When two-hop meets VoFi

In a paper titled Can I add a VoIP call?(1), the authors calculate the maximum number of VoIP calls that a WiFi (VoFi) network can support. In this paper we extend their analysis to calculate the maximum number of VoFi calls when two-hop forwarding is used in order to avoid rate adaptation at nodes with reduced received signal strength. We calculate this number for different combinations of data rates for slow node transmissions and potential two-hop transmissions. These calculations demonstrate that the use of two-hop forwarding increases the maximum number of VoIP calls in a multi-rate 802.11b network. We validate the analysis by means of simulation of G711 codec sources in a 802.11b network. Even though the earlier discussions focus on specific combinations of high data rate two-hop and low data rate one-hop transmissions in an 802.11b network, we conclude the paper by calculating the maximum number of VoIP calls that can be supported with uniform node distri- bution in 802.11b and 802.11g networks. These calculations show a significant increase in the number of VoIP calls when two-hop forwarding is used in an 802.11g network. This sig- nificant increase is due to the higher data rates and the low PHY overhead of the 802.11g MAC.