Abstract:
Graph-based algorithms for point-to-point link scheduling in Spatial reuse Time Division Multiple Access (STDMA) wireless ad hoc networks often result in a significant number of transmissions having low Signal to Interference and Noise density Ratio (SINR) at intended receivers, leading to low throughput. To overcome this problem, we propose a new algorithm for STDMA link scheduling based on a graph model of the network as well as SINR computations. The performance of our algorithm is evaluated in terms of spatial reuse and computational complexity. Simulation results demonstrate that our algorithm achieves better performance than existing algorithms.

Abstract:
Throughput capacity of large ad hoc networks has been shown to scale adversely with the size of network n. However the need for the nodes to find or repair routes has not been analyzed in this context. In this paper, we explicitly take route discovery into account and obtain the scaling law for the throughput capacity under general assumptions on the network environment, node behavior, and the quality of route discovery algorithms. We also discuss a number of possible scenarios and show that the need for route discovery may change the scaling for the throughput capacity.

Abstract:
Throughput capacity of large ad hoc networks has been shown to scale adversely with the size of network . However the need for the nodes to find or repair routes has not been analyzed in this context. In this paper, we explicitly take route discovery into account and obtain the scaling law for the throughput capacity under general assumptions on the network environment, node behavior, and the quality of route discovery algorithms. We also discuss a number of possible scenarios and show that the need for route discovery may change the scaling for the throughput capacity.

Abstract:
In this paper, we propose a distributed throughput-optimal ad hoc wireless network scheduling algorithm, which is motivated by the celebrated simplex algorithm for solving linear programming (LP) problems. The scheduler stores a sparse set of basic schedules, and chooses the max-weight basic schedule for transmission in each time slot. At the same time, the scheduler tries to update the set of basic schedules by searching for a new basic schedule in a throughput increasing direction. We show that both of the above procedures can be achieved in a distributed manner. Specifically, we propose an average consensus based link contending algorithm to implement the distributed max weight scheduling. Further, we show that the basic schedule update can be implemented using CSMA mechanisms, which is similar to the one proposed by Jiang et al. Compared to the optimal distributed scheduler in Jiang's paper, where schedules change in a random walk fashion, our algorithm has a better delay performance by achieving faster schedule transitions in the steady state. The performance of the algorithm is finally confirmed by simulation results.

Abstract:
Mobile ad hoc networks are formed by co operative association of wireless nodes communicating with each other without the use of infrastructure. Every node acts as a router in the network and enables the communication between nodes that are separated over their radio range. Typically in ad hoc networks one or more nodes may act as gateway connecting to the external world. The node acting as the gateway becomes a sink and the throughput capacity of the network in such networks becomes crucial to maintain QOS. This paper investigates throughput of many to one scenarios in wireless mesh network using Ad hoc On Demand Vector (AODV) Routing Protocol. It is proposed to specifically investigate the throughput of one hop, two hop and three hops to the sink in the wireless mesh network. Investigations are also carried out to measure the throughput of the wireless mesh network when the route timeout variable in the AODV routing protocol is decreased.

Abstract:
Mobile ad hoc networks are collections of mobile nodes that can dynamically form temporary networks without the need for pre-existing network infrastructure or centralized administration. These nodes can be arbitrarily located and can move freely at any given time. Hence, the network topology can change rapidly and unpredictably. Because wireless link capacities are usually limited, congestion is possible in MANETs. Hence, balancing the load in a MANET is important since nodes with high loads will deplete their batteries quickly, thereby increasing the probability of disconnecting or partitioning the network. Here a load balancing protocol is proposed to improve the network throughput, decrease average end-to-end delay and reduce congestion in ad hoc networks. This scheme is applied as an extension on top of existing load balanced routing protocols. Simulation results obtained using ns-2 network simulation platform show a 20-25% improvement in packet delivery ratio and average end-to-end delay.

Abstract:
Designing mobiles to harvest ambient energy such as kinetic activities or electromagnetic radiation will enable wireless networks to be self sustaining besides alleviating global warming. In this paper, the spatial throughput of a mobile ad hoc network powered by energy harvesting is analyzed using a stochastic-geometry model. In this model, transmitters are distributed as a Poisson point process and energy arrives at each transmitter randomly with a uniform average rate called the energy arrival rate; upon harvesting sufficient energy, each transmitter transmits with fixed power to an intended receiver under an outage-probability constraint for a target signal-to-interference-and-noise ratio. It is assumed that transmitters store energy in batteries with infinite capacity. By applying the random-walk theory, the probability that a transmitter transmits, called the transmission probability, is proved to be equal to one if the energy-arrival rate exceeds transmission power or otherwise is equal to their ratio. This result and tools from stochastic geometry are applied to maximize the network throughput for a given energy-arrival rate by optimizing transmission power. The maximum network throughput is shown to be proportional to the optimal transmission probability, which is equal to one if the transmitter density is below a derived function of the energy-arrival rate or otherwise is smaller than one and solves a given polynomial equation. Last, the limits of the maximum network throughput are obtained for the extreme cases of high energy-arrival rates and dense networks.

Abstract:
Recently, there have been some research works in the design of cross-layer protocols for cognitive radio (CR) networks, where the Protocol Model is used to model the radio interference. In this paper we consider a multihop multi-channel CR network. We use a more realistic Signal-to-Interference-plus-Noise Ratio (SINR) model for radio interference and study the following cross-layer throughput optimization problem: (1) Given a set of secondary users with random but fixed location, and a set of traffic flows, what is the max-min achievable throughput? (2) To achieve the optimum, how to choose the set of active links, how to assign the channels to each active link, and how to route the flows? To the end, we present a formal mathematical formulation with the objective of maximizing the minimum end-to-end flow throughput. Since the formulation is in the forms of mixed integer nonlinear programming (MINLP), which is generally a hard problem, we develop a heuristic method by solving a relaxation of the original problem, followed by rounding and simple local optimization. Simulation results show that the heuristic approach performs very well, that is, the solutions obtained by the heuristic are very close to the global optimum obtained via LINGO. 1. Introduction Cognitive radio technology [1–3] provides a novel way to solve the spectrum underutilization problem. In cognitive radio (CR) networks, there are two types of users: primary users and secondary users. A primary user is the rightful owner of a channel, while a secondary user periodically scans the channels, identifies the currently unused channels, and accesses the channels opportunistically. The secondary users organize among themselves an ad hoc network and communicate with each other using these identified available channels. As a result, a multihop multichannel CR network is formed. How to efficiently share the spectrum holes among the secondary users, therefore, is of interest. In this paper, we are interested in studying the opportunistic spectrum sharing problem among the secondary users, but our concern is on a cross-layer design of spectrum sharing and routing with SINR constraints. The main issues we are going to address include the following. ( ) Given a set of secondary users with random but fixed location, and a set of traffic flows, what is the max-min achievable throughput? ( ) To achieve the optimum, how to choose the set of active links, how to assign the channels to each active link, and how to route the flows? There have been some research works on cross-layer protocols in CR networks.

Abstract:
Collision avoidance and spatial reuse are two important approaches to improving the throughput of ad hoc networks, and many MAC protocols are proposed to achieve these goals. In most MAC protocols, collisions are reduced by solving the hidden terminal problems, but the spatial reuse remains un-optimized in these protocols, which affects network throughput dramatically. Moreover, reception of exposed terminals is not allowed in current MAC protocols even if they can receive packets successfully, which leads to lower spatial reuse. In this paper, a high throughput MAC protocol named e-MAC is proposed. To improve the network throughput, two approaches are used in e-MAC. First, a power controlled busy tone is used to eliminate hidden terminals. The receiver adjusts the transmission power of busy tone, according to a received signal strength from the transmitter, so that the spatial reused is optimized while all hidden terminals are covered by a busy tone. Second, exposed terminals are allowed to receive when the ratio between signal strength of RTS (ready-to-send) and interference satisfies the SINR (signal to interference and noise ratio) requirements, which further improves the spatial reuse. Simulation results show that the average throughput of e-MAC outperforms that of DUCHA (dual channel access) by 87%.

Abstract:
We consider the problem of determining asymptotic bounds on the capacity of a random ad hoc network. Previous approaches assumed a link layer model in which if a transmitter-receiver pair can communicate with each other, i.e., the Signal to Interference and Noise Ratio (SINR) is above a certain threshold, then every transmitted packet is received error-free by the receiver thereby. Using this model, the per node capacity of the network was shown to be $\Theta(\frac{1}{\sqrt{n\log{n}}})$. In reality, for any finite link SINR, there is a non-zero probability of erroneous reception of the packet. We show that in a large network, as the packet travels an asymptotically large number of hops from source to destination, the cumulative impact of packet losses over intermediate links results in a per-node throughput of only $O(\frac{1}{n})$. We then propose a new scheduling scheme to counter this effect. The proposed scheme provides tight guarantees on end-to-end packet loss probability, and improves the per-node throughput to $\Omega(\frac{1}{\sqrt{n} ({\log{n}})^{\frac{\alpha{{+2}}}{2(\alpha-2)}}})$ where $\alpha>2$ is the path loss exponent.