CWNP CWNA-109 Exam - Topic 6 Question 31 Discussion

Actual exam question for CWNP's CWNA-109 exam

Question #: 31
Topic #: 6

What statement is true concerning the use of Orthogonal Frequency Division Multiplexing (OFDM) modulation method in IEEE 802.11 WLANs?

AOFDM implements BPSK modulation to allow for data rates up to 7 Gbps.

BOFDM was first introduced in 802.11a and is used by the ERP, HT and VHT PHYs as well.

COFDM modulation is used only in 5 GHz 802.11 transmissions.

DOFDM was used by Frequency Hopping Spread Spectrum (FHSS) PHY devices.

Show Suggested Answer

Suggested Answer: B

OFDM is a modulation method that divides the channel bandwidth into multiple subcarriers, each carrying a single data symbol. This allows for higher data rates and more robust transmissions in multipath environments. OFDM was first introduced in the 802.11a standard, which operates in the 5 GHz band and supports data rates up to 54 Mbps. Later, the 802.11g standard adopted OFDM for the 2.4 GHz band, and the 802.11n and 802.11ac standards enhanced OFDM with features such as MIMO (Multiple Input Multiple Output), channel bonding, and higher-order modulation schemes to achieve data rates up to 600 Mbps and 6.9 Gbps, respectively. These standards are collectively known as the ERP (Extended Rate PHY), HT (High Throughput), and VHT (Very High Throughput) PHYs .Reference:[CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 163; [CWNA-109 Study Guide], Chapter 4: Radio Frequency Signal and Antenna Concepts, page 157.

by Stephen at Jul 30, 2025, 02:25 PM

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Stevie

2 months ago

Wait, OFDM only in 5 GHz? That doesn’t sound right.

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Renea

2 months ago

Totally agree, it’s used in ERP, HT, and VHT PHYs too.

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Tanja

3 months ago

OFDM and FHSS? Nope, that’s not how it works!

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Naomi

3 months ago

BPSK for 7 Gbps? That seems a bit off to me.

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Wilbert

3 months ago

OFDM was indeed first introduced in 802.11a!

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Thaddeus

3 months ago

I don't recall OFDM being linked to FHSS at all; that seems off to me, but I could be mistaken.

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Raelene

4 months ago

I practiced a question similar to this, and I believe option B is correct since OFDM is used in multiple PHYs like HT and VHT.

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Brunilda

4 months ago

I think OFDM is primarily associated with the 5 GHz band, but I might be mixing it up with other modulation techniques.

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Billy

4 months ago

I remember studying that OFDM was indeed introduced with 802.11a, but I'm not sure if it applies to all the other PHYs mentioned.

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Lettie

4 months ago

Ah, I remember learning about OFDM in my networking class. I think I've got a good handle on how it's used in 802.11 WLANs, so I should be able to identify the correct statement.

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Dulce

4 months ago

Okay, I know OFDM is a key modulation technique for 802.11, but I'm a bit fuzzy on the details. I'll try to eliminate the options that I'm sure are wrong, and then make an educated guess.

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Avery

5 months ago

Hmm, this is a tricky one. OFDM is used in 802.11, but I'm not sure about the specifics of which PHYs it's used in. I'll have to think this through carefully.

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Lashawn

5 months ago

I'm pretty familiar with OFDM, so I think I can handle this one. Let me carefully read through the options and think about what I know about OFDM in 802.11 WLANs.

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