IEEE 802.11a-1999

IEEE 802.11a is an extension of the IEEE 802.11 standards for the 5 - GHz frequency band ( ≈ 5.2 GHz to ≈ 5.8 GHz). 802.11a WLANs achieve maximum gross data rate of 54 Mbit / s

802.11a uses for data transmission the Modulierungsverfahren OFDM. This technique was later applied to the 2.4 GHz ISM frequency band - it was the concurrent expansion IEEE 802.11g. In the EU, the use of 802.11a with larger radiation power ( EIRP), or outdoor use on the simultaneous support of 802.11h is bound. Then allow 802.11a but also a greater range than 802.11b / g, despite the greater signal attenuation due to the higher transmission frequencies.

History and spread of 802.11a

The extension of IEEE 802.11a was ratified in 1999, first deliveries in 2001 to the market. Because of the legal restrictions on the use of the frequency band at 5 GHz wireless networks 802.11a / h are much less common. The terminals are due to the additional techniques of dynamic frequency selection (DFS ) and RF power control (TPC ) also more expensive than pure 802.11b/g-Geräte. When dual -band devices, the IEEE 802.11a / b or IEEE 802.11a/b/g can spark simultaneously in both bands, this disadvantage, however, increasingly disappearing.

Since the ISM frequency band at 2.4 GHz through Bluetooth, microwave ovens, baby monitors and many other applications is heavily loaded, you can view the low incidence of 802.11a / h as an advantage. Wireless Networks 802.11a / h through the little-used frequency band and dynamic frequency selection (DFS ) often considerably more reliable and less prone to failure. Due to the high allowable transmit power of 802.11a / h of maximum 1.0 W EIRP with automatic frequency selection, transmit power control and low utilization of the 5- GHz frequency band 802.11a / h is particularly suitable for the establishment of point - to-point wireless bridges in the outdoor use.

Compatibility with other WLANs

Because of the use of a different frequency band, wireless networks based on IEEE 802.11a / h is not compatible with WLANs in IEEE 802.11b / g However, there are many dual- band devices on the market, which can deal simultaneously with both frequency bands.

Bit rates

Enlargement provides bit rates up to 54 Mbit / s in front of (6, 9, 12, 18, 24, 36, 48, and 54 Mbit / s). Compatible hardware must be at least 6, the bit rates, support 12 and 24 Mbit / s.

Frequencies / channels

Transmission power ( DE)

For operation with large transmission power and for use outside of buildings in Europe, enlargement is 802.11h necessary, which should guarantee about the capabilities Transmission Power Control (TPC ) and Dynamic Frequency Selection (DFS ) operation of WLANs in the 5 GHz frequency band without interfering with military radar systems, satellite and radiolocation services.

Comparison of IEEE standards

Sources:

OFDM and DSSS are modes of transmission (also called transmission types ) and no modulation types. The corresponding modulation types in the table column ( modulation / multiplexing method ) must be neatly separated.