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- 1. WATANABE・FUJII ・HATANO LAB. A STUDY ON FREQEENCY DOMAIN EQUALIZATION FOR OFDM SYSTEM TO GAIN HIGH TRANSMISION EFFICENCY WATANABE・FUJII・HATANO LAB CHAMARA SASANKA SALGADO
- 2. WATANABE・FUJII ・HATANO LAB. Introduction to OFDM 1 Multi-carrier modulation Method of transmitting data by splitting into several components Sending each of these components over separate carrier signals OFDM(Orthogonal frequency division multiplexing) One of the multi-carrier modulation techniques that transmit signals using multiple carriers. These subcarriers are orthogonal to each other. Applications of OFDM Digital television broadcasting Wireless local area networks Asymmetric Digital Subscriber Line(ADSL)
- 3. WATANABE・FUJII ・HATANO LAB. BASIC OFDM SYSTEM 2 F F Receiving Filter Data each symbol is assigned to a carrier frequency IFFT converts frequency domain data into corresponding time domain data Generate samples of a waveform with orthogonal frequency components creates the OFDM signal by sequentially outputting the time domain samples Multipath, noise etc. OFDM data are split from a serial stream into parallel sets converts the time domain samples back into a frequency domain converts the parallel data into a serial stream to recover the original input data Data K×K K×K Transmitte r Receiver No. of subcarriers(K)
- 4. WATANABE・FUJII ・HATANO LAB. MULTIPATH CHANNEL 3 More than one transmission path between transmitter and receiver Reflections from buildings, mountains or other reflective surfaces
- 5. WATANABE・FUJII ・HATANO LAB. MULTIPATH PROBLEM 4 Part from the previous symbol Direct wave Reflected waves Receiving signal delay Time Interference from the previous symbol
- 6. WATANABE・FUJII ・HATANO LAB. MULTIPATH DELAY SPREAD TOLERANCE 5 Cyclic Prefix(CP) is used in OFDM systems to avoid the interference occurred by multipath fading. End of the symbol is copied to beginning CP Receiving part Direct wave Reflected waves delay Time CP CP CP COPY
- 7. WATANABE・FUJII ・HATANO LAB. OFDM WITH CYCLIC PREFIX 6 F F K×K K×K Transmitte r Receiver No. of subcarriers(K) copy of last part of OFDM symbol is placed in front of each symbol CP is removed
- 8. WATANABE・FUJII ・HATANO LAB. TARGET OF THE RESEARCH 7 ADVANTAGE OF CP Helps to avoid inter symbol interference(ISI) DISADVANTAGE OF CP Cyclic prefix in an OFDM system usually results an efficiency loss in an OFDM system CP, which is added at transmitter, is removed at receiver. Energy and time using for CP is useless. TARGET Applying Frequency Domain Equalization(FDE) instead of CP to gain high transmission efficiency
- 9. WATANABE・FUJII ・HATANO LAB. FREQUENCY DOMAIN EQULIZATION(FDE)(1/2) 8 I F F T F F T F F T I F F T L K× L KL K×L K K×K K×K Transmitte r Receiv er No. of subcarriers(K) No. of symbols(L)
- 10. WATANABE・FUJII ・HATANO LAB. FREQUENCY DOMAIN EQULIZATION(FDE)(2/2) 9 L : No. of symbols K : No. of subcarriers Direct wave Reflected wave CP CPCP CP CPCP CP CP FFT (L K×L K)FFT(K×K) OFDM with CP OFDM with FDE FFT(K×K) FFT(K×K) Advantages of the OFDM with FDE Effective than the OFDM with CP Diversity effect Disadvantages of the OFDM with FDE Inter symbol interference Little bit complex e.g. L = 3 COPY
- 11. WATANABE・FUJII ・HATANO LAB. SUMMARY AND FUTURE CHALLENGES 10 SUMMARY Basic OFDM system Multipath and multipath tolerance using cyclic prefix Frequency domain equalization FUTURE CHALLENGES Evaluate the efficiency of an OFDM system using FDE, by computer simulator.
- 12. WATANABE・FUJII ・HATANO LAB. A STUDY ON FREQEENCY DOMAIN EQUALIZATION FOR OFDM SYSTEM TO GAIN HIGH TRANSMISION EFFICENCY WATHANABE・FUJII・HATHANO LAB CHAMARA SASANKA SALGADO

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