Over the past decade, techniques for remote control vehicles (RCVs) have progressed a lot, and RCVs are receiving huge attention in various fields. Since RCVs, such as drones, have high mobility, it is important for operators to control RCVs reliably. Thus, to keep monitoring and controlling RCVs, operators continuously exchange control packets with RCVs by wireless. However, control packets can be delayed or lost due to any communication or network problems, which may cause collisions or crashes. To overcome this limitation, in this paper, we propose DupCon, a new control packet transmission scheme. Considering characteristics of packets, DupCon duplicates only control packets, not data packets, and transmits the originals and their duplicates through different paths, respectively. We designed and implemented DupCon on real devices. Moreover, we conduct an analysis on DupCon to demonstrate the validity of DupCon theoretically. Furthermore, we conducted various experiments, and the results show that DupCon improves reliability and stability of real-time remote vehicle control.

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.

Today’s mobile devices mostly contain more than one wireless interface for Internet connection. Smartphones mostly have both LTE and Wi‐Fi for data communication through Internet. Although the availability of Wi‐Fi is incomparable to that of cellular network, its strength lies in the low cost and high data rate due to continuous PHY and MAC advancement of 802.11 protocol extensions. In this paper, we propose a device‐centric system that performs cost‐effective network connectivity to the mobile device by selectively activating Wi‐Fi communication according to the device mobility and corresponding history of Wi‐Fi usage. By analyzing the device mobility using attached sensors, the system selects appropriate Wi‐Fi that has been often used in that mobility state. The system was implemented in actual mobile devices that were used to several experiments we designed to prove high performance of the system.

Many varied mobile device networks have been developed with the advancement of communication and network technologies. Cellular data networks are currently the most widely used, and the number of cellular network subscriptions has increased steadily. Most recent wireless access technologies employ asymmetric uplinks and downlinks because mobile subscribers usually download contents from the Internet. Therefore, most cellular network service providers allocate more bandwidth to downlinks than uplinks for mobile subscribers. However, this asymmetry can have unexpected influence on network performance, particularly TCP performance. When the uplink interface is congested, TCP ACK packets are delayed by TCP data packets on the uplink, causing considerable TCP retransmissions on the downlink channel. Thus, downlink bandwidth cannot be fully utilized, which results in significantly degraded downlink throughput. To resolve this problem, this paper proposes a feedback scheme, network traffic chunk regulator (NCR). We analyzed the aforementioned problem through the empirical study, and we designed and implemented NCR based on the analysis. NCR adaptively controls TCP according to the degree of link usage asymmetry. We evaluate NCR performance through simulations and experiments with real devices. We verify that the proposed scheme allows the downlink traffic to not interfere with the aggressive uplink traffic. Thus, NCR increases total link utilization and aggregated throughput significantly, without imposing additional overhead on base or mobile stations.

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.

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.

The 2.4 GHz ISM band is one of the most widely used radio bands, and many wireless communication techniques, such as IEEE 802.11, Bluetooth (BT), and ZigBee, use the band. Thus, the interference problem in the band has been an important issue. BT uses BT channel maps which indicate qualities of BT channels to reduce the interference. Fundamentally, the channel map is created after a connection between two BT devices is established, and it is designed to suit BT communications. Viewing the channel map from a new angle, we propose a new scheme which estimates channels' qualities of other standards, not of BT. The proposed scheme named BluS can create the channel map without any BT connection, and estimate channels' qualities of standards using the 2.4 GHz ISM band. We implemented BluS on off-the-shelf smartphones and conducted diverse experiments to verify the performance of BluS. Through the experiments, we confirm that BluS can estimate the channels' qualities accurately and that it is suitable for mobile devices because BluS uses low power.

Wireless multi-hop networks are scalable in that devices can easily connect to the network. Such scalability is also required in IoT. However, wireless multi-hop network mostly suffers from high probability of transmission failure due to interference, and nodes connected to the network often experience connection loss and subsequent segment loss which node mobility and routing update incur. Due to the fact that the congestion is not a sole reason for segment loss in wireless multi-hop network, the congestion control of TCP should consider momentary link instability, which unnecessarily reduces transmission speed. For this reason, this paper suggests adjustment of slow-start threshold (ssthresh) value which is used for congestion control algorithm. The adjustment algorithm is called adaptive ssthresh decision ASD algorithm that is to reduce unnecessary decrease of transmission speed in wireless multi-hop network.

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.

Today's 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.

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.

User's multimedia interaction is facing a paradigm shift from 2D to 3D videos. Nonetheless, it is still difficult to watch 3D videos with a mobile device. With current technological barrier in wireless networking, it is hardly imagined that the timely transmission for a 3D video streaming could be feasible with the mobile device. In this paper, we propose ReMA, a novel 3D video distribution system based on a lightweight compression, a linkadaptive transmission scheme, and a network-side assistance for processing capability. ReMA consists of a 3D data transmitter, a receiver, and an infrastructure for generating and distributing 3D videos. We implemented the proposed system in a real testbed and conducted a thorough empirical evaluation study. Based on the empirical results, the proposed system presents a great promise in streaming 3D video in real-time to the mobile device.

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.

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 CoSA's 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.