link estimation, ctp and multihoplqi. motivation data collection needs to estimate the link quality...
TRANSCRIPT
![Page 1: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/1.jpg)
Link Estimation, CTP and MultiHopLQI
![Page 2: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/2.jpg)
Motivation
• Data Collection needs to estimate the link quality– To select a good link
![Page 3: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/3.jpg)
Challenges of Link Quality Estimation
• Prevalence of intermediate-quality links
• Time-varying nature of a wireless channel– Alternating between high (100% packet reception
ratio PRR) and low (0% PRR) quality
• Link asymmetries
• Hardware variations
Ref. [LinkEstimation_1 ]: Section 1
![Page 4: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/4.jpg)
Detour: Time-varying nature of a wireless channel
![Page 5: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/5.jpg)
802.11b and 802.15.4 Spectrum Utilization
• Ref: [Implication_1] Section 3 and 4
![Page 6: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/6.jpg)
Packet Reception Ratio (PRR)
• Ref: [Implication_1] Section 3 and 4
![Page 7: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/7.jpg)
PRR vs. RSSI
• Ref: [Implication_1] Section 3 and 4
![Page 8: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/8.jpg)
Distribution of the Mode of Noise Readings
• Ref: [Implication_1] Section 3 and 4
![Page 9: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/9.jpg)
Behavior of a Single Node
• Ref: [Implication_1] Section 3 and 4
![Page 10: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/10.jpg)
Reception Probability
• [Other_1]: Figure 1
![Page 11: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/11.jpg)
Reception Probability
• [Other_1]: Figure 1
![Page 12: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/12.jpg)
Link Estimation – ETX (Expected Transmission Count)
![Page 13: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/13.jpg)
Link Estimation Metric - ETX
• Minimum Hop Count is not a good metric– Assume that links either work well or do not work
at all– Many wireless links have intermediate loss ratios
• ETX – Expected Transmission Count– Choose routes with high end-to-end throughout– Finds paths with the fewest expected number of
transmissions (including retransmissions) required to deliver a packet to the destination
Ref. [ETX_1]: Section 1, 3
![Page 14: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/14.jpg)
Why some superficially attractive metrics are not suitable?
• Hop-count– Ignoring links with loss ratios above a certain
threshold
• Product of the per-link delivery ratios– Fail to account for inter-hop interference
Ref. [ETX_1]: Sectiion 3
![Page 15: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/15.jpg)
Link Estimation Metric - ETX
• ETX– Consider the wide range of link loss ratios– The existence of links with asymmetric loss ratios– The interference between successive hops of multi-
hop paths
Ref. [ETX_1]: Section 1, 3
![Page 16: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/16.jpg)
Link Estimation Metric - ETX
• ETX of a link:– The predicted number of data transmissions required to
send a packet over a link, including retransmissions
– Calculated using the forward and reverse delivery ratios of a link
– How to measure: Broadcasting of probe packets and derives link quality information from each direction
• ETX of a route:– The sum of the ETX for each link in the route
Ref. [ETX_1]: Section 1, 3
![Page 17: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/17.jpg)
Link Estimation Metric - ETX
• Forward delivery ratio: df – The probability that a data packet successfully arrives at the
recipient
• Reverse delivery ratio: dr
– The probability that the ACK packet is successfully received
• The expected probability that a transmission is successfully received and acknowledged is df X dr
• ETX = 1 / (df X dr)
Ref. [ETX_1]: Section 1, 3
![Page 18: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/18.jpg)
How to Measure df and dr
• Each node broadcasts link probes of a fixed size, at an average period of τ
• Each node remembers the probes it receives during the last w seconds
• The ETX of a route is the sum of the link metrics
![Page 19: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/19.jpg)
Link Estimation – Four-bit Wireless Link Estimation
![Page 20: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/20.jpg)
Four-bit Wireless Link Estimation• Physical layer
– Measure channel quality during a packet– Measured for single received packet– Fast and Inexpensive– Sometimes can be misleading because the time-
varying nature– Decoding error– The physical layer can provide immediate
information on the quality of the decoding of a packet
– Example: • MultiHopLQI uses Link Quality Indication (LQI) – a
feature of the CC2420 radio• RSSI, SNR
![Page 21: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/21.jpg)
Four-bit Wireless Link Estimation
• Link layer– Measure whether packets are delivered and
acknowledged
– Such as ETX: use periodic broadcast probes to measure incoming packet reception rates
– Slow to adapt
![Page 22: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/22.jpg)
Four-bit Wireless Link Estimation
• Network layer– Knows which links are most useful for
routing
– Is a link useful?
– Keep useful links in the table
![Page 23: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/23.jpg)
[LinkEstimation_1]: Section 3.1 23
Four Bit Interface• Physical Layer – Packet decoding quality
– If set, the white bit denotes that each symbol in the received packet has a very low probability of decoding error
• Link Layer – Packet acknowledgements– A link layer sets the ack bit on a transmit buffer when it
receives a layer 2 ack for that buffer• Network Layer – Relative important links
– Pin bit: when the network layer sets the pin bit on one link table entry, the link estimator cannot remote it from the table until the bit is cleared
– Compare bit: indicate whether the route provided by the sender of the packer is better than the route provided by one or more of the entries in the link table
![Page 24: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/24.jpg)
Four Bit Interface Details
WHITEPackets on this channel experience few errors
ACKA packet transmission on this link was acknowledged
PINKeep this link in the table
COMPAREIs this a useful link?
![Page 25: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/25.jpg)
Data Collection in TinyOS 2.x
• CTP– Bi-directional probe-based link estimation
• MultiHopLQI– Only uses physical layer information to estimate
link
![Page 26: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/26.jpg)
Physical Layer Information is NOT Sufficient
Unacked
PRR
LQI
![Page 27: Link Estimation, CTP and MultiHopLQI. Motivation Data Collection needs to estimate the link quality –To select a good link](https://reader036.vdocuments.us/reader036/viewer/2022062802/56649e975503460f94b9a8bf/html5/thumbnails/27.jpg)
Physical Layer Information is NOT Sufficient
Unacked
PRR
LQI