Home Networking Basis: Transmission Environments and Wired/Wireless Protocols

Our daily living places have many commonalities. Rooms are usually separated by interior walls and interconnected by doors. Interior walls are normally made of sheetrock nailed to a wood frame from both sides and covered by paint. Electrical, telephony, cable TV, HVAC, and smoke detector wirings are typically laid within these hollow walls during the construction of a home building. Typical room dimensions range from 10 feet by 10 feet for bedrooms up to 20 feet by 20 feet for family-gathering living rooms. Room ceiling heights can range from 7 feet up to 11 feet. A single family home usually consists of one or two stories with a total living space of between 1500 and 4500 square feet. The floor separation is usually made of sheetrock for the downstairs ceiling and carpet laid over clapboard for upstairs floors. Exterior dimensions of a single family home are from 20 feet by 30 feet up to 40 feet by 60 feet. The exterior wall of a home building is usually covered by sidings of vinyl, wood, brick, or stucco. A single-family home is usually located on a private lot of from ¹/₈ to 1 acre. Children's play set, a swimming pool, or a garden are normally located in the backyard of a single-family home's private lot. The backyard is considered a part of the home living space especially during warm weather.

Existing in-home wirings, including electrical, telephony, and cable TV, are all the daisy-chain type and are connected to external service networks. From an entrance point, usually located on one side of a home at the first-floor or basement level, a few branches of wires are used to connect wall outlets or plugs at different rooms through the whole house. The length of each wire branch is related to the dimension of a house and is usually less than 100 feet. Electrical wiring usually comes to a house with a neutral wire and two hot wires of opposite phases. They are terminated at a distribution panel inside the house and connected to in-home electrical wiring through circuit breakers. A local ground wire is also introduced at the distribution panel. Each electrical wall outlet is connected to a hot wire, the neutral wire, and the ground wire for safety protection. Two phases of hot wires are used for heavy-duty home appliances such as a wall oven or a clothes dryer. Otherwise, they are randomly used throughout the whole house. In other words, electrical outlets on different walls of the same room can be of opposite phases. The telephone service network is connected to in-home telephone wiring at a demarcation box located outside a house. In-home telephone wiring can have two pairs, four pairs, or more. Some newer homes are wired with Category 5 data-grade cables in a home-run configuration, where every telephone outlet is individually connected to a central location, for telephone usage. An Ethernet can be installed over home-run in-home telephone wiring as a home network. The cable TV service is usually connected to in-home coaxial cables through a lightning protection block located outside the structure. Multiple wall plugs are all connected to the same entrance coaxial cable via splitters, which introduces 3 decibels (dB) of signal loss for every 1-to-2 split.

To take care of current as well as future home telephony, data, and entertainment networking needs in a more organized fashion, structured wiring [1] has been promoted as the correct practice for a "connected" home. External communication networks, such as telephone or DSL, and entertainment resources, such as cable or satellite TVs, are terminated in a centralized distribution panel and routed through a home via structured wiring made of Category 5 twisted pair, for telephony and data connections, and single or dual coaxial cable, for entertainment services. One of the dual coaxial cables can be used to redistribute home entertainment resources such as a DVD player to other rooms. A multiple-input and multiple-output splitter with a built-in gain is normally used to connect external and internal coaxial cables. An Ethernet hub or a home DSL router can also be located inside the distribution panel. Sometimes, stereo audio and remote control signals are also transmitted throughout a home via additional wiring. Figure 1.1 shows a centralized distribution panel with two in-coming telephone lines, four telephone wall jacks, an Ethernet hub of four connected ports, and coaxial cables connected to the cable TV signal.

Telephony, data, and TV signal plugs can be located on the same wall plate for this structured wiring approach. Figure 1.2 shows wall plates capable of different numbers of outlets or plugs. Modular telephone (RJ-11), Ethernet (RJ-45), coaxial cable, RCA (for audio), and S-video plugs, as shown in Figure 1.3, can be snapped into openings of a wall plate from behind. A blank module can be used to cover nonoccupied openings.

The installation of structured wiring is more suitable for new homes. Because the retrofit cost of structured wiring, which sometimes involves opening up walls, can be too high to justify the benefit. RF-based networking approaches are probably a better choice for most existing homes.

Because radio wave transmission cannot be confined, its use in a home environment must follow government regulations to avoid causing interference with other communication systems. Three Industrial, Scientific, and Medical (ISM) bands of 900 megahertz (MHz), 2.4 gigahertz (GHz), and 5.7 GHz have been used for home network applications. Radio waves can penetrate interior walls and ceilings with a signal strength loss of about 3 dB. Radio waves also experience a 6-dB signal strength loss when their traveling distance doubles from the source. Reference signal strength losses are about 42 dB, 50 dB, and 57 dB at a distance of 10 feet from the source for 900 MHz, 2.4 GHz, and 5.7 GHz ISM band radio waves, respectively. Within a home environment, an RF signal can arrive at one point from another through many different paths: direct, penetrated, or reflected. Radio waves arriving via different paths contribute to the overall signal strength. They partially add or subtract depending on phase differences and cause the phenomenon of significant signal strength variations also known as multipath fading. Radio waves can pass through exterior wall sidings of vinyl, wood, or brick except stucco, which contains a metal mesh. Windows and doors might still provide some limited passages in the late case. In other words, an RF home network can cover the backyard usage for houses with other than stucco sidings. Radio waves can also reach neighbors' backyards or get into their homes with additional signal strength losses of 6 to 12 dB owing to longer traveling distances and exterior walls. Some interference might exist between neighboring RF home networks. On the other hand, Infrared signals behave like light. You can bounce the signal from a remote control off the wall. In other words, you can point your remote control toward a back wall or the ceiling and a TV or a VCR might still respond to your command.