wifi modulations – what’s all this stuff?

Ok so this blog is all about how Wi-Fi sends data using different kinds of signal tricks. We’re talkin’ BPSK, QPSK, QAM, FHSS, DSSS – all that techy magic behind your wireless internet.

Don’t worry, it’s not full of boring formulas. Just short, messy, clear stuff to help you get what’s really goin’ on when bits turn into waves.

Whether you're fixing networks, just curious, or totally lost – this little guide’s for you.

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what is bpsk

BPSK means "Binary Phase Shift Keying". It turns digital bits into a wave for sending data.

It is simple. One bit goes into one wave shape. That’s it.

how bpsk works

• Each symbol carries just 1 bit – either 0 or 1.
• The bit changes the wave’s direction (called phase).
• If bit is 0, the wave goes one way.
• If bit is 1, the wave flips 180° (half turn).
• This flip is easy to spot, even with noise.
• Only one part of the wave (called I) is used. The other part (Q) is usually zero.
• Special coding (called Gray code) helps avoid errors – only one bit difference between nearby signals.
• Signal is adjusted with something called KMOD. For BPSK, KMOD = 1. That keeps power steady.

where bpsk is used

• OFDM: BPSK is used on small channels (called subcarriers). Works well for control info.
• DSSS: Older Wi-Fi uses DBPSK (a version of BPSK) for 1 Mb/s speed. It flips signal based on last one.
• HE Wi-Fi: In new fast Wi-Fi, BPSK can be used in some small parts of the signal (called RUs).
• DCM: Sometimes BPSK is doubled to use both low and high parts of the signal with mirror values. This is called Dual Carrier Modulation.

what to remember

BPSK is super simple. One bit per symbol. Very strong signal, good against noise. Used a lot in control parts and base systems.

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QBPSK

what is qpsk

QPSK means "Quadrature Phase Shift Keying". It changes digital bits into a wave, so the signal can be sent over the air.

It is like BPSK, but better. BPSK sends 1 bit at a time. QPSK sends 2 bits at the same time.

how qpsk works

• QPSK takes 2 bits, not just 1.
• The 2 bits decide how the wave turns (the phase).
• There are 4 ways the wave can turn: about 45°, 135°, -135°, -45°.
• This is done by using 2 parts of the wave: I and Q (like 2 directions).
• Bit "0" or "1" changes how strong the I and Q parts are.
• Special code (called Gray code) helps make less mistakes when signal is weak.
• The power of the signal is adjusted by a factor called KMOD. For QPSK, it is 1 divided by square root of 2.

where qpsk is used

• OFDM: Sends data on small channels. QPSK is used here a lot.
• DSSS: For slower data (2 Mb/s), a special version called DQPSK is used. It changes signal based on last signal's direction.
• HT and VHT: Used for faster Wi-Fi like 802.11n or 802.11ac.
• HE (High Efficiency): In new Wi-Fi, a special version called QBPSK is used in some fields. It helps tell different types of Wi-Fi messages apart.
• In transmitters: I and Q channels are full of power. This makes the signal stronger and clearer.

what to remember

QPSK sends 2 bits per symbol. It is better than BPSK, which sends only 1. That means more data in the same time. It is used in many kinds of Wi-Fi and wireless tech.

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QAM 

what is qam

QAM means "Quadrature Amplitude Modulation". It sends digital bits by changing both wave strength (amplitude) and direction (phase). 

It is like a mix of BPSK and QPSK – but it can send more bits at once. That means faster data.

how qam works

• Each wave can show a mix of strength and angle.
• This mix points to a “spot” in a graph – called a constellation point.
• Each spot means a different group of bits.
• More spots = more bits per wave. Here are examples:   
  • 16-QAM: 4 bits per symbol
  • 64-QAM: 6 bits per symbol
  • 256-QAM: 8 bits per symbol
  • 1024-QAM: 10 bits per symbol
• Big QAM levels send more data but are more sensitive to noise.
• Signal strength is adjusted with something called a normalization factor. Example: 1024-QAM uses 1 divided by square root of 682. 

 

where qam is used

• OFDM: Subcarriers use 16-QAM or 64-QAM to send data.
• HT and VHT Wi-Fi: Use QAM in MCS settings to set how fast and how protected the data is.
• HE Wi-Fi (very new): QAM used for data parts and special signal parts (like HE-SIG-B).
• DCM: Sometimes QAM is used with DCM (Dual Carrier Mod). It spreads data better but only works in some cases. Not used with MU-MIMO or STBC.
• Higher QAM = more speed, but only if the signal is clean and strong

 

what to remember

QAM uses both power and phase of the wave to send data. It can send lots of bits in one go. It is used in fast Wi-Fi and modern wireless stuff. The cleaner the signal, the more QAM power you can use.

 

what is 16-qam

16-QAM means "16-level Quadrature Amplitude Modulation". It sends digital bits by changing wave direction (phase) and wave strength (amplitude).

It can send more bits per symbol than BPSK or QPSK. That means more speed.

how 16-qam works

• Each symbol sends 4 bits. That’s why it’s called “16-QAM” – 2⁴ = 16 different wave shapes.
• The bits are split into two parts:
  • First 2 bits (b0, b1) set the I value (horizontal direction).
  • Next 2 bits (b2, b3) set the Q value (vertical direction).
• These bits are mapped like this:
  • I (b0b1): 00 = -3, 01 = -1, 11 = 1, 10 = 3
  • Q (b2b3): 00 = -3, 01 = -1, 11 = 1, 10 = 3
• This makes 16 unique spots on the wave map – called constellation points.
• Gray coding is used so nearby points differ by only 1 bit – less errors.
• The output wave (I + jQ) is scaled by a factor called KMOD. For 16-QAM, it is 1 divided by square root of 10.

where 16-qam is used

• OFDM Wi-Fi: Sends data at 24 or 36 Mbps. Subcarriers use 16-QAM for that.
• MCS (modulation + coding): 16-QAM is part of the list: BPSK → QPSK → 16-QAM → 64-QAM → ...
• HE Wi-Fi (802.11ax): Still uses 16-QAM in new systems. Can also be used with DCM (Dual Carrier Mod). That splits the bits over two parts of the signal.
• DCM with 16-QAM: Sends same 4 bits in two ways – bottom and top part of signal, but with different order.
• Accuracy checks: A number called EVM (Error Vector Magnitude) is used to see how close the signal is to perfect.
• Receiver sensitivity: Needs at least -74 dBm to decode well. Not as strong against noise as BPSK or QPSK.

what to remember

16-QAM sends 4 bits in each symbol. That means faster Wi-Fi. But it's more sensitive to bad signal quality. It needs clean conditions to work well.

what is 64-qam

64-QAM means "64-level Quadrature Amplitude Modulation". It sends digital bits using both wave strength (amplitude) and direction (phase).

It can send more bits than BPSK, QPSK or 16-QAM. That makes it faster, but also more sensitive to noise.

how 64-qam works

• Each symbol sends 6 bits. That’s why it’s called 64-QAM – 2⁶ = 64 wave forms.
• The 6 bits are split like this:
  • First 3 bits: set I value (horizontal part)
  • Next 3 bits: set Q value (vertical part)
• The I and Q values are picked from this list: -7, -5, -3, -1, 1, 3, 5, 7
• This makes 64 unique signal spots – called constellation points
• Gray coding is used – nearby points only differ by one bit. That helps avoid big errors.
• The output is scaled using KMOD. For 64-QAM, it is 1 divided by square root of 42.

where 64-qam is used

• OFDM Wi-Fi: 64-QAM gives high speeds like 48 Mbps (code rate 2/3) or 54 Mbps (code rate 3/4)
• MCS (Modulation and Coding Scheme): 64-QAM is part of the scale: BPSK → QPSK → 16-QAM → 64-QAM
• HE Wi-Fi (802.11ax): Used in data parts and in HE-SIG-B sections
• DCM support: Can be combined with Dual Carrier Modulation (DCM), but only in certain setups – not with MU-MIMO or STBC

signal performance

• Sensitivity: Needs clean signal to work. For 64-QAM:
  • -66 dBm (with code rate 2/3)
  • -65 dBm (with code rate 3/4)
• Adjacent Channel Rejection: 0 dB or -1 dB depending on code rate – worse than simpler modulations
• Signal accuracy: Checked using EVM (Error Vector Magnitude). Lower EVM = better signal quality

what to remember

64-QAM sends 6 bits per symbol. That means high data rate – good for fast Wi-Fi. But it needs a strong and clean signal to work well. Not great in noisy environments.

 

what is 256-qam

256-QAM means "256-level Quadrature Amplitude Modulation". It sends digital bits by changing the wave’s direction (phase) and strength (amplitude).

It sends more data than BPSK, QPSK, 16-QAM, or 64-QAM. But it also needs a very clean signal.

how 256-qam works

• Each wave (symbol) sends 8 bits. That’s a lot – 2⁸ = 256 different wave types.
• Bits are split into groups of 8.
• Each group is turned into a point on the signal map – called a constellation point.
• Gray coding is used – nearby points only change 1 bit. That helps reduce errors from noise.
• Each point is a mix of I and Q values – the real and imaginary parts of the wave.
• The exact way bits are turned into signal is in the standard, but not shown here as a full table.
• KMOD (normalization factor) isn’t always listed clearly for 256-QAM, but it keeps signal power balanced.

where 256-qam is used

• MCS (Modulation and Coding Scheme): 256-QAM is one of the top levels in Wi-Fi speed ladder.
• HE Wi-Fi (802.11ax): Used in high-speed Wi-Fi. Shows up in many frame types (like SU, ER SU, TB).
• DCM: Not used with 256-QAM. Only lower types like BPSK, QPSK, 16-QAM support that.
• Data rates: Depends on subcarrier group size, stream count, and timing. Can go from 10.6 Mbps (small setup) to 3458.8 Mbps (big setup with 8 streams).

signal performance

• EVM (Error Vector Magnitude): Must be very low. -30 dB for code rate 3/4, -32 dB for 5/6. Lower EVM = better signal.
• Sensitivity: Needs stronger signal. For 20 MHz channel:
  • -59 dBm (3/4 rate)
  • -50 dBm (on wide 160 MHz)
• Adjacent Channel Rejection: Needs good filtering. Values like -7 dB or -9 dB mean it doesn't like nearby interference.

what to remember

256-QAM sends 8 bits per symbol – super fast. But it’s picky: needs low noise, strong signal, and perfect tuning. Used in modern Wi-Fi for top speeds, but not always available if the signal isn’t good enough.

what is 1024-qam

1024-QAM means "1024-level Quadrature Amplitude Modulation". It sends digital data by changing both how strong and how angled the wave is.

It sends more data than all others – 10 bits at once. But it only works well if the signal is clean and strong.

how 1024-qam works

• Each symbol = 10 bits. That gives 1024 different signal types.
• Bits are grouped into 10s and turned into signal spots called constellation points.
• These points live on an I/Q map – showing real and imaginary parts of the wave.
• Gray coding helps keep errors low – nearby points differ by just 1 bit.
• Signal values are scaled using KMOD. For 1024-QAM, it's 1 divided by square root of 682.

where 1024-qam is used

• Wi-Fi 6 (802.11ax): 1024-QAM is used to get super high speeds.
• MCS levels: It’s used in HE-MCS 10 and 11 (both optional).
• Small RUs: Used on 26, 52, or 106-tone RUs – only if the receiver says it can handle it.
• Not for DCM: 1024-QAM cannot be used with Dual Carrier Modulation.

how fast is it

• For a small 26-tone RU with 1 stream:
  • HE-MCS 10 = 13.2 Mbps
  • HE-MCS 11 = 14.7 Mbps
• For large 2x996-tone RU with 8 streams:
  • HE-MCS 10 = 8647.1 Mbps
  • HE-MCS 11 = 9607.8 Mbps

signal requirements

• EVM: Must be very accurate.
  • -35 dB with compensation on
  • -32 dB allowed if compensation is off
• Sensitivity: Needs a strong signal
  • -54 dBm (3/4 rate)
  • -52 dBm (5/6 rate)
• Adjacent Channel Rejection: Doesn’t like nearby interference
  • -12 dB (3/4 rate)
  • -15 dB for wide channels (like 80+80 MHz)

what to remember

1024-QAM sends 10 bits in each wave. That’s super fast. But it only works when the signal is really clean and the noise is low. It’s used in Wi-Fi 6 to get top speeds, but only when the connection is really good.

what is 4096-qam

4096-QAM means "4096-level Quadrature Amplitude Modulation". It would send digital bits using wave strength and direction, like other QAM types – but even more tightly packed.

This type is not in current Wi-Fi standards yet, but we can guess how it might work.

how 4096-qam would work

• Each symbol would send 12 bits. That’s because 2¹² = 4096.
• There would be 4096 constellation points – that’s a very dense signal map.
• The wave’s I and Q values would need to be very precise to avoid mistakes.
• Gray coding would still help – nearby points would only differ by 1 bit.
• The more points you have, the harder they are to tell apart – especially if there’s noise.

what it would need

• Signal strength: Needs better signal than 1024-QAM. For example:
  • 1024-QAM already needs about -54 dBm
  • 4096-QAM would need even better – likely above -50 dBm
• SNR (Signal-to-noise ratio): Would need very clean signal. Tiny errors would ruin the message.
• EVM (Error Vector Magnitude): The allowed error would need to be even lower than -35 dB. That means the signal must be very stable and accurate.

where it might be used

• In special setups – like short-distance links in data centers
• In places with no interference, like labs or shielded rooms
• When you need very fast speed and can control the environment

what to remember

4096-QAM is not here yet, but it could come in future Wi-Fi. It would send 12 bits per symbol – super efficient. But it would only work with perfect signal quality. Not good for noisy or long-distance wireless.

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FHSS

what is fhss

FHSS means "Frequency-Hopping Spread Spectrum". It is one of the first Wi-Fi systems. It works by jumping from one frequency to another while sending data.

It was used in older Wi-Fi for the 2.4 GHz band.

how fhss works

• The radio signal does not stay on one channel.
• It hops (jumps) between channels in a set pattern.
• All devices in the network must follow the same hop pattern at the same time.
• This pattern and timing info comes from beacons and probe responses.
• Each station updates its timing and hop info using special commands.
• Every station has a "dwell time" – the time it can stay on one channel.
• If there’s not enough time to finish sending data, it must wait and try again later.

what is inside fhss

• FHSS has two main layers:
  • PLCP (Convergence layer): Prepares the frame for sending
  • PMD (Medium layer): Actually sends and receives the signals
• There is also a management layer that handles timing, antennas, and setup.

modulation used in fhss

• FHSS uses frequency modulation, not QAM like newer Wi-Fi.
• 2 Mb/s rate: Uses 4GFSK (4-level Gaussian Frequency Shift Keying)
• Other rates: Could use 2GFSK or higher, based on PLCP header
• QAM types like 1024-QAM or 256-QAM are not used in FHSS.

performance and settings

• FHSS has lower speeds compared to newer systems.
• Minimum receiver sensitivity and error rates are defined.
• FHSS supports different countries and rules via MIB attributes like:
  • dot11CurrentSet
  • dot11CurrentPattern
  • dot11CurrentIndex
• Also supports antenna settings, rate control, and more.

is fhss still used?

No, not much. FHSS is an old system. Newer Wi-Fi uses faster and more efficient systems like OFDM, HT, VHT, and HE.

The IEEE standard even says FHSS may be removed in the future. It's mostly replaced by modern Wi-Fi that can handle more speed and more interference.

what to remember

FHSS was one of the first Wi-Fi systems. It sends data by jumping across channels. It’s simple but slow. Today, it is replaced by faster tech. But it helped start wireless networking as we know it.

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