In efficient wireless networks, the interference reduction and usable spectrum efficiency enhancement have always been a concern to system developers. Theoretical modeling and experimental implementation of prototyping of Multiple-Input and Multiple-Output (MIMO) wireless systems have confirmed an order of magnitude improvement in Spectral Efficiency (SE) for a typical point-to-point communication link. Similarly, efficient modulation schemes have also become a research interest in achieving a higher data rate at a given Quality-of-Service (QoS). The emerging fifth-generation network envisages small cell network design by exploiting the potential of low power consumption and thereby realizes a green communication and energy-efficient system.

This issue contains five papers emphasizing the potential and capabilities of 5G networks adopting MIMO, OFDMA and other suitable reliability enhancement techniques. The first three papers deal with the MIMO and multicarrier-based link improvement research, while the other two are related to capacity demand and network backbone reliability. The first paper, "Challenges and Evaluation of Massive MIMO System Capacity Bounds for 5G Cellular Networks", by Amjad Quazi, Sanjeev Kumar Gupta and Paresh Rawat, studies the implementation of the massive MIMO system in the 5G cellular networks. In this paper, the lower bounds of the system capacity with respect to number of antennas have been proposed and tested. It is observed that the massive MIMO technique improves the network efficiency.

The capacity of a wireless network can be enhanced by increasing the number of transmitting and receiving antennas by mitigating the multipath fading and also incorporating the space diversity. The second paper, "Performance Evaluation of MIMO OFDM System Using Adaptive Modulation and Coding Technique", by Gyanender Kumar and Johnny Dogra, explores several techniques to capture the channel information and further discusses some policies and feasible solution to implement Adaptive Modulation Coding (AMC). The performance of AMC has been evaluated by calculating probability of Bit Error Rate (BER) under the Additive White Gaussian Noise (AWGN) wireless channel models.

The third paper, "Application of Green Communication in Energy-Saving Transmissions of OFDMA-Based Multicarrier Base Stations", by Ravi Shankar, Khushboo, Mrinal Darshan and Ritesh Kumar Mishra, discusses the green energy issues in wireless networks. The authors have proposed a new algorithm exploiting the green communication techniques to solve the power issue at the cellular base station transceiver by maintaining the QoS. The paper has considered the Orthogonal Space-Time Block Code (OSTBC) component carrier for downlink transmission of the base station.

The wireless network usability is also determined by the user density and customer demands of the coverage geographical regions involved. The fourth paper, "Estimation of Mobile Telecommunication Demand Using OLS Method with Qualitative Information to Test Economic Crashing Time", by Raufu Oluwatoyin Raheem, presents mobile consumer profile and their usable statistics based on mobile cellular monthly subscription in telecommunication industry. The results indicated that the higher the income, the higher would be the demand for mobile cellular telephone. The paper performs multiple regression and control algorithms for mobile cellular monthly subscription, GDP per capital, network investment and demand differential cost.

The last paper, "Reliability Modeling, Cost-Benefit Analysis with Inspection, Repair and Replacement Facility for Optical Fiber Network in DCRUST", by Puja Rani and Manoj Duhan, presents a survey on optical fiber network installed on a university campus and investigates its reliability , cost benefit and performance analyses. The proposed model includes an operative unit along with another standby unit as a protection link. The analysis helps in predicting profit versus failure rate, revenue/unit up time with distinct inspection rate values, failure and repair rates for future improvement of the existing system.