# A Survey of Routing Protocols in WBAN for Healthcare Applications
## 3 Classification of Routing Protocols for WBAN
### Cross-Layer Routing
#### 3.3.1 A Priority-Based Cross Layer Routing Protocol (PCLRP)  
A PCLRP was proposed by [PERSON] et al. [25], to design the protocol across the MAC (Medium Access Channel) layer and the network layer. This paper divides data into three categories and sets priority--P1 is emergency data (EM), referring to abnormal data; P2 is delay sensitive data (DS), referring to medical video; P3 is general data (GM), corresponding to the normal cycle data. The MAC superframe division stage is shown in Figure 9. The children competition access phase (CCAP) and children competition free phase (CCFP) are divided into three corresponding slots, according to priority, and the service is customized for different priority data. In order to ensure the priority transmission of P1 data, EM data are required to compete for access in the whole CCAP. Random back-off strategy, based on priority, is adopted in the whole competition stage, and the back-off time is determined, according to priority, so as to ensure the non-delay transmission of emergency data.  
In the routing phase of the PCLRP protocol, the co-operative transmission mode of relay is adopted. In the beacon phase, the coordinator judges whether the node is a relay node by the ACK information, which includes the location, energy, and current available time slot of the node. In the routing establishment phase, path planning is carried out according to data priority and the MAC slot, which achieves higher performance than a single layer protocol, and especially guarantees low delay and high reliability transmission of high priority data, and reduces conflicts and delays caused by competition. However, the protocol cannot effectively guarantee the reliable transmission of low priority data.  
3.2 Cross-Layer Design for Optimizing Transmission Reliability, Energy Efficiency, and Lifetime (CLDO)  
[PERSON] et al. [26] proposed a cross-layer design optimization scheme CLDO, which optimizes network parameters, such as transmission reliability \(\mathrm{R_{i}}\), energy efficiency \(\chi\) and network lifetime \(\mathrm{T_{life}}\), through cooperation among network layer, MAC layer, and the PHY layer. The goal is to find the best transmission power, the best relay and the best packet size to solve the above problems. Before  
Figure 9: Superframe structure of the Priority-Based Cross Layer Routing Protocol (PCLRP) protocol.  
the theoretical deduction, the author carried out simulation experiments, the results showed that an appropriate transmission power and packet size can not only ensure a reliable transmission, but can also save energy consumption and prolong network life. The best relay can ensure a successful delivery of data packets and reduced errors, and energy consumption can be greatly reduced within an acceptable delay range. Therefore, based on this experiment, a large number of complex theoretical deductions have been carried out, and more convincing corresponding propositions and proofs have been given. In the routing stage, when selecting the next hop relay, the power efficiency and energy consumption rate of the node were considered comprehensively. When the residual energy of the node was lower than a certain value, the node only transmitted its own information, and readjusted the transmission power and packet size, to protect the node with low residual energy, ensure reliable transmission, and prolong the life of the whole network.