Investigations in the areas of performance improvement in 802.11ac (draft) wlan standard over existing wlan and cellular networks

Abstract

This thesis deals with investigating performance issues in IEEE 802.11ac WLANs. IEEE 802.11ac is a Very High Throughput (VHT) WLAN standard that is designed to achieve data rates in the order of 7 Gbps in 5 GHz range of frequency. Firstly, problems faced in legacy LANS are discussed in detail. QoS and interference have been identified as the major limiting factors in WLANs. A study is undertaken with respect to the concepts underlying the 802.11n standard (prior to 802.11ac) followed by the enhancements in 802.11ac in the MAC and PHY layers. NS3 simulations show the superior performance of 802.11ac standard with respect to 802.11n. Features verified are spatial streams, channel bonding, guard interval and MCS while performance is measured with parameters such as jitter, throughput and delay. It is seen that these features contribute to enhanced throughput and reduced delay. Next, the 802.11ac performance with rate adaptation (RA) algorithms is simulated in NS3. Performance is measured for both 802.11ac and 802.11n WLANs with throughput versus SNR in the presence of parameters such as channel bonding and different spatial streams. A comparison is done to study the effect of Ideal Wi-Fi and Minstrel RA algorithms in 802.11n and 802.11ac. With Ideal RA, both 11ac and 11n perform consistently. With Minstrel, both 11ac and 11n behave similarly at 20 MHz CBW, but for 11ac, there is inconsistency at all other BWs and number of SSs. For 11ac, both Ideal and Minstrel are suitable at 20MHz and 40 MHz, but Minstrel is not recommended for 80 and 160 MHz CBWs. It is to be noted that 802.11ac standard has not yet defined rate adaptation mechanisms.