B. P. Lathi, Zhi Ding - Modern Digital and Analog Communication Systems-Oxford University Press (2009)

652 SPREAD SPECTRUM COMMUNICATIONS
COMPUTER EXERCISE 1 1. l : FHSS FSK COMMUNICATION
UNDER PARTIAL BAND JAMMING
The first MATLAB program, Exl 1_1 . m, implements an FHSS communication system that utilizes FSK
and noncoherent detection receivers. By providing an input value of 1 (with jamming) and O (without
jamming), we can illustrate the effect of FHSS against partial band jamming signals.
TABLE 11.4
Parameters Used in Computer Exercise 11 .1
Number of users
Spreading factor
(number of FSK bands)
Number of hops per symbol per bit
Modulation
Detection
Partial band jamming
m = l
L=8
Lh = l
BFSK
Noncoherent
1 fixed FSK band
In Exl 1_1 . m, the parameters of the FHSS system are given in Table 11.4. When partial band
jamming is turned on, a fixed but randomly selected FSK channel is blanked out by jamming. Under
additive white Gaussian channel noise, the effect of partial band jamming on the FHSS user is shown in
Fig. 11.22. Clearly, we can see that without jamming, the FHSS performance matches that of the FSK
analysis in Sec. 11.1 and Chapter 10. When partial jamming is turned on, the BER of the FHSS system
has a floor of 1/ (2L) as shown in Eq. (11.4). As L increase from 4 to 8, and to 16, the performance clearly
improves.
% MATLAB PROGRAM <Exll 1.m>
% This program provides simulation for FHSS signaling using
% non-coherent detection of FSK.
% The jammer will jam 1 of the L frequency bands and
Fi g ure 11.22
Performance of
FHSS
noncoherent
detection under
partial band
jamming.
10 ° .---------,..--------_,_------<----,.---,
Increasing spreading factor L
-- Analytical
-e- L = 8, no jamming
-a- L = 16, under jamming
L = 8, under jamming
L = 4, under jamming
10- 3 ---_,_ __ _.._ __ ...,_ __ _.._ __ .__ _ __. __ __,_ __ ___.
1 2 3 4 5 6
E,JN, dB
7 8 9 10