Single Carrier FDMA

May 18, 2008 Hyung G. Myung ([email protected])

Outline Introduction and Background Overview of SC-FDMA SC-FDMA Implementation in 3GPP LTE Peak Power Characteristics of SC-FDMA Signals Uplink Resource Scheduling in SC-FDMA Systems Summary and Conclusions Single Carrier FDMA | Hyung G. Myung

1

Introduction and Background Overview of SC-FDMA SC-FDMA Implementation in 3GPP LTE Peak Power Characteristics of SC-FDMA Signals Uplink Resource Scheduling in SC-FDMA Systems Summary and Conclusions

Introduction and Background

3GPP Evolution LTE HSPA+ HSUPA HSDPA

R8

R7

R6

R5

UMTS/WCDMA R99 Single Carrier FDMA | Hyung G. Myung

3

Introduction and Background

Key Features of LTE • Multiple access scheme – DL: OFDMA with CP. – UL: Single Carrier FDMA (SC-FDMA) with CP.

• Adaptive modulation and coding – DL modulations: QPSK, 16QAM, and 64QAM – UL modulations: QPSK and 16QAM – Rel-6 Turbo code: Coding rate of 1/3, two 8-state constituent encoders, and a contention-free internal interleaver.

• Advanced MIMO spatial multiplexing techniques – (2 or 4)x(2 or 4) downlink and uplink supported. • Multi-layer transmission with up to four streams.

– Multi-user MIMO also supported.

• ARQ within RLC sublayer and Hybrid ARQ within MAC sublayer. Single Carrier FDMA | Hyung G. Myung

4

Introduction and Background

Broadband Multipath Channel •

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

Standard GSM

Transmission bandwidth 200 kHz

2G IS-95 (CDMA)

1.25 MHz

WCDMA

5 MHz

cdma2000

5 MHz

3G 3.5~4G

LTE, UMB, WiMAX

Up to 20 MHz

Single Carrier FDMA | Hyung G. Myung

5

Introduction and Background

Broadband Multipath Channel

- cont.

• Multi-path channel causes: – Inter-symbol interference (ISI) and fading in the time domain. – Frequency-selectivity in the frequency domain. 3GPP 6-Tap Typical Urban (TU6) Channel Delay Profile

Frequency Response of 3GPP TU6 Channel in 5MHz Band 2.5

1 2

Channel Gain [linear]

Amplitude [linear]

0.8

0.6

0.4

1

0.5

0.2

0

1.5

0

1

2

3 Time [µsec]

4

5

6

0

0

1

2 3 Frequency [MHz]

4

5

Single Carrier FDMA | Hyung G. Myung

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Introduction and Background

Frequency Domain Equalization • 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.

Single Carrier FDMA | Hyung G. Myung

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Introduction and Background

FDE

- cont.

Time domain

∴ x = h −1 * y

Channel

x

h

y = h∗ x Fourier transform

y

Y =H⋅X Frequency domain

−1

∴ X = H ⋅Y

Single Carrier FDMA | Hyung G. Myung

8

Introduction and Background

FDE

- cont.

• 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.

CP

Symbols

Single Carrier FDMA | Hyung G. Myung

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Introduction and Background

FDE

- cont.

• Most of the time domain equalization techniques can be implemented in the frequency domain. – MMSE equalizer, DFE, turbo equalizer, and so on.

• References – M. 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

Single Carrier FDMA | Hyung G. Myung

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Introduction and Background

Single Carrier with FDE

SC/FDE

{ xn }

Add CP/ PS

Channel

Remove CP

Npoint DFT

Equalization

Add CP/ PS

Channel

Remove CP

Npoint DFT

Equalization

Npoint IDFT

Detect

OFDM

{ xn }

Npoint IDFT

Detect

* CP: Cyclic Prefix, PS: Pulse Shaping Single Carrier FDMA | Hyung G. Myung

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Introduction and Background

SC/FDE

- cont.

•

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.

Single Carrier FDMA | Hyung G. Myung

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Introduction and Background

SC/FDE

•

- cont.

References – H. Sari et al., “Transmission Techniques for Digital Terrestrial TV Broadcasting,” IEEE Commun. Mag., vol. 33, no. 2, Feb. 1995, pp. 100-109. – D. Falconer et al., “Frequency Domain Equalization for SingleCarrier Broadband Wireless Systems,” IEEE Commun. Mag., vol. 40, no. 4, Apr. 2002, pp. 58-66.

•

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

Single Carrier FDMA | Hyung G. Myung

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Introduction and Background

CDMA with FDE • Instead of a RAKE receiver, use frequency domain equalization for channel equalization. • Reference – F. Adachi et al., “Broadband CDMA Techniques,” IEEE Wireless Comm., vol. 12, no. 2, Apr. 2005, pp. 8-18.

{ xn }

Spreading

Add CP/ PS

Channel

Remove CP

Mpoint DFT

Equalization

Mpoint IDFT

Despreading

Detect

Single Carrier FDMA | Hyung G. Myung

14

Introduction and Background

Overview of SC-FDMA SC-FDMA Implementation in 3GPP LTE Peak Power Characteristics of SC-FDMA Signals Uplink Resource Scheduling in SC-FDMA Systems Summary and Conclusions

Overview of SC-FDMA

Single Carrier FDMA

•

SC-FDMA is a new multiple access technique. – Utilizes single carrier modulation, DFT-spread orthogonal frequency multiplexing, and frequency domain equalization.

•

It has similar structure and performance to OFDMA.

•

SC-FDMA is currently adopted as the uplink multiple access scheme in 3GPP LTE. – A variant of SC-FDMA using code spreading is used in 3GPP2 UMB uplink. – 802.16m also considering it for uplink.

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

Npoint DFT

Subcarrier Mapping

Mpoint IDFT

P-to-S

S-to-P

TX & RX Structure of SCSC-FDMA

Add CP / PS

DAC / RF

*N
Npoint IDFT

Subcarrier De-mapping/ Equalization

Mpoint DFT

SC-FDMA:

S-to-P

Detect

P-to-S

Channel

Remove CP

RF / ADC

+

OFDMA: Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

Why “Single Single Carrier” FDMA”? Carrier “FDMA FDMA ? “Single Carrier”

Frequency domain Npoint DFT

Subcarrier Mapping

Time domain Mpoint IDFT

P-to-S

Time domain

: Sequential transmission of the symbols over a single frequency carrier.

Add CP / PS

DAC / RF

“FDMA” : User multiplexing in the frequency domain. Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

Subcarrier Mapping • Two ways to map subcarriers; distributed and localized. • Distributed mapping scheme for (total # of subcarriers) = (data block size) × (bandwidth spreading factor) is called Interleaved FDMA (IFDMA). Xɶ 0

X0 Zeros

Zeros

Xɶ 0

X0 X1

X1 Zeros

X2

X N −1 X N −1

Zeros Zeros

Distributed

Xɶ M −1

Xɶ M −1

Localized Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

Subcarrier Mapping •

- cont.

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

Terminal 1 Terminal 2 Terminal 3

subcarriers

Distributed Mode

subcarriers

Localized Mode

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

Subcarrier Mapping

{

{ xn } :

x0

x1

x2

{X k } :

X0

X1

X2

X3

X0

0

0

X1

0

0

X2

0

0

X3

0

0

X0

0

X1

0

X2

0

X3

0

0

0

0

0

~ X l , IFDMA

{X~ ~ {X

- cont.

}

l , DFDMA

l , LFDMA

} }

X0

X1

X2

x3

2π N −1 − j nk  DFT  X k = ∑ xn e N n =0 

X3

0

0

0

0

0

0

 , N = 4 

0

0

Current implementation in 3GPP LTE

frequency Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

Time Domain Representation { xn }

x0

x1

x2

x3

{Q ⋅ xɶ

}

x0 x1

x2 x3 x0 x1 x2 x3 x0 x1 x2 x3

{Q ⋅ xɶ

m , LFDMA

}

x0

*

* x1 *

* x2 *

* x3 *

*

{Q ⋅ xɶ

m , DFDMA

}

x0

*

* x2 *

* x0 *

* x2 *

*

m, IFDMA

time

3

* = ∑ ck ,m ⋅ xk k =0

, ck ,m : complex weight Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

Amplitude of SCSC-FDMA Symbols 0.5 IFDMA LFDMA DFDMA

Amplitude [linear]

0.4

0.3

0.2

0.1

QPSK 0

10

20

30 Symbol

40

50

60

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

SCSC-FDMA and OFDMA

•

Similarities – – – –

Block-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.

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

SCSC-FDMA and OFDMA

- cont.

• Difference in time domain signal

Input data symbols OFDMA symbol SC-FDMA symbols* time * Bandwidth spreading factor : 4

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

SCSC-FDMA and OFDMA •

- cont.

Different equalization/detection aspects

OFDMA

SC-FDMA

DFT

DFT

Subcarrier Demapping

Subcarrier Demapping

Equalizer

Detect

Equalizer

Detect

Equalizer

Detect

Equalizer

IDFT

Detect

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

SCSC-FDMA and DSDS-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.

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

SCSC-FDMA and DSDS-CDMA

- cont.

• Conventional spreading

x0

x1

x2

×

Data Sequence

1

1

1

x3

1

1

1

1

1

1

1

1

1

1

1

1

1

Signature Sequence

x0 x0

x0 x0 x1 x1

x1 x1 x2 x2 x2 x2 x3 x3 x3 x3 time

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

SCSC-FDMA and DSDS-CDMA

- cont.

• Exchanged spreading

1

1

Signature Sequence

x0 x1

1

1

×

x2 x3 x0 x1 x2 x3 x0 x1 x2 x3 x0 x1 x2 x3

Data Sequence

x0 x1

IFDMA

x2 x3 x0 x1 x2 x3 x0 x1 x2 x3 x0 x1 x2 x3 time

*C. Chang, and K. Chen, “Frequency-Domain Approach to Multiuser Detection over Frequency-Selective Slowly Fading Channels,” IEEE PIMRC 2002, Lisboa, Portugal, Sep., 2002, pp. 1280-1284 Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

SCSC-FDMA and Other Schemes * Subcarrier mapping: Frequency-selective scheduling

* SC transmission: Low PAPR

SC-FDMA

* Time-compressed “chip” symbols * Time-domain detection

* DFT-based FDE * Block-based processing & CP

OFDMA

DS-CDMA /FDE

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

SCSC-FDMA with Code Spreading

Npoint DFT

Spreading

Subcarrier Mapping

Mpoint IDFT

SC-FDMA Modulation

Add CP/ PS

Channel

Remove CP

SC-FDMA Demodulation

Mpoint DFT

Subcarrier Demapping/ Equalization

Despreading

Detect

Npoint IDFT

Single Carrier FDMA | Hyung G. Myung

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Overview of SC-FDMA

N-point DFT

N-point DFT

Spatial Mapping

SCSC-FDMA MIMO Subcarrier Mapping

M-point IDFT

Add CP / PS

DAC / RF

Subcarrier Mapping

M-point IDFT

Add CP / PS

DAC / RF

Detect

N-point IDFT

Detect

N-point IDFT

Spatial Combining / Equalization

MIMO Channel

Subcarrier De-mapping

M-point DFT

Remove CP

RF / ADC

Subcarrier De-mapping

M-point DFT

Remove CP

RF / ADC

Single Carrier FDMA | Hyung G. Myung

32

Introduction and Background Overview of SC-FDMA

SC-FDMA Implementation in 3GPP LTE Peak Power Characteristics of SC-FDMA Signals Uplink Resource Scheduling in SC-FDMA Systems Summary and Conclusions

SC-FDMA Implementation in 3GPP LTE

LTE Frame Structure

• Two radio frame structures defined. – Frame structure type 1 (FS1): FDD. – Frame structure type 2 (FS2): TDD.

• A radio frame has duration of 10 ms. • A resource block (RB) spans 12 subcarriers over a slot duration of 0.5 ms. One subcarrier has bandwidth of 15 kHz, thus 180 kHz per RB.

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

LTE Frame Structure Type 1 • FDD frame structure

One radio frame = 10 ms One slot = 0.5 ms #0

#1

#2

#3

#18

#19

One subframe = TTI (Transmission Time Interval)

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

LTE Frame Structure Type 2 • TDD frame structure

One radio frame = 10 ms One half-frame = 5 ms One subframe = 1 ms One slot = 0.5 ms Subframe #0

DwPTS

Subframe #2 Subframe #3 Subframe #4 Subframe #5

GP

UpPTS

Subframe #7 Subframe #8 Subframe #9

DwPTS

GP

UpPTS

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

LTE Resource Grid One radio frame Slot #0

#19

N symb

Resource block Subcarrier (frequency)

= N symb × N scRB resource elements

N RB × N scRB

N scRB

Resource element

= 12

OFDM/SC-FDMA symbol (time) Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

Length of CP

Configuration

Nsymb

Normal CP

7

Extended CP

6

Extended CP (∆f = 7.5 kHz)†

3

Configuration

CP length NCP,l [samples]

Normal CP

160 (≈ 5.21 µs) for l = 0 144 (≈ 4.69 µs) for l = 1, 2, …, 6

Extended CP

512 (≈ 16.67 µs) for l = 0, 1, …, 5

Extended CP (∆f = 7.5 kHz) †

1024 (≈ 33.33 µs) for l = 0, 1, 2 † Only in downlink

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

LTE Bandwidth/Resource Configuration Channel bandwidth [MHz]

1.4

3

5

10

15

20

Number of resource blocks (NRB)

6

15

25

50

75

100

Number of occupied subcarriers

72

180

300

600

900

1200

IDFT(Tx)/DFT(Rx) size

128

256

512

1024

1536

2048

Sample rate [MHz]

1.92

3.84

7.68

15.36

23.04

30.72

Samples per slot

960

1920

3840

7680

11520

15360 *3GPP TS 36.104

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

LTE Bandwidth Configuration 1 slot Zeros DL or UL symbol

frequency

Resource block

N scRB

N RB × N scRB

= 12

= 300

(180 kHz)

(4.5 MHz)

Zeros time

M = 512 (7.68 MHz)

* 5 MHz system with frame structure type 1

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

UL Overview • UL physical channels – Physical Uplink Shared Channel (PUSCH) – Physical Uplink Control Channel (PUCCH) – Physical Random Access Channel (PRACH)

• UL physical signals – Reference signal (RS)

• Available modulation for data channel – QPSK, 16-QAM, and 64-QAM

• Single user MIMO not supported in current release. – But it will be addressed in the future release. – Multi-user collaborative MIMO supported.

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

UL Resource Block *PUSCH with normal CP

Reference symbols (RS)

Subcarrier

Frequency

Resource block (RB)

1 slot (0.5 ms)

One SC-FDMA symbol

Time Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

UL Physical Channel Processing

Scrambling

Modulation mapping

Transform precoding SC-FDMA modulation

DFT-precoding

Resource element mapping

SC-FDMA signal generation

IDFT operation

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

SCSC-FDMA Modulation in LTE UL

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

NDFT

Zeros

MIDFT

Parallel -toSerial

{ xɶ0 , xɶ1 … , xɶM −1} One SC-FDMA symbol

0

{ x0 , x1 … , xN −1}

SerialtoParallel

subcarrier

Zeros

M-1

Subcarrier Mapping

Single Carrier FDMA | Hyung G. Myung

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SC-FDMA Implementation in 3GPP LTE

UL Reference Signal • Two types of UL RS – Demodulation (DM) RS ⇒ Narrowband. – Sounding RS: Used for UL resource scheduling ⇒ Broadband.

• RS based on Zadoff-Chu CAZAC (Constant Amplitude Zero Auto-Correlation) polyphase sequence – CAZAC sequence: Constant amplitude, zero circular autocorrelation, flat frequency response, and low circular crosscorrelation between two different sequences.

 − j 2π r  k 2 +qk  ,  e L 2  ak =  r  k ( k +1)  π − j + qk  2   L 2  e 

k =0,1,2,⋯, L −1; for L even

* r is any integer relatively prime with L and q is any integer.

, k = 0,1,2,⋯, L −1; for L odd

B. M. Popovic, “Generalized Chirp-like Polyphase Sequences with Optimal Correlation Properties,” IEEE Trans. Info. Theory, vol. 38, Jul. 1992, pp. 1406-1409. Single Carrier FDMA | Hyung G. Myung

45

SC-FDMA Implementation in 3GPP LTE

UL RS Multiplexing

User 1 User 2 User 3 subcarriers FDM Pilots

subcarriers CDM Pilots

Single Carrier FDMA | Hyung G. Myung

46

SC-FDMA Implementation in 3GPP LTE

UL RS Multiplexing

- cont.

• DM RS – For SIMO: FDM between different users. – For SU-MIMO: CDM between RS from each antenna – For MU-MIMO: CDM between RS from each antenna

• Sounding RS – CDM when there is only one sounding bandwidth. – CDM/FDM when there are multiple sounding bandwidths.

Single Carrier FDMA | Hyung G. Myung

47

Introduction and Background Overview of SC-FDMA SC-FDMA Implementation in 3GPP LTE

Peak Power Characteristics of SC-FDMA Signals Uplink Resource Scheduling in SC-FDMA Systems Summary and Conclusions

Peak Power Characteristics of SC-FDMA Signals

PAPR Characteristics CCDF of PAPR: QPSK, Rolloff = 0.22, N = 512, N fft

0

occupied

= 128

CCDF of PAPR: 16-QAM, Rolloff = 0.22, N = 512, N fft

0

10

OFDMA

-1

-1

-2

10

Pr(PAPR>PAPR0)

10 Pr(PAPR>PAPR0)

= 128

10 OFDMA

IFDMA DFDMA

-3

10

-4

10

occupied

0

Dotted lines: no PS Dashed lines: RRC PS LFDMA Solid lines: RC PS 2

4

6 PAPR [dB]

10

-2

10

DFDMA

10

12

0

(a) QPSK

* Monte Carlo simulations (Number of iterations: > 104) * Time domain pulse shaping with 8-times oversampling * Nfft: number of total subcarriers = FFT size * Noccupied: number of occupied subcarriers = data block size * RC: raised-cosine, RRC: root raised-cosine * Rolloff factor of 0.22

LFDMA

-3

10

-4

8

IFDMA

10

0

Dotted lines: no PS Dashed lines: RRC PS Solid lines: RC PS 2

4

6 PAPR [dB]

8

10

12

0

(b) 16-QAM

*H. G. Myung, J. Lim, and D. J. Goodman, "Peak-toAverage Power Ratio of Single Carrier FDMA Signals with Pulse Shaping," IEEE PIMRC ’06, Helsinki, Finland, Sep. 2006

Single Carrier FDMA | Hyung G. Myung

49

Peak Power Characteristics of SC-FDMA Signals

PAPR Characteristics

- cont.

• PAPR and different rolloff factors CCDF of PAPR: QPSK, N = 256, N fft

0

occupied

= 64

10

IFDMA

LFDMA

-1

0

Pr(PAPR>PAPR )

10

-2

10

α=1 α=0.8

-3

10

-4

10

0

α=0.2

α=0.6

α=0.4

α=0

Solid lines: without pulse shaping Dotted lines: with pulse shaping 2

4 6 PAPR [dB] 0

*α: rolloff factor of raised cosine pulse shaping filter

8

10

*H. G. Myung, J. Lim, and D. J. Goodman, "Peak-toAverage Power Ratio of Single Carrier FDMA Signals with Pulse Shaping," IEEE PIMRC ’06, Helsinki, Finland, Sep. 2006 Single Carrier FDMA | Hyung G. Myung

50

Peak Power Characteristics of SC-FDMA Signals

PAPR of SCSC-FDMA MIMO 10

-1

TxBF (no avr. & no quant.)

SM

0

Pr(PAPR>PAPR )

10

0

10

-2

SFBC (QPSK) SFBC (16-QAM)

10

10

-3

-4

4

TxBF (avr. & quant.)

6

8 PAPR [dB]

10

12

0

*H. G. Myung, J.-L. Pan, R. Olesen, and D. Grieco, "Peak Power Characteristics of Single Carrier FDMA MIMO Precoding System", IEEE VTC 2007 Fall, Baltimore, USA, Oct. 2007 Single Carrier FDMA | Hyung G. Myung

51

Introduction and Background Overview of SC-FDMA SC-FDMA Implementation in 3GPP LTE Peak Power Characteristics of SC-FDMA Signals

Uplink Resource Scheduling in SC-FDMA Systems Summary and Conclusions

Uplink Resource Scheduling in SC-FDMA Systems

ChannelChannel-Dependent Scheduling (CDS) Channel gain

• Channel-dependent scheduling

User 2

– Assign subcarriers to a user in excellent channel condition.

User 1

• Two subcarrier mapping schemes have advantages over each other.

Frequency

– Distributed: Frequency diversity. – Localized: Frequency selective gain with CDS. Subcarriers

Single Carrier FDMA | Hyung G. Myung

53

Uplink Resource Scheduling in SC-FDMA Systems

CDS

- cont. Utility: sum of user throughput

Utility: sum of logarithm of user throughput

45

35 30 25 20 15 10 5 4 8 16

R-LFDMA S-LFDMA R-IFDMA S-IFDMA

40 Agg regate throughput [Mbps]

Aggre gate thr oughput [Mbps]

40

45

R-LFDMA S-LFDMA R-IFDMA S-IFDMA

35 30 25 20 15 10

32

64 Number of users

128

5 4 8 16

32

64 Number of users

128

*J. Lim, H. G. Myung, K. Oh, and D. J. Goodman, "Proportional Fair Scheduling of Uplink Single-Carrier FDMA Systems", IEEE PIMRC 2006, Helsinki, Finland, Sep. 2006

* Capacity based on Shannon’s upper bound. * Time synchronized uplink data transmission. * Perfect channel knowledge. * No feedback delay or error. Single Carrier FDMA | Hyung G. Myung

54

Uplink Resource Scheduling in SC-FDMA Systems

Uplink SCSC-FDMA with Adaptive Modulation and CDS Mobile terminals

Base station

User K

Channel K

DFT

Subcarrier Mapping

ConstellationM apping

User 2 User 1 Channel 2 IDFT

CP / PS

Channel 1

SC-FDMA Receiver

Resource Scheduler Data flow Control signal flow Single Carrier FDMA | Hyung G. Myung

55

Uplink Resource Scheduling in SC-FDMA Systems

Simulation Results • Aggregate throughput vs. feedback delay mobile speed = 3 km/h (f = 5.6 Hz)

mobile speed = 60 km/h (f = 111 Hz)

D

D

18 LFDMA: Static LFDMA: CDS IFDMA: Static IFDMA: CDS

16 14 12

Aggr egate throughput [Mb ps]

Agg regate throughpu t [Mbps]

18

10 8 6 4 2 0

1

2 3 Feedback delay [ms]

4

5

LFDMA: Static LFDMA: CDS IFDMA: Static IFDMA: CDS

16 14 12 10 8 6 4 2 0

1

2 3 Feedback delay [ms]

4

5

* Carrier frequency = 2 GHz * K = 64 total number of users, N = 16 subcarriers per chunk, Q = 16 total number of chunks * Utility: sum of user throughput

*H. G. Myung, K. Oh, J. Lim, and D. J. Goodman, "ChannelDependent Scheduling of an Uplink SC-FDMA System with Imperfect Channel Information," IEEE WCNC 2008, Las Vegas, USA, Mar. 2008 Single Carrier FDMA | Hyung G. Myung

56

Uplink Resource Scheduling in SC-FDMA Systems

Simulation Results

- cont.

• Aggregate throughput vs. mobile speed Feedback delay = 3 ms 18

Aggregate throughput [Mbps]

16 14

LFDMA: Static LFDMA: CDS IFDMA: Static IFDMA: CDS

12 10 8 6 4 2 0

20 (37) 40 (74) 60 (111) Mobile speed [km/h] (Doppler [Hz])

80 (148)

*H. G. Myung, K. Oh, J. Lim, and D. J. Goodman, "Channel-Dependent Scheduling of an Uplink SC-FDMA System with Imperfect Channel Information," IEEE WCNC 2008, Las Vegas, USA, Mar. 2008. Single Carrier FDMA | Hyung G. Myung

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Introduction and Background Overview of SC-FDMA SC-FDMA Implementation in 3GPP LTE Peak Power Characteristics of SC-FDMA Signals Uplink Resource Scheduling in SC-FDMA Systems

Summary and Conclusions

Summary and Conclusions

Summary and Conclusions • SC-FDMA is a new single carrier multiple access technique which has similar structure and performance to OFDMA. – Currently adopted for uplink multiple access scheme for 3GPP LTE.

• Two types of subcarrier mapping, distributed and localized, give system design flexibility to accommodate either frequency diversity or frequency selective gain. • A salient advantage of SC-FDMA over OFDM/OFDMA is low PAPR. – Efficient transmitter and improved cell-edge performance.

• Pulse shaping as well as subcarrier mapping scheme has a significant impact on PAPR. Single Carrier FDMA | Hyung G. Myung

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Summary and Conclusions

References and Resources

• H. G. Myung, J. Lim, & D. J. Goodman, “Single Carrier FDMA for Uplink Wireless Transmission,” IEEE Vehic. Tech. Mag., vol. 1, no. 3, Sep. 2006 • H. Ekström et al., “Technical Solutions for the 3G Long-Term Evolution,” IEEE Commun. Mag., vol. 44, no. 3, Mar. 2006 • D. Falconer et al., “Frequency Domain Equalization for SingleCarrier Broadband Wireless Systems,” IEEE Commun. Mag., vol. 40, no. 4, Apr. 2002 • H. Sari et al., “Transmission Techniques for Digital Terrestrial TV Broadcasting,” IEEE Commun. Mag., vol. 33, no. 2, Feb. 1995

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Summary and Conclusions

References and Resources

- cont.

• LTE Spec – http://www.3gpp.org/ftp/Specs/html-info/36-series.htm

• SC-FDMA resource page – http://hgmyung.googlepages.com/scfdma

• Comprehensive list of SC-FDMA papers – http://hgmyung.googlepages.com/scfdma2

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Summary and Conclusions

Final Word

SC-FDMA




Low PAPR

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Thank you!

May 18, 2008 Hyung G. Myung ([email protected])