Christian Lottermann

Performance evaluation of automotive off-board applications in LTE deployments

The new cellular communication standard 3GPP Long Term Evolution (LTE) promises high throughputs and low latencies, thus enabling even more bandwidth-demanding and real-time critical services for end-users. This is of particular interest for vehicle manufacturers who in the future intend to offer a huge variety of cooperative driver assistance services with different quality of service (QoS) settings. In this paper we analyze the suitability of LTE for future automotive off-board services in terms of transmission delays and reliability under various QoS settings. Our investigations are based on extensive LTE system-level simulations under different load conditions and network deployments as well as on a theoretical delay analysis. The results show that an accurate selection of the LTE QoS parameters is crucial in order to meet the delay and reliability requirements of future automotive applications, especially in high-load network conditions.

LTE for Vehicular Communications

The cellular communication networks standard 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) offers low latencies and high throughputs simultaneously, thus enabling more bandwidth-demanding and real-time critical services for end-users. This is of particular interest for vehicle manufacturers who in the future intend to offer a huge variety of cooperative driver assistance services with manifold quality of service requirements. This chapter analyzes the suitability of LTE as a wireless transmission technology for future vehicular services of the categories Infotainment, Comfort, Traffic Efficiency, and Safety. The investigations are based on extensive LTE system-level simulations under different load conditions and network deployments as well as on a theoretical delay analysis. Focus is set on transmission delays and reliability aspects under various quality of service settings. The results show that an accurate selection of the LTE quality of service parameters is crucial in order to meet the delay and reliability requirements of future automotive applications, especially in high-load network conditions.

Bit rate estimation for H.264/AVC video encoding based on temporal and spatial activities

We present a novel bit rate model for H.264/AVC video encoding which is based on the quantization parameter, the frame rate as well as temporal and spatial activity measures. With the proposed model, it is possible to trade-off the frame rate versus the quantization parameter to achieve a target bit rate. Our model depends on video activity measures that can be easily calculated from the uncompressed video. In our experiments, the model achieves a Pearson correlation of 0.99 and a root-mean-square error of less than 5% with the measured bit rate values, as verified by statistical analysis.

Potential of cooperative information for vertical handover decision algorithms

In the near term, vehicles will be connected with each other and to centralized off-board servers to provide automotive services. In this paper we analyze existing heterogeneous network selection algorithms. It is shown that the developed algorithm for network selection with additional cooperative information is well suited to improve the handover decisions compared to reference handover algorithms without additional cooperative information. The reference algorithms include a received signal strength (RSS), a Fuzzy logic- and an analytic hierarchy process (AHP) based handover decision algorithm excluding supplemental cooperative information. A detailed, simulation based, analysis of the perceived quality of service (QoS) and a cost optimization has been performed for the developed vertical handover decision algorithm (VHDA) using AHP with cooperative information.

Modeling the bit rate of H.264/AVC video encoding as a function of quantization parameter, frame rate and GoP characteristics

We present a novel analytical bit rate model for H.264/AVC video encoding which is based on the quantization parameter, the frame rate, the group-of-pictures length, the group-of-pictures structure and content-dependent parameters. The content-dependent parameters are described as a function of two standard video activity measures (temporal and spatial activity) which can easily be determined from the uncompressed video. Our bit rate model shows a Pearson correlation of more than 0.97 and a root-mean-square error of less than 2% as determined by statistical analysis.

Camera context based estimation of spatial and temporal activity parameters for video quality metrics in automotive applications

We present a low complexity approach for the estimation of the temporal and spatial activity parameters of videos which are captured by a front-facing camera of a vehicle based on context information of the vehicle. The estimated parameters are integrated into an objective video quality metric, which can be used to determine the perceptual quality of a compressed video stream. Our proposed video quality metric has very low computational complexity, which makes it suitable for live video streaming applications. It shows a high Pearson correlation of 0.98 with an average root-mean-square error of 6%, as verified by statistical analysis with data from subjective tests.

Network-aware video level encoding for uplink adaptive HTTP streaming

We study the uplink delivery of live video using adaptive HTTP streaming (AHS). In AHS, the process of simultaneously creating video levels at different rates is computationally demanding and quickly exceeds the computational capacity of mobile devices. As a remedy, we propose a network-aware video level selection approach which reduces the number of levels that need to be encoded. To this end, we develop an algorithm which selects a reduced set of video levels from a static pre-defined set based on TCP uplink throughput information. More specifically, during session start-up and after inter-RAN handovers, TCP uplink throughput information from a remote database is used while otherwise, actual TCP uplink throughput measurements are performed. We test the proposed approach in an automotive scenario to upstream the video of a vehicles front-facing camera to a remote video portal. Our results show that our proposed network-aware video level selection approach leads to a significant reduction of the number of video levels that need to be encoded. At the same time, a similar quality of experience is achieved in terms of mean subjective quality of the delivered video segments, interrupted playback duration due to stalling events, and number of quality switches when compared to an implementation which considers the static full set of video levels.

Low-Complexity and Context-Aware Estimation of Spatial and Temporal Activity Parameters for Automotive Camera Rate Control

Rate control in video compression adjusts the encoding parameters to reach a certain target bitrate for the encoded video. State-of-the-art rate controllers for hybrid video coding typically employ content-dependent video bitrate models and video quality metrics (VQMs). To capture the content characteristics, temporal and spatial video activity measures are determined from the raw video using computationally complex algorithms that require access to the uncompressed source video. In automotive deployments, however, full access to the uncompressed source video and the internal functions of video encoders is typically not possible. As a remedy, in this paper, we present a low-complexity approach to estimate the temporal activity (TA) and spatial activity (SA) measures for videos that are captured by a front-facing camera of a vehicle, based on the context information of the vehicle. To this end, we exploit information about the dynamics of the vehicle and other vehicles in the field-of-view of the front-facing camera. We apply the estimated TA and SA values to a video bitrate model and an objective VQM and use these models to solve the rate control problem to determine the optimal encoding settings for given bitrate constraints. The proposed low-complexity solution offers a similar accuracy in achieving rate constraints and similar perceptual quality characteristics as a solution that uses the computed TA and SA values, with the advantage that no access to the uncompressed source video stream or the internal functions of the video encoder is required.