Ismail Lakkis

1
Project IEEE P802.15 Working Group for Wireless
Personal Area Networks (WPANs) Submission
Title Revised Frequency Plan and PRF Proposal
for TG4a Date Submitted 27 April
2005 Source Ismail Lakkis Saeid Safavi,
Wideband Access Inc. Contact Saeid
Safavi. Voice1 858 642 9114, E-Mail
ssafavi_at_widebandaccess.com Abstract Ban
Plan, PRF, Preamble Modulation Purpose
Clarification of relationship between minimum
PRF and maximum allowed voltage level in UWB
IR 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.
2
Agenda

• Proposed system features
• Frequency Plan / PRF
• Preamble
• Modulation

3
Frequency Plan / PRF
4
Proposed System Features

• Meets requirements for TG4a baseline draft
• Frequency plan with simple PLL structure and safe
  margins to 3.1GHz and 4.9 GHz
• Support of a range of PRFs (low and high)
• Impulse-radio system
• Common preamble structure for different classes
  of nodes/receivers type ( coh./noncoh.) ranging
• Flexible adaptive data rate
• Robustness against SOP interference through
  frequency and code division
• Robustness against other in-band interference
• Scalability to trade-off complexity/performance

5
Frequency Plan Requirements

• Requirements
• Sub-banding (Three bands) with mandatory center
  band of 500MHz and an optional wider co-centric
  band of 1.5GHz
• Mandatory FCC spectral mask _at_ 3.1GHz ? at least
  10 dB attenuation constraint on filtering
• Desirable co-existence with WLAN _at_ 4.9GHz
• Implications
• A safe margin to 3.1GHz to meet FCC requirement
• For IR system using a pulser (no mixer), the BPF
  is responsible for the 3.1GHz corner filtering
• A safe margin to 4.9GHz to coexist with WLAN
• Different frequencies should be easily generated
  from the system PLL with first divisions in
  powers of 2

6
PRF Requirements

• Requirements
• Support of multiple (at least 2) PRF in band
• Limit on lowest possible PRF due to CMOS 90 nm
  technology
• Limit on highest possible PRF due to inter-frame
  interference for a non-coherent receiver
• Implications
• Supported PRFs should be easily derived from the
  PLL through simple divisions
• Low PRF as base PRF
• High PRF as second PRF
• PRF should be high enough to take advantage of
  FCC rules

7
Relationship between PRF Peak Power
8
Minimum PRF vs Peak Power (CMOS 90nm)
BW 500 MHz BW 500 MHz BW 500 MHz
Technology CMOS 90nm 2.5 Vpp, BPSK CMOS 90nm 2.5 Vpp, Ternary
TChip (nsec) 2 2
BW (MHz) 500 500
VPeak (v) 1.25 1.25
PAve (dBm) -14.31 -14.31
PPeak (dBm) 11.94 11.94
PRF (MHz) _at_ VPeak (No Margin) 1.19 2.37
PRF (MHz) _at_ VPeak (8 dB Margin) 7.48 14.97
BW 1500 MHz BW 1500 MHz BW 1500 MHz
Technology CMOS 90nm 2.5 Vpp, BPSK CMOS 90nm 2.5 Vpp, Ternary
TChip (nsec) 0.66 0.66
BW (MHz) 1500 1500
VPeak (v) 1.25 1.25
PAve (dBm) -9.54 -9.45
PPeak (dBm) 11.94 11.94
PRF (MHz) _at_ VPeak (No Margin) 10.67 21.35
PRF (MHz) _at_ VPeak (4.5 dB Margin) 30.09 60.17
9
Low PRF vs High PRF

• A low PRF system has a lower implementation cost
  when compared to high PRF system
• RF radio overall gain is lower for a low PRF
  system. A 12 MHz PRF system , for example, would
  reduce the receiver dynamic range by 7 dB when
  compared to a 60 MHz PRF system
• The ADC would run at 12 MHz instead of 60 MHz in
  the above example and the entire digital
  processor would run at a lower clock reducing the
  power by a factor of 5 in CMOS
• Easier acquisition with lower PRF due to a
  smaller sync matched filter size
• Since energy per pulse is higher (7 dB in the
  above example), a non-coherent receiver would
  perform better
• Better acquisition and tracking performance since
  a 60 MHz PRF system needs to integrate perfectly
  5 pulses to perform equivalently to a 12 MHz PRF
  system

10
Proposed Frequency Plan
Band No. 3 dB BW (MHz) Low Freq. (MHz) Center Freq. (MHz) High Freq. (MHz)
1 494 3211 3458 3705
2 494 3705 3952 4199
3 494 4199 4446 4693
4 1482 3211 3952 4693
Band No. 4
207 MHz
111 MHz
1
2
3
3
4
5
GHz
3.5
4.5
3.25
3.75
4.25
4.75
Note This plan has almost double margin to 4.9
GHz as compared to 3.1 GHz
11
Frequency Plan Details
New Band Plan (in MHz) New Band Plan (in MHz)
XTAL 26        
R 8        
Fref 3.25        
DF 494        
F2C 3952 F2L 3705 F2H 4199
F1C 3458 F1L 3211 F1H 3705
F3C 4446 F3L 4199 F3H 4693
PRF1 61.75        
N1 64 N2 56 N3 72
PRF2 30.875        
N1 128 N2 112 N3 144
PRF3 15.4375        
N1 224 N2 256 N3 288
12
Proposed PRFs

• A wide range of PRFs (total of 3) are supported
  which are compliant with the harmonic chip rate
  requirements
• The base recommended PRF is 15.4375 MHz it has
  an 8 dB peak power margin for a 500MHz BW
• PRFs of 30.875MHz and 61.75MHz are also supported
  (margin gt 4.5 dB)
• The proposed PRFs can be easily generated from
  the center frequencies of the supported bands
  (next slide)

13
PRF Generation

• All High frequency divisions are in powers of 2,
  while the low frequency divisions are only by 3
  and 7

Center Freq. (MHz)
PRF1 (MHz)
PRF2 (MHz)
PRF3 (MHz)
Harmonic Ratio
3952
61.75
30.875
15.4375
64
2
2
3458
61.75
30.875
15.4375
8x7
2
2
4446
61.75
30.875
15.4375
8x3x3
2
2
Prime Factors 7, 3
14
PLL Reference Diagram
FX
FComp
Oscillator
Reference Divider (R)
XTAL
Phase Det.
F123,c
LPF
VCO
Divider, M
8
7,8 or 9
FX (MHZ) R Fcomp (MHz)
(13,26) (4,8) 0.8125
(9.6,19.2) (24,48) 0.4
(12,24) (6,12) 2
PRF
15
Band Plan / PRF Summary

• Enough margin to 3.1GHz (111 MHz) and 4.9GHz (207
  MHz) to meet FCC requirements and to coexist with
  WLAN ( avoids expensive sharp roll-off filtering)
• Support of a wide range of XTALs
  (9.6,19.2,13,26,12,24)
• Center frequencies and PRFs can be generated from
  a single PLL with first divisions in power of 2
  and low frequency division by 3 or 7
• Support of a wide range of PRFs. The proposed
  PRFs have a peak power margin of 4.5-8 dB to
  accommodate implementation losses and take
  advantage of FCC rules

16
Acquisition Preamble Structure
17
BER of BPSK ON-OFF Keying
g (dB) ON-OFF BER Opt. Thres.
10 2.7e-2 2.72
11 1.3e-2 2.96
12 5.7e-3 3.24
13 1.94e-3 3.55
14 5.06e-4 3.91
15 9.47e-5 4.31
16 1.16e-5 4.77
18
BER Requirements

• The requirement of PER lt 1 for a 32 octets
  packet translates into a BER lt 3.926e-5
• EbN0 requirements for uncoded BPSK and ON-OFF
  keying systems
• g (BPSK) 8.9dB
• g (ON-OFF) 15.45dB
• EbN0 requirements for coded BPSK and ON-OFF
  keying systems (assuming a coding gain of 4dB and
  receiver implementation losses of 1.5 dB)
• g (BPSK) 6.4 dB
• g (ON-OFF) 13 dB

19
SNR Loss in Square Law Detectors
PRF 32 MHz 32 MHz
EbN0 13 dB 13 dB
Data Rate 2Mbps 100 kHz
EsNo 1 dB -12 dB
SNRLoss 4dB 10 dB
20
BPSK Detection False Alarm Probabilities

• PRF 16 MHz
• AWGN Channel
• 2 dB margin to account for timing/frequency
  errors other factors
• PD 95 PF 5

Data Rate 2 Mbps 1 Mbps 500 Kbps 250 Kbps 125 Kbps 62.5 Kbps 32.25 Kbps
EpN0(dB) -2.5 -5.5 -8.5 -11.6 -14.6 -17.6 -20.6

Nc 32 32 32 32 32 32 32
L 1 2 4 12 36 112 448

Nc 256 256 256 256 256 256 256
L 1 1 1 1 2 4 12
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BPSK Detection False Alarm Probabilities

• PRF 16 MHz
• Multipath Channel assuming we capture 25 of the
  energy
• 2 dB margin to account for timing/frequency
  errors other factors
• PD 95 PF 5

Data Rate 2 Mbps 1 Mbps 500 Kbps 250 Kbps 125 Kbps 62.5 Kbps 32.25 Kbps
EpN0(dB) -2.5 -5.5 -8.5 -11.6 -14.6 -17.6 -20.6

Nc 32 32 32 32 32 32 32
L 4 12 36 112 448

Nc 256 256 256 256 256 256 256
L 1 1 2 4 12 36 112
22
BPSK Detection False Alarm Probabilities
23
BPSK Detection False Alarm Probabilities
24
ON-OFF Detection False Alarm Probabilities

• PRF 16 MHz
• AWGN Channel
• 2 dB margin to account for timing/frequency
  errors other factors
• PD 95 PF 5

Data Rate 2 Mbps 1 Mbps 500 Kbps 250 Kbps 125 Kbps 62.5 Kbps 32.25 Kbps
EpN0(dB) 4 1 -2 -5 -8 -11 -14

L 32 64 96 352 1280

25
Spreading Codes Objectives

• Design a set of sequences with good
  autocorrelation (ACF) and cross correlation (CCF)
  properties that support
• Coherent receivers
• Differentially coherent receivers
• Noncoherent receivers
• The sequence set should be as large as possible
  to support multiple piconets per frequency band
  and to mitigate co-channel interference (in-band
  interference)

26
Spreading Codes Desirable Characteristics

• The autocorrelation function of a sequence can be
  characterized by the following parameters
• PAR of the PSD (back-off factor) a b PAR is
  desirable otherwise reduction in Tx power is
  required
• Zero correlation zone (ZCZ) for improved
  ranging, synchronization, channel estimation, and
  Pd vs Pf
• Merit Factor (MF) of a binary sequence of length
  N The MF measures the interference due to the
  sidelobe energies in the zone under interest (say
  1µs)
• Sequence length this determines the coherent
  processing gain during acquisition ( a short
  spreading sequence ? system is acquisition
  limited rather than PER limited)

27
Barker code 11 m-sequence 31
28
Freescale ZCZ sequences
29
Single Spreading Code System ?

• A single spreading code common to the preamble
  and frame body is not recommended as all good
  sequences have bad PSD which results in a large
  Tx power reduction (Back-off)

length ZCZ width SLL Back-Off
Barker 11 1 0 1.2 dB
m-sequence 31 NA 1 4.5 dB
Freescale 24 NA 1 2.1 dB
ZCZ 32 8 0 2.4 dB
30
Hierarchical Preamble code structure

• Let Z be the ZCZ sequence of length 3
• Create hierarchical code using zero-correlation
  Walsh sequences 1,2,3 and 5
• For ternary Z corresponds to an inverted
  sequence
• There are at least 32 ZCZ, this gives 128 SOPs

Seq1 Z Z Z Z Z Z Z Z
Seq2 Z -Z Z -Z Z -Z Z -Z
Seq3 Z Z -Z -Z Z Z -Z -Z
Seq4 Z -Z -Z Z Z -Z -Z Z
Seq5 Z Z Z Z -Z -Z -Z -Z
Seq6 Z -Z Z -Z -Z Z -Z Z
Seq7 Z Z -Z -Z -Z -Z Z Z
Seq8 Z -Z -Z Z -Z Z Z -Z
31
modulation
32
Modulation

• Spreading via random scrambling
• Use a single scrambler of length (ex 32768) and
  assign a different offset (of 16 or 32) to
  different nodes
• For ternary modulation invert sequence when
  transmitting a 0
• Number of users supported is 1024
• Perfect co-channel interference rejection
• Support virtually any data rate from 16MHz to 32
  Kbps for a PRF of 16MHz
• Spectrum is virtually flat (no back-off)