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 Angelesyhaddint@ucla.edu

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

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0-90

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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

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0-90

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0

30

6090

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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

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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

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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

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30

6090

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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

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0

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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

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0

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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