Woonghee Lee

Poster: Asynchronous Acoustic Localization using Commercial Devices

In this paper, we design and implement an asynchronous multi-device acoustic localization system. Although the relative position and distance can be useful to many applications such as drone swarming, not much research has been conducted on the field. As synchronizing multiple devices can be difficult or even impossible with certain hardware, we devised an asynchronous algorithm that provides a high accuracy ranging and localization. A high performance ranging and localization technique that uses a relatively minor source, sound, can provide a new set of characteristics. Our proposed algorithm can work on most commercial devices that have acoustic capabilities.

Wi-Fi Seeker: A link and Load Aware AP Selection Algorithm

The demand of mobile traffic increases tremendously as various Internet services are provided to mobile phones and computing devices, making mobile carriers increase the capacity of their cellular network. Since current cell towers and auxiliary devices cannot carry an excessive amount of traffic, several mobile carriers try to install low cost wireless equipment such as a Wi-Fi access point (AP) in order to offload overloaded traffic on cell towers. However, APs are installed randomly unlike cell towers because they can be installed by anyone and anywhere. The randomized allocation of APs incurs interference that causes serious degradation of wireless communication quality. Therefore, it is necessary to design mobile devices to use the environment or channel that contains the least interference for proper Wi-Fi communication. In order to make a mobile device experience the best wireless download quality, this paper proposes a novel AP selection mechanism that selects an AP that contains the least interference level compared to others with different number of communicating devices and amount of traffic load. The proposed selection mechanism does not require any additional feedback from nearby devices or APs. Performance evaluation was done by using real mobile devices with open source platform called Android.

A Collaborative Framework of Enabling Device Participation in Mobile Cloud Computing

Cloud Computing attracts much attention in the community of computer science and information technology because of resource efficiency and cost-effectiveness. It is also evolved to Mobile Cloud Computing to serve nomadic people. However, any service in Cloud Computing System inevitably experiences a network delay to access the computing resource or the data from the system, and entrusting the Cloud server with the entire task makes mobile devices idle. In order to mitigate the deterioration of network performance and improve the overall system performance, we propose a collaborative framework that lets the mobile device participate in the computation of Cloud Computing system by dynamically partitioning the workload across the device and the system. The proposed framework is based on it that the computing capability of the current mobile device is significantly enhanced in recent years and its multi-core CPU can employ threads to process the data in parallel. The empirical experimentation presents that it can be a promising approach to use the computing resource of the mobile device for executing computation-intensive tasks in Cloud Computing system.

Channel Quality Estimation for Improving Awareness of Communication Situation in the 2.4 GHz ISM Band

Supported by the technological advancements in wireless communication systems, current mobile devices are capable of utilizing diverse radio interfaces. Furthermore, there are various networks around the mobile devices in heterogeneous networks. If the mobile devices are aware of the status of channels used by different communications, the devices can utilize a wide range of network options intelligently in heterogeneous networks. However, it is not easy for mobile devices to estimate the quality of channels used by different networks because of differences among communication standards. To overcome this limitation, we view the channel map used for Bluetooth communications from a new angle. In this paper, we propose a new scheme which utilizes the channel map to estimate channels’ qualities of other standards, not of Bluetooth. Using the proposed scheme named BluS, mobile devices can estimate channels’ qualities of standards using the 2.4 GHz ISM band. Therefore, the devices with BluS are able to make decisions more intelligently and properly in heterogeneous networks. We implemented BluS on off-the-shelf smartphones and conducted extensive experiments and analysis to verify the performance of BluS.

MACoD: Mobile Device-Centric Approach for Identifying Access Point Congestion

These days, since many mobile devices support Wi-Fi, the number of Wi-Fi hotspots are increasing. At the same time, the number of places where users can use wireless LAN are increasing. Unlike the cellular network, the traffic of wireless LAN may not be distributed evenly because there is no supervisor to control the network traffic. In addition, due to the low throughput and the high packet error rate in wireless communication, the network traffic may converge at some Access Points (APs) which take a role of connecting wired and wireless communication interfaces. Therefore, congestion can easily happen at APs in wireless LAN. However, received signal strength indicator (RSSI) frequently used does not mean the network state of AP, and existing sender-based congestion detection and control protocols cannot recognize accurately where the congestion occurs. Therefore, current mobile devices continuously use the connected AP even if it is congested after the association. In this paper, we propose MACoD, the low power AP congestion detection system for mobile devices, in order to resolve aforementioned problems. Furthermore, by conducting diverse simulations, actual experiments, and power consumption analysis, we validate that MACoD can detect congestion effectively and that it is suitable for mobile devices.

CoSA: Adaptive link-aware real-time streaming for mobile devices

Programmable wireless devices which can perceive the current radio environment, decide available spectra, and dynamically change the radio access method, and networking protocols have been proposed to improve spectrum usage, interference mitigation, and connectivity. However, these transitions are currently lacking at upper layers. In this paper, we propose an upper layer cognitive system beyond channel sensing effectiveness and spectrum utilization achieved in adjusting PHY and MAC parameter settings. The proposed cognitive video streaming system achieves end-to-end goals at an upper video layer: quality of experience, service continuity, and survivability. Based on the link state of the receiver, the proposed system identifies areas of importance in the image stream, allocates higher bandwidth for the important areas compared to the other areas which is adjusted to use the less bandwidth with CoSA encoder and decoder, and receive the link state feedback from the receiver. To further understand the CoSAs benefit, we implemented two real test-beds for the cognitive video streaming system where the one uses conventional IEEE 802.11 networking technologies and the other employs a software defined radio platform, and performed a performance evaluation study in order to see the effectiveness of the proposed scheme. The results indicate that the proposed system can dynamically change actual data rates according to SINR feedback, which results in at least 180% improvement of transmission time compared to conventional method, while maintaining PSNR range between 30 to 40 dB with eminently reduced data size.

Acoustic Localization without Synchronization

In this paper, we design and implement an asynchronous multi-device acoustic localization system. Although the relative position and distance can be useful to many applications such as drone swarming, not much research has been conducted on the field. As synchronizing multiple devices can be difficult or even impossible with certain hardware, we devised an asynchronous algorithm that provides a high accuracy ranging and localization. A high performance ranging and localization technique that uses a relatively minor source, sound, can provide a new set of characteristics. Also, the proposed design uses multiple devices to enhance the performance of each and all of the ranging results. Our proposed algorithm can work on most commercial devices that have acoustic capability of emitting a specific sound and recording general sound. In this paper, the architecture of the entire system, the description of the algorithms, and the evaluation of the system are elaborated.

Improving quality of multimedia services through network performance isolation in a mobile device

Due to the advancement of hardware and software, today’s mobile devices, such as smartphones, tablet PCs, and laptops, are capable of providing a wide range of services. Among various services, a lot of users use multimedia services on mobile devices, and the size of mobile multimedia traffic is constantly increasing. Especially, the growth of social networking services and content-sharing sites stimulates creating and sharing of multimedia contents. Such environment made it possible for today’s mobile users to frequently download or upload multimedia data. Nowadays, smartphones allow users to multi-task between different services, so the multimedia service often coexists with background services in a mobile device at the same time. In these cases, the performance degradation of a multimedia service happens due to concurrently running background services in the device. In this paper, we propose MuSNet, a scheme for improving QoS and QoE of multimedia services through network performance isolation in a mobile device, which resolves the aforementioned problem by applying the concept of performance isolation to the multimedia services. MuSNet is the mobile device-based scheme without any modification on servers. Furthermore, unlike most performance isolation implemented by virtual machines, we suggest a scheme that does not require virtualization that might be heavy for mobile devices. The proposed scheme was implemented on a smartphone by modifying the kernel, and various experiments were conducted to evaluate the advanced system behavior of MuSNet.

Network Performance Isolation Scheme for QoE in a mobile device

Todays smartphones and tablet PCs are equipped with various sensor units and wireless capabilities along with high performance computing units, which make these mobile devices capable of providing a wide range of services. Because of such characteristics, mobile devices consume more network traffic and frequently use multiple Internet services at the same time. The performance degradation of a foreground service happens frequently due to concurrently running background services in a mobile device. In this paper, we propose NetPIS, Network Performance Isolation Scheme for QoE, which resolves the aforementioned problem by applying the concept of performance isolation to the foreground service. NetPIS is the receiver-based scheme suitable for mobile devices without any modification on senders. Furthermore, unlike most performance isolation implemented by virtual machines, we suggest a scheme that does not require virtualization that might be heavy for mobile devices. The proposed scheme was implemented on a smartphone by modifying the kernel, and various experiments were conducted to evaluate the advanced system behavior of NetPIS.

Link-aware AP selection for improving Wi-Fi quality

The demand of mobile traffic increases tremendously as various Internet services are provided to mobile phones and computing devices, making mobile carriers to increase capacity of cellular network. Since current cell towers and auxiliary devices cannot carry excessive amount of traffic, several mobile carriers try to install low cost wireless equipments such as Wi-Fi access points (AP) so that some part of mobile traffic can be offloaded to these wireless nodes. Unlike cell towers, APs are installed randomly since there is no specific allocation policy for these license-exempt band equipment that are open to everyone. Since the randomized allocation of APs incur interference that causes serious degradation of wireless communication quality, it is necessary to design mobile devices to communicate in the environment or channel that contains the least interference. In order to make a mobile device experience the best wireless download quality, this paper proposes a novel AP selection mechanism that selects an AP that contains the least interference level compared to others with different number of communicating devices and amount of traffic load. Proposed selection mechanism does not require any additional feedback from nearby devices or APs. Performance evaluation is done by using real mobile devices with open source platform called Android.