# Time and Energy Efficient Relay Transmission for Multi-Hop Wireless Sensor Networks
## 4 Performance Evaluation  
We conducted the simulation to evaluate the performance of the proposed protocol, comparing with other protocols. We used OMNet++ [30] as the platform for simulation. OMNeT++ is a public source, component based, and open architecture simulation platform with GUI support. It is very suitable for simulating wireless sensor networks owing to its modular structure and using NED language for simple simulation environment configuration. The IEEE 802.15.4 model in [31] is good and was used in several papers to evaluate the performance of their proposed scheme. This model applies to the latest IEEE Std. 802.15.4-2006 standard and implements the GTS mechanism as well as energy model. To evaluate the performance of the proposed scheme, we modified an INETMANET framework of a model of IEEE 802.15.4 developed for OMNeT++ [31]. Our simulation model consists of the following modules: application layer implementing the traffic generator, Battery module, Network module and Physical layer module. OMNeT++ can set the environment parameter by adjusting the variables in the omnetpp.ini configuration file. The simulations are operated in beacon-enabled mode, and all packets require ACK frame. Many previous works [32; 33; 34; 35] have analyzed the performance of the 802.15.4 MAC protocol in a star network under the assumption that sensor nodes are always active (i.e., power management is disabled). However, in this paper, we analyze the performance of MAC protocol in the cluster tree topology under the assumption that sensor nodes utilize the power management. In this simulation, we consider a cluster tree topology with a PAN coordinator, a variable number of coordinators and a set of leaf nodes (which are assumed to be the traffic sources). This network configuration could correspond to a realistic scenario of sensor network in which the leaf nodes (the sensors) consist of simple RFD end devices while coordinators could be more complex mains powered FFD nodes. In a real scenario, the PAN coordinator is in charge of programming and communicating the MAC parameters that regulates the beacon emission of the intermediate coordinators, mainly the beacon order of the whole network and the superframe orders of the coordinators. To simplify this procedure in our implementation, the configuration of these MAC parameters is defined through the file omnetpp.ini. Also, following the structure of the original code, a value for the BO and the SO is defined for every node in this file. In this simulation, we use a constant bit rate traffic generator for synthetic scenarios. All messages are always sent by all nodes to the PAN coordinator (uplink traffic). The data payload size transmitted by each leaf node is fixed at 50 bytes. Each leaf node generates data packets at a rate of one packet per second, and the data rate of each leaf node is fixed at 250 kbps. Also, in this simulation, we considered a frame error rate of approximately 10%. The radio propagation model was two- way ground; the transmission range was set to 15 m, while the carrier sensing range was set to 30 m. In this simulation, it was considered a network where various sensor nodes are placed in a 100 \(\times\) 100 m area. In this simulation, we compare the proposed protocol with the cluster-tree protocol of IEEE 802.15.4 [1] and the Adaptive Staggered sLEEp Protocol (ASLEEP) protocol [25]. To evaluate the ASLEEP protocol, we apply the ALEEP protocol to the IEEE 802.15.4 protocol. In the cluster-tree protocol of IEEE 802.15.4, the active periods of parent nodes are scheduled in TDMA, so that only a single parent and its children are active at the same time in the network. In the ASLEEP scheme, each parent node can have a different duration for its active period, depending on the traffic/channel conditions. As a consequence, nodes at the same level in the routing tree can wake up and go to sleep at different times. Clearly, factors such as the node density, the contention, collisions, and the tree level have a significant impact on the network performance.