The interested reader can refer the first part of the series here — <802.11ac PLCP Frame Format – Part 1> VHT-SIGB Field The VHT-SIGB format provides the Length and MCS rate that the 802.11ac frame was transmitted at in a Multi-User (MU) transmission. The VHT-SIGB field is one symbol and can be 26 bits in […]

The interested reader can refer the first part of the series here — <802.11ac PLCP Frame Format – Part 1> VHT Signal Fields – VHT-SIG A The VHT-SIGA field provides information on the different parameters of the frame at the receiver to configure itself to decode the received 802.11ac frame. The VHT-SIGA field is provided […]

Channel bonding in wireless LAN is the bonding of  adjacent 20 MHz channels to create a wider bandwidth channel (e.g 40MHz/80MHz etc). The higher bandwidth channel in effect will have higher bandwidth and hence higher data rate supported. One such example is shown below Fig Courtesy: Wikipedia As can be seen from the tabular column […]

The 802.11n standard introduced Multi-Input-Multi-Output (MIMO) into WLAN. This enabled Wi-Fi devices to increase their data rate. Further enhancements were also introduced in the 802.11n standard significant of which was MAC layer data aggregation, Channel bonding, transmit beam-forming and higher QAM modulation schemes. The current article delves into the basics of MIMO. MIMO stands for […]

For Transmit Beamforming to function properly, The channel characteristics between the transmitter and the receiver should be known accurately. To allow channel characteristics to be determined the concept of Null Data Packet (NDP) was introduced in the 802.11n specification. The Null Data packet does not contain any data field and purely comprises of the preamble […]

In the Pre-802.11n era, A WLAN device could have multiple antennas, but only transmit/receive the same signal on multiple antennas or use the best antenna for transmit or receive.  With the advent of MIMO, multiple data streams could in effect be transmitted on different antennas simultaneously. MIMO also provided a means of shaping the signal […]

The 802.11 Standards body defined Implicit feedback and explicit feedback as two mechanisms for calculating the channel characteristics Transmit weights that are utilized for Transmit Beamforming. In Implicit Beamforming, The reciprocity of the channel characteristics between Transmitter and the receiver is considered to be equal compute the channel weights between the Transmitter and receiver. However, […]

The interested reader can look at an understanding of Transmit beamforming here <Transmit Beamforming in 802.11n and 802.11ac>. A brief explanation of implicit and explit feedback in Transmit Beamforming can be obtained here <Implicit Feedback and Explicit Feedback for Transmit Beamforming>. As discussed in the above article, Explict feedback methods were defined by the standard […]

The Transmit Beamforming capabilities field is part of the HT Capabilities information element. It is shown below Fig Courtesy: 802.11-2012 The Transmit Beamforming Capabilities field is shown below. Fig Courtesy: 802.11-2012 Standard 802.11ac Explicit Transmit Beamforming

The 802.11ac standard simplified Transmit beamforming and removed implicit Transmit beamforming completely. It also mandated the sounding method (NDP) and feedback mechanism. Explicit Feedback was selected as the only feedback method. Furthermore, the only allowed explicit feedback type was compressed -V beamforming weights. The 802.11ac  Transmit Beamforming is widely deployed for it simplified the implementation […]