# Two-Tier Cooperation Based High-Reliable and Lightweight Forwarding Strategy in Heterogeneous WBAN
This kind of algorithm usually establishes multiple paths between the sink node and source node, and then selects the path with the largest sum of the minimum residual energy of the nodes for data transmission, according to the residual energy between the nodes on the paths [25]. Compared with single path transmission algorithms, although multi-path algorithms can significantly improve the life cycle of the whole network, node residual energy is not the only factor that can determine the forwarding capacity of nodes and the energy-saving effect of the network. For example, sensors that undertake different businesses generally have different sampling frequencies, and sensors with high sampling frequency in WBAN are mostly used to collect data, and are not suitable to participate in forwarding tasks as relay nodes [7]. Due to the particularity of medical applications, some data collection can be completed soon, but there is still energy in these collection nodes, which can provide data forwarding services for other nodes. Giving priority to the use of their residual energy and using this residual energy as early as possible can also be considered in the design of the data forwarding model [26]. In addition, there are many kinds of business data collected by WBAN medical sensors, some of which are crucial and must be guaranteed at all times, such as ECG and blood pressure. Some can be interrupted or delayed, such as body temperature and current video information. Even some nodes only have a forwarding function, but not a collection function. Obviously, according to these characteristics, defining the important position of a node in network data transmission based on the importance of collecting data or the frequency of providing forwarding services can be another decisive factor in selecting relay nodes [27]. Thus, on the basis of a multi-path mechanism, fully and comprehensively considering to select many main factors that affect the energy consumption of nodes or networks to measure the forwarding ability of nodes will ensure that the forwarding model is established closer to the actual needs. Given all of that, for the dynamic environment of WBAN caused by the irregular movement of human limbs or the gain and loss of sensor energy, how to select appropriate factors and methods to construct a high-reliable and lightweight data forwarding mechanism is very important. This paper proposes a two-tier cooperation forwarding (TTCF) mechanism to achieve the above goal, and its major contributions are as follows:  
* _TTCF leverages the STPCSE model to compress heterogeneous medical data in WBAN and solve dimension mismatch in large matrix multiplication during compression and reconstruction, so as to reduce network redundancy and the amount of data to be transmitted, cut down system energy consumption and improve forwarding efficiency._
* _TTCF measures the forwarding ability of sensor nodes by combining sampling frequency, residual energy and their important status in the network to the Entropy Weight (EW) method [28], and uses Euclidean distance to calculate the short-distance spatial transmission energy consumption between them, and then leverages the linear weighted sum of the two as the forwarding utility to measure the comprehensive ability of nodes. It not only ensures the objectivity of relay node selection as much as possible, but also further takes into account system energy consumption._
* _On the premise of making full use of the nodes that are about to exit the network, TTCF integrates the forwarding utility of measuring the comprehensive ability of nodes into Dijkstra algorithm to effectively improve the calculation of the data transmission path, and is evaluated on a simulation scenario based on a human body containing different types of sensors. Experimental results show that TTCF always exhibits better performance in terms of data reconstruction, energy consumption and throughput control.