Wireless mesh networks are expected to be widely used to provide Internet access in the near future. In order to fulfill the expectations, these networks should provide high throughput simultaneously to many users. Recent research has indicated that, due to its conservative CSMA/CA channel access scheme and RTS/CTS mechanism, 802.11 is not suitable to achieve this goal. In this paper, we investigate throughput improvements achievable by replacing CSMA/CA with an STDMA scheme where transmissions are scheduled according to the physical interference model. To this end, we present a computationally efficient heuristic for computing a feasible schedule under the physical interference model and we prove, under uniform random node distribution, an approximation factor for the length of this schedule relative to the shortest schedule possible with physical interference. This represents the first known polynomial-time algorithm for this problem with a proven approximation factor. We also evaluate the throughput and execution time of this algorithm on representative wireless mesh network scenarios through packet-level simulations. The results show that throughput with STDMA and physical-interferencebased scheduling can be up to three times higher than 802.11 for the parameter values simulated. The results also show that our scheduling algorithm can schedule networks with 2000 nodes in about 2.5 minutes.

Wireless mesh networks (WMNs) have been proposed as a solution for ubiquitous last-mile broadband access. A critical limiting factor for many WMN protocols in realizing their throughput potential is the interference between nodes in the WMN. Understanding and characterizing such interference is important for a variety of purposes such as channel assignment, route selection, and fair scheduling. Instead of using ad hoc heuristics, a recent study proposed characterizing interference in a WMN by measuring two-way interference, i.e., interference between each pair of communicating links. In this paper, we study the extent of multi-way interference, i.e., the interference caused by multiple transmitters to a communicating link. We find through simulations and through measurements of a 32-node wireless testbed that even if these transmitters individually do not interfere significantly with a given communicating link, simultaneous transmissions of them have the potential to significantly affect the throughput of the communicating link. This implies that pairwise interference measurements may be optimistic when used to drive protocols in wireless mesh networks. Encouragingly, we find that this phenomenon, although significant when it occurs, is not widespread. In particular, multi-way interference caused significant additional throughput degradation compared to pairwise interference to a small fraction of the links in the testbed over our measurement period. In addition, we find that there is a strong correlation between the impact of multi-way interference and the quality of the link under consideration. We conclude with recommendations on how protocols should take multi-way interference into account.

Abstract-We propose an efficient centralized scheduling algorithm in IEEE 802.16 based Wireless Mesh Networks (WMN) to provide high qualified wireless multimedia services. Our algorithm takes special attention on the relay function of the mesh nodes in a transmission tree which is seldom studied in previous research. Some important design metrics, such as fairness, channel utilization and transmission delay are considered in this scheduling algorithm. IEEE 802.16 employs TDMA and the selection policy for scheduled links in a time slot will definitely impact the system performance. We evaluated the proposed algorithm with four selection criteria through extensive simulations and the results are instrumental for improving the performance of IEEE 802.16 based WMNs in terms of link scheduling. I.

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Efficient usage of available capacity in wireless mesh networks is critical. Capacity is wasted due to the exposed terminal problem. In this paper, we propose a solution to mitigate the exposed terminal problem in static IEEE 802.11-based mesh networks, thereby improving the spatial reuse of the medium and increasing network throughput. Our solution is complementary to previously-proposed solutions that adjust the carrier-sense range for improved spatial reuse. The proposed solution consists of two phases. In the first phase, exposed links in the mesh topology are detected through an offline training process. Coordination of simultaneous transmissions over exposed links is then done in the second phase through the use of Request-To-Send-Simultaneously (RTSS) and Clear-To-Send-Simultaneously (CTSS) messages, which are added to the MAC protocol. Our solution preserves the distributed nature of the MAC protocol and does not require time synchronization between nodes. We present a simulation-based evaluation that demonstrates that the proposed solution effectively improves capacity usage and network throughput in representative topologies and traffic scenarios.

Time division multiple access (TDMA) based medium access control (MAC) protocols can provide QoS with guaranteed access to the wireless channel. However, in multihop wireless networks, these protocols may introduce scheduling delay if, on the same path, an outbound link on a router is scheduled to transmit before an inbound link on that router. The total scheduling delay can be quite large since it accumulates at every hop on a path. This paper presents a method that finds conflict-free TDMA schedules with minimum scheduling delay. We show that the scheduling delay can be interpreted as a cost, in terms of transmission order of the links, collected over a cycle in the conflict graph. We use this observation to formulate an optimization, which finds a transmission order with the minmax delay across a set of multiple paths. The min-max delay optimization is NP-complete since the transmission order of links is a vector of binary integer variables. We devise an algorithm that finds the transmission order with the minimum delay on overlay tree topologies and use it with a modified Bellman-Ford algorithm, to find minimum delay schedules in polynomial time. The simulation results in 802.16 mesh networks confirm that the proposed algorithm can find effective min-max delay schedules.

Wireless mesh networks are a recent architecture for multihop wireless networks. Also, standards for realizing mesh networks are being actively developed, especially in the IEEE working groups. In contrast with mobile ad hoc networks, mesh networks consist of static nodes communicating with each other over wireless links. The static nodes are essentially wireless routers. Such networks can be used, for example to provide a cost effective alternative to a wireline Internet access network. As opposed to the nodes in mobile ad hoc networks, the nodes in mesh networks are not energy constrained and node mobility is not a concern in protocol scalability. Instead, the main technical problems relate to achieving high user data rates over multihop wireless paths by using advanced MAC/routing layer solutions. This report presents a state-of-the-art analysis of wireless mesh networks, both from the point of view of standardization and academic research activities. In the standardization, we focus on the recent developments on defining new physical layer and MAC layer standards for mesh network in the IEEE 802.11 and 802.16 working groups. At the IP layer, in addition to routing, mobility management is a key issue, and these are reviewed from the point of view of recent IETF activities in the field. In academic research, the emphasis has been on identifying feasible mechanisms that can be used to mitigate the impact of interference

Community wireless mesh networks (WMNs) are increasingly being deployed for providing cheap, low maintenance Internet access. For the successful adoption of WMNs as a last-mile technology, we argue that a guarantee of perclient fairness is critical. Specifically, WMNs should support a “bitrate-for-bucks ” service model similar to other popular access technologies such as Cable/DSL. We analyze the effectiveness of both off-the-shelf and theoretically optimal approaches towards providing such a service. We propose the APOLLO system that outperforms both these approaches. APOLLO seamlessly integrates three synergistic components: theory-guided service planning and subscription, ratebased admission control to enforce the planned service, and a novel distributed light-weight fair scheduling scheme to deliver the admitted traffic. We evaluate APOLLO using simulations and testbed experiments.

Abstract — In this paper, we develop and analyze a lowcomplexity cooperative protocol that significantly increases the average throughput of multi-hop upstream transmissions for wireless tree networks. We consider a system in which transmissions are assigned to nodes in a collision free, spatial time division fashion. This protocol exploits the broadcast nature of wireless networks where the communication channel is shared between multiple adjacent nodes within interference range. For any upstream end-to-end flow in the tree, each intermediate node receives information from both one-hop and two-hop neighbors and transmits only sufficient information such that the next upstream one-hop neighbor will be able to decode the packet. This approach can be viewed as the generalization of the classical three node relay channel for end-to-end flows in which each intermediate node becomes successively source, relay and destination. We derive the achievable rate and propose an optimal schedule that realizes this rate for any regular tree network. We show that our protocol dramatically outperforms the conventional scheme where intermediate nodes simply forward the packets hop by hop. At high signal-to-noise ratio, it yields approximatively 80% throughput gain. I.

Wireless mesh networks (WMNs) are characterized by static mesh routers connected by