802.11ac vs 802.11n WiFi

已有 1054 次阅读 2017-12-18 10:33 |个人分类:技术类|系统分类:生活其它

Dazzling users with specification sheets is nothing new: screen sizes, resolutions, megapixels, memory sizes and processor speeds are just a few, but one of the most neglected and important is WiFi and its latest and greatest standard ‘802.11ac’.

802.11ac was finalised in 2013 and you will find it in every major smartphone, laptop and desktop computer and smart television. It succeeds the equally-badly named ‘802.11n’ which has been around since 2007 and brings some major benefits.

The good news is by the end of this post you will not only understand 802.11ac, but also how to get the best from your existing wireless signal.

Compatibility - Everything Works Together

I’ll start with the good news: chipsets featuring 802.11ac are fully backwards compatible with previous WiFi standards.

WiFi official logo and accepted standards

WiFi official logo and accepted standards

This means it works perfectly with 802.11a (introduced in 1999), 802.11b (2000), 802.11g (2003) and 802.11n (2007). The bad news is you will be limited to the performance of the older standard and will only get the full benefits of ‘Wireless AC’ or ‘AC WiFi’, as it is also known, if you are connecting from 802.11ac to 802.11ac. That means an 802.11ac router and an 802.11ac device.

So that out the way, what are the benefits?

802.aac theoretical speeds versus 802.11n and 802.11g - image credit Asus

802.aac theoretical speeds versus 802.11n and 802.11g - image credit Asus

802.11ac vs 802.11n Speed

You may have noticed there has been a six year gap between 802.11n and 802.11ac. This is an eternity in technology terms and the big benefit 802.11ac brings from its time in development is speed.

WiFi is always promoted using ‘theoretical’ speeds and by this standard 802.11ac is capable of 1300 megabits per second (Mbps) which is the equivalent of 162.5 megabytes per second (MBps). This is 3x faster than the typical 450Mbps speed attributed to 802.11n.

The problem is these speeds are garbage. In the real world no-one ever gets close to theoretical speeds and the fastest 802.11ac real world speeds recorded in testing are around 720Mbps (90MBps). By contrast 802.11n tops out at about 240Mbps (30MBps) so the 3x estimate is still true, just much lower.

But there is one more crucial part to understand for your real world experience: antennas.

Long term 802.11ac has the headroom to support up to eight antennas each running at over 400Mbps each, but the fastest router to date only has four antennas. The reason is because antennas add cost and take up space and the smaller the device the less antennas they can fit so it becomes pointless adding more to a router. Typically:

  • Smartphones: 1 antenna

  • USB Adaptors: 1 or 2 antennas

  • Tablets: 2 antennas

  • Laptops: 2 antennas (occasionally 3 on desktop replacements)

  • Desktops: 3 or 4 antennas (PCI Express EXPR -1.74%cards)

This is another bottleneck. If your glorious four antenna 802.11ac router is connecting to your single antenna 802.11ac smartphone then 400Mbps (50Mbps) is your theoretical maximum and 200Mbps (25MBps) is the more realistic one.

This is something of a downer, but these speeds are still faster than nearly all home broadband connections and only become a limitation for transferring files wirelessly between devices on your local network (say laptop to laptop or desktop to NAS).

Furthermore 802.11n only supports up to four antennas at roughly 100Mbps (12.5MBps) each so when you do the maths for devices using 802.11n antennas the gap begins to widen. Especially when it comes to the next big benefit of 802.11ac…

Beamforming 'Smart WiFi' - image credit Netgear

Beamforming 'Smart WiFi' - image credit Netgear

802.11ac vs 802.11n Range

So AC WiFi is much faster, but its peak speeds are not really the selling point. It’s speeds at long range are.

First the bad news: 802.11ac WiFi doesn’t really reach any further than 802.11n WiFi. In fact 802.11ac uses the 5GHz band while 802.11n uses 5GHz and 2.4GHz. Higher bands are faster but lower bands travel further.

That said my experience testing both standards finds very little difference in signal strength between 802.11ac over 5GHz and 802.11n over 5GHz and 2.4GHz.

Why? Firstly because 2.4GHz is used for everything from cordless home phones to microwaves and 5GHz remains relatively interference free for a cleaner signal.

The second key factor is ‘Beamforming’. Typically wireless signal is simply thrown out from your router equally in all directions, like ripples when throwing a stone into a pond. This is why you should place your router as close to the centre of your home or office and as high up as possible.

Beamforming is different. It is built into the 802.11ac specification and is ‘smart signal’ which detects where connected devices are and increases signal strength specifically in their direction. Yes it is still a good idea to position your router centrally, but it helps make it less vital.

All this means the performance of 802.11ac is maintained far better at long range than 802.11n. Peak performance may be tripled, but at range 5-10x the speed benefits are not unusual and this is where 802.11ac comes into its own. Some numbers for example:

  • 802.11ac at one metre: 90MBps, 10 metres: 70MBps and at 20 metres behind two solid walls: 50MBps

  • 802.11n at one metre: 30MBps, 10 metres: 20MBps and at 20 metres behind two solid walls: 5-10MBps

Of course these figures are a general guide and I’ll get into examples of more specific top 802.11ac devices to buy next.

下一篇:Comparing 052D and “aegis”


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