WiMAX
Physical Layer
lecturer：林杰龍
lecturer：林杰龍
[email protected]
2009/03/10
Content
I
Baseband Technology
I
OFDM &OFDMA
II
Signal Characteristics
III
Modulation & Coding
II
RF Technology
III
Other Technology
page-2
Basic Architecture of an
OFDM(A) System
Input Data
Randomizer
FEC
Encoder
Interleaver
Mod.
S/P
IFFT
P/S
Add CP
Tx Filter
Output Data
DeRandomizer
FEC
Decoder
DeInterleaver
P/S &
De-Mod.
Detection
FFT
Remove CP
S/P
Rx Filter
page-3
DFT and IDFT
•
There is the orthogonal property between
different subcarriers to avoid the interference
when the spectrums overlap.
e jω i t
e − jω i t
page-4
DFT and IDFT
•
Discrete Fourier Transform is implemented by the
FFT and IFFT normally.
1
IDFT _ x[ n ] =
N
N −1
∑ X [ k ]e
j
2π
kn
N
k =0
N −1
DFT _ X [ k ] = ∑ x[ n ]e
−j
2π
kn
N
n=0
N: the number of subcarrier in OFDM
x[n]: the complex input data in time domain
X[k]: the data in frequency domain
page-5
Fourier Transform
Characteristics
•
N Period:
− j 2π
WN = e (
(WN )
N)
W Nk n = W N (
k n+ N
)
N
= W N(
(
= e − j ( 2π
N)
)
N
= e − j 2π = 1
k + N )n
•
Complex Conjugate Symmetry:
•
DFT needs N2 multipliers and N(N-1) adders. This is
a high calculating complexity method.
Æ FFT or IFFT is used to reduce the complexity to
Nlog2N
•
WN[
k N −n]
= W N− k n = (W Nk n
)
∗
page-6
DIT Radix-2 FFT
x[0]
X[0]
x[2]
X[1]
x[4]
X[2]
x[6]
X[3]
x[1]
X[4]
x[3]
X[5]
x[5]
X[6]
x[7]
X[7]
page-7
Signals of Frequency
Domain
Single bit signal in frequency domain
page-8
Signals of Frequency
Domain
Subcarrier Center Point
page-9
Signals of Frequency
Domain
page-10
Physical Property –
Frequency Domain
•
•
•
•
•
Nominal Channel Bandwidth, BW
Sampling Frequency, Fs = floor(n∙BW/8000) ∙8000
Sampling factor, n = Fs / BW
Used Channel, Bandwidth = Nused ∙∆f
Carrier Spacing, ∆f = Fs / NFFT
Nused
NFFT
page-11
Physical Property –
Time Domain
•
•
•
•
Channel Effect : The different arrival time will cause the ISI.
Cyclic Prefix : Copy the last part of OFDM symbol to the
front in the time domain.
CP Length : 1/4, 1/8, 1/16, 1/32
Ts = Tg + Tb = CP x Tb + Tb
– Tb : Useful OFDM Symbol Time
– Tg : Cyclic Prefix
– Ts : Transmitted OFDM Symbol Time
• CP prevents the discontinuous effect of the guard interval.
Ts
Tg
Cyclic
Cyclic
Prefix
Prefix
Tb
Data
DataPayload
Payload
page-12
Multipath Influence
• ISI (inter-symbol interference)
– Tcp > Tdelay-spread
CP
CP
Td
Symbol
Symbol
CP
CP
CP
CP
Symbol
Symbol
Two path model
Symbol
Symbol
CP
CP
Symbol
Symbol
• ICI (inter-channel interference)
– Tcp < Tdelay-spread
CP
CP
Symbol
Symbol
Td
CP
CP
CP
CP
Symbol
Symbol
Symbol
Symbol
CP
CP
Symbol
Symbol
page-13
Circular Convolution
Path_1
Other Symbol
Path_2
Other Symbol
Path_3
Other Symbol
Cyclic
Cyclic
Prefix
Prefix
Data
DataPayload
Payload
Cyclic
Cyclic
Prefix
Prefix
Data
DataPayload
Payload
Cyclic
Cyclic
Prefix
Prefix
Data
DataPayload
Payload
Other Symbol
Other Symbol
Other Symbol
ISI Free Region
Tb Length
Y[K] = H[K] X[k]
page-14
OFDMA Scalability
Parameters
Values
System B.W.(MHz)
1.25
3.5
5
7
8.75
10
20
Sampling frequency(Fs,MHz)
1.4
4
5.714
8
9.8
11.429
22.857
FFT Size
128
512
512
1024
1024
1024
1024
Subcarrier Frequency Spacing
10.9375kHz / 11.16015625 kHz
Useful Symbol Time
91.429 us / 89.604 us
Guard Time
Tg = Tb/8 = 10.9 us / 11.2 us ( Others: Tb/4 = 22.85725 us
/ 22.401 us, Tb/16 = 5.7143 us / 5.60025 us )
OFDMA Symbol Time
102.329 us / 100.804 us (based on 28/25, 8/7 sampling
factor)
Frame Sizes
(msec)
2
2.5
4
5
8
10
12.5
20
OFDM symbols
19
24
39
49
79
99
124
198
page-15
Duplex Mode
•
802.16(e) supports both TDD, H-FDD and FDD
5 ms
F1
DL
F1
DL
5 ms
UL
DL
UL
DL
UL
F2
UL
F1
DL
DL
F2
UL
UL
F1
F2
ΔT
DL1
TDD
H-FDD
(TDD over FDD)
True FDD
DL2
DL1
DL2
UL1
UL2
UL1
Hybrid FDD
page-16
Properties of FDD & TDD
• FDD:
– Simultaneous transmission in uplink and downlink is
possible.
– Asymmetric uplink and downlink traffic can not be
supported.
– Channel reciprocity does not exit which is a
disadvantage in case of AAS.
– Paired frequency bands are required.
• TDD:
– Flexible allocation of bandwidth in DL and UL
– Allows more effective MIMO techniques
– Transceiver design is cheaper and less complex
page-17
Channel Coding
•
To overcome the effect of the channel, WiMAX adopt
different channel coding for different situations.
Channel coding is composed of 3 steps: randomizer,
FEC and interleaving.
Transmitter:
•
Receiver:
•
•
– Data Æ Randomizer Æ FEC Æ Interleaving
– Data Å Randomizer Å FEC Å Interleaving
Randomizer
Randomizer
(8.4.9.1)
(8.4.9.1)
Burst data
FEC
FEC
(8.4.9.2)
(8.4.9.2)
Bit
BitInterleaver
Interleaver
(8.4.9.3)
(8.4.9.3)
Repetition
Repetition
(8.4.9.5)
(8.4.9.5)
Modulation
Modulation
(8.4.9.4)
(8.4.9.4)
Mapping to OFDM(A)
subchannels
page-18
Randomizer
•
•
The generator polynomial: 1+x14+x15
Except the preamble and FCH.
OFDMA randomizer initial vector
page-19
Encoding - CC
•
•
Convolutional Code is the most common code.
Constraint length=7, Code rate=1/2
G1 = 171OCT For X
G2 = 133OCT For Y
page-20
Convolutional Decoder
•
Viterbi Decoding:
•
Trellis Diagram:
– Search through space of all possible sentences.
– Pick the one that is most probable given the waveform.
0/00
0/00
0/00
1/11
1/11
0/10
0/11
1/00
1/01
0/10
1/01
t2
0/00
0/11
0/11
1/11
0/01
t1
0/00
t3
0/10
0/01
t4
t5
t6
page-21
Encoding - CTC
Conventional Turbo Code
RSC1
Interleaver
RSC2
page-22
Concatenated Code
•
•
•
•
Combination of two codes provides the greater coding gain
with less implementation complexity as a comparable single
code
Typically, inner code is a convolutional code while the outer
code is a block code
Convolutional code cleans up low-input SNR’s
Block code cleans up the remaining errors
page-23
Interleaver
•
•
Interleaver can avoid long runs of lowly reliable bits.
The first permutation
– ensure that adjacent coded bits are mapped onto nonadjacent
subcarriers.
m k = ( N cbps / 12 ) ⋅ k mod 12 + floor ( k / 12 ),
•
k = 0,1,... N cbps − 1
The second permutation
– ensure that adjacent coded bits are mapped onto less or more
significant bits of the constellation.
j k = s ⋅ floor ( m k / s ) + ( m k + N cbps − floor (12 ⋅ m k / N cbps )) mod( s )
k = 0,1,... N cbps − 1
s = ceil ( N cpc / 2 )
1, 2, 4, 6 for BPSK, QPSK,16-QAM, 64-QAM
page-24
Simple Interleaver
Concept
M x N Matrix
1
2
3
4
N+1 N+2 N+3 N+4
(M(M-1)N+3
(M(M-1)N+1
(M(M-1)N+4
(M(M-1)N+2
1, N+1, 2N+1, …(M(M-1)N+1
N
2N
Output
MN
2, N+2, 2N+2,…
2N+2,… (M(M-1)N+2
page-25
Repetition Code
•
It can be used to increase signal margin over the
modulation and FEC.
•
After FEC and interleaver, the data is segmented into
slots.
– UL: Ns = multiple of R
– DL: Ns = [ R×K , R×K+(R-1) ]
– R = 2, 4 ,6
•
This scheme applies only to QPSK and in all coding
schemes except HARQ with CTC.
page-26
Modulation
•
•
The data bits are entered serially to the constellation
mapper.
The support of 64-QAM is optional for license-exempt
bands.
BPSK
QPSK
16-QAM
64-QAM
page-27
Adaptive Modulation and
Coding (AMC)
•
Tail Biting CC,
CTC without H-ARQ
CTC with Chase Combining H-ARQ
CTC with Incremental Redundancy
H-ARQ*
Modulation Types for CC
– QPSK-1/2, -3/4
– 16QAM-1/2, -3/4
– 64QAM-1/2, -2/3, -3/4 (DL only)
•
Code rate
Receiver
SNR
QPSK
1/2
5
3/4
8
1/2
10.5
3/4
14
1/2
16
2/3
18
3/4
20
FEC
–
–
–
–
•
Modulation
16-QAM
64-QAM
Modulation Types for CTC
– QPSK-1/2, -3/4
– 16QAM-1/2, -3/4
– 64QAM-1/2, -2/3, -3/4, -5/6
(DL only)
page-28
ARQ (Automatic
Repeat reQuest)
• Conventional ARQ
– Stop-and-wait ARQ
– Go-back-N ARQ
– Selective-repeat ARQ
• Hybrid ARQ
– Chase Combining (CC)
– Incremental Redundancy (IR)
page-29
Chase Combining (CC)
•
•
Each retransmission repeats the first transmission or
part of it.
Soft combining of original and retransmitted signals
are done at receiver before decoding
Same Data
Data channel
Data1
Data1
Feedback channel
Data2
Data2
ack
ack
Data2
Data2
nack
nack
Data2
Data2
nack
nack
Data2
Data2
Data3
Data3
nack
nack
ack
ack
time
Soft Combination
page-30
Incremental
Redundancy (IR)
•
•
•
Each retransmission transmit the new code bits from
the mother code to lower the code rate.
Reducing the effective data throughput/bandwidth of
a user
Combine with the CTC.
Different Data
Data channel
Data1
Data1
Feedback channel
Data2
Data2
ack
ack
IR
IRdata2
data2
nack
nack
IR
IRdata2
data2 IR
IRdata2
data2
nack
nack
nack
nack
Data3
Data3
ack
ack
time
Check puncture table and do IR Combination
page-31
Simple Throughput
Calculation
page-32
Content
I
Baseband Technology
II
RF Technology
I
Multi-Input Multi-Output
II
Space Time Coding
III
Spatial Multiplexing
IV
Collaborative SM
V
Beamforming
Other Technology
III
page-33
Multi-Input Multi-Output
N×1
y p (t ) =
∑h
n=0
pn
x n (t ) + n (t )
⎡ h00
⎢h
H = ⎢ 10
⎢ M
⎢
⎣hM 0
h01
h11
M
hM 1
MIMO Decoder
Decoder
MIMO
y1(t)
…
Y = HS + N
M×1 M×N
y
yM(t)
xN(t)
IFFT
N
y0(t)
FFT
FFT
x1(t)
IFFT
hM0
h00
h10
…
MIMO Sub-channel
Sub--channel Mapping
Mapping
Sub
MIMO
IFFT
…
MIMO Encoder
Encoder
MIMO
x0(t)
L h0 N ⎤
L h1N ⎥⎥
O M ⎥
⎥
L hMN ⎦
page-34
Antenna Diversity
Transmit
(MISO)
Receive
(SIMO)
Both
(MIMO)
page-35
Capacity of MIMO
•
•
Shannon bound:
C = log 2 (1 +
P
σ n2
)
Capacity of 1 to M:
C = log 2 (1 + M
•
(bps/Hz)
P
σ n2
)
(bps/Hz)
Capacity of N to M:
1 P
C = log 2 (det( I +
HH
N σ n2
≈ K log 2 (1 +
P
σ n2
)
H
)) =
min{ M , N }
∑
i =1
log 2 (1 +
P
σ n2
λi )
(bps/Hz)
The Shannon Theorem has been broken by diversity method.
page-36
Multipath Number vs SNR
page-37
Advanced Technology on
MIMO
Space time code (STC)
–
–
–
Reduce fade margin by spatial diversity
Open loop
Peak rate limit
–
–
–
Improve capacity
Open loop
Requires good SINR and low spatial correlation
–
–
Optimally select STC or SM to adapt to channel condition
Reduced feedback
–
–
–
–
Improve link budget
Reduce interference
#Antennas ≥ 4 for good beamforming effect
Requires CSI feedback (e.g. sounding), good for slow
varying channel
page-38
Only extends range for unit transmission
Spatial multiplexing (SM)
Adaptive MIMO switch (AMS)
AAS (beamforming)
–
Space Time Code (STC)
Encoder
Encoder
•
S/P
S/P
S1
S2
− S 2*
S1*
STC
STC
Decoder
Decoder
Transmitter：
– Antenna 0: Tx transmit s1 and s2
– Antenna 1: Tx transmit –s2* and s1*
•
Receiver:
– x’1 = h0*∙r0 + h1 ∙r1*
– x’2 = h1* ∙r0 - h0 ∙r1*
– [s’1 s’2]T = HHX = ( |h0|2 + |h1|2 )[s1 s2]T + N
• Decoding is very similar to maximum ratio
combining.
page-39
Spatial Multiplexing
(SM)
•
Each transmit antenna transmits independent information
stream for high throughput
•
Collaborative spatial multiplexing
– Mobile stations have one or two antennas, BS has multiple antennas.
– Two single transmit antenna SS's can perform collaborative spatial
multiplexing onto the same subcarrier
– Result in the uplink capacity increment by assigning same uplink
resource to two SS’s simultaneously
page-40
Matrix Book of Tx DL
•
For 2 - antenna BS, the code books are shown as
following:
⎡S
A=⎢ i
⎣ Si +1
C=
•
− Si*+1 ⎤
⎥
Si* ⎦
⎡ Si ⎤
B=⎢
⎥
⎣ S i +1 ⎦
⎡ S i + jr ⋅ S i + 3
⎢
1 + r 2 ⎣ S i +1 − r ⋅ S i + 2
1
r ⋅ S i +1 + S i + 2 ⎤
−1+ 5
⎥, r =
2
jr ⋅ S i + S i + 3 ⎦
SM operation mode for data stream:
– Vertical Encoding
– Horizontal Encoding
•
Choose matrix type and MIMO architecture, according
to the channel characteristics, system profile
(permutation type, antenna number) and encoding
schemes.
page-41
MIMO Architecture
Matrix A, Vertical Matrix B
AAfor
for2,3,4
2,3,4Tx
Tx
page-42
BBfor
for33or
or44Tx
Tx
MIMO Architecture 2
Matrix B for Horizontal Encoding
2 Layers
•
•
•
It is the same for Matrix C
The number of layers depends on the number of
encoding/modulation paths.
The number of STC output paths is the same between
vertical and horizontal.
page-43
Antenna Grouping /
Selection
•
The proposed STC code for 3Tx-rate 1 configuration with
diversity order 3 is given by 3 permutation types.
⎡ ~ ~*
⎤
⎢ S1 − S 2 0 0 ⎥
⎢ ~ ~ ~ ~ ⎥
A1 = ⎢ S 2 S1* S 3 − S 4* ⎥
⎢ 0 0 ~ ~* ⎥
S4 S3 ⎥
⎢
⎣
⎦
⎡~ ~*
⎤
⎢ S1 − S 2 0~ 0~ ⎥
⎢
⎥
A3 = ⎢ 0 0 S 4 S3* ⎥
~
~
~ ~
⎢S S *
*⎥
1 S 4 S3
2
⎢⎣
⎥⎦
⎡ ~ ~ * ~* ~ * ⎤
⎢ S1 − S 2 S 3 − S 4 ⎥
⎢ ~ ~
⎥
A2 = ⎢ S 2 S1* 0 0 ⎥
~
~
⎢ 0 0 S S* ⎥
4
3
⎢
⎥
⎣
⎦
Tx1,
Tx1, Tx2
Tx2 at
at subcarrier
subcarrier 11
Tx1,
Tx1, Tx2
Tx2 at
at subcarrier
subcarrier 11
Tx1,
Tx1, Tx2
Tx2 at
at subcarrier
subcarrier 11
Tx2,
Tx2, Tx3
Tx3 at
at subcarrier
subcarrier 22
Tx1,
Tx1, Tx3
Tx3 at
at subcarrier
subcarrier 22
Tx1,
Tx1, Tx3
Tx3 at
at subcarrier
subcarrier 22
Si = xi ⋅ e jθ for I = 1, 2, …, 8, where θ = tan −1 ( 1 )
~
S 1 = S1I + jS 3Q
~
S 2 = S 2 I + jS 4Q
~
S 3 = S3 I + jS1Q
~
S 4 = S 4 I + jS 2Q
3
Si = SiI + SiQ
page-44
Adaptive MIMO Switch
page-45
Diversity Combination
•
Switched combining: the current branch is used until
a metric fails a certain threshold (e.g. Received
Signal Strength Indicator)
– Cheap and simple, but not ideal
•
Selection combining: the most appropriate branch is
always selected. Slight performance advantage over
switch diversity.
– All diversity branches must be analysed
– RSSI is not ideal – unduly affected by interference
•
Equal Gain Combining: simply co-phase and sum all
branches
– Multiple receive chains are required
•
Maximal Ratio Combining: each branch is combined
according to its signal-to-noise ratio.
– Optimal performance
– Requires multiple receive chains and S/N calculation
page-46
Diversity Improve
Performance
BER
Frequency-selective channel
(no equalization)
AWGN
channel (no
fading)
“BER floor”
Flat fading channel
SNR
Frequency-selective channel
(equalization or Rake receiver)
page-47
MIMO Simulation
Demodulation scheme = Zero-Forcing detection
Center frequency = 2.3GHz
OFDM Symbol B.W. = 1.75MHz
FFT size = 256
Np = 8
Modulation = QPSK
Sampling Factor = 8/7
Sampling Frequency = 2MHz
Length of Symbol = 128 us
Length of guard interval = 16 us
Maximum delay spread = 5 us
No Channel Coding
Ref: A Fine Frequency Synchronization and
Tracking for Mobile WiMAX Broadcasting Systems
page-48
Adaptive Array System
(AAS)
•
Requirements:
– Requires CSI feedback (e.g. sounding), good for slow varying
channel
– #Antennas ≥ 4 for good beamforming effect
•
Advantages:
– Extend range for unit
transmission
– Improve link budge
– Reduce interference
page-49
Beamforming & Smart
Antenna
SIGNAL
BEAMFORMER
WEIGHTS
λc:
λc: wave
wave length
length
INTERFERENCE
Signal s(t)
w(r):
w(r): spatial
spatial signature
signature vector
vector
INTERFERENCE
Array data in Complex Baseband Format :
⎡ j 2λπ x1 ⋅r ⎤
⎡ x1 (t ) ⎤ ⎢ e c ⎥
⎡ n1 (t ) ⎤
⎥
⎢
x(t ) = ⎢ M ⎥ = ⎢⎢ M ⎥⎥ s (t ) + ⎢⎢ M ⎥⎥ = w(r ) s (t ) + n(t )
2π
⎢ x M ( t ) ⎥ ⎢ j λc x M ⋅ r ⎥
⎢⎣nM (t )⎥⎦
⎦ e
⎣
⎢⎣
⎥⎦
page-50
Frequency Reuse Factor
( BS num per cluster, Sector Num per BS, Useable Frequency per BS )
page-51
Fractional Frequency
Reuse
page-52
Coverage
page-53
DL Budget for WiMAX
page-54
DL Budget for WiMAX
page-55
Content
I
Baseband Technology
II
RF Technology
III
Data Allocation
I
Frame Structure
II
Zone
III
Burst
IV
Subcarrier allocation
page-56
OFDMA Frame Structure
TDD
page-57
Return
DL & UL Data Allocation
•
•
•
Slot is the minimum allocation unit.
The length of slot depends on the permutation type.
The data allocation is according to 2 dimensions
“subchannel & symbol”
page-58
OFDMA Preamble
page-59
OFDMA Preamble
Index :
[0 : 113]
IDcell :
[0 : 31]
Segment:
0,1,2
Totally 142*4=568 bits (forced to zero when fit into DC carrier)
3*568=1704, 1704-DC carrier=1703, 1703-out of range=1702page-60
Midamble and Postamble
Frame n-1
Frame n
Frame n+1
DL subframe
LP
FCH
…
Frame m
UL subframe
DL
DL
M
Burst 1
Burst 2
…
DL
Burst Y
Postamble
Midamble
Preamble
SP
UL Data
UL Data
… M
Symbol
P+1
Symbol 1
…
UL Data
P
Symbol Q
page-61
Subframe Structure
• OFDMA Subframe Structure
– Zones
•
•
•
•
STC
AAS
Permutation
Common Sync Symbol
– Bursts
– Sub-Bursts
page-62
Multiple Zones in SubFrame
•
Zone types：
•
Other Parameters：
– Normal, STC, AAS, Common Sync Symbol
– Permutation types (FUSC,PUSC,AMC)
– Midamble, Boosting, Preamble Configuration, SDMA
page-63
Permutation
Contiguous Permutation
(Band AMC)
•
Downlink Permutation
– Band AMC
(1*6, 2*3, 3*2)
– FUSC
– Optional FUSC
– PUSC
– TUSC1, TUSC2
•
Uplink Permutation
– Band AMC
(1*6, 2*3, 3*2)
– PUSC
– Optional PUSC
Diversity Permutation
(FUSC、PUSC)
page-64
Permutation Explanation
•
•
•
•
•
•
•
PUSC
–
–
Partial usage of subchannels.
Divide the subcarrier into clusters.
–
–
Advanced cluster structure.
Only for UL.
–
–
Full usage of subchannels.
Only for DL.
–
–
Advanced cluster structure.
Only for DL.
–
–
Advanced Modulation/Coding
Adjacent subcarrier permutation
–
–
Tile usage of subcarriers
Only for DL + AAS.
–
–
Tile usage of subcarriers
Only for DL + AAS
Optional PUSC
FUSC
Optional FUSC
AMC
TUSC1
TUSC2
page-65
Permutation Tradeoff
Contiguous
Permutation (Band
AMC)
Diversity Sub-carrier
Permutation
(PUSC,FUSC)
Benefits
Sub-channelization
gain、Frequency
selective loading gain
Sub-channelization
gain、Frequency
Diversity、Inter-cell
interference averaging
Scheduling
Advanced frequency
Simple scheduler,
scheduler to explore
Rely on frequency
frequency selectivity gain diversity to achieve
robust transmission
Channel
Condition
Stationary channel
Fast-changing channel
Favorable
Smart Antenna
Tech.
Beamforming
MIMO
page-66
Slot Definition
Permutation
Downlink
Uplink
AMC
1 subchannel by 2,3,6
OFDMA symbol
1 subchannel by 2,3,6
OFDMA symbol
PUSC
1 subchannel by
OFDMA symbols
1 subchannel by
OFDMA symbols
3
Optional PUSC
n/a
1 subchannel by
OFDMA symbols
3
FUSC
1 subchannel by
1 OFDMA symbol
n/a
Optional FUSC
1 subchannel by
1 OFDMA symbol
n/a
TDSC1
1 subchannel by
3 OFDMA symbols
n/a
TDSC2
1 subchannel by
3 OFDMA symbols
n/a
2
page-67
Subframe Structure
• OFDM(A) Frame Structure
– Zones
– Bursts
•
•
•
•
Allocation
Boosting
Modulation
Coding
– Sub-Bursts
page-68
Burst
•
•
For DL
–
–
–
–
Frame Control Header (FCH)
Map Data Burst (DL-MAP、UL-MAP)
Normal Data Burst
AAS Burst (Optional)
–
–
–
–
–
–
–
Initial Ranging/Handover Ranging
Periodic Ranging/Bandwidth Request
HARQ ACK Channel
Fast Feedback Channel
PAPR/Safety Zone
Sounding Zone
Normal Data Burst
For UL
page-69
FCH
•
Sub channel bit map
RNG
REP
Coding
DLDL-Map Len
Reserved
6 bits
1 bit
2 bits
3 bits
8 bits
4 bits
Frame Control Header
– Used subchannels bitmap Æ 6 groups
– Ranging Change Indicator Æ Periodic/B.W. Request
– DL-Map Coding parameters
• Repetition Coding Indicator (1,2,4,6)
• Coding Indicator CC (mandatory), BTC, CTC or ZT CC
– DL-MAP Length
– Total 24 bits
•
Fixed Location and Coding Rate:
– None FFT-128
• First 4 slots of the segment
• QPSK rate ½ with repetition coding of 4
– FFT-128
• Only the first slot
• No repetition code
page-70
DL-MAP
Coding Parameters
FCH
DL-MAP
Collect a symbol block for
FEC decoder
Coded
Information
Data
FEC
decoder
S0
S1
Sn
S0
S1
Sn
Combine
MAC Message
page-71
MAP Message Type
page-72
Downlink Map
page-73
OFDMA Ranging
•
Initial-ranging / handover-ranging
– N1 = 2 or 4 symbols
•
Periodic-ranging / BW-request
– N1 = 1 or 3 symbols
N2 = 6 for default
8 for optional
page-74
CDMA_Allocation_IE
Duration
in units of OFDMA slots
Ranging Code
CDMA code sent by the SS
Ranging Symbol
the OFDMA symbol used by SS
Ranging subchannel
indicates the subchannel used
BW request mandatory
indicates whether SS shall include
a BW request in the allocation
page-75
Ranging Code
•
•
•
A set of 256 special PN 144 bit-long ranging codes
are divided into 4 groups for initial, periodic ranging,
bandwidth requests and handover-ranging.
144bits are used to modulate the subcarriers in a
group of 6 adjacent subchannels.
These codes are BPSK modulated onto the
subcarriers in the ranging channel. (1 bit per
subcarrier)
page-76
Auto Correlation
150
decode ranging code autocorrelation
For six users
100
R(t)
60
decode ranging code autocorrelation
50
50
40
0
50
100
150
200
shift
250
R(t)
0
300
350
30
For one user
20
10
0
0
50
100
150
200
shift
250
page-77
UL ACK Channel
•
Provides feedback for Downlink HARQ
– One ACK channel occupies half subchannel by three
OFDMA symbols
• 3 pieces of 4x3 uplink tile in the case of PUSC
• 3 pieces of 3x3 uplink tile in the case of optional PUSC
– ACK coding
• If 0 for ACK, modulation vector 0,0,0 on ACK channel
• If 1 for NACK, modulation vector 4,7,2 on ACK channel
•
Tile(0)
Tile(0)
Tile(1)
Tile(1)
ACK Channel
– Modulated by the QPSK symbol
– Even and odd half subchannel
1 ACK Channel
(mini-subchannel)
Tile(2)
Tile(2)
Tile(3)
Tile(3)
Tile(4)
Tile(4)
Tile(5)
Tile(5)
page-78
Fast Feedback Channel
•
•
•
Slots are shared by multiple channels.
Controlled by CQICH IE (control/allocation)
Type:
– Normal fast feedback channel
• Used for STTD, SM, Permutation, Precoding Selection, MCS
– Enhanced fast feedback channel
• Normal + Anchor BS report
–
–
–
–
–
Band AMC differential CINR feedback
Indication Flag Feedback
Primary/Secondary fast feedback channel
Extended rtPS bandwidth request
MIMO feedback for transmit beamforming
page-79
PAPR/Safety Zone
•
•
PAPR Zone reduces the PAPR value.
Safety Zone reduces the interference between BSs.
PAPR reduction/Safety zone/Sounding zone allocation IE
page-80
Sounding Zone
UL Channel Sounding is a means of providing channel
response information to the BS on an as-needed
basis
DL-MAP
UL-MAP
UL-MAP
DL-MAP
– Intended for TDD systems where UL&DL RF reciprocity can be
leveraged
– Simple, efficient, low complexity, and effective
– Periodicity feature can be used to significantly reduce
sounding-command-IE overhead if continual sounding is
required
Frequency
•
page-81
Subcarrier Allocation in
DL PUSC
•
•
Dividing the subcarriers into the number of
physical clusters
Renumbering the physical clusters into logical
clusters
– For first DL Zone
• RenumberingSequence (PhysicalCluster)
– For others
• RenumberingSequence((PhysicalCluster) + 13⋅DL_PermBase)mod
Nclusters
•
Allocate logical clusters to group
•
Allocating subcarriers to subchannel in each
major group
– Dividing the clusters into 6 major groups
– G0: cluster 0-11, G1:12-19, … G5:52-59 for 1024-FFT
– Even group: use basic permutation sequence 6
– Odd group: use basic permutation sequence 4
page-82
Subcarrier Allocation in
DL PUSC
page-83
1024 OFDMA DL carrier
allocation - PUSC
page-84
Band AMC Allocation
•
AMC allocation can be made by two mechanisms
– Subchannel index reference in DL / UL MAP
• A slot is defined as N bines by M symbols
• NxM = 6
– Subchannel allocation in a band using HARQ map
• A group of 4 rows of bins is called a physical band
• A slot consists of 6 contiguous bins in a band
AMC slot
AMC slot
page-85
1024 OFDMA DL carrier
allocation - AMC
page-86
Pilot in Diversity
Permutation
FUSC
DL PUSC Cluster Structure
Even symbol
Odd symbol
Symbol 0
Symbol 1
Symbol 2
UL PUSC Tile Structure
UL OPUSC Tile Structure
page-87
Cluster Structure for
FUSC
•
For even symbols
•
For odd symbols
– Antenna 0 uses VariableSet#0 and ConstantSet#0
– Antenna 1 uses VariableSet#1 and ConstantSet#1
– Antenna 0 uses VariableSet#1 and ConstantSet#0
– Antenna 1 uses VariableSet#0 and ConstantSet#1
page-88
Subchannel Number for
Permutation
Downlink
Uplink
FUSC
PUSC
AMC
6X1
AMC
3X2
AMC
2X3
AMC
1X6
PUSC
AMC
6X1
AMC
3X2
AMC
2X3
AMC
1X6
FFT
128
2
3
2
4
6
12
4
2
4
6
12
FFT
512
8
15
8
16
24
48
17
8
16
24
48
FFT
1024
16
30
16
32
48
96
35
16
32
48
96
FFT
2048
32
60
32
64
96
192
70
32
64
96
192
page-89
Pilot Modulation
•
•
•
The polynomial for the PRBS generator is X11+X9+1
The sequence is 11111111111000…
The third 1 is W2=1, shall be used in the first OFDM
downlink symbol following the frame preamble
page-90
Cluster Structure for PUSC
using 4 antennas
page-91
STC in Uplink
For STTD (Space-Time Transmit Diversity) Mode
Antenna 0 (Pattern A)
Antenna 1 (Pattern B)
For SM (Spatial Multiplexing) Mode
Horizontal mode: First burst on antenna 0, Second burst on antenna 1
Vertical Mode: 2 consecutive slots are mapped instead of a single slot.
First slot of each slot pair on antenna 0.
Second slot on antenna 1.
For both modes, the pilot allocation is the same with STTD mode. page-92
Collaborative Spatial
Multiplexing
•
For 2 single transmit antenna SS’s
– One use uplink tile with pattern A
– Another one use tile with pattern B
•
For 2 dual transmit antennas SS’s
– One use uplink tile with pattern A,B
– Another one use tile with pattern C,D
Pattern C
Pattern D
page-93
Reference
•
•
•
•
•
•
•
802.16™ IEEE Standard for Local and metropolitan area networks
IEEE Std 802.16e™-2005 and IEEE Std 802.16™-2004/Cor1-2005
Performance of Convolutional Turbo Coded High-speed Portable Internet
(WiBro) System, 2007
OFDMA PHY SAP Interface Specification for 802.16 Broadband Wireless
Access Base Station
IEEE 802.16e-2005 Air Interface Overview
Timing Recovery for OFDM Transmission, Baoguo Yang, Member, IEEE,
Khaled Ben Letaief, Roger S. Cheng, Member, IEEE, and Zhigang Cao,
Senior Member, IEEE
Closed-Loop MIMO for Rel.1.x FDD Operation, Wen Tong, Peiying Zhu, MoHan Fong, SangYoub Kim, Michael Wang Nortel Networks, Aug, 2007
page-94