## 5 Incremental Cooperative Routing Protocols for WBANs  
To study the effects of three-stage incremental cooperation, we design the EInCo-CESStat protocol and compare its results to InCo-CESStat [7] and Co-CESStat [8]. The conventional cooperation is used in Co-CESStat in which the same data are forwarded by both relays. Whereas, in InCo-CESStat, incremental cooperation is used in which data are forwarded incrementally by relay nodes. However, both schemes in [7,8] utilize two relays for a single source node. EE, PER, throughput and the stability period for all three protocols are observed. We consider four-phase incremental relay-based cooperation in EInCo-CESStat by using three potential relays for each source node. In the first phase, the source transmits data to the sink, which is overheard by its three potential relays, \(R_{1}\), \(R_{2}\) and \(R_{3}\). If the destination/sink is able to detect the packet correctly in this phase, it sends back an ACK, and the relays just remain idle. If the NACK is received from the sink at the source node, it indicates that the data packet is dropped due to high BER, and data forwarding from \(R_{1}\) is needed. If \(R_{1}\) successfully detects the data packet in the first phase, it forwards the data packet to the destination (sink) in the second phase. If the data packet is received with acceptable BER at the sink, the second phase of cooperation is successfully completed. However, if the sink fails to detect the packet sent by \(R_{1}\), \(R_{2}\) is supposed to forward the packet to the sink, which was correctly received in the first phase. If the sink again fails to receive the packet from \(R_{2}\) due to high BER, failure of the third phase occurs. Finally, the last phase of communication occurs between \(R_{3}\) and sink. The system model for InCo-CESStat is also the same with two-relay cooperative communication. Therefore, InCo-CESStat consists of three communication phases accordingly. Topologies of InCo-CESStat and EInCo-CESStat protocols are shown in Figure 4 for comparison. As Co-CESStat has the same topology as InCo-CESStat, it is not mentioned in the figure. Communication flow diagram is also shown in Figure 5 for the compared protocols. There are four normal source nodes (S), four cooperative nodes (R) and a sink node (D) in the proposed and compared WBAN. Cooperative nodes, which are responsible for relaying the data of other nodes, are equipped with higher energy than normal source nodes. As cooperative nodes also have their own sensed data to be transmitted along with data to be forwarded, the selection of the relays is deterministic, _i.e._, each source node has its own pre-defined relay node for forwarding its data to the sink. Predefined/deterministic relay selection has been given priority over random/opportunistic relay selection due to two reasons: (i) to avoid imbalanced energy consumption of the nodes; and (ii) to minimize end-to-end delay, as WBAN data are critical. Some assumptions are considered for the simulations as follows [6,9,10]:  
1. The sink limits all nodes to transmit only in their own reserved time slots: if all nodes transmit simultaneously to the sink, a data collision may occur, which ultimately causes the loss of data and energy wastage. Thus, collision avoidance and network coordination are not only important for efficient energy consumption, but also to maintain QoS, as sensed data are always critical in WBANs. 2. Half-duplex communication is considered: since the sink does not send data back towards the source nodes, the consideration of half-duplex communication leads to enhanced management of resources; especially energy efficiency. 3. All nodes are within the transmission range of each other: we have considered a human body of dimensions 0.9 m \(\times\) 1.7 m. Thus, all nodes lie within the transmission range of each other. 4.