RF systems
can transmit digital data by shifting a carrier frequency in a similar way.
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Some RF transmitters use spread-spectrum technology, where the transmitter
uses a mathematical code or pattern to spread transmissions over a wide frequency
band. The receiver uses a complementary algorithm to extract the data.
Spread-spectrum transmissions have high resistance to interference and are very
secure from eavesdropping but require more complex circuits than other transmission
protocols.
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Because wireless transmissions aren??™t confined to a cable, wireless systems need
to take special care to ensure reliable transmissions. Wireless systems can implement
protocols to help data reach its destination without errors and to help the
receiving computer detect any errors that occur.
In a typical, basic wireless system, only one transmitter sends data at a time. A
primary/secondary or other protocol can help ensure that only one transmitter
is active at a time.
As Chapter 2 explained, wired links often use additional lines for flow control.
Because of the expense of adding wireless channels, wireless communications
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typically don??™t have dedicated channels for sending flow-control data. Buffers or
software flow control can help ensure that a transmitter doesn??™t send data when
the receiver isn??™t ready.
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