Bluetooth v2 + EDR in Fading Channels

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WCNC 2008

March 31
-

April 3 Las Vegas

Department of Information Engineering

University of Padova, ITALY

Throughput and Energy Efficiency of
Bluetooth v2 + EDR in Fading Channels

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WCNC 2008

March 31
-

April 3 Las Vegas

Department of Information Engineering

University of Padova, ITALY

Throughput and Energy Efficiency of
Bluetooth v2 + EDR in Fading Channels

{andrea.zanella, michele.zorzi}@dei.unipd.it

Andrea Zanella, Michele Zorzi

WCNC 2008

Special Interest Group on
NEtworking & Telecommunications

Speaker:
Marco Miozzo

WCNC 2008

March 31
-

April 3 Las Vegas

Motivations


Bluetooth was designed to be integrated in portable
battery driven

electronic devices



Energy Saving is a key issue!


Units periodically scan radio channel for valid packets


Scanning takes just the time for a valid packet to be recognized


Units that are not addressed by any valid packet are active for less
than 10% of the time


WPAN market is expanding and it aims at becoming the
standard the facto for short range communications





High Throughput is very welcome!


Bluetooth v2.0 + EDR (Enhanced Data Rate) promise bit rates up to 3
Mbps and faster node connections

WCNC 2008

March 31
-

April 3 Las Vegas

Aims of the work


Questions:


Are the Bluetooth promises maintained?


What’s the energy efficiency & throughput achieved by
EDR

frame
formats in realistic channels?


Which units shall be the
Master

in point
-
to
-
point connections?


Answer


Well, in most cases, we cannot provide univocal answers…


…but we can offer a
mathematical model

to decide case by case!

WCNC 2008

March 31
-

April 3 Las Vegas

Basic ingredients


Define realistic radio channel model


Flat Rice
-
modelled fading channel


BER curves for different modulations taken from the literature


Capture system dynamic by means of a Finite State
Markov Chain (FSMC)


State transitions driven by packet reception events


Define appropriate reward functions


Data, Energy, Time


Apply renewal reward theorem to get system
performance


Throughput, energy efficiency, energy balancing, …

WCNC 2008

March 31
-

April 3 Las Vegas

What standard says…

Bluetooth reception
mechanism

WCNC 2008

March 31
-

April 3 Las Vegas

Physical layer


Basic Rate: 1Mbps


GFSK [13]


EDR2: 2Mbps



/4
-
DQPSK [14]


EDR3


8DPSK [15]

[13] J. S. Roh, “Performance analysis and evaluation of Bluetooth networks

in wireless channel environment,” ICSNC’06

[14]

L. E. MillerandJ. S. Lee, “BER Expressions for Differentially Detected

π/4 DQPSK Modulation,” IEEE TRANSACTIONS
ON COMMUNICATIONS, vol. 46, no. 1, pp. 71

81, January1998.


[15]

N. Benvenuto and C. Giovanni,

Algorithms for Communications Systems

and their Applications. Wiley, 2002.


WCNC 2008

March 31
-

April 3 Las Vegas

0.22 ms

T
slot
=0.625 ms

T
Dxn
=nT
slot

AC

HEAD

PAYL





GFSK

0.22 ms

T
slot
=0.625 ms

T
jDxn
= nT
slot

AC

HEAD

PAYL





GFSK

GUARD

SYNC

EDR

Trailer





DPSK

Baseband frame formats

WCNC 2008

March 31
-

April 3 Las Vegas

Retransmissions

MASTER

SLAVE

A

B

B

B

B

G

F

H

NAK

ACK


Automatic Retransmission Query (
ARQ
):


Each data packet is transmitted and retransmitted until
positive
acknowledge

is returned by the destination


Negative acknowledgement is implicitly assumed!


Errors on return packet determine transmission of
duplicate packets (DUPCK)



Slave filters out DUPCKs by checking their sequence number


Slave

does
never

transmit
DUPCKs
!


Slave can transmit when it receives a Master packet


Master packet piggy
-
backs the ACK/NACK for previous Slave transmission


Slave retransmits only when needed!

H

B

A

X

B

X

DPCK

DPCK

WCNC 2008

March 31
-

April 3 Las Vegas

Mathematical Analysis

System Model

WCNC 2008

March 31
-

April 3 Las Vegas

Mathematical Model


Normal State (N)


Master transmits packets that have never been
correctly received by the slave


Duplicate State (D)


Master transmits duplicate packets (DUPCKs)

DN
ND
ND
N
P
P
P




The steady
-
state probabilities
are, then,


State transition probabilities depend on the reception events…

DN
ND
DN
D
P
P
P



WCNC 2008

March 31
-

April 3 Las Vegas

Reception
Event Index

Slaves tx

Master tx

Reception events


Reception events


Ds = Data successful


AC ok, HEAD ok, CRC ok


Df = Data failure


AC ok, HEAD ok, CRC error


Hf = HEAD failure


AC ok, HEAD error


Af = AC failure


AC error



MC state transitions


N = enter Normal State


Master tx non
-
duplicate packets


D = enter Duplicate State


Master tx DUPCKs


X = loop step


Return in the same state

WCNC 2008

March 31
-

April 3 Las Vegas

Reward Functions




E
j
E
x
j
j
x
D
D
)
(
)
(


For each state
j

we define the following reward functions


T
j
= Average amount of time spent in state
j


D
j
(x)
= Average amount of data delivered by unit x

{M,S}


W
j
(x)
= Average amount of energy consumed by unit x

{M,S}


The average amount of reward earned in state
j

is given by




E
j
E
x
j
j
x
W
W
)
(
)
(




E
j
E
j
j
T
T


Performance indexes


Energy Efficiency:





Goodput:
G





T
D
D
T
D
G
M
S
)
(
)
(
lim












)
(
)
(
)
(
)
(
lim
M
S
M
S
W
W
D
D
W
D










WCNC 2008

March 31
-

April 3 Las Vegas

Time reward ( T )





9
8
9
8
)
1
(
1
)
(
p
p
n
p
p
m
n
T







Master Frame

Slave Frame

n+m

n+1

Empty slot

WCNC 2008

March 31
-

April 3 Las Vegas

Data reward ( D )

Master’s Data

Slave’s Data

D
xn




D
ym

D
xn




---



4
0
)
(
)
(
p
p
D
L
D
ym
S





3
2
1
0
)
(
)
(
p
p
p
p
D
L
D
N
xn
M







No Useful Data

---

---

---

---

D
ym

WCNC 2008

March 31
-

April 3 Las Vegas

Master energy reward ( W
(M)
)

Tx power

Rx Power

Sx power

WCNC 2008

March 31
-

April 3 Las Vegas

Slave energy reward (
W

)


Slave’ energy reward resembles mater’ one except that,
in
D

state, Slave does not listen for the PAYL field of
recognized downlink packet since it has been already
correctly received!

WCNC 2008

March 31
-

April 3 Las Vegas

Performance Analysis

Results

WCNC 2008

March 31
-

April 3 Las Vegas

AWGN

WCNC 2008

March 31
-

April 3 Las Vegas

Rayleigh

WCNC 2008

March 31
-

April 3 Las Vegas

Conclusions


Main Contribution


mathematical framework for performance evaluation
of Bluetooth EDR links


Results


3DHn yield better performance for SNR>20 dB


2DHn perform better in the low SNR region


1DHn always show poor performance


Results refer to a specific case study, but the
analytical model is general

WCNC 2008

March 31
-

April 3 Las Vegas

Department of Information Engineering

University of Padova, ITALY

Mathematical Analysis of Bluetooth Energy Efficiency

Andrea Zanella, Daniele Miorandi, Silvano Pupolin

WPMC 2003, 21
-
22 October 2003

Questions?

WCNC 2008

March 31
-

April 3 Las Vegas

Extra Slides…

Spare slides…

WCNC 2008

March 31
-

April 3 Las Vegas





j
j
S
j
ok
j
AC













72
0
0
0
0
1
72











18
3
0
2
0
0
0
1
1
3








ok
HEAD
Conditioned probabilities

AC

HEAD

PAYLOAD

72 bits

54 bits

h
=22
0

㈷㐵bi瑳

CRC

Receiver
-

Correlator
Margin (S)

2
-
time bit rep.
(
1/3 FEC)

DHn: Unprotected

DMn: (15,10) Hamming
FEC















15
15
0
14
0
0
0
0
0
1
1
15
:
DMn
1
:
DHn
h
ok
h
ok
PL
PL













0
: BER

WCNC 2008

March 31
-

April 3 Las Vegas

Hypothesis


Single slave piconet


Saturated links


Master and slave have always packets waiting for transmission


Unlimited retransmission attempts


Packets are transmitted over and over again until positive
acknowledgement


Static Segmentation & Reassembly policy


Unique packet type per connection


Sensing capability


Nodes can to sense the channel to identify the end of ongoing
transmissions


Nodes always wait for idle channel before attempting new transmissions

WCNC 2008

March 31
-

April 3 Las Vegas

Packet error probabilities


Let us define the following basic packet reception events


A
fr
: AC does not check


Packet is
not recognized


H
f
: AC does check & HEAD does not


Packet is
not recognized


D
f
: AC & HEAD do check, PAYL does not


Packet is
recognized

but
PAYL contains unrecoverable errors


D
s
: AC & HEAD & PAYL do check


Packet is
successfully received


Packets experiment independent error events because of
the frequency hopping mechanism

WCNC 2008

March 31
-

April 3 Las Vegas

Swapping Master and Slave*

*Results not reported in the WCNC paper