doc.: ieee 802.15-05-273r0 submission may 2005 c. razzell et alslide 1 project: ieee p802.15 working...

May 2005

C. Razzell et alSlide 1

doc.: IEEE 802.15-05-273r0

Submission

Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)Project: IEEE P802.15 Working Group for Wireless Personal Area Networks (WPANs)

Submission Title: [MB-OFDM Proposal Update]Date Submitted: [ 11 May, 2005]Source: [C. Razzell] Company [Philips]Address [1151 McKay Drive, San Jose, CA 95131]Voice:[+1 408 474 7243], FAX: [+1 408 474 8131], E-Mail:[[email protected]]

Re: [TG3a Down selection Process]

Abstract: [Contains technical details of Merged Proposal #1]

Purpose: [Provides motivation and justification for the MB-OFDM proposal under consideration]

Notice: This document has been prepared to assist the IEEE P802.15. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.Release: The contributor acknowledges and accepts that this contribution becomes the property of IEEE and may be made publicly available by P802.15.

May 2005


doc.: IEEE 802.15-05-273r0

Submission

MB-OFDM Proposal Summary

C. Razzell

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Contents:

• Spectrum mask requirements• Why OFDM is preferred• Time-frequency codes for additional

spreading• MB-OFDM PHY details and performance• Summary of benefits compared with direct

sequence approach• Conclusions

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Spectrum Mask Requirements (USA)

Max. Total Tx power =-41.3 + 10log(10.6-3.1) + 30 = – 2.5dBm

For 10m range @ 100Mbps @ 4GHz need approx. –10dBm

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Ultra wideband signals using OFDM• Orthogonal Frequency Division

Multiplexing– Can efficiently multiplex many sub-carriers to

occupy ~500MHz of spectrum– OFDM intrinsically deals with multipath issues

by keeping the symbol rate low (e.g., 3.2MHz)– Technology similar to 802.11a

• But only supports QPSK, not 16-QAM nor 64-QAM– Uses less ADC precision and lower arithmetic precision

than 802.11a/g signal processing

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Why OFDM is preferred(1)

• OFDM is spectrally efficient:– IFFT/FFT operation ensures that sub-carriers do not interfere with one other.– Since the sub-carriers do not interfere, the sub-carrier can be brought closer together

High spectral efficiency.

• OFDM has an inherent robustness against narrowband interference:– Narrowband interference will affect at most a couple of tones. Do not have to drop the entire band because of narrowband interference. Erase information from the affected tones, since they are known to be unreliable. Use

FEC to recover the lost information.

IFFT

FFTChannel

H(f)

NarrowbandI nterf erer Tone

I nterf erer

May 2005


doc.: IEEE 802.15-05-273r0

Submission


• OFDM has excellent robustness in multi-path environments.1. Zero prefix preserves orthogonality between sub-carriers --- linear

convolution with the c.i.r. is made to look like circular convolution IF

FT

FFTChannel

H(f)

f

H(f)

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Why OFDM is preferred(3)• OFDM has excellent robustness in multi-path

environments:

2. Allows receiver to capture multi-path energy more efficiently.

IFFT Channel

h(t) FFT

#1 #2 #N

h(t)

t

OFDM Symbol

Main Path

Path #2

Path #3

Path #N

FFTintegrates

energy overthe N paths

Window forinput to FFT

All paths received within Zero Prefi x(60.6 ns) are collected by FFT

May 2005


doc.: IEEE 802.15-05-273r0

Submission


• Ability to comply with worldwide regulations:– Channels and tones can

be turned on/off dynamically to comply with changing regulations.

– Can arbitrarily shape spectrum in software with a resolution of ~4 MHz.

3.2 3.4 3.6 3.8 4 4.2 4.4 4.6 4.8

-80

-75

-70

-65

-60

-55

-50

-45

Frequency (GHz)

dB

m/M

Hz

Power Spectral Density Estimate via W elch

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Time-frequency codes for additional spreading

• The FCC requires that UWB systems transmit with a bandwidth of >500MHz at all times

• Direct generation of OFDM signals of ~500MHz bandwidth is feasible with current CMOS technology

• However, 500MHz bandwidth alone is not optimum– Tx power is limited to –14.3dBm under FCC rules– Limited frequency diversity– Desire a method to multiply the occupied bandwidth without

impacting signal processing requirement…

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Example OFDM UWB Tx chain

DACScramblerConvolutional

EncoderPuncturer

BitInterleaver

ConstellationMapping

IFFTInsert Pilots

Add CP & GI

Interleaving Kernel

exp(j2fct)

InputData

128 pt IFFT in 312.5ns

507.35MHz

128 pt IFFT, 100 QPSK data tones, 12 pilots

528 MHz

May 2005


doc.: IEEE 802.15-05-273r0

Submission

MB-OFDM uses sequenced multiband approach to enhance OFDM

1 2 3 4 5 6 7

x 109

-80

-75

-70

-65

-60

-55

-50

-45

-40

Frequency [Hz]

PS

D d

Bm

/MH

z

Total wideband power is

-41.25+10log10(3) +

10log10(122) +

10log10(4.125) =

-9.5dBm

Occupied bandwidth (and power) multiplied by a factor 3 with almost no signal processing overhead!

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Time Frequency Codes for Multiple Access

• Typical methods for achieving multiple access: Spreading (CDMA), Coding

• In MB-OFDM, an additional method is used: Time-Frequency (TF) Codes:

• Time-Frequency Codes:– Spread information over all three bands in a given period of time.– Designed such that (on average) only 1/3 of the symbols would collide (FEC code can

compensate for the collisions).

• Performance is governed by SIR = (Psig/Pint) (W/R).– In realistic multi-path conditions: “BW expansion = (W/R) is all that matters”. – Systems with same BW expansion have similar multiple piconet capability.

Channel Number Preamble Pattern Mode 1 DEV: 3-band Length 6 TFC

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

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Overview of Multi-band OFDM

• Key Idea #1: – Divide the spectrum into bands that are 528 MHz wide.

• Advantages:– Transmitter and receiver process smaller bandwidth

signals (528 MHz).

f3432MHz

3960MHz

4488MHz

5016MHz

5544MHz

6072MHz

6600MHz

7128MHz

7656MHz

8184MHz

8712MHz

9240MHz

9768MHz

Band #1

Band #2

Band #3

Band #4

Band #5

Band #6

Band #7

Band #8

Band#9

Band #10

Band #11

Band #12

Band #13

10296MHz

Band #14

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

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Overview of Multi-band OFDM• Key Idea #2:

– Interleave OFDM symbols across all bands.

• Advantages:– Exploits frequency diversity.– Provide robustness against multi-path / interference.– Same transmit power as if the entire band is used.

TimeFreq (MHz)

3168

3696

4752

4224

Band # 1

Band # 2

Band # 3

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Overview of Multi-band OFDM

• Key Idea #3: – Insert a zero-padded prefix before IFFT output:

• Advantages:– Prefix provides robustness against multi-path even in the worst

case channel environments.

TimeFreq (MHz)

3168

3696

4752

4224

Band # 1

Band # 2

Band # 3

Prefix

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Overview of Multi-band OFDM• Key Idea #4:

– Insert a Guard Interval between OFDM Symbols:

• Advantages:– Guard interval allows TX/RX sufficient time to switch between

channels.

TimeFreq (MHz)

3168

3696

4752

4224

Band # 1

Band # 2

Band # 3

Guard Interval

May 2005


doc.: IEEE 802.15-05-273r0

Submission

System ParametersInfo. Data Rate 110 Mbps 200 Mbps 480 Mbps

Modulation/Constellation OFDM, QPSK OFDM, QPSK OFDM, QPSK

FFT Size 128 128 128

Coding Rate (K=7) R = 11/32 R = 5/8 R = 3/4

Frequency-domain Spreading No No No

Time-domain Spreading Yes Yes No

Data Tones 100 100 100

Zero-padded Prefix 60.6 ns 60.6 ns 60.6 ns

Guard Interval 9.5 ns 9.5 ns 9.5 ns

Symbol Length 312.5 ns 312.5 ns 312.5 ns

Channel Bit Rate 640 Mbps 640 Mbps 640 Mbps

Multi-path Tolerance 60.6 ns 60.6 ns 60.6 ns

May 2005


doc.: IEEE 802.15-05-273r0

Submission

PLCP Frame Format

• PLCP frame format:

• Rates : 55, 80, 110, 160, 200, 320, 400, 480 Mb/s. – Support for 55, 110, and 200 Mb/s is mandatory.

• Preamble + Header = 13.125 ms.

PLCP PreamblePHY

HeaderMAC

HeaderHCS

TailBits

TailBits

PadBits

Frame PayloadVariable Length: 0 4095 bytes

PadBits

TailBits

FCS

55 Mb/sPLCP Header 55, 80, 110, 160, 200, 320, 400, 480 Mb/s

RATE5 bits

LENGTH12 bits

Scrambler Init2 bits

Reserved2 bit

Reserved2 bit

Reserved2 bit

Reserved3 bit

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Link Budget and Receiver Sensitivity• Assumption: BG#1, AWGN, and 0 dBi gain at TX/RX

antennas.Parameter Value Value Value

Information Data Rate 110 Mb/s 200 Mb/s 480 Mb/s

Average TX Power -10.3 dBm -10.3 dBm -10.3 dBm

Total Path Loss 64.2 dB (@ 10 meters)

56.2 dB (@ 4 meters)

50.2 dB (@ 2 meters)

Average RX Power -74.5 dBm -66.5 dBm -60.5 dBm

Noise Power Per Bit -93.6 dBm -91.0 dBm -87.2 dBm

CMOS RX Noise Figure 6.6 dB 6.6 dB 6.6 dB

Total Noise Power -87.0 dBm -84.4 dBm -80.6 dBm

Required Eb/N0 4.0 dB 4.7 dB 4.9 dB

Implementation Loss 2.5 dB 2.5 dB 3.0 dB

Link Margin 6.0 dB 10.7 dB 12.2 dB

RX Sensitivity Level -80.5 dBm -77.2 dBm -72.7 dB

May 2005


doc.: IEEE 802.15-05-273r0

Submission

System Performance: Band Group #1

• The distance at which the Multi-band OFDM system can achieve a PER of 8% for a 90% link success probability is tabulated below:

• Includes losses due to front-end filtering, clipping at the DAC, ADC degradation, multi-path degradation, channel estimation, carrier tracking, packet acquisition, etc.

Range* AWGNLOS:0 – 4

m

NLOS:0 – 4

m

NLOS:4 – 10

m

RMSDelay

Spread25 ns

110 Mbps 20.5 m 11.4 m 10.7 m 11.5 m 10.9 m

200 Mbps 14.1 m 6.9 m 6.3 m 6.8 m 4.7 m

480 Mbps 8.9 m 2.9 m 2.6 m N/A N/A

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Signal Robustness/Coexistence• Assumption: Received signal is 6 dB above sensitivity.

• Values listed below are the required distance or power level needed to obtain a PER 8% for a 1024 byte packet at 110 Mb/s and BG #1.

• Coexistence with 802.11b and Bluetooth is relatively straightforward because they are out-of-band.

• Multi-band OFDM is also coexistence friendly with both GSM and WCDMA.– MB-OFDM has the ability to tightly control OOB emissions.

Interferer Value

IEEE 802.11b @ 2.4 GHz dint 0.2 meter

IEEE 802.11a @ 5.3 GHz dint 0.2 meter

Modulated interferer SIR –9.0 dB

Tone interferer SIR –7.9 dB

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Zero IF Transceiver block diagram

ADC

ADC

3 Wire BusControl

filtercalibration

FrequencyGenerator

Frequencyhopping control

DAC

DAC

RX path

TX path

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Brief Comparison with DS-UWB technology (1)

• Both technologies occupy similar bandwidth below 5GHz (~1.5GHz)– Tx power & link distance performance are therefore similar

• MB-OFDM is a multiband technology– Allows cost-effective all-CMOS implementation– Improves feasibility of on-chip filtering for truly monolithic

solutions• Reduces cost of total solution

– System is robust to loss of one of the sub-bands• Due to a strong interferer• Due to application of a dynamic frequency selection algorithm

• DS-UWB is a single-band technology

May 2005


doc.: IEEE 802.15-05-273r0

Submission

• Multi-Band OFDM is an OFDM technology– Allows fine-grained adaptation of frequency spectrum shape for

future regulatory compliance– Channel impulse response equalization comes essentially for

free and is standard between implementations

• Multiple levels of diversity are applied – Convolutional FEC – Time-domain spreading – Frequency domain spreading

• Multiple companies have now shown silicon feasibility

Brief Comparison with DS-UWB technology (2)

All these combine to reduce impact of fading of individual sub-carriers

May 2005


doc.: IEEE 802.15-05-273r0

Submission

ConclusionsThe industry has overwhelmingly opted to support MB-OFDM as the first major wireless PAN PHY

– Inherent robustness to multi-path in all expected environments.

– Excellent robustness to U-NII and other generic narrowband interference.

• Ability to comply with worldwide regulations:– Channels and tones can be turned on/off dynamically

to comply with changing regulations.– Can arbitrarily shape spectrum because the tones

resolution is ~4 MHz.

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Conclusions

• Enhanced coexistence with current and future services:– Channels and tones can be turned on/off dynamically to coexist

with other devices.

• Scalability:– More channels can be added as RF technology improves and as

capacity requirements increase.– Multi-band OFDM is digital heavy. Digital section complexity and

power scales with improvements in technology node (Moore’s Law).

• MB-OFDM meets all the TG3a PAR requirements and offers the best trade-off between the various system parameters.

• We would welcome your support of this proposal!

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Backup

May 2005


doc.: IEEE 802.15-05-273r0

Submission

• Die size for PHY core:

• Active CMOS power consumption for PHY core:

Complexity (numbers supplied by TI)

Process Complete Analog*

Complete Digital

90 nm 3.0 mm2 1.9 mm2

130 nm 3.3 mm2 3.8 mm2

* Component area.

Process TX55 Mb/s

TX110, 200 Mb/s

RX55 Mb/s

RX110 Mb/s

RX200 Mb/s

90 nm 85 mW 128 mW 147 mW 155 mW 169 mW

130 nm 104 mW 156 mW 192 mW 205 mW 227 mW

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Frequency Synthesis

• Circuit-level simulation of frequency synthesis:

• Nominal switching time = ~2 ns. Need to use a slightly larger switching time to allow for process and temperature variations.

Switching Time = ~2 nsSwitching Time = ~2 ns

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Zero-padded Prefix• In a conventional OFDM system, a cyclic prefix is added to provide multi-

path protection.

• Cyclic prefix introducesstructure into the TX waveform structure in the signal produces ripples in the PSD.

• In an average PSD-limitedsystem, any ripples in theTX waveform will results in back-off at the TX (reduction in range).

• Ripple in the transmitted spectrum can be eliminated by using a zero-padded prefix.

• A Zero-Padded Prefix provides the same multi-path robustness as a cyclic prefix (60.6 ns of protection).

Avg. Power

FCC PSD Limit

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Proposed OFCOM (United Kingdom) Emissions Mask for UWB

-90

-80

-70

-60

-50

-40

-30

0 1 2 3 4 5 6 7 8 9 10 11 12 13

Frequency (GHz)

Pow

er (d

Bm

/MH

z)

May 2005


doc.: IEEE 802.15-05-273r0

Submission

Capacity vs. distance for UWB vs. WLAN

Theoretical capacity vs. distance

0.00E+00

1.00E+09

2.00E+09

3.00E+09

4.00E+09

5.00E+09

6.00E+09

7.00E+09

0 20 40 60 80 100

distance (m)

cap

acit

y (b

its/

sec)

UWB

WLAN

This area is ripe for exploitation

(Assumes 20MHz WLAN, 1GHz UWB bandwidth)

doc.: ieee 802.15-05-273r0 submission may 2005 c. razzell et alslide 1 project: ieee p802.15 working...

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