BSS Coloring

Wi-Fi 6 is now in full swing, boasting great Wi-Fi performance in dense networks thanks to features like OFDMA, 8 x 8 DL/UL MU-MIMO, BSS Coloring, 1024 QAM etc. While a lot of attention is paid to its revolutionary OFDMA technology, BSS Coloring seems somewhat under-appreciated in comparison. But given that it is a highly efficient way of increasing channel capacity, BSS Coloring serves a vital function and deserves some attention.  

 

 

What is BSS Coloring?

BSS Coloring is a mechanism to mark each BSS (Basic Service Set), consisting of an AP (Access Point) and its associated clients), with a “color” for differentiation.

 

Why is this important?

 

Channel is valuable resources. There are a limited number of channels available in 2.4G and 5G frequency bands. For each channel, only one device is allowed to transmit data at a time to prevent interference and collision, while others have to wait for their turn.

 

Yet in high-density scenarios like stadium, shopping mall and neighborhoods, many APs will be assigned to the same channel. Interference from neighboring wireless networks can cause issue with your wireless signal. The collision avoidance mechanism will be effected to defer transmission. Channel contention entails a lot of waste of time and space.

 

Things are different now. BSS Coloring enables:

 

• Quick recognition of the right data packets

BSS Color, as an identifier, can mark each frame and tell routers/APs/clients which data packets are coming from neighboring networks and ignore them. Only the right data is received. Co-channel interference is minimized between BSSs so they can transmit in sync. Clients in the same BSS share the same color, so they need to communicate in turn with the AP. BSS Coloring makes it possible for different BSSs to share the same channel, greatly boosting channel capacity.

 

• Adaptive tolerance of interference from neighboring BSSs

BSS Coloring allows APs/clients to ignore packets from other BSSs. Yet if two BSSs are too close, the overlapping signals can still cause interference. Just like having group discussions in a classroom, voices from close neighboring groups can make it difficult to hear people in your own group clearly.

Then what is the maximum value of BSS signal strength that decides communication in one BSS is not affected by another BSS?

 

Previous Wi-Fi standards adopted the same interference threshold value, which gave them a low tolerance for the transmissions of neighboring networks. BSS coloring introduces an adaptive threshold for interference. An adaptive threshold can change the value of the signal strength according to the current network environment. This is really useful since the networks are not static. Dynamic adjustment maximizes the simultaneous communication of Basic Service Sets.

 

• Dual airtime timers to avoid interference

What if the dynamic interference tolerance does not filter all interference? Don’t worry, BSS Coloring uses two transmission timers to tell how long the channel will be occupied.

 

Time 1 measures the time needed for clients within the same BSS. A client needs to wait for time 1 while the previous client is transmitting data. Time 2 is changeable to adjust how long the client has to wait (not necessarily Time 1).

 

For example, client 2 in BSS 1 is waiting for client 1 to finish transmission which needs 160μs, yet it hears signals in BSS 2 claiming it needs 120μs to send data. To prevent interference, client 2 has to wait until transmission is done in the neighboring BSS 2. Thus it will reset Time 2 to be 280μs. The introduction of Time 2 ensures both intra-BSS and inter-BSS transmissions.

 

 

We want better network experience whether in shopping malls, airports or neighborhoods. BSS Coloring is doing its bit to make it happen.