Industrial Dual-RF Wireless Communications with Rapid Recovery
Radio interference has
been and always will be a major concern for
wireless applications. In a wireless environment,
data transmission is over the air and due to
the characteristics of this medium, a very different
type of technical knowledge is required to ensure
a reliable wireless connection.
Because interference normally occurs at a particular frequency, if two or more different frequencies are used to communicate at the same time, then data transmission can continue even if there is interference on one of the frequencies.
Traditional Single-RF Wireless Architecture
The standard architecture of wireless infrastructures
includes access points (AP) that connect many
Clients to an Ethernet network. Since the APs
and Clients are connected by a single-RF connection,
if the RF connection fails, the system and network
behind the Client will be disconnected.
Fig. 1: Traditional Single-RF Wireless Architecture
The Latest Dual-RF Wireless Architecture
In this case, two independent RF modules are
used to form independent wireless connections
with different frequencies to avoid interruptions
in transmission.
To achieve network redundancy without needing to change the existing architecture of your wireless LAN, APs and Clients that support dual RFs can be used (usually, the two RFs are set to 2.4 GHz and 5 GHz to prevent interference)
Fig. 2: Dual-RF Architecture
Moxa's Dual-RF Redundancy
Moxa raises the bar by providing not one but
two RF modules to enable two independent wireless
connections. Moxa's AWK-5222 series products
are rugged, IEEE 802.11a/b/g-compliant, 3-in-1
industrial wireless AP/Bridge/Clients that are
equipped with the newest proprietary wireless
redundancy technology. The AWK offers a greater
variety of wireless connection configurations
for creating the most robust wireless connection
for your critical industrial wireless applications.
To achieve reliability that is
beyond wireless redundancy, Ethernet redundancy
is also very important. This is why AWK series
products have two Ethernet ports, and support
RSTP (Rapid Spanning Tree Protocol) and Turbo
Ring™ for the Ethernet side of the connection.
Thanks to Moxa's Dual-RF wireless redundancy
topology, configuring the frequency is easy,
versatile, and offers superior reliability.
Assorted Operational Modes to Fit Your Applications
The AWK series provides a variety of wireless operation modes and can essentially create any type of topology to fit your applications.
Dual-RF Redundancy Mode
You can set up two independent wireless connections between the redundant AP and redundant client devices. Usually, these 2 RFs are set to 2.4 GHz and 5 GHz to prevent interference. If one of the two wireless connections fails, the other connection will continue providing service between the redundant AP and redundant client devices.
Configuration is easy and straightforward. All you need to do is set up a redundant AP on the AP side and a redundant Client on the client side, and then set a different SSID for each RF. The following figure shows the Web console UI for Moxa's AWK-5222, in which WLAN1 is set to SSID1 and WLAN2 is set to SSID2.
Fig. 3: Dual-RF—Wireless Redundancy Mode
In addition to being able to serve one or more redundant clients, the redundant AP can also serve one or more traditional single RF Clients at the same time.
Fig. 3: Dual-RF—Wireless Redundancy Mode plus Single-RF Connection
Wireless Bridge Mode
The AWK offers another dual RF feature, called wireless bridge mode, in which WLAN 1 is configured as the "master AP" and WLAN 2 as the "slave client." The mode will not reduce the bandwidth but will extend the wireless range. More importantly, this is designed to optimize the WDS (Wireless Distribution System) mode in light of its throughput performance. WDS mode's normal throughput is 25 Mbps/(n-1), in which n is the number of WDS nodes. For example, if there are 4 mesh nodes, the throughput is around 8 Mbps.
The AWK's wireless bridge mode can upgrade the throughput from 10 to 15 Mbps. This way, the performance of each bridge connection will remain the same.
AP-Client Connection Mode
Most WLAN applications use infrastructure mode. In AP-client mode, a wireless AP is required to set up a basic infrastructure service set (BSS) for wireless connectivity. The AP can be used by itself to set up a WLAN, or can be used to connect the WLAN to a wired network. The AWK-5222 supports AP-client connections, which can be used to provide Internet access in areas where cabling would be too expensive or impractical to install.
AP-Client Operation
Moxa's Industrial Dual-RF Solution Quick Take:
- Redundant dual-RF design for rapid failover and to ensure that data is transmitted
- IEEE 802.11a/b/g compliant
- EN50155, EN50121-3-2, and EN50121-4 certified for applications in harsh environments that are subjected to EMC interference, vibration, and shock.
- 100 ms proprietary Turbo Roaming™ for rapid handover during client roaming
- Versatile operation modes
- Long-distance data transmission; over 10 km
- RSTP for dual Ethernet redundancy and to prevent looping
- Seamless network connectivity
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