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.
