BLUETOOTH LINK PERFORMANCE WITH CRC MEASUREMENT

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BLUETOOTH LINK PERFORMANCE WITH CRC MEASUREMENT

• CS 215 CLASS PROJECT
• by
• Lingtao Cao
• Wenfei Feng
• Howie Yu
• March 22, 2001

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OVERVIEW

• Introduction
• Problem Statement and Scope of Work
• Bluetooth Error Correction
• CRC Calculation Algorithm
• Glomosim CRC Implementation
• Simulation
• Summary
• Future work

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INTRODUCTION

• Wireless Technology
• Low cost
• low power
• no line of sight
• Data/Voice, Personal ad hoc networks
• wide industry support
• Piconet and scatternet

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PROBLEM AND SCOPE OF WORK

• PROBLEM STATEMENT
• Relatively new technology, Lots of research needs
  to be done
• Bluetooth Link Performance and Modeling
• Link performance parameters
• PDP (packet dropping probability)
• PEP (packet error probability)
• Bluetooth Error Detection and Correction
• Present Simulator (Glomosim) does not enable
  error detection and correction

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PROBLEM AND SCOPE OF WORK

• SCOPE OF WORK
• Study Bluetooth Specification
• Error Correction Techniques and Algorithms
• Familiarize Glomosim
• Implement CRC Error detection and Correction in
  Glomosim
• Run Simulation and Study the Link Performance

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BLUETOOTH ERROR CORRECTION
BLUETOOTH PACKET FORMAT
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PAYLOAD FORMAT

• Component
• payload header
• payload body
• CRC code

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BLUETOOTH PACKET TYPE AND ERROR CORRECTION
REQUIREMENT SUMMARY 1
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BLUETOOTH PACKET TYPE AND ERROR CORRECTION
REQUIREMENT SUMMARY 2
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ERROR CORRETION IN BLUETOOTH

• 1/3 Rate FEC
• 2/3 Rate FEC
• CRC-ARQ Scheme

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CRC CALCULATION ALGORITHM

• GENERAL ERROR CORRETION TECHNIQUES
• GOAL
• Enable the receiver of a message transmitted
  through a noisy (error-introducing) channel to
  determine whether the message has been corrupted.
  
• HOW
• Transmitter constructs a value (called a
  checksum) that is a function of the message, and
  appends it to the message.
• The receiver can then use the same function to
  calculate the checksum of the received message
  and compare it with the appended checksum to see
  if the message was correctly received.
• COMPLEXITY
• Increase CRC bits would strengthen CRC checksum

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CRC CALCULATION ALGORITHM

• FUNCTION
• WIDTH A register width wide enough to provide a
  low a-priori probability of failure (e.g. 32-bits
  gives a 1/232 chance of failure)
• CHAOS A formula that gives each input byte the
  potential to change any number of bits in the
  register.
• BASIC IDEA
• treat the message as an enormous binary number,
  to divide it by another fixed binary number, and
  to make the remainder from this division the
  checksum.
• Upon receipt of the message, the receiver can
  perform the same division and compare the
  remainder with the "checksum" (transmitted
  remainder).

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Cyclic Redundancy Check (CRC)

• Purpose calculate R (CRC bits) to detect error
  (e.g., flipped bits) in transmitted segment
• Parameters
• G 1 the upper 8 bits of the physical address
  of the master
• D data bits to be sent (payload, header)
• r number of CRC bits (16 bits for payload, 8
  bits for HEC)

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CRC Example
Want D.2r XOR R G equivalently D.2r G
XOR R equivalently if we divide D.2r by
G, want reminder R
D.2r G
R remainder
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IMPLEMENT CRC ERROR DETECTION AND CORRECTION IN
GLOMOSIM FLOW CHART AT SENDER
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FLOW CHART AT RECEIVER
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SIMULATION

• SIMULATION PARAMETERS
• Number of Piconets 1, 2, 3, 4
• Number of Nodes 8, 16, 24, 32
• Simulation Time 60 s
• Source rate 0.08 s
• Channel Noise Figure 10.0 , 5.0, 0.0

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SIMULATION
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Analysis of Results

• Execution without CRC
• Influence of CRC Checking
• Execution with CRC
• Stability of the simulation environment
• noise factors (radio and propagation ambient)
• bandwidths (30, 185, 340)
• Time effects with the increasing number of
  nodes/Piconets
• Tradeoff between time consuming and error
  detection
• It is feasible to add the CRC checking into the
  simulation when handling relative large number of
  nodes/Piconets

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SUMMARY

• Error detection and correction will generally
  help to increase Bluetooth link performance
• For light and uncrowded traffic, CRC does not
  improve the performance by much
• Link performance decrease with increased source
  access rate even with CRC correction

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FUTURE WORK

• Increase the number of Piconets and total number
  of nodes
• Implement FEC encoding and decoding in Glomosim
• Implement 3-State Model in Glomosim