Catálogo de publicaciones - libros

With the growth of broadband networks, Video-on-Demand (VoD) has become realistic. Most of the significant broadcasting schemes have been proposed to reduce the server bandwidth requirement for Constant Bit-Rate (CBR) encoded videos. The few existing proposals, which support of the bandwidth-efficient Variable Bit-Rate (VBR) encoded videos, smooth and minimize the server bandwidth requirement at the cost of data losses. The lossless and bandwidth efficient (LLBE) scheme states that minimization of the server bandwidth as a shortest path problem on a directed acyclic graph, and uses a dynamic programming method to solve the problem. However, it cannot be used for support live video broadcasting. In this paper, we propose a live harmonic broadcasting (LHB) scheme to support VBR-encoded live video broadcasting. The ideas behind the scheme are (1) support VBR-encoded videos by asynchronous downloading and playing, and hybrid division by length and size, and (2) support live videos by postponing recasting process. It is simple and effective. Using data from real videos, we conduct a simulation to evaluate our scheme. The experiment results indicate that the LHB scheme requires slightly higher server bandwidth than LLBE scheme.

Efficient H.264 video transmission over wireless/mobile networks, which is used as a dominant video coding standard in Digital Multimedia Broadcasting (DMB) and in other advanced video conferencing, becomes dominant. However, wireless video transmission suffers from deficient wireless channel conditions such as high bit error rate, error bursts due to channel fading and bandwidth limitations. In this paper, a novel design and analysis of unified error-control with cross-layer interaction over IEEE 802.11e Wireless LAN, in order to improve error protection performance, is proposed. This framework combines cross-layer error protection techniques, i.e., error correction code in the link/MAC layer, erasure code in the application layer and automatic retransmission across the link/MAC layer and the application layer. The performance of the proposed scheme in comparison to the generic scheme is demonstrated by simulation.

Increase of WLAN network deployments lead to the need of developing tools to predict coverage in terms of available service. In this paper we propose to establish service coverage based only on approximate floor plans by using the so-called PixelFlow algorithm. This algorithm is based on discrete version of the Huygens principle and appears to be rather robust to approximation in the floor plan. Measurements of service performances have been undertaken and used to calibrate the prediction results. Since the conventional calibration based on prediction errors is not the goal of service coverage prediction, a new metric has been developed to quantify differences between predicted and measured boundaries of the service coverage. Despite the complex impact of inaccuracies related to floor plan, wall material, radio propagation and WLAN protocols, it appears that the service coverage prediction proposed here is suitable to ease the radio network design of indoor Wi-Fi system.

We consider the state of the wireless channel in terms of the covariance stationary signal-to-noise ratio (SNR) process and parameterize it using the probability distribution function of SNR and lag-1 autocorrelation coefficient of associated autocorrelation function (ACF). In order to discriminate the state of the wireless channel we apply methods of statistical process control. Particularly, we use exponential weighted moving average (EWMA) change-point statistical test to detect shifts in the mean of the SNR process. The proposed approach is verified using SNR measurements of IEEE 802.11b wireless channel.

In this paper we propose the use of statistical QoS guarantees for transmission over the wireless channel. Here, instead of QoS assurances we propose to guarantee the percentage of time the QoS requirements are satisfied. We present an associated scheduling algorithm for the opportunistic multiple access system. We compare the proposed scheduler with popular schedulers from the literature. We observe that the statistical QoS guarantee is an attractive alternative to the assured QoS for the wireless platform since such strict QoS assurances decrease the wireless system performance significantly.

Location determination of mobile users within a building has attracted much attention lately due to its many applications in mobile networking including network intrusion detection problems. However, it is challenging due to the complexities of the indoor radio propagation characteristics exacerbated by the mobility of the user. A common practice is to mechanically generate a table showing the radio signal strength at different known locations in the building. A mobile user’s location at an arbitrary point in the building is determined by measuring the signal strength at the location in question and determining the location by referring to the above table using a LMSE (least mean square error) criterion. Obviously, this is a very tedious and time consuming task. This paper proposes a novel and automated location determination method called ARIADNE. Using a two dimensional construction floor plan and only a single actual signal strength measurement, ARIADNE generates an estimated signal strength map comparable to those generated manually by actual measurements. Given the signal measurements for a mobile, a proposed clustering algorithm searches that signal strength map to determine the current mobile’s location. The results from ARIADNE are comparable and may even be superior to those from existing localization schemes.

Power saving mechanisms in wireless ad hoc network nodes mainly switch off the transmission and reception hardware for a maximal amount of time and turn it on again within a given interval. Many approaches aim to synchronize the state changes of the nodes in the network through distributed beacon generation and introduce mechanisms where nodes synchronously wake up at designated points of time to exchange announcements about pending traffic. Synchronization however is difficult to achieve, in particular in ad hoc networks. This paper describes the simulation, evaluation and refinement of a recently proposed power saving approach based on asynchronous wake-up patterns and wake-up announcements integrated with AODV. We show that significant improvements of the connectivity under low wake ratios can be achieved by carefully designed forwarding strategies of AODV route request messages.

This paper proposes a new power-aware routing protocol, TDPR(Traffic load and lifetime Deviation based Power-aware Routing protocol), that does not only consider the residual battery capacity and transmission power, but also the traffic load of nodes and deviation among node lifetimes. It helps to extend the entire network’s lifetime and to achieve load balancing. Simulation using ns-2 shows better the performance of the proposed routing protocol in terms of load balancing of the entire network, the consumed energy capacity of nodes, and paths reliability. TDPR has dead nodes 72% less than AODV, and 58% less than PSR. TDPR consumes residual energy capacity 29% less than AODV, 15% less than PSR. Error messages are sent maximum 38% less than PSR, and maximum 41% less than AODV.

The performance of an energy-efficient object tracking system depends on its accuracy in predicting the next destination of a mobile event. Unfortunately, a sophisticated prediction method cannot be operated in sensor nodes which have low computational power and storage. Moreover, precise prediction alone cannot be guaranteed to eliminate error in the future destination of the object in real circumstances. In this paper, we present a location error handling technique to prevent and handle this error efficiently. Real situations such as an unexpected change in the mobile event’s direction, failure of event-detection and failure of transmitting an error message are considered when designing the error handling technique. This simple yet effective solution complements the weakness of the energy-efficient object tracking paradigm. From experiments on both real hardware and simulation, our method outperformed the existing work.