Transmission the Future from the Past

1. Transmission the Future from the Past Orthogonal Frequency Division Multiplexing (OFDM)

2. Outline. • Introduction. • What is it? • How dose it work? • Advantages & Disadvantages. • Variations of OFDM. • OFDM Applications.

3. Introduction. • History. • budding in the late 1960's. • Discretion. • multi-carrier or discrete multi-tone modulation . • Modus Operandi. • Divide and Conquer. • Transform. • Transmit .

4. Introduction-cont. • Description. • multi-carrier or discrete multi-tone modulation . • splits a signal into multiple smaller signal sets and modulates each onto a different sub-carrier

5. Introduction-cont. • Modus Operandi. • Divide and Conquer. • divided into sub-channels. • at lower data rate. • Transform. • The sub-carriers are modulated. • Transmit • Inverse Fast Fourier Transform using baseband processing.

6. Challenges to the implementation of OFDM • The need of many local oscillators, depending on the number of sub-channels, at the receiver and transmitter. • Using new advances in VLSI • Intersymbol interference. • A guard symbol (containing insignificant data) could be used and then discarded at the receiver.

7. Advantages of OFDM • Flexibility. • The sub-channels do not necessarily need to be modulated using the same modulation scheme. • don't even have to come from the same source. • Tolerant of Burst Errors. • A burst error will be spread out on an OFDM stream, error detection and correction becomes trivial. • High Spectral Efficiency. • The entire bandwidth is utilized;The Nyquist efficiency rate is nearly achieved. • Tolerance of Multipah Delays. • sub-signals are sent at lower data rates rather than a single-channel at a high data rate.

8. Disadvantages of OFDM • Sensitivity to the Doppler Effect. • particularly if the transmitter or receiver is moving at high speed (such as a vehicle). • High Effect of Phase Noise. • can actually cause demodulation errors. • Pilot sub-carriers, generated by the FFT, are usually used to compensate. • High Power Consumption. • The different components used to generate demodulate and the oscillations require a lot of power. • Mobile devices will not live very long on battery power alone.

9. Variations of OFDM • Vector OFDM (VOFDM). • Multipath signal reflections. • Antennas to capture the signals. • High-powered processing to normalize the delays into a higher throughput data stream. • Fixed-wireless metropolitan area networks (MANs).

10. Variations of OFDM • Wideband OFDM (W-OFDM). • Large space between frequency orthogonal channels. • Reduces interference • MANs by Businesses and wireless Internet service providers.

11. Variations of OFDM • Flash OFDM (F-OFDM). • Switching frequencies during a radio transmission. • Increasing in signal capacity. • Cellular-phones.

12. Variations of OFDM • MIMO-OFDM • Multiple antennas. • Transmit data, in small pieces to the receiver. • Utilizing spectrum. • Fixed broadband wireless access systems.

13. OFDM Applications • Digital Broadcasting • Digital Audio Broadcasting (DAB). • Digital Video Broadcasting (DVB). • Multipath problems. • Efficient use of the broadcast spectrum.

14. OFDM Applications • Wireless Networking • IEEE 802.11a and IEEE 802.11g standards. • Data Rate: 6-54 Mbps. • Handling wall reflections

15. OFDM Applications

16. OFDM Applications • Asymmetric Digital Subscriber Line (ADSL). • Coexists with telephone infrastructure. • Discrete Multi-Tone (DMT). • Adjust the modulations format, from 1 to 15 bits per symbol.