## 3 Related Work  
The IEEE 802.15.4 CSMA/CA mechanism is a deterministic approach that avoids collision by using the binary exponential backoff scheme without considering the status of the communication channel. Hence, the authors in [3] have designed one collision-aware backoff algorithm, where the nodes in the network can dynamically choose their backoff interval based on the status of the communication channel. However, the proposed algorithm cannot avoid collisions due to hidden  
Figure 2: Channel access mechanism of IEEE 802.15.4e. terminal problems. To reduce the collisions, the author in [4] divide the transmission durations into a number of sub-periods based on the network environment, and one device uses only one sub-period. Though it can reduce the effects of the hidden terminal problems, it cannot provide priority to the devices with higher buffer status to access the channel first. A Time-Division Multiple Access (TDMA)-based scheme is designed in [5] for real-time data transmission to ensure collision-free transmission. The proposed time-division approach can work under ideal channel conditions, which is unrealistic. Considering the hidden terminal problem, the authors in [6] have proposed one hybrid model by combining CSMA/CA with TDMA. Though the hybrid model considers the hidden terminal problem, it requires global information of the network devices. The authors in [7] analyze the throughput of IEEE 802.15.4 MAC considering the presence of the hidden terminal problem in the network. To reduce the hidden terminal problem, the authors in [8] design one algorithm that identifies the hidden nodes by analyzing the received signal powers. However, these works focus on only ZigBee devices in the network without considering any external interferences. Packet loss occurs due to interference when both WiFi and ZigBee channels overlap. The simple way to avoid the interferences among the devices in a network is to use different channels. However, the available channels are limited, for which the authors in [9] have designed a new MAC scheme with an increasing number of CCAs to alleviate the collisions in WiFi transmissions. However, the proposed mechanisms cannot avoid collisions due to the hidden terminal problem, and also, a significant amount of energy for CCAs is consumed in these methods. To detect the interference, the authors in [10] propose a new protocol that helps a device to switch adaptively into a safe channel. However, performance analysis in terms of latency and power consumption is not made in such adaptive channel switching. Under external interference, the theoretical analysis of throughput for WSNs has been studied in [11]. The authors in [12] have analyzed the interferences due to signal arrival direction and losses under the smart building scenario, though the reliability of the data communications is not considered. The authors in [13] propose one cooperative carrier signaling technique to avoid the interference between ZigBee and WiFi devices. However, the main drawback is that one dedicated ZigBee device should be present in the network to send the busy signal, which can increase the network cost. To analyze the performance of the coexistence of WiFi and ZigBee devices, the authors in [14] have designed the Markov model for normalized saturation throughput to ensure the quality of service and fairness. In the proposed method, both transmission failure devices and ready to transmit devices have equal priority to access the channel. The battery power is a major constraint for ZigBee devices, and the major power consumption by the ZigBee device is due to data retransmission when there is a collision or channel error. Hence, the authors in [15] have designed one Additional Carrier Sensing (ACS) algorithm to reduce energy consumptions by avoiding further channel access through the information during the second CCA. However, the wastage of energy is possible when the second CCA is found busy due to data transmission.