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Beamforming in 5G, MU-MIMO, 5G Antenna arrey

1. Precoding improves MIMO performance by applying weighting to symbols transmitted from each antenna port. This changes the effective channel between transmit antennas and receive antennas. 2. By properly selecting precoding weights, signals from different transmit antennas can add constructively at the receiver, improving signal strength. Weights can also be selected to cancel out interference between streams. 3. Common precoding techniques include maximum ratio transmission, which maximizes received power, and zero forcing, which cancels interference between streams at the cost of reduced power. Precoding weights are selected based on channel state information obtained from reference signals.

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Beamforming in 5G
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.
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
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
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}
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
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
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
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
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.
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
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
Beamforming in 5G Definition of basic sets of SSB Internal Basic beam set beamSetAbf_32A from different perspectives
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
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
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
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
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
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
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
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
5G MU-MIMO DL MU-MIMO for Digital Beamforming for CPRI based RUs UL MU-MIMO for Digital Beamforming for CPRI based RUs
Introduction of MIMO
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
MIMO fundamentals Mathematical modeling of MIMO
MIMO fundamentals Rank SVD = Singular Value Decomposition
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 =
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 - =
MIMO fundamentals Codebooks
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
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
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.
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.
Introduction of mMIMO & Digital Beamforming
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) …… …… …… …… …… ……
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
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
Antenna Array Theory 2D Linear array Beamer
Antenna Array Theory Rectangular array - example
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
Introduction of 5G MU-MIMO Solution
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
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
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
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
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.
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
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.
Example DMRS Design UE0 (rank 4) UE1 (rank 2) UE2 (rank 2) UE3 (rank 2) Port:2, 3 SCID: 1 Port:6, 7 SCID: 0 Port:0, 1, 4, 5 SCID: 0 Port:0, 1 SCID: 1
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.
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.
NIDD parameters Feature Configuration

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Beamforming in 5G, MU-MIMO, 5G Antenna arrey

  • 1.
  • 2.
    Beamforming in 5G Internal Frequencyvs. 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 BeamformingPrinciple 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 BeamformingPrinciple 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 Gridof 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 coverageof 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 InternalUse 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 Broadcasttransmission - 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 SSBlock 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 Definitionof 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 Supportedbeamsets 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 Definitionof basic sets of SSB Internal Basic beam set beamSetAbf_32A from different perspectives
  • 14.
    Beamforming in 5G RadioUnits ‘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 Differencebetween 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 Differencebetween 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 BeamRefinement 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 Exampleof 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 Beamrecovery 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 Beamfailure 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 Antennatilt 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-MIMOfor Digital Beamforming for CPRI based RUs UL MU-MIMO for Digital Beamforming for CPRI based RUs
  • 23.
  • 24.
    MIMO fundamentals Spatial multiplexingprinciple 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
  • 25.
  • 26.
    MIMO fundamentals Rank SVD =Singular Value Decomposition
  • 27.
    MIMO fundamentals Precoding • Performanceof 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 • Inthis 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 - =
  • 29.
  • 30.
    MIMO fundamentals Closed loopDL 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 loopUL 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 LoopTransmission (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 LoopTransmission 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.
  • 34.
    Introduction of mMIMO &Digital Beamforming
  • 35.
    What is “MassiveMIMO”? • 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 DigitalBB 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
  • 38.
    Antenna Array Theory 2DLinear array Beamer
  • 39.
  • 40.
    Beam set overview BeamSet • 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
  • 41.
  • 42.
    mMIMO & BFkey 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 RFat 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 ŸOverall 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 • MultiuserMIMO 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 correlationmetric 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.
  • 49.
    Example DMRS Design UE0 (rank4) UE1 (rank 2) UE2 (rank 2) UE3 (rank 2) Port:2, 3 SCID: 1 Port:6, 7 SCID: 0 Port:0, 1, 4, 5 SCID: 0 Port:0, 1 SCID: 1
  • 50.
    Reference Signal SRS Customer Confidential Extension of5GC000532 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 of5GC000531 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.
  • 52.