Upload
coral-peters
View
218
Download
0
Tags:
Embed Size (px)
Citation preview
Interference Effects of Multi-User Ultra-wideband Systems
Anup DoshiCarnegie Mellon University July 31, 2003
Outline
Intro
Models
Observations
Summary
What is an Ultra-wideband Signal? Short impulses in
succession
FCC Definition – Bandwidth > 25% of
center frequency 0 200 400 600 800 1000-1
-0.5
0
0.5
1
ns
Impulse Signal
0 2000 4000 6000 8000 10000-100
-80
-60
-40
-20
0
MHzPow
er S
pect
rum
Mag
nitu
de (d
B)
PSD
-0.5
0
0.5
1
Advantages of UWB
Low power levels spread over large spectrum Operates below noise floor of narrowband devices
Possibility of >500Mbps short range
GP
S
Frequency (Ghz)1.6 1.9 5
802.11a
-41 dBm/Mhz“Part 15 Limit”
UWB Spectrum 10.63.1
Source: Intel
PC
S
Potential Applications are Numerous
Personal Area Network Interconnect Computers, Devices, PDAs, Printers Entertainment...TV, Camcorder, DVD Music…MP3, Audio Systems, etc
Safety Through-wall Imaging Sensor Network
Lots of other exciting applicationsBroadband
UWBUWB
LAN/WLAN
UWB
UWB
UWB
Image Sources: Intel, AetherWire
Why Only Now?
Started as impulse radar, 1960’s Primitive forms, simple communication Studied & used by military
New technology enables digital comm., 1990’s Commercial applications seen by several companies 1998 - Petitioned FCC to review potential uses 2003 - FCC approves development of conservative
applications
Problem…
What happens when lots of UWB devices are transmitting in close proximity?
Will the combined noise level be too much for a victim narrowband receiver?
Existing studies claim minimal effects Done by various agencies and companies
Those studies do not examine all cases…
This is my job!
VICTIM
Constant-Distance DistributionMultiple UWB devices located three meters from a victim
Units turn on and off in a 2-state Markov Process
Switching times are Exponential Random Variables Time until on ~ Exponential(λ) => mean 1/λ sec Time until off ~ Exponential(µ) => mean 1/µ sec
Rho=ρ= λ/µ
Characterizing the Transmitters
UnitOff
UnitOn
λ
µ
Characterizing the Transmitters
Total Number on modeled as a Markov Chain
Steady-state probabilities:
0 1 2 N-1 N
Nλ (N-1)λ … λ
µ … Nµ2µ
N
n
n n
Np
)1(
1
2
3
4
5
6
7
8
9
10
0 0.5 1 1.5 2 2.5 3 3.5 4
How Does the System Act Over Time?
λ =1, µ=2
1
2
3
4
5
6
7
8
9
10
0 0.5 1 1.5 2 2.5 3 3.5 4
How Does the System Act Over Time?
Total Number of Units Onλ =1, µ=2
Noise Level in Victim Receiver
Each UWB signal modeled as White Noise Total Noise= N0+M(t)*N1
Ambient Noise Floor(=kTw)
Number of Transmitters On(Markov Chain)
Power Received at Victim from UWB Signal
Some Properties of This Model
Autocorrelation Spectral Density
-100 -50 0 50 1000
1
2
3
4
5
6
7
8
Hz
Ma
gn
itu
de
PSD = fft(Rx(t))
-5 0 50
0.5
1
1.5
2
2.5
tau (sec)
Ma
gn
itu
de
Rx(tau) = E(M(t)M(t+tau))
Probability of Error in Receiver
On Average:
101 *
2*))((
NiN
EQitMPP
bk
ierr
0 0.5 1 1.5 2 2.5 30
0.05
0.1
0.15
0.2
0.25
0.3
0.35Average Probabilty of Error
rho
Pe
rr
20 units
10 units
(µ=1)
Other Ways to Describe Model
Probability of Outage P(outage)=Probability( Perr > Pe* )
Pe*=.1, .01
Perr=
Expected Time of Outage E(T10) = T1+aN,1E(T20)
E(T20)=T2+aN,2E(T10)+bN,2E(T30) … E(TN0)=TN+E(T(N-1)0)
10 )(
2
NtMN
EQ
b
P(outage), Expected Time of Outage
0 0.5 1 1.5 2 2.5 30
2
4
6
8
10
12E(outage)
t (s
ec
)
rho
12 units
10 units
3m radius
0 0.5 1 1.5 2 2.5 30
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
rho
P(o
uta
ge
)
P(outage)
10 units
12 units
3m radius(µ=1) (µ=10)
VICTIM
Random-Distance DistributionUWB devices distributed uniformly in a circular area around victim
Properties of Random-Distance Model
Moved to a computer simulation
Experimentally calculated: P(outage), Expected Time of Outage, Max and mean power levels over time
Done on Matlab – Monte Carlo simulation
Example Simulation Run
0 0.5 1 1.5 2 2.5 3 3.5 4-52
-50
-48
-46
-44
-42
-40
-38
-36
-34
time
dB
m
Interference Level
0 1 2 3 4 5 6 7 8 9
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
time
dB
m
Interference Level
Example Simulation Run
Example Simulation Run
0 5 10 15 20-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
time
dB
m
Interference Level
0 5 10 15 20 25 30 35 40
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
time
dB
m
Interference Level
Example Simulation Run
P(outage) & Expected Time of Outage
0 0.5 1 1.5 2 2.5 30
0.2
0.4
0.6
0.8
1
Probability of Outage
rho
Po
uta
ge
Random-distanceradius=3m
Constant-distanceradius=3m
10 units
0 0.5 1 1.5 2 2.5 30
1
2
3
4
5
6
7
8
9Expected Time of Outage
tim
e (s
ec)
rho
Random-distanceradius=3m
Constant-distanceradius=3m
10 units(µ=1) (µ=10)
Max/Mean Power Levels
0 5 10 15 20 25 30 35 40-90
-80
-70
-60
-50
-40
-30
-20
Number of Transmitters in 10m radius
dB
m
Average Max and Mean Power Levels over 500 simulations
Average Max Power
Average Mean Power
Allowed Interference Level
Observations
Multiple transmitters will cause major problems in worst cases
Such situations may soon arise in real-life situations
Important to consider every possible case in testing
Broadband
Future Work
Need to consider many more variables Receiver type Frequency, PRR Different distributions
Once 802 Standard comes out, incorporate into model Possibly Multi-Band OFDM (TI, Intel) Possibly Dual-Band (Time Domain, Motorola)
Summary
Characterized an aggregate of UWB transmitters
Realized various methods of measuring effect on victim receiver
Concluded that as number of UWB transmitters increase, performance of victim receiver attenuates
Acknowledgments
Prof Baum
Prof Noneaker, Prof Xu
ECE Faculty and Grads
NSF