In order to improve multicast performance in wireless networks, we propose two methods for reducing the number of retransmissions and decreasing the backoff duration. Reducing the number of retransmissions is achieved by introducing a target packet delivery ratio. Acknowledgement from a member node initializes the backoff window, which decreases the backoff duration.

We derive the average achievable rate of an adaptive wireless multicast method with antenna diversity in Nakagami fading channels when the rate is selected by the minimum signal-to-noise ratio (SNR) of the multicast group. Based on the limiting distribution of the minimum SNR, we then derive an approximation to the average achievable rate, which provides accurate values easily in a wide range of channel parameters.

In this paper, we study multi-layer transmission for wireless multimedia multicast in a cell. Under the assumptions that the users in a cell are uniformly well distributed and that the BS has no channel side information, we find the optimal number of transmission layers and power allocation. This result can be used in highly dynamic dense networks and jamming networks where channel side information at the transmitter is somewhat useless.

When a mobile node that subscribes to one or more multicast groups moves to another subnet, it is essential to provide a network level multicast handoff mechanism. Previous multicast handoff schemes are based on Mobile IP. However it is known that the Mobile IP is not adequate to interactive multimedia applications such as voice over IP or video conferencing due to its large handoff delay. Additionally, few researches have paid attentions on multicast handoff in infrastructure-mode WLAN environment. This paper proposes a fast inter-subnet multicast handoff method in Mobile IP based infrastructure-mode IEEE 802.11 WLAN environment. We introduce a dedicated Multicast Access Point (MAP) that works with an access points specified in standard IEEE 802.11 WLAN in order to alleviate disruption of receiving multicast datagram. Unlike previous research, our scheme does not modify Mobile IP specifications. MAP detects the completion of link-layer handoff, sends unsolicited IGMP Membership report to its local router on behalf of the mobile station and performs unicast tunneling. We evaluate the proposed method using ns-2 simulation. The simulation result shows that the proposed method can reduce the disruption period due to inter-subnet multicast handoff to about 1/12 and the packet loss rate can be reduced to about 1/4 over 20-size multicast group compared with the standard Mobile IP based IEEE 802.11 WLAN.

In multicast congestion control, the receiver of the worst congestion level is selected as the representative and transmission rate of the sender is adjusted to TCP throughput of the representative. This approach has high scalability and TCP friendliness. However, when this approach is applied in wireless communications, wireless-caused packet loss will cause to frequent change of the representative. This is because degradation of wireless channel quality causes bursty packet loss at a corresponding receiver. Fading, one of main reasons of wireless channel degradation, is expected to be recovered after short time period, which leads to frequent change of the representative. This frequent change of representative makes the sender adjust its transmission rate to the tentative worst receiver, which brings severe performance degradation to wireless multicast. We call this technical problem, the wireless-caused representative selection fluctuation problem. Wireless-caused representative selection fluctuation problem is one of scalability problems in the wireless multicast, because this problem remarkably happens for large scale multicast. We propose two possible solutions for this problem, an end-to-end approach and a network support approach. Performance evaluation in various situation show that an end-to-end approach is sensitive for its inferring error but a network support approach shows good performance improvement.