The use of multiple antennas based on Multiple-Input Multiple-Output (MIMO) techniques is the key feature of 802.11n/ac, which in theory outperforms 802.11a/b/g by higher throughput.
Engineers who are interested in designing Wi-Fi modules are presented with the problems of whether 802.11n/ac shall be implemented and how much performance improvement can be achieved. This paper will give an overview of the evolution of the IEEE 802.11 standard.
Then, it discusses the challenges faced in 802.11 wireless channel, namely path loss, shadowing and multipath effect. Finally, MIMO techniques, a key feature in 802.11n/ac, are introduced to overcome the fading effect with higher throughput.
Since the first establishment of wireless LAN or Wi-Fi standard 802.11 by IEEE in 1997, Wi-Fi standard has evolved a lot from 802.11a/b/g to 802.11n/ac; other standards in the family (c–f, h–j) are service amendments and extensions, or corrections to previous specifications.
802.11b was the first widely accepted wireless networking standard, followed by 802.11a, 802.11g, 802.11n, and 02.11ac. 802.11b uses the ISM 2.4 GHz band which allows for only a maximum throughput of 11 Mbps.
802.11a operates around less crowded ISM 5 GHz with higher throughput up to 54 Mbps. Combining the best of 802.11a and 802.11b, 802.11g supports bandwidth up to 54 Mbps, and it uses the 2.4 GHz frequency for greater range.
The 802.11n standard is designed to improve 802.11g in the amount of throughput supported by utilizing multiple Wi-Fi signal channels and antennas instead of one. 802.11ac offers backward compatibility to 802.11b/g/n and supports data rate more than 200 Mbps. The key parameters and performances of the above 802.11 standards are summarized in Figure 1.
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