SC-FDMA and LTE Uplink Physical Layer Design · SC-FDMA and LTE Uplink Physical Layer Design...
-
Upload
truonghanh -
Category
Documents
-
view
239 -
download
4
Transcript of SC-FDMA and LTE Uplink Physical Layer Design · SC-FDMA and LTE Uplink Physical Layer Design...
SC-FDMA and LTE Uplink Physical Layer DesignSC-FDMA and LTE Uplink Physical Layer Design
Seminar LTE: Der Mobilfunk der ZukunftSeminar LTE: Der Mobilfunk der Zukunft
Burcu Hanta
University Erlangen-Nürnberg
Chair of Mobile Communications
November 18, 2009
OutlineOutline
1 Introduction
Structure of SC-FDMA vs. OFDMA
Why SC-FDMA?
2 Uplink Time and Frequency Structure
3 Uplink Physical Channel
4 SC-FDMA Transmission
Localized and Distributed Mode
Comparison Criteria for Different Carrier Modes
Transmitter Structure
Receiver Structure
5 Conclusion
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design1 /331 /33
IntroductionIntroduction
IntroductionIntroduction
Remark on Orthogonal Frequency Division Multiple Access
(OFDMA):
A multiple access scheme which provides multiple
channels for different users
Used in many applications including the downlink of LTE.
Robust to time delays especially in multiple fading
channels
If orthogonality of subcarriers cannot be ensured, high
performance degradation is observed.
Important problem: Peak-to-average power ratio (PAPR)
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design2 /332 /33
IntroductionIntroduction
Peak-to-Average Power Ratio Problem in OFDMAPeak-to-Average Power Ratio Problem in OFDMA
PAPR =Ppeak
Pavg(1)
The OFDM transmitter performs a linear transform over a
large number of i.i.d. QAM-modulated complex symbols.
The time domain OFDM symbol can be approximated as a
Gaussian waveform from the central limit theorem [1].
⇒High PAPR in the OFDM signal.
High PAPR causes:
Either non-linear operation or high power consumption in
power amplifiers due to clipping.
A brand new system is introduced for the uplink: Single
Carrier FDMA.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design3 /333 /33
IntroductionIntroduction Structure of SC-FDMA vs. OFDMAStructure of SC-FDMA vs. OFDMA
Structure of SC-FDMA vs. OFDMAStructure of SC-FDMA vs. OFDMA
�����
������� �����!�"#$��������%�������&
��'��!!�!(����&
�������
��'��!!�!���
�����&�����������
��������
������������
��
������ ���
{ }nx�����������
�������
�������
�
Figure: Transmitter and receiver structure of OFDMA [2].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design4 /334 /33
IntroductionIntroduction Structure of SC-FDMA vs. OFDMAStructure of SC-FDMA vs. OFDMA
Structure of SC-FDMA vs. OFDMAStructure of SC-FDMA vs. OFDMA
��'��!!�!(����&
�������
������ ���
��'��!!�!���
�����&�����������
��������
��������������
���������
������ ���
{ }nx�����������
�������
�������
�������
{ }
{ }kX{ }mx�
{ }lX�
�
Figure: Transmitter and receiver structure of SC-FDMA [2].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design4 /334 /33
IntroductionIntroduction Why SC-FDMA?Why SC-FDMA?
Why SC-FDMA?Why SC-FDMA?
The subcarriers are transmitted sequentially instead of in
parallel as in OFDM.
⇒ The transmitted waveform is no longer a Gaussian
waveform which is probable to have high peak variations.
This helps to reduce the PAPR.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design5 /335 /33
Uplink Time and Frequency StructureUplink Time and Frequency Structure
SC-FDMA Frame StructureSC-FDMA Frame Structure
<���#���� ����������� �� ��� �����3�!
=7 =0 =' =� =0> =0?
<��!���7����
<���" ������07��
Figure: Type 1 Frame structure [3].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design6 /336 /33
Uplink Time and Frequency StructureUplink Time and Frequency Structure
Resource GridResource Grid
�!��=7 =0?
<���" �����
��#��
��
����
.��
�&
<A;):��8A;)��&�#�!�� �
RB
RB scN N×
12
RB
scN
=
symbN
������#!���
������!���
RB
symb scN N= × ������!����
Figure: Uplink resource grid for one slot [3].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design7 /337 /33
Uplink Physical ChannelUplink Physical Channel
Physical Channel IPhysical Channel I
ScramblingModulation
mapper
Transform
precoder
Resource
element mapper
SC-FDMA
signal gen.
Figure: Uplink physical channel [4].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design8 /338 /33
Uplink Physical ChannelUplink Physical Channel
Physical Channel IIPhysical Channel II
Scrambler: scrambles the coded bits in order to
randomize the interference and thus ensure that the
processing gain provided by the channel code can be fully
used.
Modulation mapper: performs the 4QAM or 16QAM
modulation on data blocks.
Transform precoder: supports multi-layer transmission in
MIMO systems.
Resource element mapper: assignment of the data blocks
to the suitable physical resource blocks.
SC-FDMA signal generation: will be detailed investigated
in the subsequent part.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design9 /339 /33
SC-FDMA TransmissionSC-FDMA Transmission
SC-FDMA TransmissionSC-FDMA Transmission
��'��!!�!(����&
�������
������ ���
��'��!!�!���
�����&�����������
��������
������������
��
���������
������ ���
{ }nx�����������
�������
�������
�������
{ }
{ }kX{ }mx�
{ }lX�
�
Figure: SC-FDMA transmission chain [2].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design10 /3310 /33
SC-FDMA TransmissionSC-FDMA Transmission
Subcarrier Allocation Methods ISubcarrier Allocation Methods I
f0
f1
fM- 1
f0
f1
fM- 1
Subcarrier
Mapping
N-point
IFFTAdd cyclic
prefix
Parallel to
Serial
converter
M-point
DFT
Spreading
f0
f1
fM- 1
f0
f1
fM- 2
Localized
Subcarrier
Mapping
0
0
0
0
0
0
0
0
0
0
f2
f3
fM- 4f
fM-1f
fM- 3f
Localized
0 1 2 3 4Frequency Frequency
f0
f1
fM-
f0
f1
fM-
Distributed
Subcarrier
Mapping
f2f
f3f
fM-f
fM-f
fM-f
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Distributed
1
2
3
4
Serial toParallelConverter
Incoming BitStream
m bitsBit to
ConstellationMapping
Bit toConstellationMapping
Bit toConstellationMapping
m bits
m bits
x(0,n)
x(1,n)
x(M - 1,n)
Serial toParallelConverter
Bit toConstellationMapping
Bit toConstellationMapping
-
Transmission
circuitry
Figure: SC-FDMA transmitter for localized and distributed subcarrier
mappings [1].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design11 /3311 /33
SC-FDMA TransmissionSC-FDMA Transmission
Subcarrier Allocation Methods IISubcarrier Allocation Methods II
Terminal 1
Terminal 2
Terminal 3SubcarrierSubcarrier
Distributed Mode Localized Mode
Figure: Subcarrier allocation methods for multiple users (3 users, 12
subcarriers, and 4 subcarriers per user) [5].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design12 /3312 /33
SC-FDMA TransmissionSC-FDMA Transmission Localized and Distributed ModeLocalized and Distributed Mode
Localized and Distributed ModeLocalized and Distributed Mode
Localized Mode
Each terminal uses a set of adjacent subcarriers to
transmit its symbols.
Along with channel dependent scheduling (CDS), it offers
high multi-user diversity.
Distributed Mode
The subcarriers used by a single terminal are distributed
over the whole frequency band.
Since the subcarriers are spread over the different parts
of the frequency band, the subcarrier data transmitted
over different channels are subject to different fading.
This provides high frequency diversity.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design13 /3313 /33
SC-FDMA TransmissionSC-FDMA Transmission Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Comparison criteria:
System throughput
PAPR
Problem: trade-off between these criteria.
Solution: find the optimum mode for the system by
testing.
The localized carrier transmission mode is used in LTE uplink
since it offers much better performance with the arrangement
of pulse-shaping filter.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design14 /3314 /33
SC-FDMA TransmissionSC-FDMA Transmission Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Effect of CDS on System PerformanceEffect of CDS on System Performance
Key question:
“How to allocate time and frequency resources among
users while achieving multi-user diversity and frequency
diversity?” [6].
Aim:
Maximize the user utility in each transmission time
interval.
All in all, CDS improves the throughput of the system for
localized mode much more than the distributed mode where
the throughput measure is the Shannon’s channel capacity
formula, C = BW log (1 + SNR).
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design15 /3315 /33
SC-FDMA TransmissionSC-FDMA Transmission Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Effect of Pulse Shaping IEffect of Pulse Shaping I
Aim:
Mitigate the out-of-band signal energy.
Problem:
Pulse shaping increases the PAPR, especially too much for
localized FDMA.
However, the PAPR of SC-FDMA signals is still lower than
OFDMA signals and in terms of system throughput, localized
FDMA with CDS is much better than distributed FDMA.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design16 /3316 /33
SC-FDMA TransmissionSC-FDMA Transmission Comparison Criteria for Different Carrier ModesComparison Criteria for Different Carrier Modes
Effect of Pulse Shaping IIEffect of Pulse Shaping II
0 2 4 6 8 1010
-4
10-3
10-2
10-1
100
Pr(
PA
PR
>P
AP
R0)
PAPR0 [dB]
CCDF of PAPR: QPSK, Nfft
= 256, Noccupied
= 64
Solid lines: without pulse shaping
Dotted lines: with pulse shaping
IFDMA LFDMA
α=0.4α=0.6
α=0.2
α=0
α=0.8
α=1
�
0 2 4 6 8 1010
-4
10-3
10-2
10-1
100
Pr(
PA
PR
>P
AP
R0)
PAPR0 [dB]
CCDF of PAPR: 16-QAM, Nfft
= 256, Noccupied
= 64
Solid lines: without pulse shaping
Dotted lines: with pulse shaping
IFDMALFDMA
α=0.4α=0.6α=0.2
α=0
α=0.8
α=1
� '(� � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � � '�(�
�
Figure: Comparison of complementary cumulative distribution
function (CCDF) of PAPR for distributed FDMA and localized FDMA
with 256 system subcarriers, 64 subcarriers per user and rolloff
factor of α ∈ {0,0.2,0.4,0.6,0.8,1} [6].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design17 /3317 /33
SC-FDMA TransmissionSC-FDMA Transmission Transmitter StructureTransmitter Structure
Transmitter Structure ITransmitter Structure I
a1[k ]
a2[k ]M–DFT
M–DFT
W
W
A1[µ]
A2[µ] Subcarrier
Subcarrier
Mapping
Mapping
K
K
B1[ν]
B2[ν]N–IDFT
N–IDFT
VH
VH
b1[κ]
b2[κ] CP
CP
extension
extension
bc1[κ]
bc2[κ]
P in
P in
Figure: Transmitter structure of LTE uplink [5].
MIMO ISI channel.
Single user MIMO transmission with 2 transmit antennas.
Data streams are divided into blocks of length M.
ai [k ]: 4QAM or 16QAM coded complex data symbols.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design18 /3318 /33
SC-FDMA TransmissionSC-FDMA Transmission Transmitter StructureTransmitter Structure
Transmitter Structure IITransmitter Structure II
First block: M-point DFT applied to the data sequences.
This can be represented as follows:
A i = Wa i
where,
A i = [Ai [0] Ai [1] ... Ai [M − 1]]T ,
a i = [ai [0] ai [1] ... ai [M − 1]]T , and
W is unitary M-point DFT matrix with entries
wmn = 1√Mexp (− j2πmn
M), m,n ∈ {0,1,2, ...,M − 1}.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design19 /3319 /33
SC-FDMA TransmissionSC-FDMA Transmission Transmitter StructureTransmitter Structure
Transmitter Structure IIITransmitter Structure III
Second block: Subcarrier assignment.
.............
...
...
...
.............
...
..........
Zeros
Zeros
Zerosν0 Zeros
(N − M − ν0) Zeros
Ai [0]
Ai [0]
Ai [1]Ai [1]
Ai [2]
Ai [M − 1]
Ai [M − 1]
Bi [0]Bi [0]
Bi [N − 1]Bi [N − 1]
Distributed Mode Localized Mode
Figure: Subcarrier Mapping in Distributed and Localized Mode [5].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design20 /3320 /33
SC-FDMA TransmissionSC-FDMA Transmission Transmitter StructureTransmitter Structure
Transmitter Structure IVTransmitter Structure IV
B i = [0 ... 0︸ ︷︷ ︸
ν0
Ai [0] Ai [1] ... Ai [M − 1] 0 ... 0︸ ︷︷ ︸
N−M−ν0
]T = KA i
with frequency shift ν0.
The assignment matrix K is:
K =
0ν0×M
IM
0(N−M−ν0)×M
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design21 /3321 /33
SC-FDMA TransmissionSC-FDMA Transmission Transmitter StructureTransmitter Structure
Transmitter Structure VTransmitter Structure V
Third block: N-point inverse DFT. In the output of this
block, there are the time-domain transmit sequences,
b i = VHB i where V is a unitary N-point DFT matrix.
Fourth block: Cyclic prefix extension of length Lc > qh ,
where qh is the channel order. The transmission blocks
are:
b ci = [bi [N − Lc ] ... bi [N − 1] bi [0] bi [1] ... bi [N − 1]]T .
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design22 /3322 /33
SC-FDMA TransmissionSC-FDMA Transmission Transmitter StructureTransmitter Structure
Cyclic Prefix Extension ICyclic Prefix Extension I
Cyclic prefix (CP) is a copy of the last N symbols of the block
in interest which is pasted at the start of the block.
CP
copy
b i
b ci
Figure: Addition of cyclic prefix [5].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design23 /3323 /33
SC-FDMA TransmissionSC-FDMA Transmission Transmitter StructureTransmitter Structure
Cyclic Prefix Extension IICyclic Prefix Extension II
There are a couple of reasons for CP extension.
CP works as a guard interval between subsequent blocks.
⇒ prevents the inter-block interference (IBI) due to
multipath fading.
It is a copy of the last part of the block.
⇒ converts a linear convolution to a circular convolution.
⇒ provides a very simple frequency domain equalization
technique for this system.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design24 /3324 /33
SC-FDMA TransmissionSC-FDMA Transmission Receiver StructureReceiver Structure
Receiver Structure IReceiver Structure I
. . .
. . .
r1[κ]
rNR[κ]
M–IDFT
M–IDFT
WH
WH
Y1[µ]
YNR[µ]Subcarrier
Subcarrier
Demapping
Demapping
KH
KH
R1[ν]
RNR[ν]
N–DFT
N–DFT
V
V
y1[k ]
yNR[k ]CP
CP
deletion
deletionrc1[κ]
rcNR[κ]
Pout
Pout
Figure: System model of the LTE Base Station [5].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design25 /3325 /33
SC-FDMA TransmissionSC-FDMA Transmission Receiver StructureReceiver Structure
Receiver Structure IIReceiver Structure II
NR -fold receive antenna diversity.
Received signal at l th antenna is:
rl [κ] =∑2
i=1
∑L−1λ=0 hl ,i [λ]bci [κ − λ] + nl [κ]
where,
hl ,i [λ]: discrete time channel impulse response of length L
(channel order qh = L − 1) from ith transmit antenna to
the lth receive antenna,
nl [κ] is the discrete time AWGN of lth receive antenna.
First block: Cyclic prefix is removed. In other words, the
first Lc values in rl [κ] are removed.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design26 /3326 /33
SC-FDMA TransmissionSC-FDMA Transmission Receiver StructureReceiver Structure
Receiver Structure IIIReceiver Structure III
CP
deletion
r l
rcl
Figure: Deletion of cyclic prefix [5].
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design27 /3327 /33
SC-FDMA TransmissionSC-FDMA Transmission Receiver StructureReceiver Structure
Receiver Structure IVReceiver Structure IV
⇒ The following matrix model is obtained:
r l = H l ,1b1 + H l ,2b2 + n l
with the circulant channel matrices:
H l ,i =
hl ,i [0] 0 · · · 0 · · · 0.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
hl ,i [qh ] · · · hl ,i [0] 0 · · · 0
0 hl ,i [qh ] · · · hl ,i [0] 0.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
. 0
0 · · · 0 hl ,i [qh ] · · · hl ,i [0]
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design28 /3328 /33
SC-FDMA TransmissionSC-FDMA Transmission Receiver StructureReceiver Structure
Receiver Structure VReceiver Structure V
Second block: N-point DFT is applied to r l .
R l = Vr l =∑2
i=1 VH l ,iVHB i + N l
H l ,i is a circulant matrix,
⇒ H l ,iVH = VH
Λl ,i , where
Λl ,i = diag{Hl ,i [0],Hl ,i [1],Hl ,i [N − 1]}.
Since the columns of VH are the eigenvectors of H l ,i
(VH l ,iVH = Λl ,i ), the following equation is obtained.
R l =∑2
i=1 Λl ,iB i + N l
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design29 /3329 /33
SC-FDMA TransmissionSC-FDMA Transmission Receiver StructureReceiver Structure
Receiver Structure VIReceiver Structure VI
Third block: Subcarrier demapping in the frequency
domain.
Y l = KHR l
Fourth block: M-point inverse DFT applied on demapped
symbols.
y l = WHY l
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design30 /3330 /33
ConclusionConclusion
Conclusion IConclusion I
Structure: DFT-spread OFDMA.
Localized FDMA → high PAPR, high throughput.
Distributed FDMA → low PAPR, low throughput.
Lower PAPR and higher system throughput compared to
OFDMA.
Pulse shaping operation might cause performance
degradation if not carefully designed.
High power consumption at the mobile station is avoided
by applying simple equalization at the base station.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design31 /3331 /33
ConclusionConclusion
Conclusion IIConclusion II
All of these phenomena reveal that single-carrier FDMA is a
better solution than OFDMA for the uplink of the LTE radio
system.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design32 /3332 /33
ConclusionConclusion
ReferencesReferences
[1] S. Sesia, I. Toufik, M. Baker: LTE-The UMTS Long Term
Evolution: From Theory to Practice, John Wiley, 2009.
[2] H. G. Myung, J. Lim, D. J. Goodman: Single Carrier
FDMA for Uplink Wireless Transmission, IEEE Vehicular
Technology Magazine, Sep. 2006.
[3] H. G. Myung: Technical Overview of 3GPP LTE,
Internet, May 2008.
[4] 3GPP TS 36.211 V8.3.0, 2008.
[5] M. Ruder: Multiuser MIMO Receiver for the Uplink of
Long Term Evolution (LTE), Nov. 2008.
[6] H. G. Myung: Single Carrier Orthogonal Multiple
Access Technique for Broadband Wireless
Communications, Dissertation, Jan. 2007.
Burcu HantaBurcu Hanta – SC-FDMA and LTE Uplink Physical Layer Design– SC-FDMA and LTE Uplink Physical Layer Design33 /3333 /33