In this paper, we propose dynamic local lag control which dynamically changes the local lag according to the network delay for sound synchronization in joint musical performance where multiple users play musical instruments together through a network. We also make a comparison between the dynamic local lag control and the local lag control with fixed values of local lag in terms of the synchronization quality of sound, interactivity, and comprehensive quality by QoE (Quality of Experience) assessment. In the assessment, for joint musical performance, we use a networked haptic drum system in which two users play a drum set in a 3D virtual space with the same rhythm at the same tempo by using haptic interface devices As a result, we illustrate that the dynamic local lag control is effective.

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This paper proposes threshold selection interfaces for the video output scheme SCS (Switching between error Concealment and frame Skipping) in video-audio IP transmission. We conduct a subjective experiment with two threshold selection interfaces: the two mode method and the four mode method. The two interfaces are implemented with a handheld device. We then investigate the effect of user attributes on QoE. We compare the two methods with the 0 % method (pure frame skipping) and the 100 % method (pure error concealment). In the experiment, we utilize two content types: sport and drama. As a result, the threshold selection interfaces, in particular, the four mode method, achieves higher QoE than the other methods in sport. In addition, the user attributes affect preferred threshold values.

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In this paper, we propose a dynamic bandwidth allocation (DBA) algorithm for Ethernet passive optical network (EPON) systems. In the proposal, the optical line terminal (OLT) uses a proportional-integral-derivative (PID) controller to update the request threshold for each optical network unit (ONU). Each ONU uses the request threshold informed by the OLT to calculate the transmission request data length. This method allows the allocating bandwidth to converge more quickly on the target bandwidth than the conventional method while keeping the bandwidth utilization efficiency high. Simulations reveal the performance of the proposed method. We also clarify the relationship between threshold update frequency and convergence performance. The results are useful as a design guideline for the OLT's control chip.

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To improve Quality of Service in wireless networks while mobile users travel, we introduce Comfort Route Navigation (CRN) which is a navigation system based on a user centric mobility management for next generation wireless networks. CRN provides an optimal route that satisfies user needs, such as obtaining maximum wireless resources. To achieve CRN, we construct an access point (AP) map of Shinjuku city. To reflect quality of APs in this map, we evaluate throughputs at seven public Wi-Fi spots. Based on these observations, we evaluate performance of our CRN via computer simulations and in a real environment. These evaluations conduct that a CRN user could obtain higher communication quality rather than a Shortest Route (SR) user. These evaluations also conclude that CRN gain depends heavily on the quality and location of the best broadband spot.

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Mobile wireless local area networks (WLANs) are becoming popular. Mobile WLANs can be composed of WiFi devices such as portable access points (APs) and portable terminals such as smartphones, tablets and any tethering devices. Several mobile WLANs are densely deployed in a conference room or café. In this case, the WLANs have to share available channels even though they suffer from interference. The interferences coming from the same channel (intra-channel contention) or a different channel (inter-channel interference) reduce the total throughput of the WLANs. This paper investigates the throughput characteristics of several densely deployed WLANs for multimedia communications. For experiments using real machines, for example, 18 sets of WLANs, the relationship among the number of WLANs, distance of WLANs, channel assignment and total throughput was revealed. Moreover, it is shown that the number of terminals in each WLAN substantially affects the total throughput because of the nature of the multi-rate and sending opportunity fairness in CSMA/CA or a performance anomaly.

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It is important for multimedia mobile users to obtain sufficient resources and a stable capacity of resources. Network resources such as available bandwidth for mobile users, however, fluctuate depending on the level of background traffic. The deployment of several access points enables mobile users to access more network resources on the way to their destination by taking the longcut route rather than the shortcut route. These users pay an extra cost to take the longcut route but obtain greater gains in throughput over the shortcut route. Previous research has shown that the gain-to-cost ratio can be more than double for the longcut route. No considerations, however, have been made for the case in which resource fluctuation is due to network congestion. This paper investigates the quality of service (QoS) for a longcut route with fewer resources (real resources) compared with that for one with the total resources (ideal resources) in the longcut route calculation. The results show that on average, users have gains of approximately double in real resources than their gains in ideal resources. This finding indicates that users can greatly improve their gains if they can accurately predict the resource fluctuation.

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The peak signal-to-noise ratio (PSNR) used as an index of image quality usually requires original images, but this is difficult for consumer generated content such as videos on YouTube. Therefore, we developed two blind PSNR estimation methods without bit-stream analysis in which multiple support vector machines are prepared to learn differently encoded images in PSNR; using an entire frame and dividing the frame into two areas. We confirmed that higher estimation accuracy is possible for the latter method against that using the entire frame.

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A wireless communication technology that allows multiple users to communicate in real time is strongly required to support various needs such as high performance remote control systems to simultaneously move many mobile units like robots and vehicles and wireless network systems to dynamically link mobile units. This paper proposes a new multicarrier code division multiple access (MC-CDMA) scheme without the multiple access interference (MAI) and inter carrier interference (ICI) over a very large delay spread channel, which can be characterized by a block coding technique using a set of sequences with a zero correlation zone (ZCZ code) and a minimum mean square error (MMSE) RAKE receiver utilizing the pilot sequence for channel estimation to remove MAI and ICI and to reduce the influence of the inter symbol interference (ISI), respectively. It does not need a frequency domain equalization technique which has been used in multicarrier communications. The length of delay spread is related to only block size and does not depend on the size of the zero correlation zone and the number of users. In various parameters including an effective ZCZ code, the improved bit error rate (BER) performance of the proposed scheme is demonstrated by computer simulation.

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Given video inputs from multi-view cameras, our goal is to synthesize high quality free-viewpoint images in real-time. To this end, fast and accurate depth estimation from multi-view images is indispensable. Triangulation among the cameras often produces erroneous depth information, especially for textureless regions, resulting in low-quality synthesized views. To improve the quality of depth estimation while keeping fast computational speed, we combined active illuminations using a DLP projector with passive triangulation using multi-view images. The projector casts spatially incoherent patterns to the scene and makes uniform regions texture-rich so that triangulations for those regions can be greatly improved. Moreover, making the illuminations time-varying, we can further stabilize depth estimation using spatiotemporal matching, and remove the artificial patterns from the synthesized virtual views by averaging successive time frames. Our system consists of 16 video cameras synchronized with the DLP projector, and can synthesize high quality free-viewpoint image in about 10 fps.

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