Design and Performance Analysis of Schottky Terahertz Transceiver for 6G Wireless Communication
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Date
2020-11-13
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Addis Ababa University
Abstract
Wireless technology is in a rapid chase of higher data rates to satisfy the growing
demands of services and devices which will all interconnect. One of the envisioned
technologies to fulfill this is Terahertz wireless communication owing to
wide bandwidth and possible bitrates into the Tbps. Challenges however exist with
Terahertz source generation. One such candidate based on Schottky diode carrier
upconversion may be a low cost solution, nonetheless phase noise presents a bottleneck
in such an upconversion scheme for Phase Shift Keying (PSK) and Quadrature
Amplitude Modulation (QAM).
In this study, high bitrate communication was investigated with respect to phase
noise and Local Oscillator (LO) (Terahertz (THz)) obtained by frequency multiplication.
Terahertz transceivers with both Zero-Intermediate Frequency (IF) and double
conversion architectures were designed. The transceivers were evaluated with simulation
using PSK and QAM modulation schemes and examined for the optimal
frequency range. Due to the excellent properties of graphene as well as future relevance
Graphene Field Effect Transistor (GFET) and Schottky Barrier Diode (SBD)
were the primary device technologies.
High bitrate communication was possible at 209GHz with double conversion architecture.
Five Gbps was obtained with Binary Phase Shift Keying (BPSK), 10Gbps
with Quadrature Phase Shift Keying (QPSK), 15Gbps with 8 Phase Shift Keying
(8PSK), 20Gbps with 16-ary Quadrature Amplitude Modulation (16QAM) and 30Gbps
with 64-ary Quadrature Amplitude Modulation (64QAM) and had Error Vector
Magnitude (EVM) of 40.9%, 49.1%, 12.9%, 28.7% and 13.1% respectively. A 73 m
GFET was employed as the Radio Frequency (RF) transistor technology. The 185.9GHz
LO was designed with Schottky diode multiplication and had peak phase noise of
-101dBc=Hz. The frequency multiplication process was found to be limited to the
lower THz range of less than 375GHz, for satisfactory communication performance.
Active frequency multipliers degrade the phase noise for high order PSK. However
a x2 subharmonic mixer can be used, if the LO power is limiting the conversion
efficiency. Single stage Schottky multipliers with multiple harmonics and filtering
was found to produce high power but also high phase noise as result of the
Butterworth filter. As a result the single stage multipliers are suitable for Pulse Amplitude
Modulation (PAM) only. A frequency threshold for the SBD THz LO beyond
which spectrally efficient modulation is not optimal is contributed in this research.
In addition the GFET was demonstrated in its viability, by its successful use in all
THz analog circuits in the In Phase - Quadrature (IQ) (de-) modulator. Demonstrated by the high bit rates achieved in this work, Schottky multiplied THz
carriers and graphene Field Effect Transistor (FET)s make a cost effective route for 6G wireless as well as Local Area Network (LAN) and Personal Area Network (PAN)
within the lower THz range.
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Keywords
THz, Schottky, Graphene, 6G, High Bitrate Communication