Symbol-Level Multiuser MISO Precoding for Multi-level Adaptive Modulation

Symbol-level precoding is a new paradigm for multiuser downlink systems which aims at creating constructive interference among the transmitted data streams. This can be enabled by designing the precoded signal of the multiantenna transmitter on a symbol level, taking into account both channel state information and data symbols. Previous literature has studied this paradigm for MPSK modulations by addressing various performance metrics, such as power minimization and maximization of the minimum rate. In this paper, we extend this to generic multi-level modulations i.e. MQAM and APSK by establishing connection to PHY layer multicasting with phase constraints. Furthermore, we address adaptive modulation schemes which are crucial in enabling the throughput scaling of symbol-level precoded systems. In this direction, we design signal processing algorithms for minimizing the required power under per-user SINR or goodput constraints. Extensive numerical results show that the proposed algorithm provides considerable power and energy efficiency gains, while adapting the employed modulation scheme to match the requested data rate

Smart Adaptive Beam-Forming Antenna Design for Next Generation Communication Systems

Adaptive beamforming antennas open a new venue for research to achieve high data rates. Such antennas are of interest at higher frequencies, especially at millimeter-waves. Millimeter-wave band ranges from 30 GHz - 300 GHz. There is an ample bandwidth available in this spectrum. However, due to the significant path loss at high frequencies, there is a need for better error correction schemes and adaptive beam-forming antennas for this frequency band. The goal of our research is to design a novel adaptive beamforming smart antenna that is low cost, compact, power-efficient and less complex. Based on our recently awarded US patent, we have devised a novel beamforming technique in which phased array and parasitic array approaches are used in conjunction with each other. Conventionally, phased array or switched array techniques are used in smart antennas for beam-steering. In phased array antennas each antenna element has a separate excitation. Therefore, such antennas are costly and impractical for use in everyday communication devices. Switched array antennas are cost-effective and simple to implement, but the antenna beam can only be formed at a predefined location. Our proposed novel beamforming technique is based on a mathematical model. After mathematical modeling, the antenna is simulated in Ansoft High Frequency Structure Simulator (HFSS). Results of the simulated model in Ansoft HFSS and the mathematical model are in close agreement with each other, Ansoft HFSS uses the finite element method (FEM) for complex electromagnetic computations. Antenna design consists of two circular arrays of six parasitic elements. Each array has an active element in its center and there is a fixed phase difference between excitation currents to the active elements. The beam is steered either by changing the phase difference between excitation currents to the active elements or by changing reactance of the parasitic elements. Our technique is novel as this is the first time switched parasitic array and phased array approaches are efficiently used in conjunction with each other. After mathematical modeling and simulations, two antennas are designed and tested. The first antenna is centered at 2.5 GHz. This antenna is used for proof of concept. The second antenna is centered at 28 GHz. The 28 GHz band will play a key role in the next generation of wireless networks, i.e., 5G. The antenna hardware testing results are also in line with the mathematical and the simulated models. This dissertation aims to provide an overview of smart adaptive beamforming antenna design, propose a mathematical model for novel hybrid beamforming, present the application of the proposed antenna in satellite communication and airborne communication, and demonstrate the validity of the design via software simulations and hardware testing

Spacecraft Antennas

Some of the various categories of issues that must be considered in the selection and design of spacecraft antennas for a Personal Access Satellite System (PASS) are addressed, and parametric studies for some of the antenna concepts to help the system designer in making the most appropriate antenna choice with regards to weight, size, and complexity, etc. are provided. The question of appropriate polarization for the spacecraft as well as for the User Terminal Antenna required particular attention and was studied in some depth. Circular polarization seems to be the favored outcome of this study. Another problem that has generally been a complicating factor in designing the multiple beam reflector antennas, is the type of feeds (single vs. multiple element and overlapping vs. non-overlapping clusters) needed for generating the beams. This choice is dependent on certain system design factors, such as the required frequency reuse, acceptable interbeam isolation, antenna efficiency, number of beams scanned, and beam-forming network (BFN) complexity. This issue is partially addressed, but is not completely resolved. Indications are that it may be possible to use relatively simple non-overlapping clusters of only a few elements, unless a large frequency reuse and very stringent isolation levels are required

Characterization of a dense aperture array for radio astronomy

EMBRACE@Nancay is a prototype instrument consisting of an array of 4608 densely packed antenna elements creating a fully sampled, unblocked aperture. This technology is proposed for the Square Kilometre Array and has the potential of providing an extremely large field of view making it the ideal survey instrument. We describe the system,calibration procedures, and results from the prototype.Comment: 17 pages, accepted for publication in A&

The Role of Physical Layer Security in Satellite-Based Networks

In the coming years, 6G will revolutionize the world with a large amount of bandwidth, high data rates, and extensive coverage in remote and rural areas. These goals can only be achieved by integrating terrestrial networks with non-terrestrial networks. On the other hand, these advancements are raising more concerns than other wireless links about malicious attacks on satellite-terrestrial links due to their openness. Over the years, physical layer security (PLS) has emerged as a good candidate to deal with security threats by exploring the randomness of wireless channels. In this direction, this paper reviews how PLS methods are implemented in satellite communications. Firstly, we discuss the ongoing research on satellite-based networks by highlighting the key points in the literature. Then, we revisit the research activities on PLS in satellite-based networks by categorizing the different system architectures. Finally, we highlight research directions and opportunities to leverage the PLS in future satellite-based networks