Cascading:

An Overview of the Strategy

Yujie Zhu and Raghupathy Sivakumar

GNAN Research Group, Georgia Tech

Energy-Efficient Communication Strategy for Wireless Sensor Networks

Implementation

Point-to-point link, one sender, one receiver CtS strategy is used to send randomly generated data packets Both sender and receiver are implemented using RF transceiver modules Chipcon CC1010 – single chip RF transceiver

Multiplexing:

Fast-forwarding:

The energy consumed for transmitting each bit of datadecreases inverse linearly with data packet size

Motivation:

Need for energy-efficient communication from light sensors to sink Traditional communication strategy conveys information between the sender and the receiver using energy (EbT) only

Energy consumption is keb, where k is the length of the bit-stream and eb is energy per bit

Can we use time as an added dimension to convey information?Communication through Silence (CtS):

A new communication strategy that conveys information using silent periods in tandem with small amount of energy Procedure:

Sender interprets the information to be transmitted as a data value Sender transmits start signal Receiver starts to count from 0 upon receiving start signal Sender and receiver are synchronized in counting clock Sender transmits stop signal when receiver counts up to the desired value Information delivered!

The energy consumption for CtS is always 2eb irrespective of the amount of information being sent

97 !

START

1 0 0 0 0 1 1

97

97 !

1 0 0 0 0 1 1 1 0 0 0 0 1 1

97

STOP

1 2 ….

EbT

CtS

The Energy Throughput Tradeoff

The time taken to transmit a packet

of s bits is 2s using Cts The throughput of CtS decreases as s/ 2s

Example:10Mbps data rate, 10 bit data packet sizeEnergy improvement: 5 timesEffective throughput: 10Kbps The CtS strategy incurs exponential throughput decrease

Optimization Strategies – Throughput Improvement

Two or more contending sender-receiver pairs can transmit at the same time as along as the start/stop signals do not overlap Enabled by the typical long silent intervals between start and stop signals in CtS Not possible in EbT since a sender-receiver pair has to occupy the channel exclusively during transmissions

CtS with Multiplexing

C-Dstart

C-D stop

2

2

4 C-Dstart

C-D stop

A-Bstart

A-BstopBasic CtS

10 time slots!

6 time slots !

A-Bstart

A-Bstop

Consecutive data values that are monotonically increasing or decreasing can be sent in a combined “signal train” consist of one start signal, multiple intermediate signals and one stop signal instead of multiple consecutive start/stop signals The same counting process can be used for multiple packets at the same time for CtS Not possible in EbT since overlapped data packets confuse the receiver

Basic CtS

A-Bstart

A-Bstop

3A-Bstart 1

A-Binterme

diate

CtS with Cascading

3

12 time slots!

7 time slots !

5A-Bstart 2

A-Bstop 2

A-Bstop1

For multihop CtS communication, a relay node can forward start/intermediate signals before the stop signal is received Enabled by the separable signals of each packet and possibility of simultaneous counting in CtSNot possible in EbT because a packet has to be received in full before forwarding to ensure content integrity

Basic CtS[t1 t5] [t7 t11]

[t2 t6] [t8 t12]

[t13 t17]

[t14 t18]

CtS with Fastforwarding

[t3 t7]

[t4 t8]

[t5 t9]

[t6 t10]

S DR1 R2

[t1 t5]

S DR1 R2

[t2 t6]

18 timeslots !

10 timeslots !

Performance Evaluation of Optimized CtS :

0

1000

2000

3000

4000

5000

6000

7000

0 10 20 30 40 50 60

Path Length (hop)

En

erg

y (E

b/b

it) CtSmfc EbT

The throughput of integrated CtS is up to twice that of EbT The energy consumption of EbT increases faster with path length than

integrated CtS

Summary:The energy-delay trade-off of basic CtS strategy can be alleviated by Proper combination of optimization strategies Adaptation of parameters

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

0 10 20 30 40 50 60

Path Length (hop)

Th

rou

gh

pu

t (b

it/b

it s

lot)

CtSmfc EbT

Protocol Design:

Test bed Implementation:

Hardware design MAC layer solutions: reliability, addressing, sequencing

CC1010 sender

CC1010 receiver

CtS link