BLUETOOTH LINK PERFORMANCE WITH CRC MEASUREMENT

CS 215 CLASS PROJECT

by

Lingtao Cao

Wenfei Feng

Howie Yu

March 22, 2001

OVERVIEW

• Introduction

• Problem Statement and Scope of Work

• Bluetooth Error Correction

• CRC Calculation Algorithm

• Glomosim CRC Implementation

• Simulation

• Summary

• Future work

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

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

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

BLUETOOTH ERROR CORRECTIONBLUETOOTH PACKET FORMAT

PAYLOAD FORMAT

• Component:– payload header– payload body– CRC code

BLUETOOTH PACKET TYPE AND ERROR CORRECTION

REQUIREMENT SUMMARY 1

BLUETOOTH PACKET TYPE AND ERROR CORRECTION

REQUIREMENT SUMMARY 2

ERROR CORRETION IN BLUETOOTH

• 1/3 Rate FEC

• 2/3 Rate FEC

• CRC-ARQ Scheme

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

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 1/2^32 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).

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)

CRC Example

Want:

D.2^r XOR R = Gequivalently:

D.2^r = G XOR R equivalently: if we divide D.2r by G, want reminder R

R = remainder[ ]D.2^r G

IMPLEMENT CRC ERROR DETECTION AND CORRECTION IN GLOMOSIM

FLOW CHART AT SENDER

FLOW CHART AT RECEIVER

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}

SIMULATION

Simulation Time

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

0 4 8 12 16 20 24 28 32 36

Number of Nodes

Tim

e (s

)

Time with CRC

Time Without CRC

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

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

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