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 […]

Battery power is a precious resource and various mechanisms have been introduced in the 802.11 standard to protect the same. The VHT TXOP power save feature is one such feature. TXOP stands for – Transmit Opportunity. All 802.11 stations (Access Point as well as non-Access Point stations) contend for the medium as per EDCA rules […]

Medium Access Layer (MAC Layer) State-machines need to interact with the PHY Layer to meet certain Physical Medium dependent (PMD) restrictions. The Parameter list which defines the MAC-PHY interface is the Txvector and Rxvector parameters. The Txvector and Rxvector Parameter list are defined in the PHY specific parameter list of each PHY sub-clause in the […]

802.11 Radios consume a lot of power. Hence, a lot of time and effort has been expended in the area of 802.11 Power Save to make the 802.11 Devices more energy efficient. Spatial Multiplexing Power save is one such methodology which allows the 802.11 device to save more power. The 802.11 Standard in 802.11n and […]

The interested reader can get an overview of the Spatial Multiplexing feature here <Spatial Multiplexing Power Save>. Dynamic SMPS In Dynamic SMPS mechanism, an 802.11 station enables its multiple receive chains on receiving a frame addressed to it. The First frame so received shall be a single spatial stream individually addressed frame that requires immediate […]