Wifi 7 Standards and Information: The Need for SpeedOctober 5, 2023
Wifi 7 is the next evolution of the 802.11 standard, specifically 802.11be. The current approved standard is 802.11ax, or Wifi 6. Changes to the modulation format and frequency allocation improve the theoretical maximum bit rate from 9.6 GBps for WiFi-6 to 46.4 GBps for Wifi 7. Practical upload and download rates will likely never attain these speeds, even if the wired back-haul existed to support it. For most purposes, Wifi 6 will meet most user needs. Only seriously taxing applications, such as virtual reality video streaming, could take advantage of speeds in excess of 9.6G. But it’s hard to say how the computing bandwidth needs of the average consumer will change over the next ten years, and carriers are constantly increasing wired bandwidths without additional cost to the user. Perhaps the need will grow into the technology. Fortunately, Wifi 7 is designed to be backwards-compatible with Wifi 6, so other than higher equipment cost there would be no harm in early adoption.
Three frequency bands are available in the US with 20 MHz minimum width channels:
- 2.4 GHz (2.4 to 2.495 GHz), 11 channels
- 5 GHz (5.170 to 5.835 GHz), 45 channels
- 6 GHz (5.925 to 7.125 GHz), 60 channels
How is Wifi 7 Different from Wifi 6?
First, the modulation changes from 1024-bit QAM (1K QAM) to 4096 QAM (4K QAM). The 1024-bit constellation is made up of 32 rows and 32 columns of amplitude and phase points such that any one point in the constellation represents 10 bits of information. That is approximately 11.25º between adjacent points along the phase axis and 3.1% changes in amplitude along the amplitude axis, or 0.27 dB.
The 4096-bit constellation is made up of 64 rows and 64 columns such that adjacent points are separated by 5.6º and amplitude by 1.5%, or 0.14 dB. Each point represents 12 bits, a 20% increase over 1024-bit QAM. Of course, error correction reduces the effective number of bits somewhat in both cases.
Unfortunately, going from 1K to 4K QAM results in a 6 dB loss of signal to noise ratio. This cuts the coverage distance in half for an isotropic radiator. Total radiated power is limited, but clever beam-steering may make up for this loss.
Secondly, the widest channel bandwidth has been increased from 160 MHz to 320 MHz in the 6 GHz band. Three of these are available. Unfortunately, the 6 GHz band has about 75% less range than the 5 GHz band due to air and material absorption. Fortunately, Multi-Link Operation (MLO) allows aggregating Resource Units (RUs) over all three bands simultaneously.
Under the proper circumstances, Wifi 7 can offer very high-speed data throughput. The equipment design must support the dense modulation format, and testing the RF chain with a VNA is an essential part of hardware development.
What Year Will Wifi 7 Be Released?
This standard is scheduled to be released in May 2024, but will likely roll out in early 2025.
When Should We Expect Wifi 7 Routers?
They are available now. TP-Link offers a few models. Firmware is upgradable, so these early models can be brought up to date when the 802.11be standard is finally released.
How is a Vector Network Analyzer Used to Create Wifi 7 Equipment?
A Vector Network Analyzer (VNA) is used to analyze the RF systems in a Wifi modem. The final RF amplifier—whether it is integrated within a modem chip or external to it—must be extremely linear to support the demanding 4K QAM modulation. Both the phase and amplitude of the signal must be faithfully reproduced. VNA power sweeps may be used to verify both. An absolute amplifier in the VNA can be accessed during the power sweep to view the amplitude response. The phase response can also be measured. AM-AM and AM-PM distortion can be determined using these two measurements.
Figure 1 shows a power sweep of an amplifier at 4 GHz from -30 to 0 dBm. The amplifier has about 7 dB of gain, where the slight curvature on the right-hand side indicates that the amplifier is beginning to compress. Figure 2 shows the S21 measurement of the same amplifier, where the roll-off on the right-hand side more clearly shows the compression.
Figure 1 – Power Sweep at 4 GHz
Figure 2 – S21 Measurement Showing Compression
Figure 3 – Phase vs Input Power
Figure 3 shows how the amplifier phase shift changes at 4 GHz as the input/output power varies. Again, there is significant phase shift on the right-hand side as the amplifier begins to compress.
Any amplifier used for 4K QAM should be operated in significant back-off—much lower output than the 1dB compression point—to achieve adequate linearity and meet the -38 dB Error Vector Magnitude (EVM) requirement.
Wifi routers require multi-antenna diversity with beam-steering capability. The phasing of the signals which drive each of the antennas can be measured with a VNA. The Multiport SN5090 VNA from Copper Mountain Technologies is capable of measuring from six to sixteen ports simultaneously. Determining the relative phase between all antennas simultaneously would be a simple matter with this instrument.
Copper Mountain Technologies produces VNAs with a wide range of capabilities, with output frequencies from 10 kHz to 330 GHz. Configurations from one to sixteen ports are available. All VNAs provide world-class performance with excellent metrology and traceability to NIST. Copper Mountain Technologies’ expert engineers are prepared to support any questions about VNA testing.