TELECOMMUNICATIONS SYSTEMS
COMMUNICATION WIRELESS COMPUTING DEVICES
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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frequency hopping
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access encryption
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direct sequencing
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orthogonal frequency-division multiplexing
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Detailed explanation-1: -Direct sequence spread spectrum (DSSS) transmission employs a chipping code to “spread” the transmission over a wider frequency band than it would normally occupy. DSSS is a form of CDMA (see Chapter 4). But instead of a pseudorandom binary sequence (PRBS), an 11-bit Barker code is used as the spreading sequence.
Detailed explanation-2: -There are two predominant techniques to spread the spectrum: 1) Frequency hoping (FH), which makes the narrow band signal jump in random narrow bands within a larger bandwidth. 2) Direct sequence (DS) which introduces rapid phase transition to the data to make it larger in bandwidth.
Detailed explanation-3: -Direct-sequence spread spectrum employs error correction coding at the transmitter and the receiver. It requires an external hardware device called a correlator that can compare incoming sequences with those generated by the transmitter.
Detailed explanation-4: -Frequency hopping spread spectrum (FHSS) and direct-sequence spread spectrum (DSSS) are two methods of spreading a transmitted spectrum over a wide bandwidth, so that the energy at any particular frequency is not detectable without special foreknowledge of the spreading technique.