The end-to-end throughput of multi-hop communication in wireless ad hoc networks is affected by the conflict between forwarding nodes. It has been shown that sending more packets than maximum achievable end-to-end throughput not only fails to increase throughput but also decreases throughput owing to high contention and collision. Accordingly, it is of crucial importance for a source node to know the maximum end-to-end throughput. The end-to-end throughput depends on multiple factors, such as physical layer limitations, medium access control (MAC) protocol properties, routing policy, and nodes’ distribution. There have been many studies on analytical modeling of end-to-end throughput but none of them has taken routing policy and nodes’ distribution as well as MAC layer altogether into account. In this paper, the end-to-end throughput with perfect MAC layer is obtained based on routing policy and nodes’ distribution in 1-D and 2-D networks. Then, imperfections of IEEE 802.11 protocol are added to the model to obtain precise value. An exhaustive simulation is also made to validate the proposed models using ns-2 simulator. Results show that if the distribution to the next hop for a particular routing policy is known, our methodology can obtain the maximum end-to-end throughput precisely.
The IEEE 802.11 standard for ad hoc networks uses a distributed access mechanism in the shared medium that attempts to avoid collisions by performing carrier sensing, inter-frame spaces, and a backoff mechanism. This paper aims at deriving an analytical expression for the maximum throughput of a communication between two nodes. The communication is achieved in a multi-hop scenario and the path from the source to the destination consists of a chain of nodes. We analyze the multi-path communication and show that the maximum throughput can be increased with the simultaneous use of two paths: the shortest path and an appropriate alternative path that takes into account the interference problem. We also derive the constraints for this alternative path. The use of multiple alternative paths can be considered in order to achieve a load and energy balancing. This letter proposes a new approach to model the intra-flow contention problem in multi-hop networks. The model takes into consideration of neighboring interference, hidden-node collision and multi-rate scenario. It can be easily used to do admission control or to calculate the end-to-end capacity of a given multi-hop route. Simulation results validate its accuracy. TO-DCF, a new backoff scheme for 802.11, has the potential to significantly increase throughput in dense wireless LANs while also opportunistically favouring nodes with heavier traffic loads and or better channel conditions. In this paper we present an analytical model to investigate the behaviour and performance of the TO-DCF protocol with regards to operating parameters such as the number of nodes, the contention window size and the backoff countdown probabilities. We then compare numerical results from an implementation of our model with simulations. Our model shows a high level of accuracy, even when the model assumptions are relaxed, and provides guidance for network operators to correctly configure the weight functions for nodes running TO-DCF given the network’s operating conditions. This paper analyzes the communication between two points in wireless ad hoc networks operating at the IEEE 802.11 standard mode. The path from the source to the destination consists of a chain of nodes. We aim at deriving an analytical expression for the maximum throughput. We show that the maximum throughput can be increased, under certain conditions, through the use of two paths: the shortest path and an appropriately chosen alternative path that takes into account the interference problem. The alternative path strategy allows a gain up to 50 of the maximum throughput achieved in the single path strategy. This paper studies TCP performance over multihop wireless networks that use the IEEE 802.11 protocol as the access method. Our analysis and simulations show that, given a specific network topology and flow patterns, there exists a TCP window size W*, at which TCP achieves best throughput via improved spatial channel reuse. However, TCP does not operate around W*, and typically grows its average window size much larger; this leads to decreased throughput and increased packet loss. The TCP throughput reduction can be explained by its loss behavior. Our results show that network overload is mainly signified by wireless link contention in multihop wireless networks. As long as the buffer size at each node is reasonably large (say, larger than 10 packets), buffer overflow-induced packet loss is rare and packet drops due to link-layer contention dominate. Link-layer drops offer the first sign for network overload. We further show that multihop wireless links collectively exhibit graceful drop behavior: as the offered load increases, the link contention drop probability also increases, but saturates eventually. In general, the link drop probability is insufficient to stabilize the average TCP window size around W*. Consequently, TCP suffers from reduced throughput due to reduced spatial reuse. We further propose two techniques, link RED and adaptive pacing, through which we are able to improve TCP throughput by 5 to 30 in various simulated topologies. Some simulation results are also validated by real hardware experiments.