OFDM Transceiver with Gaussian and Alpha-Stable Noise. Presenter: Umber Noreen Supervisors: Ahcene Bounceur Laurent Clavier

Transcription

1 OFDM Transceiver with Gaussian and Alpha-Stable Noise Presenter: Umber Noreen Supervisors: Ahcene Bounceur Laurent Clavier 1

2 Contents What is OFDM Why OFDM for Broadband Systems OFDM Transceiver Step by Step Explanation of OFDM OFDM Transceiver and Gaussian Noise Alpha-Stable Distribution OFDM Transceiver and Impulsive Noise Simulation Results 2

3 What is OFDM?? Tremendous Growth of Wireless Communications. Key Broadband Wireless Technology Employed in 4G Wireless Systems, e.g. LTE 4G Cellular Standard LTE-A WiMAX Supports High Data Rates (around100s of Mbps) 3

4 Applications of OFDM Employed in several Wi-Fi or IEEE WLAN Standards, e.g. IEEE a IEEE g IEEE n Broadband Spectrums High Data Rates OFDM IEEE ac 4

5 Why OFDM for Broadband Systems Difference b/w the time of arrival of the earliest significant multipath component and time of arrival of the latest multipath components Broadband system of Bandwidth B = 10MHz second Symbol Time T = 1/B = 0.1µs Symbols pe Delay Spread T d 2µs 3µs f m f Fundamental in Total 0 frequency BandWidth f m ax T T d T d is 20 times Larger than T. Causes Inter Symbol Interference 5

6 ISI Problem As B the T Degradation of the performance Wireless Communication System Addressing the ISI problem is a significant challenge. So How to overcome ISI Digital data is sent using many carriers. Each sub-band is of different frequency. These sub-carriers are orthogonal to each other. Ensuring BW efficiency Form of distortion of a signal in which one Symbol interferes with subsequent symbols. 6

7 OFDM : Ground Concept H(f ) ub ands f min f Total BandWidth N 1 f max 7

8 Functional Block Diagram of a OFDM Communication System Serial Data In Serial to Parallel Constellation Mapping IFFT Parallel to Serial Cyclic Prefix Insertion Serial Data Out Parallel to Serial Constellation Demapping FFT Serial to Parallel Cyclic Prefix Removal Wireless Channel 8

9 Step by Step Explanation of Block diagram Original Bit Stream S(t) = Step1: Sampling Version of S(t) : S[n] =

10 Step by Step Explanation of Block diagram (Cont ) Step2: QAM Mapping X n [k] ; 0 k N 1 10

11 Step by Step Explanation of Block diagram (Cont ) In MCM k th sub-carrier N 1 [ k] exp( jπkft) = x ( t) X k = 0 kf is k th sub-carrier frequency. f min According to the Nyquist Theorem the sampling rate must be at least 2f max. Sampling interval T= 1/sampling frequency= 1/B. Fundamental frequency f = B/N. So the l th sample is at: f f max 11

12 Step by Step Explanation of Block diagram (Cont ) Step3: IFFT x n 1 1 N k = 0 [ l] = X [ k] N For l = 0, 1,, N-1 n exp j2πl k N l th IFFT point of X 0, X 1,, X N 1

13 Step by Step Explanation of Block diagram (Cont ) Let us consider two consecutive OFDM Samples to be transmit x (0), x (1), x (2), x (N 1) and x(0),x(1),x(2), x(n 1) If we transmit above samples consecutively then the output for x(0) will be y(0)=h(0)x(0)+ h(1) x (N 1)+ (N 1)+ h(2) x h(2) x (N 2)+ +h(l 1) x (N L+1) (N L+1) h(0)x(0) is required part. Addition of other part calls Inter Block Interference (IBI). 13

14 Step by Step Explanation of Block diagram (Cont ) Step3: Parallel to serial conversion Step4: Cyclic Prefix To avoid Inter Block Interference x n [0], x n [1],, x n [N L], x n [N l+1],, x n [N 1] Cyclic Prefix of length L Samples 14

15 Characterization of Noise in Wireless Channel Input Gaussian Noise Channel Response Wireless Channel Other Noises Output Impulse Noise 15

16 Functional Block Diagram of a OFDM Communication System Serial Data In Serial to Parallel Constellation Mapping IFFT Parallel to Serial Cyclic Prefix Insertion Serial Data Out Parallel to Serial Constellation Demapping FFT Serial to Parallel Cyclic Prefix Removal Wireless Channel 16

17 OFDM Transceiver with with Channel Response p=[1 0.8] 15 Input Symbols Output Symbols

18 OFDM Transceiver with Gaussian Noise Number of Errored Bits = 4 Transmitted Data (integers): Received Data (integers): Input Symbols Output Symbols

19 Relation between Gaussian and alpha Stable noise 19

20 OFDM Transceiver with Alpha-Stable Noise Received Signal R x = h 0 X 0 + i=1 n h i X i +N i=1 n h i X i = i=1 u h i X i Impulsive noise + i=u n h i X i Gaussian noise alpha = 1.8 ; beta = 0 gamma = ; delta = 0 20

21 OFDM Transceiver with Alpha-Stable Noise(Cont ) 15 Input Symbols Output Symbols

22 BER and PER of OFDM System with Gaussian Noise 22

23 BER and PER of OFDM System with Alpha-Stable Noise 23

24 Merci 24