What is Wi-Fi Modulation?

Modulation is the process of varying one or more properties of a high-frequency carrier signal in accordance with a lower-frequency baseband (message) signal, so that the information can be efficiently transmitted over a physical channel such as air, cable, or optical fiber. Modulation is the mapping from information to a transmittable waveform.

I/Q Modulation

Modern wireless systems such as Wi-Fi, 4G, and 5G often use I/Q modulation.

$$s(t)=I(t)\cos (2\pi f_{c}t)-Q(t)\sin (2\pi f_{c}t)$$Where:

• $I(t)$ : in-phase component
• Q(t) : quadrature component

This can also be written as:

$$s(t)=\mathrm{\Re }\left\{\right[I(t)+jQ(t)\left]e^{j2\pi f_{c}t}\right\}$$The complex baseband signal is:

$$x(t)=I(t)+jQ(t)$$Each point on the constellation diagram corresponds to one value of $I(t)+jQ(t)$.

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QAM Example

For M-QAM, each symbol carries:

$${\log }_{2}M$$bits.

Examples:

Modulation	Bits per symbol
QPSK / 4-QAM	2
16-QAM	4
64-QAM	6
256-QAM	8
1024-QAM	10
4096-QAM	12

For example, in 16-QAM, each symbol represents:

$${\log }_{2}16=4$$bits.

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Symbol Rate and Bit Rate

If the symbol rate is:

$$R_s$$​Then the bit rate is:

$$R_b=R_s{\log }_{2}M$$Where:

• $R_b$: bit rate
• $R_s$ : symbol rate
• $M$: modulation order

So higher-order modulation increases data rate, but usually requires higher SNR.

The modulation schemes in Wi-Fi 4/5/6/7

Standard	Modulation Schemes	Highest Order
Wi-Fi 4 (802.11n)	BPSK, QPSK, 16-QAM, 64-QAM	64-QAM
Wi-Fi 5 (802.11ac)	BPSK, QPSK, 16-QAM, 64-QAM, 256-QAM	256-QAM
Wi-Fi 6 (802.11ax)	BPSK, QPSK, 16-QAM, 64-QAM, 256-QAM, 1024-QAM	1024-QAM
Wi-Fi 7 (802.11be)	BPSK, QPSK, 16-QAM, 64-QAM, 256-QAM, 1024-QAM, 4096-QAM	4096-QAM

The constellation diagram in Wi-Fi 4/5/6/7