On the Impact of Fading and Inter-piconet Interference on Bluetooth Performance

1
On the Impact of Fading and Inter-piconet
Interference onBluetooth Performance
Department of Information Engineering University
of Padova, Italy
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s and enjoy!
2
On the Impact of Fading and Inter-piconet
Interference onBluetooth Performance
Department of Information Engineering University
of Padova, Italy

• Andrea Zanella, Andrea M. Tonello, Silvano Pupolin

zanella,tonello,pupolin_at_dei.unipd.it
WPMC02 Honolulu, Hawaii, October 27-30, 2002
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Department of Information Engineering University
of Padova, Italy
A note on the use of these ppt slidesWere
making these slides freely available to all,
hoping they might be of use for researchers
and/or students. Theyre 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
followingIf 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 Thank
s and enjoy!
WPMC02 Honolulu, Hawaii, October 27-30, 2002
4
Outline of the contents

• Bluetooth basic
• Motivations Purposes
• System model
• Results
• Conclusions

5
What the standard says
Bluetooth specifications
6
Main 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 (K0.3) robustness, demodulation is easy,
  low-cost radio units

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Bluetooth 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

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FH 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

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General Packet Format
PAYL

• Access Code (AC)?
• All packet exchanged in a piconet have the same
  AC
• Packets that dont 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

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Multi-slot packets
Max PAYL size
216 bit
1464 bit
2712 bit

• 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?)?

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ACL 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
  (StopWait ARQ)

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Aims of the work
Motivations Purposes
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Motivations

• Scenario
• Massive Bluetooth presence many independent
  piconets overlap in the same area
• Questions
• How does inter-piconet interference affect single
  user performance?
• Whats the impact on multi-slot packets?
• Is there an easy way to derive performance bounds?

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Aims 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

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Hypothesis and assumptions
System Model
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Interferers model
Target receiver

• 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

Interf. Piconet 1
D
Interf. Piconet 2
Interf. Piconet 3
r0
Frequency carriers
Time
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Bit Error Probability

• Prx received power
• PI interference power
• N0 noise power
• RI SIR for BER1e-3
• R0 SNR for BER1e-3

Zürbes et al. Radio Network Performance of
Bluetooth, ICC 2000
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Propagation model

• Power-addictive interference
• Ne interferers powers add up to PI

• 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

• For Rayleigh fading, we get

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Conditioned PER
DHn Unprotected DMn (15,10) Hamming FEC
2-time bit rep. (1/3 FEC)?
Correlator Threshold (CT)?
AC
HEC
PAYLOAD
CRC
54 bits
72 bits
h220?2745 bits
?0 BER ?0 normal. useful power ? normal.
interfer. power
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Average PER
Target Packet
Tslot625 µs
Effective Interferers
AC
HEAD
220 µs
PAYL





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Analysis and Simulations
Results
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Performance 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

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Results (1)?

• Parameters
• Rayleigh fading (KT-? dB)?
• r08 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 Np?10

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Results (2)?

• Parameters
• Interferers Rayleigh fading
• Target Receiver
• Rayleigh KT-? dB
• Ricean KT6 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

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Analysis Accuracy

• Analysis vs Simulations
• Simulator does consider time offsets, fading,
• Results
• ?(?theor-?sim)/?sim
• Bound is tight for
• Nplt10, r0 lt3 or r0 gt7
• Bound is loose for
• Npgt10, r0 ? 5

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Conclusions

• 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

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Thanks!
Thanks for you attention!