INTRODUCTION TO COMMUNICATIONS SYSTEMS ASSIGNMENT
1. The continuous signal whose spectrum is shown below is quantized, sampled, and transmitted using a baseband PCM system.
a) If each data sample must be known to within ±1% of the peak-to-peak full-scale value, how many binary symbols must each transmitted digital word contain?
b) Assuming that the signal is sampled at the Nyquist rate, estimate the bandwidth of the resulting PCM signal.
2. You wish to transmit an analog signal with a bandwidth B = 15 kHz via a baseband PCM code employing 7 bipolar pulses per sample.
a) Sketch a reasonable receiver up to the analog output.
b) Which types of synchronization are needed to implement the receiver?
3. Consider three ways of communicating one of 60 messages, each of which can be regarded as an L - level phase modulation technique. The first method is to encode in a binary code where each sinusoidal pulse has a phase of 0 or 180 degrees (PSK). The second method is to encode in a tertiary or 3 - level code, where each pulse has a phase of 0, 120, or -120 degrees. The final method is to encode in a 4 - level code, where each pulse has a phase of 0, 90, 180, or 270 degrees (QPSK).
a) How many pulses per message are needed for each scheme?
b) Calculate the necessary bandwidth for each scheme. Which scheme would be useful when bandwidth is at a premium?
c) How would you store the decisions on each pulse?
d) Discuss the practical hardware difficulties for each scheme.
e) Could you use differential techniques for the 3 - and 4 - level codes as well as DPSK?