Choose the best answer for the following multiple-choice:  Rapid variation of the received signal level due to the effect of multiple signal paths is known as: a. Path loss b. Time variance c. Flat fading d. Shadowing  For the log-distance path loss model, the reference distance (do) is properly defined based on: a. Signal frequencies b. Antenna Gains c. Propagation environments d. Signal bandwidths  Multipath delay spread in the wireless channels causes: a. Doppler spread b. Time dispersion c. Frequency dispersion d. Fast fading  A probability density function of the signal received in the LOS environment follows: a. Rician distribution b. Gausian distribution c. Rayleigh distribution d. Normal distribution  In the MIMO wireless system, increasing of the QAM modulation levels leads to: a. Data rate ↑, Error rate ↓ b. Data rate ↑, Error rate ↑ c. Data rate ↓, Error rate ↓ d. Data rate ↓, Error rate ↑  In multiple- antenna systems, the data rates mainly increased by: a. Spatial diversity techniques b. Beamforming techniques c. Modulation techniques d. Spatial multiplexing technique

When transmitting over a perfectly reflecting, smooth, plane earth, the path loss tends to increasea.with the square of distanceb.with the fourth power of distancec.linearly with distanced.with distance cube

Which of the following statements about the characteristics of wireless links are true?Group of answer choicesThe bit error rate (BER) of a wireless channel decreases as the signal-to-noise ratio (SNR) increases.The "hidden terminal problem" happens when A sends to B over a wireless channel, and an observer, C (that can be even closer to A than B), does not detect/receive A's transmission because of physical obstacles in the path between A and B.Multipath propagation occurs when portions of the electromagnetic wave reflect off objects and the ground taking paths of different lengths between the sender and a receiver, and thus arriving at the receiver at slightly different points in time.The "hidden terminal problem" happens when A sends to B over a wireless channel, and an observer, C (that is further away from A than B), does not detect/receive A's transmission because the signal strength of A's transmission has faded significantly by the time it reaches C.The bit error rate (BER) of a wireless channel increases as the signal-to-noise ratio (SNR) increases.Path loss refers to the dropping of link-layer frames that are being relayed among wireless access points due to buffer overflow, just as network-layer datagrams are dropped at routers with full buffers.The "hidden terminal problem" happens when A sends to B over a wireless channel, and an observer, C (that can be even closer to A than B), does not detect/receive A's transmission because of physical obstacles in the path between A and C.Multipath propagation occurs when a sender sends multiple copies of a frame to a receiver, which is relayed over different by base stations or other wireless devices to the receiver.Path loss refers to link-layer frames that are corrupted due to the higher bit error rates in wireless channels.Path loss refers to the decrease in the strength of a radio signal as it propagates through space.The "hidden terminal problem" refers to the fact that many people can never seem to find their mobile phones.

Decide if the following statements are True [ √ ] or False [ ]. Correct the false ones if any:  A log-distance shadowing model is useful when dealing with a more realistic situation [ √ ] …………………………………………………………………………………………………………..  IEEE 802.16d model is based on the log-normal shadowing path loss model [ √ ] …………………………………………………………………………………………………………..  The speed of surrounding objects around a mobile generates path loss of the wireless signal [ ] The speed of surrounding objects around a mobile generates Doppler shift, not path loss. …………………………………………………………………………………………………………..  The slow fading generates in the received wireless signal due to the multipath delay spread [ ] Slow fading is caused by shadowing effects, not multipath delay spread. …………………………………………………………………………………………………………..  The precoding matrix indicator (PMI) at the Rx feedbacks the amplitude variations to the Tx [ ] The PMI at the Rx feedbacks the preferred precoding matrix, not amplitude variations. …………………………………………………………………………………………………………..  Beamforming increases the signal strength at the Rx in proportion to the number of Tx antennas [ √ ] …………………………………………………………………………………………………………..

In free space transmission, the signal attenuation increasesa.proportionally with distanceb.proportionally with the square distancec.proportionally with distance cube

modulation is used to Select one:a. ensure information is transmitted over large distancesb. seperate different input signalsc. have practically possible height of antennad. all