Abstract—Opportunistic routing significantly increases unicast throughput in wireless mesh networks by effectively utilizing the wireless broadcast medium. With network coding, opportunistic routing can be implemented in a simple and practical way without resorting to a complicated scheduling protocol. Due to constraints of computational complexity, a protocol utilizing network coding needs to perform segmented network coding, which partitions the data into multiple segments and encode only packets in the same segment. However, existing designs transmit only one segment at any given time while waiting for its acknowledgment, which degrades performance as the size of the network scales up. In this paper, we propose CodeOR, a new protocol that uses network coding in opportunistic routing to improve throughput. By transmitting a window of multiple segments concurrently, it improves the performance of existing work by a factor of two on average (and a factor of four in some cases). CodeOR is especially appropriate for real-time multimedia applications through the use of a small segment size to decrease decoding delay, and is able to further increase network throughput with a smaller packet size and a larger window size. I.

Network coding has been a prominent approach to a series of problems that used to be considered intractable with traditional transmission paradigms. Recent work on network coding includes a substantial number of optimization based protocols, but mostly for wireline multicast networks. In this paper, we consider maximizing the benefits of network coding for unicast sessions in lossy wireless environments. We propose Optimized Multipath Network Coding (OMNC), a rate control and routing protocol that dramatically improves the throughput of lossy wireless networks. OMNC employs multiple paths to push coded packets to the destination, and uses the broadcast MAC to deliver packets between neighboring nodes. The coding and broadcast rate is allocated to transmitters by a distributed optimization algorithm that maximizes the advantage of path diversity while avoiding congestion. With extensive experiments on an emulation testbed, we find that OMNC achieves significant throughput improvement over traditional best path routing protocols, and existing multipath routing protocols with network coding. 1.

We present an overview of the 802.16 mesh protocol with a specific focus on the networking aspects of the protocol. We first review the 802.16 mesh Time Division Multiple Access (TDMA) technology, including state of the art research on scheduling algorithms required by the technology. We then propose an addressing assignment for the 802.16 mesh networks that allows the network layer to take advantage of Qualityof-Service (QoS) provided by the 802.16 mesh protocol. Our addressing scheme allows network layer management of QoS at the edge of the network, thus allowing for simplicity in design of mesh routers. We also overview the security infrastructure of 802.16 mesh networks and their flaws. We propose an end-to-end security scheme that simplifies the design of 802.16 mesh routers. 1

Abstract — This paper describes a methodology to find the achievable rate region for any static wireless multi-hop network with 802.11 scheduling. To do so, we first characterize the achievable edge-rate region, that is, the set of edge rates that are achievable on the given topology. This requires a careful consideration of the inter-dependence among nearby edges, since neighboring edges collide with and affect the idle time perceived by the edge under study. We use our results to study the optimality of IEEE 802.11 scheduling by comparing the achievable rate region of IEEE 802.11 and optimal scheduling for different scenarios and find that 802.11 is able to achieve more than 80 % of the throughput as compared to optimal scheduling for all the scenarios considered. To explain this result, we then characterize the local topologies for which 802.11 scheduling results in a significant drop in throughput as compared to optimal scheduling. I.

Abstract. Multi-service mesh networks allow existence of guaranteed delay Quality-of-Service (QoS) traffic streams such as Voice over IP and best effort QoS traffic streams such as file transfer. We present an optimization that performs a linear search for the minimum number of TDMA slots required to support the guaranteed QoS flows. At each stage of the search a linear integer program is solved to find if there is a feasible schedule supporting the required end-to-end bandwidth and delay. Our optimization results in a relative order of transmissions in the frame that guarantees a maximum end-to-end delay in the network. The ordering of the transmissions can be used later to find feasible schedules with the Bellman-Ford algorithm on the conflict graph for the network. We use the optimization in numerical simulations showing the efficiency of 802.16 mesh networks with VoIP traffic. 1

We present a measurement study of a large-scale urban WiFi mesh network consisting of more than 250 Mesh Access Points (MAPs), with paying customers that use it for Internet access. Our study, involved collecting multi-modal data, e.g., through continuous gathering of SNMP logs, syslogs, passive traffic capture, and limited active measurements in different parts of the city. Our study is split into four components — planning and deployment of the mesh, success of mesh routing techniques, likely experience of users, and characterization of how the mesh is utilized. During our data collection process that spanned 8 months, the network changed many times due to hardware and software upgrades. Hence to present a consistent view of the network, the core dataset used in this paper comes from a two week excerpt of our dataset. This part of the dataset had more than 1.7 million SNMP log entries (from 224 MAPs) and more than 100 hours of active measurements. The scale of the study allowed us to make many important observations that are critical in planning and using WiFi meshes as an Internet access technology. For example, our study indicates that the last hop 2.4GHz wireless link between the mesh and the client is the major bottleneck in client performance. Further we observe that deploying the mesh access points on utility poles results in performance degradation for indoor clients that receive poor signal from the access points.

Past approaches to routing in mesh networks either (i) do not account for the MAC-layer interactions between the links in a tractable manner, or (ii) are agnostic to load-balancing across gateways. Our answer to these problems is MaLB (MAC-aware and Load Balanced routing algorithm), a greedy, tractable, and distributed mesh routing algorithm. Since the underlying objective function has high combinatorial complexity, MaLB uses a greedy approach. MaLB finds an optimum routing forest (union of trees rooted at the gateways) by taking into account MAC-layer interaction between links, as well as optimum multi-hop association of mesh nodes to gateways. MaLB builds on top of ETP (Expected Through-Put), a recently proposed MAC-aware routing metric. We also propose a low complexity variant of MaLB called LB (Load Balanced routing algorithm) which performs load balancing in a MAC-agnostic manner. MaLB performs especially well in networks with skewed topologies that result from unplanned mesh network deployment, as well as in the presence of gateway failures. Simulations with an enhanced version of ns-2 show that MaLB results in up to 60% higher throughput than a shortest path algorithm with ETX (Expected Transmission Count). Furthermore, MaLB results in up to 30 % improvement over the LB algorithm, as well as a shortest path algorithm with ETT (Expected Transmission Time). 1.

Network coding has emerged as a promising approach that enables reliable and efficient end-to-end transmissions in lossy wireless mesh networks. Existing protocols have demonstrated its resilience to packet losses, as well as the ability to integrate naturally with multipath opportunistic routing. However, these heuristics do not take into account the inherent resource competition in wireless networks, thereby compromising the coding advantages. In this paper, we take a game-theoretic perspective towards optimized resource allocation for network coding based unicast protocols. We design decentralized mechanisms that achieve better efficiencyfairness tradeoff, for both cooperative and selfish users. Our framework features a modularized optimization of two subproblems: the multipath routing of coded information flows for each player, and the broadcast and coding rate allocation among competing players. We have implemented the framework on a wireless emulation testbed and demonstrated its high performance in terms of throughput and fairness.

Abstract — Currently deployed wireless mesh networks are based on 802.11, WiFi, technology, which is not efficient in multihop scenarios. We present a method for embedding 802.16 packets into 802.11 broadcast packets and padding the 802.11 broadcast payload, so that the broadcasts are aligned to 802.16 TDMA frame boundaries. Our method requires only software changes on the nodes using 802.11a for mesh communications. This means that the mesh networks installed with 802.11a hardware today can be upgraded with a software patch to take advantage of 802.16 MCF and do not have to wait for hardware upgrades to 802.11s. We show that despite the addition of the padding, emulated 802.16 has bandwidths comparable to the bandwidth achievable with 802.16 hardware. The efficiency of the hybrid system is significantly higher than the efficiency of 802.11 based systems. The new system can also provide deterministic guarantees on link bandwidths since it takes advantage of scheduled wireless access with 802.16 MCF. We use ns2 simulations to show the improved efficiency and guaranteed link bandwidth of the 802.11 based hardware using the emulated 802.16 MCF.

With the proliferation of wireless local area network (WLAN) technologies, wireless Internet access via public hotspots will become a necessity in the near future. In outdoor areas where the installation of a large number of wired access points is practically or economically infeasible, mobile users located at the edge of the network communicate with the access point at a very low rate and in turn waste network resources. In this work, we promote the use of tetherless relay points (TRPs) to improve the throughput of a WLAN in such environments. We first provide a high level description on how to integrate TRPs in a multi-rate WLAN architecture. We then propose an integer-programming optimization formulation and an iterative approach to compute the best placement of a fixed number of TRPs. Finally, we show in numerical analysis, through a case study based on relay-enabled rate adaptation and IEEE 802.11-like multi-rate physical model with Rayleigh fading, that for a wide range of system parameters, significant performance gain can be achieved when TRPs are strategically installed in the network.