1. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Department of Information Engineering University of Padova, ITALY Mathematical Analysis of Bluetooth Energy Efficiency of Bluetooth Energy Efficiency A note on the use of these ppt slides: We’re making these slides freely available to all, hoping they might be of use for researchers and/or students. They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. In return for use, we only ask the following: If you use these slides (e.g., in a class, presentations, talks and so on) in substantially unaltered form, that you mention their source. If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and put a link to the authors webpage: www.dei.unipd.it/~zanella Thanks and enjoy! A note on the use of these ppt slides: We’re making these slides freely available to all, hoping they might be of use for researchers and/or students. They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. In return for use, we only ask the following: If you use these slides (e.g., in a class, presentations, talks and so on) in substantially unaltered form, that you mention their source. If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and put a link to the authors webpage: www.dei.unipd.it/~zanella Thanks and enjoy!

2. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Department of Information Engineering University of Padova, ITALY Mathematical Analysis of Bluetooth Energy Efficiency {andrea.zanella, daniele.miorandi, silvano.pupolin}@dei.unipd.it Andrea Zanella, Daniele Miorandi, Silvano Pupolin WPMC 2003, 21-22 October 2003 Special Interest Group on NEtworking & Telecommunications

3. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Motivations  Bluetooth was designed to be integrated in portable battery driven electronic devices  Energy Saving is a key issue!  Bluetooth Baseband aims to achieve high energy efficiency:  Units periodically scan radio channel for valid packets  Scanning takes just the time for a valid packet to be recognized  Units that are not addressed by any valid packet are active for less than 10% of the time

4. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Aims of the work  Although reception mechanism is well defined, many aspects still need to be investigated:  What’s the energy efficiency achieved by multi-slot packets?  What’s the role plaid by the receiver-correlator margin parameter?  What’s the best Master and Slave configuration?  How do we answer such questions?  Capture system dynamic by means of a FSMC  Define appropriate reward functions (Data, Energy, Time)‏  Resort to renewal reward analysis to compute system performance

5. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 What standard says… Bluetooth reception mechanism

6. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 ACHEAD access codepacket headerpayload 72 54 0-2745 CRC Access Code field  Access Code (AC)‏  AC field is used for synchronization and piconet identification  All packet exchanged in a piconet have same AC  Bluetooth receiver correlates the incoming bit stream against the expected synchronization word: AC is recognized if correlator output exceeds a given threshold  AC does check  HEAD is received  AC does NOT check  reception stops and pck is immediately discarded PAYL

7. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Receiver-Correlator Margin  S: Receiver–correlator margin  Determines the selectivity of the receiver with respect to packets containing errors  Low S  strong selectivity risk of dropping packets that could be successfully recovered  High S  weak selectivity risk of receiving an entire packet that contains unrecoverable errors

8. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 ACHEAD access codepacket headerpayload 72 54 0-2745 CRC Packet HEADer field  Packet Header (HEAD)‏  Contains: Destination address Packet type ARQN flags: used for piggy-backing ACK information Header checksum field (HEC): used to check HEAD integrity  HEC does check  PAYL is received  HEC does NOT check  reception stops and pck is immediately discarded PAYL

9. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 ACHEAD access codepacket header payload 72 54 0-2745 CRC Packet PAYLoad field  Payload (PAYL)‏  DH: High capacity unprotected packet types  DM: Medium capacity FEC protected packet types (15,10) Hamming code  CRC field is used to check PAYL integrity: CRC does check  positive acknowledged is return (piggy-back)‏ CRC does NOT check  negative acknowledged is return (piggy-back)‏ PAYL

10. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Retransmissions MASTER SLAVE ABBBB GFH NAK ACK  Automatic Retransmission Query (ARQ):  Each data packet is transmitted and retransmitted until positive acknowledge is returned by the destination  Negative acknowledgement is implicitly assumed! Errors on return packet determine transmission of duplicate packets (DUPCK) Slave filters out duplicate packets by checking their sequence number never  Slave does never transmit DUPCKs! Slave can transmit when it receives a Master packet Master packet piggy-backs the ACK/NACK for previous Slave transmission Slave retransmits only when needed! H B A X BX DPCK

11. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Mathematical Analysis System Model

12. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Reception events   0 : both downlink and uplink packet are correctly received   1 : downlink packet is correctly received, uplink packet is received but with errors in the PAYL field   2 U  3 : downlink packet is correctly received but uplink packet is not recognized by the master unit DUPCKs  Master will transmit DUPCKs   4  9 : downlink and uplink packets are not correctly received useful packets  Master will retransmit useful packets Reception Event Index Downlink pck reception events Uplink pck reception events

13. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Mathematical Model  Normal State (N)‏  Master transmits packets that have never been correctly received by the slave  Duplicate State (D)‏  Master transmits duplicate packets (DUPCKs)‏  The steady-state probabilities are, then,  Since error events are disjoint, the state transition probabilities are given by

14. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Reward Functions  For each state j we define the following reward functions  T j = Average amount of time spent in state j  D j (x) = Average amount of data delivered by unit x  {M,S}  W j (x) = Average amount of energy consumed by unit x  {M,S}  The average amount of reward earned in state j is given by  Performance indexes  Energy Efficiency:   Goodput: G

15. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Time reward ( T )‏ MASTER SLAVE Transmission Reception/Sensing n+m n+1 MASTER SLAVE

16. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Data reward ( D )‏  Master gains Data reward when  System is in state N  Slave perfectly receives the master packet  Slave gains Data reward when  Slave recognizes the master polling  Master perfectly receives the slave packet

17. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Master energy reward ( W )‏ Receives entire uplink packet Receives till the first uncorrected field and senses till the end of the packet Receives only AC field Always transmits a downlink packet

18. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Slave energy reward ( W )‏  Slave’ energy reward resembles mater’ one except that, in D state, Slave does not listen for the PAYL field of recognized downlink packet since it has been already correctly received!

19. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Performance Analysis Results

20. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Energy Efficiency  Downlink traffic only (M>S) and S=0  Energy efficiency gets worse in Rayleigh channels  DH5 outperform other packet formats for almost every SNR value  For SNR dB =14  18, DMn outperforms DHn

21. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Master Slave swapping  Swapping Master and Slave role:  DM5 & DM3 energy efficiency increases up to 15 % for SNR  20dB  Unprotected pck types show slightly reduced performance gain  Performance gain drastically reduces for increasing values of the Rice factor K  For AWGN channels, master slave swapping does not lead to any significant performance improvement

22. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Impact of parameter S  The receiver correlator margin S has strong impact on system performance  AWGN:  improves with S, in particular for low SNR values  Rayleigh:  gets worse with S, except for low SNR values  Relaxing AC selectivity is convenient, since G gain is much higher than  loss  Impact of S, however, rapidly reduces for SNR dB >15 AWGNRayleigh

23. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Conclusions  Main Contribution  mathematical framework for performance evaluation of Bluetooth piconets  Results  In case of asymmetric connections, Slave to Master configuration yields better performance in terms of both Goodput and Energy Efficiency Slave never transmits DUPCK  Parameter S may significantly impact on performance Short and Protected packet types improve performance with S Long and Unprotected packet types show less dependence on this parameter  Next steps  Design energy–efficient scheduling algorithms for Bluetooth piconets

24. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Department of Information Engineering University of Padova, ITALY Mathematical Analysis of Bluetooth Energy Efficiency Andrea Zanella, Daniele Miorandi, Silvano Pupolin WPMC 2003, 21-22 October 2003 Questions?

25. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Extra Slides… Spare slides…

26. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Conditioned probabilities ACHEAD PAYLOAD 72 bits 54 bits h=220  2745 bits CRC Receiver- Correlator Margin (S) ‏ 2-time bit rep. ( 1/3 FEC) ‏ DHn: Unprotected DMn: (15,10) Hamming FEC  0 : BER

27. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Hypothesis  Single slave piconet  Saturated links  Master and slave have always packets waiting for transmission  Unlimited retransmission attempts  Packets are transmitted over and over again until positive acknowledgement  Static Segmentation & Reassembly policy  Unique packet type per connection  Sensing capability  Nodes can to sense the channel to identify the end of ongoing transmissions  Nodes always wait for idle channel before attempting new transmissions

28. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Packet error probabilities  Let us define the following basic packet reception events  AC er : AC does not check Packet is not recognized  HEC er : AC does check & HEAD does not Packet is not recognized  CRC er : AC & HEAD do check, PAYL does not Packet is recognized but PAYL contains unrecoverable errors  PR ok : AC & HEAD & PAYL do check Packet is successfully received  Packets experiment independent error events

29. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Notations  Let us introduce some notation:  D xn (D ym ) downlink (uplink) packet type, n=1,3,5   L(D xn ) = PAYL length (bit) for D xn packet type  w TX (X) / w RX (X)/ w ss (X)= amount of power consumed by transmitting/ receiving/ sensing the packet field X  p j = Pr(  j )‏

30. WPMC 2003 Yokosuka, Kanagawa (Japan) 21-22 October 2003 Master Slave swapping  Swapping Master and Slave role:  DM5 & DM3 energy efficiency increases up to 15 % for SNR  20dB  Unprotected pck types show slightly reduced performance gain  Performance gain drastically reduces for increasing values of the Rice factor K  For AWGN channels, master slave swapping does not lead to any significant performance improvement