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
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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
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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
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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
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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
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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
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
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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
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
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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
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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
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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
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
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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
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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
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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
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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])