We propose a novel view on efficient packet forwarding in wireless mesh networks based on a molecular analogy in which mesh routers are either nuclei or electrons in an atom that corresponds to a 802.11 cell. In this view, a mesh network appears as a collection of spatially distributed 802.11 cells operating on different channels. We define Molecular MAC that uses dynamic channel switching at neighbor mesh routers to efficiently forward packets over multiple hops. To avoid deafness, nuclei notify electrons about pending packets before electrons pull them from nuclei for reception or further forwarding. We evaluate the proposed scheme through simulation and compare with other proposals. Our results show that Molecular MAC obtains much better performance in terms of throughput, packet delivery rate, end-to-end delay, and fairness.

Many researchers have addressed the problem of QoS differentiation in 802.11 wireless networks, however no method proposed so far benefits from all desirable properties: high aggregate throughput even for a large number of contending stations, fair allocation to all stations in the same class, fast adaptation to changing conditions, and support for absolute priorities. If we consider the IEEE 802.11e standard, its EDCA (enhanced distributed channel access) access method suffers from an increased collision rate when the number of stations increases. In this paper, we propose a novel access method that supports both relative proportional throughput allocation and absolute priorities in 802.11 wireless networks. The method is efficient, scalable, and fair. It builds on the idea of the Idle Sense method that provides the optimal throughput and fairness for 802.11 WLANs [1]: each station adjusts its contention window based on the observed average number of idle slots. We achieve absolute priority differentiation by setting the target value for the number of idle slots to a small value, so that the absolute priority class gains all the available throughput. The method also supports relative proportional throughput allocation in which several classes share the available throughput according to desired ratios. Our simulations show that the proposed method achieves its objectives of relative and absolute differentiation both with respect to the aggregated throughput and the speed of convergence. Unlike 802.11e EDCA, it presents very good scalability - the throughput remains almost constant in function of the number of contending stations.

International audience

In this paper, we consider the problem of blocked stations that appears in some spatial configurations of multi-hop wireless networks based on the 802.11 DCF (distributed coordination function). The problem leads to starvation of at least one station caused by the presence of neighbor stations within its carrier sensing range that do not hear each other. We propose Forced Transmissions, a simple and efficient solution to this problem. It consists of detecting that a station is blocked by others stations and forcing a transmission. This results in a collision that increases the contention windows of blocking stations and leaves some channel time to the blocked station for transmitting. The blocked station forces transmission only with some probability adjusted in function of the time spent waiting for the channel. Our simulations show that the proposed method increases the minimal throughput of the blocked stations at the expense of a slight degradation of the total throughput, which is unavoidable in any DCF based solution.