Page 333 - Satellite Communications, Fourth Edition

Digital Signals 313

10.12. Explain what is meant by coherent detection as used for the
demodulation of PSK bandpass signals. An envelope detector is an example of
a noncoherent detector. Can such a detector be used for BPSK? Give reasons for
your answer.

10.13. Explain how a QPSK signal can be represented by two BPSK signals.
Show that the bandwidth required for QPSK signal is one-half that required for
a BPSK signal operating at the same data rate.
10.14. The input data rate on a satellite circuit is 1.544 Mbps. Calculate
the bandwidths required for BPSK modulation and for QPSK modulation,
given that raised-cosine filtering is used with a rolloff factor of 0.2 in each
case.
10.15. A QPSK system operates at a [E b /N 0 ] ratio of 8 dB. Determine the bit
error rate.
10.16. A BPSK system operates at a [E b /N 0 ] ratio of 16 dB. Determine the bit
error rate.
10.17. The received power in a satellite digital communications link is 0.5 pW.
The carrier is BPSK modulated at a bit rate of 1.544 Mb/s. If the noise power
density at the receiver is 0.5 10 19 J, determine the bit error rate.

10.18. The received [C/N 0 ] ratio in a digital satellite communications link is
86.5 dBHz, and the data bit rate is 50 Mb/s. Calculate the [E b /N 0 ] ratio and the
BER for the link.

10.19. For the link specified in Prob. 10.18, the [C/N 0 ] ratio is improved to 87.5
dBHz. Determine the new BER.

References

Bellamy, J. 1982. Digital Telephony. Wiley, New York.
Franks, L. E. 1980. “Carrier and Bit Synchronization in Data Communication: A Tutorial
Review.” IEEE Trans. Commun., Vol. 28, No. 8, August, pp. 1107–1120.
Gagliardi, R. M. 1991. Satellite Communications, 2d ed. Van Nostrand Reinhold, New York.
Hassanein, H., A. B. Amour, and K. Bryden. 1992. “A Hybrid Multiband Excitation Coder
for Low Bit Rates.” Department of Communications, Communications Research
Centre, Ottawa, Ontario, Canada.
Hassanein, H., A. B. Amour, K. Bryden, and R. Deguire. 1989. “Implementation of a 4800
bps Code-Excited Linear Predictive Coder on a Single TMS320C25 Chip.” Department
of Communications, Communications Research Centre, Ottawa, Ontario, Canada.
Pratt, T., and C. W. Bostian. 1986. Satellite Communications. Wiley, New York.
Roddy, D., and J. Coolen. 1994. Electronic Communications, 4th ed. Prentice-Hall,
Englewood Cliffs, NJ.
Taub, H., and D. L. Schilling. 1986. Principles of Communications Systems, 2d ed.
McGraw-Hill, New York.