02 lte air interface and physical layer
TRANSCRIPT
HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential
47pt
www.huawei.com
LTE Air Interface and
Physical Layer
Contents
• Key LTE PHY Technologies
• LTE PHY Structure Overview
• Downlink Physical Channels and Signals
• Uplink Physical Channels and Signals
HUAWEI TECHNOLOGIES CO., LTD. Page 3Huawei Confidential
Key LTE PHY Technologies
Single Carrier Sub-frame
Frequency
Time
Time frequency resource for User 1
Time frequency resource for User 2
Time frequency resource for User 3
System Bandwidth Sub-carriers
Sub-frame
Frequency
Time
Time frequency resource for User 1
Time frequency resource for User 2
Time frequency resource for User 3
System Bandwidth
MIMO
OFDMA
LTE
SC-FDMA
64QAMMultiple-Input Multiple-Output Adaptive Modulation and Coding (AMC)
up to 64QAM
Orthogonal Frequency
Division Multiple AccessSingle-Carrier Frequency
Division Multiple Access
HUAWEI TECHNOLOGIES CO., LTD. Page 4Huawei Confidential
OFDM Theory
• Serial data stream mapped onto many parallel sub-carriers� Lower symbol rate and longer symbols vs. single-carrier
• The sub-carriers are orthogonal� At each sub-carrier center, neighboring sub-carriers ideally have zero amplitude
� This removes need for inter-sub-carrier guard bands
• OFDM leverages the Discrete Fourier Transform (DFT) to synthesize and recover the signal� Fast Fourier Transformation (FFT/IFFT) algorithm reduces computational complexity
Frequency
OFDM Sub-Carriers
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OFDM Tx/Rx Structure
Serial to
Parallel …
s[n] IFFT
....
....
....
… …
Parallel
to Serial
Add
Cyclic
Prefix
s(t)
Constellation Mapping
Parallel
to Serial …
s[n] FFT
....
....
....… …
Serial to
Parallel
Remove
Cyclic
Prefix
s(t)
Symbol Detection
Transmitter
Receiver
bit-stream in
bit-stream out
OFDM signal out
OFDM signal in
HUAWEI TECHNOLOGIES CO., LTD. Page 6Huawei Confidential
OFDM Cyclic Prefix (CP)
TTCP
τmax
ISI-free symbol
start region
T
Multi-path arrivals
T – FFT interval
TCP – cyclic prefix guard period
T + TCP – OFDM symbol period
τmax – max multi-path delay
• CP adds overhead but provides inter-symbol interference (ISI) mitigation
• LTE defines normal CP of 4.7µs and extended CP of 16.7µs
HUAWEI TECHNOLOGIES CO., LTD. Page 7Huawei Confidential
Wireless Technology PHY Comparison
Channel or Subcarrier
SpacingSymbol PeriodTechnology
66.7 µs
0.26 µs
(1/3.84Mcps)
15 kHzLTE
5 MHzUMTS WCDMA
• Symbol period is roughly 1/(channel spacing) for single-carrier
systems, 1/(subcarrier spacing) for OFDM
• LTE: Long OFDM symbol periods and CP mitigate ISI without
equalization
• UMTS: Short symbol periods relative to delay spread requires
channel equalization (i.e. rake receiver) to mitigate ISI
• Rake receiver adds cost/complexity
HUAWEI TECHNOLOGIES CO., LTD. Page 8Huawei Confidential
OFDM Advantages
• Low-complexity UE receiver design
� Efficient IFFT/FFT processing
� Traditional equalizer not needed
• Robust fading channel performance
� Long symbol time with cyclic prefix provides tolerance to multi-
path delay spread without equalization
• Each sub-carrier modulated independently
� Allows MCS adjustment across frequency to match channel
conditions
• Improved MIMO performance due to flat frequency
response per subcarrier
HUAWEI TECHNOLOGIES CO., LTD. Page 9Huawei Confidential
OFDM Limitations
• Peak Power Problem
� The OFDM signal has a large peak to average power ratio (PAPR)
� Higher power amplifiers are needed leading to increased cost and
linearization requirements and decreased power efficiency
� Low noise receiver amplifiers need larger dynamic range
• Inter-Carrier-Interference (ICI)
� Due to narrow subcarrier spacing, frequency offsets, phase noise,
and Doppler spread destroy orthogonality and create ICI
� OFDM design parameters trade off robustness to fading (delay
spread) and Doppler (velocity)
• Capacity and Power Loss Due to Cyclic Prefix
� Cyclic prefix consumes bandwidth and transmit power
HUAWEI TECHNOLOGIES CO., LTD. Page 10Huawei Confidential
Downlink based on OFDMA
• Users are multiplexed onto time and frequency OFDM resources
• Frequency-diverse scheduling helps maximize spectral efficiency from a
system perspective
Sub-carriers
TTI: 1ms
Frequency
Tim e
Time frequency resource for User 1
Time frequency resource for User 2
Time frequency resource for User 3
System Bandwidth
Sub-band: 12Sub-carriers
Sub-frames
Groups of subcarriers
HUAWEI TECHNOLOGIES CO., LTD. Page 11Huawei Confidential
SC-FDMA
Serial toParallel
Converter
Incoming BitStream
m1 bitsBit to
ConstellationMapping
Bit toConstellation
Mapping
Bit toConstellation
Mapping
m2 bits
mMbits
x(0,n)
x(1,n)
x(M- 1,n)
Serial toParallel
Converter
Incoming BitStream
m1 bitsBit to
ConstellationMapping
Bit toConstellation
Mapping
Bit toConstellation
Mapping
m2 bits
mMbits
x(0,n)
x(1,n)
x(M- 1,n)
N-point
IFFTAdd cyclic
prefix
Parallel to
Serialconverter
M-point
FFT
of
1f
1−Mf
2−Mf
12/ −Mf
2/Mf
00
0
0
0
0
00
0
0
Channel BW
Additional step
• Single Carrier Frequency Division Multiple Access (SC-FDMA) is a form of DFT Spread-OFDM with adjacent subcarrier mapping� An additional DFT spreads information across all subcarriers� Contiguous subcarrier allocation for IFFT results in single-carrier signal
• Advantage: The single-carrier signal has generally lower peak-to-average power ratio (PAPR) which allows use of lower cost UE power amplifier (PA) and reduces UE power consumption
• Disadvantage: Single-carrier modulation results in ISI and requires equalization
DFT
HUAWEI TECHNOLOGIES CO., LTD. Page 12Huawei Confidential
Uplink based on SC-FDMA
Single Carrier Sub-frame
Frequency
Time
Time frequency resource for User 1
Time frequency resource for User 2
Time frequency resource for User 3
System Bandwidth
• SC-FDMA is used for uplink in LTE
• As with OFDMA DL,
• Users are multiplexed onto time and frequency OFDM resources
• Frequency-diverse scheduling helps maximize spectral efficiency
from a system perspective
Sub-frames
HUAWEI TECHNOLOGIES CO., LTD. Page 13Huawei Confidential
Flexible Scheduler
FrequencyFrequencyFrequencyFrequency
TimeTimeTimeTime
Benefits: Increased radio link reliability, cell capacity and coverage
• Different users experience different fading in time-frequency domain
• OFDMA and SC-FDMA in LTE support flexible DL/UL scheduling to
achieve frequency-selective scheduling gain
SINRUser 1
User 2Optimal allocation
HUAWEI TECHNOLOGIES CO., LTD. Page 14Huawei Confidential
MIMO
• MIMO adds spatial dimension to the wireless PHY interface
• Beamforming (BF) and Transmit Diversity (TD)
� Single-stream: improves SINR
� Mainly for improving coverage through the parallel transmission of
differently weighted (BF) or coded (TD) versions of a single stream
• Spatial Multiplexing (SM)
� Multiple-streams: power is shared (lower SINR per stream)
� Improves capacity through the parallel transmission of multiple
spatial streams on the same time-frequency resources
HUAWEI TECHNOLOGIES CO., LTD. Page 15Huawei Confidential
MIMO Mode Selection
SINR
Throughput
SINR-limited
(best to use beamforming
or transmit diversity)
Bandwidth-limited(best to use spatial-multiplexing)
• Low SINR: increasing SINR via BF or TD provides improved
range and/or throughput gain at the cell edge
• High SINR: throughput saturates so SM provides best
throughput gain despite lower SINR per stream
Shannon Channel Capacity Theorem
)/1(log2 NSBC +=
HUAWEI TECHNOLOGIES CO., LTD. Page 16Huawei Confidential
MIMO Impact on Throughput and Coverage
• Channel rank dictates the number of simultaneous streams
that the channel can support
� Rank-1 transmission via BF or TD improves coverage
� Spatial Multiplexing (rank > 1) increases peak rate
Throughput vs. Coverage with 4x4 MIMO
HUAWEI TECHNOLOGIES CO., LTD. Page 17Huawei Confidential
DL MIMO
codeword
S
F
B
C
Mod
Rank = 1
Rank > 1
UE
UE
UE
Pre-coder
(3) Precoding matrix indication (PMI),rank indication (RI)
(1) Reference symbols
(2) U
Es
dete
rmin
e b
est p
reco
din
gm
atrix
Transmit Diversity via SFBC
Open-Loop Spatial Multiplexing Closed-Loop Spatial Multiplexing
(Single or Multi-User)
Pre-codercodeword Mod
Beamforming
(codebook or non-codebook-based)
codeword Mod
codeword Mod
Layer 1, CW1
Layer 2, CW2
codeword Mod
codeword Mod
Layer 1, CW1
Layer 2, CW2
• LTE eNB has up to 4 Tx chains• LTE UE has up to 4 Rx chains
SU
MU
UE Feedback
HUAWEI TECHNOLOGIES CO., LTD. Page 18Huawei Confidential
UL MIMO
1x2 SIMO MRC Rx Diversity 1x2 MU MIMO (with UE pairing)
• Single-Layer transmission at UE
� Optional switched Tx-Diversity
• Maximum ratio combining
(MRC) at eNB increases uplink
range/sensitivity
• “Virtual” MIMO on UL with single-transmitter UEs
• UEs with orthogonal channels are paired
• Allows resource reuse in highly-loaded scenarios
• Degrades single-user performance due to interference
•LTE UE has 1 Tx chain• With optional switched Tx diversity
•LTE eNB has up to 4 Rx chains
HUAWEI TECHNOLOGIES CO., LTD. Page 19Huawei Confidential
Key LTE-Advanced PHY Technologies
CoMP
CA
LTE-A
Relay
Coordinated Multi-Point Transmission and Reception
In-Band Relay
Carrier Aggregation
High-Order (8x8) MIMO Support
RF
/IF
RF
/IF
RF
/IF
RF
/IF
RF
/IF
RF
/IF
RF
/IF
RF
/IF
Base Band
LT E C a rrier 1 f
LT E C a rrier 2 LT E C a rrier 3
f
B and 1
C o m bine d LT E C ar r ie r 1 a nd LT E C a rr ier 2
LT E -A C a rrier LT E C a rrier 3
f
O p era to r 2
LT E C a rr ier 2
f
B a n d 1
C o m b in e d LT E C a r rier 1 a n d LT E C a r rier 3
O p era to r 1
LT E C a rr ier 1
O p e ra t or 1
LT E C a r rie r 3
O p era to r 2
LT E C a rr ier 2
O p era to r 1
LT E -A C a rr ie r
O p era tor 1
LT E - A C a rr ier
LT E C a r r ie r 1 f
LT E
C a r r ie r 2
f
B a n d 1 B a n d 2
LT E - A
C a r r ie r
LT E -A
C a r r ie r
LT E C a r r ier 1 in b a n d 1 C o m b in e d w it h LT E ca r r ier 2 in ba n d 2
Enhanced MIMO
Improved MU-MIMO UL SM-MIMO
HUAWEI TECHNOLOGIES CO., LTD. Page 20Huawei Confidential
LTE-A Benefits
• CoMP
� DL: Controlled/canceled interference – better signal quality
� UL: Higher order diversity and aperture gain (soft combining)
• Relay
� Improved coverage and data rates, especially at edge
• Carrier Aggregation
� Higher throughput and peak data rates
� Asymmetric UL/DL
� Better utilization of discontinuous or multi-band spectrum resources
• Enhanced MIMO
� Up to 8x8 MIMO for higher throughput and enhanced coverage
� Improved DL MU-MIMO performance by addressing R8 limitations
� UL SM-MIMO for higher UL data rates
HUAWEI TECHNOLOGIES CO., LTD. Page 21Huawei Confidential
Section Review – Key Takeaways
• OFDM
� Data multiplexed onto many narrow subcarriers
� CP and long symbol time mitigate ISI
� Good MIMO performance due to flat frequency response per subcarrier
• OFDMA DL
� Low-complexity UE receiver design with robust fading channel performance, especially with MIMO
� Flexible MCS adjustment and UE allocation across time and frequency (sub-carriers) enhances spectral efficiency
• SC-FDMA UL
� Similar benefits as OFDMA but lower PAPR allows lower cost UE power amplifier and reduces UE power consumption
� Some additional receiver complexity required at eNB
• MIMO
� Spatial multiplexing at high SINR increases capacity
� Transmit diversity or beamforming at low SINR enhances range
Contents
• Key LTE PHY Technologies
• LTE PHY Structure Overview
• Downlink Physical Channels and Signals
• Uplink Physical Channels and Signals
HUAWEI TECHNOLOGIES CO., LTD. Page 23Huawei Confidential
LTE OFDM Parameters
4.7 or 16.7 µsCyclic Prefix Time
71.4 or 83.4 µsTotal Symbol Time
LTETheoryParameter
1.4, 3, 5, 10, 15, 20 MHzTotal Bandwidth
72-1200Number of Subcarriers
15 kHz (k=1)Subcarrier Spacing
66.7 µsUseful Symbol Time uT
uTkf /=∆
fNB ∆⋅=
N
CPT
CPutotal TTT +=
. . .
. . .
time
fre
qu
en
cy
totalTf∆
1
2
3
. . .
N
HUAWEI TECHNOLOGIES CO., LTD. Page 24Huawei Confidential
Frame Structure
#0 #1 #2 #3 #19
One slot, Tslot = 15360×Ts = 0.5 ms
One radio frame, Tf = 307200×Ts=10 ms
#18
One subframe
=×= slotsubframe TT 2 1 ms
• One subframe (1 ms) is an LTE transmission time interval (TTI)
HUAWEI TECHNOLOGIES CO., LTD. Page 25Huawei Confidential
Resource Grid One downlink slot, Tslot
Resource element
OFDM symbolsDLsymbN OFDM symbolsDLsymbN
Nsc
subca
rrie
rsR
B
Resource block
RBsc
DLsymb NN × resource elements
NR
BDL
subcar
riers
NscR
B×fr
eq
uen
cy
time
(RB)
HUAWEI TECHNOLOGIES CO., LTD. Page 26Huawei Confidential
UL/DL Resource Block
• A physical resource block is defined as consecutive
OFDM symbols in the time domain and consecutive
subcarriers in the frequency domain
• Multi-Media Broadcast over a Single Frequency Network
(MBSFN) combines 7.5kHz subchannel spacing with
double length symbol time and CP to handle greater delay
spread (DL only)
symbNRBscN
324
6Extended cyclic prefix
712
Normal cyclic prefix
ConfigurationDLsymbN
kHz 15=∆f
kHz 5.7=∆f
RBscN
kHz 15=∆f
MBSFN-
dedicated
cell
UL
symbN
-
6
7
HUAWEI TECHNOLOGIES CO., LTD. Page 27Huawei Confidential
LTE Numerology
120090060030018072Number of
Subcarriers
100755025156Number of
Resource Blocks
204815361024512256128FFT Size
201510531.4Transmission BW
(MHz)
HUAWEI TECHNOLOGIES CO., LTD. Page 28Huawei Confidential
Section Review – Key Takeaways
• LTE frame structure
� 0.5ms slot
� 1ms subframe
� 10ms frame
• Resource allocation
� RB is the minimum resource allocation
� Typically 7 symbols (in time) x 12 subcarriers (in frequency)
• Supported system bandwidths
� 1.4, 3, 5, 10, 15, and 20MHz
Contents
• Key LTE PHY Technologies
• LTE PHY Structure Overview
• Downlink Physical Channels and Signals
• Uplink Physical Channels and Signals
HUAWEI TECHNOLOGIES CO., LTD. Page 30Huawei Confidential
DL Physical Channels and Signals
• Physical channels
� PDSCH: Physical Downlink Shared Channel
� PBCH: Physical broadcast channel
� PMCH: Physical multicast channel
� PDCCH: Physical Downlink Control Channel
� PCFICH: Physical control format indicator channel
� PHICH: Physical Hybrid ARQ Indicator Channel
• Reference Signal (RS)
� Cell specific RS
� UE-specific RS
� MBSFN RS
• Synchronization Signal (SCH)
� Primary Synchronization Signal (P-SCH)
� Secondary Synchronization Signal (S-SCH)
HUAWEI TECHNOLOGIES CO., LTD. Page 31Huawei Confidential
Synchronization and System Information
• SCH used for:
� Symbol synchronization
� Frame synchronization
� Cell-ID determination
• BCH indicates:
� Basic L1/L2 system parameters
� Downlink system bandwidth
� Reference-signal transmit power
� Multi-media Broadcast over a Single Frequency Network
(MBSFN)-related parameters
� Number of transmit antennas
� HARQ resource allocation
SCH
10-MHz bandwidth
20-MHz bandwidth
5-MHz bandwidth
1.25-MHz bandwidth
2.5-MHz bandwidth
1.4 MHz bandwidth
3 MHz bandwidth
5 MHz bandwidth
10 MHz bandwidth
20 MHz bandwidth
SCH / BCHSCH
10-MHz bandwidth
20-MHz bandwidth
5-MHz bandwidth
1.25-MHz bandwidth
2.5-MHz bandwidth
1.4 MHz bandwidth
3 MHz bandwidth
5 MHz bandwidth
10 MHz bandwidth
20 MHz bandwidth
SCH / BCH
SCH/BCH each occupy 72 center subcarriers
regardless of system bandwidth
HUAWEI TECHNOLOGIES CO., LTD. Page 32Huawei Confidential
Time Structure of SCH/BCH
• Primary and secondary SCH (P-SCH, S-SCH) are transmitted in
consecutive OFDM symbols in the 1st and 6th subframes (every
5ms) of each frame
• BCH is transmitted in four consecutive OFDM symbols in the
first subframe of every frame, but it is only updated every 40ms
BCH
HUAWEI TECHNOLOGIES CO., LTD. Page 33Huawei Confidential
DL Reference Signals
• Downlink reference signals are used for estimation of
channel gain (for symbol demodulation) and channel
quality (for channel quality feedback to eNB)
• Ports 0-3:
� Cell-specific reference signals
� Associated with non-MBSFN (i.e. unicast) transmission
� Support for one, two, or four antenna port configuration
• Port 4: MBSFN reference signals
• Port 5: UE-specific reference signals used for beamforming
HUAWEI TECHNOLOGIES CO., LTD. Page 34Huawei Confidential
Cell-Specific Reference Signals
0=l
0R
0R
0R
0R
6=l 0=l
0R
0R
0R
0R
6=l
0=l
0R
0R
0R
0R
6=l 0=l
0R
0R
0R
0R
6=l 0=l
1R
1R
1R
6=l 0=l
1R
1R
1R
1R
6=l
0=l
0R
0R
0R
0R
6=l 0=l
0R
0R
0R
0R
6=l 0=l
1R
1R
1R
1R
6=l 0=l
1R
1R
1R
1R
6=l 0=l 6=l 0=l
2R
6=l 0=l 6=l 0=l 6=l
2R
2R
2R
3R
3R
3R
3R
� Example RS mapping for normal CP
� Other antenna ports silent during RS
transmission
� Reduced RS density on ports 2 and 3On
e a
nte
nn
a p
ort
Tw
o a
nte
nn
a p
ort
sF
ou
r a
nte
nna
port
s
l=0 l=6 l=0 l=6
l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6
l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6 l=0 l=6
Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3
Resource element (k,l)
Not used for transmission on this antenna port
Reference symbols on this antenna port
even numbered slots
odd numbered slots
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Cell-Specific RS Frequency Shift
f
Cell specific frequency shift
Cell 0 Cell 1 Cell 5
6modcell
IDshift Nv =
• RS mapping to resource elements
� To reduce RS interference between adjacent cells, a cell specific frequency shift is applied
� There are 6 shift values since the frequency interval of RS is 6 subcarriers
…
HUAWEI TECHNOLOGIES CO., LTD. Page 36Huawei Confidential
DL Control Signaling
• Control region is 1-4 OFDM symbols at the beginning of each subframe
• PCFICH – Physical Control Format Indicator Channel
� # of OFDM symbols of control region
• PHICH – Physical Hybrid ARQ Channel
� ACK/NACK signalling
• PDCCH – Physical Downlink Control Channel
� Scheduling
� UL power control
freq time
Control Region Data Region
OFDM symbols1 2 3 4 5 6 7 8 9 10 11 12 13 14
- PCFICH mini-CE
t2 t4 t1 t2 t3 t1
Mini-CE Boundary - A/N mini-CE
(symbol 1,2)
t1 t3 t2 t1 t4 t2 - Data symbols
RB1
t2 t4 t1 t2 t3 t1 - mini-CE for CCE1
- mini-CE for CCE2
RB Boundary t1 t3 t2 t1 t4 t2 - mini-CE for CCE3
t2 t4 t1 t2 t3 t1 - mini-CE for CCE4
Mini-CE Boundary
(symbol 3) - Unassigned mini-CE
t1 t3 t2 t1 t4 t2
RB2 t1 - RS for TX antenna 1
t2 t4 t1 t2 t3 t1
t2 - RS for TX antenna 2
t1 t3 t2 t1 t4 t2 t3 - RS for TX antenna 3
t4 - RS for TX antenna 4. .. .. .
1
t2 t4 t1 t2 t3 t1 2
3
4
t1 t3 t2 t1 t4 t2 5
RB6 6 12 subcarriers
7
t2 t4 t1 t2 t3 t1 8
9
10
t1 t3 t2 t1 t4 t2 11
12
PCFICH
PHICH
Data
REG for CCE1
REG for CCE2
REG for CCE3
REG for CCE4
Unassigned REG
Port 1 RS
Port 2 RS
Port 3 RS
Port 4 RS
1 RB = 12 sub-carriers
REG Boundary
REG Boundary
PDCCH
HUAWEI TECHNOLOGIES CO., LTD. Page 37Huawei Confidential
PDCCH CCE Aggregation
…
…
…
…
1 CCE
2 CCE
4 CCE
8 CCE
1 2 3 4 5 6 7 8 10 11 12 13 14 150 9
• CCE aggregation is a form of repetition coding
• The same PDCCH information is coded across 1, 2, 4, or 8 CCEs
• eNB adjusts CCE aggregation based on DL SINR operating point
• Tree-based aggregation supports blind decoding search
� 1-CCE aggregation can start on any CCE position (i=0,1,2,3,4,...)
� 2-CCE can start only on even numbered locations (i=0,2,4,6,...)
� 4-CCE on every fourth (i=0, 4, 8, ...)
� 8-CCE on every eight position (i=0, 8, ...)
frequency
HUAWEI TECHNOLOGIES CO., LTD. Page 38Huawei Confidential
Section Review – Key Takeaways
• SCH
� Symbol synchronization
� Frame synchronization
� Cell-ID determination
• BCH
� Basic L1/L2 system parameters such as: system bandwidth, reference-
signal transmit power, and number of transmit antennas
• RS
� Ports 0-3: Cell-specific, support MIMO, unique time/frequency location
per antenna port
� Ports 4 and 5: MBSFN and UE-specific for beamforming
• Control Signaling
� Control region in first 1-4 OFDM symbols per subframe
� Carries ACK/NACK, UL/DL data/paging scheduling, UL power control
� PDCCH variable aggregation based on UE SINR operating point
Contents
• Key LTE PHY Technologies
• LTE PHY Structure Overview
• Downlink Physical Channels and Signals
• Uplink Physical Channels and Signals
HUAWEI TECHNOLOGIES CO., LTD. Page 40Huawei Confidential
UL Physical Channels and Signals
• Physical channels
� PUSCH: Physical Uplink Shared Channel
� PUCCH: Physical Uplink Control Channel
� PRACH: Physical Random Access Channel
• Reference signals
� Demodulation Reference Signal (DM RS)
� Sounding Reference Signal (SRS)
HUAWEI TECHNOLOGIES CO., LTD. Page 41Huawei Confidential
UL Reference Signals
• Demodulation (DM) RS used for estimation of UL channel
gain and channel quality from active UEs
• DM RS are transmitted with data in the 4th and 11th SC-
FDMA symbols of the subframe
• DM RS are code division multiplexed (CDM) to support MU-
MIMO and inter-sector interference
0.5 ms slot
RB 1
RB 2
RB N
• Sounding Reference Signals (SRS) used to evaluate UL
channel quality for idle/lightly loaded UEs
• SRS is in the 7th SC-FDMA symbol of the subframe and is
typically wideband (on contiguous or periodic REs)
• SRS is also CDM
…
0.5 ms slot
UE1 DM RS
UE2 DM RS
UE3 DM RS
UE4 SRS
1 ms subframe
… …UE2 allocation
UE1 allocation
UE3 allocation
HUAWEI TECHNOLOGIES CO., LTD. Page 42Huawei Confidential
Uplink Control Signaling• Channel measurement indications from UE
� Channel quality indicator (CQI) – Value that points to a modulation/coding index in a 4-bit CQI table (implies SINR)
� Precoding matrix indicator (PMI) – Value that corresponds to the suggested precoding matrix codebook index
� Rank indication (RI) – Indicates the rank (# of layers) the channel can support
• Measurement indications are transmitted
� Periodically on PUCCH (alone) or PUSCH (multiplexed with data)
� Aperiodically on PUSCH (alone or multiplexed with data)
• Other signaling:
� HARQ acknowledgement (ACK/NACK) from higher layers
� Scheduling request indication (SRI) from higher layers
Wideband-onlyWideband-onlyRI
Wideband or subbandWideband-onlyPMI
Wideband or subbandWideband or subbandCQI
PUSCHPUCCH
HUAWEI TECHNOLOGIES CO., LTD. Page 43Huawei Confidential
Physical Resources for Control Signaling
• Control signaling uses reserved frequency regions at edges of BW
• A “control channel resource” is defined as N=12 subcarriers (an RB) in two consecutive 0.5ms slots located at opposite ends of the BW for frequency diversity
• Control signaling is CDM with multiple users sharing the resources via orthogonal
spreading codes
• PUCCH can cause and suffer from adjacent channel interference issues
� Especially in 700MHz band (shared with DTV, public safety, and MediaFLO)
� One solution is over-provisioning to push PUCCH allocation towards inner
subcarriers, but this hurts capacity
N=12 subcarriers
0.5ms slot 0.5ms slot
Another control channel resource
Spectr
um
allo
cation:
Mre
sourc
e b
locks
One control channel resource
… …
Slot structure for ACK/NAK
RS RS RS
0.5ms slot
RS locations for control signals
(transmitted on PUCCH)
Slot structure for CQI
RS RS
0.5ms slot
HUAWEI TECHNOLOGIES CO., LTD. Page 44Huawei Confidential
Section Review – Key Takeaways
• UL Reference Signals
� Code division multiplexed (CDM) for orthogonality between users
� DM RS – For estimation of UL channel gain and channel quality from active UEs
� SRS – Used to evaluate UL channel quality for idle/lightly loaded UEs
• Channel measurement indications from UE
� Channel quality indicator (CQI) – Indicates the channel quality observed by the UE
� Precoding matrix indicator (PMI) – Indicates the precoding matrix suggested by the UE
� Rank indication (RI) – Indicates the rank, or # of layers, the channel can support
• Physical Uplink Control Channel (PUCCH)
� Located at upper and lower edges of bandwidth
� Shared between multiple users via CDM
� Susceptible to adjacent channel interference issues (e.g. DTV, public safety, and MediaFLO) in 700MHz band
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HUAWEI TECHNOLOGIES CO., LTD. Page 46Huawei Confidential
Backup Slides
HUAWEI TECHNOLOGIES CO., LTD. Page 47Huawei Confidential
DL OFDM/MIMO Signal Generation
• Scrambling of coded bits for each codeword
� Up to two codewords transmitted at a time
• Modulation of scrambled bits to modulated symbols (e.g. QPSK,
16 QAM, 64 QAM)
• Multi-antenna blocks
� Mapping of modulated symbols to one or more transmission layers
� Precoding of symbols on each layer onto antenna ports
• Mapping of symbols on each port to resource elements
• Generation of time domain OFDM signal on each antenna port
Multi-antenna blocks
HUAWEI TECHNOLOGIES CO., LTD. Page 48Huawei Confidential
UL SC-FDMA Signal Generation
• Similar structure as for DL OFDM signal synthesis
• Additional DFT process creates single-carrier property
Modulation
mapper
DFT
precoderScrambling
SC-FDMA
signal gen.
Resource
element mapperOFDM signal generation
New element for SC-FDMA
HUAWEI TECHNOLOGIES CO., LTD. Page 49Huawei Confidential
Transport Block SizesPRBN
TBSI 1 2 3 4 5 6 7 8 9 10
0 16 32 56 88 120 152 176 208 224 256
1 24 56 88 144 176 208 224 256 328 344
2 32 72 144 176 208 256 296 328 376 424
3 40 104 176 208 256 328 392 440 504 568
4 56 120 208 256 328 408 488 552 632 696
5 72 144 224 328 424 504 600 680 776 872
6 328 176 256 392 504 600 712 808 936 1032
7 104 224 328 472 584 712 840 968 1096 1224
8 120 256 392 536 680 808 968 1096 1256 1384
9 136 296 456 616 776 936 1096 1256 1416 1544
10 144 328 504 680 872 1032 1224 1384 1544 1736
11 176 376 584 776 1000 1192 1384 1608 1800 2024
12 208 440 680 904 1128 1352 1608 1800 2024 2280
13 224 488 744 1000 1256 1544 1800 2024 2280 2536
14 256 552 840 1128 1416 1736 1992 2280 2600 2856
15 280 600 904 1224 1544 1800 2152 2472 2728 3112
16 328 632 968 1288 1608 1928 2280 2600 2984 3240
17 336 696 1064 1416 1800 2152 2536 2856 3240 3624
18 376 776 1160 1544 1992 2344 2792 3112 3624 4008
19 408 840 1288 1736 2152 2600 2984 3496 3880 4264
20 440 904 1384 1864 2344 2792 3240 3752 4136 4584
21 488 1000 1480 1992 2472 2984 3496 4008 4584 4968
22 520 1064 1608 2152 2664 3240 3752 4264 4776 5352
23 552 1128 1736 2280 2856 3496 4008 4584 5160 5736
24 584 1192 1800 2408 2984 3624 4264 4968 5544 5992
25 616 1256 1864 2536 3112 3752 4392 5160 5736 6200
26 712 1480 2216 2984 3752 4392 5160 5992 6712 7480
# bits per transport
block (TB)
Data Rate (bits/sec) = (# bits per TB) x (# of TB/TTI)
(# of RB pairs)
QPSK
16QAM
64QAM
HUAWEI TECHNOLOGIES CO., LTD. Page 50Huawei Confidential
Cell search procedure
• Step 1: OFDM symbol synchronization
and determination of cell ID� UE uses the primary synchronization sequence to
� acquire the symbol synchronization
� identify (one of three possible) cell IDs within a cell ID group
� This is done by continuously correlating three local primary
synchronization sequences with the received signal
� Symbol synchronization is obtained by detecting a time-domain
correlation peak, and the sequence corresponding to the
correlation peak indicates one of three IDs within a cell ID group
HUAWEI TECHNOLOGIES CO., LTD. Page 51Huawei Confidential
Cell search procedure (continued)
• Step 2: Radio frame synchronization and
cell ID group detection� UE uses the secondary synchronization sequence to determine
� radio frame timing
� cell ID group index of the cell detected in the first step
� The UE correlates the received S-SCH signal with each of the
secondary candidate sequences based on the symbol
synchronization acquired in the first step to determine the cell ID
group
� During the detection of secondary synchronization channel, the
CP length may also be obtained by blind detection
HUAWEI TECHNOLOGIES CO., LTD. Page 52Huawei Confidential
DL Control Signaling (2)
• PCFICH
� Indicates size (i.e. number of OFDM symbols) of control region
• PHICH
� ACK/NACK in response to uplink transmission
• PDCCH
� Scheduling grant for uplink data transmission
� Scheduling information for downlink data transmission
� Scheduling information for paging message transmission
� Scheduling information for RACH response transmission in UL
� UL power control signaling
� Each PDCCH is made up of 1, 2, 4, or 8 control channel
elements (CCEs)
HUAWEI TECHNOLOGIES CO., LTD. Page 53Huawei Confidential
PDCCH Blind Decoding
• Common and UE-specific search spaces defined
• UE blindly attempts to decode with different aggregation
assumptions
• In early 3GPP discussions, it was agreed that a maximum
of ~40 PDCCH decoding attempts by the UE would be
acceptable
� ~10 for common search space
� ~30 for UE-specific search space
HUAWEI TECHNOLOGIES CO., LTD. Page 54Huawei Confidential
MBSFN and UE-Specific Reference Signals
0=l 5=l 0=l 5=l
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
4R
0=l
5R
5R
5R
5R
5R
5R
5R
5R
5R
5R
5R
5R
0=l 6=l6=l
MBSFN RS
(Extended CP, ) UE-Specific RS
kHz 15=∆f