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Differentiate between frequency hopping and direct-sequence spread spectrum.

Mumbai University > Electronics and Telecommunication > Sem8 > Wireless Networks

Marks: 10 M

Year: Dec 2015

1 Answer
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FHSS DSSS
FH systems use a radio carrier that “hops” from frequency to frequency in a pattern known to both transmitter and receiver DS systems use a carrier that remains fixed to a specific frequency band.
A,broad,slice,of,the,bandwidth,spectrum,is,divided,into,many,possible,broadcast frequencies. The data signal is spread onto a much larger range of frequencies (at a much lower power level) using a specific encoding scheme.
Frequencies are randomize Frequency is constant
Data is constant Data are randomize
Resistance to noise Less resistant to noise
Limited throughput (2-3 Mbps @ 2.4 GHz) Much higher throughput than FH (11 Mbps)
Systm,generate wideband signals controlled by commanding the carrier frequency,(frequency hopping) Syestem,generate wideband signals controlled by the code is direct carrier,modeulation (direct sequence)
Frequency-hopping,devices,use,less,power,and,are,cheaper Performance of DS-CDMA systems is usually,better and more reliable.
FHSS are significantly less sensitive to Bluetooth interference. Though bandwidth efficiency decreases; reliability, integrity and security increase.
FHSS systems operate with SNR (Signal to Noise Ratio) of about 18 dB DSSS systems, because of the more efficient modulation technique used (PSK), can operate with SNR as low as 12 dB
FHSS spreads the signal by hopping from one frequency to another across a bandwidth of 83 Mhz. DSSS spreads the signal by adding redundant bits to the signal prior to transmission which spreads the signal across 22 Mhz
To some other receiver, FHSS appears to be a short-duration impulse noise. Thus, the data security increases To,some other receiver, DSSS appears as low-power, wideband noise and is,rejected.
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