Human-generated information has been the main interest of the wireless communication technologies designs for decades. However, we are currently witnessing the emerge of an entirely different paradigm of communication introduced by machines, and hence, the name machine type communication (MTC). Such paradigm arises as a result of the new applications included in the Internet-of-Things (IoT) framework. Among the enabling technologies of the IoT, cellular-based communication is the most promising and more efficient. This is justified by the currently well-developed and mature radio access networks, along with the large capacities and flexibility of the offered data rates to support a large variety of applications. On the other hand, several radio-access-network groups put efforts to optimize the 3GPP LTE standard to accommodate for the new challenges by introducing new communication categories paving the way to support the machine-to-machine communication within the IoT framework. In this paper, we provide a step-by-step tutorial discussing the development of MTC design across different releases of LTE and the newly introduced user equipment categories, namely, MTC category (CAT-M) and narrowband IoT category (CAT-N). We start by briefly discussing the different physical channels of the legacy LTE. Then we provide a comprehensive and up-to-date background for the most recent standard activities to specify CAT-M and CAT-N technologies. We also emphasize on some of necessary concepts used in the new specifications, such as the narrowband concept used in CAT-M and the frequency hopping. Finally, we identify and discuss some of the open research challenges related to the implementation of the new technologies in real life scenarios.

A nonstandard dual mode, double-ridge waveguide is utilized to design a compact orthomode transducer (OMT). The OMT is terminated with a standard circular waveguide common port and two standard isolated rectangular waveguide ports. The proposed structure exploits a one-fold symmetry to eliminate the coupling to the in-band higher order odd modes within the common port. The proposed concept is utilized to design a full K1-band OMT that is essential for space and mobile applications. Furthermore, the performance of the proposed OMT design is verified through a back-to-back measurement showing an excellent agreement between the full-wave simulations and measurements. Nevertheless, the proposed design achieves a measured matching level of $19$ dB for the two modes and isolation level between them beyond $30$ dB over the entire band.

A Y-junction circulator based on the ridge gap waveguide (RGW) as a hosting guiding structure is designed using a developed closed-form systematic procedure. To validate the structure, an air-filled-to-dielectric-filled transition is proposed using a substrate perforation technique. The proposed RGW circulator covers the whole Ku-band with a matching bandwidth throughout the operational bandwidth below -15 dB. A prototype is fabricated and tested, providing a satisfactory agreement with the simulated results.

Millimeter-wave (mmW) Y-junction ferrite circulators above 40 GHz have limited bandwidth due to the lack of ferrite materials having a high saturation magnetization above 5000 G and the simple and traditional circuit design approaches that cannot produce wideband circulators in this frequency range. To increase the bandwidth of mmW Y-junction ferrite circulators, novel design techniques for such circulators should be developed to achieve a functional circulator over a wide bandwidth at mmW frequencies. In this article, a Y-junction ferrite circulator is proposed, which is based on the WR15 waveguide standard with broadband performance for 60-GHz inter-satellite communications. An approximate design procedure for the core section of the proposed circulator is presented. The proposed Y-junction ferrite circulator achieves more than 20 $\%$ bandwidth centered at 60 GHz. In addition, the effect of input power and ambient temperature on the performance of the circulator is studied for an input power of 300 W and ambient temperature in the range from $-$ 80 $^\circ$ C to 80 $^\circ$ C. The experimental prototype is fabricated and measured, where the measured response is in very good agreement with the numerically anticipated counterpart. The fabricated circulator achieves beyond $-$ 17 dB matching level with $-$ 15 dB isolation and 1-dB insertion loss over the entire bandwidth of interest.

Orthogonal frequency division multiplexing (OFDM) is widely used in wireless communication systems, and it is a candidate for Cognitive Radios (CR). Shaping the spectrum of OFDM-based CR is needed to reduce the out-of-band radiations and reduce the interference delivered to the licensed user (LU). In this paper, shaping the spectrum using windowing and active cancellation carriers is discussed. It is shown that the use of windowing alone for large band is a better choice. The window choice in case of large number of subcarriers spanned by a LU is investigated and it is shown that the Hanning window outperforms the raised cosine window by 7 dB. Computational complexity analysis is introduced and it shows a huge advantage by using windowing alone for large frequency bands and multiple bands vis-a-vis cancellation carriers. Simulations show that such technique offers no effect on the bit error rate performance.

The Beyond fifth Generation (B5G) communication systems imposed several challenges on radio designers. For example, a machine is required to set up a call at a low Signal-to-Noise Ratio (SNR), as low as -10 dB, in the extended coverage mode. Moreover, only one receive antenna will be available, and virtually no frequency diversity. Such requirements present major challenges to maintaining timing and frequency synchronization. Carrier Frequency Offset (CFO) estimation is at the heart of these challenges. Different ways have been proposed for CFO estimation such as maximum likelihood based on a cyclic prefix. Nevertheless, these methods remain limited in various ways. At the same time, Machine Learning (ML) techniques showed outstanding performance in several wireless communication problems. In this work, we propose an ML-based approach for CFO estimation in OFDM systems. Specifically, we propose a Gradient-Boosting Machine (GBM)-based solution to predict the CFO given the received Primary Synchronization Signal (PSS) and Secondary Synchronization Signal (SSS). Furthermore, we make our dataset available for public access to encourage other researchers to pursue this promising direction. We compare our results with different baseline models (i.e., artificial neural networks and support vector machines). The experimental results show that our model outperforms other baseline models due to its ensemble nature which enables ensemble models to obtain a better generalization behavior.