Theory to Practical Hardware Design Research 2022

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5G Cellular User Equipment:
From Theory to Practical Hardware Design
Yiming Huo, Student Member, IEEE, Xiaodai Dong, Senior Member, IEEE, and Wei Xu, Senior Member, IEEE,
Abstract—Research and development on the next generation
wireless systems, namely 5G, has experienced explosive growth in
recent years. In the physical layer (PHY), the massive multiple-
input-multiple-output (MIMO) technique and the use of high
GHz frequency bands are two promising trends for adoption.
Millimeter-wave (mmWave) bands such as 28 GHz, 38 GHz, 64
GHz, and 71 GHz, which were previously considered not suitable
for commercial cellular networks, will play an important role in
5G. Currently, most 5G research deals with the algorithms and
implementations of modulation and coding schemes, new spa-
tial signal processing technologies, new spectrum opportunities,
channel modeling, 5G proof of concept (PoC) systems, and other
system-level enabling technologies. In this paper, we first inves-
tigate the contemporary wireless user equipment (UE) hardware
design, and unveil the critical 5G UE hardware design constraints
on circuits and systems. On top of the said investigation and
design trade-off analysis, a new, highly reconfigurable system
architecture for 5G cellular user equipment, namely distributed
phased arrays based MIMO (DPA-MIMO) is proposed. Finally,
the link budget calculation and data throughput numerical results
are presented for the evaluation of the proposed architecture.
Index Terms—5G, massive multiple-input-multiple-output
(MIMO), millimeter-wave (mmWave), user equipment (UE),
hardware.
I. INTRODUCTION
In the cellular world, tremendous efforts have been devoted
to delivering higher quality of service (QoS) and quality of
experience (QoE) since the very first cell phone call was made
in 1973. In the 3rd Generation Partnership Project (3GPP)
roadmap, several representative techniques have marked the
milestones to further accelerate such trend, namely: device-to-
device (D2D) communication for boosting geographic spec-
trum reusability [1]; heterogeneous and small-cell network
(HetSNet) targeting at deploying small cells in addition to
macro cells at the same or different carrier frequencies [2];
carrier aggregation (CA) for larger radio frequency (RF)
bandwidths; new carrier type (NCT) for increasing spectral
efficiency and spectrum flexibility, and reducing interference
and power consumption [3]; higher order modulation schemes
and more layers of spatial multiplexing (SM) for higher
spectral efficiency (SE). In 3GPP release 12, 8 × 8 multiple-
input-multiple-output (MIMO) for downlink, 4 × 4 MIMO
for uplink, 5 carrier components (CCs) and 256 quadrature
amplitude modulation (QAM) are supported to satisfy the
increasing wireless capacity needs.
Y. Huo, and X. Dong are with the Department of Electrical and Com-
puter Engineering, University of Victoria, Victoria, BC V8P 5C2, Canada
([e-mail], [e-mail]).
W. Xu is with the National Mobile Communications Research Laboratory
(NCRL), Southeast University, Nanjing 210096, China ([e-mail]).
As part of the QoS requirement of 5G networks, the 5G peak
downlink throughput (PDLT) is expected to achieve 10 Gbps in
the dense urban environments [4]. Delivering such high speed
data to end-users is an essential prerequisite for a satisfying
QoE which is perceived subjectively. Furthermore, this high
PDLT can be translated into a very high SE requirement
of at least 100 bits/s/Hz based on the maximum 100 MHz
bandwidth (BW) that a mobile network operator currently can
support through enabling 5 CCs. If the RF bandwidth is fixed,
such high SE requirement leads to using either higher order
modulation scheme, more layers of SM, or both. The PDLT
is given by
PDLT ∝ (BRF × NQAM × NCA × NMIMO) (1)
where BRF is the RF bandwidth for one single carrier, NQAM
represents the modulation order, NCA is the number of aggre-
gated carriers, and NMIMO stands for the number of MIMO
spatial multiplexing layer. Therefore, the SE can be expressed
as
SE ∝ (NQAM × NCA × NMIMO). (2)
Nevertheless, from the implementation point of view, high
modulation order and wide RF bandwidth unavoidably re-
quire power-hungry, complicated and high-performance RF
and baseband circuits. On the other hand, high order of
MIMO is confronted with the limitation of antennas’ physical
dimension, spacing, and radiation efficiency (RE). Based on
emerging UE design techniques, a mobile phone handset
can accommodate at most 4 × 4 MIMO antennas with 256-
QAM modulation [5], which theoretically boosts PDLT up
to approximately 1960 Mbps when using 5 CCs. On the
other hand, such UE design already reaches the maximum
spatial multiplexing gain due to the limited hardware area for
embedding MIMO antennas of low GHz frequency bands. As
a result, at the UE end, the highest achievable SE is around 20
bits/s/Hz. With the said SE, achieving 10 Gbps PDLT would
require at least 500 MHz bandwidth, which is currently not
possible in terms of the limited spectrum holdings of service
providers.
Meanwhile, Wi-Fi technologies have been advancing
rapidly. The cutting-edge off-the-shelf IEEE 802.11ac com-
patible wireless products can support a 4 × 4 multi-user
MIMO (MU-MIMO) for downlink. By using unlicensed 60
GHz Millimeter-wave (mmWave) frequency bands, wireless
gigabit alliance (WiGig) IEEE 802.11ad products deliver even
higher data rate for short-range communications [5]. The yet
to be released IEEE 802.11ax and 802.11ay standards that are
arXiv:1704.02540v3 [cs.IT] 19 Jul 2017

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deemed as the successors of 802.11ac and 802.11ad respec-
tively, are expected to provide improved QoS such as better
communication coverage and reduced latency. Besides WiFi,
Bluetooth, near-field communication (NFC) and global navi-
gation satellite system (GNSS) are also integrated in mobile
handset terminals. These wireless technologies will compete
with cellular for hardware resources and design budget on
an already highly compact, multi-functional, multi-standard
wireless handset terminal. For example, a huge challenge is to
integrate antenna systems for different wireless technologies
that occupy a very wide range of frequency (from 700 MHz
to almost 6 GHz), and implementing high order MIMO can
make it even more serious considering the limited dimension
of a mobile handset device.
In light of these challenging issues in sub-6 GHz, the high
GHz frequency bands used to be considered unsuitable for
commercial cellular networks are now attracting significant
attention. On July 14, 2016, the Federal Communications
Commission (FCC) voted to adopt a new Upper Microwave
Flexible Use service in the licensed bands, namely 28 GHz
(27.5-28.35 GHz), 37 GHz (37-38.6 GHz), 39 GHz (38.6-40
GHz), plus a new unlicensed band at 64-71 GHz [7]. This
initiative taken by the FCC helps mitigate the 5G UE design
challenges. First, larger continuous RF bandwidth enables
higher data rates. Second, using mmWave frequencies leads to
a significant reduction of antenna dimension, and as a result,
the form factor of the UE can be maintained while facilitating
beamforming (BF) and spatial multiplexing.
In this paper, we present a novel distributed phased array
MIMO (DPA-MIMO) architecture for 5G UE hardware design.
The remainder of this paper is organized as follows, Section II
investigates the contemporary wireless UE design and explains
the design constraints. Section III presents the details of 5G
UE hardware design challenges, and proposes a novel system
architecture to address these challenges. Section IV conducts
the performance evaluation of the proposed system based on
the link budget calculation and comparison with state-of-the-
art 5G works. Finally, Section V concludes this paper.
II. WIRELESS UE DESIGN OVERVIEW
Contemporary wireless UE design becomes more challeng-
ing and complicated than ever. In any mainstream mobile
phone, it does not only need to co-exist with several prevailing
wireless technologies, but also integrate the camera(s), audio,
battery, display, fingerprint scanner, vibrator, gyroscope, wire-
less charging, etc. In the near future, there will be a stronger
need to enable or enhance various functions and technologies,
such as virtual reality (VR), augmented reality (AR), internet
of vehicles (IoV) [8], and so on, all of which further increases
the difficulty level of UE design. In this section, the major
design methods and constraints are discussed from several as-
pects, namely battery, circuit and system, antenna and product
design, and other system design trade-offs.
A. Battery Design Constraints
As plotted in Fig. 1, the data rates of both WiFi and
cellular increase by around 10 folds for every five years.
Fig. 1. Increment of the wireless capacity versus the battery performance
improvement.
On the other hand, during the last 20 years, the battery
technique for mobile devices has been through three major
technical transitions, which starts with nickel-cadmium (NiCd)
battery, then the nickel-metal hydride (NiMH) battery, and
eventually the current mainstream lithium-ion (Li-ion) battery
[9]. From 1995 to 2014, the wireless capacity has increased
by around 10,000 times [10], while only 4-5 folds increment
of battery specific power have been achieved for the same
period. Apparently, this mismatch becomes one of the current
bottlenecks for mobile handset devices and affects the quality
of user experience. Despite the recent battery research on
new anode materials [11], before the advent of significant
breakthrough in battery performance and feasibility for mass
production, higher energy efficiency of the UE wireless system
will be critically relevant.
B. Circuit and System Design
The performance of a wireless system, from a hardware
perspective, depends on the evolution of design arts in system-
on-chip (SoC), printed-circuit board (PCB), mechanical de-
sign, and antenna design. The SoCs of high energy efficiency,
small area, low cost and high yield, are always strongly
desired. For the current SoC design, a widespread fact is
that Moore’s law slows down when the process dimension
enters the deep-nanometer regime [12]. Consequently, the
speed of energy efficiency improvement is moderated. Before
any proven success with novel IC processes based on new ma-
terials, the contemporary silicon and III-IV compound based
semiconductor processes, such as complementary metal-oxide-
semiconductor (CMOS), CMOS silicon on insulator (SOI),
fin field effect transistor (FinFET), silicon germanium (SiGe),
gallium arsenide (GaAs), gallium nitride (GaN) and indium
phosphide (InP), still play a dominant and critical role in the
future 5G SoC designs.
Likewise, the multi-layer board design of a 5G mobile hand-
set will become more compact and integrated to accommodate
an increasing number of SoC chipsets for enabling various
functions, standards, and technologies. On the main logic
board (MLB) of a mobile handset as depicted in Fig. 2, there

3Application
Processor
SRAM
Memory
Baseband
Processor
Transceivers
HB
PAs
connectors
LB
PAs
PA
Management
SIM Card
Slot
Microwave
shield cover
Antenna
Connector
Fig. 2. An example of main logic board in contemporary smartphones.
are cellular/WiFi RF transceivers, antenna switch modules,
power amplifier (PA) modules, baseband (BB) modem, NFC,
bluetooth, GNSS, application processor (AP), PA management
unit, static random-access memory (SRAM), power manage-
ment unit (PMU), etc. Nowadays, these highly customized
chipsets are supplied by various vendors who design and
fabricate them with different processes.
Similar to the trend in IC design, the footprint of PCB
is continuously downsizing to smaller trace width and trace
spacing. As a result, more chipsets can be embedded on
one single main logic board, which results in less insertion
loss (IL) and easier impedance matching. Therefore the RF
front-end loss caused by IL and impedance mismatching are
reduced, and the receiver (RX) sensitivity and transmitter (TX)
power can be improved. On the other hand, signal integrity is
an issue in a more complicated MLB design. For example,
the clock signals and their harmonics, through complicated
signal path and modulation, can end up at the receiver end
in the form of spur. Therefore, a microwave shield cover
is normally used on MLB to improve the electromagnetic
compatibility/electromagnetic interference (EMC/EMI) perfor-
mance. Another frequently seen issue is the degradation of
sensitivity, or ‘desense’, which is typically caused by TX
output leaked into the RX path due to insufficient isolation
between TX and RX ports. This issue is more serious in the
case of carrier aggregation, for example, when the harmonic
of a transmit signal falls in the receive band of a paired CA
band [13]. As can be predicted, these issues will become more
prevailing in a 5G terminal device.
C. Antenna and Product Design
Antenna design is another matter of importance in wireless
systems. Unlike any of its priors [14] in the 2G/3G era,
current mobile handset antennas are expected to support not
only multi-bands and multi-standards in a wide range of
frequency from 700 MHz to 6 GHz (with some uncovered
gaps), but also enable certain degrees of diversity and SM.
At the same time, there is requirement that high efficiency
and low specific absorption rate (SAR) are both fulfilled after
assembling antennas into the handset housing made of metallic
casing.
Therefore, the co-design of antennas, metal casing, and
handset housing is enormously challenging since the latter
two factors could generate substantial effects on antenna
performance [15]. Narrow frame and metallic casing are still
the unswerving trends currently and in the near future, because
they enable better protection, portability, heat dissipation and
aesthetic appearance. The slim form factor improves the user
experience, and can be seen in several recent mainstream
smartphones as shown in Table I.
TABLE I
DIMENSION INFORMATION OF SMARTPHONES.
Model Dimension
( H × W × D, mm)
Display
Size (inch)
Weight
(g)
Samsung
S7 edge 150.9 × 72.6 × 7.7 5.5 157
Apple
iPhone 7 plus 158.2 × 77.9 × 7.3 5.5 188
Huawei
Mate 9 156.9 × 78.9 × 7.9 5.9 190
Google
Pixel XL 154.7 × 75.7 × 7.3 5.5 168
The antenna dimension is proportional to the effective
wavelength, and this relation can be approximated as
λe= c0
f √εe
(3)
where c0 is the speed of light in vacuum, f is the frequency,
and εe is the effective dielectric constant that makes the effec-
tive wavelength shorter. Furthermore, the effective dielectric
constant can be derived using the following equations [16]
εe= εr + 1
2 + εr − 1
2
{
1
√
1 + 12 ( H
W
)
+0.04
(
1 −
( W
H
))2}
,
subject to W/H < 1
(4)
εe= εr + 1
2 + εr − 1
2
√
1 + 12 ( H
W
)
subject to W/H ≥ 1
(5)
where εr stands for the relative dielectric constant, W is the
width of antenna, and H is the thickness of the antenna
substrate. Therefore, the antenna dimension is mainly de-
termined by the frequency and substrate material. Although
higher dielectric constant reduces the antenna dimension, it
degrades the antenna performance as more radiation energy
will be confined inside the substrate instead of being radiated.
In the 5G era, the handset antenna design faces more
challenges in order to cover the legacy 3GPP standards and
new 5G standards which regulate the use of higher GHz
frequency bands. From this point of view, implementing large
scale MIMO at low GHz frequencies becomes very difficult

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Fig. 3. Disassembly of a smartphone to front and back parts.Radiation Pattern
Fig. 4. Talk mode using a specific anthropomorphic mannequin (SAM) head
phantom.
as it normally requires a minimum spacing to guarantee good
isolation. As for the mmWave antenna design, more antenna
elements can be accommodated thanks to downsizing, but the
metal casing can deteriorate the antenna performance.
D. System Design Trade-offs
In addition to the aforementioned three major design consid-
erations, there are also high-level design constraints between
the wireless subsystem and other UE components. Besides
the power budget and hardware area allocation, one more
critical technical challenge originates from the interference
among different components. For example, the display screen
can cause the RF sensitivity degradation. Therefore, a sheet
of metallic microwave (MW) shield is normally put between
the display unit and hardware part to enhance the isolation as
shown in Fig. 3 which briefly depicts a cell phone opened from
middle. Moreover, this MW shield can minimize the SAR in
the common use cases when the screen side is held close to
the head of a smartphone user, as illustrated in Fig. 4.
In other words, antennas radiate minimal signal through
the screen, and therefore it can only propagate the signal in
the direction away from the human head. Nevertheless, the
shield increases the thickness of the handset and degrades the
form factor. The placements of camera, speaker, finger scanner,
battery, MLB, also require careful consideration as they can
change the electro-magnetic (EM) field and lead to undesired
effects. To summarize here, contemporary wireless UEs need
to provide high quality of user experience determined and
contributed by comprehensive factors which not only lie in the
wireless system design, but also mechanical design, product
design, operating system design, etc. Consequently, many
design trade-offs must be considered for a high-performance
5G UE. By taking the cellular standard as an example, the
figure-of-merit (FOM) of a cellular UE can be formulated as
FOMCellular,UE =
∑n,max
n=1
PDLTBand,n
Non-CA
Beff,n Pn + ∑m,max
m=2
PDLTBands
CC,m
Beff,mPm
VUE · MUE
(6)
where PDLTBand,n
non-CA is the PDLT of the 3GPP band n when
carrier aggregation is not enabled (non-CA). Beff,n and Pn
stand for the effective bandwidth and power consumption
respectively, when the wireless UE works in the non-CA mode.
Moreover, the effective bandwidth is the bandwidth of the
used band which has excluded the guard band. Accordingly,
PDLTBands
CC,m represents the PDLT of the carrier aggregation of m
CCs, and the superscript m, max is the maximum number of
CCs, defined to be up to 5 in 3GPP Release 13. Thus, the first
and second terms of the numerator add up the energy-spectral
efficiency of both non-CA and CA cases for all cellular bands
and CA combinations supported by the wireless UE, then we
divide the result by the volume VUE and weight MUE of the
wireless UE. The denominator reflects the ‘score’ of electrical-
mechanical co-design and the portability of the wireless UE.
Therefore the unit of FOMCellular,UE is bit/Hz/Joule/mm3/gram.
It is obvious that more bands and CCs, higher SE, smaller
volume and weight, can result in a higher FOM of wireless
UE, which means a better comprehensive design. It is worth
mentioning that the material cost of the UE is not taken into
consideration in the equation for well-defined comparison.
III. 5G CELLULAR UE BASED ON A NOVEL
SYSTEM ARCHITECTURE
The foremost challenge of using high GHz frequency bands
comes from the propagation loss that is significantly higher
and more complicated than sub-6 GHz frequency bands. Based
on the most recently published 5G channel model [17], [18],
plus atmospheric absorption and rain attenuation models in
[19], [20], the path loss comparison for different propagation
scenarios are given in Table II for three frequency bands,
namely 2.6 GHz, 28 GHz, and 39 GHz.
A. Channel Model Analysis
As presented in Table II, the path loss of non-line-of-sight
(NLOS) is much larger than that of line-of-sight (LOS), and
LOS of the urban macro (UMa) scenario has similar path loss
to the LOS urban microcell (UMi) scenario. However, the path
loss in UMi Street Canyon NLOS is much more severe than
UMa NLOS or UMi Street Open. In addition, for all scenarios,
the path loss of 28 and 39 GHz are at least 20 dB larger than