Chapter 8
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Designing a wireless communication system requires deciding on a transmis-
sion medium, a modulation method if needed, and a protocol for transferring
data.
Wireless data communications typically use infrared (IR) or radio-frequency
(RF) energy. Many wireless systems can transmit and receive data in the asyn-
chronous format supported by UARTs. Some wireless protocols use other data
formats for greater data throughput, better reliability, or other benefits. When
needed, an intelligent converter module can translate between asynchronous
data and another protocol..
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Instead of transmitting raw data pulses, many wireless systems transmit a carrier
frequency with the data encoded as variations in the carrier’s amplitude, fre-
quency, phase, or a combination of these. The process of encoding information
as variations in a carrier is called modulation. Using a carrier helps the receiver
isolate transmitted data from noise and can increase the distance the data trav-
els.
For basic data communications, two popular modulation methods are on/off
key (OOK) and frequency shift key (FSK). Figure 8-1 shows both methods.
In OOK modulation, the two logic states are defined as carrier present and car-
rier absent. Another term for this type of modulation is carrier-present car-
rier-absent (CPCA) modulation. Systems that don’t transmit data continuouslyFigure 8-1: Wireless data often uses OOK or FSK modulation.