4x4 access When selecting a new Wi-Fi infrastructure, business customers are often faced with a wide range of devices. Customers with an interest in technology will always ask for equipment that meets the latest technical standards. After all, the aim is to invest in the right technology. It seems clear that the current 802.11ac standard has become the benchmark for everything. But what then are Wave 2, 2×2 MIMO, 3×3 MIMO, and 4×4 MIMO, and why is there a new 802.11ad standard.

But let’s start at the beginning: 802.11ad is a standard for networks operating in the 60 GHz band and has a range of only a few meters. It is typically used with home entertainment equipment to connect media players to TV stations. Hence, 802.11ad is not suitable for connecting laptops, smart phones or tablets.

As for the 802.11ac standard, it is important to note that it only works on the 5 GHz band and that older devices will often only support the 2.4 GHz frequency band. Luckily, most access points using 802.11ac usually contain a second radio module allowing them to offer the 2.4 GHz frequency band. This ensures that older devices can continue to operate. Older Wi-Fi clients that already use the 5 GHz band but that have not yet incorporated the new 802.11ac standard will also be able to connect because 802.11ac is backwards compatible with the rest of the 5 GHz standards.

Having said that, we still need to consider the issue of MIMO. MIMO indicates the number of transmit and receive antennas. The number of transmit antennas also determines the number of streams. The more streams an access point has, the greater the transfer rate. A 2×2 MIMO device can transmit 867 Mbit/s, while a 4×4 MIMO device reaches 1.7 Gbit/s. In order to obtain these levels, the wireless client must have the same MIMO. If a 4×4 MIMO access point is used for a wireless client with a 2×2 MIMO device, the maximum data rate will only be 869 Mbit/s. The bad news is that most laptops and tablets only come with 2×2 MIMO technology, and most smart phones have to settle for 1×1 MIMO. Therefore, a smart phone can only achieve a maximum of 433 Mbit/s.

In view of the above, there’s not much sense in using 3×3 or 4×4 MIMO as most Wi-Fi clients do not have devices that support these technologies. A 3×3 MIMO access point, or even better, a 4×4 MIMO one, is only advisable for Wave 2 models. Wave 2 represents the second wave of 802.11ac chipsets and supports MU-MIMO (Multi-user MIMO). The importance of MU-MIMO can be easily explained with the help of an example. If we have two smart phones that only support 1×1 MIMO and they connect to a 2×2 access point, the two mobile phones will connect to the first antenna. Therefore, both smart phones will share one stream. Each device will receive only half of 433 Mbit/s, that is, 216 Mbit/s. The second antenna, and consequently the second stream will remain unused.

When using a 2×2 MIMO access point with MU-MIMO technology, the process is different. The first mobile phone will connect to the first antenna and the second to the access point’s second antenna. The overall data rate will be doubled, as will the maximum number of clients that connect to the access point. Therefore, 3×3 and 4×4 MIMO only make sense if they support MU-MIMO. And there is a catch. Not only access points have to support MU-MIMO technology, but also clients. Unfortunately, this is not always the case, even with newer smart phones. Nevertheless, it is only a matter of time.

Companies that choose to install a Wi-Fi infrastructure should consider expenses. 4×4 MU-MIMO Access points are much more expensive than 2×2 MIMO ones and need a more powerful PoE switch. In addition, they need an Ethernet connection of over 1 Gbit/s to reach their full potential, which also increases the cost of the investment.

In short, I would tell anyone wanting to invest in a new infrastructure that 2×2 MIMO access points cover most business needs. Investing in more expensive 4×4 MIMO technology is only advisable if MU-MIMO-compatible access points are installed. Moreover, it is important to check whether using 4×4 MU-MIMO access points is really necessary. It could be useful for high-performance applications designed to provide Wi-Fi to a large number of clients (e.g., in conference centers). However, for most office applications, the much more economical 2×2 access points are more than enough.


About the author

Hans-Dieter Wahl
WLAN Business Line Manager

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