12-09-2013, 04:50 PM
FREQUENCY HOPPING SPREAD SPECTRUM
HOPPING SPREAD.pptx (Size: 576.63 KB / Downloads: 29)
Spread Spectrum
Principle of spread spectrum
Frequency hopping spread spectrum
Direct sequence spread spectrum
Direct sequence CDMA systems
What is Spread Spectrum?
•Spread spectrum techniques are methods by which electromagnetic energy generated in a particular bandwidth is deliberately spread in the frequency domain, resulting in a signal with a wider bandwidth
•Spread spectrum methods:
Frequency hopping spread spectrum
Direct sequence spread spectrum
Time hopping spread spectrum
Frequency Hopping Spread Spectrum (FHSS)
•Signal is broadcast over seemingly random series of radio frequencies
A number of channels allocated for the FH signal
Width of each channel corresponds to bandwidth of input signal
•Signal hops from frequency to frequency at fixed intervals
Transmitter operates in one channel at a time
Bits are transmitted using some encoding scheme
At each successive interval, a new carrier frequency is selected
Frequency Hopping Spread Spectrum (FHSS)
•Signal broadcast over seemingly random series
of frequencies
•Receiver hops between frequencies in sync
with transmitter
•Eavesdroppers hear unintelligible blips
Jamming on one frequency affects only a few
bits