Tamkang Journal of Science and Engineering, Vol. 13, No. 1, pp. 1 9 (2010) 1 Bandwidth Aggregation with Path Interleaving Forward Error Correction Mechanism for Delay-Sensitive Video Streaming in Wireless Multipath Environments Chih-Heng Ke 1, Rung-Shiang Cheng 2 *, Chen-Da Tsai 3 and Ming-Fong Tsai 4 1 Department of Computer Science and Information Engineering, National Kinmen Institute Technology, Kinmen, Taiwan, R.O.C. 2 Department of Computer and Communication, Kun Shan University, Tainan, Taiwan, R.O.C. 3 Department of Computer Science and Information Engineering, Far East University, Tainan, Taiwan, R.O.C. 4 Institute of Computer and Communication Engineering, Department of Electrical Engineering, National Cheng Kung University, Tainan, Taiwan, R.O.C. Abstract Multipath transmission which uses multiple paths for data transfer has been used in wireless networks to improve the performance of end-to-end transmission. However, wireless networks suffer from high packet loss rate, variations in end-to-end delay and available bandwidth. Hence, the Forward Error Correction (FEC) mechanism has been proposed to recover lost packets by adapting to the changing conditions in the network. Legacy multipath transmission with the FEC mechanism is used not only to improve the transmission performance by relying on bandwidth aggregation but also to reduce packet losses by relying on path selection. However, bandwidth aggregation of legacy multipath transmission with the FEC mechanism cannot select the appropriate transmission rate on each path as this needs more FEC redundancy to protect lost packets. Moreover, because the larger end-to-end delay leads to the video frame not being playable on-time at the receiver end, legacy multipath transmission with the FEC mechanism cannot be used in delay-sensitive video streaming when the FEC block length is so long that may exceed the end-to-end delay. This paper proposes the Bandwidth Aggregation with Path Interleaving FEC (BAPI-FEC) mechanism for delay-sensitive video streaming in a wireless multipath environment. The BAPI-FEC mechanism involves a mathematical analytical model with which the appropriate transmission rate, FEC block length and FEC redundancy on each path in a wireless multipath environment can be determined. Moreover, in order to overcome the burst packet loss problem, the BAPI-FEC mechanism relies on path interleaving technology to disperse burst packet losses to different FEC blocks. Key Words: Bandwidth Aggregation, Path Interleaving, Forward Error Correction, Video Streaming, Multipath Environment 1. Introduction With the ever-growing demand for video streaming *Corresponding author. E-mail: rscheng@mail.ksu.edu.tw services, there are stringent requirements with respect to end-to-end delay, bandwidth availability and packet loss. The current Internet was originally designed for data transmission [1,2] and not for video streaming applications, and thus it can only be used to provide services for
2 Chih-Heng Ke et al. wireless networks on a best efforts basis. The current situation makes the deployment of video streaming applications over the Internet an unprecedented challenge [3,4]. Accordingly, multipath transmission which uses multiple paths for data transfer has been used in wireless networks in order to improve the performance of endto-end transmission. Multipath transmission is a transmission mechanism by which the sender relays packets along more than one path at the same time and the receiver receives packets from either a single path or from multiple paths. Important benefits resulting from the use of multipath transmission arise because the packet loss patterns for different paths are independent and packet losses do not occur simultaneously, hence burst packet losses do not occur. Reducing burst packet loss is very important for video streaming applications, because it is easier to recover video content from several isolated losses. Moreover, multipath transmission makes more bandwidth available as it relies on bandwidth aggregation, which can be used for transmitting higher-quality video streaming applications [5]. Multipath transmission in wireless networks is more error prone than in wired networks because of the wireless loss problem, which is caused by wireless channel interference or low channel strength, leading to bit errors in each packet. Once wireless losses occur during transmission, the error propagates because of the dependencies within the compressed video stream [6]. As a result, the reconstructed video quality deteriorates severely. Therefore, it is important to devise new ways to protect compressed video streams from channel errors. Accordingly, Forward Error Correction (FEC) has been a commonly used mechanism that offers error protection. The FEC mechanism improves the reliability of transmission by adding extra redundant packets [7,8]. The principle of the FEC mechanism is that k source packets with h redundant packets become a block with n packets. When a receiver receives k or more packets, the decoder recovers the missing or error packets from the redundant packets [9,10]. Accordingly, legacy multipath transmission with the FEC mechanism can reduce the variability in packet loss. Reducing packet loss enhances the recovery performance of the FEC mechanism [11,12]. Previous studies haven t considered the types of packet loss, meaning congestion and wireless packet loss, and the FEC redundancy increased as the average packet loss rate increased, resulting in the self-induced congestion effect which impeded the timely recovery of video information because of packet loss and longer end-toend delays. Moreover, previous studies haven t selected the appropriate transmission rate on each path. Hence, the congestion packet loss became critical when the available bandwidth was insufficient on some paths. Furthermore, previous studies haven t selected the appropriate FEC block length. The video frame not being playable on-time at the receiver side becomes critical when the end-to-end delay is longer. Accordingly, this paper proposes the Bandwidth Aggregation with Path Interleaving FEC (BAPI-FEC) mechanism for delaysensitive video streaming in a wireless multipath environment to resolve the above-mentioned problems. This paper proposes a mathematical analytical model, with which we can find the appropriate transmission rate, FEC block length and FEC redundancy on each path in a multipath environment. Moreover, in order to overcome the burst packet loss problem, the BAPI-FEC mechanism relies on path interleaving technology to disperse the burst packet losses to different FEC blocks. The BAPI- FEC mechanism has better performance in terms of decreased Effective Packet Losses (EPL), increased Decodable Frame Rate (DFR), and increased Peak Signal-to- Noise Ratio (PSNR) compared to legacy multipath transmission with FEC mechanisms. The remainder of this paper is organized as follows. Section 2 presents relevant background information and FEC mechanisms in a multipath environment. The BAPI- FEC mechanism and mathematical model are introduced in section 3. Section 4 discusses the experimental setting and analyzes the results of simulations. Finally, the paper is summarized in section 5. 2. Background and Related Works 2.1 FEC Mechanism The conventional FEC mechanism is commonly used to handle packet loss in video streaming applications. For example, as shown in Figure 1, the FEC encoder which encodes three source packets into five decoded packets transmits in the wireless networks. When the FEC decoder can receive any three of five decoded packets, the original source packets are reconstructed. Hence, (n, k) which means (5, 3) block erasure code converts k
A FEC Mechanism for Delay-Sensitive Video Streaming 3 2.2 Legacy Multipath Transmission with Forward Error Correction The legacy path-dependent mechanism sends source data along different paths and then the FEC encoder encodes the redundancy of each path [13]. Because the packet loss patterns of the various paths are different and independent, different paths have a different number of redundancies. The legacy path-dependent mechanism can result in a reduction of packet loss for each individual path. The legacy path-independent mechanism [6] encodes the redundancy and sends all data over multiple paths. The legacy path-independent mechanism can reduce the packet loss on all multiple paths because the receiver is able to observe the average loss on multiple paths. In previous studies [6,13], bandwidth aggregation of legacy multipath transmission with FEC mechanisms cannot select the appropriate transmission rate on any path needing more FEC redundancy to protect lost packets. Moreover, because the larger end-to-end delay will lead to the video frame not being playable on-time at the receiver side, legacy multipath transmission with the FEC mechanism cannot be used in delay-sensitive video streaming when the FEC block length is too long, becoming larger than the end-to-end delay. In order to overcome the burst packet loss problem, this paper proposes the BAPI-FEC mechanism using a mathematical analytical model to find the appropriate transmission rate, FEC block length, and FEC redundancy on each path for video streaming in a wireless multipath environment. Figure 1. FEC mechanism. source packets into a group of n coded packets such that any k of the n encoded packets can be used for reconstructing the original source packets. The remaining (n k), h, packets are referred to as parity packets. The FEC mechanism codes are able to correct both errors and erasures in a block of n packets. The recovery rate of the FEC mechanism can thus be obtained by calculating the probability that more than k packets out of n are successfully received, given the degree of redundancy h. Depending on the selection of h, the recovery performance model of the FEC mechanism can achieve the desired quality of service level for robust video streaming applications. 3. Bandwidth Aggregation with Path Interleaving Forward Error Correction 3.1 Available Bandwidth Estimation We use the Packet Gap Model (PGM) to measure the available bandwidth [14]. The PGM exploits the information in the time gap between the arrivals of two successive probes at the receiver. A probe pair is sent with a time gap in; it reaches the receiver with a time gap out. Assuming a signal bottleneck and that the queue does not become empty between the departure of the first probe in the pair and the arrival of the second probe, then out is the time taken by the bottleneck to transmit the second probe in the pair and the cross traffic that arrived during in. Thus, the time to transmit the cross traffic is ( out in), and the rate of the cross traffic can be calculated as equation (1) which C is the capacity of the bottleneck. (1) 3.2 Bandwidth Aggregation A wireless multipath environment is shown in Figure 2. To avoid congestion packet loss on each path, the transmission source data packets and FEC redundant packets cannot exceed the available bandwidth on each path. The FEC redundancy increases to protect the source packets when the source data packets along a path have a Figure 2. Multipath environment.
4 Chih-Heng Ke et al. higher packet loss rate. Hence, in the first step of the BAPI-FEC mechanism, the selection of the path with smallest average packet loss rate is a top priority in order to reduce FEC redundancy. Accordingly, the BAPI-FEC mechanism not only doesn t cause congestion loss but can also select the appropriate FEC redundancy on each path. When a video streaming application requires a requested bandwidth, this is RBW bps. The transmission ratio of source data packets on each path p is M p. Hence, the transmission rate of source data packets on each path p can be calculated according to equation (2). (2) where the sum of all M p is 1. When the available network bandwidth on each path p is ABWp bps, we can calculate the congestion packet loss rate on each path p, C p, from the various values of M p according to equation (3). (5) The effective packet loss rate after the FEC decoding process, R effective_p, can be estimated according to equation (6). (6) The successful transmission rate needs to be subtracted from the effective packet loss rate after the FEC decoding process and the congestion loss data packets from the transmission rate of source data packets on each path. Hence, the appropriate transmission ratio of M p and FEC redundancy on each path can be found to rely on the calculation of maximum successful transmission rate, S BAFI_FEC, according to equation (7). (3) The FEC block length cannot lead to an unacceptable end-to-end delay on the receiver side. Hence, the packet end-to-end delay needs to be lower than the delay constraint value, DC. Because the FEC decoder decoded the original source packets, it needs to wait for the whole packets in one FEC block. Hence, the packet end-to-end delay in one FEC block length can be calculated according to equation (4). (4) The larger FEC block length, n, will lead to a longer end-to-end delay, Delay FEC. Delay FEC needs to be smaller than DC. Hence, the length of the FEC block is selected when Delay FEC is smaller than DC. Furthermore, the unsuccessfully recovered rate after the FEC recovery mechanism, UR p, for each path s average packet loss rate, loss p, can be calculated according to equation (5). (7) The BAFI-FEC mechanism uses a numerical analysis method to find the parameters S p, h, k corresponding to the maximum successful transmission rate. Once the parameters S p, h, k for maximum successful transmission are decided, the sender transmitted data packets rely on these parameters. 3.3 Path Interleaving One function of the BAPI-FEC mechanism is path interleaving, the principle of which is to disperse the burst packet losses to different FEC blocks. When sending the data packets of FEC blocks over multiple paths, the BAPI-FEC mechanism changes the transmission order of FEC blocks and sends them using path interleaving. In order to receive these for video streaming applications, the receiver has a packet buffer to absorb the impact of packet disordering. For example, Figure 3(a) shows an overview of the BAPI-FEC mechanism without path interleaving. In this example, the transmission rate in path 1 is higher than the transmission rate in path 2, which is determined by equation (6) in section 3.2. After the transmission rate of bandwidth aggregation is determined from equation (6), the sender side has several
A FEC Mechanism for Delay-Sensitive Video Streaming 5 different FEC blocks. There are two FEC blocks on the sender side in Figure 3(b). The path interleaving of the BAPI-FEC mechanism sends these blocks to the receiver along different paths. No matter how many different blocks or paths exist, the sender must follow steps in order to achieve path interleaving. First, all the FEC blocks send one packet to each path, however the transmission rate cannot be higher than the original transmission rate decided by equation (6) in section 3.2. Secondly, the packet of FEC blocks will select the other path when the transmission rate in some paths exceed the original transmission rate decided by equation (6) in section 3.2, until all the packets are transmitted. In Figure 3(b), Source 5 and FEC 3 are transmitted along path 1, and Source 2 and Source 4 are transmitted along path 2. However, FEC 1 and FEC 2 cannot be transmitted along path 2 because the transmission rate in path 2 is insufficient. Hence, when the transmission rate on each path is equivalent, the depth of path interleaving scheme is equal to the number of transmission paths. On the contrary, when the transmission rate on each path do not match, the depth of path interleaving scheme is lower than number of transmission paths. Accordingly, the proposed path interleaving scheme in this paper disperses the burst packet losses in different FEC blocks as much as possible so that the receiver can obtain better recovery performance. 4. Experimental 4.1 Experimental Setting The experimental arrangement is shown in Figure 2. The video server side transmits video streams over the Internet and the video receiver side is equipped with two wireless cards to connect two access points concurrently. The simulations are performed using the Foreman video trace from the TKN trace library [15] which has a CIF format with an IBBPBBPBB GOP structure and comprises 300 frames. A video stream is transmitted in 1 kb size packets at a rate of 30 frames per second. The requested bandwidth of Foreman streaming is 800 kbps. Finally, encoding and decoding functions of the FEC mechanism are implemented using RS code. In order to describe the wireless error property, a two-state Markov model is used. Moreover, as the evaluation condition, we use NIST Net [16] to set the available bandwidth of path 1 as 600 kbps and that of path 2 as 350 kbps. The DC of this paper is to set to 10 ms in all cases. We compare the video quality in terms of EPL, DFR [17] and PSNR value, as compared to legacy multipath transmission with FEC mechanisms. Figure 3. Path interleaving.
6 Chih-Heng Ke et al. 4.2 Experimental Results In this paper, we compare legacy multipath transmission with FEC and BAPI-FEC mechanisms in terms of EPL, DFR, and PSNR value. Figure 4 gives a comparison of the transmission EPL between legacy multipath transmission with FEC and BAPI-FEC mechanisms, when the average burst packet loss length is one. Figure 5 gives a comparison of transmission DFR between legacy multipath transmission with FEC and BAPI-FEC mechanisms when the average burst packet loss length is one. Figure 6 gives a comparison of PSNR value between legacy multipath transmission with FEC and BAPI-FEC mechanisms, when the average burst packet loss length is one. In the experimental results, for example, the average packet loss rate is 4% in path 1 and 2% in path 2. The legacy path-dependent and legacy path-independent mechanisms do not consider the available bandwidth on path 2. Both legacy path-dependent and legacy path-independent mechanisms cause very critical congestion loss problems in path 2. Hence, the EPL is larger than with BAPI-FEC mechanism. Moreover, the DFR and PSNR are less than with the BAPI-FEC mechanism. The BAPI-FEC mechanism can dynamically adjust the transmission rate, FEC block length and FEC re- Figure 4. Variation in effective packet loss rate with average packet loss rate (average burst packet loss length is one). Figure 5. Variation in decodable frame rate with average packet loss rate (average burst packet loss length is one). Figure 6. Variation in Peak Signal-to-Noise Ratio with average packet loss rate (average burst packet loss length is one).
A FEC Mechanism for Delay-Sensitive Video Streaming 7 dundancy on each path. Hence, the BAPI-FEC mechanism not only doesn t cause congestion loss problems but also the FEC redundancy is less than in the legacy path-dependent and legacy path-independent mechanisms. Furthermore, the BAPI-FEC mechanism doesn t cause unplayable video frames on the receiver side. Therefore, the BAPI-FEC mechanism performs better than legacy multipath transmission with FEC mechanisms in terms of EPL in Figure 4, DFR in Figure 5, and PSNR in Figure 6. Moreover, the FEC redundancy in legacy multipath transmission with FEC mechanisms is based on the average packet loss rate in each path. However, the BAPI-FEC mechanism first selects the minimum average loss rate path for transmitted data. Hence, the average packet loss rate is less than the average packet loss rate in each path. Hence, the FEC redundancy for the BAPI-FEC mechanism is still less than for legacy multipath transmission with FEC mechanisms. Figure 7 gives a comparison of transmission EPL between legacy multipath transmission with FEC and BAPI-FEC mechanisms, when the average burst packet loss length is three. Figure 8 gives a comparison of the transmission DFR between legacy multipath transmission with FEC and BAPI-FEC mechanisms, when the average burst packet loss length is three. Figure 9 gives a comparison of the PSNR value between legacy multi- Figure 7. Variation in effective packet loss rate with average packet loss rate (average burst packet loss length is three). Figure 8. Variation in decodable frame rate with average packet loss rate (average burst packet loss length is three). Figure 9. Variation in Peak Signal-to-Noise Ratio with average packet loss rate (average burst packet loss length is three).
8 Chih-Heng Ke et al. path transmission with FEC and BAPI-FEC mechanisms when the average burst packet loss length is three. In the experimental results shown in Figures 7, 8, and 9, the BAPI-FEC mechanism achieves the lowest effective packet loss rate as the burst packet loss length increases. These results demonstrate that the BAPI-FEC mechanism can overcome the burst packet loss problem. The BAPI-FEC mechanism achieves the highest decodable frame rate and peak signal-to-noise ratio as the length of the burst packet loss length increases. These results demonstrate that the BAPI-FEC mechanism can enhance video quality for video streaming when the burst packet loss length is three. 5. Conclusion An important benefit resulting from the use of multipath transmission is that it makes more bandwidth available, which can be used for transmitting video streaming applications. This paper proposes the BAPI-FEC mechanism to resolve the above-mentioned problems. The BAPI-FEC mechanism uses an analytical model to determine the appropriate transmission rate, FEC block length and FEC redundancy on each path in a multipath environment. Hence, the BAPI-FEC mechanism doesn t cause self-induced congestion, nor does it impede the timely recovery of video information. Moreover, in order to overcome the burst packet loss problem, the BAPI- FEC mechanism relies on path interleaving technology to disperse the burst packet losses to different FEC blocks. Hence, the BAPI-FEC mechanism yields better video communications in term of EPL, DFR and PSNR value than legacy multipath transmission with FEC mechanisms. Acknowledgment The authors thank the editor and the anonymous referees for their invaluable comments made on this paper. This work was supported by the National Science Council (NSC), Taiwan under Contract NSC 98-2221- E-507-002. References [1] Cheng, R.-S., Deng, D.-J., Huang, Y.-M., Huang, L., and Chao, H.-C., Cross-Layer TCP with Bitmap Error Recovery Scheme in Wireless Ad Hoc Networks, Journal of Telecommunication Systems, Vol. 44, DOI 10.1007/s11235-009-9226-1 (2009). [2] Deng, D.-J., Ke, C.-H., Chen, H.-H. and Huang, Y.-M., Contention Window Optimization for IEEE 802.11 DCF Access Control, IEEE Transactions on Wireless Communications, Vol. 7, pp. 5129 5135 (2008). [3] Tsai, M.-F., Shieh, C.-K., Hwang, W.-S. and Deng, D.-J., An Adaptive Multi-Hop FEC Protection Scheme for Enhancing the QoS of Video Streaming Transmission over Wireless Mesh Networks, International Journal of Communication Systems, Vol. 22, pp. 1297 1318 (2009). [4] Deng, D.-J. and Yen, H.-C., Quality-of-Service Provision System for Multimedia Transmission in IEEE 802.11 Wireless LANs, IEEE Journal on Selected Areas in Communications, Vol. 23, pp. 1240 1252 (2005). [5] Nafaa, A., Taleb, T. and Murphy, L., Forward Error Correction Strategies for Media Streaming over Wireless Networks, IEEE Communications Magazine, Vol. 46, pp. 72 79 (2008). [6] Tsai, M.-F., Chilamkurti, N. and Shieh, C.-K., A Novel Multi-Path Forward Error Correction Control Scheme with Path Interleaving for Video Transmissions, IEEE International Conference on Telecommunications, pp. 1 8 (2008). [7] Liu, H., Mathur, S., Makharia, S., Li, D. and Wu, M., IPTV Multicast over Wireless LAN Using Merged Hybrid ARQ with Staggered Adaptive FEC, IEEE Transactions on Broadcasting, Vol. 55, pp. 363 374 (2009). [8] Ahmed, A. and Marsland, I., Downlink Co-Channel Interference Cancellation in Multihop Relay Networks, Computer Communications, Vol. 32, pp. 1131 1137 (2009). [9] Tsai, M.-F., Shieh, C.-K., Ke, C.-H. and Deng, D.-J., A Novel Sub-Packet Forward Error Correction Mechanism for Video Streaming over Wireless Networks, Multimedia Tools and Applications, Vol. 47, pp. 49 69 (2010). [10] Tsai, M.-F., Chilamkurti, N. and Shieh, C.-K., A Network Adaptive Forward Error Correction Mechanism to Overcome Burst Packet Losses for Video Streaming over Wireless Networks, Selected to be published in Journal of Internet Technology.
A FEC Mechanism for Delay-Sensitive Video Streaming 9 [11] Tsai, M.-F., Chilamkurti, N., Park, J. K. and Shieh, C.-K., Multi-Path Transmission Control Scheme Combining Bandwidth Aggregation and Packet Scheduling for Real-Time Streaming in Multi-Path Environment, Accepted to be published in IET Communications. [12] Tsai, M.-F., Chilamkurti, N., Zeadally, S. and Shieh, C.-K., A Concurrent Multi-Path Transmission Control Scheme to Reduce Packet Reordering Latency at the Receiver, IEEE International Conference on Advanced Technologies for Communications, pp. 437 440 (2008). [13] Tsai, M.-F., Ke, C.-H., Kuo, C.-I. and Shieh, C.-K., Path Dependent Adaptive Forward Error Correction with Multipath Interleaving Control Scheme for Video Streaming over Wireless Networks, IEEE International Conference on Intelligent Information Hiding and Multimedia Signal Processing, pp. 1236 1239 (2009). [14] Strauss, J., Katabi, D. and Kaashhoek, F., A Measurement Study of Available Bandwidth Estimation Tools, ACM SIGCOMM Conference on Internet Measurement, pp. 39 44 (2003). [15] MPEG source trace file download, http://trace.eas. asu.edu/. [16] National institute of standards and technology, http:// www-x.antd.nist.gov/itg/nistnet/. [17] Ke, C.-H. and Chilamkurti, N., A New Framework for MPEG Video Delivery over Heterogeneous Networks, Computer Communication, Vol. 31, pp. 2656 2668 (2008). Manuscript Received: Jan. 8, 2010 Accepted: Feb. 25, 2010