Shaoen Wu

Visible light communications for 5G wireless networking systems: from fixed to mobile communications

Visible light communication, considered as a potential access option for 5G wireless communications, is gaining extensive attention. VLC has strengths in energy efficiency and ultra wide bandwidth, but also has weakness in transmission range and obstacles in transmission paths. This article aims to provide a conclusive investigation of the latest progress in research on VLC, which can be used as part of 5G wireless communication systems. This work highlights the strengths and weaknesses of VLC in comparison with RF-based communications, especially in spectrum, spatial reuse, security and energy efficiency. The article also investigates various lighting sources proposed for VLC systems. It summarizes the literature work on VLC networking into two categories: fixed and mobile VLC communications.

Rate adaptation algorithms for IEEE 802.11 networks: A survey and comparison

Rate adaptation is the determination of the optimal data transmission rate most appropriate for current wireless channel conditions. It consists of assessing channel conditions and accordingly adjusting the rate. Rate adaptation is fairly challenging due to wild channel conditions fluctuations. In the last decade, rate adaptation for IEEE 802.11 networks has been extensively investigated. This paper presents a comprehensive and detailed study of the advances of rate adaptation schemes proposed for IEEE 802.11 networks, and summarizes their characteristics. We also categorize these rate adaptation schemes based on their support of loss differentiation and their methods to sense the channel conditions. Then, this paper compares the performance of three representative schemes through simulations. Finally, open issues for rate adaptation are raised.

Security protection between users and the mobile media cloud

Mobile devices such as smartphones are widely deployed in the world, and many people use them to download/upload media such as video and pictures to remote servers. On the other hand, a mobile device has limited resources, and some media processing tasks must be migrated to the media cloud for further processing. However, a significant question is, can mobile users trust the media services provided by the media cloud service providers? Many traditional security approaches are proposed to secure the data exchange between mobile users and the media cloud. However, first, because multimedia such as video is large-sized data, and mobile devices have limited capability to process media data, it is important to design a lightweight security method; second, uploading and downloading multi-resolution images/videos make it difficult for the traditional security methods to ensure security for users of the media cloud. Third, the error-prone wireless environment can cause failure of security protection such as authentication. To address the above challenges, in this article, we propose to use both secure sharing and watermarking schemes to protect users data in the media cloud. The secure sharing scheme allows users to upload multiple data pieces to different clouds, making it impossible to derive the whole information from any one cloud. In addition, the proposed scalable watermarking algorithm can be used for authentications between personal mobile users and the media cloud. Furthermore, we introduce a new solution to resist multimedia transmission errors through a joint design of watermarking and Reed- Solomon codes. Our studies show that the proposed approach not only achieves good security performance, but also can enhance media quality and reduce transmission overhead.

Loss Differentiated Rate Adaptation in Wireless Networks

Data rate adaptation aims to select the optimal data rates for current channel conditions leading to substantial performance improvement. This paper proposes a data rate adaptation technique that: (1) exploits the periodic IEEE 802.11 beacons; (2) discriminates between frame losses due to channel fading and those due to collisions and takes actions appropriate for each type of loss; and (3) recommends and justifies the use of the lowest data rate for the very first retransmission after a frame loss. The last feature - namely retransmitting at the lowest data rate - helps in diagnosing the real cause of a frame loss. Moreover, this work analytically shows that retransmitting at the lowest data rate is more efficient, especially in poor SNR environments or when there is no knowledge of the cause of a loss (channel degradation or transmission collision). This scheme, dubbed loss differentiated rate adaptation (LDRA), is extensively evaluated through simulations and shown to perform better especially when network traffic is heavy.

Comparative Investigation on CSMA/CA-Based Opportunistic Random Access for Internet of Things

Wireless communication is indispensable to Internet of Things (IoT). Carrier sensing multiple access/collision avoidance (CSMA/CA) is a well-proven wireless random access protocol and allows each node of equal probability in accessing wireless channel, which incurs equal throughput in long term regardless of the channel conditions. To exploit node diversity that refers to the difference of channel condition among nodes, this paper proposes two opportunistic random access mechanisms: overlapped contention and segmented contention, to favor the node of the best channel condition. In the overlapped contention, the contention windows of all nodes share the same ground of zero, but have different upper bounds upon channel condition. In the segmented contention, the contention window upper bound of a better channel condition is smaller than the lower bound of a worse channel condition; namely, their contention windows are segmented without any overlapping. These algorithms are also polished to provide temporal fairness and avoid starving the nodes of poor channel conditions. The proposed mechanisms are analyzed, implemented, and evaluated on a Linux-based testbed and in the NS3 simulator. Extensive comparative experiments show that both opportunistic solutions can significantly improve the network performance in throughput, delay, and jitter over the current CSMA/CA protocol. In particular, the overlapped contention scheme can offer 73.3% and 37.5% throughput improvements in the infrastructure-based and ad hoc networks, respectively.

Rate adaptation with loss diagnosis on IEEE 802.11 networks

Rate adaptation in wireless networking aims to seek the optimal data transmission rate most appropriate for current wireless channel conditions to make full use of the channel potentials. It is important in wireless networks because (1) most of them support multiple data rates, and (2) wireless channel is unstable with fast changes on which a single rate thereby may not be proper for long. Based on a comprehensive survey of the rate adaptation for IEEE 802.1 networks in literature, this work proposes a rate adaptation scheme, dubbed effective rate adaptation (ERA), for IEEE 802.11 networks. ERA takes advantage of the fragmentation technique in IEEE 802.11 standard and utilizes the lowest rate retransmission in diagnosing frame loss cause (collision or channel degradation), diffusing collision, and promptly recovering frame losses. It also adopts an adaptive rate increase threshold concept to exploit channel potentials. Different from other rate adaptation schemes, ERA effectively addresses two challenges in rate adaptation on IEEE 802.11 networks: (1) it does not require RTS/CTS for loss diagnosis purpose; the use of RTS/CTS that are optional in IEEE standard results in inefficiency on channel utilization; (2) it promptly responds to frame failure due to channel degradation, unlike others waiting till the end of a transmission window or cycle. With extensive simulation, ERA shows its unique strength in different lossy environments, especially in collision-prone environments. Copyright

Optimal Sniffers Deployment On Wireless Indoor Localization

Location determination of indoor mobile users is challenging due the complex and volatile indoor radio propagation signals. A radio-frequency (RF) based indoor localization system, like RADAR or ARIADNE, typically operates by first constructing a lookup table mapping the radio signal strength at different known locations in the building, and then a mobile users location at an arbitrary point in the building is determined by measuring the signal strength at the location in question and searching the corresponding location from the above lookup table. Usually, the mobiles signal strength is measured by three or more sniffers deployed inside the building. Obviously, the number of sniffers and their positions greatly affect the localization performance. This paper presents a detailed analysis and experimental results that explore the impact of the sniffers deployment on the performance of the indoor localization. The results demonstrate that the best localization performance is obtained when the center of gravity of the equilateral triangular (formed by three sniffers) coincides with that of the floor plan; and in order to provide optimal localization for all positions of a large floor, it is necessary to deploy more than three sniffers in a semi-mesh style such that any position in the building is always covered by three nearby sniffers.

An Architecture of Cloud-Assisted Information Dissemination in Vehicular Networks

Vehicular network technology allows vehicles to exchange real-time information between each other, which plays a vital role in the development of future intelligent transportation systems Existing research on vehicular networks assumes that each vehicle broadcasts collected information to neighboring vehicles, so that information is shared among vehicles. The fundamental problem of what information is delivered with which vehicle(s), however, has not been adequately studied. We propose an innovative cloud-assisted architecture to facilitate intelligent information dissemination among vehicles. Within the novel architecture, virtual social connections between vehicles are created and maintained on the cloud. Vehicles with similar driving histories are considered friends in a vehicular social network (VSN). The closeness of the relation between two vehicles in a VSN is then modeled by the three-valued subjective logic model. Based on the closeness between vehicles, only relevant information will be delivered to vehicles that are likely interested in it. The cloud-assisted architecture coordinates vehicular social connection construction, VSN maintenance, vehicle closeness assessment, and information dissemination.

Adaptive Data Compression in Wireless Body Sensor Networks

This paper introduces an innovative data compression methodology in an adaptive way guaranteeing signal interpretation quality and energy efficiency in wireless body area sensor network. The approach is based on the discrete cosine transform. Under different channel conditions, the resulting wavelet coefficients are thresholded adaptively to match a user-specified percentage of root-mean-square difference. The nonzero coefficients of the thresholded vector are quantized adaptively by the linear quantizer of the lowest possible resolution. Signal interpretation quality and energy consuming are influenced by threshold Th, quantization length Q, and modulation method M which can be taken as a discrete optimization problem. A specific case study is designed to achieve better energy efficiency and guaranteed signal interpretation quality than typical efforts. The simulation results show that the proposed compression scheme can achieve considerable gains for ECG signals in wireless body area sensor networks.

ERA: effective rate adaptation for WLANs

Rate adaptation consists of using the optimal rate for a given channel quality: the poorer the channel quality, the lower the rate should be. Multiple rate adaptation schemes were proposed and studied so far. The first generation rate adaptation schemes perform well in collision free environments and manage quite well strict channel degradation. Under a congestion dominated environment, these schemes poorly perform because they do not differentiate losses due to channel degradation from those due to collisions and unnecessarily decrease the rate in response to collisions. A second generation rate adaptation schemes overcome this limitation. However, these most recent schemes usually require RTS/CTS control frames that are not in general used because they constitute an overhead that may heavily lower network performance especially when frame size is small. This work proposes an effective and practical rate adaptation scheme (ERA) that does not require RTS/CTS control frames. ERA judiciously uses fragmentation in compliance with IEEE 802.11 standard to diagnose the cause of frame loss and to promptly recover from frame losses. Through extensive simulations on ns-2, ERA exhibits a significant throughput improvement over other rate adaptation schemes.