Transcript Ingegneria dell'Informazione

Department of Information Engineering
University of Padova, ITALY
Throughput and Energy Efficiency of
Bluetooth v2 + EDR in Fading Channels
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March 31 - April 3 Las Vegas
Department of Information Engineering
University of Padova, ITALY
Special Interest Group on
NEtworking & Telecommunications
Throughput and Energy Efficiency of
Bluetooth v2 + EDR in Fading Channels
Andrea Zanella, Michele Zorzi
{andrea.zanella, michele.zorzi}@dei.unipd.it
Speaker: Marco Miozzo
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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!

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Bluetooth v2.0 + EDR (Enhanced Data Rate) promise bit rates up to 3
Mbps and faster node connections
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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!
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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)


Define appropriate reward functions


State transitions driven by packet reception events
Data, Energy, Time
Apply renewal reward theorem to get system
performance

Throughput, energy efficiency, energy balancing, …
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What standard says…
Bluetooth reception
mechanism
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Physical layer

Basic Rate: 1Mbps


EDR2: 2Mbps


GFSK [13]
/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.
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Baseband frame formats
GFSK
AC
HEAD
PAYL
0.22 ms
Tslot=0.625 ms
TDxn=nTslot
DPSK
GFSK
AC
HEAD GUARD SYNC
PAYL
EDR
Trailer
0.22 ms
Tslot=0.625 ms
TjDxn= nTslot
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Retransmissions
A
B
B
B
B
B
NAK
MASTER
ACK
G
SLAVE
A
 Automatic
F
X
H
H
B
X
DPCK
DPCK
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!
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Mathematical Analysis
System Model
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Mathematical Model

Normal State (N)


Duplicate State (D)


Master transmits duplicate packets (DUPCKs)
The steady-state probabilities are, then,
N 

Master transmits packets that have never been
correctly received by the slave
PND
PND  PDN
D 
PDN
PND  PDN
State transition probabilities depend on the reception events…
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Reception events
Reception
Event Index
Slaves tx

Reception events

Master tx
Ds = Data successful


Df = Data 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

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AC ok, HEAD error
Af = AC failure

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decompressor
are needed to see this picture.
AC ok, HEAD ok, CRC error
Hf = HEAD failure


AC ok, HEAD ok, CRC ok
Return in the same state
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Reward Functions

For each state j we define the following reward functions

Tj= Average amount of time spent in state j

Dj(x)= Average amount of data delivered by unit x{M,S}

Wj(x)= Average amount of energy consumed by unit x{M,S}

The average amount of reward earned in state j is given by
T

 jT j
E j E

Performance indexes


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D
( x)


( x)
jDj
W
( x)

E j E
 W
j
( x)
j
E j E
Energy Efficiency: 
D  D  D
  lim
 (S )
(M )
  W  
W W
Goodput: G
D  D
G  lim

  T  
(S )
(M )
(S )
(M )
D
T
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Time reward ( T )
Master Frame
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Slave Frame
Empty slot
n+m
n+1
T  (n  m)1  p8  p9   (n  1) p8  p9 
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Data reward ( D )
Master’s Data
Slave’s Data
Dxn 
Dym
Dxn 
--Dym
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D ( M )  L( Dxn )   N   p0  p1  p2  p3 
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No Useful Data
-----
D ( S )  L(Dym )   p0  p4 
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Master energy reward ( W(M))
Tx power
Rx Power
Sx power
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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!
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decompressor
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Performance Analysis
Results
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AWGN
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Rayleigh
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Conclusions

Main Contribution


Results




mathematical framework for performance evaluation
of Bluetooth EDR links
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
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Department of Information Engineering
University of Padova, ITALY
Mathematical Analysis of Bluetooth Energy Efficiency
Andrea Zanella, Daniele Miorandi, Silvano Pupolin
Questions?
WPMC 2003, 21-22 October 2003
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Extra Slides…
Spare slides…
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Conditioned probabilities
AC
72 bits
DHn: Unprotected
2-time bit rep.
(1/3 FEC)
ReceiverCorrelator
Margin (S)
HEAD
DMn: (15,10) Hamming
FEC
PAYLOAD
54 bits
CRC
h=2202745 bits
DHn : PLok  0   1   0 h
0: BER

DMn : PLok  0   15 0 1   0 14  1   0 15

HEAD ok  0   3 0 1   0   1   0 
2

3 18
 72 j
  0 1   0 72 j
ACok  0  
j
j 0 
S

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
h 15 
Hypothesis

Single slave piconet

Saturated links


Unlimited retransmission attempts


Packets are transmitted over and over again until positive
acknowledgement
Static Segmentation & Reassembly policy


Master and slave have always packets waiting for transmission
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
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Packet error probabilities

Let us define the following basic packet reception events

Afr: AC does not check


Hf: AC does check & HEAD does not


Packet is recognized but PAYL contains unrecoverable errors
Ds: AC & HEAD & PAYL do check


Packet is not recognized
Df: AC & HEAD do check, PAYL does not


Packet is not recognized
Packet is successfully received
Packets experiment independent error events because of
the frequency hopping mechanism
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Swapping Master and Slave*
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decompressor
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*Results not reported in the WCNC paper
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