricity distribution grid as a communication medium has been attempted many times for commercial and residential markets. Many utility companies can use the grid to exchange data among different facilities either over the metallic wiring or through some embedded optical fiber cores. The extra embedded fiber communication capacities are sometimes sold to business customers as a part of a private communication system. Besides common signal attenuation and noise problems of a metallic transmission system, the signal recondition at every transformer location possesses additional technical challenges to use the grid as a Wide Area Network (WAN). During the past few decades, some low-throughput (at less than 100 kbps) transmission systems have been created for WAN and home networking applications. With the utilization of advanced digital signal processing and error correction coding techniques, high-throughput transmission systems at more than 1 Mbps for the home electrical environment also become feasible. Assuming the privacy issue (for quite a few residences share the same transformer and are effectively connected as a bus) can be resolved using some encryption and authentication techniques, we need to understand the attenuation and noise characteristics as well as the time-varying nature to realize fully the transmission potential of the in-house electrical wiring environment.

In this chapter, we will examine physical and electrical parameters of typical 12 and 14 AWG cables used for in-house electrical wiring and their transmission and crosstalk characteristics. We will also study a statistical in-house electrical wiring channel model based on the dimensions of a standard house, assumptions about certain wiring practices, and some typical field measurements. We will establish a noise model also based on measurements. In addition, we will carefully interpret FCC radiation regulations related to the use of electrical wiring to derive allowed transmit power spectrum density level. Communication channel capacities on the in-house electrical wiring are then calculated based on these derived models.