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OTFS Orthogonal Time Frequency Space A novel modulation scheme - - PowerPoint PPT Presentation

Feb 11, 2023 363 likes •660 views

OTFS Orthogonal Time Frequency Space A novel modulation scheme addressing the challenges of 5G Anton Monk IEEE CTW 2016 Cohere Technologies FOUNDED IN 2009 Headquartered in Completed A, B and C Industry Leading Santa Clara, CA Rounds of

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OTFS Orthogonal Time Frequency Space

A novel modulation scheme addressing the challenges of 5G

Anton Monk IEEE CTW 2016

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Cohere Technologies ~ Proprietary & Confidential 2

Cohere Technologies FOUNDED IN 2009

Headquartered in Santa Clara, CA Completed A, B and C Rounds of Financing Industry Leading Investors

OTFSTM – An innovative form of modulation. OTFS simultaneously extracts time, frequency & spatial channel behavior resulting in greater coverage, higher capacity, and cost savings.

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Cohere Technologies ~ Proprietary & Confidential 3

OTFS Air Interface Overview

  • 2D (Delay-Doppler) Modulation scheme
  • Utilizes a Delay-Doppler channel model that explicitly

represents a stable and deterministic geometry of the channel

  • Novel 2D Basis functions spread information symbols
  • ver both time and frequency
  • Channel estimation is efficient, accurate and compact

– High density pilots can be used with both OFDM and OTFS

  • Enables linear scaling of performance with MIMO order

in all mobility scenarios

– Performance is robust against Doppler

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Cohere Technologies ~ Proprietary & Confidential 4

3GPP ETU-300 Channel: 𝑰(𝒈, 𝒖) vs 𝒊(𝝊, 𝝃)

𝐼(𝑔,𝑢) ℎ(𝜐, 𝜉)

𝐼 𝑔, 𝑢 = 𝑇𝑧𝑛𝑞𝑚𝑓𝑑𝑢𝑗𝑑 𝐺𝑝𝑣𝑠𝑗𝑓𝑠 𝑈𝑠𝑏𝑜𝑡𝑔𝑝𝑠𝑛 ℎ(𝜐, 𝜉)

300 Hz Doppler 5 usec Delay Spread

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Cohere Technologies ~ Proprietary & Confidential 5

OTFS Channel Model

  • Transmitted signal is a superposition of QAM symbols, 𝑦C,D with their

component basis functions

  • Received signal

𝑆 𝑢 = F ℎ(𝜐, 𝜉)𝑓GHIDJ𝑇 𝑢 − 𝜐 𝑒𝜐𝑒𝜉 = F 𝜚C,D 𝑢 ℎ 𝜐, 𝜉 ∗ 𝑦C,D 𝑒𝜐𝑒𝜉

𝑧C,D = Matched filter output

OOO OOO 𝜚C,D 𝑢 − 𝜐P = 𝜚CQCR,D 𝑢 𝑓GHIDRJ𝜚C,D 𝑢 = 𝜚C,DQDR 𝑢 𝑇 𝑢 = F 𝑦C,D 𝜚C,D 𝑢 𝑒𝜐𝑒𝜉 Delay-Doppler Covariance Condition

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Cohere Technologies ~ Proprietary & Confidential 6

OTFS – The 2D Approach For 5G

Orthogonal Time Frequency Space

𝑦C,D 𝑌T,J

𝑢 2D OTFS Transform

𝑧C,D 𝑍

T,J 𝑢 2D OTFS Transform-1

Transmit

Channel

Receive

Multicarrier Filter Bank Multicarrier Filter Bank 𝑍

T,J = 𝐼(𝑔, 𝑢) O 𝑌T,J

𝑧

C,D = ℎ(𝜐,𝜉) ∗ 𝑦C,D

Delay-Doppler Domain Time-Frequency Domain

(QAM)

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Cohere Technologies ~ Proprietary & Confidential 7

Received OTFS Symbols 𝜐 𝜉 Transmitted OTFS QAM Symbols 𝜐 𝜉 Delay-Doppler Impulse Response 𝜐 𝜉

∗

=

𝑦C,D ∗ ℎ 𝜐,𝜉 = 𝑧C,D

OTFS Channel Model

  • A novel, unique and time-independent relationship
  • Received OTFS symbols in the D-D domain are just the transmitted

QAM symbols convolved with the Delay-Doppler impulse response!

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Cohere Technologies ~ Proprietary & Confidential 8

Delay-Doppler (Information) to Time-Frequency (Signal)

Delay-Doppler (Information) Time-Frequency (Signal) 𝑂

T

𝑂J 𝑂J 𝑂

T

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Cohere Technologies ~ Proprietary & Confidential 9

Reference Signals

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Cohere Technologies ~ Proprietary & Confidential 10

2D OTFS Transform

  • The 2D Discrete Symplectic Fourier Transform

𝑌 𝑙,𝑚 = X X 𝑦 𝑛,𝑜

YZ[\ ]^P Y_[\ `^P

𝑐`,] 𝑙, 𝑚 𝑐`,] 𝑙,𝑚 = 𝑓

[GHI(b` Y_ [ c] YZ)

  • The 2D Discrete Inverse Symplectic Fourier Transform

𝑦 𝑛, 𝑜 = X X 𝑌 𝑙, 𝑚

YZ[\ c^P Y_[\ b^P

b`,]

∗

𝑙,𝑚 b`,]

∗

𝑙, 𝑚 = 𝑓

GHI(b` Y_ [ c] YZ )

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Cohere Technologies ~ Proprietary & Confidential 11

OTFS Basis Functions Span Time and Frequency

Delay-Doppler Domain Time-Frequency Domain

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OTFS Architecture & Compatibility

  • OTFS is a 2D extension of proposed multicarrier modulations

(OFDM, FBMC, UFMC, etc.)

  • OTFS is a 2D extension of CDMA techniques
  • OTFS is an evolutionary augmentation of OFDM

– A pre-processing / post-processing block

  • Architecturally compatible with LTE

QAM Symbols Transmitter

OTFS Pre-processing Block OFDM/UFMC Modulator OFDM/UFMC Demodulator OTFS Post- processing and Equalization

Receiver

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OTFS PILOT ARCHITECTURE

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Data & Pilot Lattices – Time-Frequency Domain

  • Data Lattice (green):
  • Pilot Lattice (red): Example – M=1, N=14

– 𝑁Δ𝑔=pilot frequency spacing; 𝑂Δ𝑢=pilot time spacing

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Cohere Technologies ~ Proprietary & Confidential 15

24 Antenna Ports (Ref Signals) - Delay Doppler Grid

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OTFS Antenna Port Multiplexing

Parameter LTE OTFS Type of Reference Signal CRS

𝑂 = 14, 𝑁 = 1 𝑂 = 14, 𝑁 = 1

# of antenna ports (AP) 4 20 88 Total Overhead (Overhead per AP) 14.3% (3.6% per AP) 7.1% (0.36% per AP) 7.1% (0.08% per AP) Supported Channel with no CSI Degradation ETU-200 ETU-200 ETU-50

  • Cohere claims OTFS can multiplex a large number of antenna

port reference signals in the Delay-Doppler domain

– Depends on maximum delay and Doppler spread

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Cohere Technologies ~ Proprietary & Confidential 17

Pilot Packing Summary

  • OTFS Delay-Doppler pilot architecture

significantly reduces pilot overhead

– Supports high Doppler

  • Flexible pilot tiling for different channel

conditions

  • Ideal for massive MIMO which requires large

number of pilots

  • Enables efficient channel prediction for

precoding

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Cohere Technologies ~ Proprietary & Confidential 18

OTFS PERFORMANCE

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Spectral Efficiency – TTI = 1ms MIMO Scalability

  • OTFS maintains Consistent Higher Capacity per Stream

Parameter Value SC spacing 15 KHz Number of subcarriers 600 Bandwidth 10 MHz Multipath model EVA, ETU Max Doppler 300 Hz Transmission Time Interval length 1 msec Transmission scheme 2x2, 4x4 MIMO-TM3 FEC Coding Turbo (LTE) Precoding TM3 for OFDM; identity for OTFS Channel estimation Ideal Equalization Genie aided MMSE-SIC & DFE

300 Hz Max Doppler

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Cohere Technologies ~ Proprietary & Confidential 20

High Mobility & Codeword Length Invariance

  • OTFS performance unaffected by codeword length
  • Performance gap increases with high Doppler
  • Performance improves with increased observation time
  • Performance gap increases with lower BLER

5 10 15 20 25 30

SNR (dB)

10-3 10-2 10-1 100

BLER EVA-200 , 1x1, LTE CQI 9 (16-QAM)

OTFS L=500, 1ms TTI OTFS L=1000 1ms TTI OTFS L=2000 1ms TTI OFDM L=500 1ms TTI OFDM L=1000 1ms TTI OFDM L=2000 1ms TTI OTFS L=500 5ms TTI OTFS L=1000 5ms TTI OTFS L=2000 5ms TTI OFDM L=500 5ms TTI OFDM L=1000 5ms TTI OFDM L=2000 5ms TTI

5 10 15 20 25 30

SNR (dB)

10-3 10-2 10-1 100

BLER EVA-600 , 1x1, LTE CQI 9 (16-QAM)

OTFS L=500, 1ms TTI OTFS L=1000 1ms TTI OTFS L=2000 1ms TTI OFDM L=500 1ms TTI OFDM L=1000 1ms TTI OFDM L=2000 1ms TTI OTFS L=500 5ms TTI OTFS L=1000 5ms TTI OTFS L=2000 5ms TTI OFDM L=500 5ms TTI OFDM L=1000 5ms TTI OFDM L=2000 5ms TTI

OTFS 5 msec OTFS 1 msec OFDM 600 Hz Doppler Spread 200 Hz Doppler Spread 16-QAM, SISO 10% 1%

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High Mobility & Codeword Length Invariance

15 20 25 30 35

SNR (dB)

10-3 10-2 10-1 100

BLER EVA-200 , 1x1, LTE CQI 13 (64-QAM)

OTFS L=500, 1ms TTI OTFS L=1000 1ms TTI OTFS L=2000 1ms TTI OFDM L=500 1ms TTI OFDM L=1000 1ms TTI OFDM L=2000 1ms TTI OTFS L=500 5ms TTI OTFS L=1000 5ms TTI OTFS L=2000 5ms TTI OFDM L=500 5ms TTI OFDM L=1000 5ms TTI OFDM L=2000 5ms TTI

15 20 25 30 35

SNR (dB)

10-3 10-2 10-1 100

BLER EVA-600 , 1x1, LTE CQI 13 (64-QAM)

OTFS L=500, 1ms TTI OTFS L=1000 1ms TTI OTFS L=2000 1ms TTI OFDM L=500 1ms TTI OFDM L=1000 1ms TTI OFDM L=2000 1ms TTI OTFS L=500 5ms TTI OTFS L=1000 5ms TTI OTFS L=2000 5ms TTI OFDM L=500 5ms TTI OFDM L=1000 5ms TTI OFDM L=2000 5ms TTI

64-QAM, SISO 10% 1%

  • High ICI accentuates performance gap
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1.2 dB 2.6 dB

Low vs Medium Spatial correlation – 16QAM

  • Performance gap increases with medium correlated channels
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Cohere Technologies ~ Proprietary & Confidential 23

Low vs Medium Spatial correlation – 64QAM

2.8 dB 4.5 dB

  • Performance gap increases with medium correlated channels
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Ultra High Mobility – OTFS-Turbo vs OFDM-LMMSE

  • 16-QAM, R=2/3
  • Doppler = 444 Hz and 1820 Hz (ICI dominated regime)

10 12 14 16 18 20 22

SNR (dB)

10-4 10-3 10-2 10-1 100

BLER EVA-444, 1#1

OTFS-Turbo16-QAM, R=2/3 OFDM-LMMSE16-QAM, R=2/3

1.4 dB 5.9 dB

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Cohere Technologies ~ Proprietary & Confidential 25

Ultra High Mobility – OTFS-Turbo vs OFDM-LMMSE

  • 16-QAM, R=3/4
  • Doppler = 444 Hz and 1820 Hz

10 12 14 16 18 20 22 24 26 28 30

SNR (dB)

10-2 10-1 100

BLER EVA-444, 1#1

OTFS-Turbo16-QAM, R=3/4 OFDM-LMMSE16-QAM, R=3/4

2.2 dB

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Cohere Technologies ~ Proprietary & Confidential 26

Summary

  • OTFS is a novel 2D modulation scheme

– QAM symbols and reference signals carried in the Delay- Doppler domain – Wide frequency and observation time exploits full diversity of the channel – All QAM symbols experience the same channel

  • Spectral efficiency advantages in high-order MIMO, low

& medium correlation and high Doppler scenarios as well as small packets and high code rate

  • Increased density & flexibility in reference signal

multiplexing

  • Opportunities for new areas of research, building on

OTFS modulation concepts and receiver architectures

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Cohere Technologies ~ Proprietary & Confidential 27

THANK YOU