It is past the cliche stage to state that WiFi devices are everywhere. It’s ubiquity and the competition with mobile (3GPP) technologies have ensured that new variants of the standard are pushed out at increasing rates accompanied by even bigger claims. Each new wifi standard has brought significant increases in performance, with current 802.11ac Wave 2 standard offering a theoretical 3.5Gbps (with 4 spatial streams, 160 MHz) and upcoming 802.11ax claiming almost 10 Gbps (with 8 spatial streams) [From https://bit.ly/2LOJhgj]
Let’s see what features of 802.11ac worked well and what did not?
Wider RF channel Bandwidths –
20 MHz & 40 MHz channel bandwidths of 802.11n are increased to 80 MHz and 160 MHz in 802.11ac. The expectation is that increase in bandwidth increases the data throughput.
Does it really work?
If you talk to deployment professionals, no one recommends deploying 160MHz except under very specific scenarios. It is hard to find 160 MHz of contiguous spectrum in most locations. It is also rare to find 11ac CLIENTS that support 160MHz. Hence it has remained more a marketing tool than a real differentiator in the field. Given these, we do not think that 160MHz RF channel bandwidth will be useful at all in real-world scenarios, especially in enterprises.
In enterprise deployments, multiple Access Points are deployed in a given area covering different channels to maximize throughput. In the 5GHz band, 160MHz channel width allows only 1 (or 2 if DFS is enabled) channels for use. Configuring for 80 MHz bandwidth, on the other hand, allows 5 different non-overlapping channels to be used in the deployment plan, thus allowing for better coverage and throughput. 40MHz and 20MHz allow even more contiguous channels to be used.
Spatial streams –
The number of spatial streams have been increased theoretically from 4 in 802.11n to 8 in 802.11ac. This feature allows multiple signals (up to 8) to be transmitted simultaneously from one access point using multiple antennas. Theoretically, this should double the performance.
Is this a standalone feature that would add value?
WiFi chips specifically designed for APs have 4 or more antennas while those for clients have usually 1 or 2 antennas. There is the rare WiFi client chip with 3 antennas, but that is not the norm. This is due to physical size, cost, utility and power constraints. High performing APs can transfer multiple streams, but clients are not capable of receiving data in the same way. Theoretically, this can be addressed with MU-MIMO where Access Points communicate with multiple clients simultaneously.
Multi User, Multiple Input & Multiple Output feature allows an AP to transmit different streams to multiple clients simultaneously. In theory, this feature will increase the performance by utilizing the channel efficiently.
Our take on this feature:
The performance of MU-MIMO is seriously limited. It needs a series of specific conditions to be met to work properly. These include the position of clients relative to each other, the total number of clients and number of receiver antennas per client relative to the Access Points. The overhead due to a sounding procedure is also reducing the efficiency. Field test results are at best sketchy on this topic (Ex: https://www.smallnetbuilder.com/wireless/wireless-features/33100-why-you-don-t-need-mu-mimo). The feature also suffers from the disadvantage that it only works in DL (AP to the Clients) whereas TCP traffic (which constitutes the bulk of real-world data) would need an efficient UL path for ACKs.
Modulation & Coding Schemes –
802.11ac introduced 256 QAM (and also 1024 QAM – proprietary to Broadcom) – theoretically a 4 ~ 16 times improvement from 11n.
Does this feature Quadruple Throughput?
Spectral efficiency measures how well the system uses available bandwidth. The throughput increase comes, however, at the cost of less tolerance of bit errors in lossy signal environments. This feature does improve efficiency with clients near AP (distance 5-10m LOS) and in a relatively clean environment. So yes, we finally do have an unequivocally useful feature
Now if you want to understand the effective user experience of 802.11ac over 11n, check out SWAT WiCheck from Alethea. You can focus your tests on what really matters to the consumer while helping you meet your SLAs.
More details at https://alethea.in/swat-wicheck