WPNC 2008
The UWB Groupat the
University of RomeLa Sapienza
UWB UWB flexible assets flexible assets ininradio, access, and networkradio, access, and network
designdesign
INFOCOM DepartmentINFOCOM DepartmentUniversity of Rome La SapienzaUniversity of Rome La Sapienza
ItalyItaly
Maria-Gabriella Di BenedettoMaria-Gabriella Di Benedetto
WPNC 2008
The UWB Groupat the
University of RomeLa Sapienza
OutlineOutline
UWB Impulse Radio features and framework ofapplication
Flexible radio
Flexible MAC
Flexible routing
33
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
UWB Impulse Radio featuresUWB Impulse Radio features
Impulse radio UWB signals are obtained by transmittingvery short pulses with typically no Radio Frequenciesmodulation
(In communication systems, “very short” refers to a duration of thepulse that is typically about a few hundred picoseconds)
This technique goes under the name of Impulse Impulse Radio (IR)Radio (IR)
44
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
UWB Impulse Radio featuresUWB Impulse Radio features
Time duration of a pulse is smaller than original symbol duration
Contrarily to conventional Spread Spectrum, increased bandwidth isnot provoked by spreading sequences, but rather by the
VeryVery short shortpulsepulse
Ultra-WideUltra-WideBandwidthBandwidth
energy is spread over a large bandwidth
extremely short pulse duration that induces ultra-wide bandwidth
55
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
UWB Impulse Radio featuresUWB Impulse Radio features
Impulse Radio systems differ in terms of modulation and coding
User data can modulate pulse amplitude with binary antipodal variations(Pulse Amplitude Modulation PAM)
User data can turn pulses on and off(On Off Keying OOK)
User data can dither pulse position(Pulse Position Modulation PPM)
66
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
On top of modulation, symbols are encoded using Time Hopping THcodes for pulse shaping and user differentiation
0 0.2 0.4 0.6 0.8 1 1.2 1.4
x 10-7
-1
-0.5
0
0.5
1
1.5x 10
-3
Time [s]
Amplitude [V]
0 0.2 0.4 0.6 0.8 1 1.2 1.4
x 10-7
-1
-0.5
0
0.5
1
1.5x 10
-3
Time [s]
Amplitude [V]
0 1 2 3 4 5 6 7 8 9 10
x 109
10-30
10-25
10-20
10-15
Frequency [Hz]
PSD in logarithmic units
0 1 2 3 4 5 6 7 8 9 10
x 109
10-40
10-35
10-30
10-25
10-20
10-15
10-10
Frequency [Hz]
PSD in logarithmic units
PPM IR UWB PPM IR UWB signal without codingsignal without coding
PPM IR UWB PPM IR UWB signal with signal with TH TH codingcoding
Power Power Spectral Spectral DensityDensity
Power Power Spectral Spectral DensityDensity
UWB Impulse Radio featuresUWB Impulse Radio features
77
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
UWB Impulse Radio featuresUWB Impulse Radio features
0 0.2 0.4 0.6 0.8 1 1.2 1.4
x 10-7
-1
-0.5
0
0.5
1
1.5x 10
-3
Time [s]
Amplitude [V]
�
s(t) = PTXTS pw (t ! jTS ! c j ! a j")j
#
PTX is the average transmitted powerTS is the pulse repetition periodpw(t) is the energy-normalized pulse shapecj<TS is the TH code value for pulse jaj is the data symbol carried by pulse jε is the PPM shift
We focus on a typical signal format: Time Hopping coding TH andbinary Pulse Position Modulation PPM
88
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
UWB Impulse Radio framework of applicationUWB Impulse Radio framework of application
Standard for low-rate WPANs:
multi-month to multi-year battery life
data rates of 20-250 kbps
power management for low powerconsumption
low complexity
.4.4
.4.4aaSame as above, plus:
location enabled: high precisionranging/location (at least 1 meteraccuracy)
ultra low power
99
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
UWB Impulse Radio in the IEEE 802.15.4a standardUWB Impulse Radio in the IEEE 802.15.4a standard
In March 2005, TG4a selected two optional PHYs:
– UWB Impulse Radio (unlicensed UWB spectrum)
– Chirp Spread Spectrum (unlicensed 2.4 GHz spectrum)
1010
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
A Flexible RadioA Flexible Radio
1111
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Flexible Flexible radio design: radio design: example example of of applicationapplication
• Different waveforms can be selected for transmission.• Waveforms lead to different spectral shapes for the transmitted signals, so that
the UWB signal can be adapted to different interference scenarios.• We suppose up to 6 possible different pulses
! """=j jjSwSTX acjTtpTPts )()( #
w = w = 1, 1, ……, 6, 6
M.-G. Di Benedetto, G. Giancola and M.D. Di Benedetto, " Introducing Consciousness in UWBnetworks by Hybrid Modelling of Admission Control," Mobile Networks and Applications,vol.11 no.4, pp. 521-534 ISSN: 1383-469X, ACM/Springer Journal on Mobile Networks andApplications, Special Issue on "Ultra Wide Band for Sensor Networks" , 2006.
1212
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Flexible Flexible radio design: radio design: example example of of applicationapplication
Scenario: a self-organizing network of low-power, low cost and lowrate IR-UWB devices (IEEE 802.15.4a like devices)
802.15.4anetwork
Multi User
Interference
External
Interference
External
Interference
1313
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Flexible Flexible radio design: radio design: example example of of applicationapplication
Frequency
W1(f) W2(f) W3(f) W4(f) W5(f) W6(f)
Energy Spectral Density
6 pulses are available for transmission
1414
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Flexible Flexible radio design: radio design: example example of of applicationapplication
• All nodes communicate through oneelected node, denoted as the ConsciousNode of the network (CNode)
• The CNode plays the role of networkcoordinator
CNode
ActiveNode
Active
NodeActive
Node
• Time Hopping (TH) coding is used for identifying users• Power control at the CNode is assumed for all uplink connections
1515
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Flexible Flexible radio design: radio design: example example of of applicationapplication
Performance of a link between one active node and the CNode is expressed by
�
BER = (1/2)erfc SNR /2( )
�
SNR =1
Rb
PRX
!p (w) + "m
2(w)(N #1)PRX
PTX is the average received powerRb is the bit rateηp(w) is the variance of noise (thermal noise + external interference)collected for one single pulse [w = 1,2,…,6]σm
2(w) is a Multi User Interference weight [w = 1,2,…,6]N is the number of active users
1616
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Evaluation Evaluation of of transmission parameterstransmission parameters
• Based on environment sensing, CNode estimates the ηp(w) andσm
2(w)
• Then, it computes the value of the minimum power Pmin that mustbe received from each node in order to guarantee SNR ≥ SNR0(minimum reference value required for synchronization)
�
Pmin (w) =!p (w)
TS
1
SNR0
"#m
2(w)(N "1)TS
$
% &
'
( )
�
SNR =1
Rb
PRX
!p (w) + "m
2(w)(N #1)PRX
1717
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Evaluation Evaluation of of transmission parameterstransmission parameters
• Since Pmin depends on the adopted waveform, the waveformpw*(t) that better adapts to the environment is the one leading tothe smallest Pmin(w) value
• CNode can thus determine:– the waveform pw*(t) to be used by active nodes in the network– the corresponding Pmin(w*)
�
Pmin (w) =!p (w)
TS
1
SNR0
"#m
2(w)(N "1)TS
$
% &
'
( )
1818
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
The The three levels three levels of of flexibilityflexibility
IntermediateFlexibility
FullFlexibility
NoFlexibility
The CNode is always capable to select theoptimum pulse shape among the 6 availablewaveforms
The CNode has reduced capabilities, sinceit is capable to select the pulse shape withina sub-set of the 6 available waveforms
The CNode randomly selects a waveform atthe beginning of network operation and doesnot perform any further selection duringnetwork lifetime
We simulated three different types of Cnode
1919
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
ResultsResults
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
x 10-3
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8x 10
-9
Time [s]
Energy [J]
No Cognition
Intermediate Cognition
Full Cognition
Interference pattern: 20 external interferers generating narrowband signals located @ 2, 4,6 and 8 GHz switching on and off, with average active and silent time of 100 µs
IntermediateFlexibility
Full Flexibility
No Flexibility
TimeTime
Spen
t Ene
rgy
Spen
t Ene
rgy
2020
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
A Flexible MACA Flexible MAC
2121
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
IR UWB flexible MAC designIR UWB flexible MAC design• IR Ultra Wide Band based on time hopping and impulse radio is
characterized by:– Low probability of pulse collision– Accurate ranging (theoretical limit far below 1 cm)
Uncoordinated, Wireless, Baseborn medium access for UWBcommunication networks (UWB)2
• Impulse Radio features with respect to MUI and synchronizationform the basis for the definition of an UWB-tailored MAC algorithm
M.-G. Di Benedetto, L. De Nardis, M. Junk,G. Giancola, " (UWB)^2: Uncoordinated, Wireless,Baseborn, medium access control for UWB communication networks," Mobile Networks andApplications, vol. 10 no.5, pp. 663-674. Mobile Networks and Applications special issue onWLAN Optimization at the MAC and Network Levels, 2005.
2222
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
(UWB)(UWB)22 MacMac
• For TH-IR, the probability of successful packettransmission for uncoordinated transmission of severalusers and in the presence of MUI is fairly high.
• Based on this result, (UWB)2 was the first MAC protocolto propose a pure Aloha approach
• For synchronization purposes (UWB)2 foresees thepresence of a synchronization trailer in each transmittedpacket The (UWB)2 approach was proposed and adopted with
large majority of votes within the IEEE 802.15.4a group
2323
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
(UWB)(UWB)22 MAC: design choices MAC: design choices
Key assumptions Design Choices
TH-CDMA:Common signaling code available
to all devices+
Dedicated data code unique foreach transmitter
No Carrier Sensing: pure Aloha(with TH coding)
Synchronization is achieved on apacket-by-packet basisSimple Synchronization Hardware
Low Data Rate and rare packets(peak rate ≤ 1 Mb/s,
average rate ≤ 20 Kb/s)
Time Hopping Impulse Radio withGHz bandwidth
Need for broadcast packets
2424
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
t0+ τ + Δ + τ + Δ
+ τ
Tx Rxt0
t0 + τ
t1=t0+τ +Δ
Time Time
The LE -> LC -> DATA packet exchange allows both Tx and Rx terminals to determine their distance
2 0
2TxRx
t td c c!
" "#= =
3 1
2RxTx
t td c c!
" "#= =
DATA
LE
LC
(UWB)(UWB)22 MAC: Transmission and Ranging procedure MAC: Transmission and Ranging procedure
t2=t0+τ +Δ
t3 + τt0+ τ + Δ + τ + Δ =
2525
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
(UWB)(UWB)22: Performance analysis: Performance analysis
• (UWB)2 was tested by simulation in a typical Low Data Rate scenario:– user rates in the range 10-100 kb/s– 1 Mb/s on the wireless channel
• Channel effect and Multi User Interference were taken into account
• Two performance indicators were considered:– Throughput - % of transmitted packets, that are correctly received– Delay - Time gap between first transmission of a packet and its correct
reception, including retransmissions of collided packets– Packet Error Probability
2626
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Throughput and delay as a function of number of terminals
Throughput Delay
(UWB)(UWB)22: Performance analysis: Performance analysis
2727
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
(UWB)(UWB)22: Performance analysis: Performance analysis
Packet Error Probability as a function of number of terminals
Packet Length: 2000 bitsPulse Rate: 1 Mpulses/sNs = 1TM = 1 ns
2828
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
A Flexible networkA Flexible network
2929
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Flexible routingFlexible routing
• Is it feasible to design a routing strategy that adapts its path selectioncriterion to internal and external network conditions?
• What is the impact of such a routing strategy in a power-constrained,interference-prone UWB network, in terms of:
• Network performance• Network lifetime
??M.-G. Di Benedetto and L. De Nardis, " Cognitive routing in UWB networks," invited paper, IEEEInternational Conference on UWB 2006 ICUWB 2006, Boston, Massachusetts, USA, September 24-27, 2006.
UWB UWB allows allows accurate accurate ranging accuracy ranging accuracy and power managementand power management
3030
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Flexible routingFlexible routing
1. Define a routing metric that determines the cost of a linkbased on internal and external conditions
2. Select the minimum cost route
�
UWBCost x,y( ) = cSync t( ) ! Sync x,y( ) + cPower t( ) ! Power x,y( ) +
+cMUI t( ) ! MUI x,y( ) + cReliability t( ) ! Reliability x, y( ) +
+cTraffic t( ) !Traffic y( ) + cDelay t( ) !Delay x,y( ) +
+cAutonomy t( ) ! Autonomy y( ) + cCoexistence t( ) !Coexistence y( )
x
y
UWBCost(x,y)
The following metric was defined
3131
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Flexible routingFlexible routing
Autonomy term
Coexistence term
�
Autonomy y( ) =1!Residual Energy y( )
Full Energy y( )
�
Coexistence y( ) =Measured External Interference y( )
Maximum Interference y( )
Delay term
�
Delay x,y( ) =1
3232
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Analysis by simulationAnalysis by simulation
• Three different coefficient sets
• Generation of external interferers– fc=3.5 GHz, B=20 MHz, Pt=10 mW– Random activity factor a in the interval (0,1]– Random position– Death/birth of interferers every 100 sec
Coefficient Set 1 Set 2 Set 3
CDelay 1 0.0001 0.0001
CAutonomy 0 1 0
Ccoexistence 0 0 1
3333
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Effect on PowerEffect on Power
3434
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
Effect Effect on Multi on Multi User InterferenceUser Interference
3535
The UWB Groupat the
University of RomeLa Sapienza
WPNC 2008
AcknowledgmentAcknowledgment
• This work was partially supported by the FP6Integrated Project PULSERS (PervasiveUltra-wideband Low Spectral Energy RadioSystems) Phase II (contract FP6-027142).
http://www.pulsers.eu/