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Example of 802.11n device capabilities to deliver quality video. Authors:. Outline. Substantiate PER requirements for video transmissions Provide an example how 802.11n device can reach the required PER with retransmissions Analyze the effect of retransmissions to delay variation budget
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Example of 802.11n device capabilities to deliver quality video Authors:
Outline • Substantiate PER requirements for video transmissions • Provide an example how 802.11n device can reach the required PER with retransmissions • Analyze the effect of retransmissions to delay variation budget • Take into account typical aggregation conditions and link adaptation behavior Michael Livshitz, Leonid Epstein Metalink
Requirements for PER based on error-free viewing • Packet error rate probabilities can be derived from the requirements for error-free video rendering • Assumed payload format LLC/IP/UDP/RTP/[7xMPEG2-TS]=1364 bytes • For example, PER of 3e-7 is required for 30min error-free viewing of 20Mbps HD MPEG2 video Michael Livshitz, Leonid Epstein Metalink
802.11n Video Transmission Parameters Notes: (1) PER (after retransmissions) needed for 30min error-free video (2) This raw BER (before retransmissions) is a target BER of Rate Adaptation algorithm (3) Number of retransmissions necessary to reach required PER (4) See next slide for example calculation Michael Livshitz, Leonid Epstein Metalink
Example delay budget for aggregated and retransmitted 11n frame • Assumed parameters: • PHY rate is 108Mbps (2SS, 16QAM, rate 1/2) • IP/UDP/RTP/(7xMPEG2-TS) • A-MPDU/BA, 9 MPDUs, 5 retransmission allowed • All retransmissions are within original TxOP • Video is AC_VI, under EDCA rules with default parameters Michael Livshitz, Leonid Epstein Metalink
Conclusion • Numeric example illustrates the possibility of delivering high quality video with 802.11n-based toolset • Retransmissions can drive media loss rate low enough to enable quality error-free viewing, while keeping delay variation bounded by relatively small threshold • Standard-based features that benefit video delivery: • High throughput, low interference: • 5GHz band, 40MHz-wide transmissions • Multiple Spatial Streams, Receive Antenna Diversity • Effective media usage: • QoS (WMM/EDCA) • A-MPDU Aggregation • Single TxOP retransmissions • Video quality Rate Adaptation • Targets low BER Michael Livshitz, Leonid Epstein Metalink