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This study proposes an efficient localization scheme in wireless sensor networks. The proposed scheme utilizes mobile anchors and is based on ring overlapping. In a wireless sensor network, the nodes that know their locations are called reference nodes, and the other nodes that are without the knowledge of their locations are called blind nodes. To localize a certain blind node, by comparing the relative RSSI (Received Signal Strength Indicator) values among nodes, mobile beacons are utilized to find out the rings that are centered at a reference node and contain the blind node. These rings are called B-Rings. Since the mobile anchors and the reference nodes know their own locations, the B-Rings can be precisely derived. Moreover, by using multiple mobile beacons, the widths of the B-Rings can be further minimized; and then by overlapping them, the location of the blind nodes can be efficiently estimated. Most existing localization schemes that utilize mobile anchors let the mobile anchors move randomly. In contrast, the proposed scheme provides regular and simple movement mechanisms for the mobile anchors. Thus, the mobile anchors consume less energy than the other schemes, in which the mobile anchors move randomly. Analytical analysis and simulation results show that the proposed localization mechanism can achieve better location accuracy as well as less movement length of the mobile anchor than the other existing related approaches. [ABSTRACT FROM AUTHOR]

Video communication over Vehicular Ad Hoc Networks (VANETs) has many applications, such as emergency video transmission, commercial advertisements and inter-vehicle digital entertainment. However, in urban vehicular scenario, delivering video streams to highly mobile vehicles is indeed a challenging task due to high radio interference, channel loss rate and burst packet losses. Thus, designing an error resilient scheme for reliable video geocasting in such harsh scenarios needs to be addressed. In this paper, we propose an error resilient scheme based on packet level Forward Error Correction (FEC) and interleaving technique for reliable video geocasting over VANET. The proposed scheme is able to adapt channel variations by using a Real Time Control Protocol (RTCP) report of vehicles within communication range of the video source. To achieve a fair comparison with other error protection schemes, we have implemented a proposed error resilient scheme in Network Simulator 2 (NS 2). The results of simulation based study show that the proposed scheme is able to improve perceived video quality and protection efficiency while minimizing bandwidth overhead (introduced by proactive error recovery) in urban vehicular scenarios. [ABSTRACT FROM AUTHOR]

The Hybrid ARQ (HARQ) mechanism is the well-known error packet recovery solution composed of the Automation Repeat reQuest (ARQ) mechanism and the Forward Error Correction (FEC) mechanism. However, the HARQ mechanism neither retransmits the packet to the receiver in time when the packet cannot be recovered by the FEC scheme nor dynamically adjusts the number of FEC redundant packets according to network conditions. In this paper, the Adaptive Hybrid Error Correction Model (AHECM) is proposed to improve the HARQ mechanism. The AHECM can limit the packet retransmission delay to the most tolerable end-to-end delay. Besides, the AHECM can find the appropriate FEC parameter to avoid network congestion and reduce the number of FEC redundant packets by predicting the effective packet loss rate. Meanwhile, when the end-to-end delay requirement can be met, the AHECM will only retransmit the necessary number of redundant FEC packets to receiver in comparison with legacy HARQ mechanisms. Furthermore, the AHECM can use an Unequal Error Protection to protect important multimedia frames against channel errors of wireless networks. Besides, the AHECM uses the Markov model to estimate the burst bit error condition over wireless networks. The AHECM is evaluated by several metrics such as the effective packet loss rate, the error recovery efficiency, the decodable frame rate, and the peak signal to noise ratio to verify the efficiency in delivering video streaming over wireless networks. [ABSTRACT FROM AUTHOR]

IEEE 802.11 protocol supports adaptive rate mechanism, which selects the transmission rate according to the condition of the wireless channel, to enhance the system performance. Thus, research of multi-rate IEEE 802.11 medium access control (MAC) performance has become one of the hot research topics. In this paper, we study the performance of multi-rate IEEE 802.11 MAC over a Gaussian channel. An accurate analytical model is presented to compute the system saturation throughput. We validate our model in both single-rate and multi-rate networks through various simulations. The results show that our model is accurate and channel error has a significant impact on system performance. In addition, our numerical results show that the performance of single-rate IEEE 802.11 DCF with basic access method is better than that with RTS/CTS mechanism in a high-rate and high-load network and vice versa. In a multi-rate network, the performance of IEEE 802.11 DCF with RTS/CTS mechanism is better than that with basic access method in a congested and error-prone wireless environment. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

To compensate for the effects of fading in wireless channels, IEEE 802.11 systems utilize a rate-adaptation mechanism to accomplish a multi-rate capability. However, the IEEE 802.11 distributed coordination function results in a fundamental performance anomaly in multi-rate networks; namely, when stations with different transmission rates collide, the throughput performance of the high-rate station is significantly degraded by the relatively longer channel occupancy time of the low-rate station. This study resolves this problem through the use of an enhanced high-performance distributed coordination function (EHDCF) protocol. While most existing solutions to the multi-rate performance anomaly problem have the form of simple contention-based protocols, EHDCF has two modes, namely a contending mode and an active mode. In the proposed protocol, new stations joining the network are assigned a contending mode, but switch to an active node (and are therefore permitted to transmit data packets) as soon as they have gained access to the channel. Having transmitted a data packet, the active node then selects the next transmission station in accordance with a probability-based rule designed such that the high-rate stations within the network receive a greater number of transmission opportunities than the low-rate stations. The simulation results show that the EHDCF protocol not only yields a significant improvement in the network throughput but also guarantees the temporal fairness of all the stations. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

WiMAX is a promising broadband wireless networking technology and is expected to take the place of broadband access solutions such as DSL and cable. Owing to its superior support in mobility, it is expected to provide integrated voice and data service to realize broadband mobile computing. In order to reach better quality-of-service (QoS) requirements for real-time applications, the IEEE 802.16e standard defines five different services among traffic categories with different multimedia requirements. However, the problem of choosing the right set of medium access control parameters and packet scheduling policy to provide strict QoS guaranteed in IEEE 802.16e Broadband Wireless Access (BWA) systems remains unsolved and left as an open issue. In this paper, we propose a novel polling-based uplink packet scheduling policy for real-time Polling Service and extended real-time Polling Service (rtPS/ertPS) traffic to support real-time applications, with strict delay requirements, such as variable bit rate (VBR) traffic in IEEE 802.16e BWA systems. The proposed transmit-permission policy can derive sufficient conditions such that all the rtPS/ertPS sources satisfy their time constraints to provide deterministic QoS guarantees. In addition to theoretical analysis, simulations are conducted to evaluate the performance of the proposed scheme. As it turns out, our design provides a good quality performance in the IEEE 802.16e BWA systems. Copyright © 2008 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

According to the latest version of the IEEE 802.11 standard, the backoff parameters of its collision avoidance mechanism are far from optimal, especially in a heavy load or error-prone WLAN environment. This strategy has a high collision probability and channel utilization is degraded in bursty arrivals or congested scenarios. Besides, the standard backoff mechanism may treat noise corruption as packet collisions. In this paper, we identify the relationship between backoff parameters, contention level, and channel BER in order to propose a simple, but yet well-performing distributed algorithm that allows a station to dynamically adjust its contention window size based on turn-around-time measurement of channel status. In addition to theoretical analysis, simulations are conducted to evaluate its performance. The proposed scheme works very well in providing a substantial performance improvement in heavy loaded and error-prone WLAN environments. [ABSTRACT FROM PUBLISHER]

This paper proposes a Random Early Detection Forward Error Correction (RED-FEC) mechanism to improve the quality of video delivered over Wireless Local Area Networks (WLAN5). In contrast to previous FEC schemes, in which the rate determination information is fed back from the receiver side, in our proposed method, the redundancy rate is calculated directly at the wireless Access Point (AP) in accordance with the network traffic load, as indicated by the AP queue length. An analytical model is developed to predict the effective packet loss rate of a video stream delivered over a WLAN with RED-FEC protection. The numerical results show that the proposed RED-FEC mechanism consistently achieves higher recovery efficiency than a conventional FEC scheme under high and low network loading conditions. [ABSTRACT FROM AUTHOR]

The main purpose of this article is to provide researchers or practitioners with greater flexibility to analyze their proposed designs for network, protocol, or video coding of MDC video transmission without being obliged to consider a particular tool set for each kind of video-quality evaluation. Therefore, a generalized simulation and evaluation frame work for video transmission is an important and useful tool to the video-coding of networking was found by research community. On the one hand, for video-coding studies, one can simulate the effects of a more realistic network on video sequences resulting from their coding schemes. On the other hand, in networking analysis, one can evaluate the impact of real video streams on proposed network protocols [ABSTRACT FROM PUBLISHER]

The failure of legacy packet markers such as the Single Rate Three Color Marker (SRTCM) and the Two Rate Three Color Marker (TRTCM) to distinguish important and less important data renders them unsuitable for MPEG video transmission in a DiffServ network. Therefore, we propose a Two Markers System (TMS) to improve the delivery quality of MPEG video streams. We use authentic MPEG4 video traffic traces to compare the performance of the proposed TMS system with those of legacy packet markers. Results show that TMS outperforms the legacy traffic markers in terms of the quality of the delivered MPEG video streams. [ABSTRACT FROM PUBLISHER]