Frequency Domain Equalization(FDE) OFDM system

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Frequency Domain Equalization(FDE) OFDM system

  1. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. 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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