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

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

Agenda

  • BT Channel Markov Model description

  • Implementation under NS-2

  • Simulated Environment

  • Simulations Results

  • Future Work


Bt packet format

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

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

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

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

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:


P crc for dh n packets

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

DTMC Model and Experimental Results


Ns 2 implementation 1

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

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

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

PEP vs Node Distance


Tcp tahoe

TCP Tahoe


Tcp reno

TCP Reno


Tcp westwood

TCP Westwood

8

7


Last ack seen from receiver

Last Ack seen from receiver


Goodput tahoe reno westwood

Goodput (Tahoe, Reno, Westwood)

613.5

671.22

683.91

721 (DH5 pkts)


Tcp and udp tahoe

TCP and UDP - Tahoe

  • UDP: 600Kbps

628.19

78.49


Tcp and udp westwood

TCP and UDP - Westwood

  • UDP: 600Kbps

628.32

63.49


Future work

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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