Support for different receiver architectures (coherent/non-coherent)
Flexible modulation format
Support for multiple rates
Support for multiple SOP
Band plan (selection from 15.4a)
Band plan versus regulation for UWB
PLL Reference Diagram
Pulse Repetition Frequency
Selected value
15.6 MHz PRF (64.10 ns of pulse repetition period PRP)
Use of binary codes, No bursts => mean PRF = peak PRF
Rationale
Typical channel delay spread for indoor applications below 25 ns in 90% of channel realizations => very limited ISI (or IPI)
Integer relationship with base frequency of the bandplan (499.2 MHz / 32) => no fractional PLL
Maximized Pulse amplitude
=> better for transmitter power consumption (between-pulses duty cycling)
=> better for pulse detectability in the receiver
=> better for threshold crossing receivers
=> compatible with low voltage CMOS technologies without I/O « tricks » (around 780 mVp-p)
A single value => simplicity
Compatible with bit rate scalability with short spreading factors
No high speed clock / long FIRs filters to generate or correlate with bursts of pulses
Preamble
PRF is the same as one of the mean PRF in 15.4a
Sp code duration:
Example with N=31 : Tpsym = 31 * PRP = 1.9871 us
To be checked if enough for a correct (Pd,Pfa) versus complexity
Number of Sp codes in the preamble
Example with Nsp = 16 : Tsync = 16 * Tpsym = 31.7936 us
This is probably a maximum value
To be checked if enough for a correct (Pd,Pfa) versus overhead
Modulation
PRF is ~ the same as one of the mean PRF in 15.4a
Spreading code length Sd
Example with N=7 (BARKER CODE) : Symbol duration Ts = 7 * PRP = 0.4488 us
Modulation : 1 bit per symbol (D-PPM) + second bit used for redundancy (D-BPSK)
DBPSK : BPSK with differential encoding (at symbol level : Sd or - Sd)
Sub-optimal but easier to implement and less sensitive to clock drift
DPPM : PPM with differential encoding (at symbol level)
The whole symbol is Time-shifted at the chip level of half the PRP value (32 ns)
DBPSK + DPPM : the whole S code can be shifted within the PRP with ½ the PRP value and be Sd or -Sd
Does not affect the mean PRF value and the spectrum shape, Is simple to implement (though a little more complex than pure DPBSK), Is compatible with non coherent / threshold crossing detectors, Is ISI compatible in the BAN context
Bit rate is adjusted with the number of pulses per symbol keeping a constant mean PRF
2.22 Mbit/s is the default uncoded data rate
5.2 and 15.6 Mbit/s are mandatory => No additional complexity & allows to reduce channel use
31.2 Mbit/s is proposed optionally for coherent receiver (uses both PPM & DPBSK)
Additional proposed FEC : systematic RS (63,55) as in 15.4a (maximum efficiency ~0.87)
The lowest rate is a compromise between “Tx_on time” and range (+clock drift compensation requirements).
Link budget
Performances analysis methodology and channel models
Goal:
Get/discuss performances at a link budget / outage probability level with the different channel models at the default 2.2 Mbps rate before digging into the design level performances
Methodology:
Perform extra measurements at CEA-Leti (for UWB 3-5GHz but also for 2.4 GHz)
Complement the IEEE802.15.6 CM3 UWB channel model with extra measurements and models and compare channel models with each other
Move towards a scenario based approach
Scenario = [at least] given (Tx,Rx) couple + given generic environment + given generic movement
Justified by the huge dispersion of the BAN radio channel
Calculate outage probabilities given the path loss and shadowing statistics
Performances: channel path loss models
Available CM3 UWB channel models as in TG6 document :
A (source NICT)
Indoor and anechoic
B (source IMEC)
Anechoic
C (source Samsung)
Indoor and anechoic
Conclusion
Huge dispersion (tens of dBs) between models
Distance is not a relevant parameter to get a path loss model
Coming back to the scenario based channel characterization is proposed
2-5 GHz, indoor and anechoic, 7 subjects, standing/walking/running, scenarios as depicted below
Log normal path loss model. Shadowing and small scale fading modeled separately.
Reference : D'Errico R.; Ouvry L.,“Time-variant BAN channel characterization” TD(09)879, COST2100, 18-19/05/2009, Valencia, Spain (Measurement set up details available on request)
Performances: extra channel measurements
On previous page:
Error bar @ 1 std of mean channel gain over subjects
Without the slow shadowing std
2.4 GHz and 3-5 GHz for comparison
On this page
UWB 3-5 GHz only
Error bar @ 2 stds of mean channel gain and slow shadowing (95% confidence interval)
Conclusions
2.5% outage probability @ ~-70dB channel loss for the 8 scenarios in indoor conditions
Higher outage in anechoic chamber depending on the scenario (not shown here)
Performances : outage probability
Starting from:
The link budget
PTx + antenna = -20.5 dBm
Sensitivity = -90.5 dBm
Includes 6dB NF, 5dB I.L. and 9dB min required EbN0
70dB total link margin
The different scenario based path loss models
CM3 UWB A back to the scenarios
CM3 UWB C back to the scenarios
CEA-Leti’s measurements
Get the outage probability performance for an EbN0
Probability that the received power is higher than the receiver sensitivity
(others available as well, including anechoic chamber cases)
Needs further update to refine comparisons, but aims at opening discussions
Performance : EbN0 requirements (DBPSK)
Conditions: DBPSK, 20 bytes PSDU, CM3 A channel
Same results (with better PER floor in highest rate) for 256 bytes
Conclusions on link performances on the different channel
The proposed link budget and system specification makes the UWB proposal feasible for most of the scenarios
outage of 5% as in TRD
1e-2 PER for 20 bytes PSDU, or
1e-1 PER for 256 bytes PSDU
Actual EbN0 requirement still to refine (current simulation with realistic receiver on CM3 gives 13dB after RS decoding, within the proposed IL values, but the CM3 multipath model is questionable)
However, large variations between the different models (CM3 A is optimistic, CM3 C is pessimistic, CM3 B and CEA-Leti’s measurement are median)
Further analysis in the 7.25-8.5 GHz band is necessary
Background design know-how (see references)
Conclusions
Proposal based upon UWB impulse radio alt-PHY of 15.4a
Advantage
Early implementations exist: experienced proposal
Selection of the most relevant modes and their adaptation to the BAN context (note: 15.4a mandatory mode is NOT the selected option for 15.6)
A standard exists which will speed up the 15.6 standard drafting steps
Modulation:
DBPSK provide robustness for a limited complexity & 2PPM allow several receiver implementations
RS FEC help to improve link budgets and parity bit will improve robustness of the DBPSK receiver
System tradeoffs
Variable bit rates allow to accommodate all applications envisaged in TG6
M. Pezzin, D. Lachartre, « A Fully Integrated LDR IR-UWB CMOS Transceiver Based on "1.5-bit" Direct Sampling », ICUWB 2007, Singapore, September 2007
D.Lachartre, B. Denis, D. Morche, L. Ouvry, M. Pezzin, B.Piaget, J. Prouvée, P. Vincent, « A 1.1nJ/b 802.15.4a-Compliant Fully Integrated UWB Transceiver in 0.13μm CMOS», ISSCC 2009, San Francisco, February 2009
European ICT PULSERS II and ICT EUWB projects deliverables
Timmons, N.F. Scanlon, W.G. "Analysis of the performance of IEEE 802.15.4 for medical sensor body area networking", IEEE SECON 2004, Santa Clara, Ca, October 2004
Questions ?
Back-up slides
Beacon-free MAC mode
In this collaborative scheme, the preamble burst can composed of
Destination adress (compuls.)
Time left to data (compuls.)
Packet length
Source adress
Need for a relaying collision resolution policy
Based on the wake-up instant during the burst (priority is given to the node which has detected the burst first)
Beacon-free MAC mode
Relationship between wake-up instant in the burst and back-off length can be of any kind (linear, logarithmic, exponential…)
