Abstract-Interference between concurrent transmissions can cause severe performance degradation in wireless sensor networks (WSNs). While multiple channels available in WSN technology such as IEEE 802.15.4 can be exploited to mitigate interference, channel allocation can have a significant impact on the performance of multi-channel communication. This paper proposes a set of distributed protocols for channel allocation in WSNs with theoretical bounds. We first consider the problem of minimizing the number of channels needed to remove interference in a WSN, and propose both receiver-based and link-based distributed channel allocation protocols. Then, for WSNs with an insufficient number of channels, we formulate a fair channel allocation problem whose objective is to minimize the maximum interference (MinMax) experienced by any transmission link in the network. We prove that MinMax channel allocation is NP-hard, and propose a distributed link-based MinMax channel allocation protocol. Finally, we propose a distributed protocol for link scheduling based on MinMax channel allocation that creates a conflict-free schedule for transmissions. The proposed decentralized protocols are efficient, scalable, and adaptive to channel condition and network dynamics. Simulations based on the topologies and data traces collected from a WSN testbed of 74 TelosB motes have shown that our channel allocation protocols significantly outperform a state-of-the-art channel allocation protocol. Index Terms-Wireless sensor network, multi-channel, channel allocation, distributed algorithm NTERFERENCE between concurrent transmissions can cause severe performance degradation in wireless sensor networks (WSNs). Multi-channel communication is an attractive approach to reducing interference and enhancing spatial reuse. Since channels are a scarce resource in a WSN, channel allocation significantly influences the performance of multi-channel WSNs. It is particularly important in Time Division Multiple Access (TDMA) based WSNs where interfering transmissions scheduled at the same time slot must be assigned different channels. It is, therefore, important to allocate the channels to reduce interference and increase the number of concurrent transmissions. Channel allocation has been widely studied for wireless ad-hoc networks. These protocols are not applicable to WSNs since the applications, routing, node resources, and network structure in WSNs are quite different from traditional ad-hoc networks. While channel allocation has also been studied for WSNs, most of them focus on simple heuristics [1], [2], [3] without any performance guarantee for channel hopping or just focus on centralized solutions [4], [5] . In this paper, we formulate optimal channel allocation as constrained optimization problems, and propose a set of distributed channel allocation protocols with theoretical bounds for WSNs. We first consider the problems of minimizing the number of channels needed to remove interference in a WSN for both receiver-based and linkbased channel allocation. A receiver-based channel allocation is suitable for both CSMA/CA and TDMA protocols. A link-based channel allocation allows better spatial reuse due to the flexibility in assigning different channels to different senders, but it is more suitable for TDMA protocols under which the receiver can switch to channels according to the expected sender scheduled in each time slot. We present distributed protocols for both receiverbased and link-based channel allocation. WSNs usually have a moderate number of channels (e.g., 16 channels specified IEEE 802.15.4), and noisy environments may further reduce the number of available channels due to blacklisting [6] . Therefore, there may not exist enough channels to remove all interference. Existing works on channel allocation with an insufficient number of channels usually consider receiver-based allocation and propose centralized heuristics [4] , [5] , [7] . A recently proposed distributed protocol for channel allocation in WSNs has addressed receiver-based allocation to minimize total interference suffered by all receivers [8] . In contrast, we formulate a link-based fair channel allocation problem whose objective is to minimize the maximum interference (MinMax) experienced by any transmission link in a WSN. The key advantage of the MinMax objective is that it can mitigate bottlenecks in a WSN where a node or link experiences excessive interference. We prove that MinMax channel allocation is NP-hard, and propose a distributed MinMax channel allocation protocol. Furthermore, since channel allocation cannot always resolve all transmission conflicts due to an insufficient number of channels, it is complemented by a time slot assignment algorithm to create a conflict-free schedule. We propose a distributed protocol for link scheduling based on MinMax channel allocation. Our contributions are: . We present distributed protocols for both receiverbased and link-based interference-free minimum channel allocation. . The authors are with the
Saifullah et al. REF introduced an idea that uses the maximum number of channels to schedule the data transmission of sensors in one time slot; however, since the number of channels is limited, occurring data collisions is possible.
Distributed Channel Allocation Protocols for Wireless Sensor Networks
IEEE Transactions on Parallel and Distributed Systems
IEEE Transactions on Parallel and Distributed Systems
Computer Science