A Study of a Millimeter-Wave Transmitter Architecture Realizing QAM Directly in RF Domain

IEEE open journal of solid-state circuits, 2021

This paper presents challenges and design perspectives for terahertz (THz) integrated circuits and systems. THz means different things to different people. From International Telecommunication Union (ITU) perspective, THz radiation primarily means frequency range from 300 -3000 GHz. However, recently, a more expansive definition of THz has emerged that covers frequencies from 100 GHz to 10 THz, which includes sub-THz (100 -300 GHz), ITU-defined THz frequencies. This definition is now commonly used by communication theorists, and since this paper is intended for people with a wide variety of expertise in system and circuit design, we have adopted the latter definition. The paper brings to the open unmitigated shortcomings of conventional transceiver architectures for multi gigabit-per-second wireless applications, unfolds challenges in designing THz transceivers, and provides pathways to address these impediments. Furthermore, it goes through design challenges and candidate solutions for key circuit blocks of a transceiver including front-end amplifiers, local oscillator (LO) circuit and LO distribution network, and antennas intended for frequencies above 100 GHz.

Physical Communication, 2014

This paper provides an in-depth view of Terahertz Band (0.1-10 THz) communication, which is envisioned as a key technology to satisfy the increasing demand for higher speed wireless communication. THz Band communication will alleviate the spectrum scarcity and capacity limitations of current wireless systems, and enable new applications both in classical networking domains as well as in novel nanoscale communication paradigms. In this paper, the device design and development challenges for THz Band are surveyed first. The limitations and possible solutions for high-speed transceiver architectures are highlighted. The challenges for the development of new ultra-broadband antennas and very large antenna arrays are explained. When the devices are finally developed, then they need to communicate in the THz band. There exist many novel communication challenges such as propagation modeling, capacity analysis, modulation schemes, and other physical and link layer solutions, in the THz band which can be seen as a new frontier in the communication research. These challenges are treated in depth in this paper explaining the existing plethora of work and what still needs to be tackled.

2018

Over the past years, carrier frequencies used for wireless communications have been increasing to meet bandwidth requirements. The engineering community witnessed the development of wide radio bands such as the millimeter-wave (mmW) frequencies to fulfill the explosive growth of mobile data demand and pave the way towards 5G networks. Other research interests have been steered towards optical wireless communication to allow higher data rates, improve physical security and avoid electromagnetic interference. Nevertheless, a paradigm change in the electromagnetic wireless world has been witnessed with the exploitation of the Terahertz (THz) frequency band (0.1-10 THz). With the dawn of THz technology, which fills the gap between radio and optical frequency ranges, ultimate promise is expected for the next generation of wireless networks. In this paper, the light is shed on a number of opportunities associated with the deployment of the THz wireless links. These opportunities offer a plethora of applications to meet the future communication requirements and satisfy the ever increasing user demand of higher data rates.

Computer Networks, 2020

Terahertz (THz)-band (0.1 THz to 10 THz) communication is envisioned as a key technology to meet the demand for faster, more ubiquitous wireless communication networks. For many years, the lack of compact, fast and efficient ways to generate, modulate, detect and demodulate THz-band signals has limited the feasibility of such communication systems. Recently, major progress within different device technologies is finally closing the so-called THz gap. For the time being, communication testbeds have been developed at sub-THz frequencies, i.e., at or near the boundary with millimeter-wave communication systems. Nonetheless, higher carrier frequencies and their associated bandwidth are needed to meet the demand for much higher data rates. In this paper, the Ter-aNova platform, i.e., the first integrated testbed for ultra-broadband wireless communications at true THz-band frequencies, is presented. The system consists of a transmitter and a receiver based on Schottky-diode frequency multiplying and mixing chains able to up & down-convert an information-bearing intermediate frequency (IF) signal up to 40 GHz-wide between 1 and 1.05 THz, i.e., the first absorption-defined transmission window above 1 THz. Guided by the experimental characterization of the THz channel in terms of path-loss and noise, tailored framing, time synchronization, channel estimation and single-and multi-carrier modulation techniques are implemented in software and realized by a state-of-the-art arbitrary waveform generator and a digital storage oscilloscope at the transmitter and the receiver, respectively. Experimental results are presented herein to highlight the opportunities and challenges to unleash the potential of the THz band.

2020 2nd 6G Wireless Summit (6G SUMMIT), 2020

This paper presents a wireless link based on a Tx and a Rx RF front-end module operating at a LO frequency of 230 GHz. The LO frequency generation paths of the Tx and the Rx are driven using two independent and unlocked frequency synthesizers. Due to this operation mode, the Tx LO leakage is down-converted in the Rx, generating a DC modulated tone that, if not properly handled, will prevent the system to operate appropriately. This paper analyses this effect and presents a solution to mitigate this impairment. Applying this, and using a 16-QAM modulation scheme, a maximum data-rate of 80 Gbps with an EVM of 12.5 % was achieved at a 1-meter distance.

Demand is increasing for higher data rate in wireless communications in order to keep up with the remarkable speed-up of fiber-optic networks such as Ethernet LANs. One of the most direct and easiest ways to achieve a higher data rate of 10-100 Gbit/s is to increase carrier frequencies to terahertz regions of from 100 GHz to 500 GHz. This paper will review our recent challenges for high-speed wireless communications technologies using terahertz electromagnetic waves.

2019

A superheterodyne transmission scheme is adopted and analyzed in a 300 GHz wireless pointto-point link. This was realized using two different intermediate frequency (IF) systems. The first uses fast digital synthesis which provides an IF signal centered around a carrier frequency of 10 GHz. The second involves the usage of commercially available mixers, which work as direct up-and down-converters, to generate the IF input and output. The radio frequency components are based on millimeterwave monolithic integrated circuits at a center frequency of 300 GHz. Transmission experiments over distances up to 10 m are carried out. Data rates of up to 60 Gbps using the first IF option and up to 24 Gbps using the second IF option are achieved. Modulation formats up to 32QAM are successfully transmitted. The linearity of this link and of its components is analyzed in detail. Two local oscillators (LOs), a photonics-based source and a commercially available electronic source are employed and compared. This work validates the concept of superheterodyne architecture for integration in a beyond-5G network, supplying important guidelines that have to be taken into account in the design steps of a future wireless system. .

—NASA has been leading the Terahertz (THz) technology development for the sensors and instruments in astronomy in the past 20 years. THz technologies are expanding into much broader applications in recent years. Due to the vast available multiple gigahertz (GHz) broad bandwidths, THz radios offer the possibility for wireless transmission of high data rates. Multi-Gigabits per second (MGbps) broadband wireless access based on THz waves are closer to reality. The THz signal high atmosphere attenuation could significantly decrease the communication ranges and transmittable data rates for the ground systems. Contrary to the THz applications on the ground, the space applications in the atmosphere free environment do not suffer the atmosphere attenuation. The manufacturing technologies for the THz electronic components are advancing and maturing. There is great potential for the NASA future high data wireless applications in environments with difficult cabling and size/weight constraints. In this study, the THz wireless systems for potential space applications were investigated. The applicability of THz systems for space applications was analyzed. The link analysis indicates that MGbps data rates are achievable with compact sized high gain antennas.

2018 52nd Asilomar Conference on Signals, Systems, and Computers, 2018

The new spectrum available in the millimeter-wave (mmWave) and Terahertz (THz) bands is a promising frontier for the future wireless communications. Propagation characteristics at these frequencies imply that highly directional transmissions should be used to focus the available power to a specific direction. This is enabled by using tightly packed large-scale antenna arrays to form narrow or so called pencil beams both at the transmitter and the receiver. This type of communication is, however, quite sensitive to imperfections of the transceivers, resulting in beam pointing errors and lost connection in the worst-case. This paper investigates the impact of such errors, originating from the local oscillators in terms of phase noise, which is a major impairment with high center frequencies. We explore the impact of these effects with different transceiver architectures, illustrate the beam shape properties, and quantify their impact on the system performance for different modulation schemes in terms of error rates. Specifically, we model the phase noise both as Wiener and Gaussian distributed to characterize the impact of phase noise on the beam accuracy and system performance.

2022 IEEE 19th Annual Consumer Communications & Networking Conference (CCNC), 2022

Sub-Terahertz communication is a key enabling technology to deliver ultra-high rates up to Terabit/s-one of 6G envisioned goals. However, hardware limitation and impairments set practical challenges in realizing real-world networks operating at such high frequency range. In this paper, based on simulation findings, we analyze the performance of different single-and multi-carrier transmission concepts in the sub-Terahertz range under hardware impairments and limitations, both from a today's New Radio (NR) up-scaling perspective, and whether it is best to deviate from the straightforward up-scaling into a new design. We therefore focus on the following sub-Terahertz network determinants: the signal peak amplitude characteristics, the phase noise of the local oscillators and the quantization effect of the analog-to-digital-converter. Insights drawn from the analysis are considered to make proposals on the signaling concepts for a practical access network design in the sub-Terahertz range. We also demonstrate how further improvement can be harvested considering signal amplitude variation optimized constellation modulation.