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+// Exa 21.7
+// To determine the PER(Packet error rate) for FH(Frequency Hopping packet) and DS(Direct spread packet).
+
+clc;
+clear all;
+
+D=1000*8;  //packet size in bits
+R=2*10^6;  //transmission rate in bps
+L=3; //msec(Dwell time)
+H=0.625; //msec(Duration of BT packet)
+
+//solution
+Tw=10^3*D/R;   //the packet duration of IEEE 802.11 in msec
+H_L=1;
+G=(H_L)*L-Tw-H;
+Gm=abs(G);
+PER_FH=1-((1-Gm/L)*(78/79)^(H_L)+Gm/L*(78/79)^((H_L)-G/Gm));
+PER_DS=1-((1-Gm/L)*(57/79)^(H_L)+Gm/L*(57/79)^((H_L)-G/Gm));
+printf('The PER for FH packet and PER for DS packet are %d percent & %.2f percent respectively',round(PER_FH*100),PER_DS*100);
+disp("The collision probability with 802.11 DS is much higher than with 802.11 FH.")