1. May 18th 2005
Project: IEEE P Working Group for Wireless Personal Area Networks (WPANs)
Submission Title: TG4a Review of proposed UWB-IR Modulation schemes
Date Submitted: 21 April 2005
Source: Philip Orlik, Andy Molisch (Mitsubishi Electric), Gian Mario Maggio (STMicroelectronics), Ian Opperman (University of Oulu)
Contact: Philip Orlik
Voice: ,
Abstract: Yet another UWB waveform
Purpose: To provide information for further investigation on and selection of the modulation /waveform for UWB Impulse Radio (low bit rate plus ranging)
Notice: This document has been prepared to assist the IEEE P 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 P
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

2. IEEE 802.15.4a PHY: UWB-IR Modulation for multiple receiver types
May 18th 2005
IEEE a PHY: UWB-IR Modulation for multiple receiver types
Many slides stolen from a
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

3. May 18th 2005
Definitions
Coherent RX: The phase of the received carrier waveform is known, and utilized for demodulation
Differentially-coherent RX: The carrier phase of the previous signaling interval is used as phase reference for demodulation
Non-coherent RX: The phase information (e.g. pulse polarity) is unknown at the receiver
-operates as an energy collector
-or as an amplitude detector
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

4. Waveform Design (1/2) Combination of BPPM with BPSK
May 18th 2005
Waveform Design (1/2)
Combination of BPPM with BPSK
Guarantee coexistence of coherent and non-coherent receiver architectures:
Non-coherent receivers just look for energy in the early or late slots to decode the bit (BPPM)
Coherent and differentially-coherent receivers, in addition, understand the fine structure of the signal (BPSK or DBPSK)
Principle: Non-coherent and differentially-coherent modes should not penalize coherent RX performance
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

5. Waveform Design (2/2) Two possible realizations:
May 18th 2005
Waveform Design (2/2)
Two possible realizations:
1) The whole symbol (consisting of Nf frames) is BPPM-modulated
2) Apply 2-ary time hopping code, so that each frame has BPPM according to TH code
Coexistence coherent/non-coherent RX:
- Special encoding and waveform shaping within each frame
- Use of doublets with memory from previous bit (encoding of reference pulse with previous bit)
- Proposed 20ns separation between pulses
- Extensible to higher order TR for either reducing the penalty in transmitting the reference pulse or increasing the bit rate (see: a for detail)
- Also possible the use of multi-doublets (see a)
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

6. Impulse Radio Modulation Scheme
May 18th 2005
Impulse Radio Modulation Scheme
Rake Receiver
Finger Np
Finger 2
Finger 1
Summer
Pulse Gen.
TH Seq
BPSK symbol mapper
Delay
Central Timing Control
Multiplexer
Coherent Receiver Td
Hybrid Transmitter
Differentially Coherent Receiver
( )2
Non-Coherent Receiver
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

7. Pros/Cons of RX Architectures
May 18th 2005
Pros/Cons of RX Architectures
Coherent
+ : Sensitivity
+ : Use of polarity to carry data
+ : Optimal processing gain achievable
- : Complexity of channel estimation and RAKE receiver
- : Longer acquisition time
Differentially-Coherent (or using Transmitted Reference)
+ : Gives a reference for faster channel estimation (coherent approach)
+ : No channel estimation (non-coherent approach)
- : Asymptotic loss of 3dB for transmitted reference
Non-coherent
+ : Low complexity
+ : Acquisition speed
- : Sensitivity, robustness to SOP and interferers
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

8. Design Parameters Pulse Repetition Period (PRP)
May 18th 2005
Design Parameters
Pulse Repetition Period (PRP)
Proposed range between 40ns (first realization) and 125ns (second realization)
Channelization (In addition to FDM)
Coherent schemes: Use of TH codes and polarity codes
Non-coherent schemes: Use of TH codes (polarity codes for spectrum smoothing only)
TH code length
Variable TH code length; proposed range: 8-16
TH code: Binary position, bi-phase
Note: For first realization, higher-order TH with shorter chip duration (multiples of 2ns) may be used
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

9. Differential Encoding: Basics
May 18th 2005
Differential Encoding: Basics
b-1 b0 b1 b2 b3 b4 b5
Tx Bits
Reference Polarity Ts
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

10. Example Signal Waveforms for data modulation (1)
May 18th 2005
Example Signal Waveforms for data modulation (1)
bi-1 = 1, bi = 1
bi-1 = 0, bi = 1
bi-1 = 1, bi = 0
bi-1 = 0, bi = 0
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

11. Example Signal Waveforms for data modulation (2)
May 18th 2005
Example Signal Waveforms for data modulation (2) Ts
« 11 »
2-PPM + TR base
M = 2
One bit/symbol
« 01 »
« 10 »
« 00 »
2-PPM + 16 chips 2-ary TH code
or 2-PPM + 8 chips 4-ary TH code
(coherent decoding possible)
Time hopping code is (2,2) code of length 8/16, can be exploited by non-coherent RX
Effectively, 28 or 216 codes to select for channelization for non-coherent scheme
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

12. Example Signal Waveforms for data modulation (3)
May 18th 2005
Example Signal Waveforms for data modulation (3) Ts
« 11 »
« 01 »
2-PPM + TR base
M = 2
(with two bits/symbol)
« 10 »
« 00 »
2-PPM + 16 chips 2-ary TH code
(coherent decoding possible)
Time hopping code is (2,2) code of length 8/16, can be exploited by non-coherent RX
Effectively, 28 or 216 codes to select for channelization for non-coherent scheme
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

13. De-Spreading TH Codes May 18th 2005 Band Matched TH r(t)
Sequence Matched
Filter
r(t)
LNA
BPF
Bit Demodulation
ADC
Case I - Coherent TH de-spreading
Band Matched TH
Sequence Matched
Filter
r(t)
Bit Demodulation
b(t)
soft info
LNA
BPF
ADC
Case II – Non-coherent / differential TH despreading
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

14. Coherent Receiver: RAKE Receiver
May 18th 2005
Coherent Receiver: RAKE Receiver
Channel Estimation
Rake Receiver
Finger 1
Demultiplexer
Rake Receiver
Finger 2
Sequence
Detector
Convolutional
Decoder
Summer
Data
Sink
Rake Receiver
Finger Np
Addition of Sequence Detector – Proposed modulation may be viewed as having memory of length 2
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

15. ‘Uncoded’ AWGN Performance
May 18th 2005
‘Uncoded’ AWGN Performance
1.5 dB
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

16. ‘Uncoded’ CM8 Performance
May 18th 2005
‘Uncoded’ CM8 Performance
1 dB
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

17. May 18th 2005
Advantages
Coherent RX gets additional benefit from coding inherent in the modulation
Waveform permits polarity scrambling to reduce required back-off
A single waveform for all receiver types
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

18. Coherent view of Hybrid Modulation
May 18th 2005
Coherent view of Hybrid Modulation
Symbols consist of sequences of doublets that have 4 possible forms
bi-1 = 1, bi = 1
bi-1 = 0, bi = 1
bi-1 = 1, bi = 0
bi-1 = 0, bi = 0
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

19. May 18th 2005
Basis functions
Symbols can be decomposed using several equivalent orthogonal basis functions (2-D) ( ) ( ) _ _ , ,
[1, 0]
[1/2, 1/2]
[-1, 0]
[-1/2, -1/2]
[0, 1]
[1/2, -1/2]
[0, -1]
[-1/2, 1/2]
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

20. Matched Filter Outputs (basis 1)
May 18th 2005
Matched Filter Outputs (basis 1)
Template signals constructed from these 2 basis functions
Barker 13 applied to TR doublets
bi-1 = 1, bi = 1
bi-1 = 0, bi = 1
bi-1 = 1, bi = 0
bi-1 = 0, bi = 0
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

21. Matched Filter Outputs (basis 2)
May 18th 2005
Matched Filter Outputs (basis 2)
Template signals constructed from these 2 basis functions
Barker 13 applied to doublets _ _
bi-1 = 1, bi = 1
bi-1 = 0, bi = 1
bi-1 = 1, bi = 0
bi-1 = 0, bi = 0
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

22. Ranging Implications ( ) So what does this mean for ranging?
May 18th 2005
Ranging Implications
So what does this mean for ranging?
Really nothing
If we want to transmit a barker sequence (or something else) we can still use our receiver to “look” for the ranging symbol
Basically we can use as a basis and view the compression code as a polarity code applied to the reference pulse and data pulse independently.
Barker 13 = [ ]
Reference code = [ ]
Data code = [ ] ( ) _ _ ,
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman

23. Barker 13 transmission Correlator output Tx waveform May 18th 2005
P.Orlik, A. Molisch, G. M. Maggio; I. Opperman