Opportunistic transmission scheme with Raptor code in IEEE 802.11 multirate WLANs

In IEEE 802.11 wireless local area networks (WLANs), a fixed low transmission rate is used for multicast transmissions regardless of the channel conditions of the receivers. This may lead to inefficient use of the wireless channel, especially when the access point (AP) has both unicast and multicast data frames in the transmission queue. In this paper, we propose an opportunistic transmission scheme with Raptor code for efficient use of the wireless channel. In contrast to the legacy WLAN AP that has a single first-in-first-out (FIFO) queue, the AP in the proposed scheme maintains two separate queues at the AP: one for unicast data and another for multicast data. When the AP accesses a wireless channel, it decides on the type of data (unicast or multicast) and the transmission rate according to the channel condition and the delay boundary of the multicast data. In addition, Raptor code is applied for reliable multicast data transmission. Our simulation results show that the proposed scheme increases the average data rate and energy consumption saving when compared to the auto rate fallback (ARF), receiver-based auto rate (RBAR), and IEEE 802.11aa, schemes, which determine the transmission data rate only by considering the channel condition.