Post on 01-Apr-2015
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:[charles.razzell@philips.com]
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
C. Razzell et alSlide 2
doc.: IEEE 802.15-05-273r0
Submission
MB-OFDM Proposal Summary
C. Razzell
May 2005
C. Razzell et alSlide 3
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
C. Razzell et alSlide 4
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
C. Razzell et alSlide 5
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
C. Razzell et alSlide 6
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
C. Razzell et alSlide 7
doc.: IEEE 802.15-05-273r0
Submission
Why OFDM is preferred(2)
• 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
C. Razzell et alSlide 8
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
C. Razzell et alSlide 9
doc.: IEEE 802.15-05-273r0
Submission
Why OFDM is preferred(4)
• 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
C. Razzell et alSlide 10
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
C. Razzell et alSlide 11
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
C. Razzell et alSlide 12
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
C. Razzell et alSlide 13
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
C. Razzell et alSlide 14
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
C. Razzell et alSlide 15
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
C. Razzell et alSlide 16
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
C. Razzell et alSlide 17
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
C. Razzell et alSlide 18
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
C. Razzell et alSlide 19
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
C. Razzell et alSlide 20
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
C. Razzell et alSlide 21
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
C. Razzell et alSlide 22
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
C. Razzell et alSlide 23
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
C. Razzell et alSlide 24
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
C. Razzell et alSlide 25
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
C. Razzell et alSlide 26
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
C. Razzell et alSlide 27
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
C. Razzell et alSlide 28
doc.: IEEE 802.15-05-273r0
Submission
Backup
May 2005
C. Razzell et alSlide 29
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
C. Razzell et alSlide 30
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
C. Razzell et alSlide 31
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
C. Razzell et alSlide 32
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
C. Razzell et alSlide 33
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)