This paper proposes COPE, a new architecture for wireless mesh networks. In addition to forwarding packets, routers mix (i.e., code) packets from different sources to increase the information content of each transmission. We show that intelligently mixing packets increases network throughput. Our design is rooted in the theory of network coding. Prior work on network coding is mainly theoretical and focuses on multicast traffic. This paper aims to bridge theory with practice; it addresses the common case of unicast traffic, dynamic and potentially bursty flows, and practical issues facing the integration of network coding in the current network stack. We evaluate our design on a 20-node wireless network, and discuss the results of the first testbed deployment of wireless network coding. The results show that COPE largely increases network throughput. The gains vary from a few percent to several folds depending on the traffic pattern, congestion level, and transport protocol.

Abstract — Wireless technologies, such as IEEE 802.11, that are used for ad hoc networks provide for multiple non-overlapping channels. Most ad hoc routing protocols that are currently available are designed to use a single channel. The available network capacity can be increased by using multiple channels, but this requires the development of new protocols specifically designed for multi-channel operation. This paper studies the problem of improving the capacity of multi-channel wireless networks by using multiple interfaces. We use the technique of interface switching to utilize all the channels, even when the number of available interfaces is smaller than the number of available channels. We propose an interface assignment strategy that can be implemented over existing IEEE 802.11 hardware, and is well-suited for ad hoc networks. We propose a new routing protocol that is specifically designed for multi-channel, multiinterface wireless networks. Simulation results demonstrate the effectiveness of the proposed approach in significantly increasing network capacity, by utilizing all the available channels, even when the number of interfaces is smaller than the number of channels. Index Terms — Ad hoc networks, routing, multiple channel, multiple interfaces I.

Recent years have seen significant interest in using the multihop wireless networking paradigm for building mesh networks, ad hoc networks, and sensor networks. A key challenge in multihop wireless networks is to provision for sufficient network capacity to meet user requirements. Several approaches have been proposed to improve the network capacity in multihop networks, ranging from approaches that improve the efficiency of existing protocols, to approaches that use additional resources. In this dissertation, we propose to use additional frequency spectrum, as well as improve the efficiency of using existing frequency spectrum, for improving network capacity. Widely used wireless technologies, such as IEEE 802.11, provision for multiple frequencyseparated channels in the available frequency spectrum. Commercially available wireless network interfaces can typically operate over only one channel at a time. Due to cost and complexity constraints, the total number of interfaces at each node is expected to be fewer than the total number of channels available in the network. Under this scenario with fewer interfaces per node than channels, several challenges have to be addressed before all the channels can be utilized. In this dissertation, we have established the asymptotic capacity of multichannel wireless networks with varying number of channels and interfaces. Capacity analysis has shown that it is feasible

Abstract—Multihop wireless mesh networks are becoming a new attractive communication paradigm owing to their low cost and ease of deployment. Routing protocols are critical to the performance and reliability of wireless mesh networks. Traditional routing protocols send traffic along predetermined paths and face difficulties in coping with unreliable and unpredictable wireless medium. In this paper, we propose a Simple Opportunistic Adaptive Routing protocol (SOAR) to explicitly support multiple simultaneous flows in wireless mesh networks. SOAR incorporates the following four major components to achieve high throughput and fairness: (i) adaptive forwarding path selection to leverage path diversity while minimizing duplicate transmissions, (ii) priority timer-based forwarding to let only the best forwarding node forward the packet, (iii) local loss recovery to efficiently detect and retransmit lost packets, and (iv) adaptive rate control to determine an appropriate sending rate according to the current network conditions. We implement SOAR in both NS-2 simulation and an 18-node wireless mesh testbed. Our extensive evaluation shows that SOAR significantly outperforms traditional routing and a seminal opportunistic routing protocol, ExOR, under a wide range of scenarios. Index Terms—C.2.1.k [Communication/Networking and Information

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.

Abstract. Fixed broadband wireless access is a promising technology allowing Internet service providers to expend their customer base in sparsely populated rural areas. Because the size of the target service area is humongous, relay infrastructure is essential. Installing and maintaining this relay infrastructure is the main cost associated with such networks. Thus, we develop an optimization framework which computes the minimum number of relay stations and their corresponding channel configurations such that a pre-specified subscribers ’ traffic demand can be satisfied. Since the problem is a mixed-integer program, we propose an efficient optimization algorithm to compute the optimal solution in a reasonable amount of time. Our numerical results show that by using a few relay stations in a rural community, broadband Internet access can be established in a cost effective manner.

Fixed Broadband Wireless Access (FBWA) technology is designed to serve as a wireless DSL replacement to provide broadband Internet access in underserved areas where no other access technology exists. Due to the enormousness of the target service area, relay equipment play an important role in such networks, and the installation and maintenance cost of the network is directly proportional to the cost of the relay equipment. To minimize the network operational cost, an optimization framework which computes the minimum number of relay stations and their corresponding placements and channel assignments in the network is desired. Because the problem is NP-hard, we propose an efficient optimization algorithm based on a modified version of Bender’s decomposition to iteratively compute converging bounds to the problem solution. Our numerical results show that by using a few relay stations in a rural community, broadband Internet access can be established in a cost effective manner. Key words: Fixed broadband wireless access, relay stations, placement and channel assignment, Bender’s decomposition, mathematical programming/optimization.

personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, to republish, to post on servers or to redistribute to lists, requires prior specific permission. Acknowledgement We would like to thank Prof. Robert Morris at MIT for letting us use their wireless testbed. We would also like to thank Karthik Lakshminarayanan, Rodrigo Fonseca and Matt Caesar for their useful comments.

Abstract — Multihop wireless mesh networks are becoming a new attractive communication paradigm. Many cities and public places have deployed or are planning to deploy mesh networks to provide Internet access to residents and local businesses. Routing protocol design is critical to the performance and reliability of wireless mesh networks. Traditional routing protocols send traffic along pre-determined paths and have been shown ineffective in coping with unreliable and unpredictable wireless medium. In this paper, we develop a Simple Opportunistic Adaptive Routing protocol (SOAR) for wireless mesh networks. SOAR maximizes the progress each packet makes by using priority-based timers to ensure that the most preferred node forwards the packet with little coordination overhead. Moreover, SOAR minimizes resource consumption and duplicate transmissions by judiciously selecting forwarding nodes to prevent routes from diverging. To further protect against packet losses, SOAR uses local recovery to retransmit a packet when an ACK is not received within a specified time. SOAR uses a combination of selective ACKs, piggyback ACKs, and ACK compression to protect against ACK loss while minimizing ACK overhead. We evaluate SOAR using NS-2 simulations. Our preliminary results show that SOAR is promising to achieve high efficiency and effectively support multiple simultaneous flows. I.