IEEE Circuits and Systems Magazine - Q4 2022 - 21

Figure 21. Illustration of the proposed ss block design for
ttd-based beam training. at the uE side, bandwidth parts
of different colors are combined from different angular directions
using a ttd array.
direction [56]. An SS block is a group of 4 consecutive
OFDM symbols with 240 subcarriers (20 resource
blocks) that carry the Primary Synchronization Signal
(PSS), Secondary Synchronization Signal
(SSS), and
DeModulation Reference Signal (DMRS). The PSS and
SSS are leveraged for synchronization between the BS
and UE, while the DMRS can be used to estimate the
received power associated with that direction, i.e., SS
block.
Since the proposed TTD beam training is fundamentally
different from beam sweeping, its compatibility
with the current 5G New Radio Standard becomes an
important problem. In our preliminary work, we proposed
a different design of the SS block, which exploits
wide available bandwidth at mmW frequencies and
supports TTD beam training, as illustrated in Fig. 21.
In the proposed design, the existing reference signals
are repeated multiple times across the operating bandwidth.
With such training waveform, the UE is capable
of receiving at least one entire legacy SS block using
its frequency-dependent beam steering. The UE can
then leverage DSP to extract the reference signals to
achieve synchronization with the BS and determine the
best steering direction. The proposed SS block design
removes the need for SS bursts and thus minimizes the
required overhead in TTD beam training. However, the
design depends on different system parameters, including
the number of subcarriers, number of UE antennas,
and resolution of UE beam probing. We plan to address
these practical design questions in our future work.
VII. Conclusion
Reconfigurable TTD arrays are essential for emerging
mmW wireless communications demanding wide
bandwidths with ultra-low-latency in direction finding
Fourth quartEr 2022
compared to current wireless standards. This magazine
article presents a comprehensive overview of
the recent developments in TTD arrays enabling multiple
SSP functions. Delay compensation techniques
are exploited to prevent beam squint during data communications
while introducing intentional beam squint
for fast beam-training. The article combines the beamtraining
algorithm with the underlying architectural
and circuit design considerations. The exciting developments
in TTD arrays presented herein lays out a future
path for enabling next-generation network and physical
infrastructure wireless solutions on a large-scale with
3D direction finding for communications-on-the-move
applications, massive machine type communications,
and standardization in emerging wireless standards.
Acknowledgment
The authors would like to thank Ruifu Li from UCLA for
his help in preparing the manuscript.
Chung-Ching Lin (Graduate Student
Member, IEEE) received the M.S. degree
in communication engineering
from Yuan Ze University, Taoyuan, Taiwan,
in 2014. He is currently pursuing
the Ph.D. degree with Washington
State University, Pullman, WA, USA. His current research
interests include low power and wideband multiantenna
transceivers, frequency synthesizer, and highspeed
I/O circuit design. He was a recipient of
the
Yu-Ziang Academic Scholarship in 2013, the Southern
Methodist University Graduate Student Travel Grant in
2018, the IEEE Circuits and Systems Society (CAS) Travel
Award in 2019, and the IEEE Custom Integrated Circuits
Conference (CICC) Educational Grants Award in
2020. He was the IEEE Radio Frequency Integrated Circuits
(RFIC) Symposium Best Student Paper Award
Nominee (out of 12 finalists) in 2020.
Veljko Boljanovic (Graduate Student
Member, IEEE) received the B.S. and
M.S. degrees in electrical and computer
engineering from the University of Novi
Sad, Novi Sad, Serbia, in 2015 and 2016,
respectively. He is currently pursuing
the Ph.D. degree with the University of California at Los
Angeles, Los Angeles, CA, USA. His research interests
include system design, network performance optimization,
and digital signal processing in wireless millimeterwave
communications. He was a recipient of the Electrical
and Computer Engineering Department Fellowship and
the Dissertation Year Fellowship at the University of California
at Los Angeles in 2017 and 2021, respectively.
IEEE cIrcuIts and systEms magazInE
21
IEEE Circuits and Systems Magazine - Q4 2022

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