| Summary: | 碩士 === 義守大學 === 資訊工程學系 === 104 === In standard IEEE 802.11-2012, many physical layers which provided multiple data rates are defined, but the approach of choosing data rate for transmitting a data frame is still an open issue. Many approaches for PHY rate control in IEEE 802.11 networks have been proposed in order to improve QoS (such as packet loss rate, throughput, delay, etc.) of the transmission under the unsteady wireless environment. However, most of rate control approaches are designed only for unicast transmission but not multicast or broadcast applications.
In MAC layer of IEEE 802.11, a multicast or broadcast frame must be transmitted without any ACK frame sent back by the receivers. This is, there is no feedback information that can be used for adjusting the transmitting data rate. Thus, the data loss rate could be continuously high if the signal quality is poor at the receiver. Especially for the applications of video streaming, it is trivial that such high data loss rate will lead to bad video playback. In IEEE 802.11aa, BlockAck mechanism is exploited to send back the information about frame reception by the receivers of multicast or broadcast frames. The transmitter can get the data loss information of each receiver and then retransmit the lost data. However, how to apply BlackAck mechanism to form an efficient multicast/broadcast retransmission approach is still open.
In this thesis, an efficient frame retransmission approach with adaptive PHY rate control for multicast/broadcast streaming services is proposed. In the proposed approach, IEEE 802.11aa BlockAck mechanism is applied to let the receiver periodically send back the status of recent frame receiving. The source then accordingly decides a new PHY rate and retransmits the lost data frames. Thus, the subscribers of the streaming services can obtain adaptively high quality of service. System simulation of the proposed approach is performed on an IEEE 802.11n network in which AP acts the source of broadcast streaming service and the stations act its subscribers. The simulation results demonstrate the effectiveness of the proposed approach.
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