OFDM Transceiver with Gaussian and Alpha-Stable Noise Presenter: Umber Noreen Supervisors: Ahcene Bounceur Laurent Clavier 1
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
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
Applications of OFDM Employed in several Wi-Fi or IEEE WLAN Standards, e.g. IEEE 802.11a IEEE 802.11g IEEE 802.11n Broadband Spectrums High Data Rates OFDM IEEE 802.11ac 4
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 8678645645564564321235111 f m f Fundamental 12111645645 in Total 0 frequency BandWidth f m ax T T d T d is 20 times Larger than T. Causes Inter Symbol Interference 5
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
OFDM : Ground Concept H(f ) ub ands 0 1 2 3 - - - - - - - - - - - - - f min f 0 8678645645564556666666666666666666 666666432123511112111645645 Total BandWidth N 1 f max 7
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
Step by Step Explanation of Block diagram Original Bit Stream S(t) = 01001010110101001111011010000 10000110111101000111101011111 000011 Step1: Sampling Version of S(t) : S[n] = 0100 1010 1101 0100 1111 0110 1000 0100 0011 0111 1010 0011 1101 0111 1100 0011 9
Step by Step Explanation of Block diagram (Cont ) Step2: QAM Mapping X n [k] ; 0 k N 1 10
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
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
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
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
Characterization of Noise in Wireless Channel Input Gaussian Noise Channel Response Wireless Channel Other Noises Output Impulse Noise 15
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
OFDM Transceiver with with Channel Response p=[1 0.8] 15 Input Symbols Output Symbols 10 5 0 0 2 4 6 8 10 12 14 16 17
OFDM Transceiver with Gaussian Noise Number of Errored Bits = 4 Transmitted Data (integers): 4 10 13 4 15 6 8 4 3 7 10 3 13 7 12 3 Received Data (integers): 4 10 13 4 15 6 8 9 7 7 10 3 13 7 12 3 15 10 5 Input Symbols Output Symbols 0 0 2 4 6 8 10 12 14 16 18
Relation between Gaussian and alpha Stable noise 19
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 = 0.001 ; delta = 0 20
OFDM Transceiver with Alpha-Stable Noise(Cont ) 15 Input Symbols Output Symbols 10 5 0 0 2 4 6 8 10 12 14 16 21
BER and PER of OFDM System with Gaussian Noise 22
BER and PER of OFDM System with Alpha-Stable Noise 23
Merci 24