Hello, everyone!
Today, I would like to continue to share a post on the novel features an open challenges of the IEEE 802.11ax amendment.
Multi-User:
As both uplink and downlink MU-MUMO and OFDMA were considered, multi-user communications will most likely be one of the key aspects of IEEE 802.11ax. Because the available transmission resources may be the same as in the case of single-user communication, using multi-user communication techniques does not always imply an improvement in system capacity.
In WLANs, however, concurrent transmission from several users is able to parallelize the enormous temporal overheads of each transmission (i.e., DIFS, SIFS, ACKs, packet headers, and so on), resulting in a significant increase in WLAN performance.
IEEE 802.11ax will improve on IEEE 802.11ac's MU-MIMO capabilities by permitting multiple concurrent transmissions in the uplink, known as uplink MU-MIMO. Uplink MU-performance MIMO's benefits have already been widely investigated, demonstrating both the benefits and the requirements and obstacles of implementing such a solution.
An open task for enabling uplink MU-MIMO, similar to DL-MU-MIMO transmissions, is to build a method that can efficiently schedule the users who will broadcast simultaneously. On the one hand, a completely decentralized solution would be simple to build with low signaling costs.
However, because it requires all STAs to complete their backoff at the same time, it may be inefficient, and those STAs may not be spatially compatible.
A pure centralized approach, on the other hand, necessitates the AP having entire CSI and buffer occupancy information from all STAs in order to identify the most appropriate group for multi-user transmission. The AP may utilize a "Trigger" frame to alert a group of selected users that they can commence a transmission after a sufficient group of STAs has been identified by the AP.
This method ensures efficient multi-user transmissions, but it adds some overhead to the AP's collection of all essential data and signaling of the selected STAs. In both circumstances, IEEE 802.11ax is planned to offer new multi-user ACKs that acknowledge all broadcasts with a single control packet.
IEEE 802.11ax is also considering multi-user OFDMA. A channel can be divided into many sub-channels and allocated to multiple users using OFDMA. In both the downlink and uplink, OFDMA is likely to be used in conjunction with channel bonding, in which each of the 20 MHz subchannels can be assigned to a distinct user.
Aside from that, a similar procedure to the multi-user MIMO situation is expected, given the obstacles are almost identical. A review of recent OFDMA WLAN ideas demonstrates how the usage of OFDMA can considerably increase WLAN performance.
In conjunction to Multi-user MIMO and OFDMA, IEEE 802.11ax has proposed the usage of Simultaneous Transmit and Receive (STR) techniques, also known as full-duplex transmission. STR allows a pair of nodes to broadcast and receive data at the same time, theoretically doubling channel capacity.
In a full-duplex transmission, both the AP and the STA start transmitting at the same time, which presents a problem. As a result, full duplex transmission data could be included in control packets or the transmission initiator's PHY headers.
