Assume that a digital communication system can be operated at a bit rate of up to 1% of the carrier frequency.

1.Assume that a digital communication system can be operated at a bit rate of up to 1% of the carrier frequency. How many audio channels at 64 kb/s can be transmitted over a microwave carrier at 5GHz and an optical carrier at 1.55 mm?

2. A 1.55 mm digital communication system operating at 1 Gb/s receives an average power of -40 dBm at the photodetector. Assuming that "1" and "0" bits are equally likely to occur, calculate the number of photons received within each "1" bit.

3. A 1.55 mm digital communication system is transmitting digital signals over 100 km at 2 Gb/s. The transmitter launches 2 mW of average power into a fiber cable, having a net loss of 0.3 dB/km. How many photons are incident on the receiver during a single 1 bit? Assume that 0 bits carry no power, while 1 bits are in the form of a rectangular pulse occupying the entire bit slot (NRZ format).

4. A 0.8-mm optical receiver needs at least 1000 photons to detect the 1 bits accurately. What is the maximum possible length of the fiber link for a 100 Mb/s communication system designed to transmit -10 dBm of average power? The fiber loss is 2 dB/km at 0.8 mm. Assume the NRZ format and a rectangular pulse shape.

5. Calculate the transmission distance over which an optical power will be attenuated by a factor of 10 for three fibers with losses of 0.2, 20, and 2000 dB/km. Assuming that the optical power decreases as exp(-αL), calculate α (in cm-1) for the three fibers.