Department of Information Engineering

University of Padova, Italy

On the Impact of Fading and Inter-piconet Interference on

Bluetooth Performance

A note on the use of these ppt slides:We’re making these slides freely available to all, hoping they might be of use for

researchers and/or students. They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. In return for use, we only

ask the following:If you use these slides (e.g., in a class, presentations, talks and so on) in substantially

unaltered form, that you mention their source.If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and put a link to the authors webpage:

www.dei.unipd.it/~zanella

Thanks and enjoy!

Department of Information Engineering

University of Padova, Italy

WPMC02 WPMC02 Honolulu, Hawaii, October 27-30, 2002

On the Impact of Fading and Inter-piconet Interference on

Bluetooth Performance

Andrea Zanella, Andrea M. Tonello, Silvano Pupolin

{zanella,tonello,pupolin}@dei.unipd.it

Department of Information Engineering

University of Padova, Italy

WPMC02 WPMC02 Honolulu, Hawaii, October 27-30, 2002

A note on the use of these ppt slides:We’re making these slides freely available to all, hoping they might be of use for researchers

and/or students. They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. In return for use, we only ask the

following:If you use these slides (e.g., in a class, presentations, talks and so on) in substantially

unaltered form, that you mention their source.If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and put a link to the authors webpage:

www.dei.unipd.it/~zanella

Thanks and enjoy!

October 27-30, 2002 WPMC02 Honolulu Hawaii 4

Outline of the contentsOutline of the contents

Bluetooth basic Motivations &

Purposes System model Results Conclusions

October 27-30, 2002 WPMC02 Honolulu Hawaii 5

What the standard says…

Bluetooth

specifications

October 27-30, 2002 WPMC02 Honolulu Hawaii 6

Main CharacteristicsMain Characteristics

Radio Band: ISM (2.45 GHz)

Available (almost) worldwide Royalties-free: cost saving

Interference Immunity Interference in ISM band has different strength and nature:

baby monitors, microwave ovens, lighting devices, WLAN,… Frequency Hopping Spread Spectrum (FHSS) modulation

Since most radio systems are band-limited, it is easy to finding a part of the 80-MHz-wide ISM band with low interference

FH_CDMA provides a good multiple access scheme Modulation Scheme

Signal Bandwidth of 1MHz (Frequency Hopping) GFSK (K=0.3): robustness, demodulation is easy, low-cost radio

units

October 27-30, 2002 WPMC02 Honolulu Hawaii 7

Bluetooth piconetBluetooth piconet

Two up to eight Bluetooth units sharing the same channel form a piconet

In each piconet, a unit acts as master, the others act as slaves

Channel access is based on a centralized polling scheme

active slavemaster

parked slavestandby

slave1

slave2

slave3

master

October 27-30, 2002 WPMC02 Honolulu Hawaii 8

FH & TDDFH & TDD

Each piconet is associated to frequency hopping (FH) channel The pseudo-random FH sequence is imposed by the master Time is divided into consecutive time-slots of 625 s Each slot corresponds to a different hop frequency

Full-duplex is supported by Time-division-duplex (TDD) Master-to-slave (downlink) transmissions start on odd slots Slave-to-Master (uplink) transmissions start on even slots

625 s

t

t

master

slave

f(2k) f(2k+1) f(2k+2)

October 27-30, 2002 WPMC02 Honolulu Hawaii 9

AC HECaccess code packet header payload

72 54 0-2745

CRC

General Packet FormatGeneral Packet Format

Access Code (AC) All packet exchanged in a piconet have the same AC Packets that don’t satisfy AC test are immediately

discarded Packet Header

Contains, among other information, slave active member receiver address, ARQ flags, payload format, header checksum field (HEC)

If the HEC test fails, the packet is immediately discarded Payload

If the CRC test fails, the packet is negative acknowledged

PAYL

October 27-30, 2002 WPMC02 Honolulu Hawaii 10

Multi-slot packets Multi-slot packets

f(k)

625 s

f(k+1) f(k+2) f(k+3) f(k+4)

f(k+3) f(k+4)f(k)

f(k)

f(k+5)

f(k+5)

f(k+5)

Packets can extend over one, three or five consecutive slots

Carrier frequency remains unchanged

Multi-slot packets reduce bandwidth losses due to header & guard time (220)

Max PAYL size

216 bit

1464 bit

2712 bit

October 27-30, 2002 WPMC02 Honolulu Hawaii 11

ACL data packet formatsACL data packet formats

ACL: Asynchronous data packet formats

1, 3, or 5 slot long Unprotected or protected by 2/3

FEC

Protected packet formats (DM): medium data capacity higher protection against errors

Unprotected packet formats (DH) higher data capacity more subject to errors

Erroneous packets are automatically retransmitted (Stop&Wait ARQ)

0

50

100

150

200

250

300

350

By

tes

1 slot 3 slots 5 slots

Paylod Capacity

Medium rate High rate

October 27-30, 2002 WPMC02 Honolulu Hawaii 12

Aims of the workAims of the work

Motivations &Purposes

October 27-30, 2002 WPMC02 Honolulu Hawaii 13

MotivationsMotivations

Scenario Massive Bluetooth presence: many independent

piconets overlap in the same area

Questions How does inter-piconet interference affect single

user performance? What’s the impact on multi-slot packets? Is there an easy way to derive performance

bounds?

October 27-30, 2002 WPMC02 Honolulu Hawaii 14

Aims of the workAims of the work

Previous works Either based on simulations or making restrictive

assumptions as Fixed length packets Destructive interference Absence of fading

Our contributions Simple method to evaluate impact of fading and inter-

piconet interference on Bluetooth performance taking into account

Fading & capture effects Packet format (FEC and packet length) Arbitrary number of potential interferers

October 27-30, 2002 WPMC02 Honolulu Hawaii 15

Hypothesis and Hypothesis and assumptionsassumptions

System Model

October 27-30, 2002 WPMC02 Honolulu Hawaii 16

Interferers modelInterferers model

We focus on a Target Receiver (TR) TR is r0 meters apart from its

transmitter TR can receive any pck type

Np “potential” interferers Uniformly distributed around TR, s.t.

fr(r)=2r/D2

Use only 1-slot long pcks Nodes are slot-synchronous

Ne “effective” interferers per slot

epe

e

nNn

e

peN n

NnP

79

78

79

1

r0

DTarget receiver

Interf. Piconet 2Interf. Piconet 3

Interf. Piconet 1

TimeTime

Frequency

carr

iers

Frequency

carr

iers

October 27-30, 2002 WPMC02 Honolulu Hawaii 17

Bit Error ProbabilityBit Error Probability

Prx: received power PI: interference

power N0: noise power RI: SIR for BER=1e-

3 R0: SNR for

BER=1e-3

*

00

RNRP

PrxBER

II

* Zürbes et al. “Radio Network Performance of Bluetooth,” ICC 2000

October 27-30, 2002 WPMC02 Honolulu Hawaii 18

Propagation model

Slow Flat Fading (envelope=) flat on 1 MHz channel constant along the entire packet Rice or Rayleigh distributions

WSSUS Signals from different transmitters incur independent fading Because of FH, successive pcks experiment independent

fading

2 rPrx

For Rayleigh fading, we get

D

Df i ,

22 22

e

e

N

iiNIP

1

Power-addictive interference

Ne interferers powers add up to PI

October 27-30, 2002 WPMC02 Honolulu Hawaii 19

jjCT

jok j

AC

72

000

0 172

,

1830

2000 113, okHEC

Conditioned PERConditioned PER

AC HEC PAYLOAD72 bits 54 bits h=2202745 bits

CRC

Correlator Threshold (CT)

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

DHn: Unprotected

DMn: (15,10) Hamming FEC

1515

014

000

00

1115,,:DMn

1,,:DHnh

ok

hok

hPL

hPL

00: BER: BER

λλ00: normal. : normal. useful useful powerpower

Λ: Λ: normal. normal. interfer. interfer. powerpower

October 27-30, 2002 WPMC02 Honolulu Hawaii 20

Average PERAverage PER

AC HEAD PAYL220 µs

Tslot=625 µs

,0BP

,,405 0okPL

0,,220 0okPL··

==

',0 AP

',0 okAC

',0 okHEC ',,280 0 okPL

0

0001

000 21

rfrPPdPER nBAxn

0

0)(0

0)( ,Peenee

p

e

e nnBAn

N

neNBA fPdnP

··

==

··

Target PacketTarget Packet

Effective Effective InterferersInterferers

October 27-30, 2002 WPMC02 Honolulu Hawaii 21

Analysis and Simulations

Results

October 27-30, 2002 WPMC02 Honolulu Hawaii 22

Performance MetricsPerformance Metrics

We focus on forward-channel performance: Packet type Dxk x{M,H}, k{1,3,5} Disregard errors in the backward channel

Performance metrics Average Packet Error Probability: PEPxk

Probability of Dxk pck dropping due to unrecoverable errors

Average Forward Throughput: xk

Average number of useful user data bit transmitted in the forward direction per unit of time

Throughput Crossing Point: Nx

Number of potential interferers for which x5 x3

October 27-30, 2002 WPMC02 Honolulu Hawaii 23

Results (1)Results (1) Parameters

Rayleigh fading (KT=- dB) r0=8 m, D = 10 m Different pck formats

Results PEP curves for DMk and

DHk get close each other as the number Np of potential interferers increases

FEC does not give benefit As expected, Dx3 formats

outperform Dx5 in terms of throughput for Np10

October 27-30, 2002 WPMC02 Honolulu Hawaii 24

Results (2)Results (2) Parameters

Interferers: Rayleigh fading Target Receiver:

Rayleigh: KT=- dB Ricean: KT=6 dB

Results The crossing point Nx is

greater than 10 when transmitter an receiver are within the nominal coverage range (10 m)

The presence of LOS has a marginal impact on Nx, but the throughput at the crossing point is higher

Shorter formats are better

October 27-30, 2002 WPMC02 Honolulu Hawaii 25

Analysis AccuracyAnalysis Accuracy

Analysis vs Simulations Simulator does

consider time offsets, fading, …

Results =(theor-sim)/sim

Bound is tight for Np<10, r0 <3 or r0 >7

Bound is loose for Np>10, r0 5

October 27-30, 2002 WPMC02 Honolulu Hawaii 26

ConclusionsConclusions

In case of inter-piconet interference DMn formats achieve very poor performance Dx5 and Dx3 formats show a performance tradeoff for

increasing number of interferers The performance crossing point Nx depends on the

distance r0 between transmitter and receiver and marginally on the presence of LOS

In case of LOS, short formats may be more suitable than long ones

Model Accuracy Analytic bound becomes loose for high number of

potential interferers and intermediate values of r0

October 27-30, 2002 WPMC02 Honolulu Hawaii 27

Thanks!

Thanks for you attention!