2×2, 3×3? What’s the difference?

Why should I choose a 3×3 Access Point over a 2×2 Access Point?

In October, Pakedge announced the release of its WX line of 3 x3 802.11 ac wireless access points (AP) designed for high-end residential and commercial applications. At the CEDIA Expo in mid October, we previewed the WK-2, a 3×3 version of our popular 802.11ac WK-1 AP. The WK-2 will be released early December.


What does 3×3 mean?

It is common to see AP product descriptions with 2×2 or 3×3. The first number is the number of transmit antennas while the second number refers to the number of receive  antennas.  For example, our WX-1 AP is 3×3, which means that it has 3 transmit antennas and 3 receive antennas.

Sometimes you will see a third number at the end preceded by a colon (e.g. 3×3:3).  The last number refers to the number of spatial streams – the number of independent wireless data transmissions that are sent over the antennas on the same channel.  These spatial streams are fundamental to MIMO (multiple input, multiple output) antenna technology which takes multiple copies of the same data signal and transmits them through physically distinct paths to a receiver which recombines the signal from the various streams. In the example of our WX-1, which is a 3×3:3 WAP, it is capable of transmitting and receiving 3 simultaneous streams of information on a single channel.

In both cases, the numbers should not be confused with the number of radios inside the WAP. There are two radios – one for the 2.4 GHz transmissions, and one for the 5 GHz transmissions.

How does a 3×3 AP provide more performance than a 2×2 AP?

All things equal, you can expect more performance from a 3×3 AP than a 2×2 for several reasons. First, for a 802.11ac AP, a 3×3 AP provides a maximum throughput is 1.3 Gbps (3 x 433 Mbps) versus 867 Mbps (2 x 433 Mbps) for a 2 x 2. Note that the maximum speeds are used for reference purposes. In real life applications, the actual throughputs observed are significantly less due to attenuation, and other factors.

Second, the increase in the number of antennas help improve signal link quality and reliability through a technique called spatial diversity. Because the antennas are physically separated from each other, each antenna sees a slightly different copy of the signal. The signal seen by one antenna may be slightly imperfect in one area of the transmission while the other antenna may see it perfectly. This is especially significant in environments where the RF environment is less than ideal due to site geometry, building materials, and interference.

Our resellers have said that they’ve seen performance gains of anywhere from 10 to 30% in the field.

How would a 3×3 make a performance difference if the client device is a 1×1?

The performance benefits are clear when you have a 3×3 AP paired with a 3×3 client device like an Apple MacBook Pro, but what about a 1×1:1 device like the Apple iPhone?  In this case, there are no MIMO gains from the additional spatial streams. However, there are still performance improvements to be had with a 3×3 AP versus a 2×2 AP.

The first improvement occurs on the AP side through a technique called Space Time Block Coding.  Since the 3 x 3 AP knows that it is only transmitting to a 1×1 client, it uses the leftover antenna chains to break up and transmit blocks of data to ensure that the client device can reconstruct the original signal even if parts of some streams get lost during transmission.

The second improvement occurs at the AP end. Even though a 1×1 client can only send 1 stream, that single stream bounces off walls, furniture, and other objects to arrive at the AP’s three receiving antennas as separate signals.  The AP uses the same signal recombination algorithm (discussed earlier – called MRC) to take the signal received on each antenna chain and piece together the original data signal by combining the strongest segments from each chain.

Based on our testing with the 3×3:3 WX-1 paired to a 1×1:1 device in a real world environment, we observed a 14 to 34% throughput improvement when these features were enabled.

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