# Impacts of Diversity Technique Application in Order to Reduce the Fading in IEEE 802.15.4 Networks
## 1 Introduction  
The Institute of Electrical and Electronics Engineers (IEEE) 802.15.4 [1] is a technical standard that defines the operation and implementation of wireless sensor networks (WSNs). IEEE 802.15.4 takes center stage in the Internet of Things (IoT) as low-rate wireless personal area networks (LR-WPANs) [2]. Wireless sensor networks consist of a large number of sensor nodes that are multifunctional and have a limited energy source; therefore, energy must be used efficiently [3]. From the energy efficiency point of view, insufficiently accurate performance estimation is likely going to cause energy loss due to retransmission in automatic repetition schemes or additional processing, due to coding and decoding, in forward error correction schemes. Along with worsened energy efficiency, fading, interference and noise negatively affect other parameters critical for normal network operation, such as latency and throughput. Therefore, an accurate network performance evaluation in the given transmission conditions is extremely valuable when deciding on many networks' specific parameters, such as distribution of the transmission power per node, the network node density, selection of error correction scheme, etc. [4]. IEEE 802.15.4 networks use several bands, among which the most popular is the 2450 MHz Industrial-Science-Medicine (ISM) band [5]. Signal transmission in wireless networks can be attenuated by noise, fading and interferences. These disturbances can cause changes in the transmitted signal to the extent that the receiver fails to correctly recognize the received symbols. Fading channels can be modeled through Nakagami-\(m\), Rayleigh, Ricean, k-\(\mu\) distribution and others [6, 7]. The reliability of the communication connection is most often reflected in the value of the bit error rate (BER) in the receiver [8]. Instead of analyzing corrupted packets or packet error rates only, the BER and related error patterns provide more in-depth insights into how the transmitted sequence is detected by the receiving node and translated back to the corresponding symbol [9]. In addition, there are other performances based on which the quality of the communication connection is assessed, such as bit error probability (BEP), packet error rate (PER) and chip error probability (CEP) [9]. Although the IEEE 802.15.4 standard uses the carrier-sense medium access with collision avoidance protocol (CSMA/CA) as a method of mitigating interference, collisions cannot be completely avoided. The CSMA/CA mechanism does not provide sufficient protection against problems caused by hidden nodes that are the root cause of co-channel interference (CCI). However, they have the ability to receive signals correctly despite a significant level of CCI [10,11]. Spatial diversity techniques are used to reduce the impact of large-scale and small-scale fading on the system performance in radio frequency (RF) channels. The most widely used is the spatial diversity technique with multiple antennas at the receiver input. Signals from antennas are combined in different ways. The combination techniques used to reduce the fading impact on the system performance are maximum-ratio combining (MRC), equal-gain combining (EGC), selection combining (SC) and switch-and-stay combining (SSC) [12,13]. Numerous papers deal with the issue of received signal quality in IEEE 802.15.4 networks [5,9,10,14,15,16,17]. In [16], the performance of the ZigBee network under WiFi interference was considered and presented through the terms for PER and BER. In [17], the PER of the ZigBee under a wireless local area network (WLAN) and Bluetooth interferences was analyzed. The impact of fading was not considered in these papers. Performance analysis of the IEEE 802.15.4 network in the form of BER, and under the impact of [PERSON] and Nakagami-\(m\) fading and in the presence of additive white Gaussian noise (AWGN) and interference is presented in [18].