Aravind Vaithilingam Chockalingam

Ikujuni Grace Olasehinde

Rozita Teymourzadeh

Universal Computer Aided Design for Electrical Machines 1

Electrical machines are devices that change either mechanical or electrical energy to the other and also can alternate the voltage levels of an alternating current. The need for electrical machines cannot be overemphasized since they are used in various applications in the world today. Its design is to meet the specifications as stated by the user and this design has to be an economical one. The design therefore revolves around designing the machine to meet the stipulated performance required, the cost available and the lasting life of the machine. This work aims to eliminate the tediousness involved in the manual hand calculations of designing the machines by making use of a graphical user interface and using iterations in situations where the data would have been assumed. I.

INTRODUCTION

The design of motor in general is a complex procedure and hence requires an easy and understandable design method and tool for the designer. CAD design for this work looks into the design of DC machine, induction machines, synchronous machines, transformers, Rotary SRM and the inductance profile of SRM [START_REF] Krishnan | Switched Reluctance Motor Drives: Modeling, Simulation, Analysis, Design, and Applications[END_REF]. The induction motor is divided into the design of three phase and single phase induction motor with each having its own GUI. Synchronous motor is divided into salient and round rotor type and the transformer is divided into the shell and core type. The designs have been made with consideration to the performance of the machine. Other limitations such as cost and insulating material have not being taken into consideration. The design of electrical machines [START_REF] Aravind | Design of electrical apparatus[END_REF], [START_REF] Vishnu Murthy | Computer Aided Design of Electrical Machines[END_REF] has looked considerable into the design of various machines. The reluctance machine design works on the inductance profile and design of the rotary SRM [START_REF] Krishnan | Switched Reluctance Motor Drives: Modeling, Simulation, Analysis, Design, and Applications[END_REF], [START_REF] Praveen | Design of Switched Reluctance Motors and Development of a Universal Controller for Switched Reluctance and Permanent Magnet Brushless DC Motor Drives[END_REF], [START_REF] Aravind | Design of reluctance motors for low speed applications[END_REF].

II. DESIGN TOOL

The analysis and synthesis way of designing electrical machines have been used in the design of the machines. The synthesis method is used for DC machine, AC machine, and transformers. The analysis method has been used for the design of switched reluctance method [START_REF] Krishnan | Switched Reluctance Motor Drives: Modeling, Simulation, Analysis, Design, and Applications[END_REF]. There is a general toolbox interface that introduces the user to the design of each electrical machine. This is as shown in the fig. 1 This introductory GUI makes use of radio buttons that links the designer to the various machine design GUI pages.

Fig. 1: Introductory GUI

The materials used for the design of electrical machines greatly depend on the hysteresis loop of the machines. Various materials have been used for the design of this toolbox and it is as shown in the fig. 2.

Fig. 2: Magnetization curves

The machine specifications for each machine design GUI include the following:  The ratings of the machine such as the voltage, KVA, peak current, speed, number of poles.  For some of the motor design, the required outer surface parameters of the machine are required such as the total diameter and length of the machine.  For SRM, stator and rotor pole arc, length of air gap required and active or passive element of the linear SRM.

 Number of phases for the machine. Fig. 3 is a generalised design procedure for electrical machines. The analysis on how to design reluctance machine is has been extensively done by [START_REF] Krishnan | Switched Reluctance Motor Drives: Modeling, Simulation, Analysis, Design, and Applications[END_REF], [START_REF] Praveen | Design of Switched Reluctance Motors and Development of a Universal Controller for Switched Reluctance and Permanent Magnet Brushless DC Motor Drives[END_REF], [START_REF] Aravind | Design of reluctance motors for low speed applications[END_REF]. The design of the other electrical machines has being done by [START_REF] Aravind | Design of electrical apparatus[END_REF], [START_REF] Vishnu Murthy | Computer Aided Design of Electrical Machines[END_REF]. The design procedure looks into the design of the main dimensions, field windings, No load calculations, performance characteristics and others. For all machines the main criteria for the design is getting the output coefficient. The output coefficient is gotten as (1) Where P is the output of the machine in KVA, D is the diameter of armature (m) and L is the gross length of armature (m), and N is the speed of the machine in RPM.

III. MACHINE DESIGN

Other relevant considerations are that of the magnetic and electric loadings and are specified as follows.

, Wb Where B av = specific magnetic loading (Wb/m 2 ), D is diameter of the armature (m) and L is the length of the armature (m) and P is the number of poles. The specific magnetic loading ,

(2) Total electric loading;

, A Where I z .Z is the total electric loading, a c is the specific electric loading in A/m. The specific electric loading,

IV. RESULTS

TRANSFORMERS

Transformers are divided into shell and core type transformers. Although shell type transformers are hardly used, they are still in used in small capacity machines. Both types of transformers have being designed. The GUI enables the user to be able to select the core type, number of phases and the winding required. For the GUI design, provisions are made so that the designer can pick if the type of core required, number of phases and windings to be used. The slip of induction motor matters a lot as it greatly affects the torque of the motor. The slip is the difference between the synchronous speed and the actual speed. The need for slip is because an induction motor does not generate voltage when the rotor is running at a synchronous speed to that of the magnetic field. This is the reason why a much difference in the slip, yields a large torque value. The graph as seen from the GUI shows that with increase in the slip of the machine, the torque is greatly increased until it gets to a value where the slow speed in movement of the rotor is not strong enough to cut across the magnetic field thereby resulting in a reduction in the torque produced. The open circuit characteristics test is taken when the generator is operating without load, running at synchronous speed and the field current is increased from zero to maximum. As seen from the graph in the GUIs', the curve is almost perfectly linear until some saturation is seen at high field currents. This is because the reluctance of the motor at an unsaturated iron frame is far less than that of the air gap thereby all mmf seem to pass through the air gap. As the iron gets saturated, the reluctance increases rather slowly. The SRM design GUI as shown above shows the torque, height of rotor and stator, back iron thickness, pole width, turns per phase, aligned and unaligned inductance and the average air gap power. If the average torque generated does not give the required output, the user is required to change some inputs parameters such as the stator and rotor pole arc. This will help move the average torque closer to the required torque. When this is achieved, the motor can then be said to have been designed.

Fig. 25: SRM inductance profile result

The inductance profile is a graph of the relationship between the inductance and the rotor position. The inductance profile shows four distinct regions. For the example SRM, the motor is at a fully aligned position when its angle is 30° while 0° is when the motor is at a fully unaligned position. The inductance profile results shown are that of the unaligned inductance, aligned inductance, torque, graphical analysis of some of the performance of the motor and the intermediate position inductance. A generalised tool box for optimisation of computer aided design for electrical machines has been built successfully. The SRM design has been verified by using analytical and cyclic integration method. [START_REF] Aravind | Design of reluctance motors for low speed applications[END_REF], [START_REF] Aravind | Design of electrical apparatus[END_REF]. Others have been verified by using manual calculations. Although these machines have being designed, this may not be the optimum design because it does not put into consideration the cost of the machine, available materials to be used, human labour available, temperature rise and other constraints.

Fig. 2 :

 2 Fig. 2: Generalized machine design flowchart

Fig. 5 :

 5 Fig. 3: Transformers CS

Fig. 7 :Fig. 10 :

 710 Fig. 7: Transformer CAD INDUCTION MOTORS The design GUI for the induction motor has been divided into single phase and three phase GUI. Stator Stator Core Stator Slot

Fig. 12 :Fig. 15 :

 1215 Fig. 12: Squirrel cage IM CAD

Fig

  Fig. 17: Salient pole CAD DC MACHINE Magnetic flux Yoke Field Pole Pole shoe Commutator Armature Shaft Interpole Air gap Field winding

Fig. 19 :

 19 Fig. 19: DC machine flowchart

  The results as shown in the GUI below, shows the inductance for each flux path, the magnetic flux density assumed for that flux path and the reluctance for the flux path. FP in the figure indicates flux path while the number in front indicates the number of flux path. B indicates magnetic flux density assumed for that path and R indicates the reluctance of the motor at that path.

Fig

  Fig. 26: SRM CAD

VI. ACKNOWLEDGMENT

The authors wish to record CERVIE, UCSI University for supporting this research work.


Rozita Teymourzadeh

Mahmud Iwan

S Ahmed

J A Abueida

Ahmad J A Abueida

RFID-BASED Prepaid Power Meter

Keywords: RFID system, prepaid power meter, GSM message I

Electrical power meter is an important component in electric energy service. In the past, many consumers have complained about reading inaccurate of the electric meter. This research presents the development of an electrical power meter equipped with RFID reader. The RFID reader reads a valid RFID card and activates the power meter so that it can supply electricity. When the credit is about low or before the electricity is auto cut off, an SMS message will be sent to the user's hand phone to alert.

INTRODUCTION

Prepaid electricity power meter may not be popular in Malaysia though it has been used in many countries. It is designed for the electric customers to have control over their electric bills. In addition, an individual can use electricity on his own bill which is useful in some situations like hotel, apartment or moving house.

This research attempts to develop a prototype of a prepaid power meter employing RFID technology [START_REF] Kamran | RFID Applications: An Introductory and Exploratory Study[END_REF]. In the current RFID power meters, many have used "read" types of RFID technology to activate the meter and supply electricity to the consumers [START_REF] Lai | RFID Electrical Power Meter[END_REF][START_REF] Huang | The Read Only RFID Reader Implementation[END_REF]. One can only program the credit by a given code in the RFID card. The code cannot be changed. Therefore, to top up different credits in the RFID card, one should use different RFID cards instead of one. For example, if the user wants to top up RM 10, RM 20 and RM 30 on the RFID power meter, he has to use three cards with different credits hold. This scenario causes users having to buy more RFID cards for different amount of credits used.

There exists another type of RFID card where it can read and write the data. This type of RFID card requires a special RFID reader to operate. The RFID reader can be connected to computer using USB cable. When the RFID card placed on the reader, the data can be transferred to the computer or from the computer to the RFID card.

For convenient use of RFID electrical power meter, the read and writer type of RFID device is chosen. This kind of RFID device can help to reduce the number of RFID cards used for different credits top up. One card can be programmed to load for different amount of credit.

II. DESIGN OF THE RFID-BASED PREPAID POWER METER

The diagram of designing the electrical power meter using RFID read/write reader is shown in Figures 3 and4 Figure 3 shows the connection diagram to communicate with RFID read/write device. The implementation shown in Figure 3 is mainly for top up the credit into the RFID card. Notice that in the top up process, no microcontroller is required. The communication between the device and the computer is via a direct connection to MAX232 IC. The MAX232 regulates the voltage level between the output of the RFID read/write device and the computer. The arrows shown in Figure 3 indicate the direction flows of data. The communication between the device and the computer is in duplex or bi-direction.

Figure 4 shows the basic RFID electrical power meter designed to read the RFID card and supplies electricity to the loads.

The working principle of the RFID power meter begins from the AC 240V power source. From the block diagram, the transformer steps down the AC 240V into AC 12V. The diode connected in bridge converts 12V AC sine wave into full wave rectifier waveform. With capacitor connected at the output, the full wave rectifier waveform is converted into DC. The capacitor actually acts as filter which removes the ripple content in the DC. With voltage regulator connect across at the output of the capacitor, the DC voltage is regulated down into 5V. The 5V is then used by microcontroller, relay, MAX232 IC and LCD display.

When the RFID reader is activated or read the correct RFID card, the data from the card is transferred to the microcontroller. The microcontroller will compute the power, credit and trigger the relay so that the AC load is connected to the AC source. Both the power and credit are displayed in the LCD screen. As the credit is low, the buzzer will be activated and an SMS message will send out to the hand phone through GSM modem.

The proposed RFID power meter works very much relying on the program embedded into the microcontroller. The algorithm of C language used to detect the RFID card and activate the power meter is designed and shown in Figure 5. From the algorithm, there are two I/O ports configurations, one is for the LCD display and the other is for microcontroller. The I/O ports configuration is very important to read and write the data.

Once the microcontroller knows the I/O ports and where the data flows, the next algorithm is read the RFID card from the RFID reader. The microcontroller computes the credit deduction, displays the power and the credit, and makes decision or comparison to trigger the buzzer and the relay and GSM modem to send the SMS message. The algorithm is then repeated from the beginning when the power is cut off.

By referring to Figure 4, there is a feedback path connected at the load. This feedback is used to determine the current in the AC circuit. In other words, the feedback is actually a current sensing circuit.

For most of the digital RFID power meters, a shunt resistance method is commonly used method to determine the current. The shunt resistance will be connected in series with the load and its value is small compared to the load resistance. When the current varies, the voltage across the shunt resistor also varies. The variation of voltage gives information of the current. Figure 6 shows the shunt resistance method used as feedback system to detect the current and convert it into equivalent voltage.

From the feedback system, there is a transformer connected in shunt across the shunt resistor. The voltage drops across the shunt resistor and input to the transformer is given by [START_REF] Thomas | Electrical Technology[END_REF]:

V = IR shunt (1)
The capacitor connected at the output of the transformer is used to convert the AC voltage into DC voltage. This DC voltage is representing the current values and it has a unit of ampere per volt. The ampere meter "A" connected in the circuit is used for calibration and observes the output Vout in relation to the current. The calibration can be done by using different AC loads. The calibration will form a reference table for the programmer to refer to. The computation of power in the microcontroller can be written by:

P = 240*I ( 2
)
where I refers to the table for different values of voltage. A value of 240 is a single phase AC source and P is an active power.

Power consumption for each light bulb

III. RESULTS

Figures 7, 8, 9 and 10 show the experimental test on the RFID prepaid power meter. The circuits are constructed on the PCB and the testing was performed.

Figure 7 shows the RFID top up system, Figure 8 shows the GUI window designed to top up any values on the RFID card, Figure 9 shows the RFID power meter and Figure 10 shows the SMS received when credit is low. Table 1 shows the results of testing on the power cutoff time for the 60W, 25W and 15W light bulbs. Figure 11 shows the graphs plotted for Table I. From the experimental test results, it is seen that within 1 minute, the light bulb of 60W is cutoff first. This is because the power consumption is higher compared to 25W and 15W light bulbs. The 60W light bulb takes 30 seconds to operate whereas the 25W light bulb takes 40 seconds to operate and 15W light bulb takes 45 seconds to operate. This shows that the higher the power consumed, the faster the meter will deduct the credit. In the experiment, RM 5 Ringgit is programmed for the testing.

Figure 12 shows the current sensing results for different light bulbs in the experimental test. The observation output is the DC voltage where it is important for the microcontroller to look up the current table and identify the equivalent values. It can be seen that, the higher the load used, the more output voltage will be produced. From the graph, the connection of 60W light bulb gives 3.5V where its current is 250mA. For the 25W light bulb, the voltage produced is 2.2V and its current value is 104.2mA. The 15W light bulb gives 1.2V at the output of the current sensing circuit and its current value is 62.5mA.

IV. CONCLUSIONS

From the experimental test, it can be seen that the operation of the RFID power meter based on the amount of credit top up is successful. This will enable the users to have control over the usage of their electric energy.

As additional feature, when the credit is about to finish, the RFID power meter will alert the users via his GSM hand phone. The electricity power supply will be cut automatically when the credit is finished.

  .

Figure 3 .

 3 Figure 3. Connection or top up the credit in the RFID card [4].

Figure 4 .

 4 Figure 4. Basic RFID electrical power meter circuit design [2].

Figure 5 .

 5 Figure 5. System algorithm design for the microcontroller work in the RFID power meter.

Figure 6 .

 6 Figure 6. The feedback system to determine the current.

Figure 7 .

 7 Figure 7. The RFID top up circuit

Figure 9 .

 9 Figure 9. Test the RFID Power Meter circuit on the PCB.

Figure 10 .

 10 Figure 10. The SMS message received about low credit.

Figure 11 .

 11 Figure 11. The operation of 60W light bulb compared to 25W, 15W light bulb

TABLE I .

 I EXPERIMENTAL TEST ON LIGHT BULBS UNDER RFID POWER METER CONTROL

Time (s) Power consumption testing on three different light bulbs Light bulb1 Light bulb 2 Light bulb 3

	5	57	14	24
	10	57	14	24
	15	57	14	24
	20	57	14	24
	25	57	14	24
	30	57	14	24
	35	0	14	24
	40	0	14	24
	45	0	14	0
	50	0	0	0
	55

TABLE II

 II

	VOLTAGE REPRESENTING THE CURRENT FOR
	DIFFERENT LIGHT BULBS
	Voltage representing the current
	60W light bulb	25W light bulb	15W light bulb
	3.5	2.2	1.2
	Figure 12. The plot for Table II.


CEng, Member IEEE/IET Rozita Teymourzadeh
email: rozita@ucsiuniversity.edu.my

Addin Salah

Ahmed

Wai Kok

Mok Vee Chan

Hoong

Smart GSM Based Home Automation System

Keywords: Home automation, Global System for Mobile Communication (GSM), Short Message Service (SMS), PIC microcontroller, RS232 standard I

This research work investigates the potential of 'Full Home Control', which is the aim of the Home Automation Systems in near future. The analysis and implementation of the home automation technology using Global System for Mobile Communication (GSM) modem to control home appliances such as light, conditional system, and security system via Short Message Service (SMS) text messages is presented in this paper. The proposed research work is focused on functionality of the GSM protocol, which allows the user to control the target system away from residential using the frequency bandwidths. The concept of serial communication and AT-commands has been applied towards development of the smart GSM-based home automation system. Home owners will be able to receive feedback status of any home appliances under control whether switched on or off remotely from their mobile phones. PIC16F887 microcontroller with the integration of GSM provides the smart automated house system with the desired baud rate of 9600 bps. The proposed prototype of GSM based home automation system was implemented and tested with maximum of four loads and shows the accuracy of ≥98%.

INTRODUCTION

In recent years, there has been a growing interest among consumers in the smart home concept [START_REF] Ahmad | Remote Home Management: An alternative for working at home while away[END_REF]. Smart homes contain multiple, connected devices such as home entertainment consoles, security systems, lighting, access control systems and surveillance. Intelligent home automation system is incorporated into smart homes to provide comfort, convenience, and security to home owners [START_REF] Ahmad | Implementation of ZigBee-GSM based Home Security Monitoring and Remote Control system[END_REF][START_REF] Begum | Design and development of activation and monitoring of home automation system via SMS through microcontroller[END_REF][START_REF] Zhai | Design of smart home remote monitoring system based on embedded system[END_REF]. Home automation system represents and reports the status of the connected devices in an intuitive, user-friendly interface allowing the user to interact and control various devices with the touch of a few buttons. Some of the major communication technologies used by today's home automation system [START_REF] Azid | Analysis and Performance of a Low Cost SMS Based Home Security System[END_REF][START_REF] Elkamchouchi | Design and prototype implementation of SMS based home automation system[END_REF][START_REF] Khandare | Mobile Monitoring System for Smart Home[END_REF] include Bluetooth, WiMAX and Wireless LAN (Wi-Fi), Zigbee, and Global System for Mobile Communication (GSM).

All GSM is one of the most widely used cellular technologies in the world [START_REF] Gu | The survey of GSM wireless communication system[END_REF][START_REF] Mingming | The System of Wireless Smart House Based on GSM and ZigBee[END_REF]. With the increase in the number of GSM subscribers, research and development [START_REF] Felix | Home automation using GSM[END_REF][START_REF] Peijiang | Design and Implementation of Remote Monitoring System Based on GSM[END_REF][START_REF] Rao | A prototype for Home Automation using GSM technology[END_REF] is heavily supported in further investigating the GSM implementation. In 2009, Das, Sanaullah, et. al. [START_REF] Das | Development of a Cell Phone based Remote Control System: an Effective Switching System for Controlling Home and Office Appliances[END_REF] developed a cell phone based remote management and control system for home appliances. However, a few limitations for the system include not being able to control multiple appliances concurrently and the home automations system could not verify the status of the appliances. ElKamchouchi and ElShafee [START_REF] Elkamchouchi | Design and prototype implementation of SMS based home automation system[END_REF] presented the design and prototype implementation of basic home automation system based on SMS technology using AT89C55 Atmel microcontroller. The microcontroller acts as the bridge between the GSM network and sensors of the home automation system. Further researches have been conducted to analyze the performance of other home automation control system [START_REF] Gill | A zigbeebased home automation system[END_REF][START_REF] Pu | An Improved Short Message Security Protocol for Home Network[END_REF][START_REF] Perumal | Development of an Embedded Smart Home Management Scheme[END_REF]. Internet and wireless communications have also been utilized in parallel with GSM for home automations [START_REF] Wei | The Design of Intelligent Household Control System Based on Internet and GSM[END_REF].

Among the cellular technologies, GSM network is preferred for the communication between the home appliances and the user due to its wide spread coverage [START_REF] Gu | The survey of GSM wireless communication system[END_REF][START_REF] Mingming | The System of Wireless Smart House Based on GSM and ZigBee[END_REF] which makes the whole system online for almost all the time. Another advantage of using the GSM network in home automation is its high security infrastructure, which provides maximum reliability whereby other people cannot monitor the information sent or received. Hence, this research work implements SMS based control for home appliances using the GSM architecture without accessing the local network.

II. SYSTEM REALIZATION

The design of our proposed smart GSM-based home automation system is given in Fig. 1. The architecture consists of mobile phone and GSM modem. In the proposed system design, incoming SMS message is sent from the user phone to the GSM modem as a text message via cellular network. The GSM modem then sends the commands in text mode to the PIC microcontroller using an RS232 interface. The RS232 voltage levels are at ±12V whereas both the microcontroller input and output operates at 0V to +5V. Since RS232 is not compatible with microcontroller, MAX232 is utilized to enable the communication between both the GSM modem and PIC microcontroller by converting RS232 level signals to TTL level signal. Outgoing message from the system containing the home appliances status is delivered to the mobile phone through GSM modem. In the proposed research work, the microcontroller receives instructions and decodes them to give device address and command, then sends corresponding signals to the driver of the power circuit. In addition, the microcontroller ensures dual independent operation action to turn on the device or switch it off. A feedback status of any devices under control whether switched on or off will be provided by the microcontroller.

The RS-232 interface standard defines the electrical and mechanical details of the interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE), which employ serial binary data interchange. The current version of the standard refers to DCE as Data Circuit terminating Equipment. Physically, interfacing between the PIC16F887 and GSM modem was implemented using RS232 standard installed on Max232.

Since the system design has not included a battery, an external power supply is connected to the system to drive sufficient amount of current through the circuit connections. Relays had been connected to the output loads for a stable electrical control because these relays can provide feeding for different voltage level loads. Hence, the output selection becomes easier at any voltage.

Fig. 2 demonstrates the simulation of the proposed GSM based home automation system being implemented in several stages. The PIC16F887 was simulated with the GSM modem by connecting it to the physical ports on the PC. MAX232 was placed to ensure proper transmission of data between the two terminals. Virtual terminal monitors the text sent from, and to the PIC16F887 while checking the transmission process and testing the algorithm. The waveform of the transmitted and received messages is monitored from the oscilloscope. While simulating the GSM modem, the "COMPIM" clock physically tests the response of the GSM modem by connecting it to a physical port on PC.

III. IMPLEMENTATION

As shown in Fig. 3, waveform is generated in the digital oscilloscope when the command is transmitted from PIC16F887 to GSM modem. This command will execute the deletion of the first message from the SIM card memory. The program reaches to a sleep state waiting for the new incoming text messages and then compares the text message with the stored commands. If both the received text message and the stored commands match, then, it will execute the intended command, which is turning on or off the output terminal. A simulation result was performed to observe the response while communicating with the GSM modem. The AT command was sent from PIC16F887 to the GSM modem as the program starts up, then the response is received from the GSM modem after very short period of time that does not exceed 500 microseconds which is fast enough to detect the incoming message from the modem. The display was used to show when the PIC is transmitting the signal.

From Fig. 4, the PIC16F887 serves as a transmitter initially and then, it receives the response from modem. The duration between the text sent and response received is less than 500 microseconds. Hence, the delay time is ignored because the data sent are limited to certain commands that do not exceed 4 or 5 characters. However, if the amount of data transferred is very huge, the response delay time is very critical and must be studied and analyzed in detail. Furthermore, the delay that must be controlled for this project is for GSM communication that is mostly governed by the SMS protocol and does not exceed 2 or 3 seconds as had been tested practically. A layout is designed using Proteus ISIS Professional, while adding Virtual Terminal and connecting it to COMPIM, which is physically the DB9 connector in the PC terminal. It can be added from the library as shown in Fig. 5. The message alert text indicates that the message has been successfully received and stored in the SIM card in the memory location. The oscilloscope is connected to the receiver side (RX) on PIC16F887 microcontroller that is connected to GSM modem to display the waveform of the detected message as soon as it reaches the GSM memory. After detecting the message, the PIC16F887 is supposed to read and decode the incoming message to execute the intended command, which is turning on the loads. The whole process is being executed within short period of time that does not exceed 2 seconds. Fig. 6 shows the command text message had been sent to activate connected loads at the same time.

After receiving the command to turn on the lights, the relay set will perform switching operation from normally opened to close the circuit, allowing the current to start lighting as illustrated in Fig. 6.

IV. RESULTS AND DISCUSSIONS

The Baud Rate Generator (BRG) is an 8-bit or 16-bit timer that is dedicated to the support of both asynchronous and synchronous EUSART operation. By default, the BRG operates in 8-bit mode. For the PIC16F887 with frequency of oscillator (FOSC) of 20MHz, desired baud rate of 9600 bps, asynchronous mode, and 8-bit BRG, (1) will yield a baud rate of 9470 bps and an error of -1.35% illustrated in Fig. 7. The prototype of the proposed GSM based home automation system is shown in Fig. 8. A 12V is supplied to the voltage regulator to power the circuit. MAX232 is connected to the GSM modem and the system run smoothly after the text message was received. The output loads were activated and automated the house in desirable basis.

Calculated Baud Rate = FOSC 64([SPBRGH : SPBRG]+1) (1)

V. CONCLUSION

Recently, the home automation market is very promising field that is growing very fast and needs vast range of developments that can be carried out in the concept of smart home. In this project design and implementation of smart GSM house was considered. PIC16F887 microcontroller with the cooperation of GSM provides the smart automated house system with the desired baud rate of 9600 bps. The proposed prototype was implemented and tested with maximum of four loads and shows the accuracy of ≥98%.

Fig. 1 .

 1 Fig. 1. Stage Realization. The 8-bit PIC16F887 microcontroller generally consists of timers, Analog to Digital Converters (ADCs), and Universal Synchronous Asynchronous Receiver Transmitter (USART).In the proposed research work, the microcontroller receives instructions and decodes them to give device address and command, then sends corresponding signals to the driver of the power circuit. In addition, the microcontroller ensures dual independent operation action to turn on the device or switch it off. A feedback status of any devices under control whether switched on or off will be provided by the microcontroller.The RS-232 interface standard defines the electrical and mechanical details of the interface between Data Terminal Equipment (DTE) and Data Communications Equipment (DCE), which employ serial binary data interchange. The current version of the standard refers to DCE as Data Circuit terminating Equipment. Physically, interfacing between the PIC16F887 and GSM modem was implemented using RS232 standard installed on Max232.Since the system design has not included a battery, an external power supply is connected to the system to drive sufficient amount of current through the circuit connections. Relays had been connected to the output loads for a stable electrical control because these relays can provide feeding for different voltage level loads. Hence, the output selection becomes easier at any voltage.Fig.2demonstrates the simulation of the proposed GSM based home automation system being implemented in several stages. The PIC16F887 was simulated with the GSM modem by connecting it to the physical ports on the PC. MAX232 was placed to ensure proper transmission of data between the two terminals. Virtual terminal monitors the text sent from, and to the PIC16F887 while checking the transmission process and testing the algorithm. The waveform of the transmitted and received messages is monitored from the oscilloscope. While simulating the GSM modem, the "COMPIM" clock physically tests the response of the GSM modem by connecting it to a physical port on PC.

Fig. 2 .

 2 Fig. 2. Simulation of the proposed GSM based home automation system.

Fig. 3 .

 3 Fig. 3. AT+CMGD=1 command to delete SMS message.

Fig. 4 .

 4 Fig. 4. Waveform of transceiver text message.

Fig. 5 .

 5 Fig. 5. Detection of incoming SMS from GSM modem.

Fig. 6 .

 6 Fig. 6. All loads switched on when text commands sent via SMS.

Fig. 7 .

 7 Fig. 7. Baud rate specification.

Fig. 8 .

 8 Fig. 8. Prototype of proposed GSM based home automation system.


Memtode Rozita Teymourzadeh
email: rozita_teymourzadeh@yahoo.com

Jim Abigo

Vee Mok

Hoong

Jalan Choo

Lip Kung

Static Quantized Radix-2 FFT/IFFT Processor for Constraints Analysis

Keywords: Static Quantized Radix-2 FFT/IFFT Processor for Constraints Analysis DFT, IDFT, FFT, IFFT, quantized, floating-point, DSP

This research work focuses on the design of a high-resolution fast Fourier transform (FFT) /inverse fast Fourier transform (IFFT) processors for constraints analysis purpose. Amongst the major setbacks associated with such high resolution, FFT processors are the high power consumption resulting from the structural complexity and computational inefficiency of floating-point calculations. As such, a parallel pipelined architecture was proposed to statically scale the resolution of the processor to suite adequate trade-off constraints. The quantization was applied to provide an approximation to address the finite word-length constraints of digital signal processing (DSP). An optimum operating mode was proposed, based on the signal-to-quantization-noise ratio (SQNR) as well as the statistical theory of quantization, to minimize the tradeoff issues associated with selecting the most application-efficient floating-point processing capability in contrast to their resolution quality.

Introduction

Discrete Fourier Transform (DFT) is amongst the most fundamental operations in digital signal processing. However, the widespread uses of DFTs make its computational requirements an important issue. The direct computation of the DFT requires approximately N 2 operations where N is the transform size. The breakthrough of Cooley-Tukey (CT) FFT comes from the fact that it reduces the complexity to an order of Nlog2N operations. The FFT is therefore an efficient algorithm to compute the DFT and its inverse (IDFT). It has several applications in the field of signal processing including the real-time processing of wireless time-domain and frequency-domain signals especially for use in Orthogonal Frequency Division Multiplexing (OFDM) systems such as Digital Video Broadcasting (DVB), Digital Subscriber Line (xDSL) and WiMAX (IEEE 802. [START_REF]IEEE Standard for binary floating-point nithmetic[END_REF]) [START_REF] Meletis | High Speed Pipeline Implementation of Radix-2 DIF Algorithm[END_REF][START_REF] Curtis | High Performance Digital Signal Processing[END_REF][START_REF] Ismail | VLSI Implementation and Performance Analysis of Efficient Mixed-Radix 8-2 FFT Algorithm with Bit Reversal for the Output Sequences[END_REF][START_REF] Diaz De Cerio | Efficient FFT on Torus Multicomputers: A Performance Study[END_REF]. These applications require large-point FFT processing, such as 1024/2048/8192-point, FFTs for multiple carrier modulation.

Many FFT algorithms based on the CT decomposition such as radix-2 2 , radix-2 3 , radix-4, radix-(4+2), prime-factor as well as split-radix algorithms, have been proposed using the complex mathematical relationship to reduce the hardware complexity. The computational complexity and the hardware requirements are greatly dependent on the algorithm in use [START_REF] Curtis | High Performance Digital Signal Processing[END_REF]. The conventional parallel architecture poses issues related to hardware cost, complexity, power consumption and is not easily flexible to meet other design constraints. As such, different architectures to efficiently map the different FFT algorithms to hardware have been proposed [START_REF] Ismail | VLSI Implementation and Performance Analysis of Efficient Mixed-Radix 8-2 FFT Algorithm with Bit Reversal for the Output Sequences[END_REF].

A first approach for these implementations concerns time non-critical applications and has small hardware requirements, but it needs a significantly large number of clock cycles to compute a full FFT. For example, in [START_REF] Diaz De Cerio | Efficient FFT on Torus Multicomputers: A Performance Study[END_REF] one butterfly unit is used for all computations and N+N.log2N clock cycles are required for the computation of the FFT. A second implementation approach is for speed demanding applications, where one butterfly unit is used for each decimation stage of a radix-2 FFT [START_REF] Su | A Grouped Fast Fourier Transform Algorithm Design for Selective Transformed Outputs[END_REF].

A pipeline architecture based on the constant geometry radix-2 FFT algorithm, which uses log2N complex-number multipliers (more precisely butterfly units) and is capable of computing a full N-point FFT in N/2 clock cycles has been proposed in 2009 [START_REF] Saeed | Efficient FPGA Implementation of FFT/IFFT Processor[END_REF]. However, this architecture requires a large amount of delay elements (memory size of N.log2N samples) and a quite complicated switching mechanism for the routing of the data. This commonly used pipeline architecture is characterized by continuous processing of input data as well as being highly regular, making it straight forward to automatically generate FFTs of various lengths [START_REF] Kollar | Bias of Mean Value and Mean Square Value Measurements Based on Quantized Data[END_REF]. All these developments have introduced their own disadvantages, in addition to the age-long finite word-length effects of digital circuitry [START_REF] Greene | A Parallel 64K Complex FFT Algorithm for the IBM/Son/Toshiba Cell Broadband Engine Processor[END_REF][START_REF] Saeed | Efficient FPGA Implementation of FFT/IFFT Processor[END_REF][START_REF] Satorius | Finite Word length Implementation of a Megachannel Digital Spectrum Analyzer[END_REF]. This paper thus, uses the pipeline architecture [START_REF] Meletis | High Speed Pipeline Implementation of Radix-2 DIF Algorithm[END_REF], [START_REF] Curtis | High Performance Digital Signal Processing[END_REF] to propose a model for the analysis of important design constraints like the finite wordlength effects and amount of resolution needed to achieve the appropriate SNR [START_REF] Saeed | Efficient FPGA Implementation of FFT/IFFT Processor[END_REF][START_REF] Satorius | Finite Word length Implementation of a Megachannel Digital Spectrum Analyzer[END_REF][START_REF] Pel-Yun | Automatic IP Generation of FFT/IFFT Processors with Word-Length Optimization for MIMO-OFDM Systems[END_REF] for the desired design needs using the statistical tools for the analysis of a range of feasible resolution.

Design Architecture

A. Algorithm development of the decimation-in-time (DIT) radix-p FFT

The DFT of an N-point sequence x[n] is given by: For k = 0, 1, 2,...,N-1 [START_REF] Meletis | High Speed Pipeline Implementation of Radix-2 DIF Algorithm[END_REF] Where .

Consider the general formula of the DIT radix-p FFT as follows:

(2) for k = 0,1,2,…,N/p-1 and r = 0,1,2,…,p-1. Using the above decomposition, the DFT can be reduced successively to N/p p-point DFTs. In general, this process can be repeated m times and therefore there are totally m stages in the implementation of the DFT.

B. Parallel Architecture

The computational structure of a butterfly unit is shown in Figure 1. It is the fundamental computational of the parallel architecture.

) (k x e k N W ) ( ) ( ) ( k X W k X k X o k N e   ) ( ) ( ) 2 / ( k X W k X N k X o k N e    1  ) (k x o + + Figure 1. Radix-2 butterfly unit
The butterfly unit requires a complex multiply and two complex additions.

Therefore, it takes a total of (N/2) Log2N complex multiplies and Nlog2N complex additions to compute all N-point DFT samples. An 8-point Radix-2 DIT FFT requires N/2 butterfly units per stage for all m stages. The input bit-reversed and inter-stage index routing gets even more complicated as the size of the unit N increases.

For larger butterflies (N > 26), the processor becomes extremely complex and slow. Hence, a simpler and faster architecture is then required. Therefore, the proposed system was designed and simulated to reduce the system complexity by using control signals. Figure 2, shows the overall pipelined system structure and its designed control signals.

C. Pipeline Architecture

The same butterfly unit can perform the N/2 butterfly operations computed in every stage sequentially. Since the two inputs of a next butterfly unit of a stage are provided from the output of the butterfly unit of the previous stage at different time points, a shuffling unit is inserted between two successive butterfly units in order to route these outputs to the corresponding inputs of the next stage. Figure 3 shows the inner layer of proposed FFT processor design. The IFFT computation uses the same fundamental Radix-2 DIT Butterfly unit.

However, the input is scaled by the factor of N (1024). These discrete input values are then sent through the processor stage, which performs the same operation except that the conjugate of the twiddle factors are used instead. The output stage simply compares the results of the proposed FFT/IFFT Processor with the idle FFT/IFFT processor and their difference is observed as system error that will be analysed in the next chapter.

Statistical Theory of Quantization

A. Uniform Quantization

One would expect that quantization has a similar effect on functions of the amplitude as sampling has on functions of time. Quantization is an operation on signals that is represented as a "staircase" function. The probability of each discrete output level equals the probability of the input signal occurring within the associated quantum band.

For example, the probability that the output signal has the value zero equals the probability that the input signal falls between , where q is the quantization box size [START_REF] Saeed | Efficient FPGA Implementation of FFT/IFFT Processor[END_REF]. Figure 6 shows the model of quantizing Figure 6. Uniform Quantize Model

The quantize error (h) is given as

h = x -Q(x) (3)
If x and h are real, with probability density function (PDF) as Px(.), then the quantization error variance is

(4) (5) ( 6
)
where q is the quantization interval, b is the number of bits. Quantization noise is defined as the difference between the output and input of the quantizer.

Since the quantized unit is designed in the proposed processor to enhance the calculations, Figure 7 illustrates a plot of the error versus the number of bits for the uniform quantizer, while Figure 8 shows a comparison of the mean, standard deviation

Q x Q(x)
as well as variance of the uniform quantization model achieved by the proposed FFT Processor. The probability of getting a given error value is the sum of probabilities of all the quantization boxes. The uniform quantize model performs uniform quantization on the signal input and thus, a linear signal is required at the input. Fixed-point numbers are considered linear since the Radix point remains fixed. However, this research was focused on floating-point numbers hence; the response of the uniform quantize to floating point input was observed. As result, the quantization noise was increased. Equation ( 6) gives an expression for the SNR of the quantizer using the ratio of the variances of the input to noise.

B. Non-Uniform Quantization

The uniform quantization model is usually not used for floating-point quantization due to the overall non-uniform characteristic of the latter. Quantization of floating-point numbers is carried out only on the mantissa hence; it is more relevant to consider the relative error ε caused by the quantization process. The relative error defined in terms of the numerical values of the quantized floating-point number Q(x) = 2 e Q(M) and the unquantized number x = 2 e M is given as [START_REF] Greene | A Parallel 64K Complex FFT Algorithm for the IBM/Son/Toshiba Cell Broadband Engine Processor[END_REF] It is possible however, to represent the floating-point quantizer using a combination of a compressor, a uniform quantizer and an expander. Figure 9 shows the non-uniform quantized model. An expression for the variance is shown in equation [START_REF] Saeed | Efficient FPGA Implementation of FFT/IFFT Processor[END_REF]. The variance from the floating-point quantization equals half that obtained from the uniform quantization which is a generally preferred characteristic. Figure 10 determines that the stability of the processor performance such that no variation occurs when the number of bits is 7 bit, unlike that of the uniform quantization which attains this stability at bit position eight 8, as shown in Figure 7. That is the advantage of the system while modelling the floating-point structure. In addition, bit position 2 of Figure 10 gives minimum swing before stability, contrary to that of Figure 7, which occurs at bit position 3. This minimum swing gives a false minimum error position and is used for less sensitive applications in which minimum error is not important. Figure 11 illustrates the comparison between mean, standard deviation when number of bit increased.

Discussion

Statistical parameters like the mean, standard deviation and variance were used to analytically develop expressions for the variation in error as a function of the quantization interval. These parameters were also known to have relationships with the SQNR. The percentage error of the non-uniform quantization generally decreased with an increase in the quantizer interval. As such, the SQNR is increased with respect to the quantization step size. The same general trend was observed in the uniform quantization, as well as the FFT and IFFT results. Figure 12 shows the error variation when the bit resolution increased.

Figure 12. Error variation of the FFT processor

The general trend observed from the results indicates that the measured dispersion can only be valuable when they are used alongside the mean since the mean actually provides the benchmark for understanding the decreasing trend. Figure 13 shows the mean standard deviation and variance when the number of bit increased. Therefore, the variance is decreased as quantization interval increased. Hence, the variance is inversely proportional to the percentage error, and as such, inversely proportional to the SQNR. This provides experimental proof to the theoretical models given earlier and provides a benchmark for the trade-off between the SQNR and the resolution. In other words, bit number increasing has significant effect on resolution improvement. As shown in Figure 14 the error variation also decreased as bit resolution increased. In addition, it proves that higher number of data point in FFT processor will leads to have high accuracy spectrum measurement.

Conclusion

The percentage error and all the measured dispersion were found to decrease as the bitresolution increased. This shows how the SQNR improves with bit-resolution. Although the power requirement for such SQNR systems are high, the proposed architecture provides an ease in the trade-off decision between the SQNR, power requirement and bit-resolution of the Radix-2 FFT/IFFT processor.

Figure 2 .

 2 Figure 2. Proposed over view of pipelined system algorithm

Figure 3 .Figure 4 .

 34 Figure 3. Proposed inner layer of FFT/IFFT ProcessorThe signal input is inserted at the control signal to program the processor

Figure 7 .

 7 Figure 7. Error of the Uniform Quantization

Figure 8 .

 8 Figure 8. Measured dispersion of uniform quantizer

Figure 9 .

 9 Figure 9. Non-uniform quantization model

Figure 10 .

 10 Figure 10. Error variance of the non-uniform quantized model

Figure 11 .

 11 Figure 11. Comparison of the measured dispersion of non-uniform quantization

Figure 13 .

 13 Figure 13. Measured dispersion of FFT/IFFT processor

Figure 14 .

 14 Figure 14. Error variation of IFFT processor


Rozita Teymourzadeh
email: rozita@ucsiuniversity.edu.my

Ahmed J A Abueida

Wai Kok

Mahmud Chan

S Iwan

Hoong Vee

Mok

Advanced Frequency Identification Power Metering System for Energy Usage

Keywords: Prepaid power meter, Global System for Mobile Communication (GSM) network, Short Message Service (SMS), Radio-frequency identification (RFID), PIC microcontroller I

Energy meter measures the amount of power consumed by electrical loads in residential, industrial and commercial applications. In this project, the focus goes to the implementation of a smart power measurement system to allocate identification for individuals and determine the client's energy usage. The incorporation of two PIC 16F877A microcontrollers and radio-frequency identification (RFID) reader in this research work make the system operation smooth and reliable. This paper presents the development of an intelligent prepaid power metering system enabling power utilities to collect electricity bills from consumers prior to the usage of power. Home owners are able to monitor reliable power consumption data for efficient power management. To conclude, a graphical user interface (GUI) has been designed to be applied for data transmission between the personal computer and RFID smart card which allows the credit to be transferred to the smart card.

INTRODUCTION

Recent hikes in home energy costs across many countries has led to the increase in global energy awareness among home owners. The smart prepayment metering system becomes the economical substitution to the conventional electromechanical meters for efficient utilization of energy. While enabling home owners to constantly monitor energy consumption data at a desired time interval, the prepaid power metering system facilitates a flexible and accurate billing scheme for electrical power usages. Along with the integration of an intelligent home automation system [START_REF] Teymourzadeh | Smart GSM based Home Automation System[END_REF][START_REF] Ahmad | Smart metering and home automation solutions for the next decade[END_REF], home owners can adjust their electricity consumption behavior by opting to switch off selected appliances remotely during peak periods. The smart prepaid electricity metering system is capable to detect and deter power theft issues which include tampering and modifying of conventional electromechanical meters resulting in lower reading on the meter. In view of the growth in global energy demand, research and development in the electrical field today has been concentrated on the development of innovative metering technologies.

Research work has been conducted in [START_REF] Kwan | PIC based smart card prepayment system[END_REF] utilizing Microsoft Visual Basic 6.0 in developing a user interface program to issue smart card ID and increase the credit in the customers' card used for the prepaid electricity metering system. ZigBee and GPRS technologies have been proposed in [START_REF] Li | Design of remote automatic meter reading system based on ZigBee and GPRS[END_REF] for the design of the wireless remote household metering system. Dang et al. [START_REF] Dang | Design of prepayment implementation and its data exchange security protection based on Power Metering Automatic system[END_REF] explored the implementation of the power metering automatic system, while addressing the complexity of the GPRS/CDMA communication channel to ensure data exchange security and stability of prepaid functions. RFID has been integrated into the power meter and outage recording system in [START_REF] Shun-Yu | Design and implementation of a RFID-based power meter and outage recording system[END_REF]. M. Wasi-ur-Rahman et al. in [START_REF] Wasi-Ur-Rahman | Design of an intelligent SMS based remote metering system[END_REF] proposed a SMS based remote metering system that utilizes GSM networks amongst many other research works [START_REF] Bo | The Design and Realization of Acquisition Equipment in Remote Reading System Base on Low Voltage Power Line Carrier[END_REF][START_REF] Li | Remote power management and meter-reading system based on ARM microprocessor[END_REF][START_REF] Zheng | Design and Implementation of Remote Meter Reading System[END_REF][START_REF] Zongming | Database design of GPRS-oriented remote meter reading system[END_REF]. Survey results from a user study about the implementation of a digital feedback system along with a prepaid electricity metering system in a Chinese university dormitory in China have been collected and recently published [START_REF] Liu | The Collective Infrastructural Work of Electricity: Exploring Feedback in a Prepaid University Dorm in China[END_REF].

II. DESCRIPTION

Top-up circuitry based package plays a significant role in the frequency identification system in this project. The top-up circuitry consists of DC power supply, regulator, RFID writer/reader module, and serial port. In proposed design, the operation management of the circuitry system takes place internally. In the operation of the RFID top-up system, the RFID reader first detects the RFID card signal and determine the validity of the card. The top-up operation can be achieved by the interfacing between the top-up circuitry and user personal computer (PC) via USB RS232 using the graphical user interface (GUI) window.

The RFID reader/writer module operates at TTL logic level whereas the serial communication in PC works on RS232 standard (±25V). Since the RS232 serial communication in a computer is not compatible with the RFID reader/writer module, MAX232 is utilized to enable the duplex communication between them by converting TTL logic levels to RS232 logic levels. The source of the power for the RFID top-up circuitry is from the DC power supply. The DC power supply will supply 7V to 15V DC to the RFID top-up circuitry. The regulator in the RFID top-up circuitry converts the input DC voltage to +5V. This output voltage will be used as the power supply for MAX232 and the RFID reader/writer device. Fig. 1 shows the fundamental system operation of the RFID based top-up circuitry at a glance. The RFID top-up circuitry is incorporated in the proposed intelligent prepaid power metering system, as illustrated in Fig. 2. Two 8-bit PIC16F877A microcontrollers have been chosen to be integrated with the prepaid electricity metering system for high efficiency usage. The program stored inside the microcontroller contains the protocol for accessing various hardware peripherals such as LCD, relay, GSM module, and etc. The microcontroller is essential in determining the credit balance from the communication between the RFID card and RFID reader, triggering the relay to turn ON the loads, and displaying the credit balance along with consumed power in the LCD display. Another PIC microcontroller is embedded in the prototype of the proposed RFID prepaid power meter which is responsible to send 5V to trigger the GSM modem in sending Short Message System (SMS) text messages as well as produce alert sound from the buzzer when the credit is low. The text messages sent to mobile phones contain feedback status indicating low credit for the prepaid power meter. Failing to transfer credits into the RFID card by consumers upon the credit reaching zero will lead to relays cutting off the supply of electricity. Once the home owners have increased credits in the RFID card using the developed credit top-up graphical user interface, the relay connects home automation and resumes the electrical supply. Once both the I/O ports and the direction of data flow have been determined, the RFID card is read from the RFID reader.

The RFID reader transmits an encoded radio signal to interrogate and validate the card. With the validated RFID card, the PIC microcontroller then computes the credit deduction and displays both power usage and credit. Due to the uniqueness of the RFID smart card, the credits will not be transferred to the card if a different RFID card is used. The algorithm is then restarted when the power is turned off. Fig. 4 demonstrates the simulation of the proposed RFID based prepaid power metering system being implemented using Proteus. A 16x2 character LCD is used to display the remaining credit and total power consumed in this proposed prepaid power meter for the ease of monitoring by home owners. Both RFID reader/writer module and RFID card are not simulated with the proposed RFID based prepaid power metering system. Hence, the value of credit balance and consumed power displayed on the LCD display during simulation are respectively zero. A feedback path is connected at the load as a current sensing circuit using resistive shunt. Commonly applied in the RFID power meter, the resistive shunt is simply a resistor placed in series with the load. A voltage is developed across the shunt that is directly proportional to the current flowing through the load. A capacitor connected to the output of the step-down transformer converts the alternating current (AC) voltage to the direct current (DC) voltage as illustrated in Fig. 5. Ammeter connected in the circuit is used for the purpose of calibration to observe the output V out in relation to the current when calibrated using different AC loads. The waveform simulation result of the top-up circuitry using Proteus software is illustrated in Fig. 6. A series of pulse generator has been used as an alternative to the RFID writer during simulation to test the operation of the circuit. The simulated waveform resembles an amplitude-shift keying (ASK) signal. The digital signal modulates on the carrier generated by MAX232. The amplitude of the carrier changes with respect to the amplitude of the digital signal. Hence, under magnification, the ASK signal is a sinusoidal waveform. The RFID top-up system is a GUI program developed for the user to increase the credit inside the validated consumer smart card for the prepayment power metering system as shown in Fig. 7. Microsoft Visual Basic 2008 is used as the tool to write the programs for communication between the personal computer and the smart card. COM port 1 has been utilized for the RFID credit top-up program.

In the graphical user interface, it displays the buttons for the user to step-by-step select the actions required to increase the credits on the RFID card. The top-up steps include RFID writer activation, RFID card authentication, reading of the current credit balance on the RFID card, and RFID credit topup. The current status of the credit top-up process is displayed on the GUI terminal. The RFID interface allows the measured power consumption data to be stored temporarily in the RFID smart card and transferred to the credit top-up graphical user interface. With the RFID smart card authenticated, an amount of credit can then be loaded by the user onto the smart card. User is notified about the success of the credit top-up process. The remaining credits inside the smart card after being increased will then be shown on the 16x2 character LCD. Fig. 8 shows that the remaining credit balance on the smart card is RM 5 upon the successful credit top-up process. Experiment tests were conducted on the operations of the RFID power metering system using different light bulbs and the results were tabled in Table 1. From the experimental test results, it is seen that within 1 minute, the light bulb rated 60 Watts has turned off. This is due to the higher power consumption by the 60W light bulb as compared to the power consumption by 25W and 15W light bulbs respectively. From this experiment test, it can be deduced that higher power consumption will lead to faster credit deduction from the power meter. The experiment was conducted on the proposed power metering system with the credit balance in Fig. 9. As the remaining credit continues to be deducted, total power consumption by electrical loads is displayed from the LCD display for the ease of energy monitoring whilst the remaining credit drops to RM 1 (Fig. 10). The PIC microcontroller then sends 5V to trigger the GSM modem which then sends text messages to home owners indicating that the credit for the power meter system is running low (Fig. 11). The delay of receiving the text message, as had been tested practically [START_REF] Teymourzadeh | Smart GSM based Home Automation System[END_REF], does not exceed 2 or 3 seconds due to GSM communication that is mostly governed by the SMS protocol. Concurrently, the alert sound from the buzzer will also be triggered to ensure that the users are aware that the electrical power will be cut off if credit has yet to be increased. V. CONCLUSION A RFID based power metering system which includes the credit top-up circuitry has been designed and implemented. The proposed power metering system enables consumers to monitor power consumption data at a desired time interval. With accurate power consumption data, home owners will be able to gain control on daily home energy usage. Experimental tests conducted on the power metering system has shown that the developed graphical user interface ensures consumers pay for their utility bill in a timely manner to prevent the electricity bill to prevent the electrical supply from being cut. With the security uniqueness of the RFID card, this proposed advanced frequency power metering system will be able to deter power theft issues.

Figure 1 .

 1 Figure 1. RFID top-up circuitry.

Figure 2 .

 2 Figure 2. Prototype of the proposed RFID prepaid power meter.

Figure 3 .

 3 Figure 3. RFID prepaid metering algorithm flowchart.

Figure 4 .

 4 Figure 4. Simulation of the proposed RFID based prepaid metering system.

Figure 5 .

 5 Figure 5. Current sensing feedback path.

Figure 6 .

 6 Figure 6. ASK signal generated during simulation of RFID top-up circuitry.

Figure 7 .

 7 Figure 7. Test run on proposed RFID based prepaid metering system.

Figure 8 .

 8 Figure 8. Credit top-up for RFID prepaid meter.

Figure 9 .

 9 Figure 9. Deduction of credits for RFID prepaid meter.

Figure 10 .

 10 Figure 10. Power metering system behaviour during low credit.

Figure 11 .

 11 Figure 11. SMS notification of low credit for RFID prepaid meter.

Table 1 .

 1 Experimental power consumption test on RFID power meter under different light bulbs.

	Time (s)	Power Consumption (in Watts) Light bulb 1 Light bulb 2 Light bulb 3
	5	57	24	14
	10	57	24	14
	15	57	24	14
	20	57	24	14
	25	57	24	14
	30	57	24	14
	35	0	24	14
	40	0	24	14
	45	0	0	14
	50	0	0	0
	55	0	0	0
	60	0	0	0


Xia Huang

Dong Ye
email: dong.ye@univ-lorraine.fr

Feng Zhou
email: fzhou@math.ecnu.edu.cn

STABILITY FOR ENTIRE RADIAL SOLUTIONS TO BIHARMONIC EQUATION WITH NEGATIVE EXPONENTS

In this note, we are interested in entire solutions for the semilinear biharmonic equation

.

Stabilité des solutions radiales entières de l'équation biharmonique avec exposants négatifs

.

introduction

In this note, we are interested in entire radial solutions for the biharmonic equation

(1.1) ∆ 2 u = -u -p , u > 0 in R N
where p > 0 and N ≥ 3.

Recently, the fourth order equations have attracted the interest of many researchers. In particular, the existence, multiplicity, stability and qualitative properties of solutions to equation (1.1) are studied in many works, especially for radial solutions. It has been proved in [START_REF] Lai | Remarks on entire solutions for two fourth-order elliptic problems[END_REF] that if 0 < p ≤ 1, the equation (1.1) admits no entire smooth solution. It is showed in [START_REF] Kusano | Radial entire solutions of even order semilinear elliptic equations[END_REF][START_REF] Mckenna | Radial solutions of singular nonlinear biharmonic equations and applications to conformal geometry[END_REF] that for any p > 1, there exist radial solutions to (1.1).

Definition 1. A solution u to (1.1) is said stable in Ω ⊆ R N if there holds Ω |∆φ| 2 dx -p Ω u -p-1 φ 2 dx ≥ 0 for any φ ∈ C ∞ 0 (Ω).
Moreover, a solution u to (1.1) is said stable outside a compact set

K if u is stable in R N \ K.
For simplicity, we say also that u is stable if Ω = R N .

We consider the following initial value problem

(1.2)      ∆ 2 u = -u -p for r ∈ [0, R α,β ) u (0) = u (0) = 0, u(0) = α, ∆u(0) = β,
for any α, β ∈ R, we denote by u α,β the (local) solution of (1.2) and by [0, R α,β ) the maximal interval of existence. Notice that the equation (1.2) is invariant under the scaling transformation

u λ (x) = λ -4 p+1 u(λx), λ > 0.
Therefore, we need only to consider the case α = 1. We will denote u 1,β by u β . Let p > 1, it's known from [START_REF] Guerra | A note on nonlinear biharmonic equations with negative exponents[END_REF][START_REF] Lai | The regularity and stability of solutions to semilinear fourth-order elliptic problems with negative exponents[END_REF][START_REF] Mckenna | Radial solutions of singular nonlinear biharmonic equations and applications to conformal geometry[END_REF]] that • There is no global solution to (1.2) if N ≤ 2.

• For N ≥ 3, there exists β 0 > 0 depending on N such that the solution to (1.2) is globally defined if and only if β ≥ β 0 . Furthermore, lim r→∞ ∆u β ≥ 0 and lim r→∞ ∆u β = 0 if and only if β = β 0 .

• For N ≥ 3, any entire solution u β is stable outside a compact set if β > β 0 .

• For N = 4, u β0 is unstable outside every compact set.

• For 5 ≤ N ≤ 12, there exists a critical value p N > 1 (see below for the precise definition) such that if 1 < p ≤ p N , u β is stable for every β ≥ β 0 ; while for p > p N , there exists β 1 > β 0 such that u β is stable if and only if β ≥ β 1 , and u β0 is unstable outside every compact set. • For N ≥ 13 and any p > 1, u β is stable for every β ≥ β 0 . Moreover, Warnault [START_REF] Warnault | Liouville theorems for stable radial solutions for the biharmonic operator[END_REF] proved that equation (1.1) admits no stable solution (radial no not) for N ≤ 4. So it remains to consider the eventual stability outside a compact set for N = 3 and β = β 0 .

The stability property of entire radial solutions is closely related to their asymptotic behaviors. Let us recall the asymptotic behaviors showed in [START_REF] Dávila | Multiplicity of solutions for a fourth order equation with power-type nonlinearity[END_REF][START_REF] Guerra | A note on nonlinear biharmonic equations with negative exponents[END_REF][START_REF] Lai | The regularity and stability of solutions to semilinear fourth-order elliptic problems with negative exponents[END_REF]. For N = 3 and β = β 0 , the following hold:

(1.3)              lim r→∞ u β0 (r)r -1 = > 0, if p > 3; lim r→∞ u β0 (r)r -1 (ln r) -1 4 = 4 √ 2, if p = 3; lim r→∞ u β0 (r)r -4 p+1 = -Q 4 - 4 p + 1 -1 p+1 =: L 0 , if 1 < p < 3,
where Q 4 is defined by

(1.4) Q 4 (m) := m(m + 2)(N -2 -m)(N -4 -m).
Remark that equation (1.1) has a singular solution u s (r)

≡ L 0 r 4 p+1 , if Q 4 -4 p+1 < 0. From [2], we know that for N = 3 there exist 3 > p + c > p c > 1 such that if p = p c or p = p + c , then -pQ 4 (m) = 9 16 with m = -4 p+1 , and if p c < p < p + c then -pQ 4 (m) > 9 16 . For N ≥ 5, p N is the unique root of -pQ 4 - 4 p + 1 = N 2 (N -4) 2 16 in (1, ∞).
Theorem A (Theorem 1.6 in [START_REF] Lai | The regularity and stability of solutions to semilinear fourth-order elliptic problems with negative exponents[END_REF]) Let N = 3, p > 1. We have:

(i) If p + c < p < 3 or 1 < p < p c , then u β0 is stable outside a compact set; (ii) If p c < p < p + c , u β0 is unstable outside every compact set; (iii) If p ≥ 3, then u β0 is stable outside a compact set.

Open problem: What is the stability behavior outside compact set when β = β 0 , N = 3, p = p c or p = p + c ? The following result gives the definite answer. Indeed, we will prove an refined asymptotic behavior for the radial solution u β0 and use the following Hardy-Rellich inequality with weights, see Corollary 5.4 in [START_REF] Caldiroli | Rellich inequalities with weights[END_REF].

Lemma 1.2. Let N ≥ 3, Ω = R N \ B 1 , then the following inequality holds Ω |∆φ| 2 dx - N 2 (N -4) 2 16 Ω φ 2 |x| 4 dx ≥ N 2 -4N + 8 8 Ω φ 2 |x| 4 ln 2 |x| dx + 9 16 Ω φ 2 |x| 4 ln 4 |x| dx, ∀ φ ∈ C ∞ c (Ω).
(1.5)

Proof of Theorem 1.1

Rewrite the equation (1.1) with the radial coordinate.

u (4) + 2(N -1) r u + (N -1)(N -3) r 2 u - (N -1)(N -3) r 3 u = -u -p .
Denote α := -m = 4 p+1 . Without confusion, from now on we omit the index β 0 and fix N = 3, p ∈ (1, 3). Let v(t) = r -α u -L 0 with t = ln r, then v satisfies

(2.1) v (4) + 2(2α -1)v + (6α 2 -6α -1)v + 2(2α -1)(α 2 -α -1)v -(p + 1)L -(p+1) 0 v + g(v) = 0, where g(v) = (v + L 0 ) -p -L -p 0 + pL -(p+1) 0 v. As 1 < p < 3, by (1.3), we have lim t→∞ v(t) = 0, so g(v) = O(v 2 ) as t → ∞.
The corresponding characteristic polynomial of equation (2.1) is

λ 4 + 2(2α -1)λ 3 + (6α 2 -6α -1)λ 2 + 2(2α -1)(α 2 -α -1)λ -(p + 1)L -(p+1) 0 = 0.
Using MATLAB, we have the following four roots of the above polynomial:

                     λ 1 = 1 2 -α + 1 2 5 + 4 h(p, α), λ 2 = 1 2 -α - 1 2 5 + 4 h(p, α), λ 3 = 1 2 -α + 1 2 5 -4 h(p, α), λ 4 = 1 2 -α - 1 2 5 -4 h(p, α), where h(p, α) = 1 + pα(2 -α)(1 + α)(α -1).
Recall that for p = p c or p + c , there holds -pQ 4 (-α) = 9 16 , i.e. pα(2 -α)(α + 1)(α -1) = 9 16 . Hence h(p, α) = 25 16 and

λ 1 = 1 2 -α + 1 2 √ 10, λ 2 = 1 2 -α - 1 2 √ 10, λ 3 = λ 4 = 1 -2α 2 , if p = p c or p + c .
As α ∈ (1, 2) for 1 < p < 3, we see that λ 1 > 0, λ 2 < λ 3 = λ 4 < 0. By the variation of parameters method, the solution v of (2.1) is given by

v(t) = 3 i=1 A i e λit + 3 i=1 B i t 0 e λi(t-s) g(v(s))ds + A 4 te λ4t + B 4 t 0 (t -s)e λ4(t-s) g(v(s))ds = A 1 e λ1t + A 2 e λ2t + A 3 e λ3t + A 4 te λ4t -B 1 ∞ t e λ1(t-s) g(v(s))ds + 3 i=2 B i t 0
e λi(t-s) g(v(s))ds + B 4 t 0 (t -s)e λ4(t-s) g(v(s))ds

where we used the fact e -λ1s g(v(s)) ∈ L 1 (R + ). As lim t→∞ v(t) = 0 and λ 1 > 0, there holds A 1 = 0. Therefore, for any ∈ (0, -λ 4 ), there exists C > 0 such that for all t ≥ 0, Thanks to (2.2), if we fix δ > 0 small enough such that 2C δ ≤ min(λ 1 , -λ 4 -), there holds

|v(t)| ≤ C e (λ4+ )t + C ∞ t e λ1(t-s) |g(v)(s)|ds + C t 0 e (λ4+
(K 1 -K 2 ) (t) = 2|v(t)| + (λ 4 + )K 1 (t) -λ 1 K 2 (t) ≤ 2C δ(K 1 + K 2 ) + (λ 4 + )K 1 (t) -λ 1 K 2 + O(e (λ4+ )t )
≤ O(e (λ4+ )t ).

Using again lim t→∞ v(t) = 0, we have readily

lim t→∞ K 1 (t) = lim t→∞ K 2 (t) = 0. Hence, (K 2 -K 1 )(t) ≤ O(e (λ4+ )t ) as t → ∞. Going back to (2.2), (2.3) |v(t)| ≤ O(e (λ4+ )t ) + 2C δK 1 (t). Consequently, K 1 (t) = |v(t)| + (λ 4 + )K 1 (t) ≤ O(e (λ4+ )t ) + (2C δ + λ 4 + )K 1 (t)
So K 1 (t) = O(e (λ4+ +2C δ)t ), we get |v(t)| = O(e (λ4+ +2C δ)t ) by (2.3). Let σ = -λ 4 --2C δ > 0, we obtain (2.4) u(r) = L 0 r α + r α O(r -σ ), as r → ∞.

Finally, let R > 0 be large enough, we apply Lemma 1.2 with N = 3. Recall that p = p c or p + c , for any φ ∈ C ∞ c (R 3 \ B R ), we have then

R 3 \B R |∆φ| 2 dx -p R 3 \B R u -p-1 φ 2 dx ≥ R 3 \B R |∆φ| 2 dx -p R 3 \B R r -4 L -(p+1) 0 -O(r -σ ) φ 2 dx = R 3 \B R |∆φ| 2 dx -pL -(p+1) 0 R 3 \B R r -4 φ 2 - R 3 \B R r -4 O(r -σ )φ 2 dx = R 3 \B R |∆φ| 2 dx + pQ 4 - 4 p + 1 R 3 \B R r -4 φ 2 - R 3 \B R r -4 O(r -σ )φ 2 dx = R 3 \B R |∆φ| 2 dx - 9 16 R 3 \B R r -4 φ 2 - R 3 \B R O(r -4-σ )φ 2 dx ≥ 0.
This implies that u is stable outside a compact set. The proof is completed.

Theorem 1 . 1 .

 11 Let N = 3, p = p c or p = p + c , the solution u β0 to equation (1.2) is stable outside a compact set.

Acknowledgements. The research of the first author is supported by NSFC (No. 11701181). The third author is partially supported by NSFC (No. 11726613, No. 11431005) and Science and Technology Commission of Shanghai Municipality (STCSM), No. 18dz2271000. The authors thank the referee for her/his useful remarks on the manuscript.