Select which two statements ARE FALSE. (1) For antennas used at lower frequencie

Question

Select which two statements ARE FALSE.

(1) For antennas used at lower frequencies to have the same gain as those used at higher frequencies, the lower frequency antennas generally have to be bigger.

(2) Antennas can have omnidirectional radiation patterns or they can have directional beams in their patterns.

(3) In a cellular architecture a forward link is the wireless link from the cell phone to the base station, and the reverse link is the other way around.

(4) ARQ is an error control technique that uses detections of bit errors, and requests retransmissions of frames with erroneous bits.
                 

(5) Free space loss is wireless propagation loss in a link where there are free O2 (ie, oxygen) molecules absorbing energy from the propagating signal, and thus further attenuating the signal.

Select which three (3) statements ARE TRUE

(1) 3G cellular systems use various forms of spread spectrum modulation and multiple access based on the spread spectrum codes.

(2) FEC can correct many erroneously received bits in wireless

(3) At cellular frequencies the main source of RF noise in the receiver of a cell phone is a combination of atmospheric noise and other people nearby talking on their desk phones.

(4) The Shannon’s capacity formula says that under certain conditions (such as when the noise is white Gaussian) the maximum capacity of a channel is proportional to that channel’s bandwidth.

(5) Mechanisms provided by cellular architectures to handle user or cell phone mobility requires having the base stations know when a cell phone is inside its coverage area. This is done by the base stations using GPS to obtain the location of each cell phone.

4. On propagation, multipath and other wireless effects and techniques

Propagation in a wireless channel is sometimes modeled using the propagation index n.

Which is True and False in each part below:

i) The propagation index n varies as function of the physical environment for the path, and the frequency. The index n is a function of the matter that make up the path, the objects, gases or liquids in the path, or pure vacuum, and it is then typically higher if there is more solid material (more objects in between), such as buildings, hills or parts of them, vegetation and trees, and other natural and manmade objects.

ii) The propagation index depends on the transmit power.

iii) The signal will travel further for a propagation index of 4 than for a propagation index of 3, for the same frequency, transmit power levels, and antenna gains.

Explanation / Answer

1.

(3) In a cellular architecture a forward link is the wireless link from the cell phone to the base station, and the reverse link is the other way around.

(4) ARQ is an error control technique that uses detections of bit errors, and requests retransmissions of frames with erroneous bits.  

2.

(1) 3G cellular systems use various forms of spread spectrum modulation and multiple access based on the spread spectrum codes.

(2) FEC can correct many erroneously received bits in wireless

4) The Shannon’s capacity formula says that under certain conditions (such as when the noise is white Gaussian) the maximum capacity of a channel is proportional to that channel’s bandwidth.

3.

i) False

ii) True

iii) true

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