IEEE 802.11WLANs use carrier sense multiple access with collision avoidance (CSMA/CA) to initiate the Request to Send / Clear to Send (RTS/CTS) handshaking mechanism that solves the hidden node problem.However RTS/CTS also causes the exposed node problem where a node is unnecessarily prevented from accessing the wireless channel even when such access will not disrupt another nodes ongoing transmission.In this paper, we present continuing evaluation of a method for reducing exposed nodes in 802.11 ad hoc WLANs using asymmetric transmission ranges for RTS and CTS frames.NS-2 simulations show that the proposed method improves overall network throughput in a topology scenario of a 3-D network faced with ceiling/floor obstructions.

Parallelization paradigms for effective execution in a Directed Acyclic Graph (DAG) application have been widely studied in the area of task scheduling. Schedule length can be varied depending on task assignment policies, scheduling policies, and heterogeneity in terms of each processor and each communication bandwidth in a heterogeneous system. One disadvantage of existing task scheduling algorithms is that the schedule length cannot be reduced for a data intensive application. In this paper, we propose a clustering-based task scheduling algorithm called Clustering for Minimizing the Worst Schedule Length (CMWSL) to minimize the schedule length in a large number of heterogeneous processors. First, the proposed method derives the lower bound of the total execution time for each processor by taking both the system and application characteristics into account. As a result, the number of processors used for actual execution is regulated to minimize the Worst Schedule Length (WSL). Then, the actual task assignment and task clustering are performed to minimize the schedule length until the total execution time in a task cluster exceeds the lower bound. Experimental results indicate that CMWSL outperforms both existing list-based and clustering-based task scheduling algorithms in terms of the schedule length and efficiency, especially in data-intensive applications.

The W-LAN Ad Hoc network tends to cause problems called "Hidden Node" and "Exposed Node".RTS/CTS mechanism has been introduced to mitigate Hidden Node and most of existing researches assume that RTS and CTS are sent at the same transmission range.This paper describes a new method to improve the network throughput by adjusting the RTS transmission range.The simulation result showed that the proposed method achieved higher throughput in some degree.

Recently packet scheduling algorithms such as Packetized GPS (PGPS), worst-case fair weighted fair queueing (WF2Q) and Self-Clocked Fair Queueing (SCFQ) have been proposed in order to guarantee deterministic or statistical delay bounds. These algorithms are based on generalized processor sharing (GPS) which is an ideal scheduling algorithm based on fluid flow model in which the traffic is infinitely divisible. GPS provides a minimum guaranteed service rate for each session and tight delay bounds for leaky bucket constrained sessions. However, the delay bounds are unnecessarily large because each session is served according to its associated constant weight until the session buffer is empty. In this paper, we present a scheduling policy called output rate-controlled generalized processor sharing (ORC-GPS). ORC-GPS is a rate-based scheduling like GPS and controls the service rate to lower the delay bounds for leaky bucket constrained sessions. In numerical experiments, we compare ORC-GPS with GPS in terms of delay bounds.