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Bob Kinicki Computer Science Department rek@cs.wpi.edu Colloquium October 5, 2007. A Glimpse at Three Wireless Networking Problems. Outline. Thoughts and Mini-Motivation Wireless Networking Primer #1 Dynamic Rate Adaptation Performance problems with ARF

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A Glimpse at Three Wireless Networking Problems


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bob kinicki computer science department rek@cs wpi edu colloquium october 5 2007
Bob Kinicki

Computer Science Department

rek@cs.wpi.edu

Colloquium October 5, 2007

A Glimpse at Three Wireless Networking Problems

outline
Outline
  • Thoughts and Mini-Motivation
  • Wireless Networking Primer
  • #1Dynamic Rate Adaptation
    • Performance problems with ARF
    • Rate Adaptation Algorithms
      • RBAR, CARA, RFT and CARAF
  • Wireless Sensor Networks (WSNs)
  • #2 Dynamic Cluster Formation
  • #3Power-Aware MAC Protocols
    • SMAC, TMAC, WiseMAC, SCP-MAC and

Crankshaft

October 5, 2007 Three Wireless Networking Problems

my research space
My Research Space

Networking

1983

2003

2006

Wireless Networking

Wireless

Sensor

Networks

October 5, 2007 Three Wireless Networking Problems

the future of sensor networks
The Future of Sensor Networks?

October 5, 2007 Three Wireless Networking Problems

lan terminolgy
LAN Terminolgy

802.3::

Ethernet CSMA/CD

802.11a/b/g::

WiFi CSMA/CA

802.15.4::

ZigBee 802.11-based

lower data rates, lower power

Bluetooth::

TDMA

- wireless Personal Area Networks (PANs) that provide secure, globally unlicensed short-range radio communication.

  • Clusters with max of 8: cluster head + 7 nodes

WSNs

October 5, 2007 Three Wireless Networking Problems

wireless lans
Wireless LANS
  • Infrastructure with AP (Access Point)
  • Mobile Ad Hoc Networks (MANETs)
  • Wireless Sensor Networks (WSNs)
  • Interacting AP Topologies

October 5, 2007 Three Wireless Networking Problems

infrastructure
Infrastructure

Internet

client

Access

Point

client

client

client

October 5, 2007 Three Wireless Networking Problems

mobile ad hoc network manet
Mobile Ad Hoc Network (MANET)

Wireless Sensor Network (WSN)

BS

October 5, 2007 Three Wireless Networking Problems

wireless lan protocols
Wireless LAN Protocols

(a) A sending an RTS to B.

(b) B responding with a CTS to A.

node D is

possible hidden terminal

Tanenbaum slide

October 5, 2007 Three Wireless Networking Problems

virtual channel sensing in csma ca
Virtual Channel Sensing in CSMA/CA
  • C (in range of A) receives the RTS and based on information in RTS creates a virtual channel busy NAV(Network Allocation Vector).
  • D (in range of B) receives the CTS and creates a shorter NAV.

Tanenbaum slide

October 5, 2007 Three Wireless Networking Problems

basic csma ca
Basic CSMA/CA

possible

collision !!

[N. Kim]

October 5, 2007 Three Wireless Networking Problems

one to one configuration ad hoc
One-to-One Configuration {Ad Hoc}

Access

Point

client

October 5, 2007 Three Wireless Networking Problems

one to one configuration ad hoc14
One-to-One Configuration {Ad Hoc}

Access

Point

client

October 5, 2007 Three Wireless Networking Problems

one to one configuration ad hoc15
One-to-One Configuration {Ad Hoc}

Access

Point

client

Distance Impacts:

attenuation

fading

interference

October 5, 2007 Three Wireless Networking Problems

802 11 physical layer
802.11 Physical Layer

‘Adjust transmission rate on the fly’

[N. Kim]

October 5, 2007 Three Wireless Networking Problems

ber vs snr
BER vs SNR

[Pavon]

October 5, 2007 Three Wireless Networking Problems

throughput vs snr
Throughput vs SNR

[Pavon]

October 5, 2007 Three Wireless Networking Problems

rate adaptation versus distance
Rate Adaptation versus Distance

[J. Kim]

October 5, 2007 Three Wireless Networking Problems

single ap multiple clients homogeneous
Single AP multiple clients (homogeneous)

client

Node Contention:

Produces collisions

client

client

Access

Point

client

October 5, 2007 Three Wireless Networking Problems

node contention
Node Contention

without RTS/CTS

[N. Kim]

October 5, 2007 Three Wireless Networking Problems

single ap multiple clients heterogeneous
Single AP multiple clients (heterogeneous)

client

client

Multiple Node Effects

Collisions

AP queue overflow

link capture

hidden terminal

performance anomaly

different NIC cards

(Rate Adaptation NOT

Standardized!!)

Access

Point

client

client

October 5, 2007 Three Wireless Networking Problems

unfairness
Unfairness

[Choi]

October 5, 2007 Three Wireless Networking Problems

multiple aps multiple clients heterogeneous
Multiple APsmultiple clients (heterogeneous)

client

client

client

client

Access

Point

Access

Point

client

client

client

client

October 5, 2007 Three Wireless Networking Problems

hidden terminals
Hidden Terminals

Without a hidden terminal, loss ratio ~5.5%.

One hidden AP with mild sending rate

(0.379 Mbps) yields:

[Wong]

October 5, 2007 Three Wireless Networking Problems

rts cts summary
RTS/CTS Summary
  • RTS/CTS can reduce collisions.
  • RTS/CTS can guard against and reduce hidden terminals.
  • RTS/CTS adds overhead that reduces throughput.
  • Normally, RTS/CTS is turned off!

October 5, 2007 Three Wireless Networking Problems

rate adaptation algorithms
Rate Adaptation Algorithms

AARF ARF AMRR

CARA CROAR DOFRA

Fast-LA HRC LA

LD-ARF MiSer MultiRateRetry

MPDU OAR ONOE

PER RBARRFT

RRAA SampleRate SwissRA

October 5, 2007 Three Wireless Networking Problems

rate adaptation algorithms29
Rate Adaptation Algorithms

1997 ARF

1998

1999

2000

2001 RBAR

2002MPDU OAR PER

2003LA MiSer SwissRA

2004AARF AMRR HRC MultiRateRetry

2005Fast-LA LD-ARF RFT SampleRate

2006 CARA CROAR DOFRA RRAA

2007

October 5, 2007 Three Wireless Networking Problems

rate adaptation algorithms30
Rate Adaptation Algorithms

Uses recent history and probes:ARF, AARF, SampleRate

Long interval smoothing:ONOE,SampleRate

Multiple rates: MultiRateRetry, AMRR, RRAA

Uses RTS/CTS:RBAR, OAR, CROAR, CARA

Uses RSSI to approximate SNR, each node maintains 12 dynamic RSS thresholds:LA

Puts checksum on header and use NACK to signal link loss error:LD-ARF

Table lookup with thresholds:HRC,MPDU(len,rSNR,count)

Fragmentation: DOFRA, RFT

Miscellaneous:PER, MiSer, SwissRA, Fast-LA

October 5, 2007 Three Wireless Networking Problems

auto rate fallback arf
Auto Rate Fallback (ARF)
  • If two consecutive ACK frames are not received correctly, the second retry and subsequent transmissions are done at a lower rate and a timer is started.
  • When the number of successfully received ACKs reaches 10 or the timer goes off, a probe frame is sent at the next higher rate. However, if an ACK is NOT received for this frame, the rate is lowered back and the timer is restarted.

October 5, 2007 Three Wireless Networking Problems

arf and aarf
ARF and AARF

October 5, 2007 Three Wireless Networking Problems

receiver based auto rate rbar
Receiver Based Auto Rate (RBAR)
  • Receivers control sender’s transmission rate.
  • RTS and CTS are modified to contain info on size and rate {not 802.11 compatible}.
  • Uses analysis of RTS reception (RSSI) to estimate SNR and send choice back to sender in CTS.
  • Receiver picks rate based on apriori SNR thresholds in a lookup table.

October 5, 2007 Three Wireless Networking Problems

collision aware rate adaptation cara
Collision Aware Rate Adaptation (CARA)

CARA uses two methods for identifying collisions:

  • RTS probing
  • Clear Channel Assessment (CCA) detection

RTS Probing

{Idea: Assume all RTS/CTS transmission failures after a successful RTS/CTS exchange must be due to channel errors.

(Note – this assumes hidden terminals are not possible) }

October 5, 2007 Three Wireless Networking Problems

rts probing
RTS Probing

CARA-1

  • Data frame transmitted without RTS/CTS.
  • If the transmission fails, RTS/CTS exchange is activated for the next retransmission. If this retransmission fails {assume channel quality problem}, then the rate is lowered.
  • If retransmission with RTS/CTS is successful {assume collision occurred}, stay at same rate and send next frame without RTS/CTS.

October 5, 2007 Three Wireless Networking Problems

clear channel assessment cca
Clear Channel Assessment (CCA)

ACK

[J. Kim]

October 5, 2007 Three Wireless Networking Problems

cca option
CCA Option
  • Case 2: It is a collision.
    • Transmit without increasing failure count and lowering the transmission rate. No RTS/CTS probe is needed.
  • Case 1 and Case 3:
    • Initiate RTS/CTS probe scheme.

October 5, 2007 Three Wireless Networking Problems

cara 1 with rts probing
CARA-1 (with RTS Probing)

[J. Kim]

October 5, 2007 Three Wireless Networking Problems

cara 2 with cca
CARA-2 (with CCA)

[J. Kim]

October 5, 2007 Three Wireless Networking Problems

802 11 mac fragmentation
802.11 MAC Fragmentation

[Zhu]

October 5, 2007 Three Wireless Networking Problems

rate based fragmentation thresholding rft
Rate-based Fragmentation Thresholding (RFT)
  • Fragmenting a frame can increase the probability of the fragment being received successfully.
  • Propose a dynamic fragmentation scheme with different fragmentation thresholds based on different channel conditions.
  • Namely, fragment sizes vary with the chosen adaptation rate.

October 5, 2007 Three Wireless Networking Problems

caraf cara with fragmentation
CARAF (CARA with Fragmentation)

Dan Courcey’s MS thesis:

Combine CARA with Fragmentation.

Top Level Scheme:

  • Upon CCA determination of collision, use fragmentation.
  • If CCA shows idle, initiate RTS/CTS probe.
  • If probe fails lower transmission rate.

{Investigate how to vary fragment size to maximize throughput and increase the likelihood of CCA case 2}

October 5, 2007 Three Wireless Networking Problems

wireless sensor networks
Wireless Sensor Networks
  • A distributed connection of nodes that coordinate to perform a common task.
  • In many applications, the nodes are battery powered and it is often very difficult to recharge or change the batteries.
  • Prolonging network lifetime is a critical issue.
  • Sensors often have long period between transmissions (e.g., in seconds).
  • Thus, a good WSN MAC protocol needs to be energy efficient.

October 5, 2007 Three Wireless Networking Problems

wireless sensor networks45
Wireless Sensor Networks
  • Another attribute is scalability to change in network size, node density and topology.
    • In general, nodes can die, join later or be mobile.
  • Often high bandwidth is not important.
  • Nodes can take advantage of short-range, mulit-hop communication to conserve energy.

October 5, 2007 Three Wireless Networking Problems

wireless sensor networks46
Wireless Sensor Networks
  • Sources of energy waste:
    • Idle listening, collisions, overhearing and control overhead.
    • Idle listening dominates (measurements show idle listening consumes between 50-100% of the energy required for receiving.)

Idle listening:: listen to receive possible traffic that is not sent.

October 5, 2007 Three Wireless Networking Problems

power measurements
Power Measurements

October 5, 2007 Three Wireless Networking Problems

wireless sensor networks48
Wireless Sensor Networks
  • Duty cycle:: ratio between listen time and the full listen-sleep cycle.
  • central approach – lower the duty cycle by turning the radio off part of the time.
  • Three techniques to reduce the duty cycle:
    • TDMA
    • Schedule contention periods
    • LPL (Low Power Listening)

October 5, 2007 Three Wireless Networking Problems

techniques to reduce idle listening
Techniques to Reduce Idle Listening
  • TDMA requires cluster-based or centralized control.
  • Scheduling – ensures short listen period when transmitters and listeners can rendezvous and other periods where nodes sleep (turn off their radios).
  • LPL – nodes wake up briefly to check for channel activity without receiving data.
    • If channel is idle, node goes back to sleep.
    • If channel is busy, node stays awake to receive data.
    • A long preamble (longer than poll period) is used to assure than preamble intersects with polls.

October 5, 2007 Three Wireless Networking Problems

choosing cluster heads forming clusters
Two-tier scheme:

A fixed number of cluster heads that communicate with BS (base station).

Nodes in cluster communicate with head (normally TDMA).

TDMA allows fixed schedule of slots for

sensor to send to cluster head and receive head transmissions.

Choosing Cluster Heads/Forming Clusters

BS

October 5, 2007 Three Wireless Networking Problems

slide52

Choosing Cluster Heads/Forming Clusters

  • Periodically select new cluster heads to minimize power consumption and maximize WSN lifetime.
  • More complex problem when size of cluster changes dynamically.
  • As time goes by, some sensor nodes die!
  • Not worried about coverage issues!

X

X

X

BS

X

X

October 5, 2007 Three Wireless Networking Problems

dynamic cluster formation
Dynamic Cluster Formation
  • TDMA cluster algorithms:
    • LEACH, Bluetooth, …
  • Rick Skowyra’s MS thesis:

‘Energy Efficient Dynamic Reclustering Strategy for WSNs’

    • ‘Leach-like’ with a fitness function and periodic reclustering.
    • He hopes to design a distributed genetic algorithm to speed the recluster time.

October 5, 2007 Three Wireless Networking Problems

tiered wsn architectures
Tiered WSN Architectures

[ Stathopoulos]

October 5, 2007 Three Wireless Networking Problems

power aware mac protocols
Power Aware MAC Protocols

1997

1998PAMAS

1999

2000

2001 SMAC

2002LPL NPSM

2003 TMAC TRAMA TinyOS-MAC EMACs

2004BMAC DMAC LMAC WiseMAC

2005PMAC ZMAC SP

2006 SCP-MAC

2007Crankshaft

October 5, 2007 Three Wireless Networking Problems

power aware mac protocols57
Power Aware MAC Protocols

Three approaches to saving power:

1. TDMA: TRAMA, EMACs, LMAC

Crankshaft

2.Schedule: PAMAS, SMAC, TMAC, DMAC, PMAC, SCP-MAC

3. Low Power Listening: LPL, BMAC, WiseMAC

Cross-Layering: SP, BSD

October 5, 2007 Three Wireless Networking Problems

slide58
SMAC
  • All nodes periodically listen, sleep and wakeup. Nodes listen and send during the active period and turn off their radios during the sleep period.
  • The beginning of the active period is a SYNC period used to accomplish periodic synchronization and remedy clock drift.
  • Following the SYNC period, data may be transferred for the remainder of the active period using RTS/CTS for unicast transmissions.
  • Long frames are fragmented and transmitted as a burst.
  • SMAC controls the duty cycle to tradeoff energy for delay.
  • However, as density of WSN grows, SMAC incurs additional overhead in maintaining neighbors’ schedules.

October 5, 2007 Three Wireless Networking Problems

slide59
SMAC

October 5, 2007 Three Wireless Networking Problems

slide60
TMAC
  • TMAC employs an adaptive duty cycle by using a very short listening window at the beginning of each active period.
  • After the SYNC portion of the active period, RTS/CTS is used in listening window. If no activity occurs, the node goes to sleep.
  • TMAC saves power at the cost of reduced throughput and additional delay.

October 5, 2007 Three Wireless Networking Problems

slide61
TMAC

October 5, 2007 Three Wireless Networking Problems

wisemac
WiseMAC
  • Algorithm focused on downlink protocol

for infrastructure WSNs:

    • Access Point (AP) is assumed to have wired link to Internet and not battery-powered.
  • Based on preamble sampling.
  • WiseMac regularly samples (via listening) for a short duration during preamble.
    • All sensor nodes sample with same constant period TW.

October 5, 2007 Three Wireless Networking Problems

wisemac63
WiseMAC
  • Normally, wake-up preamble needs to be of size TW .
    • This implies low power use when WSN is idle.
    • But this yields large power consumption overhead for reception.
  • WiseMAC AP learns and keeps the sampling schedule of all sensors in a up-to-date table.
  • Sensors’ ACKs provide info for the table.
  • WiseMAC then minimizes the preamble duration, TP .
  • Needs to deal with clock drift to get this right.

October 5, 2007 Three Wireless Networking Problems

wisemac64
WiseMAC

October 5, 2007 Three Wireless Networking Problems

zigbee mac
Zigbee MAC
  • 802.11 MAC PSM (Power Save Mode) uses beacon frames to coordinate and periodic wake-up by sensor nodes.
  • Mike Putnam’s thesis:

‘A Beaconless Protocol for Improving Energy Efficiency in Wireless Sensor Networks’

October 5, 2007 Three Wireless Networking Problems

wisemac66
WiseMAC

October 5, 2007 Three Wireless Networking Problems

scheduled channel polling scp mac
Scheduled Channel Polling(SCP-MAC)
  • With channel polling (LPL scheme), receiver efficiency is gained through cost to sender.
  • LPLs are very sensitive to tuning for neighborhood size and traffic rate.
  • By synchronizing channel polling times of all neighbors, long preambles are eliminated and ultra-low duty cycles (below the LPL 1-2% limits) are possible.

October 5, 2007 Three Wireless Networking Problems

scheduled channel polling scp mac68
Scheduled Channel Polling(SCP-MAC)
  • The issue is knowing my neighbors’ schedule information.
  • SCP piggybacks schedule info on data packets when possible or a node broadcasts its schedule in a SYNC packet in synch period (as in SMAC)
  • Knowing schedules  short wakeup tone.
  • Optimal synchronization reduces overhearing.

October 5, 2007 Three Wireless Networking Problems

scp mac
SCP-MAC

October 5, 2007 Three Wireless Networking Problems

crankshaft
Crankshaft
  • Designed specifically for dense WSNs.
  • Employs channel polling mechanism similar to SCP-MAC.
  • Employs synchronization, framing and slotting mechanisms similar to TDMA-based LMAC.
  • Unlike LMAC, Crankshaft schedules receivers rather than senders.
  • Basic principle: nodes are only awake to receive messages at fixed offsets from the start of a frame.
  • The hope is to develop modified version of Crankshaft.
  • I need students interested in exploring this idea!!

October 5, 2007 Three Wireless Networking Problems

crankshaft71
Crankshaft

October 5, 2007 Three Wireless Networking Problems

crankshaft simulations
Crankshaft Simulations
  • Focused on two traffic types that are common in WSNs:
  • Convergecast – monitoring traffic
    • All sensor nodes periodically send data to a sink node (either AP or sensor cluster head)
  • Broadcast floods – packets sent in the other direction to either send routing update or to distribute queries over the WSN.

October 5, 2007 Three Wireless Networking Problems

energy conservation results
Energy Conservation Results

October 5, 2007 Three Wireless Networking Problems

latency
Latency

October 5, 2007 Three Wireless Networking Problems

questions
Questions?

Thank You!

Go Tribe!!!

October 5, 2007 Three Wireless Networking Problems