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Chapter 4 of Hiroshi Harada Book  (OFDM Transmission)

EE578 Assignment #4. Chapter 4 of Hiroshi Harada Book  (OFDM Transmission). Abdul-Aziz .M Al-Yami Nov 1 st 2010. OUTLINE. OVERVIEW ABOUT OFDM DEFINITION AND PRINCIPLES OFDM ADVANTAGES & DRAWBACKS APPLICATIONS CONCLUSIONS AND PERSPECTIVES RESULTS. OVERVIEW ABOUT OFDM.

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Chapter 4 of Hiroshi Harada Book  (OFDM Transmission)

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  1. EE578 Assignment #4 Chapter 4 of Hiroshi Harada Book  (OFDM Transmission) Abdul-Aziz .M Al-Yami Nov 1st 2010

  2. OUTLINE • OVERVIEW ABOUT OFDM • DEFINITION AND PRINCIPLES • OFDM ADVANTAGES & DRAWBACKS • APPLICATIONS • CONCLUSIONS AND PERSPECTIVES • RESULTS

  3. OVERVIEW ABOUT OFDM • OFDM was invented more than 40 years ago. • OFDM has been adopted for several technologies: • Asymmetric Digital Subscriber Line (ADSL) services. • IEEE 802.11a/g, IEEE 802.16a. • Digital Audio Broadcast (DAB). • Digital Terrestrial Television Broadcast: DVD in Europe, ISDB in Japan • 4G, IEEE 802.11n, IEEE 802.16, and IEEE 802.20.

  4. WHY OFDM ? • High bit rate needs are clumped by the nature of communication channels. • Multi-path Propagation effects forbid increasing of transmission rates.

  5. OFDM = Orthogonal FDM Carrier centers are put on orthogonal frequencies ORTHOGONALITY - The peak of each signal coincides with trough of other signals Subcarriers are spaced by 1/Ts OFDM DEFINITION

  6. Modulation

  7. PRINCIPLES • BASIC IDEA : Channel bandwidth is divided into multiple subchannels to reduce ISI and frequency-selective fading. • Multicarrier transmission :Subcarriers are orthogonal each other in frequency domain.

  8. PRINCIPLES • Time-domain spreading: • Spreading is achieved in the time-domain by repeating the same information in an OFDM symbol on two different sub-bands => Frequency Diversity. • Frequency-domain spreading: • Spreading is achieved by choosing conjugate symmetric inputs for the input to the IFFT (real output) • Exploits frequency diversity and helps reduce the transmitter complexity/power consumption.

  9. FDM  OFDM • Frequency Division Multiplexing • OFDM frequency dividing EARN IN SPECTRAL EFFICIENCY

  10. OFDM THEORY • The baseband OFDM signals can be written as Where is the central frequency of the mth sub-channel and is the corresponding transmitted symbol. • The signals are orthogonal over [0, T ] as illustrated below:

  11. GenericOFDM Transmitter OFDM symbol bits Serial to Parallel Pulse shaper FEC LinearPA IFFT & DAC fc add cyclic extension view this as a time to frequency mapper Complexity (cost) is transferred back from the digital to the analog domain!

  12. Generic OFDM Receiver Slot & Timing AGC Sync. Error P/S and Detection Sampler FFT Recovery fc gross offset VCO Freq. Offset Estimation fine offset (of all tones sent in one OFDM symbol)

  13. OFDM ADVANTAGES • OFDM is spectrally efficient • IFFT/FFT operation ensures that sub-carriers do not interfere with each other. • OFDM has an inherent robustness against narrowband interference. • Narrowband interference will affect at most a couple of subchannels. • Information from the affected subchannels can be erased and recovered via the forward error correction (FEC) codes. • Equalization is very simple compared to Single-Carrier systems

  14. OFDM ADVANTAGES • OFDM has excellent robustness in multi-path environments. • Cyclic prefix preserves orthogonality between sub- carriers. • Cyclic prefix allows the receiver to capture multi- path energy more efficiently. • Ability to comply with world-wide regulations: • Bands and tones can be dynamically turned on/off to comply with changing regulations. • Coexistence with current and future systems: • Bands and tones can be dynamically turned on/off for enhanced coexistence with the other devices.

  15. OFDM DRAWBACKS • High sensitivity inter-channel interference, ICI • OFDM is sensitive to frequency, clock and phase offset • The OFDM time-domain signal has a relatively large peak-to-average ratio • tends to reduce the power efficiency of the RF amplifier • non-linear amplification destroys the orthogonality of the OFDM signal and introduced out-of-band radiation

  16. Standards • Digital Audio Broadcasting (DAB) • Digital Video Broadcasting (DVB) • Asymmetric Digital Subscriber Line (ADSL) • Wireless LAN IEEE 802.11a • Wireless networking, device connectivity • Proposed for 802.16 standard • Connection between subscriber's transceiver station and a base transceiver station

  17. COFDM Transmitter Digital Radio • Coded OFDM Transmitter

  18. DRM • For HF Frequencies • 4.5 – 5 kHz for half channel • Data Rates of 4 – 14.5 kbit/s • 9 – 10 kHz for full channel • Data Rates of 8 – 35kbit/s • 18-20 kHz for double channel • Data Rates of 31 – 72kbit/s

  19. ProprietaryOFDM Flavours Flash OFDM from Flarion www.flarion.com Vector OFDM (V-OFDM) of Cisco, Iospan,etc. www.iospan.com Wideband-OFDM (W-OFDM) of Wi-LAN www.wi-lan.com -- Freq. Hopping for CCI reduction, reuse -- 1.25 to 5.0MHz BW -- mobility support -- 2.4 GHz band -- 30-45Mbps in 40MHz -- large tone-width (for mobility, overlay) -- MIMO Technology -- non-LoS coverage, mainly for fixed access -- upto 20 Mbps in MMDS Wi-LAN leads the OFDM Forum -- many proposals submitted to IEEE 802.16 Wireless MAN Cisco leads the Broadand Wireless Internet Forum (BWIF)

  20. MATLAB Results • Program 4.2 (ofdm_fading)

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