These use tiny routers that can be quickly displayed in the environment or embedded platforms onto robots and wearable equipment which connects automatically with other energy-efficient devices using an advanced Device-to-Device interface technology. These Your Own Internet (YOI) devices are set on batteries that can be deployed anywhere. Obviously, the growing data traffic concerns excessive energy consumption in such dynamic wireless networks and therefore puts challenging problems to the researchers to explore and develop new technological solutions of energy savings at the network level. The emerging outlook of green techniques in communication networks, which are designed taking care of the environment, energy saving and cognitive radio for an efficient usage of shared radio spectrum resources, has emerged as an area of much interest. The important issue of enhancing the energy efficiency of cellular networks without compromising on coverage and users' perceived Quality of Service (QoS) is to reduce the overall downlink energy consumption and maintain the target of spectral efficiency.

This issue contains four papers focusing on the challenges and research strategies being adopted in the present wireless communication networks to reduce the overall energy consumption in synergy with the environment. The first two papers deal with the physical layer network performance issues, and the next two papers discuss the hardware and software design implementation techniques to improve the network performance.

The first paper, "Green Mobile Communications in India: Emerging Technologies and Challenges", by Babji Prasad Chapa and Gottapu Sasibhushana Rao, presents a review report on various technologies used in realization of green mobile communication. The paper also discusses the usage and applications of massive MIMO antennas and beamforming technique as a case study of energy-efficient architecture for a wireless network.

Research and development of microstrip array antenna in wireless communication is extensively used with an optimized compositional and structural design. The second paper, "Design and Implementation of Microstrip Array Antenna for Weather Radar System", by Kanchan H Wagh and Shashank S Shriramwar, proposes a new design of a microstrip array antenna for weather radar system utilizing corporate feeding techniques maintaining a minimum return loss. The proposed antenna resonates at 5.8 GHz but depends on its design configuration and also the feeding techniques.

The third paper, "Gilbert Cell-Based Active Mixers: A Critical Study", by Avvaru Subramanyam and R V S Satyanarayana, discusses various structural designs of CMOS-based active mixer designs applicable for down conversion mixer of the RF receiver front end. The paper discusses various performance metrics like CG, NF, third-order Intercept Point (IP3) and 1-dB compression point related to linearity, isolation of ports, supply voltage and power consumption.

The information channel for a reliable and efficient image transmission requires suitable image processing techniques and this becomes more challenging for a wireless system. The last paper, "A Novel Technique with Lo Gradient Minimization for Rain-Free Images", by S Rakoth Kandan and N Dhanasekar, proposes a novel and efficient algorithm for detection of the image in a rainy environment by removal of rain effect from the image using Lo gradient minimization approach. The proposed algorithm is used in spotting and removing the rain effect from the sequential images. The findings confirm that the proposed algorithm is extremely efficient in removing the rain successfully in case of light and heavy rain.