Chih-Ming Chen

Cross-Layer Packet Retry Limit Adaptation for Video Transport Over Wireless LANs

Video transport over wireless networks requires retransmissions to successfully deliver video data to a receiver in case of packet loss, leading to increased delay time for the data to arrive at the receiver. Delay constraint is one of the most important requirements in real-time applications. A video packet arriving later than the presentation time will become useless for the client. In this paper, we propose a cross-layer content-aware retry limit adaptation scheme for video streaming over IEEE 802.11 wireless LANs. Video packets of different importance are unequally protected with different retry limits at the media access control (MAC) layer. The error propagation effect of each packet is estimated to guide the determination of its retry limit. More retry numbers are allocated to packets of higher loss impact to achieve unequal error protection. Our scheme also analyzes the backoff time for each retry and then takes into account the estimated backoff time for retransmission scheduling. Experimental results show that the proposed adaptation scheme can effectively mitigate the error propagation due to packet loss and assure the on-time arrival of packets for presentation, so as to improve video quality significantly.

Optimal rate allocation for scalable video multicast over WiMAX

The IEEE 802.16 standard (commonly known as WiMAX), which has been proposed as a new wireless broadband standard, is capable of delivering very high data rate and covering wide area. Video multicast service would become one potential application over WiMAX with the popularity of streaming applications in the Internet. Our method mainly uses adaptive modulation to achieve the goal of rate-adaptive multicast, and combines with the concept of layered multicast. According to the size of video layer, SS distribution, and available symbols, our method adaptively changes the modulations of each video layer in each group of picture (GOP) time. We also propose a Genetic Algorithm (GA) to reduce computational complexity when finding optimal modulation. Experimental results show that the proposed method can achieve promising performance.

Robust video streaming over wireless LANs using multiple description transcoding and prioritized retransmission

Video transport over wireless Local Area Networks (LANs) usually suffers from signal fading, noise interference, and network congestion, leading to time-varying packet loss rate and fluctuating effective bandwidth. We propose in this paper an adaptive error control scheme to adaptively insert error-resilience features into a compressed video in the media gateway which serves roaming clients. Our scheme divides the error control operation into the single description (SD) and multiple-description (MD) modes according to channel condition estimation. In the SD mode, a content-based prioritized retransmission method is proposed to mitigate the error propagation due to packet loss in video transport over wireless LANs. The proposed prioritized retransmission scheme determines the retransmission schedule of a lost packet according to the packets loss impact that is obtained in a front-end encoding process. In the MD mode, we propose a channel-aware MD transcoding method to take advantage of MD coding and path diversity so as to further mitigate the error propagation due to packet loss caused by transient channel switching while roaming in wireless LANs. Experimental results show that the proposed scheme effectively mitigates the error propagation due to packet loss, while maintaining low extra computational complexity and low overhead cost. The proposed method is suitable for realtime streaming of prestored videos.

Packet Scheduling for Video Streaming over Wireless with Content-Aware Packet Retry Limit

In this paper, we propose a content-aware retry limit adaptation scheme for video streaming over IEEE 802.11 wireless LANs (WLANs). Video packets of different importance are unequally protected with different retry limits at the MAC layer. The loss impact of each packet is estimated to guide the selection of its retry limit. More retry numbers are allocated to packets of higher loss impact to achieve unequal error protection. Our scheme also analyzes the backoff time for each retry and then takes into account the estimated backoff time for retransmission scheduling. Experimental results show that our adaptation scheme can effectively mitigate the error propagation due to packet loss and assure the on-time arrival of packets for presentation, thereby improving video quality significantly

Error Resilience Transcoding Using Prioritized Intra-Refresh for Video Multicast Over Wireless Networks

In this paper, we propose a two-pass intra-refresh transcoding scheme for inserting error-resilience features to a compressed video at the media gateway of a three-tier streaming system. The proposed transcoder can adaptively vary the intra-refresh rate according to the video content and the channels packet-loss rate to protect the most important macroblocks (MBs) against packet loss. In this work, we consider the problem of multicast of video to multiple clients having disparate channel loss profiles. We propose a minmax loss-rate estimation scheme to select a single intra-refresh rate for all the clients. Experimental results show that the proposed method can effectively mitigate the error propagation due to packet loss, and its fairness for multicast

Adaptive error-resilience transcoding using prioritized intra-refresh for video multicast over wireless networks

In this paper, we propose a two-pass error-resilience transcoding scheme based on adaptive intra-refresh for inserting error-resilience features to a compressed video at the intermediate transcoder of a three-tier streaming system. The proposed transcoder adaptively adjusts the intra-refresh rate according to the video content and the channels packet-loss rate to protect the most important macroblocks against packet loss. In this work, we consider the problem of multicast of video to multiple clients having disparate channel-loss profiles. We propose a MINMAX loss rate estimation scheme to determine a single intra-refresh rate for all the clients in a multicast group. For the scenario that a quality variation constraint is imposed on the users, we also propose a grouping method to partition a multicast group of heterogeneous users into a minimal number of subgroups to minimize the channel bandwidth consumption while meeting the quality variation constraint. Experimental results show that the proposed method can effectively mitigate the error propagation due to packet loss as well as achieve fairness among clients in a multicast.

Error-resilient video streaming over wireless networks using combined scalable coding and multiple-description coding

In this paper, we propose a novel error-resilient coding technique, namely, multiple-description fine granularity scalability (MD-FGS) coding, to enhance error resiliency while retaining good temporal prediction efficiency for video transport over error-prone networks, especially for wireless channels. The proposed MD-FGS coding scheme is based on a combination of FGS and modified MD scalar quantization (MDSQ), named Base-MDSQ, in which partial prediction is utilized to control drifting error. We also propose an adaptive soft handoff algorithm to effectively mitigate video quality degradation caused by transient channel switching when a mobile client roams in wireless local area networks (WLANs). The handoff algorithm utilizes a channel estimator to decide which channels should be used for delivering video. Experimental results show that the proposed method effectively mitigates error propagation due to packet loss while maintaining good coding efficiency.

Adaptive Error-Resilience Transcoding and Fairness Grouping for Video Multicast Over Wireless Networks

In this paper, we present a two-pass intra-refresh transcoder for on-the-fly enhancing error resilience of a compressed video in a three-tier streaming system. Furthermore, we consider the problem of multicasting a video to multiple clients with diverse channel conditions. We propose a MINMAX loss rate estimation scheme to determine a single intra- refresh rate for all the clients in a multicast group. For the scenario that a quality variation constraint is imposed on the users, we also propose a grouping method to partition a multicast group of heterogeneous users into a minimal number of sub-groups to minimize the channel bandwidth consumption while meeting the quality variation constraint and achieving fairness among all sub-groups. Experimental results show that the proposed method can effectively mitigate the error propagation due to packet loss as well as achieve fairness not only among all sub-groups and also clients in a multicast group.

Error-resilience transcoding using content-aware intra-refresh based on profit tracing

In this paper, we present a two-pass error-resilience transcoding scheme based on content-aware intra-refresh (CAIR) for inserting error-resilience features to a compressed video. The proposed transcoder can adaptively vary the intra-refresh rate according to the video content and the channels packet-loss rate to protect the most important macroblocks (MBs) against packet loss. Based on the CAIR transcoder, we propose a profit tracing scheme to improve the efficacy of intra-fresh allocation of the transcoder by avoiding wasting intra-refresh resource in MBs of high error-propagation ranks in a prediction path. Experimental results show that incorporating the proposed profit tracing scheme into CAIR scheme can achieve significant PSNR performance improvement over the CAIR scheme itself

Seamless roaming in wireless networks for video streaming

Roaming across multiple basic service sets (BSS) using access points (AP) in wireless LAN (WLAN) always poses considerable challenges, as it will cause heavy packet loss error. Especially for real-time video streaming, it will damage receiving video quality. In this paper, we combine the benefits of multiple description coding (MDC) and multipath routing to maintain a best constant video quality despite packet loss when roaming in WLAN. We incorporate a channel status detection mechanism to decide which channel will be selected or multiple channels will be used to take advantage of path diversity to deliver the streaming video content. The loss-rate and round-trip time are used to determine the channel status by using active probing. Simulation results indicate that the proposed method can significantly improve the quality of streamed video when a mobile client roams in WLAN.