ving antenna, introducing a loss that can be as much as 20 to 30 dB. It is possible to compute multipath losses using complex ray tracing or other algorithms, but this is rarely done in practice. Signal Attenuation Indoors For a typical wireless network in a home or small office, multiple obstructions such as walls, floors, furniture and other objects will obstruct the propagation path from transmitter to receiver, and signal reception will tend to be very variable. Depending on its construction, transmission through a wall can introduce a loss of 3 to 6 dB or more, as shown in Table 4-18, and an additional allowance will be required in the link budget to account for this loss. In a multi-storey building, losses between floors will also depend on the building materials used, and will be very high in buildings Chapter Four Table 4-18: Typical Attenuation for Building Materials at 2.4 GHz Attenuation range Materials Loss (dB) Non tinted glass, wooden door, cinder block wall, plaster. Medium Brick wall, marble, wire mesh or metal tinted glass. Concrete wall, paper, ceramic bullet- 10-15 proof glass. Very high Metal, silvering (mirrors). with sheet steel construction. More typically, a loss of approximately 6 dB is seen between adjacent floors, rising to around 10 dB per additional floor for separations of two to three floors. The typical losses shown in Table 4-18 are highly dependent on the specific materials used and methods of construction. For example, even a stud wall can introduce a significant loss if it contains a fire retarding foil membrane. In common with multi-path fading, complex algorithms are required to calculate the various types of losses indoors, and it is therefore convenient to combine these loss components to give a single additional term in the link budget. This term, the fade margin (LFM), will generally be estimated by a rule-of-thumb, or determined by an on-site survey. Link Budget The factors considered above, transmitter power (PTX), antenna gain at the transmitter (GTX) and receiver (GRX