research article a multifunctional rf remote control for...

Research ArticleA Multifunctional RF Remote Control for Ultralow StandbyPower Home Appliances

Kwang-il Hwang and Sung-Hyun Yoon

Department of Embedded Systems Engineering, Incheon National University, Incheon 402-772, Republic of Korea

Correspondence should be addressed to Kwang-il Hwang; [email protected]

Received 10 December 2013; Accepted 16 April 2014; Published 26 May 2014

Academic Editor: Jongsung Kim

Copyright © 2014 K.-i. Hwang and S.-H. Yoon.This is an open access article distributed under the Creative Commons AttributionLicense, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properlycited.

In spite of many benefits, since a target RF should be able to react to real time user commands even during system power-off,RF remote controls generally require more standby energy than IR manner. Therefore, in this paper a multifunctional RF remotecontrol (MRRC), which is capable of providing larger coverage and various services, is introduced, and an ultralow standby poweroperation method for target RFs, utilizing an extended preamble transmission and a variable length periodic preamble sensingaccording to system power states, is proposed. In addition, a prototype and implementation details are also described. In order toevaluate the proposed MRRC, several experiments are conducted, and each performance of MRRC is also compared with ZigBeeRF4CE no power saving and power saving mode. The experimental results demonstrate that the MRRC system enables not onlyultralow standby power operation during system power-off but also low power operation even in system power-on state. In spiteof ultralow standby power operation, the experimental result also shows that the MRRC provides reasonable response time to usercommand.

1. Introduction

After the first wireless remote control, Flash-Matic developedby Eugene Polley in 1955 has been introduced and the IR(infrared) remote control has been used dominantly for TVand other home appliances for about more than 30 years.TheIR remote control provides simple and low power connec-tivity to remotely control several home appliances but alsohas the following limitations: one way communication, line-of-sight constraint, and one-to-one communication only. Inaddition, to receive commands from a remote, power of anIR receiver remains active. Recently, as the number of smartappliances is increased, the demand for a new remote controlto overcome the limitations of IR remote controls is arising.Furthermore, the rapid advances in wireless systems and userinterfaces have accelerated the advent of a new remote controlusing several wireless systems or various user interfaces [1–8].

Remotes [1, 2] using Bluetooth support simple, familiarassociation with smart phones. However, due to interferenceproblems with other wireless systems such as Wi-Fi andscalability problems that a slave is allowed to be paired withonly onemaster (target) device, the spread of a remote control

based on Bluetooth in various home appliances is limited. Inaddition, ZigBee RF4CE [5] (Radio Frequency for ConsumerElectronics) has been emerged as a representative RF remotecontrol, which enables one-to-many communications basedon two-way communications and provides larger coveragedue to no line-of-sight constraint.

In spite of many benefits, the RF remote controls, suchas RF4CE, generally require more standby energy than IRmanner, and thus it might result in increase of standby powerconsumption in home. In particular, recently as concernsabout standby power reduction is being increased muchmore, some research focuses on reducing standby power inhome appliances [9, 10, 16, 17].

Therefore, this paper deals with a problem of how toreduce standby power consumption in home, and, in par-ticular, reduction of standby power consumed in RF remotereceivers, which should be able to react to real time usercommands even if the system power is off, is focused on.Recently, as home appliances controlled by remote controlsare increased, the problem reducing standby power in homeappliances is considered to be challenging.

Hindawi Publishing CorporationInternational Journal of Distributed Sensor NetworksVolume 2014, Article ID 381430, 11 pageshttp://dx.doi.org/10.1155/2014/381430

2 International Journal of Distributed Sensor Networks

The remainder of this paper is organized as follows.In Section 2 several researches related to our work areinvestigated. Section 3 introduces RF low power listening andthe proposed idea is described in Section 4. Section 5 showsan example of theMRRCoperation. Experimental results andperformance evaluations are presented in Section 6. Section 7provides some concluding remarks.

2. Related Work

Over the last decade, there have been a number of researches[1–8] on new remote controls for various home appliancesto replace conventional IR remote controls. Kim et al. [3]proposed a new remote control interface using a touch screenand haptic interface. Park and Lee [4] proposed a remotefor smart TV using a user pattern recognition technologythrough a camera placed on TV. Even though these newinterfaces for a remote control can provide more convenientenvironment to users, these might require more complexremote control method and be difficult to apply to variousother target systems other than TV.

On the other hand, RF remote controls [5–8, 11] cantake advantage of similar user interface to conventional IRremotes and thus enhance its performance and functionalitywithout learning a new remote interface. Han et al. [5]proposed a home appliance control scheme using both IRremote and ZigBee RF communication. Each power outletand dimming lights are equipped with ZigBee RF module,and they are managed by a ZigBee controller, which iscontrolled by an IR remote control. Hwang et al. [6] proposedan enhanced version of ZigBee to IR remote [5]. ZigBeeto IR remote control performs a remote function for appli-ances requiring IR remote control, and ZPA (ZigBee PowerAdaptor) manages systems requiring power control. Kimet al. [7] proposed a universal remote control having variouscommunication interfaces using amobile device to overcomelimitations of a conventional remote control such as interfacecomplexity and specific application constraint. A mobiledevice is equippedwithWi-Fi and additional RFmodule, andRF to relay is used to control power control devices, RF to IRis also used to control conventional appliances, and Wi-Fi isused for Internet access or CCTV.

Finally, the demand for a new remote using low power RFurged to the advent of a new standard ZigBee RF4CE [8] byZigBee alliance in 2009. The RF4CE provides one-to-manycommunication and larger coverage over IR remote control,which is limited in line-of-sight. In addition, Hwang [11]proposed an interference which avoided RF4CE in 2.4GHzISM band.

In parallel with research on a new remote control, therehave been some researches [5, 12–14] on reducing standbypower in home. Tsai et al. [12] proposed a standby powerreduction method for lighting devices by adaptively control-ling lights according to human movement. Han et al. [5]and Han et al. [14] proposed a home energy managementscheme in which a power outlet has a function to cutoffstandby power if power consumption goes below a predefined

threshold and a home server allows users to control homeappliances outside the home.

In spite of a lot of efforts to reduce standby power inhome, there have been only a few research on standby powerminimization of a remote receiver. Kang et al. [13] proposeda remote control and remote receiver based on autonomouspower in which transmitter accumulates energy in receiverusing laser diode, and an IR receiver is powered by the storedenergy. However, this method requires considerable energyin transmitter.

RF standby powerminimization has been actively studiedin wireless sensor network area. In particular, LPL (lowpower listening) methods [9, 10, 16, 17] are used to reduceunnecessary listening period and our work is also based onLPL. However, sincemost existing LPLmethods are designedfor wireless sensor networks in which sensors are massivelydeployed and have no intervention of human, it is impossibleto apply the LPL itself for sensor networks to remote controlapplications.

Therefore, in this paper a novel low power RF com-munication based on LPL for RF remote control, which iscapable of minimizing RF standby power by switching theRF listening period adaptively according to the state of targetsystems, is proposed.

3. Preliminary

Unlike the IR transmission using predetermined frequencies,RF communications are capable of transmitting variousformats of data so that it is possible to provide more flexibleand smart controls. In particular, the ZigBee RF4CE standardbased on IEEE802.15.4 [15] enables low power remote con-trol. However, the IEEE802.15.4 network depends on stricttime synchronization between a coordinator and devices tomaintain a superframe structure, and thus each node mightwaist unwanted energy due to idle listening. Furthermore,CSMA/CA based network can provide irregular latency sothat users can feel some inconvenience.

Figure 1(a) shows a general RF frame structure. At thebeginning of a frame, a preamble, which is a repeatedpattern of “1” and “0” and is used as an indicator to noticethe start of transmission, is transmitted. At the end of asynchronization word for sampling data, variable length dataare transmitted and finally each frame is finished with theCRC (cyclic redundancy check), which is used to detecterrors in the frame. As shown in the figure, to receivea frame the receiver should remain active before packetreception, and the active state should be kept until the wholeframe is received. Therefore, for low power operation, anRF receiver, normally in sleep state, wakes up and receivesa frame at the time when a transmitter sends a frame andthen returns to sleep state again. In order to achieve this,the time synchronization between transmitter and receiveris required, and a duty cycle, which includes an active andsleep duration, should be maintained. However, it is difficultto correctly maintain time synchronization due to the effectof clock drift. Moreover, in remote control applications, user

International Journal of Distributed Sensor Networks 3

Preamble word Payload CRC

Extended preamble

RX

Preamble sensing

duration

Preamble detected

RX

word Payload CRC

Packet reception duration

Packet processing time

(a)

(b)

Synchronization

Synchronization

Figure 1: General RF packet structure versus extended preamble packet structure.

commands have unpredictable characteristics. That is, sincemost listening periods, which are in active state for the packetreception period, might become idle listening period; eachtarget RF wastes considerable energy.

To address idle listening problems, there have been sub-stantial researches [9, 10, 16, 17] onLPL to reduce idle listeningperiods. As shown in Figure 1(b), the LPL is different fromgeneral packet reception processing in that more expandedpreamble is transmitted and a receiver is activated repeatedlyonly for a short duration (preamble sensing duration) todetect preamble transmission and the remainder of theperiod is in sleep mode.

Even though the LPL for sensor networks brings moreenergy conservation by reducing idle listening, the charac-teristics of sensor network application, in which sensors aremassively deployed and have no intervention of human, arebasically different from home remote controls, which aredirectly controlled by human. Therefore, in the followingsection, a new RF standby power reduction method based onadaptive low power listening is presented.

4. Multifunctional RF Remote Control forUltralow Standby Power Home Appliances

In this Section, amultifunctional RF remote control (MRRC),which enables ultralow standby power operation of homeappliances, is proposed.

4.1. Ultralow Power Listening with Variable Sensing Interval.In order to minimize power consumption of each target RFassociatedwithMRRC, an extended preamble to trigger a tar-get RF prior to each command is transmitted, and each targetRF performs a periodic preamble sensing (PPS) to detect anextended preamble transmission for a very short duration.It is important to note that the length of preamble sensingduration, which is an active duration to perform preamblesensing, should be minimized to maintain a minimum dutycycle. Therefore, a minimum preamble sensing duration, anoptimal length satisfying 100% successful preamble detection,is found through experiments in which total 100 trials areconducted. As shown in Figure 2, the obtained minimumpreamble sensing duration is 4.8 milliseconds and the lengthis considerably shorter than minimum packet receptionduration (188.8 milliseconds). The result reveals that inactiveperiod of the MRRC system for an idle listening can beextended over 40 times compared to general packet receptionschemes within the same period, and it might result inconsiderable energy saving.

In addition, one of the major differences from otherLPL methods is capable of providing minimizing standbypower consumption of target RF by applying a variable lengthpreamble sensing interval (PSI) according to the state ofeach target system, despite providing reasonable responsetime to user commands. Each target RF performs a PPS tosense an extended preamble for a short period and maintains


(a) (b)

Figure 2: Preamble sensing duration versus packet reception duration.

sleep mode until the next PPS. Since an extended preambletransmission should be able to be sensed by a target RFduring a PPSwithin a PSI, the length of an extended preambletransmitted by MRRC must be longer than a period of aPSI. The MRRC utilizes two different length PPSs: long PPSand short PPS. The long PPS is used to listen to a systempower-on command by MRRC, and thus it is maintained fora relatively long period. That is, during system power-off, atarget RF performs PPS with a longer interval.The longer theperiod is, the more energy can be saved, but response timeof target RF with respect to user’s command request is alsolonger. Therefore, through experiments a suitable intervalvalue (3 seconds) is determined, which is the maximumwaiting time that a user can tolerate. However, the PPS valueis also configurable by a user. After system power-on, a targetRF performs a short PPS with a shorter interval. Throughanother experiment, a suitable short PPS time (1 second)to wait for user command during system power-on is alsodetermined.

If a user command is transmitted by MRRC, during PPSeach target RF is triggered by an extended preamble and keepsa wait-for-command state until following command data arereceived. If the target ID in the received frame is not matchedwith my ID, the target RF returns to PPS mode again.

The MRRC also supports consecutive remote commands(i.e., volume up/down, TV channel set, etc.) during systempower-on. In particular, to guarantee fast response timeto consecutive commands, after the previous command iscompleted, both MRRC and target RF remain active for thesame standby duration to wait for the next command. It isimportant to note that the commands generated during thestandby period are transmitted as a general frame without anextended preamble. This standby duration is used to makea prompt response to consecutive commands by removingredundant delay to process an extended preamble. Further-more, standby duration is reset whenever a new commandis received within the standby duration, so that responsetime to consecutive commands is considerably reduced. Ifthere is no following command for the standby duration, thestandby timer expires so that the target RF returns to PPSstate. Figure 3 shows a state transition diagram to perform avariable length PPS according to the states of a target system.

4.2. On-Demand Target Trigger. Another outstanding featureof the MRRC is asynchronous target trigger based on on-demand time synchronization. In order to cope well withon-demand user command, no global time synchronizationbut on-demand time synchronization is used in a MRRC.As mentioned in the previous subsection, to trigger a targetRF which is performing PPS, an MRRC should transmit anextended preamble longer than a period of a PPS. As shownin Figure 4, all the target RFs performing preamble sensingat different time are triggered by an extended preamble ofMRRC although preamble detection time of each target RF isdifferent, and they receive simultaneously the command datatransmitted at the end of the extended preamble. Therefore,all the target RFs and MRRC can be synchronized with eachother. It is important to notice that each device that detects apreamble should be in active state for the wait-for-commandduration. However, as shown in Figure 4, the length of wait-for-command duration of each target RF might be variedaccording to the point that a preamble is detected. That is,the earlier the preamble detection is, the longer the delayis until user command is received. Therefore, to minimizeunnecessary delay, the MRRC also provides an interactivepreamble termination method which can be applied whena target system is in user’s line-of-sight. Figure 4 illustratesan example of interactive preamble termination. Whereas anormal extended preamble shown in the first command lastsformaxpreamblelength, the second preamble is terminated assoon as the button is released. That is, a target system cannotice the MRRC user of is the preamble detection usinga LED, and thus the system can provide a faster responsetime by terminating current preamble transmission as soon asthe button of a MRRC is released. In particular, the method,which provides a flexible preamble transmission based on afeedback between user and a target system, can compensaterelatively long response time in long PPS.

4.3. Bidirectional Communication Capability. Unlike an IRremote control, the MRRC also has bidirectional commu-nication capability. In particular, the MRRC is capable ofcontrolling the length of an extended preamble througha feedback from a target system. Figure 5 illustrates anexample of flexible PPS operation based on bidirectional


LongPPS

Wait forcommand

Standby

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Timeout andsystem off

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Timeout and system on

andtarget Id mismatched

and target Id matched

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Figure 3: State transition diagram.

Target RF1

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detected

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Figure 4: On-demand target trigger by MRRC.

communication between anMRRCand target RF. A target RFis performing PPS at long preamble sensing interval (LPSI)during system power-off, and the MRRC transmits a longpreamble to trigger the target RF. At the end of a preambletransmission, user command is transmitted and target systemcarries out the received command. (As shown in Figure 5,the first command is system-power-on.) On carrying out thecorresponding command, the target RF replies to theMRRC.To handle successive user commands, both target RF andMRRC remain active for the standby duration. As mentionedpreviously, if successive user command is transmitted duringthis period, the command can be transmitted without anextended preamble so that response time of the commandis considerably reduced. Here, since the MRRC and targetRF are synchronized by the command frame followed by an

extended preamble, the two devices can maintain the samestandby time. If there is no command for the standby dura-tion, the target RF performs a PPS at short preamble sensinginterval (SPSI) and MRRC returns to sleep mode. Afterstandby duration expires, the MRRC uses a short extendedpreamble to trigger the target RF, which is performing a shortPPS. The short PPS is used to consume RF power as low aspossible even during system power-on and also provides thereduced response time over long PPS which is performedduring system power-off. In particular, utilizing standbyduration associated with short PPS enables fast response timeby removing delay in the target RF and MRRC. If a target RFreceives a system-off command from MRRC, the target RFturns off the system and responds to the MRRC. After that,to wait for additional consecutive command by user, the two


TargetRF

LPSI

Active

MRRC

Standbyduration

Standbyduration

Short PPS

SPSI

Buttonpress

Buttonpress

Standbyduration

Standbyduration

StandbydurationStandby

duration

Long PPS Long PPS

Targetsystem

Preamble Command Wait forcommand

Standbyactive PPS Preamble

detected

Max Longpreamble length

Commandresponse

Max shortpreamble length

LPSI

OFF → ON ON → OFF

Figure 5: Bidirectional communication between MRRC and target systems.

RC

RF

System

RF

System

RF

System

Light

TV

AirConditioner

Buttonpress

Standby

Buttonpress

Buttonpress

Standbyduration

LPSI

Long PPS

Standbyduration

duration

Standbyduration

Standbyduration

Standbyduration

Buttonpress

LPSI

activePreamble CommandWait for

command ActivePPSPreambledetected

Buttonrelease

A B C D E

Userperception

Commandresponse

durationStandby

StandbydurationStandby

Figure 6: An example of MRRC operation.

devices keep active state for the standby duration, and then ifthere is no command during the time, the target RF performslong PPS again to save power.

5. Controlling Multiple Target Systems

Figure 6 shows an example of controlling a light, TV, andair conditioner using a single MRRC. First, in section Athe light is already turned on, and other systems (TV andair conditioner) are powered off. TV and air conditioner

are performing long PPS to reduce standby power, andthe light is performing short PPS to react quickly to usercommands. In section B, user turns on the air conditionerand immediately controls temperature of the air conditionersuccessively. As shown in the figure, the successive temper-ature control commands are processed immediately withoutextended preamble transmission. During the time, TV thatis performing long PPS is triggered by the first commandbut returns to long PPS again after the command is receiveddue to ID mismatch. Also, the TV is not even triggered


Figure 7: MRRC prototype.

by following short commands for the air conditioner. Insection C, the user turns on TV through RF performinglong PPS. At this moment, the extended preamble doesnot last for the maxlongpreambleduration but is terminatedmidway by user that perceives LED signal on TV, informingthat a preamble is detected. That is, interactive preambletermination is used in that situation. In section D, the userswitches channel. At that moment, since TV is poweredon, RF is performing short PPS, and the MRRC sends thecommand after triggering RF by short extended preamble.This section has no more commands so that after standbyduration the RF returns to short PPS. In section E, the userturns up the volume of the TV successively. Since volumecontrols are generated successively for the short duration,the rest of the commands are transmitted without extendedpreamble transmission, except for the first command with ashort extended preamble. Therefore, the user can experiencefast response to successive commands. In the final, user turnsoff TV and air conditioner. The RF, which is performingshort PPS to provide relatively fast response, receives systempower-off command and then goes to the longPPSmode afterstandby duration, to minimize standby power.

6. Experimental Result

In this Section, a MRRC prototype and test bed are intro-duced, and experimental results are presented. In particular,each performance of the MRRC is compared with ZigBeeRF4CE, which is the most representative RF remote control.

6.1. MRRC Prototype. Figure 7 shows an MRRC hardwareprototype. The MRRC prototype is composed of 16-bit lowpower MCU and sub-1-GHz RF, which is capable of trans-mitting a variable length preamble. In addition, to generateuser commands, simple push switches are used in place of keypads. The MRRC is also designed to cope well with severaldifferent events (external interrupts, timer interrupts, RFinterrupts, etc.) through an event driven lightweight sched-uler based on HAL (hardware abstract layer), which managesdirectly hardware.This development environmentmight alsofacilitate various MRRC application developments.

6.2. Experimental Environment. For MRRC experiments,a target appliance emulator, which is a PC applicationsoftware, is implemented. As shown in Figure 8, the usedtarget emulators accept each command for light, TV and air

Figure 8: Test bed.

Table 1: System parameters.

Parameter ValueMRRC RF4CE

Supply voltage 3.3 VCurrent consumption

TX active 26.3mARX active 22.3mASleep 30 uA

MaxLongPreamble length 3.2 s —MaxShortPreamble length 2.2 s —nwkDutyCycle — 3 snwkActivePeriod — 0.183 sPPS duration 0.0156 s —PPS interval

Long PPS 3 s —Short PPS 1 s —

Standby duration 5 s —

conditioner, respectively, and individual RF is connected tothe corresponding target system via USB. Each RF and atarget can communicate with each other and the MRRC cancontrol a designated target by target ID assigned uniquely.Emulator also plays a role in storing and analyzing datareceived from an MRRC.

For comparative analysis of the proposed MRRC, ZigBeeRF4CE is also implemented on the same hardware. RF4CEis designed based on IEEE802.15.4 PHY and MAC, and twodifferentmodes are implemented, respectively: RF4CE powersaving (PS) and no power saving (NPS), which are specifiedin RF4CE standard. In NPS, all the target RFs wait forcommands from an RF4CE remote control in a fully activemode, and in PS each target maintains repeatedly a dutycycle, which includes active state for nwkActivePeriod andsleep state for the remainder period. Table 1 summarizesmainparameters used in our experiments.

6.3. Performance Evaluations. In this subsection, the MRRCperformances compared with ZigBee RF4CE through var-ious experiments are evaluated. First, how fast a target


0 100 200 300 400

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Figure 9: Response time.

system can respond to a user command is evaluated byobserving response time. Subsequently, how much energyefficient a target RF and MRRC is evaluated by analyzingenergy consumption in various experimental environments.In addition, since PPS duration guaranteeing 100% receptionratio through experiments, as mentioned in Section 4.1, isapplied, the experimental result regarding successful datatransmission ratio is not presented in this paper.

6.4. Response Time Analysis. First, response time of MRRC,RF4CE PS, and RF4CE NPS is observed, respectively. Theresponse time is a round trip time consumed froman instancewhen user presses a button of an MRRC until the MRRCreceives a reply from the target RF. For the experiment,consecutive 10 commands with one second interval at everyone minute for total 6 minutes are generated, and eachreply time from target RF is measured. Each experimentis repeated 100 times and Figure 9 shows the result that

calculates the average of measured value at each experiment.First, the RF4CE NPS presents fast response time less than250 milliseconds with respect to each command, as shownin Figure 10(a). In the case of RF4CE NPS, since each targetRF is always awaken for the packet reception, user commandcan be processed promptly without any redundant delay. Onthe other hand, RF4CE PS shows irregular response timedistribution as shown in Figure 9(b).The result presents largedeviation (300–3,000 milliseconds). In that mode, for powersaving a target RF maintains a repeated duty cycle with aperiod of nwkdutycycle, presented in Table 1. Therefore, atarget RF shouldwait to transmit the commanduntil a beaconframe is received from the target RF (in general, the targetRF plays a role in a coordinator), and finally the commandis transmitted at the active duration of target RF, which isreferred to as a superframe duration, in which a beaconframe indicates the beginning of superframe duration. Thatis, the irregular latency in RF4CE PS results from the fact


0 5 10 15 20 25

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MRRCRF4CE remote controller PS

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(c) Remote control

Figure 10: Energy consumption.

that communications between a remote control and targetRF depend on time synchronization based on a beacontransmitted periodically by target RF. Eventually, the irregularresponse time might bring users inconvenience. Finally,experimental result of MRRC is shown in Figure 9(c). Theresult shows that response time of the MRRC maintainsnormally 280 milliseconds, which is similar to the RF4CENPS. It is noticeable that the initial system-on commandshows long response time of 3,300 milliseconds. The MRRCperforms long PPS with long interval to save standby energyduring system power-off, so that initial power-on commandrequires longer response time than the following commands.However, since after system power-on each target RF per-forms short PPS, only the first commands out of consecutivecommands at every command interval show response timeof 1,400msec. Furthermore, since the rest of the consecutive

commands are transmitted without an extended preamble,they canmaintainminimum response time as in RF4CENPS.

6.5. Energy Consumption. Energy consumption is one ofthe important performance factors for home appliances andremote control. To evaluate comparative performance, totalenergy consumed for the test duration under the same testcondition is measured for MRRC, RF4CE NPS, and PS,respectively. Energy consumption of a target RF and remotecontrol, respectively, is obtained from power consumed for24 hours. More specifically, standby energy of target RFin fully standby mode in which a target system is poweroff but RF is ready to receive user command is observed,and also energy consumption in fully active mode in whichvarious user commands are performed is observed. Sincepower consumption is different according to each target


system (appliance), for our experiment power consumptionof only RF in each target system is considered. All theexperimental results present average energy consumption ofeach RF connected to each appliance emulator.

Figure 10(a) shows energy consumption of a target RFin fully standby mode (system power off) for 24 hours.It is shown that RF4CE NPS having fast response time of250 milliseconds is considerably inefficient in energy aspect.On the other hand, RF4CE PS shows more efficient energyconsumption thanNPS.This is because themodemaintains arepeated duty cycle for the standby period. It is noticeable thata target RF in MRRC shows minimum energy consumptionover RF4CE.Theultralow standby energy consumption of theMRRC results from maintaining minimum active durationonly to detect preamble transmission and utilizing variablelength PPS (e.g., long PPS during RF standby period).Furthermore, unlike RF4CE PS, MRRC does not requiresuperframe management based on time synchronization bya periodic beacon frame between a remote control and targetRF.

Figure 10(b) shows another experimental result. In con-trast with the former experiment (full a RF standby), for thisexperiment, the target system is turned on and 10 commandsare issued at every hour for total 24 hours. The resultshows that the MRRC target RF is superior to two RF4CEmodes. Two RF4CE modes also show almost similar energyconsumption as in fully RF standby mode. This is becausethe two modes utilize the same power management in bothstandby mode and active mode. On the other hand, since theMRRCmanages different length PPS according to the systempower-on/off state, the MRRC can cope well with tradeoffbetween energy and response time. In particular, even thoughthe target RF consumesmore energy over fully standbymodeby performing short PPS in systempower-on state, theMRRCtarget RF shows more energy saving than the RF4CE PS.

Figure 10(c) presents experimental result of a remotecontrol. For the experiment, user generates 10 commandsusing a remote control at every hour for 24 hours. Incontrast with the former two experiments in which energyconsumption of target RF is only focused, this experimentpresents energy consumption of a remote control of MRRC,RF4CE NPS, and RF4CE PS, respectively. The result showsthat energy saving of RF4CE NPS remote control is superiortoMRRC and RF4CE PS.This is because RF4CENPS remotecontrol is normally in sleep mode, wakes up only when usercommand is generated, and returns to sleep mode again.On the other hand, since in the RF4CE PS remote controlthe generated user command should wait until beacon isreceived from the target RF, a remote control consumes moreenergy. In the case of MRRC, the on-demand user commandcan asynchronously trigger a target RF which is performingPPS. This feature results in minimizing unnecessary energyconsumption in a remote control, and thus the MRRC showssimilar energy consumption to RF4CE NPS.

7. Conclusion

In this paper a multifunctional RF remote control, which iscapable of providing larger coverage and various services,

is introduced, and an ultralow standby power operationmethod for target RFs, utilizing an extended preambletransmission and a variable length PPS according to systempower state, is proposed. Furthermore, a target RF canpromptly respond to on-demand user command by beingasynchronously triggered by anMRRC. In addition, based onbidirectional communication between an MRRC and targetRF, user can control multiple target systems with a singleremote control.

A prototype and implementation details are alsodescribed. To evaluate the proposed MRRC, several experi-ments are conducted, and each performance of MRRCis also compared with ZigBee RF4CE NPS and PS. Theexperimental results demonstrated that the MRRC systemenables not only ultralow standby power in system power-offstate but also low power operation even in system activestate. In spite of ultralow standby power operation, theexperimental result also shows that the MRRC providesreasonable response time to user command. Finally, it isexpected that these outstanding features of MRRC will beable to contribute to constructing ultralow power homenetwork associated with smart appliances.

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper.

Acknowledgment

This work was supported by the Incheon National UniversityResearch grant in 2012.

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