WorksheetsQUIZ NO. 6 MEXE 3101
Total questions: 20
Worksheet time: 3mins
Which 802.11 PHY technique spreads each bit of data into 11 chips using a Barker sequence?
FHSS
DSSS
OFDM
HR-DSSS
In FHSS, the maximum number of hops per second in the original 802.11 standard is:
10
50
75
100
Which of the following is a major reason why OFDM performs better than DSSS in multipath environments?
It increases the power spectral density
It uses many narrowband subcarriers with long symbol durations
It relies on chip-level error correction
It spreads each bit across the entire channel bandwidth
In DSSS, the processing gain is primarily determined by:
Signal amplitude and SNR
Chip rate relative to bit rate
The number of subcarriers used
The number of available frequency hops
The original 802.11 FHSS PHY uses hop sets that span which frequency band?
2.400–2.4835 GHz
2.400–2.500 GHz
5.150–5.350 GHz
900–915 MHz
What is the symbol duration of OFDM in 802.11a/g relative to the channel bandwidth?
It becomes shorter as bandwidth increases
It is inversely proportional to the number of chips
It is long because of narrow subcarrier spacing
It is equal to the beacon interval
The OFDM PHY uses how many data subcarriers in its standard 64-subcarrier structure?
26
48
52
64
In OFDM, the cyclic prefix (guard interval) is used to:
Increase throughput by shortening symbols
Protect against ISI and multipath delay spread
Encode preambles for synchronization
Perform spread spectrum coding
The 802.11 HR-DSSS (used in 802.11b) achieves higher data rates by using:
Barker sequence spreading at higher power
Complementary Code Keying (CCK)
Increased FHSS hop sets
More subcarriers per channel
Which channel bandwidth is used by OFDM in 802.11a and 802.11g?
5 MHz
10 MHz
20 MHz
40 MHz
Why do DSSS signals require more bandwidth than the original uncoded data?
They employ multiple antennas
They convert data bits into chip sequences
They use OFDM-like tone spacing
They must compensate for higher transmission power
In 802.11 FHSS, each hop corresponds to:
A change in amplitude
A change in carrier frequency
A change in data modulation scheme
A new SSID identification code
Which modulation is used for the highest data rates in the OFDM PHY?
BPSK
QPSK
16-QAM
64-QAM
Which preamble component is used by OFDM receivers for frequency offset correction and synchronization?
Short training symbols
Long training symbols
PLCP header
CCK preamble
In OFDM, the pilot subcarriers serve to:
Increase channel bandwidth
Maintain phase and frequency reference
Perform encryption key rotation
Support CSMA/CA timing
In DSSS, if the chip rate increases while data rate stays constant, the processing gain:
Decreases
Increases
Remains unchanged
Becomes negative
The PHY header (PLCP header) in 802.11b is transmitted at which rate?
The highest supported rate
The same rate as the payload
The lowest mandatory rate
A variable rate depending on noise
Which 802.11 physical layer supports the highest theoretical data rate among those in Chapter 14?
FHSS
DSSS
HR-DSSS
OFDM
In OFDM, increasing the number of subcarriers while keeping bandwidth constant has what effect?
Decreases subcarrier spacing
Increases symbol rate
Reduces multipath tolerance
Eliminates need for guard intervals
What is the primary reason the original 802.11 FHSS PHY cannot reach the same data rates as OFDM?
FHSS uses only 1 MHz bandwidth per hop
FHSS power levels must be lower
FHSS channels are more prone to fading
OFDM uses stronger encryption
