Energy-Efficient Communication Strategy for
Wireless Sensor Networks
Yujie Zhu and Raghupathy Sivakumar
GNAN Research Group, Georgia Tech
18 timeslots !
 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!
EbT
97
97
0
0
0
0
1
 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
1
0
0 0
0
CtS
START
1
1
1
0
0
0
0
1
Basic CtS
A-B
start
A-B
stop
[t2 t6]
[t4 t8]
0.8
6000
C-D
stop
5000
CtSmfc
EbT
4000
3000
2000
C-D
start
C-D
stop
0.7
0.6
CtSmfc


A-B
stop
 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
EbT
0.5
0.4
0.3
0.2
0.1
0
10
20
30
40
50
60
0
10
Path Length (hop)
2
A-B
start
[t6 t10]
0.9
0
C-D
start
D
R2
R1
0
6 time slots !
CtS with
Multiplexing
[t5 t9]
Performance Evaluation of Optimized CtS :
10 time slots!
1
1 2 …. 97 !
S
1000
2
[t14 t18]
[t3 t7]
7000
97 !
1
[t1 t5]
CtS with
Fastforwarding
Multiplexing:
Cascading:
1
[t8 t12]
10 timeslots !
Optimization Strategies – Throughput
Improvement
4
D
R2
R1
[t2 t6]

 The energy consumption for CtS is always 2eb irrespective of the amount of
information being sent
S
[t13 t17]
Throughput (bit/bit slot)
Motivation:
[t7 t11]
[t1 t5]
Basic CtS
Energy (Eb/bit)
An Overview of the Strategy
Example:
10Mbps data rate, 10 bit data packet size
Energy improvement: 5 times
Effective throughput: 10Kbps
 The CtS strategy incurs exponential throughput decrease
20
30
40
Path Length (hop)
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
Implementation
STOP
Protocol Design:
12 time slots!
The Energy Throughput Tradeoff
Basic CtS
A-B
start 1
3
A-B
stop1
5
A-B
start 2
A-B
stop 2
 Hardware design
 MAC layer solutions: reliability, addressing, sequencing
7 time slots !
CtS with
Cascading
A-B
start
3
A-B
interme
diate
Fast-forwarding:
The energy consumed for
transmitting each bit of data
decreases inverse linearly with
data packet size
The time taken to transmit a
packet
of s bits is 2s using Cts
 The throughput of CtS
decreases as s/ 2s
CtS link
A-B
stop
 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 CtS
Not possible in EbT because a packet has to be received in full before forwarding
to ensure content integrity
CC1010 sender
CC1010 receiver
Test bed 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
50
60