Wireless Fundamentals 2

Here you will find answers to Wireless Fundamentals – Part 2

Question 1

How are omni antennas in a wireless network most commonly polarized?

A. circularly
B. horizontally
C. vertically
D. both horizontally and vertically

 

Answer: C

Explanation

Omni antennas send a signal of the same strength in all directions. Antennae in wireless networks are often vertically polarized, which makes the electric field vertical.

Note: A VERTICALLY POLARIZED antenna transmits an electromagnetic wave with the E field perpendicular to the Earth’s surface.

Vertical antenna: Electronic field perpendicular to the Earth’s surface

A HORIZONTALLY POLARIZED antenna transmits a radio wave with the E field parallel to the Earth’s surface.

Horizontal antenna: E field parallel to the Earth’s surface

 

Vertical polarization means that the wave moves up and down in a linear way. Horizontal polarization means that the wave moves left and right in a linear way.

-> We also notice that the E field is in the same direction with the antenna.

Question 2

Which governing body analyzes the applications and environments in which wireless networks are used?

A. EIRP
B. ETSI
C. FCC
D. IEEE
E. WiFi Alliance

 

Answer: D

Question 3

What does the current European Telecommunications Standards Institute rule state is the 2.4-GHz maximum transmitter output power for point-to-point installations?

A. 16dBm
B. 17dBm
C. 20dBm
D. 30dBm
E. 36dBm

Answer: B

Explanation

Currently ETSI stipulates a maximum of 20 dBm EIRP on point-to-multipoint and point-to-point installations; it also stipulates 17 dBm maximum transmitter power with 3 dBi in gain attributed to antenna and cable combination.

Question 4

What are two attributes used to characterize antenna performance? (Choose two)

A. attenuation
B. beamwidth
C. gain
D. harmony
E. interference

 

Answer: B C

Explanation

The fundamental characteristics of an antenna are its gain and half power beamwidth.

Some antennas are highly directional; that is, more energy is propagated in certain directions than in others. The ratio between the amount of energy propagated in these directions compared to the energy that would be propagated if the antenna were not directional (Isotropic Radiation) is known as its gain.

(An isotropic radiator will distribute its power equally in all directions)

Beamwidth is another of the important criteria since it specifies boundaries within the antenna radiation pattern, which are considered to be the limit of useful radiation (or reception).

Question 5

Bluetooth RF characteristics can be best described as which of the following?

A. continuous transmitting 5-GHz range
B. continuous transmitting 2.4-GHz range
C. frequency hopping 5-GHz range
D. frequency hopping 2.4-GHz range

 

Answer: D

Question 6

Which best describes an Ad Hoc Network?

A. Basic Service Set
B. Extended Service Set
C. Independent Basic Service Set
D. Mesh Network
E. WiMAX Network

 

Answer: C

Question 7

When would rate shifting down by a client occur?

A. when the distance to the AP has increased and the missed-symbol rate has increased
B. when the distance to the AP has increased and the signal level has increased
C. when multipath has decreased and the missed-symbol rate has decreased
D. when the noise level has decreased and the signal level has increased

 

Answer: A

Explanation

When a client moves away from the AP, the WLAN adapter software determines a threshold from where the client will not be able to achieve the maximum speed. This threshold is product-dependant and relies on values such as the Received Signal Strength Indicator (RSSI), packet error rate, and so on. To avoid losing too many packets or even the connection, the client reverts to a simpler modulation, thus slowing the speed of its communication with the AP.

Question 8

Which physical layer encoding technology is common to both the IEEE 802.11g and the IEEE 802.11a standards?

A. BPSK
B. CCK
C. DSSS
D. OFDM

 

Answer: D

Explanation

802.11a operates in the 5-GHz frequency range and is based on Orthogonal Frequency Division Multiplexing (OFDM). Like 802.11a, 802.11g uses OFDM for transmitting data. OFDM is a more efficient means of transmission than Direct Sequence Spread Spectrum (DSSS) transmission, which is used by 802.11b.

Question 9

Why are wireless analog video signals that are operating in the 2.4-GHz band particularly harmful to Wi-Fi service?

A. Analog video is a strong signal and increases the SN
B. Analog video is a constant signal with 100% duty cycle.
C. Analog video signals are slow frequency hopping and tend to affect the entire band.
D. Analog Video modulation is the same as Wi-Fi and causes interference.

 

Answer: B

Explanation

RF video cameras operate by exchanging information (the image stream) between a transmitter (the camera) and the receiver (linking to a video display). They usually use 100 mW and a channel narrower than Wi-Fi. But the stream of information is continuous, and will severely impact any wireless network in the neighboring channels. They are not compatible; an access point (AP) cannot receive a camera video stream and understand it.

The figure below illustrates the narrowband continuous transmitting nature of an analog video camera. The transmit power is concentrated on a very small portion of the spectrum (channels 4-8). Notice that the duty cycle of the analog video camera reaches 100% indicating that no Wi-Fi device in the vicinity will be able to operate on channels 4-8. Because of its continuous transmission nature, this device can cause prolonged periods of service disruption.

For your information, below lists popular sources of wireless interferer:

Question 10

Which two statements are true about WiMAX technology? (Choose two)

A. WiMAX is defined by 802.11i.
B. Typically, fixed WiMAX networks have a higher gain direction antenna installed near the client.
C. WiMAX is capable of working as a long-range system over several miles.
D. WiMAX works only for licensed frequencies.

 

Answer: B C

Explanation

WiMAX is defined by 802.16, that is intended for wireless “metropolitan area networks”. WiMAX can provide broadband wireless access (BWA) up to 30 miles (50 km) for fixed stations, and 3 – 10 miles (5 – 15 km) for mobile stations. In contrast, the WiFi/802.11 wireless local area network standard is limited in most cases to only 100 – 300 feet (30 – 100m).

Fixed WiMAX networks typically have a higher-gain directional antenna installed near the client (customer) which results in greatly increased range and throughput. Using 802.11 with high-gain antenna can bridge last-mile gaps, but they require more power.

WiMAX operates on both licensed and non-licensed frequencies, providing a regulated environment and viable economic model for wireless carriers. In particular, WiMax operates on the 10- to 66-GHz frequency band, so it doesn’t interfere with 802.11 LANs.