To encounter the continuous increasing of bandwidth demand at the end-users of wireless and optical communication networks, the millimeter-wave (MMW) carriers are used for future broadband wireless networks. The next generation of wireless networks is usually developed and implemented based on utilization of the available spectrum in the MMW frequency bands (30–300 GHz) to provide multi-Gigabit networks with high reliable transmission over large distances. The MMW wireless communication suffers from the channel fading which leads to limiting the coverage range and the mobility. To design the wireless networks based on the MMW spectrum, the performance of these networks must be optimized to offer huge data rate, low latency, and high spectrum efficiency.

The recent 5G wireless networks almost utilized are the subband from 28 GHz to 80 GHz in the band of MMW that extended from 30 GHz to 300 GHz. Extensive propagation measurements have been performed at 28 GHz, 38 GHz, and 73 GHz in urban microcellular, urban macrocellular, and/or indoor scenarios. Planning of the 5G wireless network by using MMW frequencies offers high performance capacity, throughput, and QoS compared with microwave frequencies which is applied in the current networks such as Long-Term Evaluation (LTE) wireless networks (2 GHz or 3.6 GHz). The ‎development technologies also make MMW possible for cheap consumer devices such as Full Duplex (FD), Massive Multiple Input Multiple Output (MIMO), Orthogonal Frequency Division Multiplexing Access (OFDMA), and ‎Generalized Frequency Division Multiplexing (GFDM).

When the frequency goes up to the range of MMW, the energy absorption caused by atmosphere, rain, and snow becomes increasingly prominent which causes limitation in signal transmission distance. In this special issue, most of the accepted papers to be published are proposed to solve these problems.

The first paper “Spectral and Energy Efficiencies in mmWave Cellular Networks for Optimal Utilization" by A. M. Hamed and R. K. Rao is proposed to examine energy efficiency (EE), spectral efficiency (SE), network latency, area spectral efficiency (ASE), and area energy efficiency (AEE) of MMW cellular network in 28 and 73 GHz bands for line-of-sight (LOS) and non-line-of-sight (NLOS) links. This paper presented a frame work for analysis of SE and EE metrics of the network for optimum utilization of network resources. The results have shown that 73 GHz band achieves better SE and the 28 GHz band is superior in terms of EE. It is observed that while the latter band is expedient for indoor networks, the former band is appropriate for outdoor networks.

The second paper “Measurement Method of Temporal Attenuation by Human Body in Off-the-Shelf 60 GHz WLAN with HMM-Based Transmission State Estimation" by Y. Koda et al. conducted a measurement of time-varying signal attenuation induced by human blockage, involving a commercially available IEEE 802.11ad wireless local area network access point (WLAN AP) and wireless station (STA). This paper has estimated signal coexisting at each sampling point using a simple two-state hidden Markov model. The measurements have been validated in that the measured time-varying signal attenuation is in agreement with knife edge diffraction theory.

The third paper “Indoor Corridor Wideband Radio Propagation Measurements and Channel Models for 5G Millimeter Wave Wireless Communications at 19 GHz, 28 GHz, and 38 GHz Bands" by A. M. Al-samman et al. has investigated the propagation characteristics at three different bands 19, 28, and 38 GHz in an indoor corridor environment for LOS and NLOS scenarios. The results have shown that the received signal power at the higher frequency band is more sensitive to the angle-of-arrival (AOA) variation. It is shown that, within a 1-m receiver movement, the received signal power decreases by up to 11 dB when using the 38 GHz band and the signal only decreased approximately 3 dB for the 19 GHz band.

The fourth paper “Combined Sector and Channel Hopping Schemes for Efficient Rendezvous in Directional Antenna Cognitive Radio Networks" by A. M. Al-Mqdashi et al. has proposed efficient schemes for achieving sector and channel rendezvous in directional antenna cognitive radio networks (DIR-CRNs). Rendezvous is a prerequisite and important process for secondary users (SUs) to establish data communications in CRNs. Two efficient coprimality-based sector hopping schemes have been proposed for providing sector rendezvous in asymmetric and symmetric role environments. The sector hopping (SH) schemes have been combined with an efficient grid-quorum-based channel hopping (CH) scheme for providing a guaranteed sector and channel rendezvous simultaneously between the SUs in DIR-CRNs.

The fifth paper “A Stochastic Geometry Approach to Full-Duplex MIMO Relay Network" by M. N. Hindia et al. has developed a tractable model to analyze the success probability and ergodic capacity of the two-hop MIMO expressions for the random nodes, using tools from stochastic geometry. The results have shown the effect of partial zero forcing (PZF) in mitigating the interferences including the self-interference to demonstrate the feasibility of FD technology even for moderate values of self-interference attenuation.

Redhwan Q. Shaddad
Ahmed M. Al-Samman
Murad A. Rassam