無線網路之影像傳輸應用上，因較高的封包遺失率導致影像品質衰敗，ARQ機制和FEC機制是兩個在AP上主要的錯誤保護機制，由於影像傳輸的時間性限制和無線網路的高變動性，相較以時間為成本的ARQ機制，FEC是以利用頻寬作為錯誤保護的成本，因此具有更好的彈性來適應這樣的應用環境。動態的FEC機制傳輸前預測網路狀況來添加適量的冗餘封包，但由於無線網路變動性大，預測往往無法與實際的傳輸結果想吻合，導致添加的冗餘封包無法有效被使用而造成浪費，我們提出一個以FEC為主的錯誤保護機制，利用ARQ機制在傳輸時協助FEC機制冗餘封包調節，提升FEC冗餘封包使用率，實驗結果顯示,我們的機制與現有的FEC機制相比大幅提升了冗餘封包的使用率並且提升FEC機制的保護能力提供觀看者更好的影像品質。

High channel lost rate bring about the degradation of quality for video streams over WLANs, Automatic Retry reQuest mechanism (ARQ) and Forward Error Correction (FEC) are main of error protection mechanism on Access point. Due to delay constraint on video streaming service and high variability on WLANs, FEC is more suitable as an error protection compared with ARQ. Dynamic FEC mechanism determining the number of FEC packets in accordance with prediction of the current network condition on wireless network. In practice, the transmitting result is always inaccurate. Therefore, this problem lead to the low utilization of FEC redundant packets. In this paper, we propose a retry-based FEC mechanism (ARFEC) for video streaming over IEEE 802.11 WLANs. The ARFEC mechanism use adaptive ARQ scheme as a modulator to improve the FEC transmission so as to increase the utilization of FEC redundant packets. Our contribution are not only determining the FEC redundant packets in accordance with network load and wireless loss before transmitting but also adjusting the FEC redundant packets in accordance with FEC recovery capability during transmitting. The experimental results show that the proposed AR-FEC mechanism achieves a significant improvement in the utilization of FEC packet compared to existing FEC mechanisms.

Reference

[1] E. Maani and A. Katsaggelos, “Unequal error
protection for robust streaming of scalable video
over packet lossy networks,” IEEE Trans.Circuits
Syst. Video Technol., vol. 20, pp. 407–416, 2010.

[2] A.Argyriou, “Cross-layer error control for
multimedia streaming in wireless/wireline packet
networks FEC scheme for TDM-OFDMbased satellite
radio broadcasting system,” IEEE Trans. Multimedia,
vol. 10,pp. 1121–1127, Oct. 2008.

[3] J. Dan, F. Pascal, and J. Aleksandar, “Forward error
correction formultipath media streaming,” IEEE
Trans.Circuits Syst. Video Technol., vol. 19, pp.
1315–1326, 2009.

[4] J. Paavola, H. Himmanen, T. Joela, J. Poikonen, and
V. Ipatov, “The performance analysis of MPE-FEC
decoding methods at the DVB-H link layer for
efficient IP packet retrieval,” IEEE Trans.
Broadcast., vol. 53, pp. 263–275, Mar. 2007.

[5] M.-H. Lu, P. Steenkiste, and T. Chen, “A time-based
adaptive retry strategy for video streaming in
802.11 WLANs,” Wirel. Commun. Mob. Comput., vol. 7,
pp. 187-203, Feb. 2007.

[6] Chih-Ming Chen, Chia-Wen Lin, Yung-Chang Chen,
"Cross-layer packet retry limit adaptation for video
transport over wireless LANs" IEEE Transactions on
Circuits and Systems for Video Technology 2010.

[7] A. Nafaa, T. Ahmed, and A. Mehaoua, “Unequal and
interleaved FEC protocol for robust MPEG-4
multicasting over wireless LANs,”in Proc. IEEE Conf.
Computer and Communications, ICC2004, Jun.2004, vol.
3, pp. 1431–1435.

[8] I. V. Bajic, “Efficient cross-layer error control
for wireless video multicast,”IEEE Trans.
Broadcast., vol. 53, pp. 276–285, Mar. 2007.

[9] K. Takahata, N. Uchida, and Y. Shibata, “Packet
error and frame rate controls for real time video
stream over wireless LANs,” in Proc. Int. Conf.
Distributed Computing Systems Workshops, ICDCSW2003,
May 2003, pp. 594–599.

[10] K. Park and W. Wang, “AFEC: An adaptive forward
error correction protocol for end-to-end transport
of real-time traffic,” in Proc. Int.

[11] S.-H. G. Chan, X. Zheng, Q. Zhang, W.-W. Zhu, and
Y.-Q. Zhang,“Video loss recovery with FEC and stream
replication,” IEEE Trans.Multimedia, vol. 8, pp.
370–381, Apr. 2006.

[12] C. H. Lin, C. K. Shieh, N. Chilamkurti, C. H. Ke,
and W. S. Hwang,“A RED-FEC mechanism for video
transmission overWLANs,” IEEE Trans. Broadcast.,
vol. 54, no. 3, pp. 517–524, Sep. 2008.

[13] L. Han, S. Park, S. Kang, and H. P. In, “An adaptive
cross-layer FEC mechanism for video transmission
over 802.11 WLANs,” in Proc. Int. Conf. Internet,
ICI 2009, Dec. 2009, pp. 209–215.

[14] C. H. Lin, C. K. Shieh, and W. S. Hwang,“An Access
Point-Based FEC Mechanism for Video Transmission
Over Wireless LANs” IEEE TRANSACTIONS ON MULTIMEDIA,
VOL. 15, NO. 1, JANUARY 2013.

[15] “NS-2 simulator,” 140.116.72.80/smallko/ns2/ns2.htm.