PERFORMANCE EVALUATION OF VFFT-OFDM SYSTEM IN THE PRESENCE OF CARRIER FREQUENCY OFFSET

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2 PERFORMANCE EVALUATION OF VFFT-OFDM SYSTEM IN THE PRESENCE OF CARRIER FREQUENCY OFFSET Ni Made Ary Esta Dewi Wirastuti, I Made Arsa Suyadnya, Duman Care Khrisne Study Program of Electrical Engineering Faculty of Engineering 2018

3 Outline: Motivation Introduction Objectives DFT, FFT dan VFFT CFO Simulation Results and Analysis Conclusion 2

4 Motivation (1) Next generation mobile: System complexity and energy efficieny Chips next generation mobile: cheaper, faster dan smaller 3

5 Motivation (2) 4

6 Introduction (1) o o o o o Need of fast data access in Multimedia communication Orthogonal Frequency Division Multiplexing (OFDM) one of the main technologies that implemented in wireless communication main candidate for future mobile generation Application: DAB, DVB, Wireless LANs, broadband wireless internet (802.16), LTE. 5

7 Introduction (2) o o o One of components OFDM that needs intensive calculation: inverse Fast Fourier Transform (IFFT) dan Fast Fourier Transform (FFT) VFFT offer lower complexity implementation that implemented in various to replace FFT Reducing FFT complexity improve power efficiency VFFT-OFDM (G- OFDM) 6

8 Pendahuluan (4) o OFDM communication systems are sensitive to the frequency synchronization in form of carrier frequency offset (CFO). CFO severely degrades the performance of the OFDM systems 7

9 Objectives o o To model OFDM and VFFT-OFDM system using LTE parameters over AWGN and Rayleigh fading channels To analyze the effect of carrier frequency offset to the OFDM and VFFT-OFDM performance 8

10 OFDM Conventional multi-carrier modulation Parallel data, Non-overlapping sub-channels, FDM Orthogonal multicarrier modulation Parallel data, Overlapping subchannels, OFDM 9

11 DFT Implementation Typical TX OFDM Typical RX OFDM 10

12 Carrier Frequency Offset (1) One of the main disadvantages of the OFDM system is the sensitivity to offset frequencies Caused by jitter on the carrier signal Doppler effect caused by movement of both the TX and Rx. 11

13 Carrier Frekuensi Offset (2) Synchronization is an important part of the receiver because the time difference in the clock and frequency of the local oscillator can cause a decrease in performance on the system. 12

14 Carrier Frequency Offset (3) Time synchronization is used to select the boundary of the symbol and frequency synchronization to equalize the oscillator between the receiver and the transmitter. The orthogonal subcarrier properties will disappear and ICI appears if both synchronizations are not performed. 13

15 Carrier Frekuensi Offset (4) Frequency synchronization error or the difference in frequency between the transmitter and receiver oscillator causes frequency offset. The result : the demodulation process by DFT sampling the wrong position. 14

16 Carrier Frekuensi Offset (5) The carrier signal power on the sampled channel decreases ("+") and the ICI appears in the adjacent subcarrier ("O") signal. This results in a decrease in the SNR value 15

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18 Simulation (1) OFDM parameter in LTE, modulation Quadrature Phase Shift Keying (QPSK). Observe the presence of offset frequency, shifted subcarrier termed as normalized frequency offset (ε) : 0.2 dan 0.05 Comparing the performance of OFDM and VFFT-OFDM systems without ICI reduction methods on AWGN and Rayleigh fading channels using the BER vs. parameter. Eb / No. 17

19 Simulation (2) o Simulation model TRANSMITTER Transmitted Data Coding & Mapping QPSK Serial to parallel converter IVFF Parallel to serial converter Guard interval insertion BER evaluation MEASUREMENT TOOL RADIO CHANNEL Rayleigh fading channel AWGN channel Received data De-coding & Demapping QPSK Parallel to serial converter VFFT Serial to parallel converter Guard interval removal RECEIVER 18

20 Simulation (3) o Parameter: Parameter Nilai yang digunakan N frame 5000 Clipping Ratio (CR) Classical Clipping = 1,4 Deep Clipping = 0,6 FFT Size 64 N of data subcarriers 64 Guard periode type Cyclic prefix N bits per OFDM 64 symbol N symbol 1 N Cyclic prefix ¼ (N of data subcarriers) Total symbol N of data subcarriers + N cyclic prefix Mbit 4 19

21 Results and Analysis (1) Frequency Offset model on OFDM over AWGN channel e j2 n /N n(n) X(m) IDFT x(n) y(n) DFT Y(k) 20

22 Results and Analysis (2) j2πnε N y( n ) = x( n ) e +n( n), N 1 ( ) j N N N Y( k) = X( l ) e + n ( m) e N 2 m l+ k j2 mk N m= 0 l= 0 m= 0. ( l k) ( ) N 1 2 n l+ k j N e n= =, N N 1 1 Y( k) = X( k) ( 0 ) + X( l) ( l- k ) + N( k), N l=0,l k 21

23 Results and Analysis (3) S N = a N ( 1 r ) 1 r, e e -. N N e e ( l+ k) ( ) ( l+ k) ( l+ k) l+ k ( l k) = j j j j N e j ( l+ k) j ( l+ k) j = e e, x x 2 sin x j j 22

24 Results and Analysis (4) ( ) N 1 j ( l+ k ) sin ( l + k) N ( l- k) = e. ( l + k) N sin N y = x + n -1 Y = F F X+ N 23

25 Results and Analysis (5) Offset Frequency model in OFDM system over Rayleigh fading channel h(n) n(n) exp(j2 n /N) X(l) x(n) y(n) Y(k) 24

26 Results and Analysis (6) AWGN 25

27 Fading 26

28 Conclusion The decrease in Bit Error Rate (BER) due to the carrier frequency offset has been successfully simulated in this study. For the decrease of BER 0.5x10-4 which can be ignored, the maximum tolerable frequency offset is less than 1% of the sub-carrier spacing on the AWGN channel. Whereas in the fading channel, the decrease in BER is 0.3x10-2 which can be ignored, maximum tolerable frequency offset is smaller than 4% of the sub-carrier spacing. 27

29 References (1) Alexandru, Dumiru N., Ligia O.A ICI Reduction in OFDM Systems Using Phase Modified Sinc Pulse. Wireless Pers Community. Ahn, J. and Lee, H. S Frequency domain equalization of OFDM signal over frequency nonselective Rayleigh fading channels, Electron. Lett., vol. 29, no. 16, pp Cooley, W. and Tukey, J. W An algorithm for the machine calculation of complex Fourier series, Mathematics of Computation, Volume 19, pp Dahlgren F , Future Mobile Phones Complex design Challenges from an Embedded System Perspective. Proceedings Seventh IEEE International Conference on Engineering of Complex Computer Systems, pp Duhamel, P. and Hallmann, H Split radix FFT algorithm, IEE Electronics Letters, Volume 20, No. 1, pp Dhahi, N. A Optimum finite length equalization for multicarrier transceivers, IEEE Trans. Communication., vol. 44, pp Lim, H. and Swartzlander, E. E Multidimensional systolic arrays for the implementation of discrete Fourier transforms, IEEE Transaction on Signal Processing, Volume 47, pp Muschallik, C Improving an OFDM reception using an adaptive Nyquist windowing, IEEE Trans. Consum. Electron., vol. 42, no. 3, pp Mourad, H. M Reducing ICI in OFDM systems using a proposed pulse shape, Wireless Person. Commun., vol. 40, pp Nst, S.S., Fahmi A., Prasetya B., Analisis Penerapan Metode Pulse Shaping Pada Sistem Orthogonal Frequency Division Multiplexing (OFDM) dalam Mereduksi Intercarrier Interference(ICI), Tugas Akhir Telkom University, Bandung. Shepherd, S. J., Eetvelt, P. W. J. van, Jones, S. M. R., Noras, J. M. and Rajamani, H. S A Lower Complexity Discrete Fourier Transform", Mathematics Today, 39, (5), pp

30 References (2) Tan, P. Beaulieu, N.C Reduced ICI in OFDM systems using the better than raised cosine pulse, IEEE Commun Lett., vol. 8,no. 3, pp V. Kumbasar and O. Kucur ICI reduction in OFDM systems by using improved sinc power pulse, Digital Signal Processing, vol. 17, Issue 6, pp Wang, Y., Lam, H.M., Tsui C.Y., Cheng R.S, W.H. Mow Low complexity OFDM receiver using Log-FFT for coded OFDM system, IEEE International Symposium Circuit and System (ISCAS), Volume 3, pp Winograd, S On computing the discrete Fourier transform, Proc. Nat. Acad. Sci., U.S., Volume 73, pp Wirastuti, N.M.A.E.D., Noras, J.M., Jones, S.M.R Performance Evaluation of G- OFDM over Multipath Fading Channels. The fourth workshop on Signal Processing for Wireless Communication (SPWC), King s College London, United Kingdom. Weinstein, S. B. dan Ebert, P. M Data Transmission by Frequency Division Multiplexing using the Discrete Fourier Transform, IEEE Transactions on Communications, Volume 19, No. 5, pp Zhao, Y. and Haggman, S. G Intercarrier interference self-cancellation scheme for OFDM mobile communication systems, IEEE Trans. Commun., vol. 49, no. 7, pp , July. Zhao, Y. and Häggman, S. G Sensitivity to Doppler shift and carrier frequency errors in OFDM systems The consequences and solutions, in Proc. IEEE 46th Vehicular Technology Conf., Atlanta, GA, pp