A bluetooth link markov model simulation and performance evaluation under ns 2
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A Bluetooth Link Markov Model: Simulation and Performance Evaluation under NS-2. CS215 - Computer Communication Networks - Winter 2001 Project March 22, 2001 Alessandro Bissacco ([email protected]) Massimo Valla ([email protected]). Agenda. BT Channel Markov Model description Implementation under NS-2

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A Bluetooth Link Markov Model: Simulation and Performance Evaluation under NS-2

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A Bluetooth Link Markov Model: Simulation and Performance Evaluation under NS-2

CS215 - Computer Communication Networks - Winter 2001 Project

March 22, 2001

Alessandro Bissacco ([email protected])

Massimo Valla ([email protected])


Agenda

  • BT Channel Markov Model description

  • Implementation under NS-2

  • Simulated Environment

  • Simulations Results

  • Future Work


BT Packet Format

16 bits

72bits

0-2745 bits

8-16 bits

54 bits

PACKET TYPES

  • Protected DM1, DM3, DM5

  • Unprotected DH1, DH3, DH5

p. head

data

CRC

FEC

payload

access code

header


What We are Modeling

slave

master

  • Radio channel propagation is characterized by three main parameters:

    • Attenuation: free space loss, absorption by foliage, partitions

    • Shadowing: obstacles between transmitter and receiver

    • Multipath: due to the different phases on different paths

Indoor, fixed terminals

moving obstacles


SNR Transitions and Markov Chain

Q

eG= 0

G

NL2

p

P

B

q

eB

NL1

a

b

S

eS= 1

d

SNR (at receiver)

  • L0 = 0, L1 = 1, L2 = 2.5

  • S = Synchronization Failure (AC or HEAD error)

  • B = Bad State (non zero residual bit error probability)

  • G = Good State (totally error free condition)

L2

L1

L0

time


The BT Channel Model

q

p

Q

S

B

G

P

3-state Discrete-Time Markov Chain

  • The transition time TS of the Markov Chain is the BT bit time (TS=1 ms)

  • The Markov Chain is initialized after each frequency hop (-> at each BT packet)

  • Each state of the Markov Chain corresponds to a bit-error probability ei:

    ei = Pr(bit error | Markov Chain state = i)

    We define:

    PDP = Pr(unrecoverable error in the HEADER or AC fields of the BT packet)

    PCRC = Pr(unrecoverable error in the PAYLOAD of the BT packet)

    PEP = Pr(unrecoverable error in the BT packet)

    PEP = PDP + (1-PDP)*PCRC

    PDP = PS

    PCRC depends on the packet type (protected, unprotected) and payload size.


Error vector, Steady State Pr. and Transition Pr.

  • The error vector e=[eS eB eG] is:eS = 1, eG = 0 and eB = 2.5E-3 is obtained empirically from measured PCRC

  • SSP:

    • fG = p.d.f of SNR G(t)

  • The transition probabilities ti,j are computed using the SNR thresholds crossing rates:


PCRC for DHn packets

  • There is an analytical formulation for PCRC for DHn packets:

  • Where:

    • L same as J with neg. sqr. root

    • hb = 1 – eB

    • N = BT payload length (in bits) for current packet


DTMC Model and Experimental Results


NS-2 Implementation (1)

Wireless

Phy

Set error_ = 1 if PAYLOAD error

Added to NS-2

BTWireless

Drop packet if AC or Head Error

  • Class BTWirelessPhy: public WirelessPhy

sender

receiver

BT MAC

BT MAC

Wireless

Phy

Wireless

Phy

Channel


NS-2 Implementation (2)

  • Pseudo-code:

    For each new incoming BT packet:

    based on SNR at the receiver, init. the MC:compute PDP = PS, PG, PB and all other parameters;

    sample a random number r1 between 0 and 1;

    if r1 < PDP then

    drop packet;

    else {

    using packet type (DM or DH) and payload length, compute PCRC;

    sample a random number r2 between 0 and 1;

    if r2 < PCRC then

    error_ = 1; // packet will be dropped by the MAC layer

    send up packet to the MAC layer;

    }


Simulation Environment

master

slave

  • Simulation Parameters:

    • Node distance 8 mt.

    • Simulation time: 15 sec.

    • Propagation Model: Free Space (NS-2 module)

    • Traffic source: FTP (started at 1 sec.)

    • TCP segments: 1,000 bytes

    • BT buffer: 1,000 DH1 packets (i.e. 30,000 bytes)

    • Various TCP versions: Tahoe, Reno, Westwood

0

1


PEP vs Node Distance


TCP Tahoe


TCP Reno


TCP Westwood

8

7


Last Ack seen from receiver


Goodput (Tahoe, Reno, Westwood)

613.5

671.22

683.91

721 (DH5 pkts)


TCP and UDP - Tahoe

  • UDP: 600Kbps

628.19

78.49


TCP and UDP - Westwood

  • UDP: 600Kbps

628.32

63.49


Future Work

  • Deeper analysis of current simulation results

  • Do more simulations to measure:

    • packet drops

    • rtxs

    • delays and RTTs

  • Simulations using Scatternets to increase RTT due to delays on gateways

  • More simulations using different node distances to increase PEP

  • Simulations with multiple TCP and UDP flows

  • Thanks: Rohit Kapoor (NS-2 and BT MAC help) and Andrea Zanella (project mentor)


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