The first wireless LAN (WLAN) standard was created by the IEEE committee in 1997, and was called 802.11. However, 802.11 standard supported only up to 2 Mbps of bandwidth, and quickly became obsolete. Subsequently, IEEE created the 802.11a, and 802.11b standards.
The following are the advantages of the IEEE 802.11a standard compared to 802.11b:
802.11a uses 5GHz frequency band which is less crowded and hence has relatively smaller interference problem.
802.11a supports up to 54Mbps of bandwidth, which is much faster than the 11Mbps bandwidth provided by 802.11b standard devices.
802.11a offers as many as 12 non-overlapping channels. With more channels, larger number of users can be accommodated with no performance degradation.
Some of the disadvantages of using the 802.11a standard are:
Not many client devices such as note book computers, PDAs support 802.11a standard. Most of these support either 802.11b or Bluetooth standards.
It is more expensive compared to other contemporary technologies like 802.11b and Bluetooth.
802.11a standards are not compatible with 802.11b. Hence, devices manufactured complying with 802.11a and 802.11b respectively, are not interoperable.
The distance covered will be slightly less compared to 802.11b due to higher operating frequency (5 GHz). Note that, higher the radio frequency, lower the propagation distance for a given output power.
You may consider using 802.11g in place of 802.11a for reasons of cross compatibility.