What is OFDMA?

What's the difference between OFDM and OFDMA?

OFDM (orthogonal frequency-division multiplexing) is an older, related technology for increasing wireless capacity and efficiency. OFDM has been used in areas such as cellular networking and broadcast media and in previous versions of Wi-Fi.

OFDMA is essentially a type of OFDM for multiple users. It allocates in both the time domain and the frequency domain, allowing for multiple users—even those with widely varying use patterns or data loads. By comparison, OFDM can allocate only sequentially.

What problems does OFDMA solve?

Previous Wi-Fi standards were intended for web browsing and email in low-density situations. Today's users aren't just greater in number; they're performing more data-intensive functions in more settings than ever before. Network congestion caused by simultaneous requests causes slowdowns, since clients must form a queue to complete transmissions. OFDMA solves the congestion problem by accommodating multiple users at the same time and allocating bandwidth more efficiently.

How does OFDMA work?

One way to understand OFDMA is to use delivery trucks as an analogy. Prior to Wi-Fi 6, each "truck" could carry only a single user's cargo. But with Wi-Fi 6 and OFDMA, the truck can be loaded with multiple users' cargo loads. Also, its drop-off schedule can be optimized for speed and efficiency.

OFDMA divides a Wi-Fi channel into smaller frequency allocations, called resource units (RUs). An access point can communicate with multiple clients by assigning them to specific RUs.

OFDM divides channels into 64 312.5-kHz subcarriers, all of which are used to transmit data to a single client. By spacing these carriers orthogonally, OFDMA allows Wi-Fi 6 and beyond to divide channels into smaller individually addressable units without interference.

The number of RUs assigned to each client is determined by factors such as device constraints, quality-of-service (QoS) requirements, and packet size. Wi-Fi 6 only allowed a single user to be assigned to one RU and often resulted in empty RUs being transmitted. Wi-Fi 7 added MRU, allowing one user to be assigned multiple RUs. The flexibility in scheduling along with the parallel nature of OFDMA increases the productive airtime efficiency and Wi-Fi 7 continues to build on OFDMA efficiencies.

Is OFDMA used in 5G / LTE technologies or other cellular networks?

Yes. OFDMA is used in the air interface stage of 5G / LTE, which allows for mobile connectivity. OFDM, the older technology, is one of the primary enabling technologies of 3G and 4G cellular service.

Where is OFDMA used?

OFDMA technology can be applied anywhere data is sent along radio waves, including the:

• Mobility mode of the IEEE 802.16 wireless standard known as WiMAX
• Wireless LAN (WLAN) standard IEEE 802.11ax (Wi-Fi 6 and beyond)
• IEEE 802.20 mobile wireless metropolitan-area network (WMAN) standard
• Downlink of the 3GPP Long-Term Evolution (LTE) fourth-generation mobile broadband standard (4G)

Attributes of OFDMA

OFDMA is the enabling technologies underpinning all Wi-Fi protocols since Wi-Fi 6, with numerous network benefits.

High throughput

OFDMA's innovations allow radio waves to carry more data in shorter timeframes.

Low latency

OFDMA reduces response times and enhances performance for video, artificial intelligence (AI), and virtual- and augmented-reality applications.

IoT optimization

OFDMA prevents Internet of Things (IoT) devices from using disproportionate network resources.

More efficient power consumption

OFDMA allows per-channel or per-subchannel power and lower maximal transmission power for low-data-rate users, eliminating pulsed carriers and conserving battery life in devices.

Benefits of OFDMA

Wireless-enabled breakthroughs

Wi-Fi 7 enables even more latency-sensitive applications like video AI calculations, augmented reality and virtual reality to share the same network. Medical images can be accessed quickly by caregivers in the field, retailers can make greater use of AR online or in stores, and manufacturers can use Wi-Fi to control automated processes.

High-density access

OFDMA helps provide better service in high-density venues such as airports, lecture halls, and sports arenas. Wi-Fi 7 brings additional efficiency providing even better user experiences in large public venues.

Application development

Wi-Fi 7 with OFDMA can inspire a new era of wireless computing, since higher capacity and more efficient networks can enable businesses to meet the ever-increasing latency demands of modern applications at scale.

In addition, high-performance wireless access can support the development of new applications, as software engineers invent new ways to take advantage of the speed and capacity of Wi-Fi 7 with OFDMA.