Slide 1

Tutorial 8 Mobile Communications Netrowks Slide 2 Prob.1 Construct 4 Walsh (Orthogonal) codes for 4 different users by two methods. Assume that 4 users transmit their data with 22Kbps (before spreading) using these codes such that: User 1 transmits +1 @ 500m User 2 transmits -1 @ 1000m User 3 transmits -1 @ 1200m User 4 transmits -1 @ 1500m Carrier Freq.=3GHz Path Loss Factor=2. a) Construct the transmitted and decoded (de-spread) signals for the 4 users. Assuming users 1,2,3&4 see the following attenuation L1X, L2X, L3X and L4X; where Li is the path loss factor with (n=2) plus the following Noise Level; U1: +0.5p, U2: -1p, U3: +0.5p, U4:+1p. Find the decoded signals and calculate the average bit error rate based on X. Given that 0 = +4L 1 X -2p>0 1 = -4L 2 X < 0 -1 = -4L 3 X < 0 -1 = -4L 4 X< 0 -1 L1= L2= L3= L4= (-2L 1 X-0.5 +2L1X-0.5 +2L1X-0.5 +2L1X-0.5) (-2L2X+1 -2L2X-1 +2L2X+1 -2L2X-1) (-2L 3 X-0.5 +2L3X-0.5 -2L3X+0.5 -2L3X+0.5) (-2L4X-1 -2L4X+1 -2L4X+1 +2L4X+1) Slide 8 X is the attenuation factor due to the shadowing effect with Standard deviation =32dB = +4*253.3p X -2p>0 1 = -4*63.3p X < 0 -1 = -4*43.9p X < 0 -1 = -4*28.14p X< 0 -1 As 0 ( 1.974*(10^-3))^2 So: Attenuation>-54 dB or Attenuation