Introduction to Wireless Networking

Wireless networking is, potentially, a quick, easy and economical alternative to running wires around your home or office. It also opens up possibilities for connecting buildings which are up to several kilometres apart. The table below summarises some of the features for each standard.
Standard Phi Rate Frequency Comment

802.11a

54 Mbps

5.1-5.8GHz

Very popular for outdoor links due to isolation from all the 2.4GHz band rubbish. Still waiting to really take off for indoor use but a lot popular now that a couple of years ago. The surge in popularity of Apple devices has certainly helped increase popularity. The large number of non-overlapping channels compared with the 2.4GHz band will probably help make 5GHz the standard in a few years time. Uses OFDM over all speeds so theoretically better non-line-of-site capabilities.

802.11b

11 Mbps

2.4GHz

The first system to appear at mass-market pricing. Suitable for both internal and inter-building applications though poor penetration and scatter of 2.4GHz radio can reduce effectiveness for both indoor and remote bridging applications. Not seen much nowadays.

802.11g

54 Mbps

2.4GHz

OFDM 2.4GHz standard gives much the same functionality as 802.11b but at higher data rates. The OFDM standard is supposed to give improvements over the older 11b products for indoor (non-line-of-site) use though this is offset, to some extent, by the OFDM function only operating at speeds above 20Meg.

11n

Up to 300Mbps (or even 600Mbps)

Available for 2.4Ghz and 5GHz frequencies

Uses 40MHz wide channels (though devices normally have the option to use single stream 20MHz WiFi channels – so-called ‘half-n’) and several other packet efficiency tricks to improve data throughput – typically three or four times the throughput of ‘normal’ 54Meg WiFi but theoretically can go can even higher than that. On paper it’s a lot better for non-line-of-site operation either indoors or outdoors but in practice the jury seems to still be out on this point. Due to pressures from the WiFi chip manufacturers, 11n is now the de-facto standard.
11ac Up to 1.7Gbps 5GHz Bands 11n to the next stage. Uses 80MHz or 160MHz wide channels - so pretty much ALL of the 5GHz band! Offers the potential for a significant performance jump over 11n but, tbh, in practice, 11n isn't really as fast as we were promised so I wouldn't be too optimistic of 11ac wifi links really going as fast as they're saying!

11ac2

 As above As above

The original 11ac, introduced c. 2013, was a slightly limited iteration of the full 11ac functionality. c. 2015, so-called 11ac Wave 2, started to appear which, essentially, was full spec. 11ac. Key differences were the ability to bond two 80meg channels and treat it as a 160meg wide channel. This allowed the potential to go to 2.5Gbps speed. Also, Wave 2 allowed 4 spatial streams but you need 4 antenna on both AP and client for this functionality. If supported by the hardware then this promised a further speed boost. Saying that I haven't seen any client devices with 4 antenna! The final big difference with Wave 2 was a feature called Mu-MiMo. This allows an access point to split its streams to service multiple clients at the same time. So, for example, a 4 stream capable AP could service 4 clients with a single stream at the same time. tbh, in the real world, Wave 2 sounds great but it's not been well supported by client devices so, although it's boosted sales of purveyors of Wifi hardware, it's had little change in the real world.
11ax

3.5Gbps
(single stream, up to 4 streams supported)

Combines 2.4GHz band with 5GHz band.

Designed for high-density public environments, like trains, stadiums and airports. But it also will be beneficial in Internet of Things (IoT) deployments, in heavy-usage homes, in apartment buildings and in offices that use bandwidth-hogging applications like videoconferencing. Uses a more packed data stream protocol than 11ac gives the potential for an extra 40% throughput (ref. 11ac). Wave 2 11ac allowed Mu-MiMo at the ratio of 4:1. 11ax can support up to 8:1 expanding on the ability to service high-density environments. Further, the Mu-MiMo can simultaneously talk to receivers and transmitters – 11ac2 could only use Mu-MiMo for downlink transmissions. 11ac operates in the 5Ghz range only. 11ax operates in both the 2.4Ghz and 5Ghz ranges, thus creating more available channels. For example, early chipsets support a total of 12 channels: Eight in the 5Ghz and four in the 2.4Ghz range.

Range

You will see specifications for different brands of wireless networking devices quoting wildly different ranges. Take these claims of huge range with a pinch of salt. Unless the manufacturers have got something very wrong, or are operating at illegal power output levels, then products from different sources will behave much the same within similar parameters. Any variations in the true range between products, assuming the comparison is done with products running at similar power levels, comes down to factors such as antenna gain (different gain alters beam spread and also alters the affective receive sensitivity), receive sensitivity, and (particularly for indoor use) the ability to cope with multi-path reflection affects.

There are two types of application in which wireless networking is used: internal and inter-building.

Indoors
Radio waves travel in straight lines and at 2.4GHz do not penetrate obstacles very well. Some surfaces reflect the signals quite well whilst others tend to absorb them. Water, which comprises most of you, is particularly good at absorbing the energy, so you will find that putting your hand over an antenna can reduce the signal substantially. (Your hand won't warm up because output power is limited to 100mW in Europe - well below the power output of your mobile phone!). 5GHz wireless suffers from similar problems BUT, with better scatter, it can give improved non-line-of-site (NLOS) capabilities over 2.4GHz devices.

As a general rule, 802.11g/n devices will usually cover a house quite well but there are no guarantees. You might also find that the connection speeds will drop in order to get a reliable link. In fact, often an 11n product with up to 300meg potential will only give a fraction of its maximum throughput. The signal passes better through wooden floors and ceilings than through brick walls and has no chance at all through concrete or stone. The use of an access point in the loft connected to a directional antenna pointing down from the rafters has proved an effective way to get full coverage in a typical house. For a more restrictive range, the built-in antennas often work very well.

802.11a/ac/5GHz radio, although costing a little more than 2.4GHz products, has much better scatter making it theoretically better for indoors operation where it needs to reach remote rooms. 11n WiFi based on 5GHz is almost the future for wireless networking in buildings (mind you we’ve been saying that for years now and still waiting for it to take over from 2.4GHz products!)

 

You can read more information on 5GHz wireless in our '5GHz Frequency Bands' Article.


Outdoors
The following table is a guide to the distances you might expect to achieve using 'off-the-shelf' wireless devices a standard 100mW access point with a given antenna gain at both ends. A receiver sensitivity of about -83dB is assumed.

 

Effective Gain Line of sight range for 2.4GHz
(20db UK power limit)		 Line of sight range for 5.4GHz
(30db UK power limit)

0dB

200m

280m

4dB

440m

620m

7dB

620m

868m

10dB

1.25Km

1.75Km

13dB

2.8Km

5Km

16dB

5Km

7Km

20dB

12.5Km

17.5Km

24dB

31Km

43Km

 

  • Effective gain takes into account the antenna gain and also any losses in cabling. For instance if you have a 12dB antenna but lose 5dB in the cable to it, then you have an effective gain of 7dB.

  • The table should only be used as a rough guide, we are not promising that you will achieve these numbers, nor that the figures represent maximum or minimum limits.

  • Please also see our article about line-of-sight signal propagation.

  • You should ensure that you do not exceed any legal power density limits which apply in your region.

  • Metal external antennas can make good lightning conductors! Consider what equipment you are putting at risk if you choose not to invest in a lightning arrester.

  • The distance figures for 5GHz operation may not look that much better when compared to 2.4GHz but it's worth remembering that the permitted power output levels for 5GHz are 10 times those for 2.4GHz wireless (100mW vs 1W)! That means, if you stick to the legal power limits, then the practical range for 5GHz devices is further than the equivalent 2.4GHz equipment. Unfortunately, in the real world very few people stick to legal RF power limits so you will often find people using 2.4GHz outdoor units over huge distances.

 

Antenna Gain

Q. How does an antenna produce gain?
A. By focusing the available radio energy in one direction.

Q. OK, so how can an 'omni-directional' antenna have gain?
A. Because it radiates around itself in a disc pattern, stealing power from above and below.

The above Q&As should help you get a feel for the radiation pattern for different types of antennas. A 0dB antenna radiates equally over a complete sphere. Bearing in mind that 3dB represents a doubling of radiated power, you could imagine a 3dB directional antenna radiating its signal into one half of that sphere. A 3dB omni-directional antenna would have a radiation pattern in the shape of a sphere with a cone removed from the top and bottom.

11n/ac/ax MiMo Receivers

Unlike the older 11a or g standards, the successor WiFi standards have the capabilities to use multiple streams for sending/receiving signals. For example,11n modes greater than 150Meg use using multiple streams spread over different antenna. 11ac uses 80Meg channels with 433Mbps per channel. There are several advantages with breaking the signal up like this and different modes implement the signal differently: Some modes send the same stream over each antenna in order to improve signal reliability. Other modes split the data stream in order to improve throughput. The way the signal is split or implanted is set by the MCS number but normally this would be left as 'Auto' - let the wifi units sort out the mode which is best for speed and stability.

 

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