Cheng-Hsin Hsu

On burst transmission scheduling in mobile TV broadcast networks

In mobile TV broadcast networks, the base station broadcasts TV channels in bursts such that mobile devices can receive a burst of traffic and then turn off their radio frequency circuits till the next burst in order to save energy. To achieve this energy saving without scarifying streaming quality, the base station must carefully construct the burst schedule for all TV channels. This is called the burst scheduling problem. In this paper, we prove that the burst scheduling problem for TV channels with arbitrary bit rates is NP-complete.We then propose a practical simplification of the general problem, which allows TV channels to be classified into multiple classes, and the bit rates of the classes have power of two increments, e.g., 100, 200, and 400 kbps. Using this practical simplification, we propose an optimal and efficient burst scheduling algorithm. We present theoretical analysis, simulation, and actual implementation in a mobile TV testbed to demonstrate the optimality, practicality, and efficiency of the proposed algorithm.

Design and Evaluation of a Proxy Cache for Peer-to-Peer Traffic

Peer-to-peer (P2P) systems generate a major fraction of the current Internet traffic, and they significantly increase the load on ISP networks and the cost of running and connecting customer networks (e.g., universities and companies) to the Internet. To mitigate these negative impacts, many previous works in the literature have proposed caching of P2P traffic, but very few (if any) have considered designing a caching system to actually do it. This paper demonstrates that caching P2P traffic is more complex than caching other Internet traffic, and it needs several new algorithms and storage systems. Then, the paper presents the design and evaluation of a complete, running, proxy cache for P2P traffic, called pCache. pCache transparently intercepts and serves traffic from different P2P systems. A new storage system is proposed and implemented in pCache. This storage system is optimized for storing P2P traffic, and it is shown to outperform other storage systems. In addition, a new algorithm to infer the information required to store and serve P2P traffic by the cache is proposed. Furthermore, extensive experiments to evaluate all aspects of pCache using actual implementation and real P2P traffic are presented.

Building book inventories using smartphones

Manual generation of a book inventory is time-consuming and tedious, while deployment of barcode and radio-frequency identification (RFID) management systems is costly and affordable only to large institutions. In this paper, we design and implement a mobile book recognition system for conveniently generating an inventory of books by snapping photos of a bookshelf with a smartphone. Since smartphones are becoming ubiquitous and affordable, our inventory management solution is cost-effective and very easy to deploy. Automatic and robust book recognition is achieved in our system using a combination of spine segmentation and bag-of-features image matching. At the same time, the location of each book is inferred from the smartphones sensor readings, including accelerometer traces, digital compass measurements, and WiFi signatures. This location information is combined with the image recognition results to construct a location-aware book inventory. We demonstrate the effectiveness of our book spine recognition and location estimation techniques in recognition experiments and in an actual mobile book recognition system.

Flexible Broadcasting of Scalable Video Streams to Heterogeneous Mobile Devices

We study the scalable video broadcasting problem in mobile TV broadcast networks, where each TV channel is encoded into a scalable video stream with multiple layers, and several TV channels are concurrently broadcast over a shared air medium to many mobile devices with heterogeneous resources. Our goal is to encapsulate and broadcast video streams encoded in scalable manner to enable heterogeneous mobile devices to render the most appropriate video substreams while achieving high energy saving and low channel switching delay. The appropriate streams depend on the device capability and the target energy consumption level. We propose two new broadcast schemes, which are flexible in the sense that they allow diverse bit rates among layers of the same stream. Such flexibility enables videos to be optimally encoded in terms of coding efficiency, and allows the coded video streams to be better matched with the capability of mobile devices. We analyze the performance of the proposed broadcast schemes. In addition, we have implemented the proposed schemes in a real mobile TV testbed to show their practicality and efficiency. Our extensive experiments confirm that the proposed schemes enable energy saving differentiation: between 75 and 95 percent were observed. Moreover, one of the schemes achieves low channel switching delays: 200 msec is possible with typical system parameters.

ISP-friendly peer matching without ISP collaboration

In peer-to-peer (P2P) systems, a receiver needs to be matched with multiple senders, because peers have limited capacity and reliability. Efficient peer matching can reduce the cost on Internet Service Providers (ISPs) for carrying the P2P traffic. We study the following peer-matching problem: given a set of potential senders, find the best subset of them that will minimize the transit cost on ISPs. This problem is fairly general and the proposed algorithms for solving it can be used in many P2P systems. We propose two ISP-friendly algorithms for solving this problem: ISPF and ISPF-Lite. These two matching algorithms leverage public available information, such as BGP tables, to infer the network topology, and to minimize the cost on ISPs. The inference algorithms, however, are fairly complex, and we propose optimization techniques to reduce the inference time and to lower the memory requirement. We use trace-driven simulations to show that the proposed algorithms outperform other popular matching algorithms by a large margin. Between the two proposed algorithms, ISPF results in better matching, but incurs higher complexity. Hence, we recommend ISPF if resources are not stringent, otherwise ISPF-Lite is recommended.

A framework for cross-layer optimization of video streaming in wireless networks

We present a general framework for optimizing the quality of video streaming in wireless networks that are composed of multiple wireless stations. The framework is general because: (i) it can be applied to different wireless networks, such as IEEE 802.11e WLAN and IEEE 802.16 WiMAX, (ii) it can employ different objective functions for the optimization, and (iii) it can adopt various models for the wireless channel, the link layer, and the distortion of the video streams in the application layer. The optimization framework controls parameters in different layers to optimally allocate the wireless network resources among all stations. More specifically, we address this video optimization problem in two steps. First, we formulate an abstract optimization problem for video streaming in wireless networks in general. This formulation exposes the important interaction between parameters belonging to different layers in the network stack. Then, we instantiate and solve the general problem for the recent IEEE 802.11e WLANs, which support prioritized traffic classes. We show how the calculated optimal solutions can efficiently be implemented in the distributed mode of the IEEE 802.11e standard. We evaluate our proposed solution using extensive simulations in the OPNET simulator, which captures most features of realistic wireless networks. In addition, to show the practicality of our solution, we have implemented it in the driver of an off-the-shelf wireless adapter that complies with the IEEE 802.11e standard. Our experimental and simulation results show that significant quality improvement in video streams can be achieved using our solution, without incurring any significant communication or computational overhead. We also explain how the general video optimization problem can be applied to other wireless networks, in particular, to the IEEE 802.16 WiMAX networks, which are becoming very popular.

Rate-distortion optimized streaming of fine-grained scalable video sequences

We present optimal schemes for allocating bits of fine-grained scalable video sequences among multiple senders streaming to a single receiver. This allocation problem is critical in optimizing the perceived quality in peer-to-peer and distributed multi-server streaming environments. Senders in such environments are heterogeneous in their outgoing bandwidth and they hold different portions of the video stream. We first formulate and optimally solve the problem for individual frames, then we generalize to the multiple frame case. Specifically, we formulate the allocation problem as an optimization problem, which is nonlinear in general. We use rate-distortion models in the formulation to achieve the minimum distortion in the rendered video, constrained by the outgoing bandwidth of senders, availability of video data at senders, and incoming bandwidth of receiver. We show how the adopted rate-distortion models transform the nonlinear problem to an integer linear programming (ILP) problem. We then design a simple rounding scheme that transforms the ILP problem to a linear programming (LP) one, which can be solved efficiently using common optimization techniques such as the Simplex method. We prove that our rounding scheme always produces a feasible solution, and the solution is within a negligible margin from the optimal solution. We also propose a new algorithm (FGSAssign) for the single-frame allocation problem that runs in O(nlog n) steps, where n is the number of senders. We prove that FGSAssign is optimal. Furthermore, we propose a heuristic algorithm (mFGSAssign) that produces near-optimal solutions for the multiple-frame case, and runs an order of magnitude faster than the optimal one. Because of its short running time, mFGSAssign can be used in real time. Our experimental study validates our analytical analysis and shows the effectiveness of our allocation algorithms in improving the video quality.

Time Slicing in Mobile TV Broadcast Networks with Arbitrary Channel Bit Rates

Mobile TV networks have received significant at- tention from the industry and academia, as they have already been deployed in several countries and their expected market potential is huge. In such networks, a base station broadcasts TV channels in bursts with bit rates much higher than the encoding bit rates of the videos. This enables mobile receivers to receive a burst of traffic and then turn off their receiving circuit till the next burst to conserve energy. The base station needs to construct a transmission schedule for all bursts of different TV channels. Constructing optimal (in terms of energy saving) transmission schedules has been shown to be an NP-complete problem when the TV channels are encoded at arbitrary bit rates. In this paper, we propose a near-optimal approximation algorithm to solve this problem. We prove the correctness of the proposed algorithm and derive its approximation factor. We also conduct extensive evaluation of our algorithm using real implementation in a mobile TV testbed and simulations. Our experimental and simulation results show that the proposed algorithm: (i) is practical and produces correct burst schedules, (ii) achieves near-optimal energy saving for mobile devices, and (iii) runs efficiently in real time.

Mobile augmented reality for books on a shelf

Retrieving information about books on a bookshelf by snapping a photo of book spines with a mobile device is very useful for book-stores, libraries, offices, and homes. In this paper, we develop a new mobile augmented reality system for book spine recognition. Our system achieves very low recognition delays, around 1 second, to support real-time augmentation on a mobile devices viewfinder. We infer user interest by analyzing the motion of objects seen in the viewfinder. Our system initiates a query during each low-motion interval. This selection mechanism eliminates the need to press a button and avoids using degraded motion-blurred query frames during high-motion intervals. The viewfinder is augmented with a books identity, prices from different vendors, average user rating, location within the enclosing bookshelf, and a digital compass marker. We present a new tiled search strategy for finding the location in the bookshelf with improved accuracy in half the time as in a previous state-of-the-art system. Our AR system has been implemented on an Android smartphone.

Broadcasting video streams encoded with arbitrary bit rates in energy-constrained mobile TV networks

Mobile TV broadcast networks have received significant attention from the industry and academia, as they have already been deployed in several countries around the world and their expected market potential is huge. In such networks, a base station broadcasts TV channels in bursts with bit rates much higher than the encoding bit rates of the videos. This enables mobile receivers to receive a burst of traffic and then turn off their receiving circuits till the next burst to conserve energy. The base station needs to construct a transmission schedule for all bursts of different TV channels. Constructing optimal (in terms of energy saving) transmission schedules has been shown to be an NP-complete problem when the TV channels carry video streams encoded at arbitrary and variable bit rates. In this paper, we propose a near-optimal approximation algorithm to solve this problem. We prove the correctness of the proposed algorithm and derive its approximation factor. We also conduct extensive evaluation of our algorithm using implementation in a real mobile TV testbed as well as simulations. Our experimental and simulation results show that the proposed algorithm: 1) is practical and produces correct burst schedules; 2) achieves near-optimal energy saving for mobile devices; and 3) runs efficiently in real time and scales to large scheduling problems.