Link Range and (In)Stability on Sensor Network Architecture Bhaskaran Raman, Kameswari Chebrolu, Naveen Madabhushi, Dattatraya Y. Gokhale, Phani K. Valiveti, Dheeraj Jain Indian Institute of Technology, Kanpur The First ACM International Workshop on Wireless Network Testbeds, Experimental evaluation and CHaracterization (WiNTECH 2006), A MOBICOM 2006 Workshop Presenter : Ahey Date : 2007/05/07
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Link Range and (In)Stability on Sensor Network Architecture Bhaskaran Raman, Kameswari Chebrolu, Naveen Madabhushi, Dattatraya Y. Gokhale, Phani K. Valiveti,
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Link Range and (In)Stability onSensor Network Architecture
Bhaskaran Raman, Kameswari Chebrolu, Naveen Madabhushi, Dattatraya Y. Gokhale, Phani K. Valiveti, Dheeraj JainIndian Institute of Technology, KanpurThe First ACM International Workshop on Wireless Network Testbeds, Experimental evaluation and CHaracterization (WiNTECH 2006), A MOBICOM 2006 Workshop
Presenter : AheyDate : 2007/05/07
Outline
Motivation External antenna communication range
study Link stability measurements Conclusions Discussions
Motivation (1/2) The authors have two claims here:
(1) Use of external antenna improve communication range more single hop links simplify protocol design energy efficient
(2) Dynamic metric based routing questionable due to the high variability of RSSI
Sumit
Need to say why fairness is a requirement. Motivation for fairness.
Motivation(2/2)
What should be the network architecture?
– What is the radio communication range?
Study communication range, with the use of external antennae
– Expected number of hops from/to base node
Temporal stability of links’ error rate, RSSI, LQI
– Does dynamic distributed routing make sense?
– If so, at what time scale? If not, what else?
Sumit
Need to say why fairness is a requirement. Motivation for fairness.
Outline
Motivation External antenna communication range
study Link stability measurements Conclusions Discussions
External Antenna: Preliminaries Cost: $50-$120 Form factor: 0.5-1m, 0.5- 5kg dBi (decibels relative to isotropic) G is said to be the gain of the antenna When we want to compare antenna gain to an
absolute level, we use dBi = 10·log10(G) The antenna gain is referenced to an isotropic
antenna Link symmetry is not affected by antenna type
because transmit gain = receive gain
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Experimental Setup (1/2)
Tmote sky with CC2420 (802.15.4 compliant) Internal antenna: 3.1dBi gain External connector: SMA – Grid (24dBi, 8o), sector (17dBi, 90o), omni
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Experimental Setup (2/2) Transmitter:– 6000 packets, about 2 minutes, with one 24 byte
packet sent every 20ms– Transmit power: 0dBm (max. possible) Receiver:– TOSBase, connected to laptop– Collect RSSI, LQI values Environment:– Dense foliage (with heavy path loss)– Narrow road (with mostly line-of-sight path)
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Range in Dense Foliage Receiver: – on tripod (1.5m)– Internal ant. only Transmitter:– 1.5m– 6000 packets (60 bins x 100 pkts) Computer avg. pkt. error rate and avg. RSSI over 100 packet bins
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Range in Narrow Road (1/2)
Transmitter:– at 3.8m for sector/grid antennas Rows with bold font Indicate the approximaterange of the particulartransmitter antenna Not always the farther, the higher
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Range in Narrow Road (2/2)
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Implications of Link Range More one-hop nodes, lesser # hops
==> better network lifetime Foliage: range of about 90m
– Useful for applications such as the redwood study
– Can have just a single-hop network! Volcano monitoring: 200-400m range reported Range of about 800m with grid antenna
– Useful in situations like Volcano monitor, BriMon
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Outline
Motivation External antenna communication range
study Link stability measurements Conclusions Discussions
Controlled Calibration: Setup Step attenuator: varied from 0dB to 93dB 5000 packet = 50 bins x 100 packets For each bin: error rate, and avg. RSSI The receive sensitivity can be found
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Receive Sensitivity around 90dB
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
RSSI Variability in Other Environment
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
RSSI Variability in Other Environment Results similar to Emnet 2006 “RSSI is
underappreciated” Good correlation between RSSI and error
rate above some threshold But larger spread region (large variability)
for multi-path prone environment (foliage) LQI variability similar to RSSI variability
– 1/LQI, 1/PSR metrics would be unstable
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Temporal variability in RSSI Omni-50m, foliage, avg. pkt. error rate is 7.2%
(neither close to 0% or 100%) , without binning Large variation (about 15dB)
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
good unstableunstable
Sumit
Tell people that dash lines are interfering nodes (neighbor). It says there on the slide but still you need to tell people.
Outline
Motivation External antenna communication range
study Link stability measurements Conclusions Discussions
Conclusions Range: 500-800m– Number of one-hop nodes can be increased– Better life-time Variability in time-scales of 2s, 20s, hours– Dynamic metric-based routing may not be useful– Plan for “ good” links, use centralized routing Problems arise when RSSI window overlaps with
the steep region– Provide sufficient link margin to plan the
deployment to have “ good” links at the beginning
– Dynamic routing metrics unnecessary
Conclusions Base node is a powerful node anyway
– Can do centralized routing
–Design, implementation, network might easier
Think real hard before falling for: randomly deployed sensor nodes, self-organizing, distributed dynamic routing
– Good for solving nice problems on paper
– Practical value questionable
Outline
Motivation External antenna communication range
study Link stability measurements Conclusions Discussions
Discussions Contributions & Strength:
A good survey about using external antenna to improve radio range
Give some insight about the possibility of one-hop sensor network and dynamic routing (for outdoor application)
Provide temporal variation of RSSI within one node (which is not discussed in the previous Emnet paper)
Discussions Weakness:
Though RSSI variation is large, it can be a not bad link quality predictor as the experiment results show. The conclusion here is too strong but not totally convincing.
The duration of the experiment is not long enough ( about 2 hours).
Relevance to our research Han got similar conclusion for our testbed. Static
routing metrics (to decide whether it is a stable link by RSSI from the very beginning) may be enough.
However, for the medium quality links, more experiments can be done to quantify the accuracy using RSSI, LQI as the predictor of PRR dynamically.
Is one-hop or multi-hop better? Need more network overhead v.s reachability analysis.