An Energy Efﬁcient Multiagent Middleware for Physical

Complex System

Jean-Paul Jamont

, Michel Occello

and Andr

e Lagr

eze

Institut National Polytechnique de Grenoble, LCIS, 26000 Valence, France

Universit

e Pierre Mend

es, LCIS/INPG, 26000 Valence, France

Abstract. Open physical complex artiﬁcial systemsinvolve wireless autonomous

entities submitted to strength constrainted energetic policies. Their features natu-

rally lead to apply multiagent techniques to ensure both the autonomy of entities

and the best whole system organization. We propose a multiagent approach for

wireless communication robust management for such physical system using self-

organization mechanisms. We show the performances of this approach by com-

parison to usual wireless protocols. The genericity of our contribution is high-

lighted by the proposition of a middleware layer integrated in agent. We give an

insight to a real world instrumentation application using the middleware.

1 Introduction

A complex system can be deﬁned as composed of many elements which interact each

other and with their environment. These interactions are often non-linear and gener-

ally contain feedback loops. At the global level, these systems are characterized by

the emergence of not observable phenomena at a local level: an external observer will

understand differently the system than an internal observer. Complex systems are thus

characterized by the emergence at a global level of new properties and of a new dynamic

which is not easily predictible from the observation and the analysis of the elementary

interactions.

Working with physical systems like collective robotics or massive instrumentation

imposes the use of wireless technology. The features of such complex cognitive physical

system leads to naturally apply multiagent techniques to ensure both the autonomy of

entities and the best whole system organization [3].

This paper presents the different steps of the design of an energy efﬁcient middle-

ware. In a ﬁrst section we present the necessity to adopt a message oriented middle-

ware (MOM) for our applications. We then propose our multiagent approach based on

self-organization to manage the communication of these decentralized embedded nodes

networks. We give ﬁnally an insight to some quantitative results showing the beneﬁt of

a multiagent approach compared to traditional protocols in a real world application of

an underground river system intrumentation.

Jamont J., Occello M. and Lagrèze A. (2005).

An Energy Efﬁcient Multiagent Middleware for Physical Complex System.

In Proceedings of the 1st International Workshop on Artiﬁcial Neural Networks and Intelligent Information Processing, pages 72-81

DOI: 10.5220/0001196200720081

 SciTePress

2 Necessity of an energy efﬁcient MOM

Our research works deal with embedded multiagent systems (MAS) like collective ro-

botics or physical instrumentation. Considering complex embedded control systems as

networks of decentralized cooperative nodes is an attractive way to design physical in-

telligent applications [6,3].

Multihop communication. In wireless networked system, communication between

two hosts is generally not direct. To communicate, entities require help from other hosts

(multihop communication). Such a requirement creates an important routing problem

because the location updating of neighbors is difﬁcult. All adapted wireless routing

protocols use ﬂooding technics. In a ﬂooding technique, a host gives the message to all

its neighboors which do the same. These wireless protocols can be classiﬁed by their

families : The reactive protocols using no routing table, the proactive protocols using

routing tables, periodically updated and hybrid protocols adopting a reactive protocol

behavior and, if necessary, using routing tables for increasing efﬁciency.

Limited power ressources. Agents have limited power ressources. One of the

whole system aim is so to reduce as much as possible the energy expense. When they

have nothing to do generally for sparing energy they enter in a sleep mode. When they

communicate they must use good routing protocols and optimal ways (generally the

criteria will be the number of hops). But they must decrease as much as possible the

ﬂooding scheme because the associated power cost is very high. An agressive environ-

ment like underground river system (as for one of our applications) can cause some

internal faults for agent. The communication infrastructure must be very adaptive, fault

tolerant and self-stabilized : an agent failure must not have an important impact on the

system. This system must provide reliable communications and, sometimes, must adapt

to ”real-time” constraints. Furthermore, in the case of mobile devices the infrastructure

of sytems are not persistant.

Message oriented middleware. We need to design a mobile communication man-

agement layer to manage the wireless communications between the different agents in

the system. This layer must increase interoperability, portability and ﬂexibility of an

application by allowing the application to be distributed over multiple heterogenous

agents. It must reduce the complexity of agent development. This layer will be a Mes-

sage Oriented Middleware (ﬁgure 1).

3 A multiagent approach to design energy efﬁcient MOM

3.1 Multiagent systems

Multiagent method. Multiagent methods aim at decreasing the complexity of system

design by a decentralized analysis. We will follow the method of multiagent design dis-

cussed in [7] based on the AEIO according to four axes collectively accepted today:

The agent aspect gathers all elements together for deﬁning and constructing these en-

tities. The environment aspect for dealing with the analysis of environment elements

and with capability such as the perception of this environment and the actions one can

do on it. The interaction aspect includes all elements which are in use for structuring

Fig.1. Our embedded multiagent system architecture

the external interactions among the agents (communication language, interaction proto-

cols). The organization aspect allows to order agent groups in organization determined

according to their roles.

Multiagent systems and wireless networks. The distributed and open nature of

sensor networks means that the multiagent approach is an adapted answer. Another ad-

vantage of this approach is the external representation of the interactions and of the

organization. External representations offer multiple possibilities such as the monitor-

ing by an external observer.

A few works reaching the same objectives show that the approach is interesting. We

can quote the ActComm [2] project which is a military project for which the routing of

information is essential: it aims at studying the communication management between

a soldier team and a military camp via a satellite. We can also mention the work on

wireless networks of mobile autonomous intelligent sensors [9] where agents are used

to achieve open ﬂexible cell assembly.

Our Message Oriented Middleware (MOM) must be economic in an energy point of

view : it is one of the main differences with the other works on multiagent based mid-

dleware [1,5].

3.2 The agent aspect

An agent is a software entity situated in an environment which it can perceive and in

which it acts. It is endowed with autonomous behaviors and has objectives. Autonomy

is the main concept in agent issue: it is the ability of agents to control their actions

and their internal states. The autonomy of agents implies no centralized control. The

power of an agent decomposition is the decentralization of the intelligence, i.e. the

decision capabilities, and of entities’ knowledge. A MAS is a set of agents situated in a

common environment, which interact and attempt to reach a set of goals. Through these

interactions a global behavior can emerge. The emergence process is a way to obtain,

from cooperation, dynamic results that cannot be predicted in a deterministic way.

These agents have hybrid architectures, i.e. a composition of some pure types of

architectures. Indeed, the agents will be of a cognitive type in case of a conﬁguration

alteration, it will be necessary for them to communicate and to manipulate their knowl-

edge in order to have an efﬁcient collaboration. On the other hand, in normal use it will

be necessary for them to be reactive (stimuli/response paradigm) to be most efﬁcient.

All the agents have the same communication capabilities but the communicated data

depend of their roles.

3.3 The environment aspect

This part of the analysis deals with elements necessary for the MAS realization such as

the perception of this environment and the actions one can do on it. The environnement

can be [10]: Accessible, if an agent using the primitives of perception can determine

the state of the environment. When an environment is inaccessible it is then necessary

for the agent to memorize features in order to record the modiﬁcations which occur.

Determinist, or not, according to whether the future state of the environment is, or not,

ﬁxed by its current state and the actions of the agent. Episodic if the next state of the

environment does not depend on the actions carried out by the agents. Static if the state

of the environment is stable while the agent reasons. Discret if the set of the feasible

actions and states of the environment is ﬁnished.

The environment will be made of measurable information. It is deterministic, non

episodic, dynamic and continuous. Agents can move in this physical environment but

don’t know their position.

3.4 The organization aspect

In this type of application no one can control the organization a priori. Relations be-

tween agents are going to emerge from the evolution of the agents’states and from their

interactions. We are going to be content with ﬁxing the organization parameters, i.e.

agents’tasks, agents’roles.

Fig.2. Group organization

Our organizational basic structures are constituted by (see ﬁg 2) : one and only

one group representative agent (r) managing the communication in its group, some

connection agents (c) which know the different representative agents and can belong

to several groups, some simple members (s) which are active in the communication

process only for their own tasks.

With this type of organizational structure, the message path between the source (a)

and the receiver (b) is ((a, r),

∗

[(r, c), (c, r)], (r, b)). If the source is a representative

agent the ﬁrst term doesn’t exist. If the receiver is a representative agent the last term

doesn’t exist.

Because a representative agent is the most sollicited agent in a group, the best one

is the one having the most important level of energy and the most important number

of neighbors. We use a role allocation based self-organization mechanism involving the

election of a representative agent based on a function which estimates the adequation

between its desire to be the boss and its capacity to be: so the organization is modiﬁed

only when a problem occurs. We don’t try to maintain it if we have no communication.

The energy saving is obtained owing to the fact that the ﬂooding is only directed to

the representative agents of the groups and to some connection agents. To give an order

of idea, a receiver path research with ﬂooding techniques will cost, in the case of a

traditional wireless network, a number of emissions equal to the number of stations. In

the case of a clustered wireless network, the number of transmitted messages are about

twice the numbers of representative agents (all the representative agents are contacted

via one connection agent ).

However, the networks with an organizational structure must take care of the main-

tenance of their routing table. Generally, the adaptive features of these tables come from

periodical exchanges between the different nodes. In our approach we do not wish to

use this technique to ensure the maintenance of coherence. Indeed, our principle will

be ”if we do not need to communicate, it is useless to spend energy to ensure the co-

herence maintenance”. However, we will thus use eavesdropping of surrounding agent

communications. We extract knowledge from these messages exchange to update our

beliefs about our neighboors. Moreover, our self-organization mechanism will integrate

an energy management policy. These structures will thus emerge.

Our algorithm (ﬁgure 3) can be adjusted by other agents’ suggestions such as an

organization inconsistency. Moreover, an agent can give up its role because its power

level quickly fall or fall under a limit that the agent thinks dangerous for its integrity.

So it can become a sample member.

3.5 The interaction aspect

The agents will interact only with the agents in acquaintance. Agents interact by asyn-

chronous exchange of messages. Among the different protocols that we use, the choice

of an introduction protocol is essential. Indeed, this protocol allows to the agents to

be known, i.e. to bring their knowledge and their know-how to the agents’ society. An

other important protocol is the ”best representant election” protocol seen previously.

These protocols are an arrangement of some of the thirteen different types of small

messages deﬁned in the following: WhoAreMyNeighbors is used by an agent to know

who its neighbors are. This message is transmitted when an agent is created (the ﬁrst

goal of a new agent is to know its neighbors) or when an agent feels that its neighbor

table is not coherent with reality. IAmOneOfYourNeighbors makes it possible for an

agent to answer the preceding request. With this message, it thus provides its identiﬁer,

Fig.3. Self-organization algorithm

its role and its membership group. IChangeMyRole is used by any agent to inform its

neighbors that it decides to change its role. AskConnectionAgentGroup is used by rep-

resentative agents which want to update their knowledge on the close groups. It obliges

the connection agent to answer. AnswerConnectionAgentGroup is used by a connec-

tion agent to announce to a representative agent the other representative agent that it

can contact. VerifyNeighborGroupConsistency is sent by an agent, to its representative,

which believes to have detected an inconsistency with a close group. There is an in-

consistency between two groups when two agents of different groups see themselves

and their representative cannot communicate with a short path (ﬁxed by a time-to-live).

ConﬂictRepresentativeResolution is used by a representative agent, in conﬂict with one

or more other representative agents, to communicate its score. ISuggestYouToBeRep-

resentative is a suggestion given by a representative to one of the agents of its group.

FindPacketPath is used by a representative agent which wants to know the path (list

of representative agents) to join another agent. PacketPathResult is the answer of the

representative of the recipient of the F indP acketP ath message. ACKMessage is a

conﬁguration message used to conﬁrm to the transmitter that its message arrived to its

destination. BadWay is a message sent by a representative who noticed a problem. This

message takes the erroneous road and the organization veriﬁes its consistency. Encap-

suledData is a message which encapsulates data.

For example, the introduction protocol consists in transmiting WhoAreMyNeigh-

bors, receiving the answer of neighbor agents (IAmOneOfYourNeighbors), choosing a

role according to the algorithm (ﬁgure 3) and transmiting a IAmOneOfYourNeighbors

message.

4 Implementation and evaluation

4.1 Implementation

Therefore, we will demonstrate the feasibility of our approach in the case of the instru-

mentation of an underground hydrographic system [3]. In a subterranean river system,

the interesting parameters to measure are numerous: temperature of the air and the wa-

ter, air pressure, pollution rate by classical pollutants, water ﬂow, draft speed etc. All

these information will be collected at the immediate hydrographic network exit by a

workstation. These data will be processed to activate alarms, to study the progress of a

certain pollution according to miscellaneous measuring parameters, to determine a pre-

dictive model of the whole network by relating the subterranean parameters measures of

our system with the overground parameter measures more classically on the catchment

basin.

We have chosen for sensors a classical three-layers embedded architecture. We use

the physical layer which is employed by NICOLA system, a voice transmission system

used by the French speleological rescue teams. This layer is implemented in a digital

signal processor rather than a full analogic system. Thereby we can keep a good ﬂex-

ibility and further we will be able to apply a signal processing algorithm to improve

the data transmission. The link layer used is a CAN (Controller Area Network) pro-

tocol stemming from the motorcar industry and chosen for its good reliability. The

applicative layer is constituted by the agents’ system. A hybrid architecture enables

to combine the strong features of each of reactive (to the message) and cognitive capa-

bilities (to detect inconsistency and re-organisation ). The ASTRO hybrid architecture

[6] is especially adapted to a real time context. The integration of deliberative and reac-

tive capabilities is possible through the use of parallelism in the structure of the agent.

Separating Reasoning/Adaptation and Perception/Communication tasks allows a con-

tinuous supervision of the evolution of the environment. The reasoning model of this

agent is based on the Perception/Decision/Reasoning/Action paradigm. The cognitive

reasoning is thus preserved, and predicted events contribute to the normal progress of

the reasoning process.

The communication module calls the MAS middleware services supplied through

a component. The agent must use a WCommunication package, write in Java lan-

gage and translated into C++ langage because a lot of physical plateforms use this

langage. This package contents two abstracts classes (Identifier and Message)

and two main classes called Communication and BitField. In the Message ab-

stract class the designer must implement the primitives to convert the message in a bit

ﬁeld (BitField MessageToBitField(Message m) and the recipocal primi-

tive Message BitFieldToMessage(BitField b)). In the Identiﬁer abstract

class the designer must implement the type of identiﬁer and two primitives BitField

IdentifierToBitField()and Message BitFieldToMessage(BitField

b). The primitive to convert the identiﬁer in a bit ﬁeld must be implemented by the de-

signer. The Communication class contains a list of couples (Identifier,Message)

for the emission and the reception. This list is private and must be accessed via Bool

SendMessage(Identifiant, Message)and CoupleIdentifierMessage

ReceiveMessage().

The package must be connected to the operating system. The operating system

must give the battery energy level (primitive SetBatteryLevel(Float l) to the

Communication class and must give the bit ﬁeld which arrives. In an other hand, the

middleware gives to the operating system the bit ﬁeld to send by calling BitField

GetBitFieldToSend().

These agents are embedded on autonomous processor cards equipped with com-

munication modules and with measuring modules. The KR-51 (the real time kernel’s

name) allows multi-task software engineering for C515C microcontroller. We can pro-

duce one task for one capability. We can then quite easily implement the parallelism

inherent to agents and satisfy the real-time constraints.

4.2 Evaluation

In order to evaluate and improve such agents’ software architectures and the coopera-

tion techniques that they involve, we introduce a simulation stage in our development

process. The simulation ﬁrst allowed us to experiment our approach and the software

solutions that we provide for the various problems.

The simulation step. The simulation software structure is very basic. We have two

types of components: SimSensor and SimNetwork. A SimSensor component simulates

the sensor behavior. It possesses its own model and architecture. All the sensors have

the same communication capabilities. They transmit their requests to the SimNetwork

component which sends this information to all sensors which can receive them, in the

environment. SimNetwork can appear as the inference mechanism for the simulation.

We have compared our MAS to three traditionnal solution based on ad-hoc pro-

tocols. The DSDV protocol (Destination-Sequenced Distance-Vector protocol [8]) and

the natural DSR protocol (Dynamic Source Routing protocol [4]) do not appear in this

comparaison because its efﬁciency were lower than the ehanced version of DSR which

uses a route maintenance (memorization of the main route). We thereafter call efﬁciency

the ratio between the theoretical useful volume of the optimal way divided by the vol-

ume of each transmitted communication.

Case of an application with unidirectional communication. All agents communicate

only with the workstation situated at the end of the undergound river system : it is a

unidirectionnal protocol. In this case, messages are small. For this example, three mes-

sages are send by ﬁve seconds. The same scenario is applied for the different protocols.

We can see that the beneﬁt (ﬁg 4) of our approach is important. Our routing method

can deliver quickly all messages with a good efﬁciency. Higher is the number of sensors

better is the reactivity of our approach. We must note that if the system knows no per-

tubation or mobility variation of DSR will be better from an efﬁciency point of view is

normal because in this case DSR learns all the routes (succession of sensors) allowing

to communicate with the workstation. It is not really the case of our approach which

reasons about the group and not from the sensors. One consequence is that the routes

used by the messages with our approach are not optimal. We can see that our approach

support the addition of a lot of sensors. The number of groups don’t explose with the

number of sensors but their density increases.

Case of an application with multidirectionnal communication. In this case, we en-

visage communication between collaborative sensors. We choose to give to the message

a size of thirty bytes (elaborated measure). In this case the behavior of our approach is

Fig.4. Approach comparison for unidirectionnal use case

Fig.5. Approach comparison for the multidirectionnal use case

much better than DSR because its route management is more complicated. If we add

some perturbations on these scenarios (one perturbation by three minutes) the efﬁciency

is nearly the same (it is not the case for the DSDV protocol).

5 Conclusion

We have presented in this paper a MAS to manage wireless communication between

agents in respect to energy constraints. From our different works on physical complex

systems, we concluded that more genericity can be introduced in communication man-

agement. We have built a multiagent middleware based on a multiagent approach which

allows to make abstraction of this energy efﬁcient communication management at the

application level. We use this middleware in the case of a wireless sensor network.

In this application, all the agents have a hybrid decisionnal architecture based on the

ASTRO model. The middleware is included in the ASTRO communication module.

Agents present interesting features of software engineering such as genericity allow-

ing an easy evolution of the applications. Generic aspects of agents allow us to envisage

differents applications for this network type such as diagnosis, risk management, data

fusion...

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