Inter-vehicle communication (IVC) systems (i.e., systems not relying on roadside infrastructure) have the potential to radically improve the safety, efficiency, and comfort of everyday road travel. Their main advantage is that they bypass the need for expensive infrastructure; their major drawback is the comparatively complex networking protocols and the need for significant penetration before their applications can become effective. In this article we present several major classes of applications and the types of services they require from an underlying network. We then proceed to analyze existing networking protocols in a bottom-up fashion, from the physical to the transport layers, as well as security aspects related to IVC systems. We conclude the article by presenting several projects related to IVC as well as a review of common performance evaluation techniques for IVC systems.

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Inter-vehicle communication systems: a survey

Quality of experience (QoE) is the perceptual quality of service (QoS) from the users' perspective. For video service, the relationship between QoE and QoS (such as coding parameters and network statistics) is complicated because users' perceptual video quality is subjective and diversified in different environments. Traditionally, QoE is obtained from subjective test, where human viewers evaluate the quality of tested videos under a laboratory environment. To avoid high cost and offline nature of such tests, objective quality models are developed to predict QoE based on objective QoS parameters, but it is still an indirect way to estimate QoE. With the rising popularity of video streaming over the Internet, data-driven QoE analysis models have newly emerged due to availability of large-scale data. In this paper, we give a comprehensive survey of the evolution of video quality assessment methods, analyzing their characteristics, advantages, and drawbacks. We also introduce QoE-based video applications and, finally, identify the future research directions of QoE.

From QoS to QoE: A Tutorial on Video Quality Assessment

https://www.eng.auburn.edu/~szm0001/papers/ChenCOMCOM2007.pdf

Directional geographical routing for real-time video communications in wireless sensor networks

Although there has been a growing literature on cooperative diversity, the current literature is mainly limited to the Rayleigh fading channel model, which typically assumes a wireless communication scenario with a stationary base station antenna above rooftop level and a mobile station at street level. In this paper, we investigate cooperative diversity for intervehicular communication based on cascaded Nakagami fading. This channel model provides a realistic description of an intervehicular channel where two or more independent Nakagami fading processes are assumed to be generated by independent groups of scatterers around the two mobile terminals. We investigate the performance of amplify-and-forward relaying for an intervehicular cooperative scheme assisted by either a roadside access point or another vehicle that acts as a relay. Our diversity analysis reveals that the cooperative scheme is able to extract the full distributed spatial diversity. We further formulate a power-allocation problem for the considered scheme to optimize the power allocated to the broadcasting and relaying phases. Performance gains up to 3 dB are obtained through optimum power allocation, depending on the relay location.

/pdf/cooperative-diversity-for-intervehicular-communication-jbjjjzmp5s.pdf

Cooperative Diversity for Intervehicular Communication: Performance Analysis and Optimization

Live streaming platforms bring events from all around the world to people's computing devices. We conducted a mixed methods study including interviews (N = 42) and a survey (N = 223) to understand how people currently experience events using Facebook Live, Periscope, and Snapchat Live Stories. We identified four dimensions that make remote event viewing engaging: immersion, immediacy, interaction, and sociality. We find that both live streams and the more curated event content found on Snapchat are immersive and immediate, yet Snapchat Live Stories enable quickly switching among different views of the event. Live streams, on the other hand, offer real time interaction and sociality in a way that Snapchat Live Stories do not. However, the interaction's impact depends on comment volume, comment content, and relationship between viewer and broadcaster. We describe how people experience events remotely using these social media, and identify design opportunities around detecting exciting content, leveraging multiple viewpoints, and enabling interactivity to create engaging user experiences for remotely participating in events.

What Makes Live Events Engaging on Facebook Live, Periscope, and Snapchat

We present a new cross-layer ARQ algorithm for video streaming over 802.11 wireless networks. The algorithm combines application-level information about the perceptual and temporal importance of each packet into a single priority value, which drives packet selection at each retransmission opportunity. Hence, only the most perceptually important packets are retransmitted, delivering higher perceptual quality and less bandwidth usage compared to the standard 802.11 MAC-layer ARQ scheme. H.264 video streaming based on the proposed technique has been simulated using ns in a realistic home network scenario, using the standard ARQ technique for all interfering traffic. Results show that the proposed method consistently outperforms the standard MAC-layer 802.11 retransmission scheme, delivering more than 1.5 dB PSNR gains using approximately half of the retransmission bandwidth.

https://multimedia.polito.it/wordpress/wp-content/uploads/2011/02/bucciol_globecom2004.pdf

Cross-layer perceptual ARQ for H.264 video streaming over 802.11 wireless networks

This paper evaluates the performance of video streaming in inter-vehicular environments using the 802.11 ad hoc network protocol. We performed transmission experiments while driving two cars equipped with 802.11b standard devices in urban and highway scenarios. Different sequences, bitrates and packctization policies have been tested. The experiments show that each scenario presents peculiar characteristics in terms of average link availability and SNR, which can be exploited to develop more efficient applications. In this paper we also determine the best packetization policies for the two scenarios, showing that large packets lead to better performance in the highway scenario and vice versa. Perceptual quality results indicate that the best packetization policy achieves consistent gains in terms of PSNR values (up to 5 dB), and reduced quality variations, with respect to a fixed-policy transmission technique

Performance Evaluation of H. 264 Video Streaming over Inter-Vehicular 802.11 Ad Hoc Networks

Cloud gaming enables playing high-end games, originally designed for PC or game console setups, on low-end devices such as netbooks and smartphones, by offloading graphics rendering to GPU-powered cloud servers. However, transmitting the high-resolution video requires a large amount of network bandwidth, even though it is a compressed video stream. Foveated video encoding (FVE) reduces the bandwidth requirement by taking advantage of the non-uniform acuity of human visual system and by knowing where the user is looking. Based on a consumer-grade real-time eye tracker and an open source cloud gaming platform, we provide a cloud gaming FVE prototype that is game-agnostic and requires no modifications to the underlying game engine. In this article, we describe the prototype and its evaluation through measurements with representative games from different genres to understand the effect of parametrization of the FVE scheme on bandwidth requirements and to understand its feasibility from the latency perspective. We also present results from a user study on first-person shooter games. The results suggest that it is possible to find a “sweet spot” for the encoding parameters so the users hardly notice the presence of foveated encoding but at the same time the scheme yields most of the achievable bandwidth savings.

Cloud Gaming with Foveated Video Encoding

The H.264/SVC video codec extends the H.264/AVC standard with scalability features. In this paper we introduce a traffic prioritization algorithm suitable for the transmission of both H.264/SVC and H.264/AVC video over 802.11e ad hoc wireless networks. The proposed algorithm exploits the traffic prioritization capabilities offered by 802.11e to provide better protection to the most perceptually important parts of a video while achieving efficient network resource usage. We evaluate the algorithm by simulating video transmissions in an ad hoc network scenario. Results show that the H.264/SVC codec particularly benefits from the proposed algorithm, which enables a graceful video quality degradation in congested network conditions, as well as PSNR gains up to 2 dB with respect to the H.264/AVC codec using the same amount of network resources.

/pdf/traffic-prioritization-of-h-264-svc-video-over-802-11e-ad-5dgy73vy79.pdf

Traffic Prioritization of H.264/SVC Video over 802.11e Ad Hoc Wireless Networks

This paper presents an analysis-by-synthesis technique to evaluate the perceptual importance of multimedia packets for rate-distortion optimized streaming. The proposed technique, instead of relying on a priori information, computes the distortion that would be caused by the loss of each single packet, including the effects of error propagation and receiver-side error concealment. A rate-distortion optimized streaming algorithm is presented to compare the perceptual performance obtained using content-adaptive analysis-by-synthesis distortion values versus distortion values obtained using a priori knowledge of the statistical importance of the elements of the compressed multimedia bitstream. Simulations with video test sequences compressed with the MPEG-2 coding standard show that the proposed technique delivers substantial and consistent PSNR gains (1.2-2.8 dB) with respect to ideal frame type-driven a priori distortion evaluation for a wide range of channel conditions. Compared to distortion-agnostic streaming techniques such as SoftARQ, the gain is even more pronounced.

/pdf/analysis-by-synthesis-distortion-computation-for-rate-1axinhphf7.pdf

Enrico Masala

Papers

Cross-layer perceptual ARQ for H.264 video streaming over 802.11 wireless networks

Performance Evaluation of H. 264 Video Streaming over Inter-Vehicular 802.11 Ad Hoc Networks

Cloud Gaming with Foveated Video Encoding

Traffic Prioritization of H.264/SVC Video over 802.11e Ad Hoc Wireless Networks

Analysis-by-synthesis distortion computation for rate-distortion optimized multimedia streaming