Wireless Sensor Networks Presented by Fikret Sivrikaya Joint work - - PowerPoint PPT Presentation

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Wireless Sensor Networks Presented by Fikret Sivrikaya Joint work - - PowerPoint PPT Presentation

Aug 14, 2022 169 likes •541 views

1 Contention-Free MAC Protocols for Wireless Sensor Networks Presented by Fikret Sivrikaya Joint work with Costas Busch, Malik Magdon-Ismail, Bulent Yener Computer Science Department, Rensselaer Polytechnic Institute New York, USA

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 1

Contention-Free MAC Protocols for Wireless Sensor Networks

Presented by Fikret Sivrikaya Joint work with Costas Busch, Malik Magdon-Ismail, Bulent Yener Computer Science Department, Rensselaer Polytechnic Institute New York, USA

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 2

Outline

  • Introduction

– Sensor networks – MAC protocols – Previous work

  • Model & Motivation
  • Our Approach

– LooseMAC Algorithm – TightMAC Algorithm

  • Practical Considerations
  • Summary & Future Work
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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 3

Wireless Sensor Networks

  • A large number of limited power sensor nodes
  • Distributed, multi-hop, ad-hoc operation; no

infra-sctructure, no central control point

  • Collect and process data from a target domain

and transmit information back to specific sites

  • Usage scenarios…

– disaster recovery – military surveillance – health administration – environmental monitoring.

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 4

Wireless Sensor Networks

Each node has a transmission range, which determines its neighbors Representation of the network as a graph same transmission ranges  symmetric links  undirected graph

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 5

Interference / Collisions

Interference on node b (“Hidden terminal problem”) a b c a b a b c d Interference on node b a and b interfere and hear noise only

Packets which suffered collisions should be re-sent. Ideally, we would want all packets to be sent collision- free, only once…

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 6

MAC (Medium Access Control) Protocols

  • Specify how nodes in a network access the

shared communication channel.

  • Two basic types

– contention-based – contention-free

  • Desired Properties of a Sensor Net. MAC Protocol

– distributed – contention-free (collision free) – self-stabilizing – not require common global time reference

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 7

Previous Work

  • Contention-based (random access)

– ALOHA – CSMA (Carrier Sense Multiple Access) – IEEE 802.11

  • Contention-free

– FDMA – TDMA – CDMA

  • Multi-layered approach

– ASCENT (nodes decide themselves to be on or off) – S-MAC (virtual clusters based on common sleep schedules)

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 8

Notations Used…

  • k-neighborhood of a node v:

k(v)

  • k-neighborhood size of a node v:

k(v) = |k(v)|

  • max k-neighborhood size (in the network):

k = maxv k(v)

  • Let n be the number of nodes in the network

1-neighbors or “neighbors” of v 2-neighbors of v

v

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 9

Our Approach

  • TDMA-like framed approach

frame time slot time

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 10

Our Approach

  • LooseMAC

– Same frame size at all nodes – Simple – Lower throughput (due to large frames)

  • TightMAC

– Nodes may have different frame sizes – More complex – Higher throughput (due to smaller frames)

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 11

LooseMAC – Basic Idea

i j k

Schedule nodes’ transmission times so that neighbor nodes do not transmit at the same time.  Repeatly select a random time slot until it is collision-free in the 2-neighborhood.  

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 12

LooseMAC - Hidden Terminal Problem

i k j

i reports the collision between j and k, so that they

select new random slots.

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 13

Algorithm LooseMAC

Algorithm LooseMAC(node i)

1:

Divide time into frames of size ;

2:

ready  FALSE;

3:

while not ready do

4:

Select a slot i randomly in the frame;

5:

Send a “beacon” message in slot i;

6:

Listen for a period of  time slots;

7:

if no collision is detected by i and no neighbor of i reports a conflict then

8:

ready  TRUE;

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 14

A node leaves the network…

j k j  k i No problem!...

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 15

A node joins the network…

j k j  k i Problem!... j and k are now 2-neighbors and have conflicting time slots...

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 16

…remedy: “fresh” nodes

  • When a node joins the network, it is in a special status

called “fresh”

  • A fresh node i informs its neighbors about its status by

control messages

  • When a neighbor node j of i receives this message, it

becomes non-ready

  • We guarantee that every neighbor of i receives the “fresh”

control message from node i

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 17

Probability Analysis for Convergence

Z

i fails to become ready if one or more of the following occurs:

1. a neighbor of i coflicts with i p1 2.

i hears a collision during Z

p2 3.

i receives a conflict report during Z

p3

|Z| =  i

i Probability of failure = p1 + p2 + p3 for some c

      / 16 8 2

3 1 3 1 2 1 1

    c

Set   413  probability of failure  1/4

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 18

Convergence of LooseMAC

  • For some constant c, if   c min{13,22}, with probability at least

1-1/n:

– all non-ready nodes become ready within  log n time slots – each node sends at most O(log n) control messages.

  • Each message has size O(log n) bits:

– sender’s id (log n bits)+ fresh status (1 bit) + coflict report (1 bit)

  • After convergence all transmissions are collision-free, and we

define throughput of each node to be the inverse of its frame size; 1/

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 19

Algorithm TightMAC

  • Nodes may have different frame sizes.
  • Runs on top of LooseMAC.
  • Motivation: “tighten” the frames to

increase throughput.

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 20

Fi Fj

sj

TightMAC Frame Size

 

 

j

i j i 2

2

max  

 

  • Node i selects a frame size proportional to i, where

[max 2-neighborhood size among i’s 2-neighbors]

coincidence set Cji(sj)

  • Each node selects a frame size which is an exact power of 2
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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 21

2-neighborhood size

  • 2-neighborhood size calculation

– receive ids from all neighbors, and broadcast them all – then a node receives ids of all 2-neighbors – take union; exact 2-neighborhood size, but high msg complexity

  • Alternatively

– receive ids from neighbors, and broadcast the count – then a node receives 1-neighbor counts from all neihbors – take the sum; an upper bound on the 2-neighborhood size, less msg complexity

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 22

How is i calculated?

send id send count (# of neighbors) send total send max

i  take max

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 23

Ready levels

  • All 2-neighbors of a node i should be ready so

that i can proceed to TightMAC phase.

  • Introduce five “ready levels”;

– ready-0 (a.k.a. ready) – ready-1 – ready-2 – ready-3 – ready-4

  • When all neighbors of i are ready-k, i becomes

ready-(k+1).

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 24

Ready levels

non-ready ready-0 (ready) ready-1 ready-2 ready-3 ready-4

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 25

Ready levels

non-ready ready-0 (ready) ready-1 ready-2 ready-3 ready-4

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 26

Ready levels

non-ready ready-0 (ready) ready-1 ready-2 ready-3 ready-4

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 27

Ready levels

non-ready ready-0 (ready) ready-1 ready-2 ready-3 ready-4

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 28

Ready levels

non-ready ready-0 (ready) ready-1 ready-2 ready-3 ready-4

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 29

Ready levels

non-ready ready-0 (ready) ready-1 ready-2 ready-3 ready-4

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 30

Ready Levels - another view

send id send count (# of neighbors) send total send max

i  take max

ready ready-1 ready-2 ready-3 ready-4

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 31

Algorithm TightMAC

Algorithm TightMAC(node i)

1:

repeat

2:

Execute LooseMAC(i)

3:

until i becomes ready-4

4:

Transmit neighborhood information and compute i;

5:

Create the tight frame Fi with |Fi| = 2log 6i;

6:

Inform neighbors for the relative position of Fi, with respect to i’s loose slot;

7:

Execute FindTightSlot(i);

8:

Start using the tight frame;

|Fi| = 2log 6i  find smallest power k of 2 such that 2k  6i

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 32

Algorithm FindTightSlot

Algorithm FindTightSlot(node i)

1:

while true do

2:

with probability 1/i:

3:

Select a random slot si in Fi;

4:

Send the position of si (relative to its loose slot);

5:

Listen for a period of  time slots;

6:

if no conflict is reported by any neighbor then

7:

return si;

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 33

Complexity of TightMAC

  • The network stabilizes within O(12 log n) timeslots, with

probability at least 1-1/(n)

  • Each node sends O(log n) messages
  • Each message is of size O(log n) bits.
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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 34

Practical Considerations

  • How does a node detect collisions?

– distinguish collisions from bakground noise by a threshold

  • What if time slots are not alligned?

– corectness not affected, performance affected only by a constant factor

  • What about clock skew?

– either run a simple clock skew algorithm – or re-run and self-stabilize whenever the skew causes collisions.

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 35

Summary and Future Work

  • Presented distributed, contention-free, self-

stabilizing MAC protocols for sensor networks.

– LooseMAC – TightMAC

  • Future research directions

– Simulation analysis (e.g. for analyzing the effects of topology change rate) – Compare the performance with existing protocols

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Fikret Sivrikaya <sivrif@rpi.edu> Contention-Free MAC Protocols for Wireless Sensor Networks 36

References

  • C. Busch, M. Magdon-Ismail, F. Sivrikaya, B. Yener, “Contention-Free MAC

protocols for Wireless Sensor Networks.” Technical Report, Rensselaer Polytechnic Institute, 2004. Available at http://www.cs.rpi.edu/research/tr.html.

  • N. Abramson, “The ALOHA System - Another Alternative for Computer

Communications.” Proceedings of the AFIPS Conference, vol. 37, pp. 295-298, 1970.

  • “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY)

Specifications.” IEEE standards 802.11, January 1997.

  • W. Ye, J. Heidemann, D.Estrin, “Medium Access Control with Coordinated,

Adaptive Sleeping for Wireless Sensor Networks.” [SMAC] IEEE/ACM Transactions

  • n Net-working, vol. 12, no. 3, pp. 493-506, June 2004.
  • A. Cerpa, D. Estrin, “ASCENT: Adaptive Self-configuring Sensor Network

Topologies.” Proceedings of INFOCOM’02, 2002.