Energy Consumption Optimization in Real Time Applications for WSN using IR-UWB Technology

* Anouar Darif, Driss Aboutajdine LRiT-GSCM (Unite associe au CNRST URAC 29)

FSR, Universite Mohamed V-Agdal

Rabat, Morocco

anouar.darif@gmail.com aboutaj@fsr.ac.ma

Abstract- Energy consumption optimization in Wireless sensor

networks (WSN) applications is a major issue and constraint to

which researchers are continuously faced to, due to the direct

dependence of the network's life time to it. Real time applications using WSN have some requirements to be accomplished; in this

paper we targeted the factors influenang real time's peiformance

such as latency time and packets delivery ratio which were

studied with different s cenario. We present the status of WSN

based on Zigbee and IR-UWB technologies, and the specificities

of each one. A simalation of a sink based architecture network

with various nodes' number has been peiformed to prove the good impact when using IR-UWB technology to decrease the energy

consumption and reduce the latency time. We used MiXiM

platform under OMNet++ simalator to analyze and compare the

peiformance of the IEEE 802.15.4 and IEEE 802.15.4a standards

with the considered factors.

Keywords-WSN, IR-UWB, Zigbee, IEEE802.15.4a,

IEEE802.15.4, Energy consumption, Real time, CSMAlCA, ALOHA, OMNet++, MiXiM.

I. INTRODUCTION

A wireless sensor network is a collection of nodes

organized into a cooperative network [ 1].Their role is to sense a particular phenomenon and to report it to a base station (sink) through intermediate nodes for analysis. Such

kind of networks can be used for applications like monitoring, local area control, industrial processes, civil safety, house automation and tactical applications [2], they

achieve the goal of truly ubiquitous computing and smart environments.

Wireless technologies emerge in the recent few years,

providing large opportunities in terms of low power consumption, high and low rate and are promising for real time applications.

Applications that require bounded delay latency are referred to as real-time applications. They require a delay latency time varying from about few seconds in environment

monitoring applications to less than milliseconds in tactical applications using army equipments.

IR-UW B technology as a next generation of the

IEEE802.1S.4 standard is a promising solutions for WSN due to its various advantages such as its robustness to severe mu Itipath fading even in indoor environments, its potential to

provide accurate localization, its low cost and complex ity, and low energy consumption [3]. In addition, it can fulfill the exchange of one information bit in about 3S.0 1 nanoseconds

(in the 27MB/s mandatory) offering a huge opportunity for real time applications.

Rachid Saadane SIRC2SILASI

EHTP, Km 7, Oasis, route El Jadida

Casablanca, Morocco

saadane@ehtp.ac.ma

The present paper is organized as follows. ill Section 2 we introduced Wireless Sensor Networks. ill section 3 and 4 we presented the IEEE802.1S.4 and the IEEES02. IS.4a

standards res pectively. Section S presents the Energy consumption in WSN, the simulation and its results are presented in section 6; finally, Section 7 concludes the paper.

II. WIRELESS SENSOR NE TWORKS

A. Wireless technologies presentation

Various wireless technologies are used in WSN; the most

commonly used are ZigBee, the various forms of IEEE 802.11 or W i-Fi, Bluetooth , and UWB with the two standards IEEE 802.1S.3a/4a(IR-UWB).

The initial IEEE 8 02.11 specification in 1997 was a standard for wireless local area networks (WLAN ). Most recently, the 802.11 n standard is under development to

achieve more than 100 Mbits/s for high data rate applications. Wi-Fi was widely adopted in various applications and due to its complexity and higher energy

consumption compared to ZigBee and IR-UWB, this technology has been applied only to perform some particular functions in WSN [4].

B. Application domains ofWSN

ill a typical application, a WSN is deployed in a region where it is meant to collect data through its sensor nodes.

The applicable area of WSN includes military sensing, data broadcasting [S], environmental monitoring [6], illtelligent Vehicular Systems [7], multim edia [8 ], patient

monitoring [9 ], agriculture [10][11], industrial automation [12][13][ 14 ] and audio [IS] etc. WSN networks have not yet achieved widespread deployments, although they have been

proven capable to meet the requirements of many applications categories. WSN has some limitations as lower computing power, smaller storage devices, narrower network

bandwidth and very lower battery power.

III. OVERVIE W OF THE IEEE 802.1S.4 STANDARD

The IEEE 802.IS.4 [16] protocol defines two modes of

operation: beacon enabled and non beacon enabled. In the former, a coordinator, called the Piconet Coordinator (PNC) sends periodic beacons. Beacons are followed by a so-called

Contention Access Period (CAP), during which all nodes can compete independently for channel access using a CSMA algorithm, and by a Collision Free Period (CFP), during

which nodes communicate during time slots exclusively allocated by the PNC. In the non beacon enabled mode,

978-1-4673-6374-7/13/$31.00 ©2013 IEEE

nodes use a CSMA/CA protocol in their communication. ZigBee Alliance [17] defmed the protocol stack upper layers. The introduction of an UWB-IR P HY layer in the IEEE

S02.15.4A standard made this protocol unable to operate, since it relies on CCA (in both of its modes). Therefore, adaptations were defmed in the standard. In particular, the

CSMA/CA mode is replaced by an ALOHA mode that does not rely on CCA. MAC Access Mechanisms: The MAC protocol in IEEE

S02.15.4 can operate on both beacon enabled and non beacon modes. In the non-beacon mode, a protocol is a simple Carrier Sense Multiple Access with Collision Avoidance

(CSMA/CA). Th is necessitates a constant reception of possible incoming data. In our simulation works, we have considered this mode. In the beacon-enabled mode, all

communications are executed in a super-frame structure.

I V. TH E IEEE S02. 15.4A ST ANDARD

The IEEE S02.15.4 standard [IS] defmes physical and

medium access control layers for wireless sensor networks. The IEEE S02.15.4a working group's aim was the creation and the development of an alternative physical layer that

would provide communications and high precision ranging. The standard consists of two physical layers: an ultra wideband impulse radio layer and a chirp-spread spectrum

layer. The S02.l5.4a standard will extend S02.15.4 to reach

longer range, greater robustness harsh multipath

environments, and precision ranging. UWB is the candidate leading technology for S02.15.4a due to its robustness to mu Itipath fading effects, accurate ranging ability, and simple

low-power hardware. The IEEE S02.15.4a standard is in the early stages of reviewing proposals, and future proposals should spawn innovative ideas for ubiquitous UWB

networks.

A. Physical layer

IR -UWB signals are transmitted in form of very short

pulses with low duty cycle (figure 1).

Trallslnitterl

Trallsmitter2

Figure I: Collision illustration

IR-UW B is a promising technology to address Wireless Sensor Network constraints. However, existing network simu lation tools do not provide a complete WSN simu lation

architecture, with the IR-UWB specificities at the physical (pHY) and the Medium Access Control (MAC) layers.

The medium is divided into frames and each frame is

shared in Nh chips. The frame and chip duration are Tr and

Tc, respectively. The transmitted symbol can be repeated

following a pseudo random sequence to avoid catastrophic collision under multiuser access conditions [19]. Using the Time Hopping Binary Pulse Amplitude Modulation

(THBPAM) scheme for example, the kth user transmitted

signal S�k) (t) can be expressed as

+00

S�) (t) = I jE;;xtx(t - j. Tr - cf. Tc) j=-oo

Where Etx is the transmitted pulse energy;

ttx(t )denotesthe basic pulse shape and {cf} represents the

/h component of the pseudo random Time Hopping Sequence. The received signal ret) when only one user is present can be expressed as

ret) = A. Stx (t - r) + net)

+00

ret) = I A. jE;;xtx(t - j. Tr - cf. Tc - r) + net)

j=-oo

Where r represents the pulse propagation delay and net) is N

Additive White Gaussian Noise (A WGN) with -:f power

density and A represents the signal attenuation observed during propagation [16 ]. It depends on the considered

channel model in terms of path loss, multipath, shadowing.

In a multi user scenario where Nu users are active, the

received signal is expressed as

k=Nu

ret) I Ak ·st/t - rk ) + net)

k=l

Nu

ret) = A1· Stx(t - r1) + I Ak · Stx(t - rk ) + net)

k=2

Where lk represents the delay associated to the propagation

and a synchronism between clocks [19]. Ak represents the

attenuation of the kth user's signal (k=1 represents the signal

of the user interest). This formulation can be used to characterize the TH-IR-UWB PHY layer in a multi user scenario; however the used propagation delay does not

represent the real propagation delay for the real deployment configuration. The used Bit Error Rate (BER) versus the Signal to Interference and Noise Ratio (SINR) is also based

on a perfect power control assumption which is not always realistic.

B. Radio state machine

Since the power cons umption is derived fro m the time spent in each of the radio modes, it is important to model these accurately. We use the fmite state machine illustrated on

figure 2, with three steady states Sleep, Rx and Tx, and four transient states SetupRx, SetupTx, SwitchRxTx and Sw itch TxRx. The radio can always leave any state (steady or

transient) and immediately enter sleep mode.

The time s pent in a trans ient state is a constant TrrState, the

power consumption in each state is PState and the energy cost

of a transition from one steady state to another is ErrState.

...... --- ---- ......... }-_�<;;;::� ____ :\..I -----<of

" " ... ---- - - --

- ---.........

\ Switch Rx Tx '

............ _-------_ ...... '"

Figure 2: Detailed radio m o del including transient st ates.

C. IR-UWB Advantages

There are several features of IR-UWB signals which make them attractive for a wide range of wireless applications.

Some of the major advantages of IR-UWB are, low complexity, low power consumption, and good time-domain resolution allowing for location and tracking applications.

With all these advantages, the IR UW B approach has been selected by the IEEE 802.15.4a standard as the alternative PHY for the IEEE 8 02.15.4 standard "in providing

communications and high preCISIOn ranging/location capability (1 meter accuracy and better), high aggregate throughput, and ultra low power; as well as adding scalability

to higher data rates, longer range, and lower power consumption and cost."

D. MAC Layer

ALOHA [20, 21] was one of the first deployed wireless computer networks. With ALOHA, a node having a packet to

send waits for a random time interval (called a backoff time), sends its packet and listens for an acknowledgment. If no acknowledgment arrives after a certain time (this event is

sometimes called a NACK), it is assumed that the packet was not correctly received by the other side. In that case, the node waits for a new random backoff time and retries the

transmission. ALOHA's main drawback is that the probability of collisions quickly increases with the number of users attempting transmission. This is due to the long

vulnerability window, or the time interval during wh ich another transmission can collide with an ongoing transmission. If all packets are of equal duration t, the

ALOHA vulnerability window is equal to 2T [22].

1) ALOHA throughput

The probability that n packets arrive in two packets time is given by:

Where G is traffic load. The probability P(O) that a packet is successfully received

without collision is calculated by letting n=O in the above equation. We get:

peO) = e-2G

We can calculate throughput S with a traffic load G as

follows:

s = c. peO) = C. e-2G

The Maximum throughput of ALOHA (G=JI2) is:

1 Smax = - "" 0.184

2e

2) Transition diagram of ALOHA

With ALOHA the transmitter does not care about the channel state, once it has a packet to send, it transmits it on

the medium, according to its own THS. As the received packets are not acknowledged here, no retransmission is needed. This protocol leads to low latency and gives a high

priority to new events to be notified to the base station in a WSN application. It well suits applications where latency and new events notification are critical. Th is diagram shown in

figure 3.

Figure 3 : Transition diagram of ALOHA

V. ENERGY CONSUMPTION

A. Energy Model

In WSN [24 ], the energy consumed in a node is mainly

due to packet transmission (EtxJ, reception (ErxY and channel

sensing (EesJ to check whether it is clear. The total energy

consumed is thus expressible as

Erx = v x f· Irx Trx

Ees = v x I es Tes

Wherefis the packet size, Irx, Itx and Ics denote the current

required during transmission, reception and channel sensing,

respectively, V is the voltage supply and Ttx, Trx and Tcs refer

to the corresponding activity durations.

B. Types of Energy Waste

All protocols [25 ] must deal with five types of energy: • Collisions,

• Overhearing, • Id Ie listening, • Signaling overhead,

• Over-emitting. Collisions happen when transmissions occur

simultaneously in such a manner that message reception fails for at least one of the intended recipients. Overhearing

occurs when a transceiver uselessly listens to a message. Idle

listening happens when the radio is in reception mode while

no transmission takes place. Signaling overhead is the

energy cost incurred by signaling data such as acknowledgments and synchronization packets. Lastly, over­

emitting is the energy cost associated to transmitting packets

when the destination node is not ready to receive them. Figure 4 represents these five cases and the associated radio

states.

Overhearing

Overemitting

Reception Mode Transmission Mode

Figure 4 : Types of energy \Wste in MAC prot ocols and asso ciated radio states

VI. SIMULATION AND RESULT S

A. OMNet++ and MiXiM simulation platform

OMNeT++ is an extensible, modular, component-based C++ simulation library and frame work which also includes an integrated development and a graphical runtime

environment; it is a discreet events based simulator and it provides a powerful and clear simulation framework. MiXiM joins and extends several existing simulation frameworks

developed for wireles s and mobile simu lations in OM NeT ++.

It provides detailed models of the wireless channel, wireless connectivity, mobility models, models for obstacles and many communication protocols especially at the Medium

Access Control (MAC) level. Moreover, it provides a user­friendly graphical representation of wireless and mobile networks in OMNeT++ , supporting debugging and defming

even complex wireless scenarios. [23]

B. Simulation parameters

We performed the simulations in the MiXiM2.1 release

framework on top of the OMNeT++ 4.2 network simu lator. We used a tree based topology, where nodes transmit packets to a Sink node; also we ran several simu lations with different

numbers of nodes. Figure 5 show the network structure chosen in the 49 nodes' number scenario, with a sink node in the corner.

Sensor nodes

.--1\ •

•

•

•

•

•

•

•

• • • • •

•

•

•

•

•

•

•

• • Sink node

•

•

•

•

•

•

•

•

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

• • •

Figure 5 : The 49 nodes' nunber scenario

For the energy consumption (see Table I) we used the following radio power consumption parameters:

T ABLE I: ENERGY P ARAME 1ERS

Parameter Value

PRx 36.400 mW

PTx 1.212 mW

PSleep 0.120 mW

PSetupRx 36.400 mW

PsteupTx 1.212 mW

PswTxRx 36.400 mW

PswRxTx 36.400 mW

For the radio timing we used the parameters shown bellow in Table II.

In Table III and Table IV we have regrouped respectively the CSMA/CA and the Nic8 02154_ TI_ CC2 420 parameters used during simulations.

TABLE II: TiMING PARAMETERS

Parameter Value

TSetupRx 0.000103 s

TSetupTx 0.000203 S

TSwTxRx 0.000120 S

TSwRxTx 0.000210 s

T RxToSleep 0.000031 S

TTxTosleep 0.000032 s

Bit rate 0.850000 Mbps

T ABLE TIT: CSMAICA PARAME TE RS

Parameter Value

minBE 3

maxBE 5

MaxCSMABackoffs 4

Max FrameRetries 3

AckWaitDuration 86 4 /ls

A Un itBackoftPeriod 320 /ls

CCADetectionTime 128 /ls

TAB LE IV: Nlc802154_IT_CC242 0 PARAMETERS [26]

Parameter

TSetupRx TSetupTx

TSwTxRx

TSw RxTx

For the physical layer we provided by M iXiM .

used

Value

l.792 IllS

l.792 IllS

192 fls 192 flS

Phy LayerUW BI R class

For the MAC layer we developed our own class

"PureAlohaMacLayer" to implement the ALOHA MAC protocol.

C. Simulation results

As mentioned in the paper's title, the two features we have de focus on are power consumption and real time; the following parameters are studied:

The packets arrival delays (latency), the packets delivery ratio, and the energy cons umption for both technologies: IR­UWB and Zig bee.

Figure 6 shows a close analysis of the packet arrival delays (latency) parameter for different nodes' number values 4, 9, 16, 25, 36 and 49. It show; an arrival delays

averages for the Zigbee case between 3.86 and 4.55 IllS; for the IR-UWB, it varies from 0.49 to 1.271llS. Moreover, these averages are close to the minimal values in both cases, which

mean that almost all the nodes' packet arrival delays are very close to these average values. Therefore, it shows clearly the

good results manifested by the IR-UWB technology compared to the Zig bee technology that it is approximately four times quick. Another remarkable point is that the Zig bee

maximal arrival delays begin to take large values from 25 nodes' case, in contrast to the UWB maximal arrival delays

which are stable in all studies cases. This point shows that some packets in the Zigbee case will be received with a delay; this delay causes a quality of service degradation and

is absent in the UWB case 30

25 +-----�--�-----+��-r __ �

/ 20+-----�--�-----+-----r--�

u; / ! 1

5+-----�--�-----+-----r--�

� 10 +----+----4-�/--4---�----�

5 .� � b Of -l - '-- � -, I

o j '==-1 , 1 9 �6 �5

-5 I I I I �9 I

.Zigbee min arrival delays

-+-Zigbee max arrival

delays

" Zigbee arrival delays average

+lR·UWBmin arrival delays

"lR·UWBmax arrival delays

"lR·UWB arrival delays average

Nodes' number

Figure 6 : Packets arrival delays (latency)

To ensure an acceptable quality of service in any real time

system, we were obliged to study the Packets delivery ratio parameter. Figure 7 shows a good packets delivery ratio in the Zigbee

case which reaches 100% in all scenarios except in the 49 nodes' number scenario which is equal to 99.95%. ill the UWB, this ratio varies from 100% for the four nodes

scenario to 94.19% for the 49 mobile nodes scenario. It proves clearly the influence of the number of mobile nodes on this parameter. Because the packets delivery ratio

parameter is a direct result of the efficiency of the MAC protocol and due to the dropping MAC frames observed during simulations, we have to deal with the improvement or

do some modifications on the used MAC protocol in this experIments.

100.00 -... • ............. H .......... ......... HHHH1.H .. H.HH. , -

� � 80.00 ·.'Packets delivery .� ... ratio (Zigbee) e 60.00 t> ... Packets delivery . � ratio (IR· UWB)

� 40.00

tl � 20.00 �

� 0.00 I I I I Nodei!' number

4 9 16 25 36 49

Figure 7 : Packets delivery ratio

IR -UWB technology was mainly introduced in the field of WSN due to its various specificities and advantages, and especially its low energy consumption advantage. This was

concretized by the results shown in Figure 8. It shows that the energy consumption of the IR -UW B scenarios is

remarkably less that the Zigbee scenarios. The mean power consumption of the IR-UWB nodes vary from 43.02 to 43.44 mW and those of Zigbee nodes vary from 62.036 to 62.038

mW.

7

0

I I I I I I §2 60 ....................................................... .

.E. 5O +--+--+---+----J.----..j I::

.8 - . . r- . . - . . - . . - . .

�40+--+--+---+---+-----.j E: � � +--+--+---+---�-� I:: g 2O +--+--+---+---+----..j .... "" 3 10 +--+--+--+---+--� C

Q",

16 25 36 49

� ... Zigbee Nodes I � .. IR·UWB Nodes I

Nodes' number

Figure 8 : Nodes' pO\\er consumption average

VI I. CONCLUSION AND FUfURE WORKS

Energy was and is an interesting issue that is still a factor

in the development of WSN protocols especially in the MAC

and network layers. This factor affect directly the lifetime of the network. In this work we showed the gain brought by the

use of the IR-UWB technology in terms of energy consumption compared to the use of the Zigbee technology.

Also we proved that real t ime systems requiring latency

less than 4 ms in a 7 hops maximum networks are largely satisfied if we choose to use IR-UWB based WSN.

We aim, as a future work, to provide a solution for the

packets loss encountered in this work which influences the packets delivery ratio to improve the quality of service required by such systems.

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