IEEE Access

Point cloud streaming has recently attracted research attention as it has the potential to provide six degrees of freedom movement, which is essential for truly immersive media. The transmission of point clouds requires high-bandwidth connections, and adaptive streaming is a promising solution to cope with fluctuating bandwidth conditions. Thus, understanding the impact of different factors in adaptive streaming on the Quality of Experience (QoE) becomes fundamental. Point clouds have been evaluated in Virtual Reality (VR), where viewers are completely immersed in a virtual environment. Augmented Reality (AR) is a novel technology and has recently become popular, yet quality evaluations of point clouds in AR environments are still limited to static images. In this paper, we perform a subjective study of four impact factors on the QoE of point cloud video sequences in AR conditions, including encoding parameters (quantization parameters, QPs), quality switches, viewing distance, and content characteristics. The experimental results show that these factors significantly impact the QoE. The QoE decreases if the sequence is encoded at high QPs and/or switches to lower quality and/or is viewed at a shorter distance, and vice versa. Additionally, the results indicate that the end user is not able to distinguish the quality differences between two quality levels at a specific (high) viewing distance. An intermediate-quality point cloud encoded at geometry QP (G-QP) 24 and texture QP (T-QP) 32 and viewed at 2.5m can have a QoE (i.e., score 6.5 out of 10) comparable to a high-quality point cloud encoded at 16 and 22 for G-QP and T-QP, respectively, and viewed at a distance of 5m. Regarding content characteristics, objects with lower contrast can yield better quality scores. Participants’ responses reveal that the visual quality of point clouds has not yet reached an immersion level as desired. The average QoE of the highest visual quality is less than 8 out of 10. There is also a good correlation between objective metrics (e.g., color Peak Signal-to-Noise Ratio (PSNR) and geometry PSNR) and the QoE score. Especially the Pearson correlation coefficients of color PSNR is 0.84. Finally, we found that machine learning models are able to accurately predict the QoE of point clouds in AR environments. The subjective test results and questionnaire responses are available on GitHub: https://github.com/minhkstn/QoE-and-Immersion-of-Dynamic-Point-Cloud.

This paper investigates the effects of parasitic elements on the performance of MIMO patch antenna. Multiple square parasitic elements are added in close proximity to each of the rectangular patch elements. These parasitic elements affect the electromagnetic field distribution and consequently reduce the mutual coupling. In addition, wider bandwidth is also achieved. Two MIMO antennas coupled in H-plane and E-plane are designed and measured to demonstrate the proposed concept. The measured results show that both designs have a wide impedance bandwidth of 14% with isolation of more than 20 dB across the whole band (with a small antenna profile of 0.05λ0). For 40-dB isolation, the H-coupled and E-coupled design achieve a bandwidth of 2.7% and 1.5%, respectively. Compared to other methods, the proposed method has much simpler structure, wider bandwidth and comparable improvement in isolation, with the tradeoff in larger antenna element size.

This paper presents a low-profile circularly polarized (CP) antenna with wideband and polarization-reconfigurable characteristics. The proposed antenna consists of a truncated-corner patch working as a CP source and a non-uniform metasurface (MS) acting as parasitic elements for performance enhancement. The non-uniform MS is utilized to produce additional operating bands in the higher frequency range, which are then combined with the lower band produced by the driven patch to significantly broaden the overall operating bandwidth. The polarization switching mechanism is based on the ON/OFF states of two p-i-n diodes. The fabricated prototype shows the measured overlapped bandwidth between -10 dB impedance and 3-dB axial ratio is 25.6% and peak broadside gain is 7.3 dBic.