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Top1. Introduction
The exponential growth in the wireless multimedia devices has fuelled the need for very high-speed wireless connectivity beyond the capabilities of existing communication networks (Baldemair et al., 2013). The fiber optic links can support higher data rates but cost and deployment of such link is often prohibitive in many applications (Ghassemlooy, 2015). Wireless links, on the contrary, can provide a cost-effective alternative to interconnect the areas where the fiber link cannot be laid. The current wireless technologies like 4G and WIMAX standards are using Orthogonal Frequency-Division Multiple Access (OFDMA) and multiple-input multiple-output (MIMO) techniques in order to achieve maximum possible spectral efficiency (Elkashlan et al., 2014). However the expected spectral efficiency for future wireless networks is still beyond our reach. In this context, Wireless communication in the MMW band seems to be a promising candidate to support multi-gigabits per second (Gbps) data rate for the next generation communication networks especially the 5G systems where in the basic criteria is to provide higher speed data transmission, larger radio channel capacity, lower latency, and handle massive devices connections (Shubair, 2016). The main motivation for using MMW communication is to exploit the huge unexploited spectrum from “30 GHz to 300 GHz” (Chong, 2007). Other reasons that motivate the use of MMW communication for next generation mobile networks are (Shi, 2016; Akyildiz et al., 2014; Huang & Wang, 2011):
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One of the alternative technologies of MMW communications is Free Space Optical (FSO) communication which offers very large available bandwidths however it has certain inherent limitations in its practical implementation like transmitter receiver misalignments, low transmission power budget limits for eye safety. These limitations in turn effect the achievable data rate and communication range of such systems.
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MMW Band offers huge unexploited bandwidth which in turn can provide high-speed links with throughput of the order of 10 Gbps with higher degree of spectrum sharing as compared to lower frequencies.
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Small antenna size which facilitates the fabrication of large antenna arrays over a small area like postage stamp.
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Millimeter wavelengths allow modest size antennas to have a very narrow beam width which in turn provides the better spatial resolution.
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Ease of the Integration of Processors, memories and other MMW circuitry on a Monolithic Microwave Integrated Circuit (MMIC) chip which in turn helps in achieving the device compactness and facilitates the fast processing and storage of the received data.
The very large bandwidth, higher resolution and narrower beam width provided by the MMW band frequencies makes them suitable for wide range of applications which demand ultra-high data rates. Cellular systems may incorporate MMW communication links to provide higher bandwidths to solve the problems of spectrum crunch. Data centers and computational platforms may replace traditional wired interconnects with high-speed MMW wireless interconnects (Rappaport, 2014). Backhaul wireless links, inter satellite communication, Internet of Things, Failure recovery and redundancy, MMW WPAN/WLAN, Wireless Gigabit Adhoc networks, intra-vehicular and inter-vehicular communication, aerospace communications are also some of the emerging and attractive applications of MMW Communication systems and have been the subject of research and some market developments (Park & Rappaport, 2007; Zheng et al., 2015). Despite of many advantages offered for high potential applications envisaged in the usage of millimeter band, there are number of research challenges and open issues that must be addressed prior to the successful deployment of this technology. This requires innovative solutions and even the revision of well-established concepts in wireless communications. In order to exploit the benefits of MMWs, various Standards have been released which are discussed as follows (Al-Falahy & Alani, 2019):