Performance Study of Live Video Streaming over Highway Vehicular

Ad hoc Networks

Author:Fei Xie, Kien A. Hua, Wenjing Wang, and Yao H. Ho

2007 IEEE

Speaker: L.Y.-Wu

Outline

• I. INTRODUCTION

• II. RELATED WORK

• III. DATA FORWARDING SCHEMES

• IV. EXPERIMENTAL STUDY

• V. CONCLUDING REMARKS

I. INTRODUCTION

• Live Video streaming over Vehicular Ad hoc Networks (VANET) is an attractive feature to many applications, such as emergency live video transmission, road-side video advertisement broadcasting and inter-vehicle video conversation.

• The performance of video streaming suffers from the delay and packet loss incurred by the long time disconnection.

• In disaster recovery or traffic accident, it is important to support the first responders with live multimedia information about the emergency situation.

• Transmission the multimedia information over the inter-vehicle network is a good alternative in the case where there is no available communication infrastructure in the emergency area or when a driver is unable to respond in the critical time.

• Roadside businesses, such as restaurants and hotels, can broadcast the video advertisement via roadside infrastructure (e.g., 802.11 access point) to vehicles driving through.

• Passengers in nearby cars can setup a video conversation by using the inter-vehicle streaming technology. Drivers or passengers could also enjoy watching live news or football match, while the video data is conveyed by other relay vehicles.

• Thus the node in VANET is powerful to forward continuous video data to other vehicles or roadside receivers.

• Furthermore, the IEEE 802.11 standard can support up to 54Mbps transmission rate. Even between high speed driving vehicles, it is reasonable to expect a 1Mbps data rate.

• As to the transmission data rate required by compressed video, if we assume a 320*240 screen with 16 bits color, a frame rate about 15fps, the widely-used MPEG compressed video stream rate is estimated to be about 100 to 150kbps.

• Hence there is enough bandwidth to support video streaming between vehicles.

• Two network metrics, packet delay and packet loss, greatly affect the quality of the video in the receiver end.

• In video streaming, a single video frame is decomposed into many smaller packets and sent into the network.

• If the percentage of lost packets excesses the bound of error correction, the receiver can not playback this frame.

• Similarly, if the packet arrival time is later than the playback deadline of the corresponding frame, it will also be dropped by the decoder in receiver.

• The challenge of video streaming over VANET can be interpreted by the high dynamics of the vehicles.

• The high velocity and limited communication range of the vehicles incur frequent link disconnection and even network partition.

• It takes time for vehicle to catch up with other vehicles ahead and reconnect the network. We call this amount of time as catch-up delay .

• During the catch-up phase, the routing protocol uses the store-and-forward (SF) scheme to buffer the packet and send it in the next chance.

• In this paper, we are interested in forwarding video data in highway, because vehicle density in highway is more suitable to support continuous video streaming.

• We use real video data and NS2 to study the performance of video streaming under different traffic conditions and different data forwarding schemes.

• Instead of using delay and packet loss ratio, we evaluate the Peak Signal to Noise Ratio (PSNR) as the quality of the decoded video in the receiver.

• PSNR is widely used as the major performance metric in the research of video streaming

II. RELATED WORK

• The procedure of the video streaming application over VANET has two phases.

– First phase is to send a video trigger to the area of interest or vehicle via other vehicles.

– The second phase is to transmit the streaming video data back from the video source.

• Authors proposed a fast triggering method which uses a distributed method to estimate the backward and frontward transmission ranges of vehicles.

• V3 presented an architecture for live video streaming over VANET.

• However, because no real video data are used in their simulation, only the delay is reported in the experimental study.

• The end to end delay can not directly reflect the performance of video streaming, since in many cases, the delay variance could be absorbed by the receiver buffer.

• Although there are many researches on video over MANET using mpeg video data, their network simulation are statistical model based.

• As for data forwarding in VANET, there are three classes of schemes that could be applied to VANET.

• One class is the traditional route based forwarding, like DSR and AODV.

• The second and third classes are sender based and receiver based forwarding respectively. Both classes incorporate geographic information and greedily decide the next relay node.

• There are some routing protocols in VANET using the street topology information to help the data forwarding.

• Since we focus on highway scenario in this research, the topology is not a concern.

• Decoded video quality at the receiver is therefore affected by two factors:

– encoder compression performance.

– distortion due to the packet loss or late arrivals.

• The video distortion can be modeled as:

• The encoder distortion may be modeled by:

• Where R is the rate of the video stream, and the parameters D0, θ and R0 are estimated from empirical rate-distortion curves via regression techniques.

• In this work, we are interested in Dloss,which can be modeled by

• where Dpkt_loss and Ddelay represent the distortion contributed by packet loss or delay respectively.

III. DATA FORWARDING SCHEMES

• To compare the sender based forwarding (SBF) and receiver based forwarding (RBF) schemes in highway, we implement two data forwarding schemes SBF-H and RBF-H which are representatives of RBF and SBR respectively.

• In a highway scenario, there are typically two directions.

– Denote as forwarding direction of packet p. – as node driving direction.

• The video sender decide based on the receiver’s location piggybacked in the video trigger.

Destination

• Let denote the distance from node to the destination .

• We use to denote value of the velocity of .

• We denote as:

• The SBF-H is an extension of GPSR while the RBF-H modifies the CBF. The SBF-H is an extension of GPSR while the RBF-H modifies the CBF.

• In SBF-H, nodes maintain a data structure called neighbor list (NL).

• Nodes periodically broadcast its location, velocity and driving direction information.

• Other nodes receive this broadcast packet store the information in its NL.

• A node chooses the next hop to forward packet p based on the following three rules:

• Rule 1 has the highest priority.

• We apply Rule 2 to the nodes which satisfy Rule 1, unless there is no node meets Rule 1.

• The threshold in Rule 2 could be the safe distance between cars.

• Rule 3 is applied to the nodes selected by Rule 2.

• In Rule 3, we choose the nodes with the maximum velocity and driving in the same direction as the packet forwarding direction.

• In RBF-H, a relay node broadcast the packet p to all the neighboring nodes.

• If the destination receives this packet, it broadcasts an ACK packet right away.

• Other nodes receiving the ACK simply discard the packet.

• Each node in the contention uses (2) to estimate t, which is the time to reach the destination.

• is the velocity of the destination. If the destination is static, is zero, or we simply can use the highway speed limit as .

IV. EXPERIMENTAL STUDY

• A. Simulation Setup

• We encoded the 10 seconds CIF video sequence Foreman into MPEG4 data format at 30 fps. Each frame is packetized into packets of 1024bits and sent to the network at their playout time in the sender.

• B. Performance Evaluation

• We transmit a 10 second encoded video over a 2 km road section with different traffic densities.

• Each data point is the average result of 100 simulations with different randomly generated mobility trace.

V. CONCLUDING REMARKS

• We study the performance of video streaming over highway VANET.

• We propose two data forwarding schemes particularly for highway environment, which are SBF-H and RBF-H.

• These two schemes try to choose the best packet forwarder in a bi-directional multiple lanes highway.

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