FPGA Based Signal Security Using FHSS

Size: px

Start display at page:

Download "FPGA Based Signal Security Using FHSS"

Lydia Lewis
6 years ago
Views:

1 FPGA Based Signal Security Using FHSS Pralay Shende, Nilay Neve, Faizan Momin, Rutuja Deshmukh SavitribaiPhule Pune University. Abstract: Security of the data, information is the major topic of concern in the today s world of technology. Only password protection security is not sufficient from the intentional interference of data. This work is based on the data protection using FHSS (Frequency Hopping Spread Spectrum) which is one of the best techniques in the field of communication where the data is hidden in the background noise by modulating it with high frequency carrier and spreading its bandwidth using pseudorandom sequence [1]. As FPGA s makes the hardware implementation simple because of its advantages of high speed, flexibility, etc. [2]. The main objective of this work is to build the hardware implementation of FHSS transmitter using FPGA having Xilinx Simulator and verifying the result on Spectrum Analyzer. On the similar hands the receiver can also be design.along with this, this paper will be giving idea of how the lives can be saved of people living on coastal areas and protection of country using FHSS. Keywords: Spread Spectrum, FHSS, FPGA, Xilinx, PRBS, Modulation. I. INTRODOUCTION As advancements and the usage in the field of communication increasing, it became necessity to increase the security so that the significant information should not get into the hands of unauthorized person. Using FHSS it is possible to have protected communication and immune channel against any external interference. It uses pseudorandom sequence which spreads the spectrum, thus signal after spreading appears as the noise to the receiver. Only the intended synchronized receiver having same PN sequence can decode the code and extract the information [1]. In FHSS available spectrum bandwidth is divided into huge number of non-overlapping frequency slots. This FHSS signal is broadcast over a seemingly random series of radio frequencies. Here, Frequency does not stable over the particular band of spectrum despite it keeps on changing from one frequency to other at every moment of time. It has having numerous advantages like protection against intentional interferencelike jamming, as different codes are assigned for the signals from different users and even the single channel is used for the transmission there is no unintentional takes place, self-interference avoidance due to multipath propagation, LPI, encrypting message to obtain privacy. Because of this advantages FHSS is used extensively in communication, mostly it is used in Wi-Fi and Bluetooth. Moreover its application can be extended in saving the lives of peoples living on coastal areas. People on coastal areas are mostly fishermen. They don t have advance tracking system so, light house is the only their source of path during nights and even ships carrying prestigious things also follows light house. During unhealthy environment if they lost their path and come in contact with light house of other territory or country, they would consider its guide of path and unfortunately reached to the wrong destination. In order to save them from landing into mammoth trouble FHSS can be used. Using FHSS they can remain in contact with the base station located at coastal areas. Even if they lost their track, using FHSS trans- receiver module they can identify that the bay to which they are near at is desire destination or incorrect one and using PN sequence they can communicate with local base station and find the lost track. Along with this if someone gets into trouble in the middle of ocean, using FHSS immediate help can be send to person. Thus lives of local people of coastal areas and ships carrying important materials can be saved. Using FHSS tracking system it is possible to identify the unauthorized person or terrorist entering the territory, thus provides protection to country. II. TRANSMITTER DESIGN METHODOLGY Now, focusing on the transmitter module of FHSS, first modulation with high frequency carrier and then spreading the modulated signal with 286

2 pseudorandomsequence is to be done. Following fig. shows the block diagram of transmitter module. Fig. 2 PRBS generator using 4 bit LFSR Fig. 1. Block Diagram The block diagram consists of BPSK Modulation, Frequency Synthesizer, PN sequence, FHSS. Following sections cover the detail explanation of each block. 1. PRBS generator: A PRBS (Pseudorandom bit sequence) can be generated by using a linear feedback shift register (LFSR). Fig. 2 shows an example of a 4-bit LFSR and its shifting data pattern. When all 1 s bit entered in shift register, the table below shift register illustrates how the register contents change and put out a series of PRBS. Just after the final bit, it returns to the top of the bit stream. There are 15 bits of pseudorandom bit stream generated. An L-bit LFSR generates (2L -1) bits of PRBS. With careful looking at the bit pattern in the shift register, you can see there are all 4-bit combinations except all 0 s. If you feed the pattern of 0000, the shift register would be stuck and it generates only 0 s infinitely. So bit pattern must not be all 0 s. Hence, one of the 15 4-bit patterns can be accepted as i/p bit pattern. The PRBS bit generated as above will have the following characteristics:- 1. The length of the sequence generated by it, m = (2N-1), where N = number of bits (i. e., Flip-flops) of the shift register. 2. After every m number of binary bits, the sequence will be repeating itself. Using this PRBS generator logic, PN sequence is generated on Xilinx simulator. By adding no of flip flops in shift register, the PN sequence can be increased and hence the no. of frequency components needed for FHSS modulation can be increased. PN sequence generated on Xilinx is mapped on the LCD pins of FPGA and hence varying signals from LCD pins of FPGA according to 287

PRBS logic is taken out, as shown in fig. 1, and send for the processing of the same for spreading of signal. 2. Pull-up Circuit: Fig. 4 Voltage Divider Circuit. Fig. 3 pull-up circuit.

It switchess between 0V and 5V. The output of the pull up circuit is given to the voltage divider circuit as shown in fig. 1.

3 PRBS logic is taken out, as shown in fig. 1, and send for the processing of the same for spreading of signal. 2. Pull-up Circuit: Fig. 4 Voltage Divider Circuit. Fig. 3 pull-up circuit. Signal obtained from FPGA are of insufficient voltage for modulation. So, Pull up circuit is used to pull the input received from the FPGA. The transistor used is 2N222A. It acts as a switch. It switchess between 0V and 5V. The output of the pull up circuit is given to the voltage divider circuit as shown in fig. 1. Voltage divider divides the voltage received from the pull up circuit in order to make it compatible with the VCO unit. The voltage it gets is either 5V or 0V, as the transistor acts as a switch. Variable resistors are used in place of R1 and R2 so as to allow the user to vary the voltage as per requirement. 4.VCO unit: 3.Voltage Divider Circuit: 288

Fig. 6 Power Divider Power dividers are passive devices used in the field of RFtechnology. The power divider used is JS4PS-1W which has 4 input ports and 1 output.

It can be treated as switch selecting one of four VCO inputs. 6.BPSK unit: BPSK (Binary phase shift keying) modulation technique is used. For the modulation following components are used. a. Mixer ADE 1L for modulation.

4 Fig. 6 Power Divider Power dividers are passive devices used in the field of RFtechnology. The power divider used is JS4PS-1W which has 4 input ports and 1 output. Thus it divides the power between the four inputs arrived at power divider from VCO. It is having wideband frequency range between 5 to 1000 MHz. It can be treated as switch selecting one of four VCO inputs. 6.BPSK unit: BPSK (Binary phase shift keying) modulation technique is used. For the modulation following components are used. a. Mixer ADE 1L for modulation. b. 4MHz signal from FPGA. c. External signal ranging from 2 khz to 20 khz. The BPSK signal is generated by mixing 4 MHz square wave and the external carrierr frequency. The mixer selected can handle frequencies ranging from 2MHz to 50 MHz. Fig. 5 VCO unit 7.Mixer Unit: A VCO (voltage-controlled oscillator) is an electronic oscillator whose oscillation frequency is controlled by ainput voltage applied. The applied input voltage determines the instantaneous oscillation frequency. The VCO used is V560MC03. 5.Power Divider: Fig. 7 Mixer unit 289

5 The above diagram shows the circuit diagram of the mixer unit. It consists of 2 mixers ADE1L and ADE 12.The input to the ADE 1L is the carrier frequency and the 4MHz signal from FPGA. It gives BPSK output. Input to second mixer ADE-12 is BPSK signal and PN signals obtained from Power divider output. Thus, it spreads the modulated carrier over the spectrum which is nothing but the FHSS signal. III. Test Results: 1. BPSK output: BPSK signal generated using 4 MHz square wave from FPGA and external carrier frequency of 15KHz is shown below IV. CONCLUSION: FHSS signal hopping from one frequency to other frequency is depicted in spectrum analyzer. Thus FHSS signal is appears as a noise to all receivers but the intended receiver having the PN sequence which is same as the transmitter sequence can decode the signal and extract the information. Thus the signal security is obtained. In the similar manner receiver can be build. Project in Implemented in FPGA because it is cost effective and flexile as number of changes can be done in Xilinx simulator to verify the result. V. REFERENCES Fig. 8 BPSK output. 2. FHSS output: FHSS outputt is obtained by mixing the signals from power divider circuit and BPSK signal is shown spectrum analyzer. Fig. 9 FHSS signal [1] Adeel Ahmad, RahatUllah, ShahidLateef Efficient Transmission of Information using Transmission Code along FHSS, International Journal of Computer Applications ( ), Volume 40 No.9,February [2] KhushbooSewak, Praveena Rajput and Amit Kumar Panda FPGA Implementation of 16 bit BBS and LFSR PNSequence Generator: A Comparative Study IEEE Students Conference on Electrical, Electronics and Computer Science. Pages from [3] Mr.RaviBadiger, Dr. M. Nagaraja, Dr. M. Z Kurian, Prof.ImranRasheed Analysis, Design and Testing of Frequency Hopping Spread Spectrum Transceiver Model Using MATLAB Simulink International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering, Volume 3, Issue 2, February [4] G. Bouzid. H. Trabelsi, Z. Elabed, M. Masmoudi FPGA Implementation of FHSS- Conference on FSK MOdulator International Design & Technology of Integrated System in Nanoscale Era ISBN: /08. [5] Santiago T. Perez, Jesus B. Alonso, Carlos M. Travieso, Miguel A. Ferrer, Miguel A. Ferre, Jose F. Cruz Implementation of a Fast Frequency Hopping Spread Spectrum modulator with System Generator on a FPGA. proceedings of the 11 th WSEAS Int. Conf. on Mathematical Methods, Computational Techniques And Intelligent 290

6 Systems.ISSN: ISBN: [6] A.B.Carlson, P B Crully, J C Rutledge, Communication Systems, Fourth Edition, McGraw Hill Publication. [7] H. Taub, D. L. Schilling, Principles of Communication Systems, Second Edition, McGraw-Hill, New York, 1986 [8] Sorin M.SCHWARTZ, FHSS and DSSS in Broadband wireless Access (BWA) and Wireless LAN (WLAN), - schwartz.com 291

Analysis, Design and Testing of Frequency Hopping Spread Spectrum Transceiver Model Using MATLAB Simulink

Analysis, Design and Testing of Frequency Hopping Spread Spectrum Transceiver Model Using MATLAB Simulink Mr. Ravi Badiger 1, Dr. M. Nagaraja 2, Dr. M. Z Kurian 3, Prof. Imran Rasheed 4 M.Tech Digital