Development of Active RFID System Using ZigBee Standard with Non Beacon Mode 1
M.A Shahimi1, Z. Abdul Halim2, W. Ismail1
Auto-ID Laboratory, School of Electrical and Electronic Engineering 2 CEDEC (Collaborative µElectronic DesignExcellentCenter) Universiti Sains Malaysia, Engineering Campus 14300 Nibong Tebal, Seberang Perai Selatan, Pulau Pinang, Malaysia E-mail:
[email protected]: +604-5937788 ext. 6009, Fax: +604-5941023 Abstract- An active radiofrequency identification using ZigBee standard with sleep mode configuration has been developed. Tags are designed using non beacon mode with periodic data communication and intermittent data communication. Both tags are programmed in sleep mode. In periodic data communication, the tag is programmed to sleep for 5s and wakeup for 2.6s to check if there is a signal coming from the reader. In intermittent data communication, a reset button is used to generate a signal to connect the tag to the network. The transmission range and current consumption are measured. Data show that the maximum transmission range is 60m with 3 dBm antenna output power. Results also show that the tag with periodic data communication will use more power compared to the intermittent data communication.
Keyword: Active RFID, tag, reader, sleep mode I.
INTRODUCTION
ZigBee is an IEEE 802.15.4 standard for data communication that is designed for low power consumption, low cost, and wireless mesh networking applications [1]. ZigBee provides wireless personal area network (WPAN) in the form of digital radio connections between computers and related devices. It is applicable in home automation, smart energy, telecommunication applications, and personal home applications. Compared to other standards like Bluetooth and IrDA, ZigBee provides low data rate, which is limited to a through-rate of 250 kbps on a 2.45 GHz ISM band. Such is suitable for WPAN application and available throughout most of the world. Bluetooth and IrDA address the requirements of high data rate applications of up to 1 Mbps and are suitable for voice, video, and LAN communications [1]. In data communication, ZigBee provides three typical traffic types, namely, periodic data, intermittent data, and repetitive data [1]. In periodic data, the application dictates the rate and the sensor activates, checks for data, and deactivates. In intermittent data, the application and other stimuli determine the rate. The device connects to the network only when communication is necessary. In repetitive data, data is repetitive and the rate is fixed a priori. Depending on allotted time slots, the device operates in fixed durations. In data traffic, Zigbee employs either a beacon or a non beacon mode [1]. Beacon mode is used when the coordinator runs on battery power, thus offering maximum power savings. In nonbeacon mode, the coordinator is mains-powered.
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In the beacon mode, a device will anticipate the beacon of the coordinator that transmits data periodically, locks on, and looks for messages addressed to it. If message transmission is completed, the coordinator sets the next beacon and the device goes to sleep mode. In beacon mode, the device must know when they will communicate with each other, and timing must be accurate to ensure that the beacon will not be missed. In the non beacon mode, devices wake up and confirm their continued presence in the network at random intervals. Other stimuli determine the interval, and the devices are nearly always in sleep mode. However, there is a possibility that the sensor will not find the channel because the channel is busy, and if this is the case, the receiver will miss a call. The non beacon mode operates within a peer-to-peer network topology and therefore it is not dependent upon Master/Slave relationships. This means the device remain synchronized without use of master/slave configurations and each device in the networks can be master or slave. Radio frequency identification (RFID) is a kind of telecommunication application that uses ZigBee technology [23]. It is used in tracking and monitoring, such as in military applications, home appliances, seismic applications, patient monitoring, structure monitoring, and environment monitoring. Devices with specifications that have low data rate consume significantly low power, which results to longer battery life. Low power consumption and longer battery life are important criteria in RFID application to ensure battery life efficiency and to delay battery replacement. Low-power consumption features are required for only two major modes, namely, Tx/Rx and sleep modes. One of the methods to achieve a longer battery life is to use a sleep mode when there is no communication activity. This paper discusses the development of an active RFID tag using a Zigbee standard. The tag is programmed in sleep mode with a non beacon mode. In non beacon mode, the tag must poll the reader once it wakes from sleep to determine if the reader has sent a message for it. The tag communicates with the reader using periodic data traffic and intermittent data traffic. Both of these data communication methods can be used in different applications. For example, a RFID tag with periodic data communication can be used in asset inventory. In this application the reader sends a command to all tags, and tags respond immediately once they receive the signal. A missing tag shows that the tag or the asset is unavailable.
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A RFID tag with intermittent data communication can also be used in asset monitoring in a different manner [4]. For example, a movement sensor can be integrated with a RFID tag, and if there is a movement on the tag, it can generate a stimulus to trigger the RFID tag. The tag immediately sends a signal to the reader. The reader triggers an alarm to show that the asset has moved to another place. In this paper, the tag with periodic data communication is programmed to sleep for 5 s and wake up for 2.6 s to check if there is an incoming signal. For the tag with intermittent data communication, a reset button is used to wake up the tag. The power consumption and battery life of both tags are also discussed. II.
Tag using periodic data communication Figure 2 shows the block diagram of an RFID tag using periodic data communication. The tag consists of a 3 V battery as the power supply and a Zigbee module (Xbee module). The tag is programmed with a sleep mode of 5 s and a wake up mode of 2.6 s to check if there is an incoming signal. If there is an incoming signal, the tag responds to the signal. If there is no incoming signal, the tag resumes a sleep mode.
HARDWARE DEVELOPMENT
Reader The two main components of an active RFID system are the reader and the tag [5]. Basically, the reader contains a module that consists of a transmitter, a receiver, a control unit, and a coupling element or antenna. Figure 1 shows a block diagram of the reader. The reader consists of a ZigBee module (Xbee moduleMax3232), a LED indicator, a reset button, and a voltage regulator. The Xbee module operates at 2.45 GHz with a data rate of 250 kbps. Max3232 is used to convert the data level between the ZigBee module and the host (PC). A voltage regulator (LM1117) is used to regulate the voltage from 9 to 3.3V.A LED indicator is used to show the status of the reader, and a reset button is used to reset the reader. The reader has its own channel to communicate with the tags. It continues to search for its own channel if the channel is in conflict with other readers [6]. In one system, the address of the tag must be identical to the address of the reader. The identity of the tag can be programmed with a maximum of 20 characters, meaning every system can consist of up to 1,048,576 tags. The tags respond to the reader when they are in the coverage zone. The coverage zone depends on the output power levels of the reader.
Figure 2: Block diagram of an active RFID 2.45 GHz tag without a reset button
Tag using intermittent data communication Figure 3 shows a block diagram of the tag using intermittent data communication. The tag consists of a battery as the power supply, a ZigBee module (Xbee module), a reset button, and a LED. The tag is programmed with a sleep mode. The tag wakes up only when the reset button is pressed. That gives a logic ‘0’ to the sleep control pin of the Xbee module. A LED is used as an indicator to show that the reset button is pressed. When the reset button is pressed, it generates a stimulus to communicate with the reader. The address of the tag is programmed as 1000, and the identity of the tag is programmed as Tag2.
Figure 3: Block diagram of a tag with intermittent data communication III.
Figure 1: Block diagram of an active RFID 2.45 GHz reader
EXPERIMENTAL SET-UP
Three sets of experiments are conducted in this project. The first experiment is conducted to establish the maximum distance of the transmission range. Four different output power levels are set in the reader. A command is sent to the tag, and the maximum distance in which the tag is still able to read the signal is recorded.
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The second experiment is conducted to establish the power consumption of the tag with periodic data communication. The tag uses a 3 V coin battery. A reader sends commands to the tag once a day. If the tag can receive the signal, it responds to the reader by sending its identity (Tag1) on the PC. The voltage level of the battery is measured every hour. Current consumptions during the sleep mode and during the transmission mode are also measured.
the reset button is pressed, the logic at the sleep control line pin is ‘0’ (Figure 5), and the tag starts finding a channel to communicate with the reader. After acquiring the channel, the tag is associated to the network and is ready to transmit or receive data. The association is shown in Figure 6, where the signal is toggled.
The third experiment is conducted to establish the power consumption of the tag with intermittent data communication. The tag uses a 3 V coin battery. The reset button is pressed once a day, and the identity (Tag2) is displayed on the PC. The voltage level of the battery is measured every hour. Current consumption during the sleep mode and during the transmission mode is also measured. IV.
Figure 5: Voltage signal at the sleep control line pin
RESULT AND DISCUSSION
Transmission Range For the indoor application, the output power level versus distance is summarized in Table 1. Data show that, when the output power level increases, the maximum distance also increases. The maximum distance for the indoor application is 60 m with an output power level of 3 dBm. For the tag with periodic data communication, the voltage signal at associated indicator pin is shown in Figure 4. The tag is in a sleep mode (logic ‘1’) for 5 s and wakes up after 5 s. After it wakes up, it is ready to receive and transmit data, where the indicator pin is toggled for 2.6 s. This means that the tag has associated itself to the reader and is waiting for the signal from the reader. The measured current during the sleep mode is 3.9 mA, whereas the measured current during the transmission mode is 14.3 mA.
Figure 6: Voltage signal at the associated indicator pin
For intermittent data communication, current consumption during the sleep mode is 0.8 mA, whereas current consumption during the transmission mode is 17 mA. Readings are summarized in Table 2.
TABLE1 Output power level versus distance
Power Level 4 3 2 1
Figure 4: Voltage signal at the associated indicator pin for the tag with periodic data communication
Tag with Intermittent Data Communication The tag is triggered when the reset button is pressed. The reset button is connected to the sleep control line pin. During the sleep mode, the sleep control line pin is considered as logic ‘1’. When
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Output Power Level (dBm) 3 1 -1 -3
Max Distance (m) 60m 55m 50m 20m
TABLE 2 Current consumption of tags
State(mode)
Transmission/receive Sleep
Tag intermittent data communication 17mA 0.8mA
with sleep mode. Results show that the tag with periodic data communication uses more power in comparison to the tag with intermittent data communication.
Tag with periodic data communication
References
14.3mA 3.9mA
1.
Data show that the tag with intermittent data communication (with reset button) uses more power during the transmission/receipt mode but uses less power during the sleep mode in comparison to the tag with periodic data communication (without reset button). In periodic data communication, the tag reasonably wakes up automatically to check the incoming data from the reader. If there is no communication activity, the device wakes up every 5 s and returns to sleep mode after 2.6 s. These activities consume more current in comparison to the tag with intermittent data communication, which is always in sleep mode as long as the sleep control line pin is not triggered. The battery voltage values before and after running for 110 hours are shown in Figure 7. The initial voltage for the tag with periodic data communication is 3.2 V, and after 110 hours, the voltage is 2.8 V. The initial voltage for the tag with intermittent data communication is 3.2 V, and after 110 hours, the voltage is 3.17 V. The difference of the original and final voltage levels of the tags with periodic data communication and intermittent data communication after 110 hours is 36.5% and 2.1%, respectively. Voltage level of battery 3.3 3.25 3.2
Voltage
3.15 3.1
tag w ith intermitten data c ommunication
3.05
tag w ith periodic data c ommunication
3 2.95 2.9 2.85 2.8 0
20
40
60
80
100
120
Hour
Figure 7: Voltage level after 110 hours V.
CONCLUSION
This paper discusses the development of an active RFID using a ZigBee technology. The frequency used is 2.45 GHz with a data rate of 250 kbps. For indoor applications, the maximum transmission range is 60 m with an output power of the reader at 3 dBm. Two types of tags have been developed in this project. The difference of these tags is the data communication type. The first tag uses periodic data communication and the second tag uses intermittent data communication. Both tags are developed
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