1 / 12

Analysis of CAP of IEEE 802.15.4 Superframe

Analysis of CAP of IEEE 802.15.4 Superframe. Iyappan Ramachandran University of Washington November 15, 2005. Model Assumptions. Beacon-enabled Star M nodes attached to a coordinator All nodes within the carrier sensing range of each other No inactive period in the superframe, i.e. BO=SO

Download Presentation

Analysis of CAP of IEEE 802.15.4 Superframe

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Analysis of CAP of IEEE 802.15.4 Superframe Iyappan Ramachandran University of Washington November 15, 2005

  2. Model Assumptions • Beacon-enabled Star • M nodes attached to a coordinator • All nodes within the carrier sensing range of each other • No inactive period in the superframe, i.e. BO=SO • Contention access part (CAP) occupies active period fully • No acknowledgements • Poisson arrival of packets, i.e. probability p of packet arrival every backoff slot. • Packet length is fixed and equal to N backoff slots • No buffering at nodes • Only Uplink

  3. Approximations to simplify analysis • Presence of beacons and beacon boundaries have negligible effect • Every node sees a probability pic that channel is idle in the first of two CCA backoff slots • Not slot-to-slot independence; probability that channel is idle in the second CCA backoff slot is pci|i • Independence for backoff slots separated by a backoff • Channel sees a probability ptn that a node begins transmission in any generic slot • Geometrically distributed backoff durations with same mean as original uniform distribution • Validity of approximations will be verified by simulations

  4. Consequences of approximations • CAP can be simply analyzed as non-persistent CSMA • Channel and nodes have been virtually decoupled • Each node can be analyzed independent of the others • Probability pkn that node will get out of kth backoff stage

  5. Node state model (see handout #1) • Node stays in IDLE state with prob. (1-p) and goes to BO1 with prob. p • BO1  CS11 with prob. p1n • CS11CS12 with prob. pic and BO2 with prob. (1-pic) • CS12TX with prob. pi|ic and CS12 with prob. (1-pi|ic) … • … and so on • TXIDLE with prob. 1 after N backoff slots • CS51IDLE and CS52 IDLE with probabilities (1-pic) and (1-pi|ic) respectively

  6. Channel state model (handout #2) • Channel stays in (IDLE, IDLE) state when no node begins transmission (prob.α=(1-pt|iin)) • (IDLE, IDLE)SUCCESS when exactly one node transmits (prob. β=Mpt|iin(1-pt|iin)M-1) • (IDLE, IDLE)FAILURE when more than one node transmit (prob. δ=1-α-β) • Channel stays in SUCCESS/FAILURE state for N backoff slots • SUCCESS(IDLE,IDLE) and FAILURE(IDLE,IDLE) with probability 1

  7. Calculation of channel throughput • Approximations have led to virtual decoupling of nodes’ activities • Solve node state chain to find ptn in terms of pic (1) • Solve channel state chain to find pic in terms of ptn (2) • Solve (1) and (2) numerically to find picand ptn • Aggregate channel throughput, S is the fraction of time spent in SUCCESS state

  8. Calculation of average power consumption • Chipcon CC2420 radio for illustration (see handout #3) • Four energy states: shutdown, idle, transmit, receive • Included beacon receptions • Considered two cases • Stay in idle state if no packet is waiting  included idle-to-receive ramp-up for beacon reception and CCA • Shutdown node if no packet is waiting  included shutdown-idle-receive ramp-up for beacon reception and CCA

  9. Simulations • All simulations were run in NS-2; used IEEE 802.15.4 module developed by J. Zheng and M. J. Lee, CUNY • Same model assumptions, but NO approximations • No. of nodes, M=12; Packet length, N=10 backoff slots • BO=6  Beacon Interval=3072 backoff slots=0.983 sec; Beacon length=2 backoff slots

  10. Simulations (cont.)

  11. Conclusions • Analysis predicts very accurate throughput and power consumption estimates • Although shutting down has the ramp-up overhead time, it saves considerable energy at low traffic • Analysis can be extended • Easily to include acknowledgements • With some effort to include inactive part

  12. Thank you!

More Related