WiFi 802.11 bf - Roles and Configurations

 A WLAN sensing procedure uses two sets of roles:

• Sensing initiator and sensing responder: to discriminate between the STA, called sensing initiator, that initiates the WLAN sensing procedure (i.e., the STA that supports a sensing application), and the STA, called sensing responder, that participates in the procedure by responding to the sensing initiator.

• Sensing transmitter and sensing receiver: to discriminate between a STA, called sensing transmitter, that transmits PPDUs to allow for sensing measurements and a STA, called sensing receiver, that receives PPDUs sent by the sensing transmitter to perform sensing measurement.

Below figure summarizes the possible role combinations and associated message exchanges. We can first observe that the sensing measurements are obtained with the transmission of NDPs. And then, the sensing report can only be sent by a sensing responder acting as a sensing receiver or both sensing receiver and sensing transmitter.

The configuration Fig. a) uses an approach analogous to the approach employed by legacy IEEE 802.11 STAs to perform beamforming (the initiator sends NDP and the compressed beamforming beam steering matrix inferred from the channel response is reported), and as such, requires few modifications for vendor/implementors to support sensing. (What modifications ?)
The downside of this approach:
1. A reporting phase is needed from the sensing responder(s) to the sensing initiator, generating additional overhead.
2. The reporting phase may lead to information loss due to CSI encoding for measurement reporting.

The configuration Fig. b) is of interest, for example, when the sensing initiator wants to be the STA processing the sensing measurements, possibly taking advantage of proprietary algorithms.
The main advantage of this architecture is that it does not require a reporting phase as the sensing initiator receives directly the NDPs and can thus perform sensing measurements. This architecture does not incur additional overhead nor produce any loss of information.

The configuration Fig. c) is beneficial when the channel reciprocity assumption (including RF front-ends) does not hold as it allows to obtain sensing measurements in both “directions”.

The configuration Fig. d) the sensing responder performs monostatic sensing. As discussed before, the IEEE 802.11bf amendment does not explicitly address this case for WLAN sensing. (?)