Also presented is a glimpse of the ideal wireless multi-hop routing protocol along with several open issues. The Perk Lab Dr.
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The letter of award states:. After receiving the data frame, the MAC layer of the coordinator ascertains if the relay address field in the data frame indicates its address. If the relay address field in the data frame is equal to its address, it searches its relay table to find the coordinator related to the destination device. Then, it adds an address of the selected coordinator to the addressing field.
In Figure 16 , because the next device is the PAN coordinator, the coordinator set the relay address field to the PAN coordinator address and transmits the received data frame to the PAN coordinator. The MAC layer of the PAN coordinator ascertains if the relay address and the destination address fields in the data frame indicates its address.
Otherwise, it discards the received data frame. Figure 19 shows the flow chart for the proposed relay scheme. When the coordinator receives a frame from its higher layer or other devices, it ascertains a message type. And then, after it adds the relay address to the addressing field, it transmits a data frame to a relay device. If the coordinator receives a frame from other devices, the MAC layer ascertains if the relay address field and the destination address field in the received data frame indicates its address. If the value of the relay address field in the received frame is equal to the coordinator address and the value of the destination address field is not equal to the coordination address, the MAC layer selects the relay coordinator and transmits the received data frame to the selected device.
We conducted the simulation to evaluate the performance of the proposed protocol, comparing with other protocols. It is very suitable for simulating wireless sensor networks owing to its modular structure and using NED language for simple simulation environment configuration. Our simulation model consists of the following modules: application layer implementing the traffic generator, Battery module, Network module and Physical layer module.
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 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. 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 kbps. 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.
Lin Cai Ph.D.
In this simulation, we compare the proposed protocol with the cluster-tree protocol of IEEE In the cluster-tree protocol of IEEE 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.
Therefore, we consider these factors in our simulation. In this simulation, we consider two scenarios to evaluation the proposed scheme.
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In both scenarios, the PAN coordinator transmits a data frame to a leaf node. The target node is randomly selected among network nodes. In the proposed scheme, the PAN coordinator transmits the data frame to a neighbor coordinator in the RP and then the coordinator forwards a data frame to the leaf node in the GTS without the contention. In the two legacy protocols, the PAN coordinator transmits the data frame to a neighbor coordinator in its active period. Then, the coordinator transmits the data frame to the leaf node in its active period.
In the first scenario, to configure the cluster tree, we implemented a simple tree formation algorithm based on the hop count 2, and in the second scenario, we evaluate the network performance according to the increase of the tree depth. In this simulation, we define that the delivery ratio is the ratio between the number of messages correctly received by the destination and the number of messages sent by the PAN coordinator. And we define that the average energy consumption is the average energy consumed by an intermediate coordinator in the network.
We also define that the average latency is the average value of the latency measured from the instant at which the PAN coordinator sends a message to the instant at which the destination node correctly receives the same message. To evaluate the consumed energy, the energy model of the CC, which is a single chip 2. The energy model in [ 36 ] defines four modes for the radio: transmitting, receiving, idle and sleep modes. The energy consumption is calculated by calculating the time spent on radio in each state multiplied by the energy consumption in that mode.
Because the CPU consumption is very low compared to energy consumption by the radio [ 31 ], we do not consider the CPU consumption in this simulation. The common simulation parameters are summarized in Table 2. Figure 20 shows the delivery ratio as a function of the traffic load in the network. In this simulation, we define the traffic load to the number of data frames transmitted by devices during the BI.
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In this simulation, all leaf nodes transmit data frames to the PAN coordinator, and the PAN coordinator transmits data frames to the selected leaf node. Also, we fixed the number of devices in the network to As shown in Figure 20 , the delivery ratio of the cluster-tree protocol and the ASLEEP protocol decrease as the traffic load on the network increases.
This result is related to the fact that the contention for the channel access and the collision probability increases as the traffic load on the network increases. In Figure 20 , because the ASLEEP protocol can slightly adjust the superframe duration within the limited bounds, it can provide the transmission probability higher than the cluster-tree protocol. However, as the traffic load increases, the superframe duration of the ASLEEP protocol reaches the envelope and cannot avoid the increased competition.
Meanwhile, in the proposed scheme, a coordinator does not contend with other leaf nodes for the channel access since it relays data frames to the next hop coordinator in the CFP. Therefore, the proposed scheme shows the similar delivery ratio regardless of an increase of the traffic load, and we can show that the delivery ratio of the proposed scheme is higher than two legacy protocols.
Figure 21 shows the delivery ratio as a function of the number of devices in the network. In this simulation, the traffic load in the network is fixed to 5. As shown in Figure 21 , when the number of devices in the network increases, the delivery ratio of two legacy protocol decreases.
This result is because the probability of correct delivery to the next hop reduces due to the increased collision probability. The ASLEEP protocol provides the transmission probability higher than the cluster-tree protocol, but it cannot remove the increased contention. Figure 21 shows that the proposed scheme provides the performance of the delivery ratio higher than two legacy protocols regardless of the node density.
In the proposed scheme, when the coordinator relays data frames to the next hop device in the proposed protocol, it transmits data frames in CFP.
Thus, it does not contend with other devices for the channel access and is influenced less by the node density. Therefore, the proposed scheme provides better delivery ratio than two legacy protocols. Figure 22 shows the end-to-end delay as a function of the traffic load in the network.
In this simulation, the number of devices in the network is fixed to As illustrated in Figure 22 , when the traffic load on the network increases, the end-to-end delay of two legacy protocols also increases. This result is related to the fact that messages are queued at each parent node for the duration of the active period before they can be forwarded up to the tree. In other words, in two legacy protocols, when the traffic load on the network increases, the contention among devices is intense for the channel access, and the possibility to relay data frame in the same superframe is lower.
However, the ASLEEP protocol can slightly regulate the superframe duration, and it can reduce the end-to-end delay somewhat. Meanwhile, in the proposed scheme, because the coordinators can relay data frames to the next hop devices in CFP, it can provide the constant end-to-end delay regardless of the traffic load. Therefore, the end-to-end delay of the proposed scheme is superior to two legacy protocols. Figure 23 shows the end-to-end delay as a function of the number of devices in the network. In Figure 23 , the end-to-end delay of two legacy protocols increases as the node density increases.
Because the ASLEEP protocol can adjust the length of the active period and can react the increase of the node density, it shows the superior end-to-end delay performance to the cluster-tree protocol. However, when the node density increases largely, like the cluster-tree protocol, the end-to-end delay of the ASLEEP protocol largely increases due to the contention among devices. However, in the proposed scheme, because the coordinator using the proposed scheme can relay the data frame without the contention, it can provide the constant end-to-end delay regardless of the node density in the network.
Therefore, the performance of the proposed scheme is superior to two legacy protocols. Figure 24 shows the energy consumption as a function of the traffic load in the network.