What is the Difference Between 2.4GHz and 5GHz Wireless LAN in Industrial Applications?

 

by: Rolf Nilsson, CEO connectBlue

As the use of wireless technologies is increasing in the process and manufacturing industry, so is the installed base of IEEE 802.11b/g/n products that operate in the worldwide free 2.4GHz ISM band. Besides Wireless LAN IEEE 802.11b/g/n, other wireless technologies like Bluetooth technology, IEEE 802.15.4/ ZigBee/Wireless HART and several proprietary technologies operate in the 2.4GHz band.

With so many technologies crowding the same frequency band, interference problems can occur. To make sure that industrial wireless solutions are robust, there are basically two solutions: either to carry through extensive frequency planning and use special antenna solutions (like leakage cables) in the industrial 2.4GHz setting, or to use the 2.4GHz band for office and IT communication and then use the 5GHz band for the manufacturing and M2M communication.

Differences in Channels and Usage for the 2.4 and 5GHz Bands

The Wireless LAN IEEE 802.11b/g radios utilize the 2.4GHz frequency band (2.412 – 2.472GHz) and the IEEE 802.11a radio utilizes the 5GHz frequency band (5.180 – 5.825GHz). IEEE 802.11n radios can operate in either frequency band. There are the following worldwide implementation attributes:

  • The 2.4GHz ISM band provides 13 overlapping channels spread equally over the frequencies plus a 14th channel used in Japan with the center frequency 2.484GHz. This leaves available only three non-overlapping channels in the 2.4GHz band. In order to avoid interferences between the Wireless LAN connected devices, these channels have to be used very efficiently Installation requires careful frequency planning or expensive installation of solutions such as leakage cables. In other words, the installation costs can easily become higher than the actual wireless equipment installed.
  • The 5GHz ISM band is divided up into sub-bands called U-NII bands (Unlicensed National Information Infrastructure) and are usually named U-NII-1, U-NII-2, U-NII-2e, and U-NII-3 where U-NII-3 is not freely available worldwide. In total, this gives 23 non-overlapping channels where four of these have limitations based on location*. Today, most available Wireless LAN solutions in the 5GHz band use the U-NII-1 band (5.18-5.24 GHz) with frequency channels 36-48. However, there are also some suppliers that have extended the range to include the U-NII-2/2e band (5.26-5.70 GHz) with frequency channels 52-140.

Channel

U-NII Band

Frequency (MHz)

United States
40/20 MHz

Europe
40/20 MHz

36

1

5180

Yes

Yes

38

1

5190

No

No

40

1

5200

Yes

Yes

42

1

5210

No

No

44

1

5220

Yes

Yes

46

1

5230

No

No

48

1

5240

Yes

Yes

52

2

5260

Yes

Yes

56

2

5280

Yes

Yes

60

2

5300

Yes

Yes

64

2

5320

Yes

Yes

100

2e

5500

Yes

Yes

104

2e

5520

Yes

Yes

108

2e

5540

Yes

Yes

112

2e

5560

Yes

Yes

116

2e

5580

Yes

Yes

120

2e

5600*

No

Yes

124

2e

5620*

No

Yes

128

2e

5640*

No

Yes

132

2e

5660*

No

Yes

136

2e

5680

Yes

Yes

140

2e

5700

Yes

No

149

3

5745

Yes

No

153

3

5765

Yes

No

157

3

5785

Yes

No

161

3

5805

Yes

No

165

3

5825

Yes

No

Caption 1: Table of U-NII bands in the 5GHz frequency band. (ref. www.wikipedia.com)

Pros and Cons of the 2.4GHz and 5GHz Standards

Wireless LAN IEEE 802.11b/g/n is already well-established with its huge installed base and a wide range of products made available. Besides its wide use, the 2.4GHz band offers the advantage of operating in a worldwide available ISM band. Further, the achieved range using the same output power is better on 2.4GHz compared to radios using the higher frequency 5GHz band.

As shown in the table above, the entire 5GHz ISM band is not available for use worldwide. Further, availability of components and products are still somewhat limited compared to the 2.4GHz band.

The greatest strength of the 5GHz band is the availability of 23* non-overlapping channels; 20* more channels than what is available in the 2.4GHz band. Since there is no other wireless technology that "fights" for the radio space, the 23* available non-overlapping channels can provide a possibility for easier planning of an interference-free and stabile wireless communication. Another advantage of the 5GHz band is that the greater number of available channels provides for increased density, which means that more wireless devices can be connected in the same radio environment.

5GHz Band Radar Detection – Dynamic Frequency Selection (DFS)

The use of Wireless LAN in the U-NII-2/2e bands (channel 52 -140, frequency range 5.260––5.725GHz) requires radar detection. Within the operation context of the Dynamic Frequency Selection (DFS) function, a device shall operate as either a master or a slave. The requirements for a slave device, which is typically a client in an infrastructure, are as follows:

  • A slave device shall not transmit data before receiving an appropriate enabling signal from a master device.
  • A slave device shall stop all its data transmissions whenever instructed by a master device.
  • Devices operating as a slave shall only operate in a network controlled by a device operating as a master.

Requirements for a master device, which is typically an access point or a master in an ad-hoc mode network, are different from the requirements for a slave device. The requirements for a master device are as follows:

  • A master device shall detect radar signals.
  • A master device shall only start operations on available channels.
  • During normal operation, a master device shall monitor the operating channel (in-service monitoring).
  • If a master device has detected a radar signal during in-service monitoring, the master device shall instruct all its associated slave devices to stop transmitting on this channel.

Some devices are capable of communicating in an ad-hoc manner without being attached to a network. Ad-hoc devices form a point-to-point communication channel, with one of the devices taking the role of master and therefore taking on the requirement for DFS and all of the applicable requirements for a master.

Range and Performance

The radio wave length in the 5GHz band is half of the wave length in the 2.4GHz band. And as a consequence, a radio module using the 5GHz band will have a narrower range than a radio operating on the 2.4GHz band using the same output power. How much less the range will be is hard to predict as it depends on the radio conditions at the location in consideration. Further, diverse materials absorb frequencies differently which also in turn affects the range dramatically.

In order to learn the exact range, the solution has to be tested live.

Tests in factories in the 5GHz band have shown that the range can be between 50 meters up to 100 meters in free line-of-sight. Obstacles, interference, materials and use of large data packages can decrease the range substantially.

Caption 2: connectBlue offers two Wireless LAN Rugged Ethernet Port Adapters – one for the 2.4 GHz band and one for the 5GHz band. These ready-to-use wireless devices are especially well-suited for mobile, rotating and temporary installations where there is a need for replacing the Ethernet cable with a robust and maintenance-free wireless connection, or to connect to a Wireless LAN infrastructure.

Caption 3: Today, most available Wireless LAN solutions in the 5GHz band use the U-NII-1 band (5.180-5.24 GHz) with channels 36-48. connectBlue Wireless LAN products have extended the range to include the U-NII-2/2e band (5.260-5.725 GHz) with channels 52-140*. One of the products that offer the expanded frequency channel range is the Wireless LAN SPI Module OWL253.


Summary

By using the 5GHz band for Wireless LAN communication, a number of advantages and cost decreases can be achieved. By adding 23* possible Wireless LAN channels, frequency planning, density (the number of active wireless devices within the radio coverage space) and the installation complexity can be dramatically improved. An extra bonus would be the freeing up of the 2.4GHz band for other radio technologies.

These advantages together with increasing availability of 5GHz industrial products will increase the use of the 5GHz band greatly in the near future. Up till now, the use of the 5GHz band in industrial applications has been more or less limited to products such as smaller access points and small compact clients (based on the same platforms as the access points). Already available on the market are OEM wireless modules for integration in various industrial products as well as serial Wireless LAN clients for integration of smaller devices and existing serial communication based products.

*) For FCC channels 120 – 132, use is restricted near airports due to the interference risk of the Terminal Doppler Weather Radar (TDWR). (ref. FCC KDB 443999). Canada requires a restriction on the channels 120 – 128.

About connectBlue

connectBlue® is a leading provider of robust Industrial and Medical wireless solutions , designed and tested for the most demanding applications and environments. Based on Classic Bluetooth technology, Bluetooth low energy technology, Wireless LAN (WLAN) and IEEE 802.15.4 / ZigBee, connectBlue provides ready-to-use products and modules as well as custom design solutions. connectBlue has its head office in Sweden and local offices in Germany and USA. For more information, please visit  www.connectblue.com.

connectBlue® is a registered trademark of connectBlue AB.

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