2. Beamforming in 5G
Internal
Frequency vs. Pathloss vs Beamwidth
Free Space Propagation
( )2
2
4 r
P
G
G
P t
t
r
r
p
l
=
Pathloss proportional to the square of wave lenght
• Where does the power go?
Effective area of radiating element is proportional to square wavelength
Solution : Increase number of radiators per polarization, when going to higher
frequencies.
Drawback: beamwidth becomes smaller with higher antenna gain (higher number of
radiators)
Antenna does not cover whole sector at once anymore.
Special methods are needed for Broadcast (BCH) and Random Access (RACH).
Adaptive user tracking needed.
3. Beamforming in 5G
Internal
Beamforming Principle
Waves transmitted from multiple antennas will add constructively/destructively in space. By changing the phases and amplitudes
of the individual antennas we can change the azimuths of these specific areas → beam pattern
4. Beamforming in 5G
Internal
Beamforming Principle
Waves transmitted from multiple antennas will add constructively/destructively in space. By changing the phases and amplitudes
of the individual antennas we can change the azimuths of these specific areas → beam pattern
5. Beamforming in 5G
Internal
Grid of Beams principle
gNB operates on a set of predefined beams in UL and DL.
Sets of beam weights are stored in the RU and beam
synthesis is taken over by RU.
Beam selection is done by RAU and is indicated to RU by
beam index.
One benefit is reduction of baseband capacity requirement
as calculation of beamforming weights on the fly is very
demanding on the computation power.
The drawback of this solution is non-optimal
beamforming towards users.
Beam weights are shared by orthogonal degree antenna
polarizations, i.e. each beam is cross-polarized and can send
two multiplexed streams.
(RU)
(RF part of gNB-DU)
CPRI/eCPRI One beam
AirScale System Module
ASIK+ABIL
System Module (RAU)
(gNB-DU excl. RF part)
Antenna
elements
MAC scheduler, adapt rank,
MCS, beam, PMI
UE data
Rank,
PMI,
MCS
GoB
Beam_1: {w1,w2… wn}
Beam_2: {w1,w2… wn}
…
Beam_n: {w1,w2… wn}
6. The continuous coverage of the cell area is not there
anymore. The problem is: how to provide common control
channels. These channels need to be heard by all UEs in
the coverage area of the given cell.
The answer is: sweeping. At predefined amounts
of time, the broadcast information is being sent
sequentially across all beams – think about a
lighthouse for a real-world reference.
Beamforming in 5G
Beamforming - common channels coverage
Internal Use
7. Beamforming in 5G
Beamforming
Internal Use
The transmission of
data (& control
information) to any
individual UE is done
with the help of the
narrow beams.
Each individual beam is a signal limited in space (narrow beam), that is intended to reach the user (or
users) placed in the coverage zone of that specific beam but that is not visible to other users (it’s still
detected by others, but with low level)
time
8. Beamforming in 5G
Beamforming – Downlink and uplink
Internal Use
The TDD transmission mode means that there could be DL or UL frames at the same carrier frequency.
The DL and, respectively, UL scheduler will choose the beam direction that will be used during the
incoming TTI, according to the frame type (direction)
time
Downlink transmisson,
followed by uplink
transmission. The
switching can be done
on slot basis, or on
symbol basis
9. Beamforming in 5G
Broadcast transmission - summary
Internal Use
PSS SSS PBCH
PSS PBCH
SSS
PBCH
PBCH
PSS PBCH
SSS
PBCH
PBCH
PSS PBCH
SSS
PBCH
PBCH
PSS PBCH
SSS
PBCH
PBCH
PSS PBCH
SSS
PBCH
PBCH
Below
6GHz
Above
6GHz
2 x
4 x
3 to
6GHz 8 x
64 x*
SS Block
SS Burst SS Burst Set
PSS, SSS and PBCH (carrying
MIB) are time and frequency
multiplexed
That set compose SS Block
in four consecutive OFDM
symbols
Above
6GHz
SS Blocks form SS Burst that is a
set of consecutive SS blocks
SS Bursts compose SS Burst set used
for multi beam sweeping
*Up to 32 according to
NRCELLGRP:numberOfTransmittedSsBlocks
parameter range
10. Beamforming in 5G
SS Block Burst Set: multi-beam sweeping
SS
block
0
SS
block
1
SS
block
2
SS
block
3
SS
block
L
… …
Multi-beam
sweeping
…
• Within an SS/PBCH burst set, beams are mapped in consecutive SS/PBCH blocks in increasing order of beam index
• The beam indexes are numbered from 0 to L-1 where L represents the maximum number of beams where SS/PBCH blocks
are broadcasted within a SS/PBCH burst set
• The beam indexing initialization is such that the beam 0 is transmitted in the first SS/PBCH block of the first radio frame
carrying SS/PBCH block
SS
block
0
SS
block
1
SS
block
2
SS
block
3
SS
block
L
…
The number of SS Blocks in SS Burst Set equals
the number of beams. Parameter
NRCELLGRP:numberOfTransmittedSsBlocks
defines the number of transmitted SS Blocks
…
SS Burst Set 0 SS Burst Set 1
beam #0 beam #1 beam #2 beam #3 beam #L-1 beam #0 beam #1 beam #2 beam #3 beam #L-1
… …
Value Name
1 1 beam
2 2 beams
4 4 beams
6 6 beams
8 8 beams
9 9 beams
12 12 beams
15 15 beams
18 18 beams
21 21 beams
24 24 beams
32 32 beams
The main purpose of SS Burst sets is to support DL beam sweeping, in which DL
Tx beams are sequentially transmitted in order to cover the whole service area
in one SS Burst Set.
11. Beamforming in 5G
Definition of basic sets of SSB
Beam sets and basic beam sets
The basic beam sets shall be defined using the nomenclature #k#l#m ...
the number of columns in a row is given by the respective integer, preceded by the
character '#'
rows are counted from top to bottom, i.e., the first row is the one with highest
pointing beams, the last row is the one with lowest pointing beams
Examples:
• basic beam set #4#4 denotes a beam set with 2 rows and 4 columns in each row
• basic beam set #3#3#2 denotes a beam set with 3 rows, most upper row and
middle row with 3 beams each, lowest row with 2 beams only
Internal Use
basic beam set #4#4
basic beam set #3#3#2
azimuth
elevation
Number of beams in basic beam set must match with number of
transmitted SS blocks set by NRCELLGRP-
numberOfTransmittedSsBlocks parameter
12. Beamforming in 5G
Supported beamsets
Internal
basicBeamSet Beam pattern # of
panel
s
# of
bea
ms
Azimuth
opening
[deg]
Elevation
opening
[deg]
Note
beamSetAbf_32A ooooooooooooooo
oooooooooooooo
O
1 32 -60, 60 87, 123 Valid only for single panel radios
beamSetAbf_32B oooooooooo
ooooooooo
oooooooooo
1 32 -40, 40 72, 108 Valid only for single panel radios
beamSetAbf_32C oooooooooo
ooooooooo
oooooooooo
1 32 -40, 40 72, 108 Valid only for single panel radios
Legacy beam sets defined in 5G19 Analog Beamforming for CPRI
RUs are supported by 1-panel RUs.
Note: Final beamsets may be subject to further optimizations
13. Beamforming in 5G
Definition of basic sets of SSB
Internal
Basic beam set beamSetAbf_32A from different perspectives
14. Beamforming in 5G
Radio Units ‘example’
400 MHz 3 GHz 30 GHz
10 GHz 90 GHz
6 GHz
cmWave mmWave
Carrier BW n * n * 100 MHz 1-2GHz
Duplexing * TDD
Cell size Macro Small Ultra small
higher capacity and massive throughput, noise limitation à
ß continuous coverage, high mobility and reliability, interference limitation
28 GHz 39 GHz
3.5GHz Radio Unit
3.5 GHz 3.7 GHz
3.7GHz Radio Unit
28GHz Radio Unit 39GHz Radio Unit
DIGITAL
Beamforming
• UL/DL 2x2 SU-MIMO
• UL/DL 2x2 SU-MIMO
• DL: 4x4 SU-MIMO / UL: 2x2 SU-MIMO
• 16UL/16DL MU-MIMO
ANALOG
Beamforming
Internal Use
15. Beamforming in 5G
Difference between Analog and Digital Beamforming
Internal Use
• In Analog Beamforming, there is a single TRX per polarization. Beam pattern is obtained by modification of the RF signal
between the TRX and the antenna elements.
• A planar array of 16x16 radiating elements is used. RF signal is modified by an RF Integrated Circuit (RFIC) in the RU.
• This is applicable for FR2 (frequencies above 6 GHz).
…
w1 w3
w2 wn
TRX1
UE data
stream
16. Beamforming in 5G
Difference between Analog and Digital Beamforming
Internal Use
• In Digital Beamforming, beam pattern is synthesized by manipulating weights of the individual TRXs
• Beamforming weights are applied between the fronthaul and TRXs.
• Beamforming weights are applied in RU, while beam selection is done by RAU.
TRX1
TRX2
TRX3
TRXn
UE data
stream …
w1 w3
w2 wn
17. Beamforming in 5G
Beam Refinement
In case of operating with a grid of beam (GoB) and especially with carrier frequencies below 6GHz with limited number
of SSB beams, beam refinement on 5G-NB side is used to achieve higher SINR for a single UE in both DL and UL
direction, as well as better separation of UEs in case multiple UEs are served on the same time and frequency resources,
i.e., MU-MIMO operation.
To enable execution of respective measurements by UEs, CSI-RS have to be transmitted for beam refinement. The
antenna ports used for these CSI-RS have to be mapped to the beams used for refining a respective SSB beam
4 refined beams per SSB beam are implemented.
Internal Use
SSB beam
Refined beams
Beam refinement is activated by setting parameter
NRCELL-beamSet.nrBtsBeamRefinementP2 = true
18. Beamforming in 5G
Example of refined beams
Basic beam set #3#3#2 with refined beams from different perspectives (not
all refined beams shown)
Internal Use
basic beam set #3#3#2
19. Beamforming in 5G
Beam recovery
Internal
In case of beam failure, i.e., the UE may no more be reached via the best beam
last known at gNB side, a procedure to reconnect the UE has to be executed.
1. 5G-UE detects a misaligned serving beam to gNB e.g. by
NACKed UL data sent or by interrupted DL data allocation.
Potential reasons:
• 5G-UE measures the source beam with L1-RSRP below
minimum link budget,
2. 5G-UE measures a new target beam with strongest L1-RSRP
3. 5G-UE starts Beam Recovery by sending Random Access
Preamble on a best target beam
4. UL and DL transmissions are resumed on a new beam
PRACH
20. Beamforming in 5G
Internal
Beam failure and recovery process
gNB UE
SSB
TX
Scan SSB beams
And select best
RX PRACH
Measure SSB associated
PRACH procedure
as in initial access
Initiate PRACH procedure if meet
failure criterion
Periodic
checking
Initial access procedure
• Beam failure detection uses default RRC configuration with
active PDCCH TCI state.
• Failure triggered if SSB RSRP beam meets failure criterion.
• Beam recovery reference signal measurement based on
RRC configuration for CBRA.
• Beam recovery follows initial access PRACH procedure.
TX
21. Beamforming in 5G
Antenna tilt for 2D GoB
introduces a tilt function for RF units with an integrated antenna with 32 or 64 TRX
using a GOB pattern for cmWave frequency range.
The tilt is operator configurable per cell and applied at cell setup as tiltOffset. The
tiltOffset range is +/-13° degrees around the pre-Tilt defined by the HW radio design
and with a step size of 1°.
It is assumed that the shape of GoB beam set is kept, i.e. a possible calculation error
is not exceeding a specific threshold. This ensures that the beam orthogonally
required for later MU operation is not affected
This feature supports in this release CPRI RUs (NRCELL.beamSet.tiltOffset).
Internal Use
RU
tilt
22. 5G MU-MIMO
DL MU-MIMO for Digital Beamforming for CPRI based RUs
UL MU-MIMO for Digital Beamforming for CPRI based RUs
24. MIMO fundamentals
Spatial multiplexing principle
h11
h12
h21
TX
antenna
port 0
TX
antenna
port 1
RX1
RX2
MIMO
receiver
x1
x2
y1
y2
x1
x2
Animation
Wireless channel coefficients
(known from Reference Signal)
2
12
1
11
1 x
h
x
h
y +
=
2
22
1
21
2 x
h
x
h
y +
=
h22
known
unknown
• MIMO = Multiple Input Multiple Output
• Different symbols are sent by transmit antennas in the
same time and frequency
• As symbols propagate over the wireless channel, their
phase and amplitude changes according to the
channel coefficient (complex value)
• Channel between each pair of the TX and RX antennas
is different due to different propagation conditions
• Receiver needs only to solve a set of equations.
Channel coefficients are known from reference signals,
so the only unknown is the transmitted symbols
27. MIMO fundamentals
Precoding
• Performance of the MIMO system can be improved with precoding.
• Let’s start with an easy example: 2x2 MIMO, 1 codeword, 1 layer:
Scrambling
Modulation
mapper
Layer
mapper
Precoding
Resource element
mapper
OFDM signal
generation
Resource element
mapper
OFDM signal
generation
Scrambling
Modulation
mapper
layers antenna ports
codewords
1
-1
1
TX
antenna
port 0
TX
antenna
port 1
RX1
RX2
MIMO
receiver
x1
x2
y1
y2
x1
x2
-1
I
Q
1
x
I
Q
1
11x
h
2
12x
h
I
Q
2
x
I
Q
1
21x
h
2
22x
h
h11
h12
h21
h22
ú
û
ù
ê
ë
é
-
-
=
ú
û
ù
ê
ë
é
1
1
1
1
22
21
12
11
h
h
h
h
• In this example, channel coefficients from the TX antenna port 2 are rotated 180 degrees to the TX antenna 1, and
have the same magnitude:
• Effectively, received signals at each RX antenna cancel each other out.
Only the noise is received!
• In this example, precoder is simply duplicating the symbols received from
the layer to the antenna ports. Symbols transmitted on the antenna ports
are exactly the same.
;
1
1
ú
û
ù
ê
ë
é
=
W
Received symbols
cancelled out
Received symbols
cancelled out
Animation
Only noise is
received
2
1 x
x =
28. MIMO fundamentals
Precoding
Animation
• In this example, let’s change the precoding weights:
• x2 is now rotated 90 degrees to x1
Scrambling
Modulation
mapper
Layer
mapper
Precoding
Resource element
mapper
OFDM signal
generation
Resource element
mapper
OFDM signal
generation
Scrambling
Modulation
mapper
layers antenna ports
codewords
1
-1
1
TX
antenna
port 0
TX
antenna
port 1
RX1
RX2
MIMO
receiver
x1
x2
y1
y2
x1
x2
-1
I
Q
1
x
I
Q
1
11x
h
2
12x
h
I
Q
2
x
I
Q
1
21x
h
2
22x
h
• Symbols experience channel coefficients same as on previous example as they propagate,
but now something is received at the UE antennae.
• Signal to Noise Ratio (SNR) can be improved by selection of proper precoder setting. This is
called Precoding Gain. Precoding gain depends on the chosen precoding weights.
;
1
1
1
ú
û
ù
ê
ë
é
-
=
®
ú
û
ù
ê
ë
é
=
j
W
W
Received
symbol
1
2 jx
x -
=
30. MIMO fundamentals
Closed loop DL MIMO
gNB UE
RF
precoder
layers
RF
Channel
estimation
Rank and
precoding
calculation
codebook
2 3
Part of UCI
“…and this PMI”
I want this rank…”
Animation
7
6
MIMO
control
5
U P L I N K C O N T R O L I N F O R M A T I O N
D O W N L I N K C O N T R O L I N F O R M A T I O N
Part of DCI
“Here is your data, and I used this
number of layers…”
“…and this PMI”
codebook
4
layers
8
PDSCH
receiver
1
9
#
o
f
l
a
y
e
r
s
5GC000531/5
GC000605
CSI-RS
31. MIMO fundamentals
Closed loop UL MIMO
UE gNB
RF
precoder
layers
RF
Channel
estimation
Rank and
precoding
calculation
codebook
Part of DCI
Please send SRS
signal to me
Animation
D O W N P L I N K C O N T R O L I N F O R M A T I O N
D O W N L I N K C O N T R O L I N F O R M A T I O N
Part of DCI
“I want to used this number of
layers…”
“…and this TPMI”
codebook
layers
PUSCH
receiver
5GC000532
SRS
32. DL Closed Loop Transmission (Report Quantity = CRI-RI-PMI-CQI)
DL Closed loop:
gNB transmits CSI-RS and UE reports CSI-RS
feedback (CRI-RI-PMI-CQI).
gNB selects the rank and the precoding matrix
according to the UE's CSI feedback.
33. UL Closed Loop Transmission
Closed Loop 2x2 MIMO
5G18A gNb implements a Codebook based
transmission scheme.
Rank and PMI are decided at gNB based on received UL
reference signals SRS and DMRS on PUSCH.
35. What is “Massive MIMO”?
• Massive MIMO is the extension of traditional MIMO
technology to antenna arrays having a large number of
controllable antennas
• MIMO = Multiple Input Multiple Output = any transmission scheme
involving multiple transmit and multiple receive antennas
– Encompasses all implementations:
» RF/Baseband/Hybrid
– Encompasses all TX/RX processing methodologies:
» Diversity, Beamforming, Spatial multiplexing,
» SU & MU, joint/coordinated transmission/reception, etc.
• Massive è Large number: >> 8
• Controllable antennas: antennas (whether physical or otherwise)
whose signals are adaptable by the PHY layer (e.g., via gain/phase
control)
(0,0) (0,1) (0,N-1)
(M-1,N-1)
……
(M-1,0) (M-1,1)
(1,0) (1,1) (1,N-1)
……
……
……
……
……
……
36. Why “Massive MIMO”
• Benefits:
– Enhance Coverage è High gain adaptive beamforming
• Focus energy more towards the user, increase SINR
– Enhance Capacity è High order spatial multiplexing
• Multiple parallel spatial streams to a single user (SU) or to multiple users (MU)
• Relevance to 5G:
– Lower operating frequencies (e.g., <6GHz) are more interference limited
• LTE already designed for high spectral efficiency (<8 Antenna ports)
• Capacity-enhancing solutions become essential
– Higher operating frequencies (e.g., >>6GHz) have poor path loss
conditions
• Coverage-enhancing solutions become essential
37. 5G Beamforming solutions
Digital BB beamforming
• Mainly for below 6GHz (but also for cmWave)
• Requires RF phase/amplitude calibration of IF+TRX+Filter
• Requires high front haul interface bandwidth
• Requires high number of TRXs (8 … 128)
Digital RF beamforming
• Mainly for above 6GHz (hybrid BF), but also for below 6GHz
• Beamformer implemented in RF module
• Requires RF phase/amplitude calibration of TRX+Filter
• Requires high number of TRXs (8 … 256)
Analog RF beamforming
• For cmWave & mmWave specturm
• Beamformer implemented in RFIC or through lens Antenna
• Requires RF phase/amplitude stability of RFIC
• Requires high number of radiators per array
40. Beam set overview
Beam Set
• One beam set includes those SSB & fine beams which can be used concurrently for some scenario
• In each beam set, both SSB beams and fine beams can have several rows
• Number of beams in each row can be different
• Some overlap between neighbour beams to have good coverage
• Typically more beams for outer part of a cell and less beams for inner part of a cell
𝝋_l
𝝋_r
SSB5
SSB4
SSB3 SSB2
SSB1
SSB0
SSB7
SSB6
Example of 8 SSB beams
𝝋_l
𝝋_r
Example of 32 fine beams
42. mMIMO & BF key features
Digital beamforming
§ Up to 8 x-pol coarse beams
(< 6 GHz)
§ Up to 32 refined beams for
UE specific channels
§ Scheduling of a single UE
per slot per direction and
carrier
DL SU MIMO
§ For digital BF
§ 2 refined x-pol beams are
used to provide 4x4 MIMO
on PDSCH
§ UEs with 2 RX antennas are
supported with 4x2
transmission
DL/UL MU MIMO
§ For digital BF
§ UEs are scheduled at the
same time on the same
frequency resources over
different beams
§ Support of up to
§ 8 UEs with 2x2 SU-
MIMO on DL or UL
§ 4 UEs with 4x2 or 4x4
SU-MIMO on DL
UL SU MIMO
§ For digital BF
§ One refined x-pol beams are
used to provide 2x2 MIMO
on PUSCH
43. MU-MIMO Overview
Before & after MU-MIMO features
Before
• Single user can be scheduled using 2x2 or 4x4 MIMO on
dedicated time and frequency resources
After
• Up to 8 UEs (16 streams) can be scheduled on the same
time and frequency resources using spatial multiplexing
• Peak cell throughput and spectral efficiency increase,
mostly for static users
Customer Confidential
44. MU-MIMO Overview
mMIMO RF at 3.5 GHz
64 antenna elements
dual polarization ±45°
Carrier 100MHz
Baseband Unit
RF calibration
centrally from RM
100MHz carrier
±45°
0.376m
0.536m
2
x
T
R
X
2
x
T
R
X
2
x
T
R
X
M
D
R
D
F
E
F
P
G
A
Q
S
F
P
Q
S
F
P
Q
S
F
P
Q
S
F
P
P
S
U
D
F
E
F
P
G
A
D
F
E
F
P
G
A
D
F
E
F
P
G
A
2
x
T
R
X
RF
module
64TRX
8 x
Filters
Antenna
feed
and
division
network
0.5λ
0.7λ
~0.2m2
4 rows x 8 columns x dual Polarizations
45. MU-MIMO Overview
§ Mechanics
Ÿ Overall dimensions (without
solar shield):
Ÿ H = 850 mm
Ÿ W = 460 mm
Ÿ D = 144 mm
Ÿ Housing material: ALSI 12 ,
Die-casting/Extrusion
Ÿ Weight:~45KG
Ÿ Volume:56.3L
QSFP RJ45
DC IN
• mMIMO RF at 3.5 GHz
46. MU-MIMO Overview
Introduction
• Multiuser MIMO allows to transmit signal to many users in
downlink or uplink at the same time and in the same
frequency resources by using beamforming and spatial
multiplexing.
• It increases cell peak rate, but not user peak rate
• It increases average cell and user throughput
• DL 2x2 MIMO with up to 8 UEs can be co-scheduled per TTI.
If 4X4 MIMO is enabled, up to 4 UEs can be co-scheduled
per TTI.
• UL 2x2 MIMO with up to 8 UEs can be co-scheduled per TTI.
47. When is correlation metric high and when is it low?
• Intuitively, factor is low when beamforming factor Ui and Uj are not similar to each other.
From beamforming perspective, this means that beams of ith and jth UE will point in different
directions.
• The best situation is when correlation is equal to 0, the worst situation is when correlation is
equal to 1.
Pairing algorithm
Correlation
U1 ≠ U2
Low correlation
U1 ≈ U2
High correlation
48. MU-MIMO Receiver
Overview
In 5G18A, the UL receiver is still SU-MIMO PoC receiver. It works well if only one UE is scheduled per TTI.
But to support concurrent UL scheduling for up to 8 UEs, this approach cannot get optimal UL
performance. Even the UL pairing algorithm selects paired UEs which have the maximum orthogonality
with each other.
The non-orthogonality of UL channels between co-scheduled UEs will introduce interference with each
other. The SU-MIMO based receiver cannot well handle this interference. To involve MU-MIMO receiver
to mitigate interference from co-scheduled UEs is the way we need to go.
50. Reference Signal
SRS
Customer
Confidential
Extension of 5GC000532
Before MU
combOffset = 0
cyclicShift = 0
Only one UE can send SRS in one
symbol.
After MU
combOffset = 0 or 1
cyclicShift = 0 ~ 3
Up to 8 UEs can send SRS in one
symbol.
51. Reference Signal
CSI-RS
Customer
Confidential
Extension of 5GC000531
Before MU
other = 000001
Only one UE can measure CSI-RS for
CSI in one symbol.
After MU
other = 000001 ~ 100000
Up to 6 UEs can measure CSI-RS for CSI
in one symbol.
