WiFi 7 Physical Layer Block diagram covering transmitter Modules for Access Points (APs) and Stations

The physical layer (PHY) of WiFi 7 introduces several key advancements over its predecessor, WiFi 6 (802.11ax). Let us break down the Wi-Fi 7 PHY and its modules for the Access Point (AP) and Station (STA) transmitter parts using block diagram. WiFi 7 specifications for PHY layer have been defined by the IEEE 802.11be standard.

Wi-Fi 7 physical layer is designed to handle the growing demands of modern wireless networks, supporting applications that require high data rates and low latency, such as AR/VR, 4K/8K streaming and real-time gaming.

802.11be WiFi-7 PHY parameters

Following table mentions PHY parameters specified in WiFi-7 802.11be IEEE standard.

As mentioned in the table, WiFi 7 PHY aims to achieve extremely high throughput (EHT) by enhancing the existing capabilities and introducing new features. Key enhancements in Wi-Fi 7 PHY compared to its predecessors (11n, 11ac, 11ax) include following.
• Channel bandwidths up to 320 MHz (compared to 160 MHz in Wi-Fi 6), which allows significant higher data rates.
• WiFi-7 uses 4096-QAM (Quadrature Amplitude Modulation), up from 1024-QAM in Wi-Fi 6 which increases the data carried per symbol.
• Wi-Fi 7 supports Multi-Link Operation (MLO) which can utilize multiple frequency bands (2.4 GHz, 5 GHz, and 6 GHz) simultaneously, optimizing data transmission and improving reliability.
• Wi-Fi 7 supports enhanced Resource Unit (RU) Allocation which allows more flexible and efficient use of spectrum through improved RU allocation.
• it supports Preamble Puncturing. This feature allows the exclusion of certain portions of the spectrum affected by interference, thus improving throughput in challenging environments.

WiFi 7 802.11be Physical layer Transmitter for AP and STA

The transmitter part of the WiFi 7 PHY for both Access Point and Station includes common modules as follows.
1. Scrambler : It randomizes the data to prevent long sequences of zeros or ones, ensuring a balanced signal for the subsequent modulation steps.
2. Forward Error Correction (FEC) Encoder : It is used to enhance data integrity. Wi-Fi 7 uses LDPC (Low-Density Parity-Check) codes for robust error correction, improving the reliability of data transmission.
3. Interleaver : This module rearranges the coded bits to ensure that errors caused by noise and fading are spread out, making them easier to correct during reception.
4. Modulator : Wi-Fi 7 supports higher-order modulation schemes up to 4096-QAM. This modulator maps the interleaved bits onto complex symbols corresponding to the chosen modulation scheme.
5. Resource Unit (RU) Mapper : It assigns data symbols to specific subcarriers within the allocated RUs. Wi-Fi 7 provides enhanced flexibility in RU allocation, allowing more efficient spectrum use.
6. Inverse Fast Fourier Transform (IFFT) : The IFFT converts the frequency domain symbols into time domain signals, which are used to form the OFDM (Orthogonal Frequency Division Multiplexing) waveform.
7. Cyclic Prefix (CP) Insertion : The CP is added to each OFDM symbol to protect against inter-symbol interference (ISI) caused by multipath propagation, ensuring signal integrity over various environments.
8. Windowing and Filtering : This step smooths the signal transitions, reducing out-of-band emissions and helping meet regulatory spectral masks.
9. Digital-to-Analog Converter (DAC) : The DAC converts the digital time-domain OFDM signal into an analog waveform suitable for transmission over the air.
10. RF Front-End : The analog signal is amplified, filtered, and up-converted to the appropriate RF channel for transmission. The RF front-end includes power amplifiers, mixers, and filters specific to the 2.4 GHz, 5 GHz or 6 GHz bands.

802.11be WiFi 7 Physical layer Receiver

Following are the common modules in 802.11be physical layer receiver.
1. Signal Reception and RF Front-End :
• Antenna and RF Front-End: The signal is received through the antenna and passed through the RF front-end, which performs amplification, downconversion from RF to baseband, and filtering to isolate the desired signal.
2. Analog-to-Digital Conversion (ADC) :
• The analog signal is converted into a digital signal using an ADC, preparing it for further digital signal processing.
3. Time Synchronization and Frequency Offset Correction :
• Time Synchronization: Ensures that the receiver is aligned with the start of each OFDM symbol, which is critical for accurate demodulation.
• Frequency Offset Correction: Compensates for any frequency shifts due to Doppler effects or oscillator mismatches between the transmitter and receiver. This step uses pilot signals embedded in the data stream for precise corrections.
4. FFT Processing :
• FFT (Fast Fourier Transform): Converts the received time-domain OFDM symbols into the frequency domain, allowing the receiver to separate the subcarriers and recover the transmitted data.
5. Channel Estimation and Equalization :
• Channel Estimation: Utilizes known pilot symbols embedded within the OFDM symbols to estimate the channel response. This step determines how the channel has altered the transmitted signal, including effects like multipath fading and phase shifts.
• Channel Equalization: Corrects the signal by reversing the effects of the channel using the estimated channel response.
6. EHT (Extremely High Throughput) Data Demodulation :
• Demodulation: Maps the received constellation points back to data bits. For 4096-QAM, this involves identifying each point within a dense 4096-point constellation, demanding high accuracy due to the small distance between points.
7. De-Interleaving and FEC Decoding :
• De-Interleaving: Reorders the received bits into their original sequence to reverse the interleaving process done at the transmitter. This helps correct burst errors that affect multiple consecutive bits.
• FEC Decoding (LDPC/BCH): Applies Forward Error Correction using LDPC or BCH decoding algorithms to correct errors introduced during transmission.
8. Descrambling
• The descrambler reverses the scrambling applied at the transmitter to recover the original data stream.
9. MAC Layer Processing • After the physical layer processing is complete, the demodulated and decoded data is passed to the MAC layer for further processing, such as frame assembly, error checking, and acknowledgment handling.

Key Differences in AP and STA Transmitter Design

While the fundamental PHY modules are similar for both AP and STA, there may be differences in implementation based on device capabilities.
➨Power Levels: APs typically have higher transmission power compared to STAs, impacting the design of power amplifiers and RF front-end.
➨Antenna Configuration: APs might support more antennas for MIMO (Multiple Input Multiple Output) operations, enhancing spatial streams and beamforming capabilities.
➨Resource Management: APs often have more sophisticated resource management and scheduling functions to optimize communication with multiple STAs.

Summary

WiFi 7, defined under IEEE 802.11be, introduces a significantly enhanced physical layer that boosts performance, capacity and efficiency for both Access Points (APs) and Stations. As mentioned above, WiFi 7 supports key features such as wider channel bandwidths (up to 320 MHz), advanced modulation schemes (4096 QAM), 16 spatial streams for improved multi-user capabilities, OFDMA and MU-MIMO enhancements.

WiFi 6 Resources as per IEEE 802.11ax

WiFi 7 Resources as per IEEE 802.11be

Useful Links to Legacy WLAN Standards

Other Standard wireless physical layers

RF and Wireless Terminologies