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Understanding Practical Ethernet Commissioning

When choosing which type of industrial wireless Ethernet to commission for

your application, several aspects should be considered...

Which Wireless Ethernet Is Right For My Application?

There are several factors which should be considered when

choosing which industrial wireless Ethernet is right for your

application: of course country speciﬁc regulatory requirements

are foremost.

Reliable Communications Distance

Reliable wireless Ethernet communications is fundamentally

determined by a few key factors: the amount of Radio

Frequency (RF) power emitted from the antenna (government

regulated), the lowest level that the receiving module can

reliably demodulate (ie receiver sensitivity) and the frequency

waveform properties relative to the terrain over the distance

required of the application.

Alternative products RF power and receiver sensitivity are ﬁxed

in manufacturing. When choosing a wireless product, care

should be taken to compare the amount of RF power and the

receiver sensitivity of alternate product options.

Frequency and Terrain

Radio signals are transmitted between the sending and

receiving units. The radiated radio signals form an elliptical

path of concentric circles known as a Fresnel zone. The radio

path may be described as either obstructed or line of sight.

It is the level of obstruction relative to the frequency waveform

and its Fresnel zone that determines the success level of

communications. Higher frequencies such as 2.4 and 5GHz

have smaller waveforms and can be susceptible to obstructed

paths. 2.4GHz waveforms are relatively less susceptible due

their bigger size but may suffer from congestion in the 2.4GHz

spectrum.

RF Power

Receiver

Sensitivity

Fresnel Zone

Terrain

Distance

Image demonstrates the Fresnel zone between two antennas over the

distance required of the application. It is the amount of obstruction relative to

the waveform Fresnel zone (and other factors) that determines success.

What causes congestion in the 2.4GHz band?

The IEEE 802.11 standard speciﬁes the number/separation of

channels in the 2.4 and 5 GHz spectrums. Country regulations

dependent, the 2.4 GHz 802.11b/g IEEE standard uses up to 14

channels with only three non-overlapping channels (1, 6, 11).

With the overhead and communication frames of the 802.11

standard, shared channels can create an RF environment

which can be heavily congested when multiple 2.4 GHz

systems are within hearing/receiving range of each other.

* Channel

* Center Frequency (GHz)

2.412

2.417

2.422

2.427

2.432

2.437

2.442

2.447

2.452

2.457

2.462

2.467

2.472

2.484

1 Turbo Channel (40MHz: 108Mbps)

Image shows 2.4 GHz shared channels; 1, 6 and 11 are non-overlapping.

The 802.11 5GHz Spectrum

The IEEE 802.11a (5 GHz) standard speciﬁes, country

regulation dependent, up to 24 non-overlapping channels.

There also can be additional radiated power (ie EIRP) from the

antenna allowing greater distance Ethernet communications.

20MHz

5.18

5.20

5.22

5.24

5.26

5.28

5.30

100

5.32

104

5.50

5.52

108

112

116

5.54

5.56 5.58

120

* Channel

* Center Frequency (GHz)

124

128

5.60

5.62

132

5.64

5.66

136 140

5.68

149

5.70

5.745

153

157

161

5.765

5.785

5.805

165

5.825

1 Turbo Channel

(40MHz: 108Mbps)

2 Turbo Channels

(40MHz: 108Mbps)

Image shows 5 GHz spectrum with up to 24 non-overlapping channels.

Data Rate Throughput and Modulation

The IEEE 802.11 standard has ratiﬁed four modulation

techniques since 2007 including: 802.11 a, b, g and n.

Standard Frequency Data Rate

802.11b 2.4 GHz 1-11 Mbps

802.11g 2.4 GHz 6-54 Mbps

802.11a 5.0 GHz 6-54 Mbps

802.11n 2.4 GHz 6-200+ Mbps

The respective modulation techniques range from single to

multi-spatial dimensional transmissions; particularly 802.11n

which requires multiple antenna arrays. The 802.11 a, g

standards allow for data throughputs to 108Mbps in turbo

mode. However these standards do not use the antenna arrays

of 802.11 n and are therefore more readily commissioned over

distance applications.

In summary the above considerations should be taken into

account when deploying industrial wireless Ethernet in your

application.

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