Tanir Ozcelebi

Client intelligence for adaptive streaming solutions

In state-of-the-art adaptive streaming solutions, to cope with varying network conditions, the client side can switch between several video copies encoded at different bit-rates during streaming. Each video file version is divided into chunks of equal duration. To achieve continuous video playback, each chunk needs to arrive at the client before its playback deadline. The perceptual quality of a chunk increases with the chunk size in bits, whereas bigger chunks require more transmission time. Therefore, there is a tradeoff between the overall video quality and continuous playback, which can be optimized by proper selection of the next chunk from the encoded versions. This paper proposes a method to compute a set of optimal client strategies for this purpose.

End-to-end stereoscopic video streaming with content-adaptive rate and format control

We address efficient compression and real-time streaming of stereoscopic video over the current Internet. We first propose content-adaptive stereo video coding (CA-SC), where additional coding gain, over that can be achieved by exploiting only inter-view correlations, is targeted by down-sampling one of the views spatially or temporally depending on the content, based on the well-known theory that the human visual system can perceive high frequencies in three-dimensional (3D) from the higher quality view. We also developed stereoscopic 3D video streaming server and clients by modifying available open source platforms, where each client can view the video in mono or stereo mode depending on its display capabilities. The performance of the end-to-end stereoscopic streaming system is demonstrated using subjective quality tests.

Exploring user-centered intelligent road lighting design: a road map and future research directions

Traditional road lighting systems are outdated and should be replaced with systems which can sense their environment, i.e., users and their consumer electronics (CE) devices, and react intelligently. Realizing such a system requires an interdisciplinary approach which analyzes the efficient system architecture and communication technology while taking into account the user needs. To understand these necessities, subjective experiments should be conducted in a practical testbed, similar to ours. In this paper, we first present the state-of-the-art solutions in the literature. Then, we describe the system architecture of our testbed deployed on a real street along with the preliminary experiments. Finally, we discuss the open challenges and research directions on designing a future intelligent road lighting system.

Smart lighting using LED luminaries

The target of a smart lighting system is to control light sources in an environment (e.g. home, office) adaptively according to user contexts and preferences. Literature work in this area focuses on traditional light sources such as incandescent and fluorescent lights, whereas this paper takes a step towards adopting LED luminaries. A novel illumination model for distributed LED luminary control is presented. A prototype system is designed and implemented using several LED luminaries and light sensors. Experiments carried out on the reading space use case show that the desired illumination can be achieved based on user preferences, irrespective of the existence of external light sources.

Smart indoor solid state lighting based on a novel illumination model and implementation

Smart lighting research traditionally focuses on conventional incandescent and fluorescent luminaries. However, in addition to its higher energy efficiency and longer lifetime, Solid State Lighting (SSL) offers better control of spectral, spatial, temporal polarization, and color properties of light. Combined with the recent developments in smart environments research, SSL utilizing Light Emitting Diodes (LED) creates a new playground for user-light interaction. We present a novel illumination model for SSL and implement this model on a wireless sensor network (WSN). The light sensors and actuators in the WSN provide services for sensing illumination changes and dynamically adjusting luminary brightness according to user preferences. Experiments conducted two key scenarios, i.e. reading and watching TV, show that the preferred illumination levels in an activity space can be achieved and maintained, irrespective of external light variations.

Delay-Distortion Optimization for Content-Adaptive Video Streaming

We propose a new pre-roll delay-distortion optimization (DDO) framework that allows determination of the minimum pre-roll delay and distortion while ensuring continuous playback for on-demand content-adaptive video streaming over limited bitrate networks. The input video is first divided into temporal segments, which are assigned a relevance weight and a maximum distortion level, called relevance-distortion policy, which may be specified by the user. The system then encodes the input video according to the specified relevance-distortion policy, whereby the optimal spatial and temporal resolutions and quantization parameters, also called encoding parameters, are selected for each temporal segment. The optimal encoding parameters are computed using a novel, multi-objective optimization formulation, where a relevance weighted distortion measure and pre-roll delay are jointly minimized under maximum allowable buffer size, continuous playback, and maximum allowable distortion constraints. The performance of the system has been demonstrated for on-demand streaming of soccer videos with substantial improvement in the weighted distortion without any increase in pre-roll delay over a very low-bitrate network using AVC/H.264 encoding

Resource and service management architecture of a Low Capacity Network for smart spaces

A smart space is typically composed of heterogeneous networks of communicating and collaborating nodes with varying capacities of resources such as processing power, memory and energy. Recent developments in wireless communication technology and miniaturization of Consumer Electronics (CE) hardware have made Low Capacity Networks (LCN) such as Wireless Sensor and Actuator Networks (WSAN) an important element of smart spaces. However, resource and service management in LCNs that interoperate with resource-rich nodes of a smart space is still a challenge. We propose and implement an architecture for lightweight resource and service management in LCNs. Furthermore, we present a validation of the proposed architecture through performance analysis in comparison to an existing interoperability architecture.

Enhancing End-to-End QoS for Multimedia Streaming in IMS-Based Networks

Convergence of the emerging IP Multimedia Subsystem(IMS) includes unlicensed, nondedicated and nondeterministic hence uncontrollable. computer access, networks for IP multimedia services. It enables provision of resource demanding real-time services and multimedia communication raising new end-to-end Quality-of-Service (QoS) challenges, for which quality adaptation using resource management is proposed as a solution in this paper. This is an integrated solution taking both IMS and computer access networks into account as well as the two end-devices and the application servers (AS) involved in communication. The best user experience is targeted under real-time variation of available network (e.g. bandwidth, buffer space) and end-device (e.g. battery, CPU, memory, storage) resources throughout a session. The multimedia content is dynamically adapted to fit the resource availability variations, achieving maximum system (i.e. network and end-devices) resource utilization and enhanced QoS. The resource availability update signalling is carried over Session Initiation Protocol (SIP) during the session. This is work in progress.

An Analysis of Constant Bitrate and Constant PSNR Video Encoding for Wireless Networks

In wireless networks, transmission of constant-quality, high bitrate video is a challenging task due to channel capacity and buffer limitations. Content adaptive rate control, is used as a solution to this problem. Instead of transmitting all of the video content at low quality, the most important content can be transmitted at high quality while still preserving an acceptable quality for the remaining segments. Furthermore, the rate control strategy inside the individual temporal segments plays a key role for the network performance and viewing quality. Although constant quality video encoding inside the temporal segments is preferable for the best viewing experience, it causes more network packet losses due to adverse bitrate fluctuations in the video stream. In cases when the network is too much loaded, it may be better to employ constant bitrate encoding for network friendliness. In this paper, a performance analysis of constant bitrate and constant peak signal-to-noise ratio encoding for content adaptive rate controlled video streaming over wireless networks is presented. Experimental results obtained using AVC/H.264 encoding in a CDMA/HDR multi-user environment with cross-layer optimized scheduling show performance comparisons of CBR and CPSNR encoding.

Minimum delay content adaptive video streaming over variable bitrate channels with a novel stream switching solution

We present a new channel adaptive stream switching solution for variable bitrate video transmission, where the receiver buffer status is used for making switching decisions and instantaneous transmission rate is determined by means of explicit channel feedback or TCP friendly rate control. Receiver buffer status is used in selecting from a set of pre-encoded bitstreams avoiding buffer underflows and overflows. A pre-roll delay to buffer data at the receiving side is necessary in order to compensate for variations in the channel throughput and the encoding bitrate. For each stream, content dependent video coding parameters are chosen by means of dynamic programming such that the maximum overall video quality and minimum pre-roll delay are achieved for a finite number of transmission rates. Experimental results show that buffer violations are successfully avoided using the proposed stream switching framework as opposed to a regular non-adaptive streaming case.