Question: Explain FHSS different types of frequency hoping, advantages, disadvantages, Applications of FHSS system.
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Mumbai University > Electronics and Telecommunication Engineering > Sem 6 > Data Communication

Marks: 10 Marks

Year: Dec 2016

 modified 2.3 years ago  • written 2.3 years ago by Sayali Bagwe • 2.1k
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Different bytes of frequency hopping:- Slow and fast frequency hopping.

FHSS: It combines spread spectrum modulation with MFSK. It is the process of modifying frequency of MFSK signal using frequency hope generated by bits of PN sequence.

1) FHSS Transmitter:-

2) Symbol table:-

00 $f_1$
01 $f_2$
10 $f_3$
11 $f_4$

3) Let $C_k = 00111010011101$

Number of bits considered to generate hop frequency = 3

Number of different hops possible = $2^3 - 1 = 7$

4) Hop frequency table:

0 0 1 $f_{H1}$
0 1 0 $f_{H2}$
0 1 1 $f_{H3}$
1 0 0 $f_{H4}$
1 0 1 $f_{H5}$
1 1 0 $f_{H6}$
1 1 1 $f_{H7}$

Let number of symbol transmitted per hop = 2

5) If more than one symbol are transmitted in single it is called as slow frequency hopping. In slow frequency hopping - Rate of change of symbol.

6) If one symbol is transmitted using more than one frequency hope then it is called fast frequency hopping.

For eg:- In this case symbol - 11, 01 are transmitted with same frequency hop $f_{H1}$ for first time. This is slow frequency hope receiver tuning is fast then we can decode slow frequency hoping.Rate of hop frequency is greater than rate of change in fast frequency hoping.

7) Let $C_K$ = 001 110 100 1....

Information signal = 11 01 01 00 11

Advantage of FHSS system:

1) The serial search system with FHSS needs shorter time for aquisition

2) The synchronization is not greatly dependent on distance.

3) The processing gain is higher than that of DSSS system.

Disadvantage of FHSS system:-

1) Complex and costly digital frequency synthesizers are required to be used.

2) Bandwidth of FHSS system is too large (GH2)

Applications of FHSS

1) Wireless local area network (WLAN) standard for wi-fi

2) Wireless personal area network (WPAN) standard of bluetooth.