MAC Retransmission Research Articles

Efficient MAC for Real-Time Video Streaming over Wireless LAN

Wireless communication systems are highly prone to channel errors. With video being a major player in Internet traffic and undergoing exponential growth in wireless domain, we argue for the need of a Video-aware MAC (VMAC) to significantly improve the throughput and delay performance of real-time video streaming service. VMAC makes two changes to optimize wireless LAN for video traffic: (a) It incorporates a Perceptual-Error-Tolerance (PET) to the MAC frames by reducing MAC retransmissions while minimizing any impact on perceptual video quality; and (b) It uses a group NACK-based Adaptive Window (NAW) of MAC frames to improve both throughput and delay performance in varying channel conditions. Through simulations and experiments, we observe 56--89% improvement in throughput and 34--48% improvement in delay performance over legacy DCF and 802.11e schemes. VMAC also shows 15--78% improvement over legacy schemes with multiple clients.

Quality-Driven Capacity-Aware Resources Optimization Design for Ubiquitous Wireless Networks

In this paper, we propose a probability-statistical capacity-prediction scheme to provide probabilistic quality-of-service (QoS) guarantees under the high traffic load of IEEE 802.11 wireless multimedia Mesh networks. The proposed scheme perceives the state of wireless link based on the MAC retransmission statistics and calculates the statistical channel capacity especially under the saturated traffic load. Via a cross-layer design approach, the scheme allocates network resource and forwards data packets by taking the interference among flows and the channel capacity into consideration. Extensive experiments have been carried out on the basis of IEEE 802.11 protocols in order to demonstrate the superiority of the proposed scheme over the existing location-based QoS optimization delivery algorithm in terms of retransmission count, successful delivery rate, and end-to-end delay on the condition of time-varying multi-hop wireless links.

MAC-Aware and Power-Aware Image Aggregation Scheme in Wireless Visual Sensor Networks

Traditional wireless sensor networks (WSNs) transmit the scalar data (e.g., temperature and irradiation) to the sink node. A new wireless visual sensor network (WVSN) that can transmit images data is a more promising solution than the WSN on sensing, detecting, and monitoring the environment to enhance awareness of the cyber, physical, and social contexts of our daily activities. However, the size of image data is much bigger than the scalar data that makes image transmission a challenging issue in battery-limited WVSN. In this paper, we study the energy efficient image aggregation scheme in WVSN. Image aggregation is a possible way to eliminate the redundant portions of the image captured by different data source nodes. Hence, transmission power could be reduced via the image aggregation scheme. However, image aggregation requires image processing that incurs node processing power. Besides the additional energy consumption from node processing, there is another MAC-aware retransmission energy loss from image aggregation. In this paper, we first propose the mathematical model to capture these three factors (image transmission, image processing, and MAC retransmission) in WVSN. Numerical results based on the mathematical model and real WVSN sensor node (i.e., Meerkats node) are performed to optimize the energy consumption tradeoff between image transmission, image processing, and MAC retransmission.

Emulation of multipath effects on a wireless testbed and its impact on MAC layer performance

Field experiments are an important part of research in wireless networks. Since the wireless channel varies with location and time, the results vary for the same field experiment at a different place and time. Assumptions about the wireless environment can lead to biased results. It is necessary to shield wireless transmission from uncontrolled interference in order to make the experiment repeatable. This paper describes $$\underline{A}$$ dvanced wirele $$\underline{SS}$$ $$\underline{E}$$ nvironment $$\underline{R}$$ esearch $$\underline{T}$$ estbed (ASSERT) which uses shielded co-axial cables as the communication media for radio signals to conduct reliable, scalable and accurate wireless experiments. Shielding the transmission also protects the signal from random burst of noise introduced by the environment. The paper describes how the combination of programmable attenuators and RF splitters/combiners, which are part of ASSERT, helps in emulating complex and varying environments including those in which multipath interference plays a significant role. Our experimental results indicate that (1) tweaking the MAC layer and retransmissions at the application layer neutralize, to an extent, the impact of multipath effects when the received signal strength is extremely good, and (2) when the received signal strength falls below a certain threshold multipath interference plays a significant role.

CRRT: Congestion-Aware and Rate-Controlled Reliable Transport in Wireless Sensor Networks

For successful data collection in wireless sensor networks, it is important to ensure that the required delivery ratio is maintained while keeping a fair rate for every sensor. Furthermore, emerging high-rate applications might require complete reliability and the transfer of large volume of data, where persistent congestion might occur. These requirements demand a complete but efficient solution for data transport in sensor networks which reliably transports data from many sources to one or more sinks, avoids congestion and maintains fairness. In this paper, we propose congestion-aware and rate-controlled reliable transport (CRRT), an efficient and low-overhead data transport mechanism for sensor networks. CRRT uses efficient MAC retransmission to increase one-hop reliability and end-to-end retransmission for loss recovery. It also controls the total rate of the sources centrally, avoids the congestion in the bottleneck based on congestion notifications from intermediate nodes and centrally assigns the rate to the sources based on rate assignment policy of the applications. Performance of CRRT is evaluated in NS-2 and simulation results demonstrate the effectiveness of CRRT.

Performance study of link layer and MAC layer protocols to support TCP in 3G CDMA systems

Providing support for TCP with good quality link connection is a key issue for future wireless networks in which Internet access is going to be one of the most important data services. A number of schemes have been proposed in literature to improve the TCP performance over wireless links. In this paper, we study the performance of a particular combination of link layer protocol (e.g., radio link protocol or RLP) and MAC retransmissions to support the TCP connections over third generation (3G) wireless CDMA networks. We specifically investigate two metrics - the packet error rate and the delay provided by RLP and MAC retransmissions - both of which are important for TCP performance. For independent and identically distributed (i.i.d) error channels, we propose an analytical model for RLP performance with MAC retransmission. The segmentation of TCP/IP packets into smaller RLP frames, as well as the RLP buffering process, is modeled using a Markov chain. For correlated fading channels, we introduce an analytical metric called RLP retransmission efficiency. We show that: 1) the RLP frame size has significant impact on the overall 3G system performance, 2) MAC layer retransmissions significantly improve the TCP performance, and 3) the RLP retransmission scheme performs better in highly correlated channels, while other scheme performs better in low correlated channels. Simulation results also confirm these conclusions.