# The Latest Advances in Wireless Communication in Aviation, Wind Turbines and Bridges
## 2 Wireless Communication and Protocols' Characteristics
### Wireless Communication Protocols Overview
802.11n began to use MIMO technology using multiple antennas to transmit and receive, improving coverage and performance. With MIMO, the radio signal is split into several streams, which are independently transmitted and received by several receivers simultaneously [5]. Figure 2 presents the architecture of the Zigbee protocol, also known as IEEE 802.15.4. This standard is aimed at defining the MAC layer and physical layer for Low-Rate Wireless Private Area Networks (LR-WPAN). As this standard is intended for low power consumption, a low data rate, and a low-cost wireless network, it is most often used in sensor networks. Compared to Wi-Fi, this network uses less power, but at the expense of speed. The most commonly associated with this standard is the ZigBee protocol. This standard also includes ISA100.11a, WirelessHART, MiWi, 6 LoWPAN, Thread, and SNAP. In contrast to the 802.11 standards working in the 2.4/5 GHz band, 802.15.4 operates on several different bands depending on the region, e.g., Europe works on various bands different to North America [6]. WiMAX (which stands for Worldwide Interoperability for Microwave Access) is a wireless data transmission technology based on IEEE 802.16 standard to provide broadband wireless access (see Figure 3 for architecture details). Initially, the technology was subject to several restrictions, mainly related to the frequency band used (initially the 10-66 GHz band) and line of sight (LOS) requirements. The proposed IEEE 802.16d amendment eliminated this problem by reducing the frequency to a maximum of 11 GHz. Additionally, HARQ (Hybrid Automatic Repeat Request) transmission control mechanisms and Quality of Service (QoS) implementation were introduced to reduce transmission delay and introduce process priorities. The latest approved version is the 802.16e standard introducing mobility of devices in the 2-6 GHz band. The mobility of devices has been achieved by implementing mechanisms for the handover of connections from one base station to another while the connection is active. This method is known from the mobile network, providing transparency of switching the whole state of the transmission session to another base station, which ensures better quality of transmitted signal [7]. Figure 2: Zigbee protocol architecture [6]. It is expected that the 5G communication will reach the market by 2021. Subsequently, it is expected that 6G communication will be launched between 2027 and 2030. It is challenging to achieve the 5G/6G targets and the Internet of Things based on the touch Internet. There are a number of critical and challenging issues and these include: low latency, low power consumption, high bandwidth, high security, massive connectivity, high QoE, and reliable connectivity for 5G communication systems. The RF systems are the only ones not able to satisfy the increased demands of future 5G/6G and IoT networks. Optical wireless communication (OWC) technologies are the best complementary RF network solution. It is the coexistence of RF and optical wireless systems that can achieve the objectives of the above-mentioned networks [8]. Table 1 presents the comparison of selected parameters of different wireless standards. Figure 3: WiMAX protocol architecture [7].