802.11n supported 76 MCS rates and the tabular column showing the throughput obtained via the combination of MCS rate, Modulation scheme, channel bonding, guard band are shown below Modulation and coding schemes MCS index Spatial streams Modulation type Coding rate Data rate (in Mbit/s)[a] 20 MHz channel 40 MHz channel 800 ns GI 400 ns GI 800 ns GI 400 ns GI […]

802.11n and later WLAN standards introduced the concept of data frame aggregation. Even in earlier 802.11 standards, it was possible to send certain frames aggregated with a data frame (for e.g. CF-END frame with a QoS Frame), however, Data frames were never aggregated till then. The reason for aggregation of data frames can be depicted […]

The 802.11ac standard provided the number of spatial streams to be 8 and also increased the channel bonding size to 160 MHz (also 80+80MHz operation was allowed). This increased the theoretical throughput available to around 6 Gbps. The below table provides the data rate supported by 802.11ac. Spatial Streams VHT MCS Index Modulation Coding Rate […]

The A-MPDU Parameters define the size of an aggregated packet and also define the proper spacing between aggregated packets so that the receive side WLAN station is able to decode the packet properly. The A-MPDU parameters are part of the HT Capability Information element and the VHT Capability information fields. The A-MPDU parameter set in […]

The High-Throughput (HT) Immediate Block Ack was also introduced in 802.11n along-with aggregation of data packets. The combination of Immediate Block Ack and aggregation was a significant improvement on the Contention Free burst and block ack request/block ack mechanism. The earlier legacy block ack mechanism required the WLAN device to send a block ack request […]

Similar to delayed block Ack, an HT-Delayed Block Ack session provides the WLAN station to receive/transmit a Block Ack frame at a later time from the time when an A-MPDU was transmitted. HT-Delayed Block Ack is an optional feature. The HT-Delayed Block Ack support is advertised in the HT capabilities information field. Fig Courtesy – […]

The Block Ack session is negotiated per Traffic Identifier (TID). Hence, in essence if a Block Ack session is negotiated for each TID – then The Block Ack bitmap for each of the sessions need to be saved. Also, the packets that are awaiting an Ack via the Block Ack frame need to be saved […]

The 20/40 BSS Coexistence element is used by STAs to exchange information that affects 20/40 BSS coexistence. The 20/40 co-existence element is shown below. Fig Courtesy: 802.11 Standard As per the standard, the fields are defined below Information request field The Information Request field is used to indicate that a transmitting STA is requesting the recipient […]

In the legacy Block Ack Mechanism, the bitmap size was 128 bytes. This was due to the fact that fragmentation was allowed in 802.11a/b/g. A block Ack frame could ack 64 complete MPDUs and each MPDU could in theory be broken into 16 fragments. Hence, a packet could comprise of 2 octets (bytes) in the […]

An 802.11n HT station supports three modes of transmissions. Legacy 802.11 transmission Mode HT-Mixed Mode Transmission Mode HT-Green Field Mode Transmission Mode Legacy 802.11 transmission Mode The Frame Transmission is understandable by all 802.11 stations including legacy 802.11a/b/g stations. L-STF – Legacy Short Training Field L-LTF – Legacy Long Training Field L-SIG – Legacy Signal […]