# Distributed Reliable and Efficient Transmission Task Assignment for WSNs
## 1 Introduction  
Task assignment is an essential issue in wireless sensor networks (WSNs). In such multi-sensor systems, task allocation is based on the deadline and the priority of tasks, and different tasks are reasonably assigned to the sensor nodes for best perception performance. However, task allocation schemes that only aim at reducing energy consumption are not sufficient for several applications with high-reliability requirements. That is, whether tasks with high-reliability requirements in WSNs such as measurement, monitoring, and configuration can be completed in a timely manner depends on how the transmission tasks in WSNs can be reliably and efficiently assigned. As is known, energy-savings and high reliability are two conflicting goals, and it is thus challenging to assign high reliability and low energy tasks to appropriate nodes in WSNs.  
In recent years, task priority assignment in WSNs has attracted the attention of researchers and satisfactory research results have been achieved. Most existing methods for practical applications are centralized algorithms, as the centralized task assignment method based on a single sink node still has the problem of poor reliability and scalability, so offline execution is selected due to computational complexity. Besides, the communication overhead and delay of task assignment will be significant in large-scale network scenarios or frequent network and dynamic changes. Therefore, it is very urgent to investigate novel distributed, reliable, and efficient task assignment methods for WSNs.  
Aiming to solve the reliable and efficient distributed task assignment problem in WSNs, task-aware reliable and efficient task allocation for WSNs is investigated in this paper. The contributions of this paper are summarized as follows:  
1. A global network view consisting of a multi-level view (including physical topology, routing topology, and task view) is constructed as a conceptual basis for global optimization;
2. A reliability evaluation model is established from the perspective of the task, and the constraint factors and objective functions of the task allocation are analyzed;
3. We propose the transmission-oriented reliable and energy-efficient task allocation (TRETA)-Cluster, in which the sink assigns reliability to all cluster heads according to the reliability requirements, and the cluster head performs local task assignment according to the assigned phase target reliability constraints. Simulation results show that TRETA-Cluster reduces the communication cost and latency of task assignment compared to centralized task allocation;
4. We propose the TRETA-Multi-Sink, where the global view is obtained by fetching local views from multiple sinks. Multiple sinks have a consistent comprehensive view of global optimization. The ways to respond to local task assignment requirements without the need to communicate with remote nodes overcomes the disadvantages of centralized task assignment in large-scale WSNs with significant communication overhead and delay, and have better scalability.  
The remainder of this paper is structured as follows. Section 2 introduces the related work, the task allocation problem in WSNs is described in Section 3, and a global network view consisting of a multi-level view is proposed in Section 4. Next, we present a reliable and efficient task allocation algorithm for WSNs in Section 5, including centralized task allocation and two distributed task assignments. The performance is evaluated by theoretical analysis and simulation in Section 6, and finally, concluding remarks and future work are discussed in Section 7.