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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 (bissacco@cs) Massimo Valla (mvalla@cs). 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

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

CS215 - Computer Communication Networks - Winter 2001 Project

March 22, 2001

Alessandro Bissacco (bissacco@cs)

Massimo Valla (mvalla@cs)

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
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

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)