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1This work was supported in part by the Semiconductor Research Corporation (SRC) and DARPA.
Millimeter-wave Rainbow Beam-based OFDMA for Low Latency Massive Multiple Access
Han YanAdvisor: Prof. Danijela Cabric
University of California, Los [email protected]
2
Industry IoT in beyond 5G
eMBB
(mmW / sub-6)
URLLC
(sub-6)
eMTC
(sub-6)
Data rate ~1Gbps ~100Kbps ~100Kbps
Latency 5-10ms ~1ms ~1s
Reliability Medium High Low
Connection
DensityLow-Medium Low High
Power/Cost High High Low
[1] Figure source: https://www.supplychain247.com/article/are_drones_a_sky_high_vision_for_the_future_of_logistics
Applications for industry IoTIndustrial wireless sensor network (IWSN), intelligent drone swarm, etc
Challenges of Industry IoT in mmW/sub-THz
Power and Cost
Antenna array in the RF
Multi-GHz processing BW in the baseband
Latency
Beam search latency
Multi-user resource scheduling latency
Connection Density
The narrow beam limits flexibility of orthogonal frequency division multiple-access (OFDMA)
NR-Lite2-4
(mmW / sub-6)
10-100Mbps
5-10ms
Medium
Medium
Medium
[2] 3GPP, “RP 191047 NR-Lite for industrial sensors and wearables,” Jun. 2019. [Online]. Available: https://www.3gpp.org/ftp/TSGRAN/TSGRAN/TSGR84/Docs/
[3] 3GPP, “RP 190844 NR-Lite for rel-17 Qualcomm views,” Jun.2019. [Online]. Available: https://www.3gpp.org/ftp/tsgran/TSGRAN/TSGR84/Docs
[4] 3GPP, “RP190831 Key directions for release17,”Jun.2019. [Online]. Available: https://www.3gpp.org/ftp/tsgran/TSGRAN/TSGR84/Docs
3
Rainbow Beam OFDMA Overview
Latency Reduction
Fast beam alignment
Arrive-and-go grant-free scheduling scheme
Connection Density Enhancement
Joint frequency (OFDMA) and spatial resource sharing to support massive connection
Features of proposed mmW/sub-THz IoT Network
Power and Cost Reduction
Terminal: narrow bandwidth in the baseband
Base station: low complexity DSP backend
Subcarrier/frequency
BW
Rainbow beam steering
Color indicates subcarrier/frequency
Frequency-Angle Mapping
BWu
UE1
UE1
Research objective:
PHY layer: efficient BS signal processing for rainbow beam
MAC/Link layer: protocol design to enhance multiple access & latency performance
UE2 UEu UEU
UE𝑈
…
4
Building Blocks of Rainbow Beam
…
Freq-flat steering vector 𝐰 in CP-OFDM waveform (all 𝑴 subcarriers)
#1
#N OFDM
Demod
…
Phase shift
Steer a wideband signal into a single direction, e.g., 𝚫𝝓 = 𝟎
-20
-15
-10
-5
0-90
-60
-30
0
30
6090
• Phase shift can be introduced in either RF, analog BB, or digital
• RF-chain (down-converter) and ADC omitted
5
Building Blocks of Rainbow Beam
27.800GHz
27.825GHz
27.850GHz
27.875GHz
27.900GHz
27.925GHz
27.950GHz
27.975GHz
28.000GHz
28.025GHz
28.050GHz
28.075GHz
28.100GHz
28.125GHz
28.150GHz
28.175GHz
28.200GHz
-20
-15
-10
-5
0-90
-60
-30
0
30
6090
-20
-15
-10
-5
0-90
-60
-30
0
30
6090
…
Time delay
Freq-dependent steering vector 𝐰[𝑚] in CP-OFDM waveform (𝒎-th subcarrier)
#1
#N
[1] H. Yan, V. Boljanovic, and D. Cabric, "Wideband millimeter-wave beam training with true-time-delay array architecture," (invited paper) in Asilomar Conference on Signals, Systems, and Computers, Nov. 2019.
[2] V. Boljanovic, H. Yan, E. Ghaderi, D. Heo, S. Gupta, and D. Cabric, “Design of millimeter-wave single-shot beam training for true-time-delay array,” (invited paper) in Proc. IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), May 2020
OFDM
Demod
• Time delay can be introduced in either RF, analog BB, or digital
• RF-chain (down-converter) and ADC omitted
6
-20
-15
-10
-5
0-90
-60
-30
0
30
6090
𝑲 MIMO layers for 𝑓𝒎
27.800GHz
27.825GHz
27.850GHz
27.875GHz
27.900GHz
27.925GHz
27.950GHz
27.975GHz
28.000GHz
28.025GHz
28.050GHz
28.075GHz
28.100GHz
28.125GHz
28.150GHz
28.175GHz
28.200GHz
-20
-15
-10
-5
0-90
-60
-30
0
30
6090
-20
-15
-10
-5
0-90
-60
-30
0
30
6090
Rainbow beam layer 𝑘
Spatially Reusing Rainbow Beam
Spatially reusing freq-dependent steering vector 𝐰𝑘[𝑚] (𝑚-th subcarrier, 𝑘-th MIMO layer)
27.800GHz
27.825GHz
27.850GHz
27.875GHz
27.900GHz
27.925GHz
27.950GHz
27.975GHz
28.000GHz
28.025GHz
28.050GHz
28.075GHz
28.100GHz
28.125GHz
28.150GHz
28.175GHz
28.200GHz
-20
-15
-10
-5
0-90
-60
-30
0
30
6090
-20
-15
-10
-5
0-90
-60
-30
0
30
6090
Layer 1
… …
OFDM
Demod
…
Phase shiftTime delay
Layer 𝑘
…
OFDM
Demod
[1] H. Yan, V. Boljanovic, and D. Cabric, "Wideband millimeter-wave beam training with true-time-delay array architecture," (invited paper) in Asilomar Conference on Signals, Systems, and Computers, Nov. 2019.
[2] V. Boljanovic, H. Yan, E. Ghaderi, D. Heo, S. Gupta, and D. Cabric, “Design of millimeter-wave single-shot beam training for true-time-delay array,” (invited paper) in Proc. IEEE International Workshop on Signal Processing Advances in Wireless Communications (SPAWC), May 2020
Rainbow beam layer 1
7
Low-Complexity Digital Rainbow Beam
RF-Chain
RF−Chain
RF−Chain
ADC
ADC
ADC
…
Cyclic-Shift 𝐉0
Cyclic−Shift𝐉𝑁−1
Cyclic-Shift 𝐉𝑛−𝟏
𝐚1 ∈ ℂ𝑀
sample-wise
𝑁-ptDFT
w/ 𝐾output
OFDM FFT
OFDM FFT
OFDM FFT
𝐚𝑘 ∈ ℂ𝑀
𝐚𝐾 ∈ ℂ𝑀
……
BS Rx Fully-Digital Array
- CP
- CP
- CP
…
𝐲1
𝐲𝑛
#1
#𝑁𝐲𝑁
Proposed digital rainbow beam scheme (𝑲 = 𝜷𝑵 MIMO layers)Backend complexity
Complex multiplication per sample durationAntenna size 𝑁; MIMO layer 𝐾 = 𝑁𝛽
RF-Chain
RF−Chain
RF−Chain
ADC
ADC
ADC
- CP
- CP
- CP
……
OFDM FFT
OFDMFFT
OFDM FFT
Spatial EQ.
for SC 𝑚
𝐚𝑚 ∈ ℂ𝐾
……
𝐲1
𝐲𝑛
𝐲𝑁
𝑀 slices of 𝑁P SC
#1
#𝑁
EQ Comp.
𝐚𝑀 ∈ ℂ𝐾
CSI
Conventional MIMO-OFDM (𝑲 = 𝜷𝑵 MIMO layers)
Time delay Phase shift
70X complexity saving as rainbow beam requires 𝐾 OFDM demod
𝑲 demod
𝑵 demod
8
-90
-60
-30
0
30
60
90
0
50
100
Low Latency Grant-Free Access
Latency = 𝑁align +𝑁ARQ (𝐿 + 3) + 𝑁s [ms]
OFDMA Resource Selection by UE
Proposed grant-free uplink mmW IoT access(A: frame alignment; T: transmission; BP: base station processing;
F: feedback; UP: UE processing)
BS
path#1
#2
#3
-90
-60
-30
0
30
60
90
0
50
100
Collision & Interference
(𝐾 layers on a given frequency resource)
Assumptions
• UE has analog phased array (single stream)
• UE has access to a portion of BW (narrowband UE)
• Time & frequency synch has reached
• UE knows the 𝐾 layers BS rainbow beam codebook
• UE do not know instantaneous path gain
• No coordination b/w UEs
Interference
(same freq & different MIMO layer)
Collision
(same freq &MIMO layer)
Data created
...UE
BS
time
time
A T1 TL
BP1st Lth
BP...
UP
NACK
Initial transmission
... UP
ACKT1 TL
BP BP
HARQ retransmission
F ... F
9
Latency & Reliability in Massive Access
Simulation setting:
All-digital BS has 𝑁R128 antennas and 𝐾=32 MIMO layers are used; phased array UE has 𝑁T = 16 antennas; Channel has 𝐿=3 paths; 𝑈={100,200,300} active UEs; Total BW = 1GHz with RB=256 resource blocks;
Latency vs Reliability
First transmission
Second transmission
(HARQ-1)
Third transmission
(HARQ-2)
• Diversified requirement in beyond 5G mmW/sub-THz
eMBB – few UEs with extreme data rate
mmW IoT – trading rate for other metrics (connection num. & latency)
• Novel rainbow beam MIMO-OFDMA signal processing
Significantly reduced complexity (vs conventional MIMO-OFDM)
• Grant-free access protocol
Angular separation to avoid mutual interference
• Future works
Theoretical analysis on latency & reliability performance
Study on impact of ADC quantization noise
[ms]
10
Logistic Information
Task Number Task.002
PI and studentsPI: Danijela Cabric
Student: Han Yan, Veljko Boljanovic, Benjamin Domae
Liaison for this task Once (2020.01.08)
Publications associated
with task
[1] H. Yan, V. Boljanovic, and D. Cabric, "Wideband millimeter-wave beam
training with true-time-delay array architecture," (invited paper) in Asilomar
Conference on Signals, Systems, and Computers, Nov. 2019.
[2] V. Boljanovic, H. Yan, E. Ghaderi, D. Heo, S. Gupta, and D. Cabric, “Design
of millimeter-wave single-shot beam training for true-time-delay array,” (invited
paper) in Proc. IEEE International Workshop on Signal Processing Advances in
Wireless Communications (SPAWC), May 2020
11
Anonyms List
OFDMA Orthogonal frequency division multiple access BS Base station
eMBB Enhanced mobile broadband PHY Physical (layer)
URLLC Ultra reliable and low latency communication MAC Medium access control
eMTC Enhanced machine type communication DSP Digital signal processing
IoT Internet of things CP Cyclic prefix
RF Radio frequency BB Baseband
BW Bandwidth ADC Analog to digital converter
UE User equipment demod demodulation
MIMO Multiple-input multiple-output
Joint University Microelectronics Program