563489578934

Problems 667
the IF band of the satellite transponder. Let (CN) dn denote the IF CNR ratio at the downlink
receiving ground station when the satellite is sending a perfect (noise-free) signal. Show that the
overall operating CNR ratio at the IF of the receiving ground station, (CN) ov , is given by
1
(C>N) ov
=
1
(C>N) up
+
8–41 For the wireless device link that is described in Study Aid Example SA8–3, use MATLAB to plot
the path loss (in dB) as a function of distance over a range of 50 to 500 feet.
★ 8–42 A PCS cellular site base station operates with 10W into an antenna with 18 dB gain at 1800 MHz.
The path loss reference distance is d 0 = 0.25 miles, X dB = 0, and the PCS phone antenna has
0 dB gain. Find the received power in dBm at the antenna output of the PCS phone when the PCS
phone is located at distances of 1 mile, 2 miles, 5 miles, and 10 miles from the BS if the path loss
exponent is
(a) n = 2 (free space condition).
(b) n = 3.
(c) n = 4.
8–43 The transmitter of a PCS CDMA cellular phone feeds 200 mW into its 0 dB gain antenna. The
PCS signal is spread over a bandwidth of 1.25 MHz in the 1900 MHz band. Calculate the signal
power received in dBm at the output of the base station antenna where the PCS phone is located
2 km from the BS. Assume a path loss model given by Eq. (8–47), where d 0 = 100 m, n = 3 and
X dB = 0. The BS antenna has a gain of 16 dB.
8–44 Given a CDMA cellular phone link as described in Prob. 8–43 and by the IS-95 standard shown
in Table 8–11. The base station receiving system has a noise figure of 8 dB and multiple access
interference (MAI) from other phones adds 20 dB to the noise level at the front end of the BS
receiver. Compute the CNR, (CN) dB , after despreading (i.e., at the data detector input) in the BS
receiver. Also, find (E b N 0 ) dB after despreading. Assume that the bandwidth after despreading is
1
B = 19.2 kHz, since the data rate with coding is 19.2 kbs (9.6 kbs payload data rate with rate
2
coding) on each I and Q BPSK carrier of the QPSK signal.
8–45 Assume that an analog TV station is licensed to operate on TV Channel 35 with an effective radiated
visual power of 1000 W. The tower height is 400 ft, and the transmission line is 450 ft long. Assume
that a 1 5 8 -in.-diameter semirigid 50-Ω coaxial transmission line will be used that has a loss of
0.6 dB100 ft (at the operating frequency). The antenna has a gain of 5.6 dB, and the duplexer
loss is negligible. Find the PEP at the visual transmitter output.
★ 8–46 An analog TV visual transmitter is tested by modulating it with a periodic test signal. The envelope
of the transmitter output is viewed on an oscilloscope as shown in Fig. P8–46, where K is
an unknown constant. The output of the transmitter is connected to a 50-Ω dummy load that has
1
(C>N) dn
1.0 K
0.75 K
0.5 K
4.76 msec
53 msec
10.5 msec
Figure P8–46
t