Researches in Broadband Single Carrier Multiple Access Techniques

Workshop on Fundamentals of Wireless Signal Processing for Wireless SystemsTohoku University, Sendai, 2016.02.27Dr. Hyung G. Myung, Qualcomm

Outline

1

Introduction

Summary and References

Single Carrier FDMA

Frequency Domain Equalization

2

Prof. Adachi Prof. David Goodman

NTT DOCOMO AT&T Bell Labs

Tohoku U. Polytechnic U.

WICAT Workshop on SC-FDMA

12 oral presentations4 IEEE Fellows including prof. Adachi (keynote speaker)

3

Outline

4

Introduction

Summary and References

Single Carrier FDMA

Frequency Domain Equalization

Number of Mobile Users

5

0

1

2

3

4

5

6

7

8

1980 1985 1990 1995 2000 2005 2010 2015

Global Mobile Subscribers (billions)

Evolution of Mobile Traffic

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Voice DataMultimedia

Data

Mobile Data Increase

7

Fundamental Constraints

Shannon’s capacity upper bound

8

Signalquality

Channelbandwidth

𝐶 = min(𝑁𝑇 , 𝑁𝑅) ∙ 𝐵𝑊 ∙ log2 1 +𝑆

𝑁

Spatialmultiplexing

Wider Bandwidth

Demand for higher data rate is leading to utilization of wider transmission bandwidth.

9

GSM IS-95 UMTS/WCDMA LTE LTE-Advanced

200 kHz 1.25 MHz5 MHz

20 MHz

100 MHz

Wireless Channel

Wireless channel experiences multi-path radio propagation.

10

Multi-Path Channel

Multi-path channel causes:Inter-symbol interference (ISI) and fading in the time domain.

Frequency-selectivity in the frequency domain.

11

0 1 2 3 4 5 60

0.2

0.4

0.6

0.8

1

Time [sec]

Am

plit

ude [

linear]

3GPP 6-Tap Typical Urban (TU6) Channel Delay Profile

0 1 2 3 4 50

0.5

1

1.5

2

2.5

Frequency [MHz]

Channel G

ain

[lin

ear]

Frequency Response of 3GPP TU6 Channel in 5MHz Band

Multi-Path Channel

For broadband wireless channel, ISI and frequency-selectivity become severe.

To resolve the ISI and the frequency-selectivity in the channel, various measures are used.

Channel equalization in the time domain or frequency domain

Multi-carrier multiplexing

Orthogonal Frequency Division Multiplexing (OFDM)

Frequency hopping

Channel-adaptive scheduling

Channel coding

Automatic repeat request (ARQ) and hybrid ARQ (H-ARQ)

12

- cont.

Orthogonal Frequency Division Multiplexing

Orthogonal Frequency Division Multiplexing (OFDM)Divide the broadband channel into much smaller subcarriers. Flat-fading on each subcarrier.

Transmit data in parallel using orthogonal subcarriers.

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Frequency

Channel response

Subcarrier

OFDM

Design issues of OFDMCyclic prefix (CP): To maintain orthogonality among subcarriers in the presence of multi-path channel, CP longer than the channel impulse response is needed. Also CP converts linear convolution of the channel impulse response into a circular one.

High peak-to-average power ratio (PAPR): Since the transmit signal is a composition of multiple subcarriers, high peaks occur.

Carrier frequency offset: Frequency offset breaks the orthogonalityand causes inter-carrier interference.

Adaptive scheme or channel coding is needed to overcome the spectral null in the channel.

14

- cont.

Outline

15

Introduction

Summary and References

Single Carrier FDMA

Frequency Domain Equalization

Frequency Domain Equaliztion

16

hx y

1 *

y h x

x h y

1

Y H X

X H Y

Time domain

Frequency domain

Fourier

transform

Channel

FDE

For broadband multi-path channels, conventional time domain equalizers are impractical because of complexity.

Very long channel impulse response in the time domain.

Prohibitively large tap size for time domain filter.

Using discrete Fourier transform (DFT), equalization can be done in the frequency domain.

Because the DFT size does not grow linearly with the length of the channel response, the complexity of FDE is lower than that of the equivalent time domain equalizer for broadband channel.

17

- cont.

FDE

In DFT, frequency domain multiplication is equivalent to time domain circular convolution.

Cyclic prefix (CP) longer than the channel response length is needed to convert linear convolution to circular convolution.

Or, perform overlap-and-add at the receiver without using CP.K. Takeda, H. Tomeba & F. Adachi, "Iterative Overlap FDE for DS-CDMA without GI," IEEE VTC-2006 Fall, Montreal.

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CP Symbols

- cont.

FDEMost of the time domain equalization techniques can be implemented in the frequency domain.

MMSE equalizer, DFE, turbo equalizer, and so on.

ReferencesM. V. Clark, “Adaptive Frequency-Domain Equalization and Diversity Combining for Broadband Wireless Communications,” IEEE J. Sel. Areas Commun., vol. 16, no. 8, Oct. 1998

M. Tüchler et al., “Linear Time and Frequency Domain Turbo Equalization,” Proc. IEEE 53rd Veh. Technol. Conf. (VTC), vol. 2, May 2001

F. Pancaldi et al., “Block Channel Equalization in the Frequency Domain,” IEEE Trans. Commun., vol. 53, no. 3, Mar. 2005

F. Adachi et al., “Broadband CDMA Techniques,” IEEE Wireless Comm., vol. 12, no. 2, Apr. 2005

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- cont.

Single Carrier with FDE

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Channel

N-

point

IDFT

Equalization

N-

point

DFT

SC/FDE

OFDM

DetectRemove

CP nxAdd

CP/

PS

* CP: Cyclic Prefix, PS: Pulse Shaping

Channel Equalization

N-

point

DFT

DetectRemove

CP

N-

point

IDFT

Add

CP/

PS nx

SC/FDE

SC/FDE delivers performance similar to OFDM with essentially the same overall complexity, even for long channel delay.

SC/FDE has advantage over OFDM in terms of:Low PAPR.

Robustness to spectral null.

Less sensitivity to carrier frequency offset.

Disadvantage to OFDM is that channel-adaptive subcarrier bit and power loading is not possible.

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- cont.

Outline

22

Introduction

Summary and References

Single Carrier FDMA

Frequency Domain Equalization

Single Carrier FDMA

Single carrier FDMA (SC-FDMA) is an extension of SC/FDE to accommodate multiple-user access.

It has similar structure and performance to OFDMA.

SC-FDMA is currently adopted as the uplink multiple access scheme in 3GPP LTE.

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TX & RX structure of SC-FDMA

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Subcarrier

Mapping

Channel

N-

point

IDFT

Subcarrier

De-

mapping/

Equalization

M-

point

DFT

DetectRemove

CP

N-

point

DFT

M-

point

IDFT

Add

CP / PS

DAC

/ RF

RF

/ ADC

SC-FDMA:

OFDMA:

+* N < M

* S-to-P: Serial-to-Parallel

* P-to-S: Parallel-to-Serial

P-t

o-S

S-t

o-P

S-t

o-P

P-t

o-S

Why “Single Carrier” “FDMA”?

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Subcarrier

Mapping

N-

point

DFT

M-

point

IDFT

Add

CP / PS

DAC

/ RF

Time

domain

Frequency

domain

Time

domain

“FDMA”

“Single Carrier”

P-t

o-S

: Sequential transmission of the symbols

over a single frequency carrier.

: User multiplexing in the frequency domain.

Subcarrier Mapping

Data block size (N) = 4, Number of users (Q) = 3, Number of subcarriers (M) = 12.

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subcarriers

Terminal 1

Terminal 2

Terminal 3

subcarriers

Distributed Mode Localized Mode

IFDMA, Block-IFDMA LTE Uplink

SC-FDMA and OFDMA

SimilaritiesBlock-based modulation and use of CP.

Divides the transmission bandwidth into smaller subcarriers.

Channel inversion/equalization is done in the frequency domain.

SC-FDMA is regarded as DFT-precoded or DFT-spread OFDMA.

DissimilaritiesLower transmit peak power.

Equalization performance.

Multi-carrier MIMO receiver algorithm.

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SC-FDMA and DS-CDMA

In terms of bandwidth expansion, SC-FDMA is very similar to DS-CDMA system using orthogonal spreading codes.

Both spread narrowband data into broader band.

Time symbols are compressed into “chips” after modulation.

Spreading gain (processing gain) is achieved.

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SC-FDMA: Comparison

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SC-FDMA

OFDMADS-CDMA

/FDE* DFT-based FDE

* Block-based processing & CP

* SC transmission: Low PAPR

* Time-compressed “chip” symbols

* Time-domain detection

* Subcarrier mapping: Frequency-selective scheduling

SC-FDMA Modulation in LTE UL

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Serial-to-

Parallel

M-IDFT

N-DFT

Zeros

0 1 1, , Nx x x

Parallel-to-

Serial

0 1 1, , Mx x x

Subcarrier Mapping

sub

ca

rrie

r

0M

-1Zeros

One SC-FDMA

symbol

Localized mapping with an option of adaptive scheduling or random hopping.

LTE-Advanced: Carrier Aggregation

Uplink multiple access schemeClustered DFT spreading: N-times DFT-spread OFDM (per CC).

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20 MHz

100 MHzCarrier

Component(CC)

60 MHzNon-

contiguous

20 MHzR8 LTE

60 MHzContiguous

What’s Next for Single Carrier?

Ultra-wideband transmission5G expected to increase bandwidth up to 3~400 MHz

Single carrier transmission in mmWaveUltra-wideband transmission

Point-to-point transmission

RF contraints

Single carrier multiple access for Internet-of-Things (IoT)Narrowband opportunistic transmission

Low power operation

Different classes of latency requirement

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Outline

33

Introduction

Summary and References

Single Carrier FDMA

Frequency Domain Equalization

Summary

Using DFT-precoding and frequency domain equalization, single carrier transmission can be as effective as multi-carrier transmission for broadband channels.

Salient feature of single carrier is low peak transmit power.Well-suited for uplink or power-constraint transmission.

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References

Frequency domain equalizationH. Sari et al., “Transmission Techniques for Digital Terrestrial TV Broadcasting,” IEEE Commun. Mag., vol. 33, no. 2, Feb. 1995.D. Falconer et al., “Frequency Domain Equalization for Single-CarrierBroadband Wireless Systems,” IEEE Commun. Mag., vol. 40, no. 4, Apr. 2002.F. Adachi et al., “Broadband CDMA Techniques,” IEEE Wireless Comm., vol. 12, no. 2, Apr. 2005.

IFDMAT. Frank et al., "IFDMA: A Scheme Combining the Advantages of OFDMA and CDMA," IEEE Wireless Commun., vol.14, no.3, June 2007.

SC-FDMAH. G. Myung et al., “Single Carrier FDMA for Uplink Wireless Transmission,” IEEE Vehicular Technology Mag., vol. 1, no. 3, Sep. 2006.H. G. Myung & D. Goodman, Single Carrier FDMA: A New Air Interface forLong Term Evolution, John Wiley & Sons, Nov. 2008.

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Congratulations! Thank you!

Workshop on Fundamentals of Wireless Signal Processing for Wireless SystemsTohoku University, Sendai, 2016.02.27Dr. Hyung G. Myung, Qualcomm