1 Outline Standard OFDM Systems OFDM systems Intersymbol

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Outline Standard OFDM Systems OFDM systems Inter-symbol interference Inter-carrier interference ICI Self-Cancellation Method Several ways to allocate data in ICI SC Proposed schemes of ICI SC Papers reference 2

OFDM model 3

Inter-Symbol Interference(ISI) p caused by ： （1） Multipath Propagation ：the transmitted signal would be scattered, reflected, diffracted and blocked by the environment （2） Symbol Timing Offset ： transmitter and receiver do not have a common time reference 4

Multipath Propagation • With the effect of multipath propagation, receiver receives the signals at time k is ISI term AWGN noise 5

Symbol Timing Effect p Add cyclic prefix(CP) in OFDM systems （1）FFT sampling interval chooses the sampling point before the original symbol （2） FFT sampling interval chooses the sampling point after the original symbol 6

Inter-Carrier Interference(ICI) p Caused by the synchronization problem between transmitter and receiver. （1） Sampling Frequency Offset （SFO） （2） Carrier Frequency Offset （CFO） （3） Doppler Effect p Caused by imbalances between in-phase and quadrature receiver components. → I/Q Imbalance Loss of subcarriers orthogonality 7

OFDM System and ICI Problem • Transmitted signal after IFFT� • n：n-th sample of the OFDM transmitted signal • ：the modulated symbol on l-th subcarrier • ：the total number of subcarriers • ：the channel frequency offset normalized by the subcarrier separation 8

OFDM System and ICI Problem • Received signal in time domain� ：AWGN ↑ phase rotated error • The corresponding frequency domain response after FFT � • desired signal ICI effect between l-th and k-th subcarriers 9

OFDM System and ICI Problem • Example of ICI effect � 10

OFDM System and ICI Problem • ICI coefficient between l-th and k-th subcarriers� 模擬環境： =0 = 64 =0. 1 、0. 2 、0. 3 11

Several Methods to Mitigate ICI • 1 � Frequency-domain equalization • 2 � Time-domain windowing • 3 � ICI self-cancellation ★ • 4 � Frequency offset estimation and correction • 5 � Correlative coding • 6 � Compensation techniques • 7 � Doppler diversity 12

ICI Self-Cancellation Method 13

ICI Self-Cancellation Method • ICI SC mapping has several ways to allocate data： A� Adjacent data-conversion scheme （ASR） original B� Symmetric data-conversion scheme （SSR） C� Adjacent real constant weighted data-conversion scheme D� Adjacent plural weighted data-conversion scheme E� Adjacent data-conjugate scheme （ACSR） F� Adjacent weighted data-conjugate transformation G� Symmetric data-conjugate scheme（SCSR） H� Mirror symbol repetition（MSR） I� Mirror symbol-conjugate repetition（MCSR） ：

ICI Self-Cancellation Method of Data-Conversion Scheme • A� Adjacent data-conversion scheme ◎ ICI SC modulation ： , → The data allocation would be done at the block of ICI SC modulation at the transmitter. 15

ICI Self-Cancellation Method of Data-Conversion Scheme 16

ICI Self-Cancellation Method of Data-Conversion Scheme • The transmitted signal on subcarrier k , on subcarrier k+1 , • In such a case, the ICI coefficient is denoted as 17

ICI Self-Cancellation Method of Data-Conversion Scheme • ◎ ICI SC demodulation ： The received signal on subcarrier k , The total sum of ICI coefficient is denoted as 18

ICI Self-Cancellation Method of Data-Conversion Scheme 19

ICI Self-Cancellation Method of Proposed Data-Conversion Scheme • A� Proposed ASR：add CFO estimator → pre-conditions ：If , a unique estimator can be calculated by K：length of CP M：the number of symbols used for averaging 20

ICI Self-Cancellation Method of Proposed Data-Conversion Scheme use DQPSK for signal mapping Simulation block diagram of the proposed system 21

ICI Self-Cancellation Method of Proposed Data-Conversion Scheme 模 擬 環 境: 演算法： ICI self-cancellation N_symbol = 20000 OFDM_chip = 64 Channel: AWGN, CFO Delta-f = 0. 1/0. 3/0. 4 22

ICI Self-Cancellation Method of Symmetric Data-Conversion Scheme • B� Symmetric data-conversion scheme → data allocation： , → the desired signal is recovered in the receiver as 23

ICI Self-Cancellation Method of Real Constant Weighted Data-Conversion Scheme • C� Adjacent weighted data-conversion scheme → data allocation ： , → the desired signal is recovered in the receiver as 24

ICI Self-Cancellation Method of Plural Weighted Data-Conversion Scheme • D� Adjacent plural weighted data-conversion scheme → data allocation ： , → the desired signal is recovered in the receiver as ↑ ICI signal 25

ICI Self-Cancellation Method of Plural Weighted Data-Conversion Scheme • 模擬環境： N_symbol=1000 N_subcarrier=512 Mod. Method=QAM Channel：AWGN Carrier offset=0. 2 26

ICI Self-Cancellation Method of Data-Conjugate Scheme • E� Adjacent data-conjugate scheme → data allocation ： , → the desired signal is recovered in the receiver as 27

ICI Self-Cancellation Method of Weighted Conjugate Scheme • F� Adjacent weighted conjugate transform scheme • → data allocation ： , → the desired signal is recovered in the receiver as → proposed method , ：the optimal value which depends on normalized frequency offset 28

ICI Self-Cancellation Method of Weighted Conjugate Scheme • 模擬環境：Channel BW = 10 MHz The total number of subcarriers N =1024 , QPSK modulation, ε ∈(0. 05, 0. 25) , AWGN fading channel 29

ICI Self-Cancellation Method of Weighted Conjugate Scheme 30

ICI Self-Cancellation Method of Weighted Conjugate Scheme • 31

ICI Self-Cancellation Method of Weighted Conjugate Scheme • 模擬環境： 32

ICI Self-Cancellation Method of Weighted Conjugate Scheme • 33

ICI Self-Cancellation Method of Weighted Conjugate Scheme • 34

ICI Self-Cancellation Proposed Method • Proposed SC scheme：Modification of WCT → data allocation ： , → the received signal within k-th and (k+1)-th subcarriers given as and 35

ICI Self-Cancellation Proposed Method • The desired signal is recovered as → the symbol on subcarrier “ 0” is our desired signal 36

ICI Self-Cancellation Proposed Method • 模 擬 環 境: N_symbol = 128, 000 N_subcarrier = 128 FFT_size = 128 Modulation：BPSK Channel：AWGN, CFO Delta-f = 0. 05 37

ICI Self-Cancellation Proposed Method • 模 擬 環 境: N_symbol = 128, 000 N_subcarrier = 128 FFT_size = 128 Modulation：BPSK Channel：AWGN, CFO Delta-f = 0. 1 38

ICI Self-Cancellation Proposed Method • 模 擬 環 境: N_symbol = 128, 000 N_subcarrier = 128 FFT_size = 128 Modulation：BPSK Channel：AWGN, CFO Delta-f = 0. 25 • 39

ICI Self-Cancellation Proposed Method • 40

ICI Self-Cancellation Proposed Method • I/Q imbalance in OFDM system → the demod. I/Q baseband sampled signals , ( ： freq. offset, → → subcarrier ( parameter → and ：gain mismatch , ：phase mismatch ) is the k-th sampled signal for making symbol decision on the m-th are the distortion factors for IQ imbalance ) , → 41

ICI Self-Cancellation Proposed Method • H� MSR scheme ∵SSR、SCSR are still incapable of resisting the crosstalk between the mirror subcarriers due to IQ imbalance → data allocation： → the received samples on mirror subcarriers ： → the ICI term will vanish if 42

ICI Self-Cancellation Proposed Method • I� MCSR scheme → data allocation： → the received samples on mirror subcarriers ： → eliminates the crosstalk between mirror subcarriers completely 43

ICI Self-Cancellation Proposed Method • 44

ICI Self-Cancellation Proposed Method • 45

ICI Self-Cancellation Proposed Method • 46

Paper Reference • [1] Performance Analysis of a New ICI-Self-Cancellation-Scheme in OFDM Systems • [2] A New Approach to Improve ICI Self-Cancellation Technique in OFDM Systems • [3] BER Analysis of OFDM with Improved ICI Self-Cancellation Scheme • [4] A New ICI Self-Cancellation Method with Double Bandwidth Efficiency in OFDM Systems • [5] A Novel Effective ICI Self-Cancellation Method • [6] An Improved ICI Self Cancellation Method to Reduce ICI in OFDM Systems • [7] Optimized Data Allocation & Combining Scheme for ICI Self Cancellation in OFDM Systems • [8] A New Scheme of ICI Self-Cancellation in OFDM Systems 47

The End Thanks for your listening. 48