要旨
Nowadays we are rapidly moving from a mainly textual-based to a
multimedia-based Internet, for which the widely deployed IEEE 802.11 wireless
LANs can be one of the promising candidates to make them available to users
anywhere, anytime, on any device. However, it is still a challenge to support
group-oriented real-time multimedia services, such as video-on-demand, video
conferencing, distance educations, mobile entertainment services, interactive
games, etc., in wireless LANs, as the current protocols do not support
multicast, in particular they just send multicast packets in open-loop as
broadcast packets, i.e., without any possible acknowledgements or
retransmissions. In this thesis, we focus on MAC layer reliable multicast
approaches which outperform upper layer ones with both shorter delays and
higher efficiencies. Different from polling based approaches, which suffer from
long delays, low scalabilities and low efficiencies, we explore a feedback
jamming mechanism where negative acknowledgement (NACK) frames are allowed from
the non-leader receivers to destroy the acknowledgement (ACK) frame from the
single leader receiver and prompts retransmissions from the sender. Based on
the feedback jamming scheme, we propose two MAC layer multicast error
correction protocols, SEQ driven Leader Based Protocol (SEQ-LBP) and Hybrid
Leader Based Protocol (HLBP), the former is an Automatic Repeat reQuest (ARQ)
scheme while the later combines both ARQ and the packet level Forward Error
Correction (FEC). We evaluate the feedback jamming probabilities and the
performances of SEQ-LBP and HLBP based on theoretical analyses, NS-2
simulations and experiments on a real test-bed built with consumer wireless LAN
cards. Test results confirm the feasibility of the feedback jamming scheme and
the outstanding performances of the proposed protocols SEQ-LBP and HLBP, in
particular SEQ-LBP is good for small multicast groups due to its short delay,
effectiveness and simplicity while HLBP is better for large multicast groups
because of its high efficiency and high scalability with respect to the number
of receivers per group.
