Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
33 Cards in this Set
- Front
- Back
|
What can be described by the way the signals overlap? |
Interferenece |
|
|
What occurs when two or more transmitters use the same channel? |
Co-channel Interference |
|
|
When both transmitters are busy sending data the channel becomes _____________. The two signals begin to ____________ with each other and cause data _____________, which causes devices to _______________ lost data, which uses more ____________. |
1. Congested 2. interfere 3. corruption 4. retransmit 5. airtime |
|
|
Due to the limited number of channels, what is a necessary evil? |
Co-channel interference |
|
|
A best practice is to place a transmitter on a channel only if its signal will be at least ______ above any other received signal |
19 dBm |
|
|
When two transmitters are placed on two different channels and the channels are spaced too closely together, the interference is called what? |
Neighboring Channel Interference |
|
|
The 802.11 standard defines these channels as NON overlapping channels. |
adjacent channels |
|
|
__________ channels cannot overlap but ___________ channels can. |
adjacent channels cannot overlap, but neighboring channels can. |
|
|
What are three non 802.11 devices that cause interference? |
1. Microwave Oven (2.42-2.48) 2. 2.4-GHz FHSS cordless phones 3. Wireless video cameras |
|
|
When you receive interference from a microwave oven, cordless phone, or wireless camera, it is called what? |
Non-802.11 Interference |
|
|
Whenever an RF signal is transmitted from an antenna, its amplitude decreases as it travels. Even if there are no obstacles in the path between the transmitter and receiver. This is called what? |
Freespace path loss |
|
|
What causes the wireless signal strength to weaken in Free Space Path Loss? |
expansion or spreading |
|
|
What is the equation for calculating Free Space Path Loss (FSPL)? |
FSPL (dB) = 20log10(d) + 20log10(f) + 32.44 d = distance from transmitter in kilometers f = frequency in megahertz |
|
|
FreeSpace Path Loss is a function of _____________ and _______________ only. |
FreeSpace Path Loss is a function of distance and frequency only. |
|
|
What are four important components of the link budget? |
Transmit Power Cable Loss Antenna Gain Free Space Path Loss |
|
|
In the FSPL equation, as the _____________ increases, so does the loss. |
In the FSPL equation, as the frequency increases, so does the loss. |
|
|
As a wireless device moves closer to a transmitter, what two things increase? |
1. RSSI 2. SNR |
|
|
As conditions are favorable for good signal quality and higher data rates, a complex modulation and coding scheme is used. When the conditions deteriorate, less-complex schemes can be selected. This is called what? |
Dynamic Rate Shifting (DRS) |
|
|
What are three other names that Dynamic Rate Shifting can be known by? |
1. Link adaptation 2. Adaptive modulation and coding (AMC) 3. Rate adaptation |
|
|
As a receiver moves further from the transmitter, list the modulation and coding from greatest to least in the 2.4-GHz band. |
1. OFDM 64-QAM 2. OFDM 16-QAM 3. OFDM QPSK 4. DSSS CCK 5. OFDM BPSK 6. DSSS CCK 7. DSSS DQPSK 8. DSSS DBPSK |
|
|
Indoor objects such as metal furniture, filing cabinets, and metal doors can cause what type of RF effect? |
Reflection |
|
|
Name three objects that can cause reflection. |
1.) Body of water 2.) Class on a building 3.) Surface of the earth |
|
|
When reflection takes a different path than the original, this causes the signal to arrive slightly later. This is known as what? |
Multipath |
|
|
What are the two outcomes for multipath? |
Single radio chain = one poor error-prone composite signal Multiple radio chains = further processing can improve the signal quality or extract multiple data streams |
|
|
When an RF signal passes into material that takes some of its energy, it is called what? |
Absorption |
|
|
Name eight objects and elements that would cause RF absorption |
1. Gypsum 2. Drywall 3. Solid concrete 4. Rain 5. Snow 6. Hail 7. Fog 8. Human body |
|
|
What type of interference can occur when a wireless signal passes through a dusty or sandy environment? |
Scattering |
|
|
What type of interference is best viewed as concentric waves, rather than an oscillating signal, so that its effect on the actual waves can be seen? (The signal tends to bend around the object and eventually rejoin to complete the wave) |
Diffraction |
|
|
What type of wireless interference is especially important to avoid in narrow line of sight wireless transmission? |
Diffraction |
|
|
What type of wireless signal is focused into a tight cone-shaped pattern? |
Line-of-Sight |
|
|
Over a very long distance with a Line-of-Sight wireless signal, what is an additional obstacle to take into concept? |
The curvature of the earth (after approx 2 mi) |
|
|
What is an elliptical-shaped volume around the line of sight that must also remain free of obstructions? |
Fresnel Zone |
|
|
As a rule, how high should you raise the antennas of a line-of-sight system? |
You should raise the antennas until the bottom of the Fresnel zone is higher than any obstruction |
