With the advent of channel bonding in the 802.11n standard, a mechanism had to be developed that would allow a station operating in a 20 MHz channel to co-exist with a station operating in a 40 MHz channel. The station could be a legacy pre-802.11n device or an 802.11n device that was operating in 20 […]

An HT Station can perform a pure HT transmission (termed green-field mode) which is not understandable to legacy 802.11 stations (802.11b/g).  An HT station that intends to perform HT transmissions which will not be decipherable by a non-HT station needs to perform protection of such transmissions. The HT Operation element describes the HT protection field […]

PLCP Stands for PHY Layer Convergence Protocol. It is the lower most encapsulation of the 802.11 packet. It contains the Frame Preamble that is required by 802.11 receivers to detect whether an incoming transmission is an 802.11 Transmission or not. The PLCP also contains other information, such as length of packet, data rate and HT […]

802.11b specified two PLCP formats – long and short PLCP. The PLCP formats are provided below Fig Courtesy – 802.11 standards As can be seen from the pictorial representation for long and short 802.11b plcp – the format is different in the number of sync preamble bits that are sent out. The SFD/SIGNAL/SERVICE/LENGTH and CRC […]

The 802.11g standard supported a number of different PPDU (preamble and header) formats. The different PPDU formats could be classified under 3 categories and are provided below 11b Long Preamble format and the short Preamble format for 802.11b which was optional in 802.11b The Optional DSSS-OFDM at all OFDM rates and optional ERP-PBCC at all […]

One can refer the first part of this blog here — <802.11g PLCP Frame Formats – Part 1> DSSS-OFDM (Long Preamble Format) The DSSS-OFDM Preamble provides co-existence with legacy 802.11b devices as the Preamble and the PLCP header are sent at a rate that the legacy 802.11b devices can hear and understand. The DSS-OFDM PPDU […]

One can refer the first part of this blog here — <802.11g PLCP Frame Formats – Part 1> ERP-OFDM format The ERP-OFDM format is similar to the 802.11a OFDM PPDU format. The only change is that a signal extension field is added to the OFDM format of 802.11a as is done for all other 802.11g […]

The PLCP supported by 802.11a systems is shown below. The description of the different members of the PLCP is also incorporated. Fig Courtesy: 802.11 standards PLCP starts with training sequence (PLCP preamble), followed by the SIGNAL field and data. Both the training sequence and the 24 bit SIGNAL field are transmitted at 6Mbps rate. The […]

The 802.11n standard supports the legacy 802.11a/b/g PPDU formats. In addition it also supports two new PPDU formats. They are Mixed Mode PPDU format (allows co-existence with older clients) Green-field mode PPDU format (pure 11n client network) – optional The above two formats are termed as HT PPDU formats. The HT-Mixed mode format and the […]

The 802.11ac PPDU format supports the legacy 802.11a/n PPDU formats and the 802.11ac Very High Throughput (VHT) format. As 802.11ac is a 5GHz only standard – it does not have to support 802.11b/g PPDU formats. The PPDU format is shown below Fig Courtesy: 802.11 Standard The 802.11ac standard does not support a pure VHT format […]