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The Next Generation Challenge for
Software Defined Radio
Mark Woh1, Sangwon Seo1, Hyunseok Lee1, Yuan Lin1,
Scott Mahlke1, Trevor Mudge1, Chaitali Chakrabarti2, Krisztian Flautner3
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Advanced Computer Architecture Lab, University of Michigan2Department of Electrical Engineering, Arizona State University3ARM, Ltd.
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3G Wireless
Large Coverage
Outdoor - High Mobility
Up to 14Mbps
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Expected Wireless Growth
The growth of wireless will require more bandwidth
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4G Wireless
What we need
Adaptive high performance transmission system
Great candidate for SDR
Large Coverage 100Mbps Coverage
Outdoor - High Mobility
Macro CellsPico Cells
Isolated HotSpots 1Gbps Coverage
Indoor Very Low Mobility
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Next Generation Wireless 4G
MIMO
decoder
DEMOD
(OFDM)
Channel
Decoder
MIMOencoder
MOD(OFDM)
ChannelEncoder
.
..
..
.
IFFT
FFT STBC
VBLAST
..
.
Turbo code
LDPC code
TX
RX
Antenna
.
..
3 Major Components to 4G
Modulation/Demodulation
Multiple-Input Multiple-Out (MIMO)
Channel Decoder/Encoders
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Modulation - OFDM
0 fsc Nfsc
..
-Nfsc -fsc
Properties of OFDM-High Spectral Efficiency
-Low Intersymbol Intereference
-Flat Fading Subcarriers
Can sustain high data rates with
multiple users
Can be implemented with IFFT/FFT
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Major Component of Modulation FFT/IFFT
Very wide data level parallelism
Requires complex operations
complex
mult
x[1]
eiw
complex
add
complex
sub
x[0]
X[1]
X[0]
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MIMO (Multiple Input Multiple Out)
Previously we used single antenna systems
Now we use multiple antennas to increase the channel
capacity
Diversity - High Reliability
Space Time Block Codes (STBC)
Multiplexing High Throughput
Vertical-BLAST (V-BLAST)
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Space Time Block Codes (STBC)
CombinerChannel
Estimation
Channel
Estimation
Tx1 Tx2Transmit Antennas
x[1]
-x[2]*
x[2]
x[1]*
h11 h22
h21 h12
Channel
Rx1 Rx2
Time
Receive Antennas
n11
n12
n21
n22
~x[1]
~x[2]
h11
h12 h22
h21
Noise
y11 = h11x[1] + h12x[2] + n11
y12 = -h11x[2]* + h12x[1]* + n12
y21 = h21x[1] + h22x[2] + n21
y22 = -h21x[2]* + h22x[1]* + n22
Received
Signal
~x[1] = h11*y11 + h12y12* + h21*y21 + h22y22*
~x[2] = h12*y11 - h11y12* + h22*y21 - h21y22*
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STBC
Requires complex operations
Low Data Movement
Highly parallelizable
Complex
MultiplyAccumulate
Channel
Estimation
h22 h21 h12 h11
y21 y11
y22* y12*
Receiver Antenna 1 and 2
~x[1] ~x[2]
Conjugate
+Negation
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Vertical-BLAST (V-BLAST)
S/P
Mod
Mod
V-Blast
Detector
Demod
Demod
M Transmitters R Receivers
1 2 3 4 1 2 3 4 1 2 3 4
5 6 7 8 5 6 7 8 5 6 7 8
9 10 11 12 9 10 11 12 9 10 11 12
13 14 15 16 13 14 15 16 13 14 15 16
Data Stream of 4 TxLinear Combination
of Data
Channel
Estimation
Nulling
Vector
1 2 3 4
Subtract
Strong Signal
Repeat
Strongest
Signal
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V-BLAST
Implementation Based on Square Root Method for V-BLAST
Original requires repeated pseudo-inverse calculation for finding the
strongest signal
This algorithm has reduces complexity
Complexity
Requires matrix operations on complex numbers
Many Matrix Transformations
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Channel Decoding
3G Technologies in 4G
Viterbi
Turbo Decoder
New to 4G
LDPC
Better performance characteristics compared to Turbo and Viterbi
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LDPC
0 1 0 1 1 0 0 1
1 1 1 0 0 1 0 0
0 0 1 0 0 1 1 1
1 0 0 1 1 0 1 0
H =
E0
L0 L1 L2 L3
E1 E2 E3
L4 L5 L6 L7
L Node Original Value Message from Check Nodes Decision
L0
L1
L2
L3
L4
L5
L6
L7
1
1
0
1
0
1
0
1
E1 0 E3 1 1
0
0
1
0
1
0
1
E0 0 E1 0
E1 1 E2 0
E0 0 E3 1
E0 1 E3 0
E1 0 E2 1
E2 0 E3 0
E0 1 E2 1
E0
L0
L1
L2
L3
E1 E2 E3
L4
L5
L6
L7
1 1 0 01 1 0 1
E0
L0
L1
L2
L3
E1 E2 E3
0
L4
L5
L6
L7
1 1 0 01 1 0 1
Message Sent = [ 1 0 0 1 0 1 0 1 ]
Message Recieved = [ 1 1 0 1 0 1 0 1 ]
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LDPC
Min-Sum Decoding Used
Regular LDPC code
Can get benefit from Wide SIMD
Can do the Bit Node and Check Node
Alignment of Check and Bit nodes is a problem
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SODA PE Architecture
SIMD
Reg.
FileE
X
SIMD
ALU+
Mult
SIMD
Shuffle
Net-
work
(SSN)
W
B
Scalar
ALU
W
B
E
X
Scalar
RF
Local
SIMD
Memory
Local
Scalar
Memory
S
T
V
AGU
RFE
X
W
B
AGU
ALU
1. SIMD pipeline
2. Scalar pipeline
4. AGU pipeline
V
T
S
Pred.
Regs
W
B
SIMD
to
Scalar
(VtoS)ALU
RF
DMA
Global
Memory
SODA
DSP
5. DMA
3. Local
memory
SystemInterconnect
SIMD 32 Wide, 16-bit datapath, Predicate Execution
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Key 4Galgorithms
100 Mbps 1 GbpsMCycle/s MCycle/s
FFT 2x360 4x360
IFFT 2x360 4x360
STBC 240 -
V-BLAST - 1900
LDPC 7700 4x18500
4G Workload on SODA
100 Mbps 4G requires 8Ghz SODA PE
1 Gbps 4G requires 20Ghz SODA PE
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SODA With Technology Scaling
0
500
1000
1500
2000
2500
3000
3500
4000
180nm 130nm 90nm 65nm 45nm 32nm 22nm
Frequency(Mhz)
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
Power(W)
ITRS Scaled Frequency Fixed Scaled Frequency Scaled Power
180nm 130nm 90nm 65nm 45nm 32nm 22nm
Vdd (V) 1.8 1.3 1.1 1.1 1 0.9 0.8
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We cant do any of 4G with technology scaling on one core
Would 8GHz cores even be an energy efficient solution?
What about 1Gbps?
Are we ever going to get a 20GHz core?
Cannot rely on technology scaling to give us 4G for free
4G SDR will require algorithmic and architectural innovations
SDR Challenges In 4G
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4G Algorithm-Architectural Co-design
Architectural improvements (SODA II)
Specialized functional units
CISC-like complex arithmetic operations
Specialized data movement hardware
Less strain on the memory system
Wider SIMD
How wide can we go? More PEs
What does the interconnect look like?
Algorithmic optimization through parallelization
Reduce intra-kernel communication Reduce memory accesses
Arithmetic is much cheaper than data movement
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Thanks
Questions?
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Successive Cancelling for V-BLAST
V-BLAST successive interference cancelling (SIC)
The ith ZF-nulling vectorwi is defined as the uniqueminimum-norm vector satisfying
Orthogonal to the subspace spanned by the contributions to yi due
to the symbols not yet estimated and cancelled and is given by theith row of H
~
Al ti S h
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Alamouti Scheme
Assumption: the channel remains unchanged over two consecutive symbols Rate = 1
Diversity order = 2
Simple decoding
Ad t f S ft D fi d R di
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Advantages of Software Defined Radio
Multi-mode operations
Lower costs
Faster time to market
Prototyping and bug fixes
Chip volumes
Longevity of platforms
Enables future wireless communication
innovations
Cognitive radio
UWB EDGE 802.16a
802.16aBluetooth
802.11b WCDMA 802.11n
SDR