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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. 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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  1. 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)

  2. Agenda • BT Channel Markov Model description • Implementation under NS-2 • Simulated Environment • Simulations Results • Future Work

  3. 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

  4. 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

  5. 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

  6. 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.

  7. 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:

  8. 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

  9. DTMC Model and Experimental Results

  10. 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

  11. 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; }

  12. 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

  13. PEP vs Node Distance

  14. TCP Tahoe

  15. TCP Reno

  16. TCP Westwood 8 7

  17. Last Ack seen from receiver

  18. Goodput (Tahoe, Reno, Westwood) 613.5 671.22 683.91 721 (DH5 pkts)

  19. TCP and UDP - Tahoe • UDP: 600Kbps 628.19 78.49

  20. TCP and UDP - Westwood • UDP: 600Kbps 628.32 63.49

  21. 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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