Compatible Antenna for Software Defined Radio and multi range RFID reader using ATU Salman khan pattan #1, Suresh Angadi *2, # Final Year B.Tech, Dept. of ECE, KL University, Vaddeswaram, AP, India * Assistant Professor, Dept. of ECE, KL University, Vaddeswaram, AP, India Abstract: Software defined radio is a wireless communication platform where the hardware components used in communication systems are replaced with software components. The signals can be received using different types of antennas like Smart Antenna systems and the Automatic antenna Tuning Unit system. RFID is the detection of the Radio Frequencies with the use of extremely low powered tags. Readers are present for this purpose but are only for the limited frequency ranges. But by fixing Automatic antenna Tuning Unit to the combination of RFID reader and SDR, multi range frequencies can be detected. This provides a better result in the RFID technology. Key words software defined radio (SDR), Radio Frequency Identification (RFID), smart antenna, Automatic antenna Tuning Unit (ATU). I.INTRODUCTION Software defined radio is a wideband communication system in which all the hardware components used for signal processing are implemented on a software platform using highly sophisticated software tools embedded into Digital Signal Processors and Field Programmable Gate Arrays. Generally for the purpose of perfect modulation and demodulation we are using modulators, demodulators and mixers using different hardware circuits but this method sometimes generates erroneous results and also the components used are expensive. To avoid these problems replacing all these circuits with SDR is an appropriate solution. Any new changes in the procedures can be easily modified, dumped and can be implemented. Development of the concepts on the SDR were started earlier in 1990s and now this technology has become a sophisticated module in the wireless communications. Moreover, SDR became the basis for the 3G and 4G wireless communications. From the world s first wireless technology introduced in the olden days to the present 2G communication there were several and rapid changes involving huge amount of innovations. As SDR introduced such a highly sophisticated environment, it would be worth full to use other interfaces to also be with the same pace. Thus the major interface of signals with the circuitry i.e the antennas used are smart antennas and ATUs. A smart antenna consists of an array of antennas which deploy the methods of Direction of Arrival (DoA) estimation, spatial multiplexing and vector channel estimation. Different architectures and models were developed by Joint Tactical Radio System (JTRS) Joint Program Executive Office (JPEO) and Object Management Group (OMG). ATU consists of a tunable antenna circuit which tunes the antenna by detecting the signal in order to receive a particular signal. RF MEMS are used in the ATU for the purpose of switching and also changing the impedance values. RFID technology is the detection of the unique code embedded in a small chip attached to the antenna by the process of transmitting and receiving the reflected signal from the RFID tags. For the purpose of transmitting special devices are available in the markets which are called RFID readers. Generally the RFID readers available in the market detect only particular range of frequencies. But by implementing the ATU with the RFID readers and SDR it is possible to detect any radio frequency, thus deriving a multi range RFID reader. II.SOFTWARE DEFINED RADIO An SDR is a wireless communication system that can tune up to frequencies in the range 500MHz- 2GHz, receive the arrived signal, process the signal to the specific requirements using the software tool kit and then if necessary it transmits the signal with the specified frequency range. SDR contains different blocks as shown in the figure 1. The receiver receives the signals, and then the down converter changes the frequency from a higher range to the lower level. The purpose of down converting is that the electronic ISSN: 2231-5381 http://www.ijettjournal.org Page 1821
devices don t support such high frequencies and sometimes the equipment may get damaged. Now the down converted analog signal is digitized using the Analog to Digital converter (ADC). All the digital signals are now processed using the software tool kits. The software operations can be performed in either Digital Signal Processors (DSPs) or Field Programmable Gate Arrays (FPGAs). But the number of operations in the SDR are more because of more processes are involved for the signal processing. So the DSPs are not sufficient because the present DSPs can only process only ten thousand MIPS (Million Instructions per Second). Thus using the DSPs in the SDR makes the equipment much costlier. The other alternative cum advanced technology available for such multiple functions is FPGA which is cheaper and also performs the functions at the required rate. All the software techniques designed for SDR like modulation, mixing etc are done using FPGA. After FPGA the application is done on the specified module or handset. If the signal is to be transmitted from the device then the reverse procedure is followed. To perform different operations in the SDR respective algorithms are developed. The main advantage of the SDR is that if the processes are to be changed then an algorithm for the procedure is developed, it can be embedded into the integrated chip and can be executed. Thus it becomes easier for any type of modification to be done. There are different software organizations like JTRS JPEO to develop the algorithms. Fig 1 Block diagram of Software Defined Radio III. ANTENNA USED FOR SDR For the purpose of detection of signals we have different types of antennas, but among the available varieties the most suitable and efficient types are Automatic antenna Tuning Unit system and Smart antenna systems. This paper describes the usage of these antennas for the SDR communication systems. a) Automatic antenna Tuning Unit (ATU) To have an effective and efficient communication between different modules, the antennas should be highly gainful so that there is no loss in signal reception. ATU is one such antenna that provides a wideband signal reception capability. Different blocks present in the ATU system is shown in Fig 2. The tunable patch antenna with a surface mounted variable capacitor circuit is used for the purpose of signal detection. The patch antenna is shown in the fig 3 and the relevant variable capacitor circuit is shown in fig 4. When the signal is reached at the antenna then the electromagnetic wave gets induced into the inductor in the capacitor circuit, which generates the voltage. Depending upon the voltage received at the capacitor side of the circuit the capacitance gets adjusted. Suppose when the signal is not there at the inductor side then the voltage is zero and the diode gets switched OFF, which makes only one capacitor C1 to work making the circuit a passive circuit. Thus at this level the system becomes inactive. Now when any signal is received, then the voltage is increased, the circuit gets activated and the capacitance gets adjusted by varying C1 and C2. An impedance synthesizer circuit is present which always tries to match the circuit impedance with the received wave impedance. In this process if different frequencies are received at different times, then different impedances are to be provided. So for this purpose RF MEMS (Radio Frequency Micro electro Mechanical System) are used to switch from one value to the another value. RF MEMS are nothing but the electronic components of which moving sub milli meter sized parts provide RF functionality. The impedance synthesizer is connected to the patch antenna using an SMA (Sub Miniature Version A) connector whose impedance is 50 ohms. These impedance synthesizers have combinations of different inductors and capacitors and these are mainly used to match the received signal with the circuit. In order to constantly monitor the signal to noise ratio the incident and reflected power levels are measured with the help of the RF power sensor placed next to the impedance synthesizer. The SNR should be high so that we get a proper signal instead of noise. The directional coupler is used to allow the reasonable and correct signals into the SDR module. After the signal is undergone all these steps it is sent to the towards the SDR unit where further proceedings will take place. This type of ATU can be used to detect the frequencies in the range of 500MHz-2GHz. The SDRs are mainly concentrated on the newly sophisticated wireless communications, ISSN: 2231-5381 http://www.ijettjournal.org Page 1822
so for the purpose of such speedy communications we need such type of antennas which can exist at any type of communication environments. Moreover the applications that are being developed now a days are demanding the Automatic antenna Tuning Unit systems for their efficient performance in the real time communication systems. Fig 2 ATU system Block diagram Fig 3 patch antenna used for ATU Fig 4 Equivalent circuit of variable capacitor b) SMART ANTENNAS Smart antennas (SA) consists mainly an array of antennas which are used to spatially detect the signals in order to avoid the effects like multipath fading, interference etc. A specification was defined for the smart antenna system named SA API (Smart Antenna Application Programming Interface) which mainly concentrated on the software components and algorithms related to a particular model. For the purpose of SA systems different models were developed since the research on SA was started in 1960s. But for the SDR like applications a Platform Independent Model (PIM) was developed in which the software only knows the elements of SA system, but after implementing such a PIM the Platform Specific Model (PSM) was developed in which all the software required for the SA system was embedded. Smart antenna system consists of different subsystems which are shown in the figure 5. All these subsystems are considered to be a SA System. By using this SA system a perfect signal can be received/generated. Antenna Array consists of multiple antennas which are spatially placed, moreover the purpose of using multiple antennas is to receive the signal without any loss. Most of the times the signals are very much affected to the losses like multipath fading and interference. To avoid such losses, use of multiple antennas to cover each and every part of the signal is advisable. RF/IF subsystems consists of different blocks like low noise amplifiers (LNA), mixers, IF section, A/D or D/A converters etc. The Modem subsystem is for performing the actions on the signals like modulation and demodulation. SA subsystems consists of the algorithms, calculation units etc. MAC layer subsystem is used to provide multiple channels on a single platform. Based on the signal processing technique used the SA systems are of different types like Beam forming systems, Diversity combining systems, Multiple input Multiple output systems and space time equalization systems. The main advantage of smart antennas is that they always gives the details of Direction of Arrival(DoA) which can be used to align the antennas for the future reception to be perfect. Beam forming systems mainly concentrates on the beam pattern in order to receive and transmit in a specific direction. Beam forming is also known as spatial filtering or spatial diversity combining. In this technique all the signals of the respective antennas are collected by using their complex weights and then combined to generate the specified output. y= w* x Where y is the output from antenna, w is the beam forming weights and x is the individual antenna components. The above equation gives the summed result of each antenna s component multiplied to its complex weight. Adaptive beam forming is a technique in which the antennas are steered in the particular direction automatically in which the signal strength is better. Various beam forming algorithms were developed for optimizing the SNR and minimizing the interference. Finally among different types of Smart Antenna systems available the most advantageous system is beam forming system because it is covering all types of defects present in transmission process. ISSN: 2231-5381 http://www.ijettjournal.org Page 1823
b) RFID readers Fig 5 Smart Antenna system Methodology IV.RFID TECHNOLOGY Radio Frequency Identification (RFID) is a latest technology that is mainly used for detecting a unique code specified for a particular object. Now a days this technology is replacing the barcode detecting devices because of its efficient performance and also power consumption parameters. RFID technology is being used for collecting tolls without stopping vehicles, counting the number of items, offices, airports etc. The main components needed for using the RFID technology are RFID tag, RFID reader and the programming unit. Generally the programming unit that could be used is the Microcontroller unit. In the microcontroller the programming is done using either embedded C language or Assembly language. The details of the tags are stored in the microcontroller and can be accessed during the presence of the tag. The problems related to this type of procedure and solutions are discussed in this paper along with the range extension solution for the RFID reader. a)rfid tags RFID tags are a combination of a small integrated chip and a coil which acts as an antenna. These two components are joined together and used as a tag (transponder) which are in the shape of a small identity card provided in the offices. The IC consists of an EPC (Electronically Programmable Code) embedded into it during the time of manufacturing. Figure 6 shows an RFID tag. There are two types of RFID tags, Active tags and Passive tags. Active tags have a battery embedded into them, where as the passive tags doesn t have any battery. The power supply is obtained by the signal that is transmitted form the RFID reader. Fig 6 RFID tag RFID readers are the devices which detect the EPC embedded into the IC. RFID reader generates a signal of particular frequency of its specified range, when the tag is brought near the RFID reader then this signal gets induced into the coil (antenna) fixed in the tag. This induced signal generates a very small current in the coil and is passed along the coil towards the IC. When the current reaches the IC, it gets activated and reflects the current back along with the EPC. Now these reflected signals encounter with the antenna of the RFID reader. Then the reader detects the code present in the RFID tag. RFID readers are available in different ranges of frequencies as listed in the table 1. Frequency range Range 13.6 MHz 1 m 433 MHz 1-100 m 902-928 MHz 1-2 m 2450-5800MHz 1-2 m 3.1-10 GHz 1-200 m c) Programming unit The code received from the tag should be sent to the programming device in order to know what action has to be taken on the tag. For this purpose we can consider the microcontroller unit or ARM processor. But the microcontroller has some delays and moreover in order to process the tag we need to have memory. For example the tolls that should be collected from huge number of vehicles, are to be stored in a single IC which is to be implemented at every toll plaza. But such implementation of memory devices at many places is expensive and non affordable. We can use another alternative as SDR for the purpose of processing and storing the details of the tag. V. Multi Range RFID reader USING ATU and SDR The readers available in the market are operated only in a particular frequency ranges but by using Automatic antenna Tuning Unit system we can make the RFID reader to detect the signal of any frequency range depending on the efficiency of the ATU developed. The ATU discussed in this paper detects the frequency in the range of 500 MHz-2GHz. ISSN: 2231-5381 http://www.ijettjournal.org Page 1824
The block diagram of multi range RFID reader using ATU and SDR is shown in figure 7. Fig 7 multi range RFID reader using ATU and SDR The RFID readers available consists of normal antennas depending on the frequency range used for the reader. Now these antennas can be replaced with the ATU system. By replacing this the frequencies in the ATU detecting range can be accessed easily. Thus a multi range RFID reader could be developed which can work for any kind of RFID tags. By implementing this module the memory required for storing is reduced and also the accessing speed is also increased. for performance characterization of RFID tags IEEE transactions on instrumentation and measurement, VOL 61, No 4, APRIL 2012. [3].Muhammad islam, M A Hannam, S A samad and A. Hussain Software defined radio for RFID Application. [4].sung hoon oh, hang song, james T.aberle, bertan Bakkaloglu and caitali chakrabarti Automatic antenna tuning unit for software defined and cognitive radio. [5].KE-LIN DU & M.N.S.SWAMY WIRELESS COMMUNICATION SYSTEMS for RF subsystems to 4G enabling Technologies. [6]. Software Defined Radio Forum, 2007 [online] Available: http://www.sdrforum.org. [7]. Kin Seong Leong, Synchronization of RFID Reader Environments, IEEE from Proceedings of 2006 Symposium on Applications and Internet, Jan. 2006 [8]. Afshin Haghighat, A review on essentials and technical challenges of software defined radio, IEEE British Crown, 2002 [9]. Aberle J, Bakkaloglu B, Charkrabarti C, et al. Automatically tuning antenna for software-defined and cognitive radio. Proceedings of the 2005 Software Defined Radio Technical Conference, 2005. [10]. Oh S-H. Automatically Tuning Antenna System for Software Defined and Cognitive Radio. Ph.D. Dissertation, Arizona State University, May 2006. [11]. Aberle J, Oh S-H. Reconfigurable antenna technology for VHF/UHF applications. Technical Report, General Dynamics Decision System, Oct 2004. An SDR is placed after the RFID reader, which is used to process the received tag information. A common database could be maintained on the internet. When the tag reaches the toll plaza the code is detected and sent to the SDR. The SDR now using the database available on the internet checks for the code and can cut the required amount from the account of the user. VI. CONCLUSION In this paper the antennas used for the SDR were discussed. The SDR is going to be the main basic module for the future wireless communication technologies like 3G and 4G communications. The process of implementation of the multi range RFID reader using ATU and SDR is also discussed. The software tools used in the SDR are making easier task to embed any software and change the communication techniques like modulation, mixing etc. The hardware and software tools used in the SDR are making the wireless communication system cheaper compared to the present day technologies. Thus SDR is going to replace many wireless technologies in the future. REFERENCES [1].Seungheon Hyeon, June Kim, and Seungwon Choi, Hanyang University Evolution and standardization of the smart antenna system for software defined radio. [2]. Luca catarinucci, Danilo De Donno, Riccardo Colella, Fabio Ricciatio and Lucianno tarricone A cost effective SDR platform Biography Salman khan pattan was born in 1991, Vijayawada,Andhra Pradesh. He is studying final year B-tech in K L University. He has done a project on RFID technology. His area of interest is communications. Email: salmanece857@gmail.com Suresh Angadi * is presently working as a Asst.Professor in K L University. He received his B.Tech degree in electronics and communication in G.V.P College of Engineering, vizag, 2007 and completed M.Tech in Maulana Azad National Institute of Technology (MACT) in 2009, Bhopal. His research interested area is communications. Email: Suresh.a@kluniversity.in ISSN: 2231-5381 http://www.ijettjournal.org Page 1825