Silicon Labs UG103.17 User Manual
UG103.17: Wi-Fi® Coexistence Fundamentals
This document describes methods to improve coexistence of 2.4
GHz IEEE 802.11b/g/n Wi-Fi and other 2.4 GHz radios such as
Bluetooth®, Bluetooth Mesh, Bluetooth Low Energy, and IEEE
802.15.4-based radios such as Zigbee® and OpenThread. These
techniques are applicable to the EFR32MGxx and EFR32BGxx
families.
Silicon Labs’ Fundamentals series covers topics that project managers, application designers, and developers should understand before beginning to work on an embedded
networking solution using Silicon Labs chips, networking stacks such as EmberZNet PRO
or Silicon Labs Bluetooth®, and associated development tools. The documents can be
used as a starting place for anyone needing an introduction to developing wireless networking applications, or who is new to the Silicon Labs development environment.
For additional details about the implementation of managed coexistence for EFR32 devices refer to the following application notes:
• AN1128: Bluetooth® Coexistence with Wi-Fi®
• AN1017: Zigbee® and OpenThread Coexistence with Wi-Fi®
• AN1243: Timing and Test Data for EFR32 Coexistence with Wi-Fi (available under
non-disclosure from Silicon Labs Sales).
KEY POINTS
• Wi-Fi impact on Bluetooth, Zigbee, and
OpenThread (802.15.4) radios
• Improving unmanaged coexistence
• Improving managed coexistence
• Summary points for Wi-Fi and Bluetooth
and Wi-Fi and 802.15.4 coexistence
For evaluating the Silicon Labs EFR32 software coexistence solution, order EFR32MG
Wireless SoC Starter Kit (WSTK) #SLWSTK6000B and Coexistence Backplane EVB
(#SLWSTK-COEXBP). Detailed instructions for using the Starter Kit and Backplane EVB
are found in UG350: Silicon Labs Coexistence Development Kit (SLWSTK-COEXBP). To
see a demonstration of Wi-Fi coexistence, access links for ordering the WSTK and EVB,
and to download additional coexistence documentation, visit the
istence Learning Center.
Silicon Labs Wi-Fi Coex-
silabs.com | Building a more connected world. Rev. 0.2
UG103.17: Wi-Fi® Coexistence Fundamentals
Introduction
1 Introduction
The 2.4 GHz Industrial, Scientific and Medical (ISM) band supports Wi-Fi, Bluetooth, and 802.15.4. The simultaneous and co-located
operation of these different 2.4 GHz radio standards can degrade performance of one or more of the radios. To improve interference
robustness, each of the 2.4 GHz ISM radio standards support some level of collision avoidance and/or message retry capability. At low
data throughput rates, low power levels, and/or sufficient physical separation, these 2.4 GHz ISM standards can co-exist without significant performance impacts. However, recent customer trends are making coexistence more difficult:
• Increased Wi-Fi transmit power level for “extended range.”
+30 dBm Wi-Fi Access Points are now common.
• Increased Wi-Fi throughput.
Depending on achievable Signal-to-Noise Ratio (SNR), high throughput requirements for file transfers and/or video streaming may
result in high Wi-Fi duty cycle within the 2.4 GHz ISM band.
• Integrating Wi-Fi, Bluetooth, and 802.15.4 into the same device for gateway functionality.
This is required by Home Automation and Security applications and provides easier end-node commissioning.
This document note includes three sections:
• Section 2 Wi-Fi Impact on Bluetooth and 802.15.4 Radios provides general information on Bluetooth and 802.15.4 channel mapping.
• Section 3 Unmanaged Coexistence describes design considerations to improve coexistence without direct interaction between Blue-
tooth, 802.15.4, and Wi-Fi radios.
• Section 4 Managed Coexistence describes the Silicon Labs Packet Traffic Arbitration (PTA) support to coordinate 2.4 GHz RF traffic
for co-located Bluetooth, 802.15.4, and Wi-Fi radios. PTA support is available for the EFR32MGx only.
Note: Zigbee and Thread devices (802.15.4) operate at less than +20 dBm transmit power level. With normal network activity,
Zigbee/Thread solutions have a relatively low RF duty cycle and Bluetooth solutions implement Adaptive Frequency Hopping
(AFH). Silicon Labs’ testing of Bluetooth blocked by Zigbee/Thread shows low impact on Bluetooth with AFH enabled and normal
Zigbee/Thread network activity. However, if 100% RF duty cycle, Zigbee/Thread can degrade co-located Bluetooth performance.
silabs.com | Building a more connected world. Rev. 0.2 | 2
UG103.17: Wi-Fi® Coexistence Fundamentals
Wi-Fi Impact on Bluetooth and 802.15.4 Radios
2 Wi-Fi Impact on Bluetooth and 802.15.4 Radios
Worldwide, Wi-Fi supports up to 14 overlapping 20/22 MHz bandwidth channels across the 2.4 GHz ISM band with transmit power levels
up to +30 dBm. Bluetooth supports 40 non-overlapping channels at 2 MHz spacing with transmit powers up to +20 dBm (Bluetooth Core
Specification v5.0). IEEE 802.15.4 supports 16 non-overlapping 2 MHz bandwidth channels at 5 MHz spacing with transmit powers up to
+20 dBm. The Bluetooth and 802.15.4 channel mappings are shown in the following figure, where yellow highlighted channels are the
three Bluetooth advertising (ADV) channels.
Figure 2-1. Wi-Fi, Bluetooth, and 802.15.4 Channel Mapping (World-Wide)
Actual channels available vary by country. For example, in the USA, only Wi-Fi channels 1 through 11 are available. Bluetooth channels
0 through 39 are available worldwide and Zigbee channels 11 through 26 are available, although channels 25 and 26 require reduced
transmit power levels to meet FCC requirements (North America only).
2.1 Impact of a 100% Duty-Cycled Wi-Fi
Silicon Labs completed testing to understand the effects of Wi-Fi on Bluetooth and 802.15.4 radios. The following subsections summarize
the key findings and results from this testing.
2.1.1 Bluetooth
To better understand the effects of Wi-Fi on Bluetooth, Silicon Labs measured the impact of a 100% duty-cycled 802.11n (MCS3, 20 MHz
bandwidth) blocker transmitting at various power levels while receiving a Bluetooth 1Mbps 37-byte payload message transmitted at power
level sufficient to achieve 0.1% BER (receive sensitivity). The results for co-channel, adjacent channel, and “far-away” channels are
shown in the following figure. All 802.11n and Bluetooth power levels are referenced to the Silicon Labs EFR32MG21 RF input. The test
application was developed using the Silicon Labs Bluetooth 2.11.0 or later stack with the soc-dtm sample application running on the
EFR32 DUT (Device Under Test) and a test script to control the DUT and RF test equipment.
silabs.com | Building a more connected world. Rev. 0.2 | 3
UG103.17: Wi-Fi® Coexistence Fundamentals
Wi-Fi Impact on Bluetooth and 802.15.4 Radios
Figure 2-2. Bluetooth Low Energy Receive Sensitivity with 100% Duty-Cycled 802.11n (MCS3/20 MHz) Wi-Fi Blocker
From the figure above, the key observations about the impact of Wi-Fi (channel 1, MCS3/20 MHz) on Bluetooth are:
Co-Channel (Bluetooth overlapping Wi-Fi):
• For Bluetooth RF channels 0 through 10, EFR32MG21 can receive a Bluetooth 1Mbps signal at 4 dB weaker than aggregate Wi-Fi
transmit power (100% duty cycle).
• This receive sensitivity limitation impacts both co-located and remote, not co-located, Bluetooth radios.
Adjacent Channel (Bluetooth within one Wi-Fi bandwidth):
• At Bluetooth RF channel 11, EFR32MG21 can receive a -90 dBm Bluetooth 1Mbps with -40 dBm or weaker Wi-Fi transmit power
(100% duty cycle).
“Far-Away” Channel (Bluetooth beyond one Wi-Fi bandwidth):
• At Bluetooth RF channels 19 through 39, EFR32MG21 can receive a -96 dBm Bluetooth 1Mbps signal with -40 dBm or weaker Wi-Fi
transmit power (100% duty cycle).
In a real-world environment, Wi-Fi is typically not 100% duty cycle and only approaches 100% duty cycle during file transfers or video
stream in low Wi-Fi SNR conditions. As seen in the previous figure, the EFR32xGxx receive sensitivity varies as the Wi-Fi blocker turns
ON/OFF. The net result is the ability to see weaker signals when Wi-Fi is OFF, but not when strong Wi-Fi is ON (actively transmitting).
silabs.com | Building a more connected world. Rev. 0.2 | 4
UG103.17: Wi-Fi® Coexistence Fundamentals
EFR32 Bluetooth Device
Wi-Fi Impact on Bluetooth and 802.15.4 Radios
The following figure illustrates the receive range of a node (blue node) near a strong Wi-Fi transmitter. Relative to the blue Bluetooth
node, the area inside the green circle represents the receive range when Wi-Fi is ON. The area between the green and yellow circles
represents the receive range when Wi-Fi is OFF. From this figure:
• The green node is always receivable by the blue node.
• The yellow node is only receivable by the blue node when Wi-Fi is OFF.
• The red node is never receivable by the blue node.
• The yellow and red nodes are always receivable by the green node.
EFR32 Bluetooth
Bluetooth Device
Bluetooth Device
Bluetooth Device
EFR32 Bluetooth
Figure 2-3. EFR32 Receiver Desensitized when Wi-Fi Transmitting
Depending on each Bluetooth device’s TX level, RX sensitivity vs. blocker, channel, and relative attenuation and Wi-Fi TX level and duty
cycle, the impact of strong Wi-Fi turning ON/OFF will vary. Based on the figure above, the following example assumes:
• Wi-Fi co-located with Blue device
• Bluetooth channel is “far-away” (RF channel 39) from Wi-Fi channel (channel 1), indicating minimum Bluetooth RX sensitivity vs. Wi-
Fi RX levels:
• Typical radio TX levels:
silabs.com | Building a more connected world. Rev. 0.2 | 5
UG103.17: Wi-Fi® Coexistence Fundamentals
Wi-Fi Impact on Bluetooth and 802.15.4 Radios
• Attenuation between radios
• Bluetooth device RX success/fail with Wi-Fi OFF:
• Bluetooth device RX success/fail with Wi-Fi ON:
For Figure 2-3
using the example assumptions, all radio communication is maintained between Wi-Fi ON/OFF except:
• Blue device receives yellow device when Wi-Fi ON, but not Wi-Fi OFF.
• Green device receives red device when Wi-Fi ON, but not Wi-Fi OFF.
If devices are Bluetooth devices (point-to-point), blue device communication with:
• Green device is not impacted by Wi-Fi TX.
• Yellow device is erratic as Wi-Fi TX goes ON/OFF.
• For high-duty cycle Wi-Fi TX, connection can become unstable as multiple connection intervals fail.
• Red device is not possible.
If devices are Bluetooth mesh devices (mesh network), blue device communication with:
• Green device is not impacted by Wi-Fi TX.
• Yellow device shows erratic communication as Wi-Fi TX goes ON/OFF.
• For high-duty cycle Wi-Fi TX, communication would require a relay to forward/repeat missed RX messages from yellow device
to blue device.
• Red device is not directly possible, and a relay is required to forward messages between blue device and red device.
• If green device is relay, communication with red device shows erratic communication as Wi-Fi TX goes ON/OFF.
• If yellow device is relay, communication with red device is not impacted by Wi-Fi TX.
silabs.com | Building a more connected world. Rev. 0.2 | 6
UG103.17: Wi-Fi® Coexistence Fundamentals
Wi-Fi Impact on Bluetooth and 802.15.4 Radios
2.1.2 802.15.4
To better understand the effects of Wi-Fi on 802.15.4 radios, Silicon Labs measured the impact of a 100% duty-cycled 802.11n (MCS3,
20 MHz bandwidth) blocker transmitting at various power levels while receiving an 802.15.4 message transmitted at power level sufficient
to achieve 1% PER (receive sensitivity). The following figure shows the results for co-channel, adjacent channel, and “far-away” channel.
All 802.11n and 802.15.4 power levels are referenced to the Silicon Labs’ EFR32MG21 RF input. The test application was developed
using Silicon Labs’ EmberZNet PRO (Zigbee) stack with NodeTest running on the EFR32 DUT (Device Under Test) and a test script to
control the DUT and RF test equipment.
Figure 2-4. 802.15.4 Receive Sensitivity with 100% Duty Cycled 802.11n (MCS3/20 MHz) Wi-Fi Blocker
These are the key observations about the impact of Wi-Fi on 802.15.4 from the figure above.
Co-Channel (Zigbee overlapping Wi-Fi):
• At channel 12, Zigbee can receive an 802.15.4 signal down to 9 dBm weaker than aggregate Wi-Fi transmit power (100% duty cycle).
• This receive sensitivity limitation impacts both co-located and remote, not co-located, 802.15.4 radios.
• At channel 12, Zigbee with and without LNA (Low Noise Amplifier) can receive an 802.15.4 signal down to 9 dB weaker than aggregate
Wi-Fi transmit power (100% duty cycle).
• 802.15.4 transmits can also be blocked by Wi-Fi transmit power tripping the 802.15.4 -75 dBm CCA (Clear Channel Assessment)
threshold.
Adjacent Channel (Zigbee within one Wi-Fi bandwidth):
• At channel 15, Zigbee can receive a -87 dBm 802.15.4 signal with -30 dBm or weaker Wi-Fi transmit power (100% duty cycle).
• Maximum receive sensitivity is attained at -38 dBm or weaker Wi-Fi transmit power (100% duty cycle).
• At channel 15, Zigbee without LNA can receive a -87 dBm 802.15.4 signal with -30 dBm or weaker Wi-Fi transmit power (100% duty
cycle); -34 dBm or weaker with LNA enabled.
“Far-Away” Channel (Zigbee beyond one Wi-Fi bandwidth):
• At channels 17 through 26, Zigbee can receive a -96 dBm 802.15.4 signal with -30 dBm or weaker Wi-Fi transmit power (100% duty
cycle).
• Maximum receive sensitivity is attained at -40 dBm or weaker Wi-Fi transmit power (100% duty cycle).
• At channels 17 through 26, Zigbee without LNA can receive a -96 dBm 802.15.4 signal with -30 dBm or weaker 100% Wi-Fi transmit
power (100% duty cycle); -34 dBm or weaker with LNA enabled.
silabs.com | Building a more connected world. Rev. 0.2 | 7
UG103.17: Wi-Fi® Coexistence Fundamentals
802.15.4 Node
EFR32MGx
802.15.4 Node
802.15.4 Node
EFR32MGx
802.15.4 Node
Wi-Fi Impact on Bluetooth and 802.15.4 Radios
In a real-world environment, Wi-Fi is typically not 100% duty cycle and only approaches 100% duty cycle during file transfers or video
stream in low Wi-Fi SNR (Signal to Noise Ratio) conditions. As seen in the figure above, the EFR32xGxx receive sensitivity varies as the
Wi-Fi blocker turns ON/OFF. The net result is the ability to see weaker signals when Wi-Fi is OFF, but not when strong Wi-Fi is ON
(actively transmitting).
The following figure illustrates the receive range of a node (blue node) near a strong Wi-Fi transmitter. Relative to the blue 802.15.4 node,
the area inside the green circle represents the receive range when Wi-Fi is ON. The area between the green and yellow circles represents
the receive range when Wi-Fi is OFF. From this figure:
• The green node is always receivable by the blue node.
• The yellow node is only receivable by the blue node when Wi-Fi is OFF.
• The red node is never receivable by the blue node.
• The yellow and red nodes are always receivable by the green node.
Always Receivable
Wi-Fi ON or OFF
Receive Range
with Wi-Fi ON
Only Receivable
Wi-Fi OFF
Never Receivable
Wi-Fi ON or OFF
Receive Range
with Wi-Fi ON
Figure 2-5. EFR32MGx Receiver Desensitized when Wi-Fi Transmitting
Depending on each node’s type (Coordinator, Router, or End Device) and the Wi-Fi duty cycle, the impact of strong Wi-Fi turning ON/OFF
will vary.
In a Zigbee network:
• Coordinator: Tasked with network creation, the control of network parameters, and basic maintenance, in addition to performing
an application function, such as aggregating data or serving as a central control point or gateway.
• Router: In addition to running an application function, a Router can receive and retransmit data from other nodes.
• End Device: Typically, a battery-powered device (Sleepy End Device or SED) running an application function and able to talk to a
single parent node (either the Coordinator or a Router). End Devices cannot relay data from other nodes.
In an OpenThread network:
• Border Router: Provides network node connectivity to other devices in external networks (for example, Internet access).
• Router: In addition to running an application function, a Router can receive and retransmit data from other nodes and provide join and
security capability. When routing function is not needed by network, a Router can downgrade to a Router-Eligible End Device (REED).
• REED: In addition to running an application function, a REED can receive and retransmit data from other nodes. When additional
routers needed by network, a REED can upgrade to a Router.
• SED: Typically, a battery-powered device running an application function and able to talk to a single parent node (either a Border
Router, Router, or REED). SEDs cannot relay data from other nodes.
Two Zigbee cases are considered below, but many other cases are possible.
Case 1: Zigbee Coordinator near strong Wi-Fi plus three end-nodes
silabs.com | Building a more connected world. Rev. 0.2 | 8
UG103.17: Wi-Fi® Coexistence Fundamentals
Wi-Fi Impact on Bluetooth and 802.15.4 Radios
For this case, the figure above is composed of:
• Coordinator: Blue node
• End Devices: Green, Yellow, and Red nodes
In this simple network, each end device attempts to join the network formed by the coordinator. However, the red node is outside of
receive range and cannot join. With Wi-Fi OFF, both the green and yellow nodes successfully join the network and have no issues sending
messages to the Coordinator. Regardless of Wi-Fi ON/OFF duty cycle, the green node remains successful sending messages to the
Coordinator.
With Wi-Fi ON/OFF at low-duty cycle, some messages from the yellow node are periodically blocked, but Zigbee retry mechanisms are
effective in getting the messages to the coordinator. However, with Wi-Fi ON/OFF at high-duty cycle, many messages from the yellow
node are blocked and Zigbee retry mechanisms may be exhausted. Even when retry mechanisms are successful, the message latency
increases. If the yellow node is a battery-powered Sleepy End Device, it must remain active longer to execute retries, reducing battery
life.
Case 2: Zigbee Coordinator near strong Wi-Fi, Router within always receive range, plus two end-nodes
For this case, the figure above is composed of:
• Coordinator: Blue node
• Router: Green node
• End Devices: Yellow and Red nodes
In this simple network, the green Router forms a route directly to the Coordinator, maintained regardless of Wi-Fi ON/OFF duty cycle.
With Wi-Fi OFF, the yellow node forms a route directly to the blue Coordinator at a lower route cost than a route via the green Router.
The red node cannot be received by the Coordinator and its messages are also routed through the Router to the Coordinator.
With Wi-Fi OFF, the green Router, the yellow node, and the red node (via the green Router) have no issues sending messages to the
Coordinator. Regardless of Wi-Fi ON/OFF duty cycle, the green Router and the red node (via the green Router) remain successful
sending messages to the Coordinator. With Wi-Fi ON/OFF at low-duty cycle, some messages from the yellow node are periodically
blocked, but Zigbee retry mechanisms are effective in getting the messages to the Coordinator.
With Wi-Fi ON/OFF at high-duty cycle, many messages from the yellow node are blocked and Zigbee retry mechanisms may be exhausted. If Wi-Fi ON/OFF stays at high-duty cycle for enough time, the network responds by restructuring the yellow node to route
messages to the Coordinator via the Router. However, this route rediscover takes time and messages may be lost. If Wi-Fi ON/OFF
remains high-duty cycle, the yellow node messages will continue to go through the Router, which forwards messages to the Coordinator.
However, when Wi-Fi ON/OFF returns to low-duty cycle, the network will, due to lower route cost, return to the original structure with the
yellow node sending messages directly to the Coordinator.
Under conditions with Wi-Fi ON/OFF switching between low and high duty cycles, the network may switch back and forth between these
two route states. During these switching events, messages from the yellow end-node to the Coordinator are lost.
silabs.com | Building a more connected world. Rev. 0.2 | 9
Loading...