Abstract — Multiple channels are available for use in IEEE 802.11. Multiple channels can increase the available network capacity, but require new protocols to exploit the available capacity. This paper studies the problem of improving the capacity of multi-channel wireless networks by using multiple interfaces. We consider the scenario when multiple interfaces are available, but the number of available interfaces is lesser than the number of available channels. We provide a classification of interface assignment strategies, and propose a new strategy that does not require modifications to IEEE 802.11. We also identify routing heuristics that are suitable for use with the proposed interface assignment strategy. I.

We describe a new carrier–sense multiple access (CSMA) protocol for multihop wireless networks, using multiple channels and a distributed channel selection scheme. The proposed protocol divides the available bandwidth intoÆchannels where the transmitting station selects an appropriate channel for packet transmission. The selection criterion is based on the interference power measurements on the channels. We show via simulations that this multichannel CSMA protocol provides a higher throughput compared to its single channel counterpart by reducing the packet loss due to collisions. 1

Abstract — Wireless technologies, such as IEEE 802.11a, that are used for ad hoc networks provide for multiple nonoverlapping 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 presents protocols for improving the capacity of multi-channel wireless networks. Our protocols simplify the use of multiple channels by using multiple interfaces, although the number of interfaces per node is typically smaller than the number of channels. We propose a link layer protocol to manage multiple channels, and it can be implemented over existing IEEE 802.11 hardware. We also propose a routing protocol that operates over the link layer protocol, and is specifically designed for multichannel, multi-interface ad hoc 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.

We develop an anycast mechanism at the link layer for wireless ad hoc networks. The goal is to exploit path diversity in the link layer by choosing the best next hop to forward packets when multiple next hop choices are available. Such choices can come from a multipath routing protocol, for example. This technique can reduce transmission retries and packet drop probabilities in the face of channel fading. We develop an anycast extension of the IEEE 802.11 MAC layer based on this idea. We implement the protocol in an experimental proof-of-concept testbed using the Berkeley motes platform and S-MAC protocol stack. We also implement it in the popular ns-2 simulator and experiment with the AOMDV multipath routing protocol and Ricean fading channels. We show that anycast performs significantly better than 802.11 in terms of packet delivery, particularly when the path length or effect of fading is large. Further we experiment with anycast in networks that use multiple channels and those that use directional antennas for transmission. In these networks, deafness and hidden terminal problems are the main source of packet loss. We implemented anycast as extension of 802.11 like protocols that were proposed for these special networks. We are able to show that anycast is capable of enhancing the performance of these protocols by simply making use of the path diversity whenever it is available. 1.

This paper examines the effectiveness of combining multiple description coding (MDC) and multiple path transport (MPT) for video and image transmission in a multihop mobile radio network. The video and image information is encoded nonhierarchically into multiple descriptions with the following objectives. The received picture quality should be acceptable, even if only one description is received and every additional received description contributes to enhanced picture quality. Typical applications will need a higher bandwidth/higher reliability connection than that provided by a single link in current mobile networks. For supporting these applications, a mobile node may need to set up and use multiple paths to the desired destination, either simply because of the lack of raw bandwidth on a single channel or because of its poor error characteristics, which reduce its effective throughput. In the context of this work, the principal reasons for considering such an architecture are providing high bandwidth and more robust end-to-end connections. We describe a protocol architecture that addresses this need and, with the help of simulations, we demonstrate the feasibility of this system and compare the performance of the MDC-MPT scheme to a system using layered coding and asymmetrical paths for the base and enhancement layers.

Typical video applications may need a higher bandwidth and/or higher reliability connection than that provided by a single link in current or emerging wireless networks. We propose to employ path diversity to provide higher bandwidth and more robust end-to-end connections than that affordable by a single path. Under this transport environment, two viable strategies for video coding are multiple description coding (MDC) and layered coding (LC). MDC is more effective when the underlying application has a very stringent delay constraint and the round trip time on each path is relatively long. LC can be a good alternative when limited retransmission of the base layer is acceptable and when it is feasible to apply unequal error protection over different paths. This paper describes the general issues involved in integrating MDC/LC with multiple path transport, and compares the performances of MDC and LC, under different path conditions.

Busy tone multiple access protocols have been used in multihop networks to reduce the effect of the hidden terminal problem. This paper demonstrates another approach to reduce the effect of the hidden terminal problem namely the use of multiple channel schemes. A protocol that uses both the busy tone and the multiple channel techniques achieves the best performance. Using a Markov chain model and an approximation, the throughput performance of the multiple channel nonpersistent CSMA protocol and the multiple channel conservative BTMA protocol in a large network is evaluated and compared. The results show that the multichannel CSMA and BTMA schemes exhibit a better performance over their single channel counterparts in a multihop network. 2 1. Introduction In a companion paper[1], we have analyzed the performance of the nonpersistent CSMA, conservative BTMA and idealistic destination based BTMA protocols in large multihop networks. It was assumed that around each terminal, a single ch...

Abstract — In this paper, we develop two new MAC protocols for multichannel operation in wireless ad hoc and mesh networks. The first protocol, Extended Receiver Directed Transmission protocol (xRDT) is based on a previously known multichannel solution called Receiver Directed Transmission (RDT) that uses a notion of quiescent channel. xRDT solves the problems faced by RDT, such as multichannel hidden terminal and deafness, by using an additional busy tone interface and few additional protocol operations. We also develop a novel single interface solution, called Local Coordination-based Multichannel MAC (LCM MAC). LCM MAC performs coordinated channel negotiations and channel switching to provide multichannel support. We demonstrate the effectiveness of these two protocols over two other wellknown multichannel protocols – MMAC and DCA – via extensive ns2 simulations. I.

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.

In this paper, we consider the channel assignment problem in single radio multi-channel mobile ad-hoc networks. Specifically, we investigate the granularity of channel assignment decisions that gives the best trade-off in terms of performance and complexity. We present a new granularity for channel assignment that we refer to as component level channel assignment. The strategy is relatively simple, and is characterized by several impressive practical advantages. We also show that the theoretical performance of the component based channel assignment strategy does not lag significantly behind the optimal possible performance, and perhaps more importantly we show that when coupled with its several practical advantages, it significantly outperforms other strategies under most network conditions.