Task 4 – Overview of Wireless Communication

a) List the different mechanisms by which electromagnetic signals can transfer information.

b) Describe the distinct types of small-scale fading effects.

c) Indicate two major advantages of digital transmission over analog transmission.

d) For radio transmission in free space, signal power is reduced in proportion to the square of the distance from the source, whereas in wire transmission, the attenuation is a fixed number of dB per kilometre. The following table (Table 1 - Task 4d) is used to show the dB reduction relative to some reference for free-space radio and uniform wire. Fill in the missing numbers (in grey cells) to complete the table.

e) The audio power of the human voice is concentrated at about 300 Hz. Antennas of the appropriate size for this frequency are impracticably large, so that to send voice by radio the voice signal must be used to modulate a higher (carrier) frequency for which the natural antenna size is smaller. What is the length of an antenna one-half wavelength long for sending radio at 300 Hz?

f) An alternative to Task 4(e) is to use a modulation scheme for transmitting the voice signal by modulating a carrier frequency, so that the bandwidth of the signal is a narrowband centred on the carrier frequency. Suppose we would like a half-wave antenna to have a length of 1m. What carrier frequency would we use?

g) For a 6 Mbps LTE data stream, 600 subcarriers are created. What would be the symbol time (or symbol rate)?

h)    LTE assigns subcarriers in resource blocks of 200 kHz. Given the information in Task 4(g), how many subcarriers are in a resource block? Approximate B_S≈r_b.