No / Passive and active devices are essential devices in mobile and base stations’ transceiver. Consequently, these devices dominated the large part of the PCB of the today’s transceiver. However, the tomorrow’s mobile terminals without circuit tunability would be extremely large in size to accommodate present and future radio access technologies (RATs). The stand-alone transceiver for one single RAT is comprised of single passive and active devices and adding two or more RATs for the same transceiver would require adding two or more devices, since all of these RATs standards work on different frequency bands. Apparently, without tunability approach, this will increase the complexity of the system design and will cover a large part of the circuit space leading to power consumptions, loss which results to the poor efficiency of the transceiver. In this work, a miniaturized RF MEMS tunable bandpass is developed to operate in the frequency range from 1.8 to 2.6 GHz.

Support of many different services, approximately 1000x increase of current data rates, ultra-reliability, low latency and energy/cost efficiency are among the demands from upcoming 5G standard. In order to meet them, researchers investigate various potential technologies involving different network layers and discuss their trade-offs for possible 5G scenarios. Waveform design is a critical part of these efforts and various alternatives have been heavily discussed over the last few years. Besides that, wireless technology is expected to be deployed in many critical applications including the ones involving with daily life activities, health-care and vehicular traffic. Therefore, security of wireless systems is also crucial for a reliable and confidential deployment. In order to achieve these goals in future wireless systems, physical layer (PHY) algorithms play a vital role not only in waveform design but also for improving security. In this dissertation, we draft the ongoing activities in PHY in terms of waveform design and security for providing spectrally efficient and reliable services considering various scenarios, and present our algorithms in this direction. Regarding the waveform design, orthogonal frequency division multiplexing (OFDM) is mostly considered as the base scheme since it is the dominant technology in many existing standards and is also considered for 5G new radio. We specifically propose two approaches for the improvement of OFDM in terms of out-of-band emission and peak to average power ratio. We also present how the requirements of different 5G RAN scenarios reflect on waveform parameters and explore the motivations behind designing advanced frames that include multiple waveforms with different parameters, referred to as numerologies by the 3GPP community, as well as the problems that arise with such coexistence. On the security aspect, we firstly consider broadband communication scenarios and propose practical security approaches that suppress the cyclic features of OFDM and single carrier-frequency domain equalization based waveforms and remove their vulnerability to the eavesdropping attacks. Additionally, an authentication mechanism in PHY is presented for wireless implantable medical devices. Thus, we address the security issues for two critical wireless communication scenarios in PHY to contribute a confidential and reliable deployment of wireless technologies in the near future.