1. 1 4 th Workshop COST289 – April 11 th 2007 D-STAR MAC Protocol: a Cross Layer Solution for Wireless Sensor Networks Endowed with Directive Antennas Gianfranco Manes, Romano Fantacci, Francesco Chiti, Michele Ciabatti, Giovanni Collodi, Davide Di Palma, Ilaria Nelli, and Antonio Manes Department of Electronics and Telecommunications University of Florence

2. 2 4 th Workshop COST289 – April 11 th 2007 Outline 1. Motivations  WSNs  Directive antennas 2. Proposed protocol  Discovery phase  Regime phase 3. Performance analysis 4. Conclusions Outline Outline

3. 3 4 th Workshop COST289 – April 11 th 2007 Wireless Sensor Networking  Enabling technology to the aim of intelligent environments instrumenting  Affordable solution to some challenging problems:  environmental sensing,  productive chains control,  real-time phenomena monitoring,  safety and rescue application.  WSNs represent a special case of the more general wireless Ad Hoc networking paradigm with additional constraints:  limited energetic, storage, processing and communication capabilities  low degree of mobility  presence of a small number of sinks 1. Motivations 1. Motivations

4. 4 4 th Workshop COST289 – April 11 th 2007 Wireless Sensor Networking  This challenge might be got over through careful system design with particular regard to the communications protocols:  MAC layer:  management of both sleep and active power states  PHY layer:  introduction of directional antennas and their integration within the communications framework 1. Motivations 1. Motivations

5. 5 4 th Workshop COST289 – April 11 th 2007 Directive Antennas  Expected benefits  Antenna gain maximization towards desired directions, concentrating energy in smaller area:  Transmitted power decreasing  Power consumption reduction  Network life time increasing  Received power increasing  Coverage range increasing  Error probability reduction 1. Motivations 1. Motivations

6. 6 4 th Workshop COST289 – April 11 th 2007 Directive Antennas  Expected benefits  Radiation towards undesired directions minimization  Interference caused by other transmissions reduction  Co-channel interference mitigation  multiple-access problems mitigation  Collision probability reduction  Adaptability to time varying communication conditions:  Mote’s failure  Channel errors  Congestion 1. Motivations 1. Motivations

7. 7 4 th Workshop COST289 – April 11 th 2007 Directive Antennas  Criticalities  Cost and size  On board integration  Beam switching management:  Set-up phase signaling overhead  Latency for end-to-end communications setting-up  Algorithm complexity  Switching agility  Support both to synchronous (source-initiated) and asynchronous (event-based) sensing 1. Motivations 1. Motivations

8. 8 4 th Workshop COST289 – April 11 th 2007 Directive-Synchronous Transmission Asynchronous Reception (D-STAR)  STAR MAC concept for time synchronization [Chiti et al. in Proc. of IEEE ICC’06]  Cross-layer protocol design (MAC+PHY)  Space-time synchronization  Suitable for flat topology  Scalable 2. Proposal 2. Proposal

9. 9 4 th Workshop COST289 – April 11 th 2007 Directive-Synchronous Transmission Asynchronous Reception (D-STAR)  Hypothesis  Beam width = θ [rad]  N possible angular sectors:  N = 2π/θ  Quasi ideal switching  T switch << T pkt 2. Proposal 2. Proposal θ = π/2 [rad] N = 4 T switch ≈ μs << T pkt ≈ ms

10. 10 4 th Workshop COST289 – April 11 th 2007 D-STAR: State Diagram DISCOVERY 1 < EmptySectors < N s Emptysectors = N s Switch on n f < N fd Battery < Battery_low REGIME Battery < Battery_low n f =N fd INIT OFF 2. Proposal 2. Proposal

11. 11 4 th Workshop COST289 – April 11 th 2007 D-STAR: Discovery phase 1.Duty cycle δ = 100%  Listening mode for a time interval T set-up  Beacon (HELLO) broadcasting:  1 beacon  angular sector  Node ID and Phase (φ) transmission (time to the next awakening)  Waiting for a fixed time duration τ s in search of reply messages  Switching to the following angular sector  Exit condition:  (T set-up is expired, i.e., N fd frame periods) 2. Proposal 2. Proposal

12. 12 4 th Workshop COST289 – April 11 th 2007 D-STAR: Discovery phase 2. Proposal 2. Proposal δ = 100% T set-up time HELLO …

13. 13 4 th Workshop COST289 – April 11 th 2007 D-STAR: Regime phase  Each node sends:  HELLO messages to known neighbors belonging to different angular sectors according to the phase transmitted in previous HELLO messages,  several HELLO messages in background with the proper period to unknown neighbors in the empty angular sector.  Upon the replying of a node, a logical channel is established:  The channel access is managed by means of a CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) approach.  Each node remains in the regime phase until there is at least one neighbor, otherwise if the number of empty angular sector is equal to N s it re-enters the discovery phase in search of connectivity. 2. Proposal 2. Proposal

14. 14 4 th Workshop COST289 – April 11 th 2007 D-STAR: Regime phase 2. Proposal 2. Proposal TfTf time listening sleep δ T f HELLO … HELLO + FWD … HELLO * FWD HELLO … 1 HELLO broadcasting per sector

15. 15 4 th Workshop COST289 – April 11 th 2007 Operative hypothesis  FP6-IST-1-508744-IP ‘‘GoodFood’’ reference scenarioGoodFood  Monitored area = 25 ∙ 25 [m 2 ]  Number of WSN nodes: [10…50]  N = 1, 2,4, 6, 8 angular sectors  HELLO pkt length = 8 bytes  Bit rate = 250 kbps  Packet Error Rate = 5%  Number of channel sensing for CSMAC/CA algorithm = 6  Frame period: 10,25,50,75,93 s  Duty-cycle: [1…5]% 3. Performance 3. Performance

16. 16 4 th Workshop COST289 – April 11 th 2007 Università degli Studi di Firenze 3. Performance 3. Performance Network lifetime vs nodes

17. 17 4 th Workshop COST289 – April 11 th 2007 Network lifetime vs duty-cycle 3. Performance 3. Performance

18. 18 4 th Workshop COST289 – April 11 th 2007 Network lifetime vs frame period 3. Performance 3. Performance

19. 19 4 th Workshop COST289 – April 11 th 2007 Number of nodes Occupied Channel Probability Number of nodes Collision Probability S S' R S R R' Hidden node analysis 3. Performance 3. Performance

20. 20 4 th Workshop COST289 – April 11 th 2007 Number of nodes Normalized Throughput Number of nodes Overhead [pkt/T f ] Signaling Overhead Resource Utilization Efficiency and complexity 3. Performance 3. Performance

21. 21 4 th Workshop COST289 – April 11 th 2007 Conclusions  Energy efficient WSN protocol design  Cross-layer approach (MAC+PHY)  Performance:  Energetic consumption  Lifetime  Latency  Collision probability  Signaling overhead  Good tradeoff  Easy to implement 4. Conclusions 4. Conclusions