Aspects of this disclosure relate generally to telecommunications, and more particularly to techniques for sounding sequence protection in multi-user multiple-input-multiple-output (MU-MIMO) communications for wireless local area networks (WLANs).
The deployment of WLANs in the home, the office, and various public facilities is commonplace today. Such networks typically employ a wireless access point (AP) that connects a number of wireless stations (STAs) in a specific locality (e.g., home, office, public facility, etc.) to another network, such as the Internet or the like. A set of STAs can communicate with each other through a common AP in what is referred to as a basic service set (BSS). Nearby BSSs may have overlapping coverage areas and such BSSs may be referred to as overlapping BSSs or OBSSs. In some scenarios, communications that occur in nearby BSSs can result in collisions and failure in the transmission of information.
In dense enterprise deployments of WLANs, such as in stadiums, airports, or other large venues, for example, there may be multiple APs deployed, and the coverage of several of those APs can overlap creating OBSS scenarios. For example, in these dense deployments, multiple STAs can be in the common coverage of multiple BSSs. Moreover, when these dense deployments are unplanned, some of the APs may be automatically configured to work on the same channel, which may cause transmission collisions between OBSSs. The collisions that occur may result in sounding sequence failures and, upon detection of a sounding sequence failure, an AP may terminate a transmission opportunity (TxOP) and would need to contend for the medium again. System throughput can be severely impacted if this happens frequently.
For MU-MIMO transmissions, however, the WLAN standards (e.g., IEEE 802.11-based standards) have not defined a specific mechanism that may be used for MU-MIMO sounding sequence protection. One option for MU PLCP Protocol Data Unit (PPDU) protection is to send multiple RTSs one by one to all of the STAs that will be part of the subsequent MU PPDU transmission and expect a CTS from each of those STAs. However, this solution may not be practical for MU-MIMO sounding sequence protection because it incurs a large overhead that may not be needed in non-OBSS scenarios.
Accordingly, for scenarios that create OBSSs between nearby BSSs and that can result in sounding sequence collisions and failures, it may be desirable to have a mechanism that protects the sounding sequence while providing low overhead.