Frame counter: Achieving Accurate and Real-Time Link

Estimation in Low Power Wireless Sensor Networks

Daibo Liu, Zhichao Cao, Mengshu Hou and Yi

Zhang

IPSN 2016

Link Estimation in Low Power Wireless Sensor Networks

Accurately count arrived data frame for each active link

Monitor all routing/non-routing links in real-time during active state

Wireless sensor networks General network structure Low power transmission mode

Low Power Listening Protocol

X-MAC protocol Short frame Receive early ack

Sender

Receiver

Sender

Receiver

Receive wakes up

Target Address

Listen for additional Data

Listen for additional Data

Ideal Approach in Low Power WSNs

State-of-the Art

Passive Estimation & Active Estimation

Ignored receiving information

at non-routing links

Ignoring the lost

frame in routing

link

Ignoring the lost frame

Treating it as one frame loss

Capture of CorruptedFrames

Observation 1: The RSSI of corrupted frames can be captured in real-time.

Observation 2: It is feasible to distinguish ZigBee from other 2.4GHz technologies with RSSI features.

Non Real-Time

Root cause: Asynchronous transmission & nocentral coordinator

Results: Routing selection based on outdated estimation

Actions: Except for routing beacon, ignoring neighbors’data frames; Inaccurately counting beacon frame.

Defect of State-of-the-art and Observation

Empirical Study of Low Power WSNs

Inaccuracy Root cause: No synchronization mechanism

Results: Overestimation

Actions: Ignoring all lost frames if at least one frame is received; Treat no frame reception as one loss.

New Challenges

Duty cycle and asynchronous radio work mode

Accurate and Real-Time Link Estimation

Data transmission is organized as repeated data frames

Count all arrived frames (decoded or not decoded)

Several nodes may successively transmit

Monitor all neighboring links in real-time

As a neighbor, it is difficult to know which frame is corrupted

During active state, the transmitted frames by any neighbor

should be counted

Sender information of not decoded data frames is unknown

Overview the Basic Idea

Tx

Neighbor

Rx

Decoded data frame

Lost data frame

Sampled RSSI sequence

Repeat data frame transmission until be ACKed1

Frames arrive at receiver (decoded or lost)2

Sampled received signal strength in time domain4

Decoded frames math corresponding RSSIs5

#1 #3

#3

Neighbor also overhears arriving frames3

Necessary Information for Accuracy Estimation

Ongoing Sender

Which node is transmitting data frame?

Total arrived frames

How many frames have arrived during the node’s active state?

Decoded frames

How many frames have been successfully decoded by the node?

Solution 1: Extracting ID from decoded frame

Solution: Using RSSI sequence to count

Solution: Counting it according to frame receiving event

Solution 2: Using RSSI Feature to infer

Necessary Information for Accuracy Estimation

Ongoing Sender

Which node is transmitting data frame?

Total arrived frames

How many frames have arrived during the node’s active state?

Decoded frames

How many frames have been successfully decoded by the node

Solution 1: Extracting ID from decoded frame

Solution: Using RSSI sequence to count

Solution: Counting it according to frame receiving event

Solution 2: Using RSSI Feature to inferPurposes: To know the ongoing sender, number of arrived frames during

radio active state, number of decoded frames.

Utilization of RSSI Sequence

Frame Transmission by sender

Sampled RSSI Sequence at

Receiver/Neighbor

Noise floor

Signal strength

Translated to Step Pulse Signal

Low level

High level

Rising edge

Falling edge

Procedure

Counting the detected pulses to represent the

number of arrived frames

Impacts on Accurate Data Frame Counting

Coexistent Interference in 2.4GHz ISM Band

Distinguish ZigBee Data Frame and ACK Frame

Frame Type On-air time Interval

Data Frame [576, 4256] μs Larger than 512μs

ACK Packet 352μs Between 192μs and 512μs

ZigBee Frame Identification

Shorter on-air time

longer on-air time

Feature #1: On-air time

Valid range of on-air

time

Feature #2: Frame interval

Shorter packet intervalFixed frame interval

Longer packet interval

ZigBee Frame Identification

Feature #3: PAPR (Peak-to-Average Ratio) Feature #4: RSSI < Noise floor

Flat sequence

Large variation

TRUE

FALSE

ZigBee

Determination of Transmitter

Extracting transmitter ID from decoded frame

Exploiting low power RSSI features

Fixed inter-frame interval

Inter-frame interval (Tifi) is fixed;System congestion backoff > Tifi.

Check|Tifi(k) - Tifi|≤ δ

Valid RSSI bias, 1dBm

Determine whether two successive frames

are transmitted by the same sender.

Parameter forframe segment

Computing average frame RSSI Ravg;Comparing Ravg with each neighbor A’s RSSI (R(A)) by:Steadily

averaged RSSI |Ravg – R(A)|≤ Rδ

If passes the check, A is a possible candidate transmitter. If

more than one candidate, adopt deferred determination.

Deferred Transmitter Determination

…. ….

….

…. ….

Neighbor A

Neighbor B

Neighbor C

timeline……..

Time unit, 1wakeup interval

A{1, 0, 1, 0, 0, 0}

B{0, 1, 0, 0, 0, 0}

C{0, 0, 0, 0, 1, 1}

Neighbor Transmitting Time Bitmap

Neighbor A

Neighbor B

Neighbor C

Neighbors transmits data frames in different time

Different bit corresponds

to different time.

Using averaged RSSI features and compressed transmitting time to

accurately determine the transmitter.

Implementation and Evaluation

Implementation Evaluation setup

TinyOS-2.1.1

Combining with LPL

Beneath collection tree protocol (CTP)

Multiple-hop networks

Indoor & outdoor testbeds

Comparing with the state-of-the-art

With/without coexisting interference

Correct False negative False positive

Radio 97.3% 0.8% 1.9%

Accuracy

Number of arrived frames Determination of transmitter

For segment vectors, more than

92.5% with <6% FN, and 89.4% with

<8% FP.

Overall accuracy

About (>) 60% segments are determined

by decoded frames, for the remainder:

Averaged RSSI Deferred determination

Accuracy 95.8% 98.9%

DF

Averaged RSSIDeferred

determinationDecoded frame

≈60%

Timeliness

Link Quality Update Period

97.9% links can be updated

within 200 seconds.

Comparing with 4-bit link estimator

Estimation window size: 5 frames

Indoor & outdoor testbed with multiple-hop data collection networks

Trickle controls routing probe

Data packet interval: 2 minutes

More than 50% links can not

be updated one time for 8

minutes by 4-bit

Collection Tree Protocol Performance

Network reliability, Energy consumption, Delay, and Path length

More reliable Less energy

Lower delayLess transmission

hops

Conclusion

Existing passive and active link estimators can not

achieve accurate and real-time link estimation

Implement on configurable indoor/ourdoor testbed

Validate performance

Resolve accurate and real-time link estimation in Low

Power WSNs

Using decoded frames to directly determine the transmitter

RSSI features for ZigBee frame identification and frame counting

Averaged RSSI and deferred determination to accurately infer

transmitter

Q&A