OFDMA vs. MU-MIMO: 10 Key Comparisons

OFDMA and MU-MIMO both enable advanced wireless networking, but they are also different in several ways.

October 6, 2022

As networking technology evolves, new standards and communication techniques must be adopted so that enterprises can keep up. Orthogonal Frequency Division Multiple Access (OFDMA) and Multi-User Multiple Input Multiple Output (MU-MIMO) are two components driving rapid advancements in wireless connections. This article discusses 10 critical comparisons between OFDMA and MU-MIMO. 

What Is OFDMA? 

OFDMA means Orthogonal Frequency Division Multiple Access. It can be viewed as new technology or an improvement upon already existing technologies. OFDMA is one of the technologies that make up the high functionality of WiFi 6. It improves the performance of wireless networks by creating and modulating subcarriers within network frequency bands. With such an approach, higher WiFi standards like WiFi 6 and, subsequently, WiFi 7 will foster simultaneous transfer between multiple clients and users. 

Orthogonal Frequency Division Multiple Access is a feature of the WiFi 6 standard that enables access points to serve more than one client at the same time. OFDMA is a multi-user version of the already existing, well-known Orthogonal Frequency Division Multiplexing (OFDM) digital modulation scheme. OFDMA makes multiple access possible where OFDM could not by creating and assigning subsets of subcarriers to different end clients. 

Orthogonal Frequency Division Multiple Access is an improved version of the OFDM, improving upon the previous Frequency Division Multiplexing (FDM) technology. OFDMA  technology is in synchrony with the switch of internet carriers and routers to WiFi 6 technology. It also aligns with the launch and use of 5G network and 4G network over 3G and 3G LTE for phone services. OFMDA replaces the old analog modulation technique in multiplexing with carrier signal waves in a digital format. 

OFDMA technology is guided by a series of rules and algorithms created to transmit data between more than one terminal. A terminal could be any device such as a phone, laptop, game console, iPad, etc. The transmission is done through a wireless network. 

With the previous technologies like FDM and OFDMA, there were several loopholes and minimal utilization of resources. 

FDM requires spacing between signals to avoid overlap, leading to the use of a wide range of frequencies and less usability. With OFDM, these frequencies are positioned strategically, and the access points can more easily differentiate between the different data transmissions. Signals are allowed to overlap so that data can still be sent effectively. Therefore, a lower range of band frequencies is used in OFDM. OFDMA trumps all these as it goes further to create subcarriers within each frequency. 

How does OFDMA work?

In the past, networks used WiFi standards for low-traffic email and web browsing. There were fewer devices using WiFi networks. The devices in the past also performed less data-intensive functions than today’s mobile phones, computers, and electronics. All these led to the rising need for new technology that can withstand increased traffic and congestion of data packets. This led to the formation of OFDMA. A frequency division technique that drastically reduces the effect of multiple devices performing multiple tasks on band frequencies.

OFDMA takes one WiFi channel and breaks it into more minor frequencies called resource units. Each resource unit is assigned to a client, and in that manner, an access point can communicate with multiple devices simultaneously. In WiFi 5, the channels were divided into 64 carriers transmitting individual data. In WiFi 6, OFDMA mediates the division of these channels to even smaller units and arranges them to avoid interference. 

Orthogonal Frequency Division Multiple Access determines the number of resource units (RU) assigned to each client using factors like the size of the data packet, device constraints, and the quality of service expected of that data packet. This means that devices sending high-priority, large or sensitive packets will be assigned more resource units, whereas devices with a low volume of packets are given fewer resource units. Overall, it makes the transmission process very effective and limits the waste of resources. 

A good analogy to understand how OFDMA works is using a delivery company with multiple trucks. Each truck is a band frequency capable of carrying the goods destined to a single location and particular client. With OFDMA, however, each truck can carry goods and items belonging to different clients and drop them in order along the delivery route. This way, OFDMA optimized the computer network to be fast and effective. 

See More: Wifi 5 vs. Wifi 6: Understanding the 10 Key Differences

What Is MU-MIMO? 

When connecting one device to regular routers, there is excellent network performance and speedy data transfer. The more you add additional devices to the same router network, the more overall performance slows down. This is because most routers used that are used currently were created with SU-MIMO technology that allows just one device to receive data at one instance in time. 

SU-MIMO means Single User, Multiple Input, Multiple Output. This technology implies that when multiple devices are connected to a network, each has to wait its turn to receive data, leading to slow performance. 

MU-MIMO is a new technology that changes the ball game. It is a wireless technology that allows several client devices to interact simultaneously. MU-MIMO is a multipath wireless technology used to transmit information across devices and uses multiple antennas to create an environment for better communication by allowing multiple connections to the same device simultaneously. 

MIMO is how an access point revolves around internet bandwidth, breaks it up, and distributes it to peripheral devices. MIMO technology was a Single User MIMO (WiFi 4). Now, Multi-User MIMO is replacing the older technology. MU-MIMO was introduced as a part of the second wave of WiFi 5 (IEEE 802.11ac) and now WiFi 6 (IEEE 802.11ax). 

MU-MIMO allows more than one WiFi device to simultaneously receive different streams of data. In its initial release and part of WiFi 5 wave 2, MU-MIMO was only 4×4. This meant that access points or routers with MU-MIMO support and up to 4 antennas could broadcast internet signals to up to four clients simultaneously. WiFi 6 supports 8×8 MU-MIMO, meaning they can broadcast to up to eight 1×1 clients without delay in transmission. 

Another thing to understand about the current MU-MIMO technology is that it is still being developed. Currently, the technology is only available for downlink connections. Uplink MIMO connecting peripheral nodes to the access point still exists as SU-MIMO. 

How does MU-MIMO work?

Multi-User MIMO is a set of multiple input and multiple output (MIMO) technologies that create numerous paths for wireless communication between devices and routers or terminals. It allows terminals to send waves across more than one antenna to different devices. It is a more advanced method compared to the SU MIMO, which involves communication between one multi-antenna node and another device with the same type of antenna. 

In the same way, the OFDMA adds multiple access functions to the existing OFDM, and MU-MIMO adds a multi-user function to MIMO. MU-MIMO is currently a communication method that works with downlink wireless connections, from one access point to several client devices. To fully grasp the working mechanism of MU-MIMO, we must understand how MIMO technology works too. 

In MIMO, clients and access points must each have more than one radio antenna. These antennas should be identical and arranged physically apart from each other. A spatial stream is a data set sent by the transmitting radio chain (access point); the spatial stream is now received by the receiver radio chain (client) and reconstructed to match the original message. In MIMO, each radio chain (antenna) sends out a spatial stream of the same frequency which is then received by the receiver on each of its antennas.

Beamforming is also another way to understand MU-MIMO. Beamforming eliminates directionless transmission and instead sends signals toward the intended device. Beamforming thus helps MU-MIMO to increase both the speed and range of signals. Signals are sent from the access point to multiple but specific users. 

Therefore, MU-MIMO works in simple steps. The access point first broadcasts a sounding frame. Compatible clients then send back matrix data to the access point. The access point calculates its position and selects a group of clients for simultaneous transmissions. The access point then transmits the data stream and critical phase offsets to the users. Finally, the access point seeks and receives confirmation of received data from the client devices. Altogether, downlinking MU-MIMO leads to wireless networks that are better and faster. 

See More: Modem vs. Router: Understanding the Key Differences

OFDMA vs. MU-MIMO: Key Comparisons and Similarities 

Orthogonal Frequency Division Multiple Access and Multi-User Multiple Input Multiple Output technologies are used in the most current WiFi standards and are inbuilt into new routers. However, these two technologies are not the same, as there are seven key differences between the two. 

1. Type of technology 

The primary difference between OFDMA and MU-MIMO is that both work in different ways and are based on different principles. They have different approaches to meeting the goal of better wireless communication technology. The Orthogonal Frequency Division Multiple Access, or OFDMA, uses the idea of dividing frequencies into smaller channels and subcarriers that are individually assigned to devices based on their needs. Instead of assigning an entire channel to a mobile phone, it assigns sub-carriers to the phone for specific purposes and only for the period needed.

On the other hand, Multi-User Multiple Input Multiple Output (MU-MIMO) enables access points to transmit information in the form of radio signals directly to more than one device simultaneously. This is very different from how OFDMA works but, in a way, complements it perfectly to make communication as seamless as possible. 

2. Bandwidth specificity 

Bandwidth refers to the maximum volume of data transmitted across a channel over the internet within a specific time. Bandwidth describes how ‘wide’ a lane is, directly correlating to the number of cars traveling side by side within a time frame. OFDMA and MU-MIMO technologies have different bandwidth specificity. This means that OFDMA facilitates data transmission across a particular bandwidth, while MU-MIMO functions better with another type of bandwidth.

Specifically, OFDMA technology of splitting channels into subcarriers is ideal for low bandwidth networks. Networks like the internet of things (IoT) deal mostly with transmissions of low data packets and are a perfect environment for OFDMA. It reduces the latency and increases the efficiency of the network by serving several devices with small data packets simultaneously in a way that MU-MIMO cannot. 

When multiple devices require high bandwidth to receive a large volume of data, MU-MIMO becomes the ideal technology to implement. A good example is when streaming a movie or playing games. These high bandwidth networks can be achieved at maximum speed per user using MU-MIMO. Routers have both technology and can switch and combine both transmission methods for the best performance depending on the requirement. 

3. Effect on network speed

Speed is a fundamental problem that every technology must have in mind when providing different solutions. Some technologies are better suited to increasing the device’s speed, whereas others do not participate actively in increasing speed. 

In OFDMA, speed is not a priority but a by-product of more effective transmission. OFDMA increases efficiency, eliminates waste, and reduces latency for a given network. These combined may mean that data transmission is faster for each device, but it is not a direct effect of OFDMA.

MU-MIMO makes the network have a higher transmission capacity and directly increases the speed of each device connected to the transmitter. In MU-MIMO, multiple lanes are created, and data can move faster.

See More: What Is Network Topology? Definition, Types With Diagrams, and Selection Best Practices for 2022

4. Direction dependency 

Data transmission is mostly bi-directional. This means that data can be transmitted from one device to the other and in the reverse direction. Transmission from the access point to the user is called downlink, while transmission from users to access points is called uplink. 

OFDMA can foster the bidirectional transmission of data in IEEE 802. ax standard. MU-MIMO, on the other hand, is only capable of unidirectional downlink transmission. When uplink transmission occurs in MIMO, it is through SU-MIMO. This means that although one access point can simultaneously transmit to multiple devices, clients can only transmit one at a time to the access point.

5. Constancy of signals 

Signals can be sent in a consistent stream or broken up into batches. This is applicable in MU-MIMO and OFDMA technologies. OFDMA does not support the constant perpetuation of a channel between the access point and a client. It is need-driven and allocates carriers only when necessary. Therefore, the signal is not constant.

In MU-MIMO, access points can maintain a constant signal for each connected device without interruptions. This serves as a significant benefit of the technology. It shares bandwidth among devices without cutting the signal or compromising speed. 

6. The use of antennas 

Antennas are aerial components of a device that transmit or receive radio waves for communication purposes. Antennas are part of most devices that communicate with others, like routers. However, they are used to different degrees by different technologies. 

Orthogonal Frequency Division Multiple Access is not an antenna-based technology. It simply divides a single channel into numerous sub-channels, which are used as needed. 

MU-MIMO, on the other hand, functions primarily through antennas. The more the number of antennas, the more devices one can add to the network. MU-MIMO uses spatial streams to physically direct signals and separate end devices from each other. 

7. Network capacity 

Network capacity is a significant consideration, especially as current trends encourage individuals to own multiple devices. MU-MIMO increases the capacity of the network to transmit higher loads. It allows access points to perform WiFi-intensive activities that would be otherwise impossible or very slow in an alternative technology. This is not the case with OFDMA.

See More: GSM vs. CDMA: Understanding the 10 Key Differences

OFDMA vs. MU-MIMO: Notable Similarities

Despite these seven differences between OFDMA and MU-MIMO, they are also similar in the following ways:

1. Multi-user 

OFDMA, as well as MU-MIMO technology, are two techniques used in wireless communication that both involve multiple devices. Gone are the days when data transmission could only exist in a bidirectional path between two devices. Now, OFDMA allows an access point to assign carriers to multiple devices, and MU-MIMO enables the creation of different channels for different devices. 

2. Use in Wi-Fi network 

WiFi networks have been in place since the 1990s. Several technologies for wireless transmission have also been created and modified since then. OFDMA has undergone several modifications from FDM to OFDM and now OFDMA. MU-MIMO has also been improved since it was initially created as MIMO technology. However, these two have become part of the fundamental architecture behind the more recent wifi standards. OFDMA and MU-MIMO are both implemented on WiFi 6.

3. Reduction of latency 

Latency describes the time required to send a data packet from one point (transmitter) to another (receiver). OFDMA and MU-MIMO reduce data transmission’s latency period, resulting in faster communication. 

See More: What Is Wifi 6? Meaning, Speed, Features, and Benefits 

Takeaway

Ultimately, OFDMA and MU-MIMO act as complementary technologies, despite being different in remarkable ways. With the rise of IoT devices, OFDMA will be highly relevant for companies looking to deploy small-packet IoT applications. Alongside this, MU-MIMO can help boost capacity and efficiency in high bandwidth apps. Together, they improve your holistic networking capabilities. 

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Chiradeep BasuMallick
Chiradeep is a content marketing professional, a startup incubator, and a tech journalism specialist. He has over 11 years of experience in mainline advertising, marketing communications, corporate communications, and content marketing. He has worked with a number of global majors and Indian MNCs, and currently manages his content marketing startup based out of Kolkata, India. He writes extensively on areas such as IT, BFSI, healthcare, manufacturing, hospitality, and financial analysis & stock markets. He studied literature, has a degree in public relations and is an independent contributor for several leading publications.
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