Performance enhancement of WLAN IEEE 802.11 for asymmetric traffic

Most studies about the performance of IEEE 802.11 consider scenarios of ad-hoc topology and networks where all stations have the same traffic load (symmetric traffic conditions). This paper presents a study of performance parameters of more realistic networks. We focus the attention on WLAN with infrastructure networks, where the traffic distribution is asymmetric. In this case, the traffic load at the access point is much heavier than that at user stations. These studies are more realistic because most nowadays installed WLAN are infrastructure topology type, due to the fact that they are used as access networks. In this case, the access point has to retransmit all incoming traffic to the basic service set and therefore its traffic load is higher. Finally, the paper presents the tuning of the contention window, taken from IEEE 802.11e, used to increase the system performance under asymmetric traffic conditions, and the proposal of an adaptive algorithm to adapt the MAC layer settings to the system traffic load.Peer Reviewe

Effect of power randomization on saturation throughput of IEEE 802.11 WLAN

In this paper, we evaluate the saturation throughput for an IEEE 802.11 based wireless network considering capture effect at the receiver, while nodes transmit with random powers. In this respect, we consider a scenario consisting of a specific number of wireless nodes. Then, we derive the transmission as well as collision probabilities with respect to the perfect capture effect. In order to maximize the saturation throughput we set up an optimization problem and obtain how to compute optimum values for the probabilities corresponding to different power levels. By providing the numerical results, we deduce that power randomization may lead to a significant improvement in saturation throughput

A Unifying Framework for Local Throughput in Wireless Networks

With the increased competition for the electromagnetic spectrum, it is important to characterize the impact of interference in the performance of a wireless network, which is traditionally measured by its throughput. This paper presents a unifying framework for characterizing the local throughput in wireless networks. We first analyze the throughput of a probe link from a connectivity perspective, in which a packet is successfully received if it does not collide with other packets from nodes within its reach (called the audible interferers). We then characterize the throughput from a signal-to-interference-plus-noise ratio (SINR) perspective, in which a packet is successfully received if the SINR exceeds some threshold, considering the interference from all emitting nodes in the network. Our main contribution is to generalize and unify various results scattered throughout the literature. In particular, the proposed framework encompasses arbitrary wireless propagation effects (e.g, Nakagami-m fading, Rician fading, or log-normal shadowing), as well as arbitrary traffic patterns (e.g., slotted-synchronous, slotted-asynchronous, or exponential-interarrivals traffic), allowing us to draw more general conclusions about network performance than previously available in the literature.Comment: Submitted for journal publicatio

Topology-aware transmission scheduling for distributed highway traffic monitoring wireless sensor networks

Wireless sensor networks have been deployed along highways for traffic monitoring. The thesis studies a set of transmission scheduling methods for optimizing network throughput, message transfer delay, and energy efficiency. Today\u27s traffic monitoring systems are centrally managed. Several studies have envisioned the advantages of distributed traffic management techniques. The thesis is based on previously proposed hierarchical sensor network architecture, for which the routing and transmission scheduling methods are derived. Wireless sensor networks have a lifetime limited by battery energy of the sensors. The thesis proposes to assign schedules for nodes to transmit and receive packets and turning off their radios during other times to save energy. The schedules are assigned to minimize the end-to-end packet delivery latency and maximize the network throughput. Conflict-free transmission slots are assigned to sensors along road segments leading to a common intersection based on locally discovered topology. The slot assignment adopts a heuristic that rotates among segments, assigns closest possible slots to neighboring nodes in a pipelined fashion, and exploits radio capture effects when possible. Based on the single-intersection approach, centralized and distributed multi-intersection scheduling methods are proposed to resolve conflicts among nodes belonging to different intersections. The centralized approach designates a controller as the leader to collect topology information of a set of contiguous intersections and assign schedules using the same single-intersection algorithm. The distributed approach has each intersection determine its own schedule independently and then exchange the topology information and schedules with its adjacent intersections to resolve conflicts locally. Based on simulation studies in ns-2, the centralized approach achieves better performance, while the distributed approach tries to approach the centralized performance at much lower communication costs. A communication cost analysis is performed to assess the trade-off between the centralized and distributed approaches

CAMA: Efficient Modeling of the Capture Effect for Low Power Wireless Networks

Network simulation is an essential tool for the design and evaluation of wireless network protocols, and realistic channel modeling is essential for meaningful analysis. Recently, several network protocols have demonstrated substantial network performance improvements by exploiting the capture effect, but existing models of the capture effect are still not adequate for protocol simulation and analysis. Physical-level models that calculate the signal-to-interference-plus-noise ratio (SINR) for every incoming bit are too slow to be used for large-scale or long-term networking experiments, and link-level models such as those currently used by the NS2 simulator do not accurately predict protocol performance. In this article, we propose a new technique called the capture modeling algorithm (CAMA) that provides the simulation fidelity of physical-level models while achieving the simulation time of link-level models. We confirm the validity of CAMA through comparison with the empirical traces of the experiments conducted by various numbers of CC1000 and CC2420-based nodes in different scenarios. Our results indicate that CAMA can accurately predict the packet reception, corruption, and collision detection rates of real radios, while existing models currently used by the NS2 simulator produce substantial prediction error

A Study of Energy-efficient Routing Supporting Coordinated Sleep Scheduling in Wireless Ad Hoc Networks

A wireless ad hoc network is a collection of wireless computing devices that self-configure to form a network independently of any fixed infrastructure. Many wireless ad hoc network devices such as smartphones and tablets are usually powered by batteries with a limited operation time. This poses a significant challenge to the design of low-power network protocols. On one hand, energy-efficient routing protocols are widely discussed to reduce the end-to-end transmission energy by controlling the transmission power at senders. Recently, opportunistic routing (OR) has attracted a lot of attention for maximizing energy efficiency by exploiting the gains of multi-receiver diversity. On the other hand, sleep scheduling is commonly adopted as an effective mechanism to further reduce power wasted in overhearing and idle listening. However, the prior work has mainly treated energy-efficient routing and sleep scheduling as two separate tasks, which leads to a serious problem that neither component can fully minimize the network-wide energy consumption. In this thesis, we study how energy-efficient routing can be coordinated with sleep scheduling to increase network-side energy efficiency. We identify a trade-off between the decreased transmit power at senders due to multi-receiver diversity and the increased power at forwarders with the incorporation of coordinated sleep scheduling. Moreover, we provide a comprehensive evaluation of coordinated sleep scheduling impact on energy-efficient routing performance based on a 2-D grid topology and time division multiple access (TDMA) medium access control (MAC). Extensive simulation results demonstrate the effectiveness of the integrated function of coordinated sleep scheduling, significant impact of coordinated sleep scheduling on the energy-efficient routing performance and relationship between the network conditions (in terms of the traffic load and node density) and overall system performance achieved by different energy-efficient routing protocols

Distributed MAC protocol for networks with multipacket reception capability and spatially distributed nodes

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2007.Includes bibliographical references (p. 123-127).The physical layer of future wireless networks will be based on novel radio technologies such as Ultra-Wideband (UWB) and Multiple-Input Multiple-Output (MIMO). One of the important capabilities of such technologies is the ability to capture a few packets simultaneously. This capability has the potential to improve the performance of the MAC layer. However, we show that in networks with spatially distributed nodes, reusing MAC protocols originally designed for narrow-band systems (e.g., CSMA/CA) is inefficient. It is well known that when networks with spatially distributed nodes operate with such MAC protocols, the channel may be captured by nodes that are near the destination. We show that when the physical layer enables multi-packet reception, the negative implications of reusing the legacy protocols include not only such unfairness but also a significant throughput reduction. We present a number of simple alternative backoff mechanisms that attempt to overcome the throughput reduction phenomenon. We evaluate the performance of these mechanisms via exact analysis, approximations, and simulation, thereby demonstrating that they usually outperform the legacy backoff mechanisms. We then discuss the implications of the results on developing realistic MAC protocols for networks with a multi-packet reception capability and in particular for UWB networks.by Guner Dincer Celik.S.M