6.2 Transmission Speeds and Standards
Since the creation of the 802.11 standard, various enhancements have followed. Therefore, a number of different physical layers, abbreviated as ‘PHY’, exist today in the standard documents. Each PHY has been defined in a different document and a letter has been put at the end of the initial 802.11 document name to identify the different PHYs (Table 6.1).
|Standard||Frequency band||Speed (Mbit/s)|
|802.11b ||2.4 GHz (2.401–2.483 GHz)||1–11|
|802.11g ||2.4 GHz (2.401–2.483 GHz)||6–54|
|802.11a ||5 GHz (5.150–5.350 GHz and 5.470 to 5.725 GHz)||6–54|
|802.11n||2.4 GHz (as above)||6–600|
|5 GHz (as above)|
The breakthrough for WLAN was the emergence of the 802.11b standard that offers datarates from 1 to 11 Mbit/s. The maximum datarate that can be achieved in a real environment mainly depends on the distance between the sender and the receiver as well as on the number and kind of obstacles between them such as walls or ceilings—11 Mbit/s can only be achieved over short distances of a few meters.
To ensure connectivity over a larger distance, the number of bits used for redundancy is automatically adapted. This reduces the speed down to 1 Mbit/s under very bad conditions. Many vendors specify a maximum range of their WLAN adapters of up to 300 m. In practice, such a distance is only achieved outdoors where no obstacles absorb signal energy, and only at a speed of 1 Mbit/s.
The 802.11b standard uses the 2.4-GHz ...