Reducing PAPR with Optimization Based Spectrum Sensing Using FPGA Configuration

Transcription

1 Volume 118 No ISSN: (on-line version) url: Reducing PAPR with Optimization Based Spectrum Sensing Using FPGA Configuration 1 Mr.B.Maheswara Rao 1 Research scholar, Dept of E&C Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, Chennai 62 maheswar414@gmail.com 2 Dr.S.Baskar 2 Professor, Dept of E&E Vel Tech Rangarajan Dr. Sagunthala R&D Institute of Science and Technology, Chennai 62 drbaskar@veltechuniv.edu.in April 27, 2018 Abstract Cognitive radios are evolving as flexible all-purpose radios that can implement new and different standards or protocols through reprogramming. Cognitive radio provides seamless services by time sharing the processing resources. It provides the ability to connect with various networks on a single device. Field Programmable Gate Arrays (FPGAs) can offer more bandwidth to many signal processing applications by providing hardware parallelism. FPGAs are more advantageous to implement front end designs than digital signal processors (DSP)[1]. FPGAs physical bit level programming architecture is desired for digital signal processing algorithms as it is suitable for implementing many arithmetic applications while DSPs provide a fixed multiply-andaccumulation (MAC) operation support. Lately with the 1

2 rise in the use of Partial Reconfiguration (PR) many such applications have been implemented with improved performance [2]. Key Words:Cognitive radio, PAPR, Spectrum sensing, OFDM 1 INTRODUCTION Many of these applications require reconfiguration during run time. On the fly partial reconfiguration implementation of such systems facilitates faster reconfiguration and better resource utilization. Partial Reconfiguration is a very unique way of keeping the critical static processes alive while the system is being reconfigured. In this way the reconfigurable time is considerably reduced. Also the space required to contain the design is reduced as the FPGA holds only the designs necessary for a particular configuration and not all the details of the system. Hence whenever a change in configuration is required a new partial bit stream is loaded into the space and operated. In 3rd generation, IEEE standard implements the OFDM for uplink and downlink. In next generation, LTE (Long Term Evolution) used orthogonal Frequency Division Multiplexing (OFDM) for its downlink and single-carrier Frequency-Division Multiple Access(SC-FDMA) for its uplink. Therefore in this generation, OFDM becomes a main multicarrier scheme for communication system. OFDM has emerged as promising air interface technique. In Context of wired environments, OFDM techniques are also known and Discrete Multi Tone (DMT) transmission and are employed in the American National Standards Institute s (ANSI), ADSL, HDSL and VDSL[3]. In multicarrier transmission schemes, subcarriers are uniformly spaced and sub channel filters are identical, an efficient digital implementation is possible and its generally referred to as filtered multi tone modulation (FMT). It is based on a fast Fourier transform (FFT) followed by low rate sub channel filtering. Channel frequency selectivity introduces inter carrier (ICI) and inter symbol (ISI) interference at the receiver[4]. the design of the sub channel filters and he choice of the subcarrier spacing in FMT system aim at subdividing the spectrum into a number of sub channels that do not overlap in the frequency domain such that we 2

3 can avoid the ICI and get low ISI contributions. 2 REVIEW OF LITERATURE Despite the advantages of OFDM signals like high spectral efficiency and robustness against ISI, the OFDM signals have some disadvantages among which the main one is the high PAPR. This high PAPR signal when transmitted through a nonlinear power amplifier creates spectral broadening and also an increase in the dynamic range of the digital to analog converter (DAC). To overcome this impact, several techniques for reducing the PAPR have been proposed. Some of the most important techniques are selected mapping (SLM) [5] which is in frequency domain and PTS [6] which is in time domain. In [7] authors proposed phase weighting method, sub-block phase weighing but they didnt achieve complexity reduction. Here with applying the new phase sequence by first generating the matrix of phase sequence and then partitioning it based on the requirement for PAPR reduction and also complexity. With this new phase sequence the complexity of PTS reduces significantly as it reduces the number of IFFT but it only degrades the PAPR performance slightly. One of the major problems of OFDM signal is the high PAPR which leads to power inefficiency in RF section of the transmitter and increased complexity in the analog to digital and digital to analog conversion. The distortion and distortion-less (scrambling) technique has been developed to overcome high PAPR problem of OFDM signals [8]. Selected mapping (SLM) is one of the most promising among all these techniques because it is simple to implement, introduces no distortion in the transmitted signal, and can achieve significant PAPR reduction. With this technique, the price to pay is a loss in data rate due to the transmission of several side information bits. To avoid the need for explicit side information transmission in SLM, a few techniques have been proposed such as the scrambling method described in [9], partial transmission sequence (PTS) and the maximum likelihood (ML) decoding scheme introduced in [10]. In [11] that the input oscillator has a single, fixed frequency, and employ a second reconfiguration technology, Dynamic Recon- 3

4 figurable Port (DRP), to reconfigure the DCM output frequency while the radio is operating. The technique of DRP could be combined with PR to address the difficulties of communication standard or mode switching in terms of clock frequency and dependent functionalities. This architecture increases hardware reusability significantly and permits standard or mode switching with ease according to the customers requirements. 3 OBJECTIVES To use a novel frequency guard extending technique which can meet the spectral leakage requirements, offering good out of band attenuation allowing deployments for dynamic spectrum access. To obtain optimal solutions generated by a CR engine to handle the trade-offs between multi-objective optimization parameters. To reduce the PAPR of the OFDM signals, using a method that mixes tone reservation (TR) technique and phase information of the pilot symbols. This can be done by employ complementary cumulative distribution function (CCDF) of the PAPR for the transmitted signal 4 OFDM BASED CR ARCHITECTURE The OFDM applications to CR bring new features and challenges to system design. An OFDM based CR model is shown in Figure 1. The cognitive engine is the main unit of this model. Basically, cognitive engine is an intellectual unit that is responsible for making the intelligent decisions and configures the PHY parameters. The decision unit can identify the spectral opportunities based on the information from policy engine through local and network spectrum sensing data [10]. 4

5 Figure 1- Research challenges in CR and OFDM After that, policy engine gives information to the cognitive engine regarding to the present policies to be measured depending on the system location. When the necessary information is available, the decision unit can make an execution in a proper way for the system. The decision encompasses selecting the suitable channel coding, modulation bandwidth and operating frequencies. At this present stage, OFDM technology has advantages over other similar transmission technologies with its adaptive and flexibility features. The cognitive engine system can correspond with different radio access technologies in the environment by only changing the configuration parameters of OFDM. The radio circuit is divided into digital and analog parts. The digital part consists of digital IF, ADC, and DAC. The antenna parameters (beam forming, number of antennas) can be configured in order to improve the system performance. 5 PROPOSED SYSTEM The structure of the proposed system is illustrated in Figure 2. This system is divided into three blocks. They are cognitive radio, transmitter and receiver. The key idea is to construct the cognitive radio block in standalone software running on a soft processor core, or implemented in hardware in a separate part of the FPGA. 5

6 FIGURE 2- ARCHITECTURE OF PROPOSED SYSTEM The transmitter block follows frequency division technique to transmit the data and hence feedback channel is selected. This cognitive feedback channel sense the spectrum based on optimization based unit. So that the optimal spectrum can be selected. This selected spectrum must be equalized with certain bandwidth allocation system and that will be done by novel frequency guard extending technique. In the receiver side the Synchronization and channel estimation technique is in contact with the cognitive radio link. As a result of receiver part the PAPR can be reduced using complementary cumulative distribution function (CCDF) of the PAPR for the transmitted signal. 6 NOVEL FREQUENCY GUARD EX- TENDING TECHNIQUE The length of the guard interval (CP or ZP) is set longer than or equal to the maximum delay of a multipath channel, the ISI effect of an OFDM symbol on the next symbol is connected within the guard interval so that it may not affect the FFT of the next OFDM symbol, taken for the duration of (). Guard interval should be longer than maximum delay of the multipath channel for maintaining the orthogonality among the subcarriers. 7 MATHEMATICAL EXPRESSION Clark model is applicable to mobile reception in general scattering environments. R. k Clark modeled the mobile channel as a Rayleigh fading channel. R. K Clark considered non-los between 6

7 the transmitter and the receiver. The radio signal is reflected and scattered due to obstacles such as buildings, mountains and trees. Clark has also considered the Doppler effect because of motion of mobile unit. The phase and angle of arrival of each element wave will be statistically independent. Clark model expresses the carrier signals received at the mobile whose phases are supposed to be Gaussian random variables and the phase angle is uniformly distributed on the interval 0 to 2π. Doppler shift is given by: (1) where, (2) is the carrier frequency v is the mobile velocity is the angle λ is the carrier wave length According to the Clark assumption, the Efiled can be represented as an in phase and quadrature. (3) (4) (5) Here, and both are Gaussian random processes. Those are uncorrelated zero-mean Gaussian random variables and variance is equal which given by: (6) Then, the magnitude of E-field is specified by: (7) Rayleigh distribution is given by in (8) where, is the variance of the Rayleigh distributed variables. 8 MATHEMATICAL DEFINITIONS The theoretical BER for BPSK or QPSK using AWGN channel: (9) where, is spectral noise density and is energy per bit. The theoretical BER for BPSK or QPSK using Rayleigh fading channel: 7

8 (10) where, is spectral noise density and is energy per bit. 9 PAPR REDUCTION The complementary cumulative distribution function (CCDF) of the PAPR for the transmitted signal are plotted in Figure 3 and 4, where the PAPR technique being employed by the iterated clipping and filtering. It is evident from these results that the PAPR can be improved by using iterated clipping and filtering. FIGURE 3- PAPR REDUCTION USING QPSK WITH CLIPPING AND FILTERING In the Figure 3, by increasing PAPR, we observed that CCDF is 10-3 at 10.8 db; but during next iteration, same 10-3 is achieved at less PAPR 9.95 db. At fourth iteration, PAPR is 6.7 db. 8

9 FIGURE 4- PAPR REDUCTION USING QAM16 WITH CLIPPING AND FILTERING In the Figure 4, by increasing PAPR, we observed that CCDF is 10-3 at 10.6 db; but during next iteration, same 10-3 is achieved at less PAPR 9.7 db. At fourth iteration, PAPR is 6.65 db. In the system, repeated clipping and filtering significantly reduce PAPR, where modulation schemas are QPSK, and QAM16. PAPR of QAM16 is low compared to QPSK which gives better result can be as seen in Figure 5. According to the fourth iteration, PAPR are given respectively Fig 4,5, and 6.65 db for QPSK, and QAM16. Finally, it can be concluded that QAM16 is given better result compared to the QPSK. 10 CONCLUSION This Paper presented an overview of Orthogonal Frequency Division Multiplexing (OFDM) and Cognitive Radio (CR). This dissertation proposes a novel non-contiguous OFDM (NC-OFDM) technique, where the implementation achieves high data rates of noncontiguous subcarriers while simultaneously avoiding any interference to the transmissions. The main goal of this thesis work was to investigate PAPR reduction techniques for non-contiguous bands of OFDM based CR system. Simulation results of PAPR reduction has shown that the performance of QAM16 is good compared to others modulation schemes such as BPSK, QPSK. 9

10 References [1] Upadhyaya, BK, Sanyal SK. Design of a novel FSM based reconfigurable multimode interleaver for WLAN application International Conference on Devices and Communications (ICDeCom); 2011 Feb p. 15. [2] K.G.Nezami, P.W.Stephens, S.D.Walker, Handel-C Implementation of Early-Access Partial-Reconfiguration for Software Defined Radio. Wireless Communications and Networking Conference, IEEE.,2008,pp [3] Lu Zhaogan, Rao Yuan, Zhang Taiyi, Wang Liejun. Multiuser MIMO OFDM Based TDD/TDMA for Next Generation Wireless Communication Systems Wireless Pers Commun 52: , Springer (2010) [4] Berger,C.R.; Gomes, J.; Moura, Sea-trial results for cyclicprefix OFDM with long symbol duration J.M.F. OCEANS, 2011 IEEE Spain [5] Cosovic, I.; Brandes, S.; Schnell, M. Subcarrier weighting: A method for sidelobe suppression in OFDM systems. IEEE Commun. Lett. 2006, 10, [6] Selim, A.; Doyle, L. Real-time sidelobe suppression for OFDM systems using advanced subcarrier weighting. In Proceedings of the 2013 IEEE Wireless Communications and Networking Conference (WCNC), Shanghai, China, 710 April 2013; pp [7] Cosovic, I.; Mazzoni, T. Suppression of sidelobes in OFDM systems by multiple-choice sequences. Eur. Trans. Telecommun. 2006, 17, [8] Li, D.; Dai, X.; Zhang, H. Sidelobe suppression in NC-OFDM systems using constellation adjustment. IEEE Commun. Lett. 2009, 13, [9] Pagadarai, S.; Rajbanshi, R.; Wyglinski, A.M.; Minden, G.J. Sidelobe suppression for OFDM-based cognitive radios using 10

11 constellation expansion. In Proceedings of the Wireless Communications and Networking Conference, 2008 (WCNC 2008), Las Vegas, NV, USA, 31 March3 April 2008; pp [10] Selim, A.; Ozgul, B.; Doyle, L. Efficient sidelobe suppression for OFDM systems with peak-to-average power ratio reduction. In Proceedings of the 2012 IEEE International Symposium on Dynamic Spectrum Access Networks (DYSPAN), Bellevue, WA, USA, 1619 October 2012; pp [11] Ke He & Louise Crockett & Robert Stewart, Dynamic Reconfiguration Technologies Based on FPGA in Software Defined Radio System In Proceeding of 33rd ISCA (International Symposium on Computer Architecture). Boston, MA USA, June 1721,

12 Mr.B.Maheswara Rao received his B.Tech in (Electronics & Communication Engineering) from Sri Raja Rajeswari Engineering College (JNTUH) in 2006 and M.Tech (VLSI System Design)-From Hyderabad Institute of Technology & Management (JNTUH) in 2010 and Advanced Diploma in Data Science and Big Data Analytics from National Institute of Electronics and Information Technology, Calicut, in March-July 2017, Student Member of IEEE, respectively. Currently, working towards the Ph.D. degree in Electronics and Communication Engineering, from Veltech Rangarajan Dr.Sagunthala R&D Institute of Science and Technology, Avadi, Chennai India. His research interests include VLSI Technology & Design, Wireless Communication and Networks, MIMO-OFDM, Cognitive Radio Networks. Dr.S.Baskar received his B.E (Electrical & Electronics Engineeering) from Annamalai University and M.Tech (Power Electronics) from Vellore Institute of Technology, India. He has completed his Ph.D EEE in the specialization area of FACTS controllers from Annamalai University. He is currently working as Professor in the Department of Electrical and Electronics Engineering, at Veltech Rangarajan Dr.Sagunthala R&D Institute of Science and Technology, Avadi, Chennai, India. His research interests include Power Electronics, Control and Modeling of FACTS Controllers and its application to power system 12