Progress of MB-OFDM UWBProgress of MB-OFDM UWBBaseband SystemBaseband System

Wen-Hua Wu

May 26, 2006May 26, 2006

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OutlineOutline

• Transmitter Architecture• Channel Model• Receiver Architecture• Simulation Results• Word Length Simulation• Future Works• Conclusions

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Transmitter Architecture

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System ParametersSystem Parameters

Info. Data Rate (MAC to PHY) 480 Mbps

Modulation/Constellation OFDM/DCM

IFFT/FFT Size 128

Spreading Rate 1

Information Tones 100

Data Tones 100

Information Length 242.4 ns

Zero-padded Suffix 60.6 ns

Guard Interval 9.5 ns

Symbol Length 312.5 ns

Sampling Frequency 528 MHz

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Rate-dependent ParametersRate-dependent Parameters

DataRate

(Mb/s)Modulatio

n

Coding

Rate(R)

ConjugateSymmetric

Input to IFFT

TimeSpreadin

gFactor

OverallSpreadin

gGain

Coded Bits

per OFDM

Symbol

53.3 QPSK 1/3 Yes 2 4 100

55 QPSK 11/32 Yes 2 4 100

80 QPSK 1/2 Yes 2 4 100

106.7 QPSK 1/3 No 2 2 200

110 QPSK 11/32 No 2 2 200

160 QPSK 1/2 No 2 2 200

200 QPSK 5/8 No 2 2 200

320 DCM 1/2 No 1 1 200

400 DCM 5/8 No 1 1 200

480 DCM 3/4 No 1 1 200

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Transmitter ArchitectureTransmitter Architecture

• Inner transmitter w/ frequency interleaving

Scrambler/Encoder

Scrambler/Encoder

IFFTIFFT ZPZP DAC LPF BPF

Pilot/Guard/NullSub-carriers

Puncturer/InterleaverPuncturer/Interleaver DCMDCM

PreambleGenerationPreamble

GenerationMulti-BandGenerationMulti-BandGeneration

DataSourceData

Source

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Transmitted SignalsTransmitted Signals

• 30 preambles, including… & data– 21 packet synchronization sequences– 3 frequency synchronization sequences– 6 channel estimation sequences

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Channel Model

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Multipath Channel Model (1/2)Multipath Channel Model (1/2)

• 4 channel models are defined

• LOS: Line of sight– No obstacles between Tx and Rx

• NLOS: Non-line of sight

Channel model LOS/NLOS Transmit Distance

Achievable data rate

CM 1 LOS 0~4 m 480 Mb/s

CM 2 NLOS 0~4 m 200 Mb/s

CM 3 NLOS 4~10 m 110 Mb/s

CM 4 NLOS extreme -

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Multipath Channel Model (2/2)Multipath Channel Model (2/2)

• CM1~CM4

• Linear convolution– lost linearity in frequency domain

Channel model Delay Spread (ns) Number of Paths

CM 1 28.5 15

CM 2 32.3 17

CM 3 55.1 29

CM 4 91.2 (> 70.1) 48

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CFO & SFOCFO & SFO

Rx CFORx CFO Rx SFORx SFO

Tx CFOTx CFO

• CFO: carrier Frequency offset• SFO: sampling frequency offset

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Channel ImpairmentChannel Impairment

• 4 effects are added to simulate this system

MultipathChannel Model

CarrierFrequency

Offset

SamplingFrequency

OffsetAWGNTxTx RxRx

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Receiver Architecture

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Receiver ArchitectureReceiver Architecture

PacketDetectorPacket

DetectorBoundaryDetectorBoundaryDetector

CFOCompensator

CFOCompensator

ZPRemover

ZPRemover FFTFFT FEQFEQ

PhaseTrackerPhase

TrackerFFT WindowController

FFT WindowController

De-MapperDe-Mapper

CFOEstimator

CFOEstimator

A/DRFRF

ChannelEstimatorChannel

Estimator

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Packet DetectorPacket Detector

D(495)

()*

…

…

Shift Registers (128)÷ DecisionVar.>0.5?

RxInput

()2

()2

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Boundary DetectorBoundary Detector

KNOWN PREAMBLE

RxInput …

Shift Registers (128)

…

Shift Registers (128)

* * *…

Shift Registers (?)

PeakDetection

* is MAC

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CFO EstimatorCFO Estimator

D(495)

()*

…

Shift Registers (128)

RxInput

tan-1()

SamplingFrequency

÷-2*π*495

EstimatedCFO

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CFO Compensator & ZP CFO Compensator & ZP RemoverRemover

exp( )*

j2π(estimated CFO)t

RxInput

CFO Compensated

Data

D(1)

Comparator128 & 165 (++/--) flag

0

1

add-drop occurrence

flag

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Channel Estimator (1/2)Channel Estimator (1/2)

OUT 1 OUT 2 OUT 3 OUT 4 OUT 128

CE SEQUENCE 01CE SEQUENCE 02… …ReceivedCE Seq.

Shift Registers (128) Shift Registers (128)

…

÷ ÷ ÷ ÷ ÷…

KNOWN CE SEQUENCE * 2…

Register Files (128)

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Channel Estimator (2/2)Channel Estimator (2/2)

MagnitudeMagnitude

PhasePhase

MagnitudeMagnitude

PhasePhase

Actual ChannelActual Channel Estimated ChannelEstimated Channel

Actual ChannelActual Channel Estimated ChannelEstimated Channel

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Phase TrackerPhase Tracker

KNOWN PILOTS

POLARITY

…

÷

…

Register Files (127)

ReceivedPilot

Register Files (12)

tan-1()

( 正頻 )

Accumulator ( 負頻 ) ÷360

EstimatedSlope

÷12

EstimatedRCFO

• Extract pilots from FEQ

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FFT Window Controller (1/4)FFT Window Controller (1/4)

Register Files (12)

KNOWN PILOTS

POLARITY

…

÷

…

Register Files (127)

ReceivedPilot

tan-1()>π?

<-π?

Comparatormin indexwanted

index whereadd-drop occurs

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FFT Window Controller (2/4)FFT Window Controller (2/4)

• If sampling time is earlier 1 sample time than the original sampling time, …– drop 1 sample (fft window moves backward)– in contrast, add 1 sample (fft window moves forwar

d)

2 knN -1 -N

n=0

R'(k)= r(n - T)* e

2πk(n- T) 2πk TN -1 - -N N

n=0

= r(n - T)* e * e

2πk T-N= R(k)* e

Window DriftWindow Driftk: sub-carrier idxk: sub-carrier idx

n: t-domain sample idxn: t-domain sample idx

N: FFT sizeN: FFT size

△△T: window drift amountT: window drift amount

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FFT Window Controller (3/4)FFT Window Controller (3/4)

• Observing phase drift amount @...– max_positive_freq_idx & min_negative_freq_idx

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FFT Window Controller (4/4)FFT Window Controller (4/4)

AWGN, SNR = 10 dB

CFO/SFO = 40/40 ppm

With add-drop

data OFDM symbol # = 200

AWGN, SNR = 10 dB

CFO/SFO = 40/40 ppm

No add-drop

data OFDM symbol # = 200

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Simulation Results

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QPSK v.s. DCMQPSK v.s. DCM

• Simulation environment:– under AWGN channels

• DCM is better than QPSK about 1~1.5 dB

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Carrier Frequency OffsetCarrier Frequency Offset

• Simulation environment:– under AWGN channels

• CFO seems not degrade system performance a lot

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Data Payload LengthData Payload Length

• Maximum data payload length is 4,095 octets– system performance degrades a little

• The following simulation use 2,500 octets

Saturate @ SNR 10Saturate @ SNR 10-4-4

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Multipath CM1~CM4 (1/2)Multipath CM1~CM4 (1/2)

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Multipath CM1~CM4 (2/2)Multipath CM1~CM4 (2/2)

• Target @ good channels of each CM• CM1~CM3 reach SNR 10-3 @ about 13, 14 dB

• Word length simulation targets @ 10, 14, 18 dB

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Word Length Simulation

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Introduction to WL sim. (1/2)Introduction to WL sim. (1/2)

• 2 criteria for determining word length of each signal @ this circuit– Reduce hardware cost– Maintain the same system performance

as in floating-point simulation

• According to system performance, …– 10 dB should achieve BER 10-2

– 14 dB should achieve BER 10-3

– 18 dB should achieve BER 10-4

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Introduction to WL sim. (2/2)Introduction to WL sim. (2/2)

• Assume transmit 2.6921 from block A to block B, and quantized to 10 bits

• Preserve 1 bit for sign bit (LSB)

AA BB2.69212.6921

2.69212.6921*2*2(10-1-2)(10-1-2)==344.5888344.5888

+344 (+344 (01010110000101011000) is transmitted) is transmitted

+344 (+344 (01010110000101011000) is received) is received

344/2344/2(10-1-2)(10-1-2)==2.68752.6875

2.68752.6875

sign bitsign bit integer bitinteger bit

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Word length of each block @ TxWord length of each block @ Tx

55 1010

99 99

DCMDCM IFFTIFFT

ZPZP MB Gen.MB Gen.

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Word length Sim. @ RxWord length Sim. @ Rx

• WL simulation starts from AD’s output

1414

ADAD

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Future WorksFuture Works

• Complete word-length simulation• Fixed-point simulation (FPGA emulation)

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ConclusionsConclusions

• UWB’s fundamental receiver architecture is proposed

• Transmission data rate can be up to 480 Mbps

• RCFO will speed up the occurrence of add-drop

• ZP seems not better than CP• Word-length simulation takes time, but it is

necessary

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ReferenceReference

[1] 802.15 working group, “IEEE Std 802.15.3TM-2003,” U.S. New York, NY 100 16-5997, Sep. 29, 2003.

[2] J. Foerster, Ed., “Channel modeling sub-committee report final,” IEEE802.15-02/490.

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Appendix

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Multi-Band (1/3)Multi-Band (1/3)

• Band allocation, 5 bands are defined

frequency

Band#1

3432MHz

Band#2

Band#3

Band#4

Band#5

Band#6

Band#7

Band#8

Band#9

Band#10

Band#11

Band#12

Band#13

Band#14

3960MHz

4488MHz

5016MHz

5544MHz

6072MHz

6600MHz

7128MHz

7656MHz

8184MHz

8712MHz

9240MHz

9768MHz

10296MHz

Band Group #1 Band Group #2Band Group #3 Band Group #4Band Group #5

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Multi-Band (2/3)Multi-Band (2/3)

• Time-frequency codes and preamble patterns for band group 1

TFC Numbe

r

Base sequence /

Preamble

Mode 1 (mandatory): Length 6 Time-Frequency Code

1 1 1 2 3 1 2 3

2 2 1 3 2 1 3 2

3 3 1 1 2 2 3 3

4 4 1 1 3 3 2 2

5 5 1 1 1 1 1 1

6 6 2 2 2 2 2 2

7 7 3 3 3 3 3 3

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Multi-Band (3/3)Multi-Band (3/3)

• OFDM symbols’ transmit orders: frequency jumps for each OFDM symbol

…

Band #1

Band #2

Band #3

Band #4

Band #5

Band #6

…

Time

Synchronization(24 symbols)

Channel Estimation(6 symbols)

Header(12 symbols)

Payload(1~4096 bytes)

13.125 μsec (Preamble + Header)

…

Frequency

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Packet FormatPacket Format

• 30 preambles must be transmitted during 9.375μs, with each preamble 165 samples

• The sampling frequency at the receiver must be faster than or equaled to 528 MHz

PLCPPreamble

PLCPPreamble

PHYHeader

PHYHeader

TailBitsTailBits

MACHeader

MACHeaderHCSHCSTail

BitsTailBits

PadBitsPadBits

PLCP Header53.3 Mb/s

53.3, 80, ..., 480Mb/s

528Msamples/s

Frame Payload:Variable LengthFrame Payload:Variable LengthFCSFCS Tail

BitsTailBits

PadBitsPadBits

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Preamble GenerationPreamble Generation

• There are 3 different kinds of preambles for UWB

Packet Sync. Sequence21 OFDM symbols

Packet Sync. Sequence21 OFDM symbols

Frame Sync. Sequence3 OFDM symbols

Frame Sync. Sequence3 OFDM symbols

Channel Est. Sequence6 OFDM symbols

Channel Est. Sequence6 OFDM symbols

…PS1PS1 … CE6CE6

0…0 C0 C1…C127 0 0 0 0 00…0 C0 C1…C127 0 0 0 0 0 0…0 -C0 -C1…-C127 0 0 0 0 00…0 -C0 -C1…-C127 0 0 0 0 0

32 consecutive 0’s

PS2PS2 PS21PS21 FS1FS1 FS2FS2 FS3FS3 CE1CE1 CE2CE2

32 consecutive 0’s 32 consecutive 0’s

0 T1…T610 0 0 0 0T-61…T-10 T1…T610 0 0 0 0T-61…T-1

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IFFTIFFT

• Pilot tones: #±5, #±15, #±25, #±35, #±45, #±55

• Guard tones: #±57, #±58, #±59, #±60, #±61

IFFT

012

61626364656667

126127

012

61626364656667

126127

...

...

...

...

...

...

...

...

NULL# 1# 2

# 61NULLNULLNULLNULLNULL# -61

# -2# -1F

req

uen

cy-D

om

ain

In

pu

ts

Tim

e-D

om

ain

Ou

tpu

tsM(n)

n - 56n - 55n - 54n - 53n - 52n - 51n - 50n - 49n - 48n - 47n - 46n - 45n - 44n - 43

n = 01≦n≦9

10≦n≦1819≦n≦2728≦n≦3637≦n≦4546≦n≦4950≦n≦5354≦n≦6263≦n≦7172≦n≦8081≦n≦8990≦n≦98

n = 99

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Sampling Frequency Sampling Frequency CalculationCalculation

• The sampling frequency at the output end of the transmitter is 528 MHz

• Take info. data rate 480 Mb/s for example:

DCMDCMPilot/Guard/Null toneInsertion

Pilot/Guard/Null toneInsertion

IFFTIFFT AddZP/GIAdd

ZP/GI

480Mb/s

OuterTransmitter

OuterTransmitter

DataSourceData

Source

640Mb/s

320Msample/s

409.6Msample/s

528Msample/s