CCIT 517 Wireless Data Networks
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CCIT 517 Wireless Data Networks spring 2020 Homework Assignment #2 Due in 26/02/2020 Name: Number: 1. Choose the correct answer (one only): _involves varying some parameter of a carrier wave (sinusoidal waveform) at a given frequency as a function of the message signal. Modulation ii. Frequency Diversity iv. Antenna Multiple access schemes describe How multiple users can buy licensed spectrum il. How multiple modulation techniques are used together l. How users can share spectrum. iv. None of the above. What is true about radio signal loss (attenuation)? i. Signals of higher frequencies suffer more loss. il Signal of lower frequencies suffer more loss. ii. Attenuation is independent of frequency iv. Attenuation is dependent on phase shift. ISM bands are i. Unlicensed bands ii. Used for loT and WiFi. iii. Used in industry. iv. All of the above. For successful reception of wireless signal 1. Received signal must avoid taking multipaths il. Received signal must have enough strength so that the receiver can interpret the signal ii. Received signal must be retransmitted. iv. Received signal must have enough bandwidth to travel across large distances What is true about MIMO: i SU-MIMO supports multiple parallel streams of more than one user. ii. SU-MIMO supports multiple parallel streams of one user only. . MU-MIMO supports multiple parallel streams of one user only Iv. MU-MIMO is way faster than SU-MIMO. ARQ mechanisms may suffer from poor time outs. il may lead to too many retransmissions. i. may lead to frequent error detections iv. may suffer from parity checks. What is NOT true about line of sight (LOS)? LOS is required for all wireless communications. ii. Even with LOS, radio signals would suffer from attenuation. ii. LOS can achieve high data rates. iv. LOS assumes no obstructions. What is NOT true about wireless channel capacity? Shannon limit is the theoretical capacity limit of a channel. ii. It is independent of the signal bandwidth ill. It is affected by the signal-to-noise ratio (SNR). iv. Channel capacity is the maximum data rate over the channel 2. List and briefly describe the five basic propagation mechanisms. 3. What are wireless channel impairments? Explain them. 4. List and briefly describe 3 techniques for improving wireless channel. 5. What is the difference between Cyclic Redundancy Check (CRC) code and a forward correction (FEC) code? 6. What is Automatic Repeat Request (ARQ) mechanism? What is it used for? 7. What is adaptive modulation and coding (AMC) and why it is effective? 8. Briefly define OFDM, OFDMA, and SC-FDMA 9. The audio power of the human voice is concentrated at about 750 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. (Assume 3x10 m/s) a. What is the length of an antenna three-quarter wavelength long for sending radio at 750 Hz? b. An alternative 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 centered on the carrier frequency. Suppose we would like a three-quarters-wave antenna to have a length of 0.75 m. What carrier frequency would we use? 10. Suppose a transmitter produces 60 W of power. C Express the transmit power in units of dBm and dBW. d. If the transmitter's power is applied to an antenna with a 900 MHz carrier frequency, what is the received power in dBm at a free space (LOS) distance of 100 m? e. Repeat (b) for a distance of 10 km and compare the results. 11. Calculate the pairwise Hamming distances among the following codewords: a. 00000 and 10101 hd- b. 10101 and 01010 hde c. 000000 and 01010 hd- d. 010101 and 101010 hd e. 110110 and 010101 hde 12. Assume LOS, you want to check the loss in the WiFi 2.4 GHz and 5 GHz. How would you check that compare between them mathematically? (choose any distance!) 13. What is QAM? 14. What are the four usages of space diversity of antennas? Describe them briefly. 15. Consider the following constellation diagrams. Identify what modulation scheme each diagram represents 1 010 011 100 111 136
