This article expands on a Wireless Application Guidelines article providing an overview of EtherNet/IP operation in a wireless environment. It focusses on the Radio Frequency attributes and configurations recommended to give the best chance of success. The first requirement for successful wireless deployment is a complete site survey, and cooperation on bandwidth management between IT and Operational disciplines.
1. Wireless Spectrum
5 GHz frequency band is recommended for industrial wireless applications. Because of limited number of channels and much higher chance of interference, the 2.4 GHz band is not recommended to use for critical Industrial Automation Control Systems (IACS) applications, such as machine control. However, 2.4 GHz band can be used for personnel access and low throughput non-critical applications
Number of available channels and existing bandwidth utilization is the critical factor when implementing wireless IACS applications.
Proper spectrum management policy and coordination between IT, OEM, and controls engineers is critical.
As the rules constantly change, refer to the local regulatory authority and product documentation for the most recent compliance information and channel availability in a particular country.
Use only channels 1, 6, and 11 in the 2.4 GHz band. Use of non-standard channels or more than 3 channels in 2.4 GHz band will cause adjacent channel interference and lower throughput.
Use non-DFS (Dynamic Frequency Selection) channels in 5 GHz band when possible.
If DFS channels are used, thorough site survey and subsequent monitoring of DFS channels is required before and after the installation. Particular caution should be used when operating near airports, sea ports, military bases, or large cities.
RF spectrum analysis is critical for IACS applications with high bandwidth utilization and low latency requirements. Adequate time should be spent analyzing the channels to detect intermittent interference.
Many sources of interference are intermittent, and new sources may appear over time. It is important to proactively monitor for radio interference in the industrial environment, before and after the deployment.
Properly defined and enforced spectrum policy on site is critical for interference prevention.
2. Wireless Coverage
Access Point coverage area where desired data rate can be supported depends on many factors and can only be determined during the site survey. Changes in the environment and interference levels also dynamically change the coverage.
For EtherNet/IP applications, recommended parameters that should be maintained in the coverage area are:
- Minimum RSSI of -67 dBm
- Minimum SNR of 25 dB
For CIP Sync traffic, the cell coverage area should be designed to sustain 54 Mbps data rate.
Professional site survey is critical for WLAN implementation.
3. RF Parameters
Spatial Division Multiplexing has limited benefit for the real-time EtherNet/IP traffic. Multiple spatial streams make communication less reliable, dependent on higher SNR, and more susceptible to multipath fading. Single spatial stream is more suitable for control communication.
20 MHz channel width (no channel bonding) is recommended with IACS applications.
Frame aggregation can be beneficial for point-to-point type of communication, or with small number of nodes. The positive or negative effect of aggregation should be determined in the application testing.
Configure 6, 12, 24, 54 Mbps data rates as basic, and disable other legacy rates
It is not always desirable to use the maximum transmit power in the cell. Limiting transmit power creates smaller coverage cell size with less signal propagation outside the intended area and less chance for distant clients to join the AP.
Channel allocation scheme should provide maximum distance separation between same channels, if possible.
Proper spectrum management policy and coordination between IT, OEM, and control engineers is critical.
Dynamic RF configuration with Radio Resource Management (RRM) in Unified WLAN is not recommended:
- RRM can be used during an initial site survey to determine channels and power settings and optionally during maintenance periods to check settings.
- RRM can be used for slow applications that can tolerate gaps of 60ms, however testing is recommended. Static channel assignment is also recommended. Roaming time will be increased by 60ms as well.
To learn more about recommendations for EtherNet/IP in wireless, sign up for the Industrial IP Advantage industrial network design training here