What is OFDMA (orthogonal frequency-division multiple access)? | Definition from TechTarget

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What is OFDMA (orthogonal frequency-division multiple entry)?

Orthogonal frequency-division multiple entry (OFDMA) is a expertise of Wi-Fi 6 (802.11ax) that lets entry factors serve multiple purchasers on the similar time. OFDMA follows a algorithm created for the transmission of knowledge between multiple terminals or purchasers over a transmission medium. The terminal could possibly be any machine on the finish of a transmission channel, similar to a pc or cellphone, and the medium could possibly be a wi-fi community.
Orthogonal frequency-division multiplexing is a sign modulation method that makes use of multiple subcarriers throughout the similar communications channel. These subcarriers are intently spaced, transmit in parallel and carry low-bit fee information. The usage of multiple subcarriers makes the method resilient to selective fading and interference in addition to supplies pretty excessive spectral effectivity.
OFDM is itself primarily based on frequency-division multiplexing and was generally used prior to now for mobile networking, broadcast media and older Wi-Fi requirements like IEEE 802.11ac (Wi-Fi 5). OFDMA is a variant of the OFDM scheme. Particularly, it is a multi-user variant of OFDM, which means it permits for multiple entry and simultaneous information entry for various customers. This type of communication is an improve to each FDM and OFDM.

The variations between OFDM, FDM and a single wideband channel frequency wi-fi information transmission scheme. OFDMA is a variant of the OFDM scheme.

How OFDMA works

Conventional multiplexing applied sciences used analog modulation. In distinction, OFDMA makes use of provider sign waves, known as subcarriers, to maneuver small bits of data in a extra streamlined trend. These subcarriers could also be information subcarriers, reference-signal subcarriers or null subcarriers. Solely the information subcarriers are used for information transmission. The channel is cut up into smaller frequencies often called useful resource models (RUs), so wi-fi carriers can effectively occupy and use the frequency bands they’re licensed to make use of.
By assigning subsets of time-frequency RUs to multiple customers (e.g., entry factors), OFDMA permits customers to speak with multiple purchasers and concurrently transmit information. The RUs are assigned relying on the bandwidth wanted by the person in addition to different elements, similar to high quality of service necessities, packet measurement and machine constraints. Customers may have various utilization patterns or information masses however they’re all accommodated in OFDMA due to using multiple closely-spaced subcarriers and versatile RU allocation.
An instance of how OFDMA works is when two telephones ship information over the identical cellphone line. A time-interval could also be assigned to every cellphone in order that they’ll take turns sending their sign over the road at their assigned intervals. Nonetheless, these time frames are imperceptibly small, making it appear that the information transfers by each telephones are occurring concurrently and seamlessly.


FDM is a communications expertise wherein multiple indicators are mixed after which transmitted over a single channel. The full out there bandwidth is divided into multiple non-overlapping frequency bands. Overlapping is prevented because of the presence of guard bands, which discuss with unused frequencies that separate the assigned bands. On the sending finish, the modulated indicators are mixed with a multiplexer. The person indicators are then extracted from the mixed sign on the receiving finish utilizing a demultiplexer.
OFDMA is an up to date model of FDM that parallels web carriers’ change to Wi-Fi 6 wi-fi in addition to the improve of cellphone carriers upgrading to 4G and 5G LTE. As an alternative of the normal analog modulation utilized in multiplexing, OFDMA makes use of provider sign waves as subcarriers to maneuver small bits of data in a extra streamlined trend.

OFDMA in Wi-Fi 6

OFDMA is one of many expertise enhancements launched in Wi-Fi 6. Wi-Fi 6 provides speeds of as much as 9.6 Gbps, a pointy enchancment over the three.5 Gbps out there in Wi-Fi 5. The upper velocity may be cut up throughout multiple gadgets, so every machine can profit from doubtlessly larger speeds.
With the introduction of OFDMA, Wi-Fi 6 will increase community capability to mitigate the entry points which are widespread when multiple Wi-Fi gadgets are lively on a single community. No matter what number of gadgets are added to the community or their information calls for, OFDMA ensures robust connections and uninterrupted entry over Wi-Fi 6, in addition to decrease latency for real-time functions like audio/video conferencing and on-line gaming. OFDMA can even enhance the utmost throughput of a Wi-Fi community and enhance the ability effectivity of Wi-Fi-enabled cellular gadgets.

Benefits and drawbacks of OFDMA

One of many largest benefits of OFDMA transmission is that it would not undergo from intracell interference. That mentioned, OFDMA is considerably vulnerable to intercell interference, which may result in degradation of sign high quality. Nonetheless, it is doable to mitigate intercell interference utilizing strategies similar to packet scheduling, frequency reuse and interference coordination.
Aside from low intracell interference, different benefits of ODFMA embody the next:

  • Increased variety frequency.
  • Extra effectively packed subcarriers within the frequency spectrum, making certain optimum spectral effectivity.
  • Extra flexibility, as channels and subchannels may be toggled on and off.
  • Provision for multiple impartial channels.
  • Higher protection over networks.

Owing to those benefits, OFDMA is often utilized in wi-fi LAN (Wi-Fi), long-term evolution (LTE or 4G) and WiMAX programs.
Potential disadvantages of OFDMA embody the next:

  • The variety of frequencies is conditional on how subcarriers are assigned to customers, which may turn into complicated.
  • It requires further energy as a result of it is at all times on and able to ship a transmission.
  • It has the next sensitivity than different channel varieties to frequency offset.

Study extra about Wi-Fi 6 and the way OFDMA works. See the distinction between OFDMA vs. MU-MIMO in Wi-Fi 6. Discover 5 advantages of Wi-Fi 6 for enterprise networks. Take a look at the variations between Wi-Fi 6 vs. Wi-Fi 6E and the Wi-Fi 6 glossary of 12 necessary phrases and phrases.

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