This paper presents a novel solution for estimating simulator sickness in HMDs using machine learning and 3D motion data, informed by user-labeled simulator sickness data and user analysis. We conducted a novel VR user study, which decomposed motion data and used an instant dial-based sickness scoring mechanism. We were able to emulate typical VR usage and collect user simulator sickness scores. Our user analysis shows that translation and rotation differently impact user simulator sickness in HMDs. In addition, users’ demographic information and self-assessed simulator sickness susceptibility data are collected and show some indication of potential simulator sickness. Guided by the findings from the user study, we developed a novel deep learning-based solution to better estimate simulator sickness with decomposed 3D motion features and user profile information. The model was trained and tested using the 3D motion dataset with user-labeled simulator sickness and profiles collected from the user study. The results show higher estimation accuracy when using the 3D motion data compared with methods based on optical flow extracted from the recorded video, as well as improved accuracy when decomposing the motion data and incorporating user profile information.

Despite the increasing popularity of VR games, one factor hindering the industry’s rapid growth is motion sickness experienced by the users. Symptoms such as fatigue and nausea severely hamper the user experience. Machine Learning methods could be used to automatically detect motion sickness in VR experiences, but generating the extensive labeled dataset needed is a challenging task. It needs either very time consuming manual labeling by human experts or modification of proprietary VR application source codes for label capturing. To overcome these challenges, we developed a novel data collection tool, VRhook, which can collect data from any VR game without needing access to its source code. This is achieved by dynamic hooking, where we can inject custom code into a game’s run-time memory to record each video frame and its associated transformation matrices. Using this, we can automatically extract various useful labels such as rotation, speed, and acceleration. In addition, VRhook can blend a customized screen overlay on top of game contents to collect self-reported comfort scores. In this paper, we describe the technical development of VRhook, demonstrate its utility with an example, and describe directions for future research.

To provide a reliable transmission in 3GPP WCDMA systems, in the Radio Link Control (RLC) sublayer of the WCDMA, an Acknowledgement Mode (AM) is defined where an ACK frame is sent to indicate the data frame receiving status. In order to design a well-performed AM scheme, in this paper, we first investigate the AM protocol behavior and present the delay performance of the standard periodical AM-RLC scheme in the Bernoulli channel. Then, based on the observation from the performance above, we propose a dynamic AM scheme in RLC over a more general time-varying Markov channel. It is demonstrated that a much better delay performance can be achieved compared with the standard AM scheme with periodical acknowledgements.

Multimedia decoding is one of the key parts of many popular mobile multimedia applications, such as video telephony, streaming, and video playback. Since the multimedia decoding consumes a significant amount of energy on processors, it is crucial to lower the power consumption and prolong the battery life. In this paper, the statistical analysis of more than 600 processor load trace files is first presented. From the analysis, we found that it is feasible to predict the processor load of multimedia applications accurately using a low order linear time series model if the load is sampled using the feature period, which is obtained with Fast Fourier Transformation. Based on the analysis, we propose a novel interval-based DVS scheme to achieve penalty controllable energy reduction. The DVS scheme does not need any task profile or involvement of application program, and it is compatible with the service model of general purpose mobile operating systems. In addition, the proposed DVS scheme can handle the nonstationary behavior using an efficient online change detector, and important parameters, such as coefficients of the linear time series model, are estimated on the fly. More importantly, the proposed scheme can keep the Overscaling Rate (OSR) around a certain predefined value. Since the OSR has a simple and stable relationship with the Deadline Miss Rate (DMR), the penalty incurred by DVS is effectively controlled. Experimental results show that the proposed DVS scheme achieves a much smaller prediction error than previous approaches and achieves a significant processor energy reduction with adjustable and controlled penalty.

The life of battery power available time is a crucial character of the battery powered mobile device. In this paper, we investigate the performance issues of upper layer protocol, such as TCP, in IEEE 802.11 LAN's power saving mode. We discuss the tradeoff of energy saving, networking throughput and response time at the points of user experience. A novel power efficiency scheme is proposed to control the traffic transmission in power saving mode, which takes the QoS requirements of applications into account. Finally, we show that the proposed schema achieves higher user experience in our experiment.

When applying dynamic power management (DPM) techniques to pervasively deployed embedded systems, the technique needs to be very efficient so that it is feasible to implement the technique on low end processors and tight-budget memory. Furthermore, it should have the capability to track time varying behavior rapidly, because the time variance is an inherent characteristic of real world systems. Existing methods, which are usually model-based, may not satisfy the aforementioned requirements. In this paper, we propose a model-free DPM technique based on Q-learning. Q-DPM is much more efficient because it removes the overhead of parameter estimator and mode-switch controller. Furthermore, its policy optimization is performed via consecutive online trialing, which also leads to very rapid response to time varying behavior.

In this paper, we consider a coded ultra-wide band (UWB) impulse radio system. At the receiver, to estimate multipath delays and amplitudes, the soft information output from a soft-input soft-output (SISO) decoder is used to assist the estimation. The SISO decoder and the channel estimator work in an iterative way and no training sequence is used in the estimation. Compared with the non data-aided channel estimation without using the soft information output from the SISO decoder, the performance of this iterative channel estimation is better. We also explain this iterative method by using the expectation maximization (EM) algorithm, which can be used to prove the convergence of this iterative method.

The software codec on mobile device introduces significant power consumption because the energy efficiency of general processor based system is much lower than that of the dedicated hardware such as ASIC based accelerator. Dynamical Voltage Scaling (DVS) is one of the most efficient techniques to promote the energy efficiency. Most existing papers on this topic use simple heuristics to predict processor load, and poor prediction accuracy is observed in experiments. We advocate intensive analysis on processor load before designing DVS framework and algorithm. Hence, we conduct load analysis on more than 600 processor load trace files for 57 test sequences and 98 representative clips from Internet. Basic statistical analysis and time series analysis are applied intensively to identify major characteristics of the processor load. The analysis shows that it is feasible to predict processor load using low order linear time series model if the load is sampled using feature period. Moreover, there is indeed significant potential to reduce the energy consumption. Based on the analysis results, we develop a fully adaptive DVS technique to adjust supply voltage online with controllable penalty.

IEEE 802.15.3 is designed for short-distance wireless connectivity within a wireless personal area network (WPAN). It has great significance for applications such as home networking. Security is one of the fundamental issues in IEEE 802.15.3 WPAN. Although several security mechanisms have been defined in the standard, there are many others open and left for implementation. Therefore, in this paper, by utilizing the unique characteristics of the IEEE 802.15.3 WPAN, we propose a certificate-based trust management (including device initialization and certificate management) and key establishment scheme to protect the IEEE 802.15.3 WPAN.

The Dly-ACK scheme in IEEE 802.15.3 is designed to reduce the overhead of the ACK and improve the channel utilization. However, the way to use the Dly-ACK is open for implementation. In this paper, we first investigate the problems of applying the fixed Dly-ACK scheme to the TCP stream and show that the TCP performance is rather poor. Then, we propose two enhancement mechanisms for TCP with Dly-ACK over the 802.15.3 system. The first one is to request the Dly-ACK frame adaptively or change the burst size of Dly-ACK according to the queue size. The second is a retransmission counter to enable the destination DEV to deliver the packets to the upper layer timeously and in orderly fashion. Simulation results show that, with our enhancements, the TCP throughput can be improved more than 40% compared with the conventional Imm-ACK. We also investigate the impacts of some important system parameters such as the buffer size on the TCP performance. Some guidelines for the Dly-ACK design are given. Finally, it is worth pointing out that our enhancements are compatible with the standard.

An M-ary orthogonal pulse polarity modulation (OP/sup 2/M) using modified orthogonal variable spreading factor codes (OVSF), i.e., a set of orthogonal Walsh codes, for time hopping ultra wideband (TH-UWB) communication systems is proposed. Under FCC power spectrum density (PSD) constraint for UWB, the proposed M-ary OP/sup 2/M system proves to be more power efficient than traditional bi-phase shift-keying (BPSK) modulation, binary and M-ary pulse position modulation (PPM) systems. OVSF codes are modified in OP/sup 2/M to smooth the signal PSD for meeting FCC PSD mask for UWB system. Reduced complexity receiver architecture provides tractable system complexity. Analytical and simulation results show that the proposed 32-ary OP/sup 2/M TH-UWB system is more power efficient than previous PPM and BPSK modulations.

In this paper, we develop a deterministic UWB multipath channel model based on time-domain uniform geometrical theory of diffraction (TD-UTD) technique. The solution includes the three basic ray mechanisms of geometrical optics (GO) and UTD, i.e., directed ray, multireflected rays from lossy surfaces, and diffracted ray from lossy edge. Since the analysis is conducted in time-domain electromagnetic field, unlike statistical model, the approach for UWB channel model can determine not only signal attenuation, but also waveform distortion in terms of pulse shape and pulse duration when the UWB signal propagates in multipath environments. Here, a generic impulse response model by taking into account channel impulse response as well as transmitter and receiver antenna impulse responses is given. Then, the analytical description of time-domain single reflected ray and reflection coefficients of horizontal polarization and vertical polarization is provided. The time-domain multiple reflected rays are expressed by the convolution of individual reflection coefficient from lossy surfaces with different electromagnetic properties. The time-domain diffraction ray is described as time-domain diffraction coefficients and reflection coefficient. Finally, the simulation results in a typical office room are presented.

In this paper, we discuss the security issue in wireless home network (WHN) and give solution. First, we summarize the security threats and requirements of WHN, and analyze the characteristics of WHN and their influences to the design of security mechanisms. Then, based on the security threats and requirements that we have analyzed, we introduce some security mechanisms to protect the WHN. Furthermore, some alternative mechanisms are proposed for the variety of devices to choose according to their security requirements and capabilities, for example, the security delegation service (SDS) provides an efficient solution for wireless devices with low computation capability and resources to use the widely applied security protocols such as LPSEC and TLS. Finally, the security analysis is presented to demonstrate that the proposed security mechanisms are robust and efficient to secure the WHN.