Unveiling the Myth of 4 x 4
If someone told you that a vehicle with more wheels would always be faster than one with fewer wheels, would you believe them? Take a look at the pedal car above; do you think it’s faster than the 3-wheeled cyclecar? Without the powerful engine, aerodynamic design and advanced electronics, a pedal car, although 4-wheeled, can’t give you the performance of a modern 3-wheeled cyclecar.
In the wireless industry, vendors often claim better Wi-Fi performance because their access points have more Tx/Rx antenna chains. However, like our car analogy, more antenna chains doesn’t necessarily mean better performance. High wireless performance is not delivered by a single component of an access point, but from the entire system’s implementation.
So is 4x4: 3 really better than 3x3: 3?
The answer might be yes if that were the only component considered. With the 4th antenna chain in some 3SS (spatial stream) APs, the antenna’s signal strength can be increased by up to 1.2db to enhance the AP transmit and receive performance. However, the potential gain from the extra antenna chain can be wiped out if the access point has poor circuit board design or inferior grade antennas. It is important to keep in mind that the number of antenna chains is not the only factor that impacts the entire Wi-Fi performance. To get a complete story, you should also consider other AP factors such as CPU, design and antenna placement, and software optimization. Lacking any one of these could lead to inaccurate conclusions, like Cisco’s 4x4 superior performance claim.
The real story: Factors that impact AP performance
Cisco has claimed its AP-3700, with its purpose-built innovative chipset and RF architecture, is the only Wave 1 access point that supports 4x4 MIMO and 3 spatial streams. They claim it is capable of delivering more capacity and reliability than competing access points. What’s the real story? Let’s break it down and look at the facts.
Cisco’s chipset in AP-3700 is actually the same legacy CPU (the manufacturer, Freescale, classifies the CPU as Low End) from Cisco’s 11n AP-3600 series. It supports Single Core at 800 MHz or Dual Core at 480 MHz, but Cisco’s dated AP software only supports single core operations. Using a legacy chipset in the new 802.11ac Wave 1 access point may cut costs and provide a comfort zone for Cisco, but it won’t improve the performance of the WLAN system, especially in a high density environment.
The comparable AP-225 from Aruba is designed with the truly innovative Dual Core 800 MHz CPU, and unlike Cisco’s product, it has ArubaOS, a full multi-core operating system that can take advantage of the CPU. The AP-225 delivers high performance, especially in extremely high-density environments. With the faster packet processing speed per second and the large memory, the AP-225 is able to associate with more clients, keep more non-associate clients around, and handle more interference at one time, delivering a truly unprecedented user experience in high device density areas.
AP design and antenna placement
While Cisco touts its RF architecture, the truth is that their AP-3700 compromises its antenna placement and AP design for modularity to future-proof an elusive platform that can’t handle high peak throughput. Now that Cisco has launched its Wave 2 AP-1850, the question is: where is the Wave 2 module that can be added on to AP-3700 to be field upgradable to Wave 2? And even if a Wave 2 module was coming soon, how well would it perform given the small surface area that would force the 4 antenna elements to be located too closely together to reach peak performance, while relying on the same low performing AP CPU?
There are multiple factors that can impact the effectiveness of additional chains, such as antenna patterns and interactions, processor capability, and rate adaption. Aruba has addressed these system level factors in their product designs. The Aruba AP-225 is purpose-built for high-density environment. Many factors are considered at the design level to deliver a high performance wireless network with a first-class user experience. One example is the Aruba Advanced Cellular Coexistence (ACC) feature that is supported in AP-225 and other Aruba APs to deal with interference from cellular and distributed antenna systems. With Wave 2 clients on the horizon, Aruba is delivering a new purpose-built AP in the AP-325 that can handle the demands of MU-MIMO and 4SS processing to allow customers to prepare their networks.
Single AP performance is great, but for the overall system to perform, you need intelligent software optimizations. Aruba ClientMatch is a great example of technology that factors in client OS and applications, to improve overall system performance. The AppRF technology brings application awareness to WLANs, prioritizing applications, and enhancing device utilization for each user.
Cisco Optimized Roaming, a “me-too” attempt from Cisco, is blind to the application and the client OS when attempting to improve roaming.
The test: Aruba 3x3 vs. Cisco 4x4
Now that we understand the critical components in AP design, let’s run some tests and see how relevant it is to simply look at the number of antenna chains in isolation.
To verify Cisco’s 4x4 claim, we tested the Cisco AP-3700 with .3at POE+ and .3af POE power, respectively. Like many 11ac APs, running on .3af power reduces some functionality. In the case of the AP-3700, when it runs on 802.3af power, the supported antenna chains are turned from 4x4 to 3x3. Before the test, we assumed that its 4x4 mode would outperform its 3x3 mode because of the additional antenna chains in the same design. To our surprise, there is almost no performance difference between these two modes in the AP-3700 (see chart below).
Next, we ran the same tests (with .3af POE+ power) with the Aruba AP-225 that supports 3x3. The results show significant improvement when compared to the Cisco 4x4 AP-3700, especially when the clients have more spatial streams. The results below are from the tests run at 120 feet, where an increase in signal strength should make the most difference.
The results are clear — Aruba designs a system, not a component!
Looking ahead to Wave 2 with 4x4:4SS support: Aruba vs. Cisco
The Cisco Wave 2 AP-1850, with 4x4 antenna chains, is positioned by Cisco as only being suitable for small and medium businesses with low-density needs. They state that since it lacks Cisco HDX and CleanAir, it is not suitable for high density and mission critical deployments, and they recommend that customers instead deploy Cisco Wave 1 AP’s, AP-2700, or AP-3700.
The Aruba Wave 2 320 series, with 4x4 antenna chains and a full AP system designed for Wave 2, delivers the highest performance in high-density environments. The integrated enhanced ClientMatch groups Wave 2 capable clients to Wave 2 APs and boosts the simultaneous data transmission process. This is especially critical during the current technology transition stage where there are not many Wave 2 clients on the market. The integrated Aruba BLE, which provides location and push notification services, simplifies the remote management for a network of Aruba battery-powered beacons, greatly improving network efficiency and user experience.
To learn more about Gigabit Wi-Fi, refer to our 802.11ac technology overview page.
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