1. COST273, Barcelona, 15-17 January, 2003 Department of Information Engineering University of Padova, Italy Mathematical Analysis 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. COST273, Barcelona, 15-17 January, 2003 Department of Information Engineering University of Padova, Italy Mathematical Analysis of Bluetooth Energy Efficiency {zanella, pupolin}@dei.unipd.it Andrea Zanella, Silvano Pupolin COST273 Barcelona, 15-17 January 2003

3. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Outline of the contents Motivations & Purposes Bluetooth reception mechanism System Model Results Conclusions

4. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 What & Why… Motivations & Purposes

5. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 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

6. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 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 amount of energy drained by Master and Slave units? Our aim is to provide answers to such questions! How?  Capture system dynamic by means of a FSMC  Define appropriate reward functions (Data, Energy, Time)‏  Resort to renewal reward analysis to compute system performance

7. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 What standard says… Bluetooth reception mechanism

8. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 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

9. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 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

10. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 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

11. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 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

12. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 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

13. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 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 Slave filters out duplicate packets by checking their sequence number  Slave never transmits duplicate packets! 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

14. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Mathematical Analysis System Model

15. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Mathematical Model System dynamic can be modelled by means of a discrete time independent process {e n } with state space E Each state corresponds to a specific system behaviour For each state E j  E, we define the following reward functions  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}  T j = Average amount of time spent in state E j Denoting by  j the probability of event E j, the average amount of reward earned in state E j is given by:

16. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 System Dynamic We need to determine:  State space E  System behaviour in each E j  E System dynamic depends on the packet reception events that occur at Slave and Master units Let us first focus on events that may occur during the reception of a single packet

17. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Packet reception events 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  CRC ok : AC & HEAD & PAYL do check Packet is successfully received Furthermore, we introduce the following notation  Recognition Error: REC er ={AC er or HEC er }  Recognition OK: REC ok ={CRC er or CRC ok }

18. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Basic reception events (1)‏ Looking at the reception status of both the downlink (master to slave) and uplink (slave to master) packets, we can identify four basic reception events  r 1 : both downlink and uplink packet are recognized by the slave and master unit, respectively  r 2 : downlink packet is not recognized by the slave unit (uplink packet is not returned)  r 3 : downlink packet is recognized by the slave unit, but PAYL is not correct, uplink packet is not recognized by the master unit  r 4 : downlink packet is successfully received by the slave unit, uplink packet is not recognized by the master unit

19. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Basic reception events (2)‏ Note that,  Basic events are disjoint:  Their probabilities adds to one: The occurrence of each basic event determines a specific system dynamic for a given number of steps  We define a state E i to each basic event r i : r i  E i  State E i collects the system dynamic after the occurrence of the basic event r i

20. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Notations Let us introduce some notation:  D xn = downlink (Master to Slave) packet type, n=1,3,5  D ym = uplink (Slave to Master) packet type, m=1,3,5  L(D xn ) = number of data bits carried by the D xn packet type  w TX (X)= amount of power consumed by transmitting packet field X  w RX (X)= amount of power consumed by receiving packet field X  w 0 = average amount of power consumed by the receiving unit in case the incoming packet is not recognized, i.e., REC er occurs:

21. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 System Dynamic: E 1 Rewards earned in state E 1 are given by:  Time spent is E 1  Energy consumed by Master  Energy consumed by Slave  Data delivered by Master  Data delivered by Slave MASTER SLAVE Transmission Reception T1T1

22. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 System Dynamic: E 2 Rewards earned in state E 2 are given by:  Time spent is E 2  Energy consumed by Master  Energy consumed by Slave  Data delivered by Master  Data delivered by Slave MASTER SLAVE Transmission Reception T2T2

23. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 System Dynamic: E 3 Rewards earned in state E 3 are given by:  Time spent is E 3  Energy consumed by Master  Energy consumed by Slave  Data delivered by Master  Data delivered by Slave MASTER SLAVE Transmission Reception T3T3

24. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 System Dynamic: E 4 T4T4 State E 4 is entered when r 4 event occurs:  Downlink packet is perfectly received, while uplink packet is not recognized Master keeps retransmitting duplicate pcks until a return pck is recognized Slave listens only for AC and HEAD fields of duplicate packets and returns an uplink packet for each duplicate packet it recognizes State E 4 is left when r 1 event occurs:  Both downlink and uplink packets are recognized by the respective units

25. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Performance Analysis Results

26. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Performance Indexes From the renewal reward analysis, we can evaluate the following performance indexes  Goodput: G Amount of data successfully delivered per unit of time  Energy Efficiency:  Amount of data successfully delivered per unit of energy consumed

27. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 AWGN channel: M>S Asymmetric connection: M>S  Data flows from Master to Slave SNR dB < 14, G  0 SNR dB =14  18, DMn outperforms DHn SNR dB >18, DHn achieves better G Energy efficiency curves resemble Goodput curves However, performance gap between Dx5 and Dx3 pck types is reduced

28. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 AWGN channel: S>M Asymmetric connection: S>M  Data flows from Slave to Master Swapping Master and Slave role:  DM5 & DM3 Goodput increases up to 15 %  Other pck types do not improve, but neither lose performance… Energy efficiency improvement for DM5 & Dm3 pcks is up to 22 % However, for greater SNR values, performance improvement is lower…

29. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Rayleigh channel: M>S Performance in Rayleigh channels is drastically reduced! SNR dB <14, G  0 SNR dB <18, DMn & DHn types achieve similar performance Saturation is achieved for SNR dB >40 Energy efficiency curves resemble Goodput curves Curves shape is smoother than for AWGN

30. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Rayleigh channel: S>M For Rayleigh fading channel, S>M configuration is much better performing than M>S configuration, for almost all the packet types  DM5 & DM3 Goodput increases up to 55 %  DH5 & DH3 Goodput increases up to 15 % All the packet types improve energy efficiency performance  For DM5 & DM3, Δ  up to 88 %!!!  For DH5 & DH3, Δ  up to 20 %

31. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Impact of parameter S The receiver correlator margin S has strong impact on system performance  G improves for high S values (from 30% up to 230% for SNR dB =15)‏   improves for DM n and DH1 types   slightly decreases for DH5 & DH3 types (less 6 % performance loss)‏ Relaxing AC selectivity is convenient, since G gain is much higher than  loss Impact of S, however, rapidly reduces for SNR dB >15

32. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 Conclusions Average traffic rate shows a tradeoff between different packet types  Unprotected and long types yield better Goodput for SNR> 18  For lower SNR, better performance are achieved by short and protected formats  Performance gap between protected and unprotected formats is drastically reduced in fading channels Slave to Master configuration yields performance improvement in terms of both Goodput and Energy Efficiency  Server (slave) never retransmits pcks that were already received by the client (master)‏ 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 Results may be exploited to design energy–efficient algorithms for the piconet management

33. COST273, Barcelona, 15-17 January, 2003 TD (03)-028 That’s all! Thanks for you attention!